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Revisiting the Key Driving Processes of the Decadal Trend of Aerosol Acidity in
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4, 346-353
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REVISITING THE KEY DRIVING PROCESSES OF THE DECADAL TREND OF AEROSOL ACIDITY IN
THE U.S
* Guangjie Zheng
Guangjie Zheng
Minerva Research Group, Max Planck Institute for Chemistry, Mainz 55128,
Germany
More by Guangjie Zheng
https://orcid.org/0000-0002-8103-2594
,
* Hang Su
Hang Su
Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz
55128, Germany
More by Hang Su
https://orcid.org/0000-0003-4889-1669
, and
* Yafang Cheng*
Yafang Cheng
Minerva Research Group, Max Planck Institute for Chemistry, Mainz 55128,
Germany
*Email: yafang.cheng@mpic.de
More by Yafang Cheng
https://orcid.org/0000-0003-4912-9879
Cite this: ACS Environ. Au 2022, 2, 4, 346–353
Publication Date (Web):May 6, 2022
PUBLICATION HISTORY
* Published online6 May 2022
* Published inissue 20 July 2022
https://doi.org/10.1021/acsenvironau.1c00055
Copyright © 2022 The Authors. Published by American Chemical Society
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Supporting Info (1)»Supporting Information Supporting Information
SUBJECTS:
* Acidity,
* Aerosols,
* Ammonia,
* Anions,
* pH
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ACS Environmental Au
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ABSTRACT
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Acidity is one essential parameter in determining the aqueous phase physical and
chemical processes in the atmosphere and strongly influences the climate,
ecological, and health effects of aerosols. Traditionally, aerosol acidity is
thought to increase with emissions of atmospheric acidic substances (SO2, NOx,
etc.) and decrease with that of alkaline ones (NH3, dust, etc.). However,
decade-long observations in southeastern U.S. seem to disagree with this
hypothesis: while the emissions of NH3 versus SO2 enhanced by over three times,
the predicted aerosol acidity is stable, and the observed particle-phase
ammonium-to-sulfate ratio is even decreasing. Here, we investigated into this
issue with the recently proposed multiphase buffer theory. We show that
historically, there is a transition in the dominant drivers of aerosol acidity
in this region. Under the ammonia-poor conditions before ∼2008, the acidity is
governed by HSO4–/SO42– buffering and the water self-buffering effect. Under the
ammonia-rich conditions after ∼2008, aerosol acidity is mainly buffered by
NH4+/NH3. Buffering from the organic acids is negligible in the investigated
period. In addition, the observed decrease in ammonium-to-sulfate ratio is due
to the increased importance of non-volatile cations, especially after ∼2014. We
predict that until ∼2050, the aerosols will remain in the ammonia-buffered
regime, and the nitrate will remain largely (>98%) in the gas phase in
southeastern U.S.
KEYWORDS:
* aerosol acidity
* multiphase buffer system
* driving processes
* long-term trend
* organic acids buffering
* ammonium-to-sulfate ratio
* non-volatile cations
*
*
*
1. INTRODUCTION
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
Aerosol acidity is one central parameter in atmospheric research, which largely
regulated the thermodynamics and chemical kinetics in atmospheric multiphase
chemistry, (1−4) therefore influencing the effects of aerosols on health,
ecosystem, and climate. (3,5−9) Traditionally, aerosol acidity is thought to
increase with emissions of atmospheric acidic substances (SO2, NOx, etc.) and
decrease with that of alkaline ones (NH3, Na+, Ca2+, K+, Mg2+, etc.). (2,10−16)
However, analysis of the long-term trend of aerosol acidity in southeastern U.S.
(SE-US) is against this hypothesis. Over the past two decades, sulfate in
southeastern U.S. has decreased by 70%, while the gas-phase ammonia
concentration shows a constant or even slowly increasing trend. (10,16,17) This
is expected to result in an increase of both pH and the ammonium-to-sulfate
ratio in the particle phase. (3) In contrast, thermodynamic models predict a
small change of pH varying between ∼0 and 2, while the observed
ammonium-to-sulfate ratio even decreased slightly. (10) In this sense, the U.S.
aerosols behave like a “buffered system” that resists pH changes upon addition
of acids or bases within a certain range.
The pioneer study of Weber et al. (10) tried to explain the above
counterintuitive phenomenon with a concept model, referred to as the W16 model
hereinafter. This model assumes that (i) the resistance of U.S. aerosol pH
changes upon changing ammonia/sulfur emissions is due to the (NH4)2SO4-NH4HSO4
transition in the aerosol water, where the relative ratio of (NH4)2SO4/NH4HSO4
is regulated through the partitioning of ammonia between gas and particle phase;
and (ii) the observed decrease in ammonium-to-sulfate ratio is due to the
limited available partitionable ammonium. However, this concept model is
ambiguous in the following points. First, the governing factors of
(NH4)2SO4-NH4HSO4 transition remain unclear. Second, the regulation effect of
ammonia partitioning requires the HSO4–/SO42– transition. Therefore, it cannot
explain the similar “buffering” effect observed in other places with higher pH
levels, especially when aerosol compositions are dominated by NH4NO3. Third, the
explanation for decreasing ammonium-to-sulfate ratio of limited ammonium is
against the equilibrium law (i.e., Le Chatelier’s principle; see Section 5).
The recently proposed multiphase buffer theory (1) provided new insights into
these issues. Here, we revisited the determinants of the U.S. aerosol acidity
trend with this theory. We found that (i) under ammonia-rich conditions, the
resistance of pH changes is mainly due to the buffering effect of NH4+/NH3, not
(NH4)2SO4-NH4HSO4 transition; (ii) under ammonia-poor or highly acidic
conditions, the water self-buffering effect is also an important factor that
resist the aerosol pH from dropping below 0, in addition to the HSO4–/SO42–
buffering effect; and (iii) the observed decrease in ammonium-to-sulfate ratio
is actually due to the increased importance of non-volatile cations (NVCs,
mainly Na+, Ca2+, K+, Mg2+), not the limited availability of partitionable
ammonium. (10) Based on the projected emissions until ∼2050 in southeastern
U.S., aerosol acidity is predicted to remain in ammonia buffered regime and
increase only slightly (from 1 to below 2), in which pH ranges the nitrate will
remain almost all (>98%) in the gas phase.
2. METHODS
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
Long-term observations of aerosol compositions and gas species are conducted at
the Centreville site (CTR, 32.902°N, 87.250 °W, altitude 126 m; AL, U.S.A.), as
part of the Southeastern Aerosol Research and Characterization (SEARCH) network.
Detailed site and instrumentation information are documented elsewhere. (18−20)
The summer (June to August) data during 2004 to 2016 are analyzed here. The
PM2.5 chemical compositions, gas-phase ammonia mixing ratios, and meteorological
parameters are used in this study.
The aerosol acidity is defined as the free molality of protons, (2,21) which is
estimated by thermodynamic models of the ISORROPIA v2.3 (ref (22)) and the E-AIM
(model IV; http://www.aim.env.uea.ac.uk/aim/aim.php; last access: April 23,
2022). (23−25) The E-AIM model is usually considered as the “benchmark”
thermodynamic models, (2) and its results are used to examine the potential
influences of thermodynamic models applied on the identified driving factors.
The ISORROPIA model is used as it can consider the influences of Ca2+, K+, and
Mg2+, which will be discussed in Section 5. In addition, results from ISORROPIA
are directly comparable with the pioneering study of Weber et al. (10) The
ISORROPIA model is run in forward mode and with the metastable assumption, and
the predicted ammonia partitioning agreed well with the observations (Figure
S1). Calculations of multiphase buffer capacity and the treatment of
non-ideality are detailed elsewhere (1,21) and are briefly explained where
needed.
3. ROLE OF AMMONIA: REGULATING (NH4)2SO4/NH4HSO4 RATIOS VS MULTIPHASE BUFFERING
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
3.1. W16 MODEL
The W16 concept model proposed that the gas–particle partitioning of NH3 would
regulate (NH4)2SO4/NH4HSO4 ratios in the aerosol phase, which will thereby
constrain the aerosol pH between ∼0 and 3, as the pH of pure aqueous NH4HSO4
aerosols is around 0 while that of pure aqueous (NH4)2SO4 aerosols is around 3
(ref (10)). This process can be represented as follows:
(1a)
(1b)
In this model, the aerosol pH is regulated by the specific compounds of
(NH4)2SO4/NH4HSO4 and is essentially a neutralization process (Figure 1a): when
sulfate is decreased and the total ammonia (TA) to total sulfate (TS) ratio (3)
is increased, the increased availability of partitionable ammonia works as
additional bases (NH4OH) into the aerosol phase, which combined with the acidic
substance (NH4HSO4) to form the neutralized salt (i.e., (NH4)2SO4) and water.
Therefore, the W16 model is in principle a neutralization model, where the
aerosol pH is regulated by the degree of aqueous phase neutralization; see Weber
et al. (10) for more details about this concept model.
FIGURE 1
Figure 1. Comparison of multiphase buffer theory and the pioneering W16 concept
model in explaining aerosol acidity variations in SE-US. Over the last decade in
SE-US, SO42– has decreased substantially while the total ammonia is roughly
constant, and thus the TA/TS ratios have increased. However, the pH is roughly
the same. (a) W16 concept model attributed this stable pH to the conversions in
(NH4)2SO4/NH4HSO4 ratios, (10) while (b) multiphase buffer theory explained it
as the multiphase NH4+/NH3 buffering effect. (1) Note that the amount of sulfate
shown in (b) indicate the charge equivalent concentrations.
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3.2. MULTIPHASE BUFFER THEORY
The recently proposed multiphase buffering theory provided a new insight into
the role of ammonia in regulating aerosol pH in that NH4+(aq)/NH3(g) works as a
buffering pair, keeping aerosol pH at a certain level (around its peak buffer
pH) (ref (1)). The buffering agents are conjugate acid/base pairs that differ
only by one proton, which can partially absorb the added H+ or OH– through
dissociation equilibrium. The decrease of sulfate works like removing strong
acids from the multiphase system; therefore, H+ will decrease while OH– will
increase. Some of the increased OH– would be converted to NH4OH through the
following equilibria (Figure 1b):
(2a)
with the corresponding effective acid dissociation constant, Ka*, being
(2b)
where Ka,NH3 is the acid dissociation constant of ammonia in bulk aqueous phase,
AWC is the aerosol water content, ρw is the water density, T is the temperature,
HNH3 is Henry’s constant for NH3, R is the gas constant, and [NH3(g)] is the
equivalent molality (mol kg–1 water) of NH3(g) defined as (1)
(2c)
where pNH3 is the partial pressure of NH3 in atm.
The additional terms of Ka* compared to Ka represent the influence of
gas–particle partitioning. In multiphase systems, the formed NH4OH(aq) can
volatilize into the gas phase, reducing NH4OH molality, further promoting the
conversion of OH– into NH4OH; see Zheng et al. (1) for more details about the
multiphase buffer theory.
Although Weber et al. (10) pointed out the importance of gas–particle
partitioning of NH3 in regulating aerosol pH through shifting (NH4)2SO4/NH4HSO4
in aqueous phase, compared with their model, the major advance of multiphase
buffer theory lies in the following aspects. First, it revealed that ammonia
works as the buffering agent through dissociation equilibrium, with the Ka*
largely controlled by AWC at a given temperature. Therefore, its buffering pH
ranges, pKa* ± 1, depend weakly on the anions it is associated with (e.g., HSO4–
or SO42– or NO3–) assuming that AWC is the same. (21) In comparison, the W16
model emphasized the importance of (NH4)2SO4-NH4HSO4 transition, which are the
major forms of NH4+(aq) in SE-US; but on the other hand, it limited the
application of W16 in explaining the buffering effects in other regions where
the sulfate is fully neutralized into (NH4)2SO4 and NH4HSO4 is negligible, such
as the ammonia-rich periods in northern China or western Europe. Second, the
multiphase buffer theory pointed out the governing factors of aerosol pH
quantitatively, with an emphasis on the dominate role of AWC and temperature in
the ammonia buffered region, which is new to the W16 model.
4. RELATIVE IMPORTANCE OF AMMONIA UNDER DIFFERENT REGIMES
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
4.1. CONTRIBUTORS OF MULTIPHASE BUFFERING CAPACITY
Resistance of pH changes of a multiphase buffer system can be represented by the
buffering capacity β as follows: (1,21)
(3)
where nacid or nbase is the amount of acid or base added to the system in mol
kg–1, Kw is the water dissociation constant, and Xi is a given buffering agent.
Contribution of Xi to total β, βi, is determined by Ka,i* and [Xi]tot*. Ka,i* is
the effective acid dissociation constant that determines the buffering pH range
of Xi, while [Xi]tot* is the total equivalent molality of Xi including those
existing in the gas phase, as the gas–particle partitioning also plays a role
(Figure 1). [Xi]tot* determines the maximum buffer capacity Xi, which is found
at pH = pKa,i*. Note that the first two terms in eq 3 ([H+] and Kw[H+]−1)
represent the water self-buffering effect, which is the intrinsic inertia of
water against pH changes at highly acidic or alkaline (high [OH–]) conditions.
This effect arose from the linear-log scale relationship of [H+] or [OH–] and
pH, which exists even for a non-buffered system.
4.2. CHANGES IN MAJOR BUFFER CAPACITY CONTRIBUTORS
Here, we reanalyzed the historical trend of U.S. aerosol acidity by the
multiphase buffer theory, with a focus on identifying the contribution of
individual drivers. For illustration, buffering capacity curves of southeastern
U.S. aerosols are calculated under past (summer 2004) and current (summer 2016)
conditions (Figure 2), based on measurement at the SEARCH-CTR site. Data from
the same measurement site has been used in the analyses in Weber et al. (10) but
only until 2013 (Section 2). Here, the results are based on the ISORROPIA model,
the same as in Weber et al.; (10) while results estimated by the E-AIM model
lead to the same conclusions (Figure S2). Judging from the average TA/TS ratios,
the 2004 and 2016 scenarios are ammonia-poor (TA/TS < 2) and ammonia-rich (TA/TS
> 2) conditions, respectively. (3) Major buffering agents considered here are
HNO3(g + aq)/NO3–(aq), HSO4–(aq)/SO42–(aq), and NH3(g + aq)/NH4+(aq).
FIGURE 2
Figure 2. Buffering capacity curve for US scenario. The inputs are based on
average summertime SEARCH data at the CTR site. Here, the influence of NVCs is
not considered (see Section 5), while NH3(g) is included. In panel (c), the left
Y axis correspond to β shown by the shaded areas, while the right Y axis
correspond to the pH shown by the filled black circles. As the NH3(g)
measurements are missing in 2011, it was assumed to be the average of NH3(g) in
2010 and 2012 (the hollow circle in Figure 2c). The black dashed line indicates
the fitted annual pH trends for reference. The result shown here is based on the
ISORROPIA model, while that based on the E-AIM model is shown in Figure S2.
Although the detailed pH values predicted by these two models can differ by ±0.3
units, both models indicate the same variations in the dominant buffering
regimes. Note that the pH jump in 2008 is likely related to minor bugs in the
ISORROPIA algorithm (see Figure S3).
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For both scenarios, the buffering ranges of these species are quite different
from that under the bulk conditions (Figure 2a,b). Abundances of total HNO3 is
too low to offer any efficient buffering. Although being a weak base in bulk
solutions, NH3(g + aq)/NH4 + (aq) is generally buffering in the range of 0–3,
determined by the AWC concentrations (eq 2). Non-ideality elevated its buffering
range only slightly (∼0.4). (21) In comparison, the non-volatile
HSO4–(aq)/SO42–(aq) pair is not influenced by AWC but is strongly influenced by
the non-ideality due to the larger sensitivity of their activity coefficients.
(21) Its pKa moved from ∼2 under ideal conditions to −0.9 to −0.5 considering
the non-ideality.
Average compositions of 2004 is in the ammonia-poor conditions (TA/TS = 1.65),
and the sulfate cannot be fully neutralized into (NH4)2SO4 (ref (3)). At the
predicted pH of ∼0, β is dominated by water self-buffering effect and
HSO4–/SO42–, while ammonia plays a minor role. In contrast, in 2016 (Figure 2b)
when the aerosols are ammonia-rich (TA/TS = 3), β is solely dominated by NH3(g +
aq)/NH4 + (aq) at the predicted pH levels of ∼0.8.
4.3. SMOOTH PH TRANSITION DESPITE REGIME TRANSITIONS
Analysis of the long-term trends of SE-US acidity (Figure 2c) shows a shift in
the dominant β contributor from the water–HSO4–/SO42– regime to the NH4+/NH3
regime around 2008, consistent with the transition of ammonia-poor to
ammonia-rich conditions. Interestingly, the pH changes are smooth despite the
regime transitions. This is mainly due to the low AWC levels in SE-US, which
renders the NH4+/NH3 buffering pH ranges (0–3) adjacent to that of [H+] and
HSO4–/SO42–. Therefore, the system β is constantly high over a wide range of pH
< 3 (Figure 2a,b). This is also the reason as to why calculating the pH
with/without NH3(g) would result in a small difference in predicted pH (∼ 1
unit) in the U.S. (10,26,27) In regions with higher aerosol mass concentrations,
the patterns can be quite different. (1)
4.4. POTENTIAL CONTRIBUTIONS OF ORGANIC ACIDS TO BUFFERING CAPACITY
Organic acids can also serve as the buffering agents, and their potential
importance needs to be addressed given the high emissions of biogenic volatile
organic compounds (BVOCs) in SE-US. Here, we examined the potential
contributions of organic acids to the system buffering capacity following the
method outlined in Supporting Information Section S7 and Figure S12 of Zheng et
al. (1) Three dominant organic acids, HCOOH, CH3COOH, and (COOH)2, are
investigated based on the observation in fall 2016 in an agriculturally
intensive rural SE-US site, (28) which is near the CTR site. For a first-order
estimation, we assume that the concentrations of these acids are constant within
the study period. As shown in Figure 3a, in 2016 when the inorganic
concentrations are low, the maximum buffer capacity of HCOOH and CH3COOH can be
comparable with that of ammonia. However, they are both buffering in the
alkaline pH ranges of >9. At the actual aerosol pH ranges of 0–2, their
contribution to the buffer capacity is negligible. This large gaps in the pKa*
and pH are always present in SE-US (Figure 3b). In comparison, while oxalic acid
(COOH)2 can buffer at pH ∼3, its concentrations are too low to be important
(Figure 3a). Therefore, the contributions of organic acids to the buffering
capacity are negligible in summer SE-US.
FIGURE 3
Figure 3. Potential influence of organic acids in the buffer capacities in
SE-US. (a) Example buffering capacity curve based on the average summer 2016
conditions at the CTR site. (b) Annual trends in ISORROPIA-predicted pH and
ideal pKa* of major organic acids in summer SE-US. The total (gas + particle)
concentrations of the three investigated organic acids, HCOOH, CH3COOH, and
(COOH)2, are based on the observation in an agriculturally intensive rural SE-US
site in fall 2016, (28) which is near the CTR site. These concentrations are
expected to be satisfactory as an order-of-magnitude estimation of the
concentrations in the summer CTR site.
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5. VARIATIONS OF AMMONIA-TO-SULFATE RATIOS: IMPORTANCE OF NVCS
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
Besides the relatively stable pH, another puzzling effect of the U.S. acidity is
the unexpected decrease in aerosol ammonium-to-sulfate molar ratios (RSO4)
(Figure 4a). From 2004 to 2016, the aerosols in SE-US turned from ammonia-poor
(TA/TS < 2) to ammonia-rich (TA/TS > 2), while the observed RSO4 decreased from
1.8 to 1.4. This disagrees with the theoretical pattern that in a H2SO4–HNO3–NH3
system, RSO4 should monotonically increase approaching 2 (i.e., when sulfate is
fully neutralized) with increasing TA/TS. (29,30)
FIGURE 4
Figure 4. Explanations for the decreasing trend of ammonium-to-sulfate molar
ratios RSO4, where RSO4 = ([NH4+] – [NO3–])/[SO42–]tot. (a) Observed trend of
TA/TS, RSO4, and NVCs/TS in SEARCH-CTR site in summer 2004 to 2016. (b)
Simulated trend with decreasing SO42–, assuming constant NH3(g) of 0.23 μg m–3
(decadal mean of CTR site). (c) Simulated variation of the difference between
the corrected ratios, RSO4,f, and RSO4 with sulfate and gas-phase NH3.
Simulation in panels (b) and (c) reproduced settings in Figure 2 of Weber et
al.10, i.e., assuming a constant Na+ = 0.03 μg m–3, total HNO3 = 0.08 μg m–3,
total HCl = 0.02 μg m–3, temperature of 298 K, and RH at 73.8%.
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Weber et al. (10) attributed this “counterintuitive” phenomenon to the limited
available neutralizing ammonia according to their concept model. That is, at
lower SO42–, there is less available ammonium, thus a larger relative loss of
NH4+ when establishing equilibrium with NH3(g). The ISORROPIA thermodynamic
model simulations seemed to support this assumption, which showed decreasing
RSO4 with decreasing SO42– (Figure 4b). However, the model shows simultaneously
increases in HSO4–/SO42– and pH (Figure 4b), which is self-contradictory. Based
on the W16 model, as NH4+ volatilizes and RSO4 decreases, the (NH4)2SO4/NH4HSO4
ratio should also decrease, and so does pH (Figure 1). Even if we consider the
HSO4–/SO42– buffering effect, which would partially weaken the extent of pH
decrease, it cannot be completely offset – well known as the equilibrium law (or
Le Chatelier’s principle). (29,30) Therefore, the larger relative loss of NH4+
must result in a simultaneous RSO4 and pH decrease, which is against their
modeling result (Figure 4b). In addition, predicted changes in NO3– are
negligible and cannot explain the changes in RSO4.
Here, we re-examined the model simulations and observations and found that the
decreased RSO4 is due to the increasing importance of NVCs. As the NVCs could
neutralize part of the sulfate before it can be neutralized by the volatile NH3,
the “free” total sulfate (TSf = TS – 0.5NVCs) to participate in the
H2SO4–HNO3–NH3 equilibrium is reduced. Therefore, both TA/TS and RSO4 would
underestimate the neutralization degrees. Replacing TS with TSf in the system
gives the corrected definition of the ammonium to “free” sulfate ratios, RSO4,f,
as
(4)
which should be used in conditions with large NVCs/[SO42–]tot ratios.
The decreased RSO4 with increasing TA/TS as shown in both observation and
simulation results can be explained with this corrected definition of eq 4. As
the NVCs are assumed constant, decreasing SO42– will increase NVCs/TS, thereby
enlarging gaps between RSO4 and RSO4,f (Figure 4b). While RSO4,f is kept around
2 all the time (not shown but investigated around all SO42– and NH3(g) ranges),
RSO4 would decrease substantially as the system transitioned from the
H2SO4–HNO3–NH3 system to a H2SO4–HNO3–NH3–NVC system, and so would their
differences (i.e., RSO4f – RSO4; Figure 4c). The observed gap between TA/TS and
RSO4 also correspond to the increased NVCs/SO42– in recent years (Figure 4a).
The mixing states may also change the gas–particle partitioning of NH3 and HNO3
and therefore the RSO4 under given TA/TS conditions. We performed a test with
the fully external mixture assumption, and the difference in RSO4 is small
(Figure S4).
6. IMPLICATIONS
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
Our finding suggested that the U.S. acidity have undergone the following three
regimes: (i) the ammonia-poor conditions before ∼2008, with high acidity and
therefore intrinsic stable pH levels; (ii) the NH3/NH4+ buffered H2SO4–HNO3–NH3
system (∼2006 to ∼2014), where TA/TS and RSO4 can be used as the indicator of
NH3 richness and the particle phase sulfate neutralization degrees; and (iii)
the NH3/NH4+ buffered H2SO4–HNO3–NH3–NVC system after ∼2014, where contribution
from NVCs cannot be ignored but still cannot fully neutralize sulfate (i.e.,
NVCs/TS < 2) and RSO4 is not representative of the sulfate neutralization
degrees.
We further did a rough estimate of future aerosol pH variation trends in SE-US.
We applied two scenarios, the “Ref” scenario based on the prediction of the
GCAM-USA model following the work of Shi et al., (31) while the “U50” scenario
is a more stringent scenario, assuming 50% reduction target is applied in 2050
compared to the Ref scenario. (32) We assume the reduction of sulfate and total
nitrate is in proportional to the SO2 and NOx reduction percentages compared to
2015, while other species are kept constant. As shown in Figure 5, under both
scenarios, SE-US aerosol acidity is predicted to remain in the ammonia-buffered
regime and will increase only slightly, and nitrate will remain largely in the
gas phase, in agreement with the conclusion of Weber et al. (10)
FIGURE 5
Figure 5. Predicted future U.S. pH trends. (a) “Ref” scenario is based on Shi et
al., (31) while (b) “US50” scenario is more stringent as assumed in Ou et al.
(32) The shaded area indicates the NH3 buffered pH ranges (i.e., the ammonia
pKa*,ni ± 1).
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The above analysis shows how the multiphase buffer theory can be applied to
explain the long-term trends in aerosol acidity against changes in aerosol
compositions. The stable pH in the past and as projected in the future
illustrated the strong capacity of ammonia in buffering aerosol acidity and the
secondary inorganic aerosol compositions against stringent reductions of acidic
gases in the U.S. As the SE-US is projected to remain in the ammonia-buffered
regime, the sulfur emission controls are projected to result in effective
sulfate reductions, without causing higher particulate nitrate concentrations.
SUPPORTING INFORMATION
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acsenvironau.1c00055.
* Supplementary Figures S1–S4 showing model validation and comparisons and the
influence of mixing states on the ammonium-to-sulfate ratios (PDF)
* vg1c00055_si_001.pdf (487.88 kb)
Revisiting the Key Driving Processes of the Decadal Trend of Aerosol Acidity in
the U.S
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Supporting Information for
Revisiting the key driving processes of the decadal trend of aerosol acidity in
the U.S.
Guangjie Zheng
1
, Hang Su
2
, Yafang Cheng
1
*
1
Minerva Research Group, Max Planck Institute for Chemistry, Mainz 55128, Germany
2
Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz
55128, Germany
2
Fig.
S1
Evaluation of the ISORROPIA thermodynamic model through comparison of
the model predicted
NH
3
(g) concentrations against the measured ones.
Data are based on the hourly measurements in SEARCH CTR
site in summer 2004 to 2016, when NH
3
(g) measurements are available.
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Most electronic Supporting Information files are available without a
subscription to ACS Web Editions. Such files may be downloaded by article for
research use (if there is a public use license linked to the relevant article,
that license may permit other uses). Permission may be obtained from ACS for
other uses through requests via the RightsLink permission system:
http://pubs.acs.org/page/copyright/permissions.html.
AUTHOR INFORMATION
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
* Corresponding Author
* Yafang Cheng - Minerva Research Group, Max Planck Institute for Chemistry,
Mainz 55128, Germany; https://orcid.org/0000-0003-4912-9879; Email:
yafang.cheng@mpic.de
* Authors
* Guangjie Zheng - Minerva Research Group, Max Planck Institute for
Chemistry, Mainz 55128, Germany; https://orcid.org/0000-0002-8103-2594
* Hang Su - Multiphase Chemistry Department, Max Planck Institute for
Chemistry, Mainz 55128, Germany; https://orcid.org/0000-0003-4889-1669
* Author Contributions
Y.C., H.S., and G.Z. designed the study. G.Z., Y.C., and H.S. performed the
research. G.Z. wrote the manuscript with input from Y.C. and H.S.
* Funding
Open access funded by Max Planck Society.
* Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
The research was supported by the Max Planck Society (MPG). Y.C. acknowledges
the Minerva Program of MPG.
REFERENCES
ARTICLE SECTIONS
Jump To
* Abstract
* 1. Introduction
* 2. Methods
* 3. Role of Ammonia: Regulating (NH4)2SO4/NH4HSO4 Ratios vs Multiphase
Buffering
* 4. Relative Importance of Ammonia under Different Regimes
* 5. Variations of Ammonia-to-Sulfate Ratios: Importance of NVCs
* 6. Implications
* Supporting Information
* Author Information
* Acknowledgments
* References
--------------------------------------------------------------------------------
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Q.; He, K.; Carmichael, G.; Pöschl, U.; Su, H. Reactive nitrogen chemistry
in aerosol water as a source of sulfate during haze events in China. Sci.
Adv. 2016, 2, e1601530 DOI: 10.1126/sciadv.1601530
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5
Reactive nitrogen chemistry in aerosol water as a source of sulfate during
haze events in China
Cheng, Yafang; Zheng, Guangjie; Wei, Chao; Mu, Qing; Zheng, Bo; Wang,
Zhibin; Gao, Meng; Zhang, Qiang; He, Kebin; Carmichael, Gregory; Poeschl,
Ulrich; Su, Hang
Science Advances (2016), 2 (12), e1601530/1-e1601530/11CODEN: SACDAF;
ISSN:2375-2548. (American Association for the Advancement of Science)
Fine-particle pollution assocd. with winter haze threatens the health of
more than 400 million people in the North China Plain. Sulfate is a major
component of fine haze particles. Record sulfate concns. of up to ∼300 μg
m-3 were obsd. during the Jan. 2013 winter haze event in Beijing.
State-of-the-art air quality models that rely on sulfate prodn. mechanisms
requiring photochem. oxidants cannot predict these high levels because of
the weak photochem. activity during haze events. We find that the missing
source of sulfate and particulate matter can be explained by reactive
nitrogen chem. in aerosol water. The aerosol water serves as a reactor,
where the alk. aerosol components trap SO2, which is oxidized by NO2 to
form sulfate, whereby high reaction rates are sustained by the high
neutralizing capacity of the atm. in northern China. This mechanism is
self-amplifying because higher aerosol mass concn. corresponds to higher
aerosol water content, leading to faster sulfate prodn. and more severe
haze pollution.
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6. 6
Li, W.; Xu, L.; Liu, X.; Zhang, J.; Lin, Y.; Yao, X.; Gao, H.; Zhang, D.;
Chen, J.; Wang, W.; Harrison, R. M.; Zhang, X.; Shao, L.; Fu, P.; Nenes,
A.; Shi, Z. Air pollution–aerosol interactions produce more bioavailable
iron for ocean ecosystems. Sci. Adv. 2017, 3, e1601749 DOI:
10.1126/sciadv.1601749
[Crossref], [PubMed], [CAS], Google Scholar
6
Air pollution-aerosol interactions produce more bioavailable iron for ocean
ecosystems
Li, Weijun; Xu, Liang; Liu, Xiaohuan; Zhang, Jianchao; Lin, Yangting; Yao,
Xiaohong; Gao, Huiwang; Zhang, Daizhou; Chen, Jianmin; Wang, Wenxing;
Harrison, Roy M.; Zhang, Xiaoye; Shao, Longyi; Fu, Pingqing; Nenes,
Athanasios; Shi, Zongbo
Science Advances (2017), 3 (3), e1601749/1-e1601749/6CODEN: SACDAF;
ISSN:2375-2548. (American Association for the Advancement of Science)
It has long been hypothesized that acids formed from anthropogenic
pollutants and natural emissions dissolve iron (Fe) in airborne particles,
enhancing the supply of bioavailable Fe to the oceans. However, field
observations have yet to provide indisputable evidence to confirm this
hypothesis. Single-particle chem. anal. for hundreds of individual atm.
particles collected over the East China Sea shows that Fe-rich particles
from coal combustion and steel industries were coated with thick layers of
sulfate after 1 to 2 days of atm. residence. The Fe in aged particles was
present as a "hotspot" of (insol.) iron oxides and throughout the acidic
sulfate coating in the form of (sol.) Fe sulfate, which increases with
degree of aging (thickness of coating). This provides the "smoking gun" for
acid iron dissoln., because iron sulfate was not detected in the freshly
emitted particles and there is no other source or mechanism of iron sulfate
formation in the atm.
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7. 7
Dockery, D. W.; Cunningham, J.; Damokosh, A. I.; Neas, L. M.; Spengler, J.
D.; Koutrakis, P.; Ware, J. H.; Raizenne, M.; Speizer, F. E. Health effects
of acid aerosols on North American children: respiratory symptoms. Environ.
Health Perspect. 1996, 104, 500, DOI: 10.1289/ehp.96104500
[Crossref], [PubMed], [CAS], Google Scholar
7
Health effects of acid aerosols on North American children: respiratory
symptoms
Dockery D W; Cunningham J; Damokosh A I; Neas L M; Spengler J D; Koutrakis
P; Ware J H; Raizenne M; Speizer F E
Environmental health perspectives (1996), 104 (5), 500-5 ISSN:0091-6765.
We examined the respiratory health effects of exposure to acidic air
pollution among 13,369 white children 8 to 12 years old from 24 communities
in the United States and Canada between 1988 and 1991. Each child's parent
or guardian completed a questionnaire. Air quality and meteorology were
measured in each community for a 1-year period. We used a two-stage
logistic regression model to analyze the data, adjusting for the potential
confounding effects of sex, history of allergies, parental asthma, parental
education, and current smoking in the home. Children living in the
community with the highest levels of particle strong acidity were
significantly more likely [odds ratio (OR) = 1.66; 95% confidence interval
(CI) 1.11-2.48] to report at least one episode of bronchitis in the past
year compared to children living in the least-polluted community. Fine
particulate sulfate was also associated with higher reporting of bronchitis
(OR = 1.65; 95% CI 1.12-2.42). No other respiratory symptoms were
significantly higher in association with any of the air pollutants of
interest. No sensitive subgroups were identified. Reported bronchitis, but
neither asthma, wheeze, cough, nor phlegm, were associated with levels of
particle strong acidity for these children living in a nonurban
environment.
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8. 8
Freedman, M. A.; Ott, E.-J. E.; Marak, K. E. Role of pH in Aerosol
Processes and Measurement Challenges. J. Phys. Chem. A 2019, 123, 1275–
1284, DOI: 10.1021/acs.jpca.8b10676
[ACS Full Text ], [CAS], Google Scholar
8
Role of pH in Aerosol Processes and Measurement Challenges
Freedman, Miriam Arak; Ott, Emily-Jean E.; Marak, Katherine E.
Journal of Physical Chemistry A (2019), 123 (7), 1275-1284CODEN: JPCAFH;
ISSN:1089-5639. (American Chemical Society)
PH is one of the most basic chem. properties of aq. soln., but its
measurement in nanoscale aerosol particles presents many challenges. The pH
of aerosol particles is of growing interest in the atm. chem. community
because of its demonstrated effects on heterogeneous chem. and human
health, as well as potential effects on climate. The authors have shown
that phase transitions of aerosol particles are sensitive to pH, focusing
on systems that undergo liq.-liq. phase sepn. Currently, aerosol pH is
calcd. indirectly from knowledge of species present in the gas and aerosol
phases through the use of thermodn. models. From these models, ambient
aerosol is expected to be highly acidic (pH ∼ 0-3). Direct measurements
have focused on model systems due to the difficulty of this measurement.
This area is one in which phys. chemists should be encouraged to contribute
because of the potential consequences for aerosol processes in the
environment.
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9. 9
Zheng, G. J.; Duan, F. K.; Su, H.; Ma, Y. L.; Cheng, Y.; Zheng, B.; Zhang,
Q.; Huang, T.; Kimoto, T.; Chang, D.; Pöschl, U.; Cheng, Y. F.; He, K. B.
Exploring the severe winter haze in Beijing: the impact of synoptic
weather, regional transport and heterogeneous reactions. Atmos. Chem. Phys.
2015, 15, 2969– 2983, DOI: 10.5194/acp-15-2969-2015
[Crossref], [CAS], Google Scholar
9
Exploring the severe winter haze in Beijing: the impact of synoptic
weather, regional transport and heterogeneous reactions
Zheng, G. J.; Duan, F. K.; Su, H.; Ma, Y. L.; Cheng, Y.; Zheng, B.; Zhang,
Q.; Huang, T.; Kimoto, T.; Chang, D.; Poschl, U.; Cheng, Y. F.; He, K. B.
Atmospheric Chemistry and Physics (2015), 15 (6), 2969-2983CODEN: ACPTCE;
ISSN:1680-7324. (Copernicus Publications)
Extreme haze episodes repeatedly shrouded Beijing during the winter of
2012-2013, causing major environmental and health problems. To better
understand these extreme events, we performed a model-assisted anal. of the
hourly observation data of PM2.5 and its major chem. compns. The synthetic
anal. shows that (1) the severe winter haze was driven by stable synoptic
meteorol. conditions over northeastern China, and not by an abrupt increase
in anthropogenic emissions. (2) Secondary species, including orgs.,
sulfate, nitrate, and ammonium, were the major constituents of PM2.5 during
this period. (3) Due to the dimming effect of high loading of aerosol
particles, gaseous oxidant concns. decreased significantly, suggesting a
reduced prodn. of secondary aerosols through gas-phase reactions.
Surprisingly, the observational data reveals an enhanced prodn. rate of
secondary aerosols, suggesting an important contribution from other
formation pathways, most likely heterogeneous reactions. These reactions
appeared to be more efficient in producing secondary inorgs. aerosols than
org. aerosols resulting in a strongly elevated fraction of inorgs. during
heavily polluted periods. (4) Moreover, we found that high aerosol concn.
was a regional phenomenon. The accumulation process of aerosol particles
occurred successively from cities southeast of Beijing. The apparent sharp
increase in PM2.5 concn. of up to several hundred μgm-3 per h recorded in
Beijing represented rapid recovery from an interruption to the continuous
pollution accumulation over the region, rather than purely local chem.
prodn. This suggests that regional transport of pollutants played an
important role during these severe pollution events.
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10. 10
Weber, R. J.; Guo, H.; Russell, A. G.; Nenes, A. High aerosol acidity
despite declining atmospheric sulfate concentrations over the past 15
years. Nat. Geosci. 2016, 9, 282– 285, DOI: 10.1038/ngeo2665
[Crossref], [CAS], Google Scholar
10
High aerosol acidity despite declining atmospheric sulfate concentrations
over the past 15 years
Weber, Rodney J.; Guo, Hongyu; Russell, Armistead G.; Nenes, Athanasios
Nature Geoscience (2016), 9 (4), 282-285CODEN: NGAEBU; ISSN:1752-0894.
(Nature Publishing Group)
Particle acidity affects aerosol concns., chem. compn. and toxicity.
Sulfate is often the main acid component of aerosols, and largely dets. the
acidity of fine particles under 2.5 μm in diam., PM2.5. Over the past 15
years, atm. sulfate concns. in the southeastern United States have
decreased by 70%, whereas ammonia concns. have been steady. Similar trends
are occurring in many regions globally. Aerosol ammonium nitrate concns.
were assumed to increase to compensate for decreasing sulfate, which would
result from increasing neutrality. Here we use obsd. gas and aerosol
compn., humidity, and temp. data collected at a rural southeastern US site
in June and July 2013 (ref. 1), and a thermodn. model that predicts pH and
the gas-particle equil. concns. of inorg. species from the observations to
show that PM2.5 at the site is acidic. PH buffering by partitioning of
ammonia between the gas and particle phases produced a relatively const.
particle pH of 0-2 throughout the 15 years of decreasing atm. sulfate
concns., and little change in particle ammonium nitrate concns. We conclude
that the redns. in aerosol acidity widely anticipated from sulfur redns.,
and expected acidity-related health and climate benefits, are unlikely to
occur until atm. sulfate concns. reach near pre-anthropogenic levels.
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11. 11
West, J. J.; Ansari, A. S.; Pandis, S. N. Marginal PM25: Nonlinear Aerosol
Mass Response to Sulfate Reductions in the Eastern United States. J. Air
Waste Manage. Assoc. 1999, 49, 1415– 1424, DOI:
10.1080/10473289.1999.10463973
[Crossref], [PubMed], [CAS], Google Scholar
11
Marginal PM2.5: nonlinear aerosol mass response to sulfate reductions in
the eastern United States
West, J. Jason; Ansari, Asif S.; Pandis, Spyros N.
Journal of the Air & Waste Management Association (1999), 49 (12),
1415-1424CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
Redns. in airborne sulfate concn. may cause inorg. fine particulate matter
(PM2.5) to respond nonlinearly, as nitric acid gas may transfer to the
aerosol phase. Where this occurs, redns. in sulfur dioxide (SO2) emissions
will be much less effective than expected at reducing PM2.5. As a measure
of the efficacy of redns. in sulfate concn. on PM2.5, we define marginal
PM2.5 as the local change in PM2.5 resulting from a small change in sulfate
concn. Using seasonal-av. conditions and assuming thermodn. equil., we find
that the conditions for PM2.5 to respond nonlinearly to sulfate redns. are
common in the eastern United States in winter, occurring at half of the
sites considered, and uncommon in summer, due primarily to the influence of
temp. Accounting for diurnal and intraseasonal variability, we find that
seasonal-av. conditions provide a reasonable indicator of the time-averaged
PM2.5 response. These results indicate that redns. in sulfate concn. may be
up to 50% less effective at reducing the annual-av. PM2.5 than if the role
of nitric acid is neglected. Further, large redns. in sulfate will also
cause an increase in aerosol nitrate in many regions that are the most
acidic.
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12. 12
Pinder, R. W.; Adams, P. J.; Pandis, S. N. Ammonia Emission Controls as a
Cost-Effective Strategy for Reducing Atmospheric Particulate Matter in the
Eastern United States. Environ. Sci. Technol. 2007, 41, 380– 386, DOI:
10.1021/es060379a
[ACS Full Text ], [CAS], Google Scholar
12
Ammonia Emission Controls as a Cost-Effective Strategy for Reducing
Atmospheric Particulate Matter in the Eastern United States
Pinder, Robert W.; Adams, Peter J.; Pandis, Spyros N.
Environmental Science & Technology (2007), 41 (2), 380-386CODEN: ESTHAG;
ISSN:0013-936X. (American Chemical Society)
Current regulation aimed at reducing inorg. atm. fine particulate matter
(PM2.5) is focused on redns. in SO2 and NOx ≡ NO + NO2; however, controls
on these pollutants are likely to increase in cost and decrease in
effectiveness in the future. A supplementary strategy is redn. in NH3
emissions, yet an evaluation of controls on ammonia has been limited by
uncertainties in emission levels and in the cost of control technologies.
We use state of the science emission inventories, an emission-based
regional air quality model, and an explicit treatment of uncertainty to
est. the cost-effectiveness and uncertainty of ammonia emission redns. on
inorg. particulate matter in the Eastern USA. Since a paucity of data on
agricultural operations precludes a direct calcn. of the costs of ammonia
control, we calc. the ammonia savings potential, defined as the min. cost
of applying SO2 and NOx emission controls in order to achieve the same
redn. in ambient inorg. PM2.5 concn. as obtained from a 1 ton decrease in
ammonia emissions. Using 250 scenarios of NH3, SO2, and NOx emission
redns., we calc. the least-cost SO2 and NOx control scenarios that achieve
the same redn. in ambient inorg. PM2.5 concn. as a decrease in ammonia
emissions. We find that the lower-bound ammonia savings potential in the
winter is $8,000/ton NH3; therefore, many currently available ammonia
control technologies are cost-effective compared to current controls on SO2
and NOx sources. Larger redns. in winter inorg. particulate matter are
available at lower cost through controls on ammonia emissions.
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13. 13
Tsimpidi, A. P.; Karydis, V. A.; Pandis, S. N. Response of Inorganic Fine
Particulate Matter to Emission Changes of Sulfur Dioxide and Ammonia: The
Eastern United States as a Case Study. J. Air Waste Manage. Assoc. 2007,
57, 1489– 1498, DOI: 10.3155/1047-3289.57.12.1489
[Crossref], [CAS], Google Scholar
13
Response of inorganic fine particulate matter to emission changes of sulfur
dioxide and ammonia: the Eastern United States as a case study
Tsimpidi, Alexandra P.; Karydis, Vlassis A.; Pandis, Spyros N.
Journal of the Air & Waste Management Association (2007), 57 (12),
1489-1498CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
A three-dimensional chem. transport model (PMCAMx) was used to investigate
changes in fine particle (PM2.5) concns. in response to changes in sulfur
dioxide (SO2) and ammonia (NH3) emissions during July 2001 and Jan. 2002 in
the eastern United States. A uniform 50% redn. in SO2 emissions was
predicted to produce an av. decrease of PM2.5 concns. by 26% during July
but only 6% during Jan. A 50% redn. of NH3 emissions leads to an av. 4 and
9% decrease in PM2.5 in July and Jan., resp. During the summer, the highest
concn. of sulfate is in South Indiana (12.8 μg / m-3), and the 50% redn. of
SO2 emissions results in a 5.7 μg / m-3(44%) sulfate decrease over this
area. During winter, the SO2 emissions redn. results in a 1.5 μg/m-3 (29%)
decrease of the peak sulfate levels (5.2 μg/m-3) over Southeast Georgia.
The max. nitrate and ammonium concns. are predicted to be over the Midwest
(1.9 μg/m-3 in Ohio and 5.3 μg/m-3 in South Indiana, resp.) in the summer
whereas in the winter these concns. are higher over the Northeast (3 μg/m-3
of nitrate in Connecticut and 2.7 μg/m-3 of ammonium in New York). The 50%
NH3 emissions redn. is more effective for controlling nitrate, compared
with SO2 redns., producing a 1.1 μg/m-3 nitrate decrease over Ohio in July
and a 1.2 μg/m-3 decrease over Connecticut in Jan. Ammonium decreases
significantly when either SO2 or NH3 emissions are decreased. However, the
SO2 control strategy has better results in July when ammonium decreases, up
to 2 μg/m-3 (37%), are predicted in South Indiana. The NH3 control strategy
has better results in Jan. (ammonium decreases up to 0.4 μg/m-3 in New
York). The spatial and temporal characteristics of the effectiveness of
these emission control strategies during the summer and winter seasons are
discussed.
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14. 14
Pinder, R. W.; Gilliland, A. B.; Dennis, R. L. Environmental impact of
atmospheric NH3 emissions under present and future conditions in the
eastern United States. Geophys. Res. Lett. 2008, 35, L12808, DOI:
10.1029/2008GL033732
[Crossref], [CAS], Google Scholar
14
Environmental impact of atmospheric NH3 emissions under present and future
conditions in the eastern United States
Pinder, R. W.; Gilliland, A. B.; Dennis, R. L.
Geophysical Research Letters (2008), 35 (12), L12808/1-L12808/6CODEN:
GPRLAJ; ISSN:0094-8276. (American Geophysical Union)
Recent regulations require large-scale emission redns. of NOx and SO2 in
the eastern United States. These emission changes will alter the
partitioning of ammonia between the gas and particle phases. Furthermore,
ammonia emissions are expected to increase in the future. How will these
changes impact the contribution of ammonia to inorg. particulate matter and
nitrogen deposition We use a chem. transport model and emission scenarios
representing years 2001, 2010, and 2020 to est. the future change of the
sensitivity of iPM2.5 to ammonia emission redns. and change in nitrogen
deposition to ecosystems. We find that during winter conditions,
particulate matter concns. in several locations in the Midwestern US
continue to have significant sensitivity to NH3 emissions. In addn., the
total nitrogen deposition near NH3 emission sources increases 10-40%.
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15. 15
Heald, C. L.; Collett, J. L., Jr.; Lee, T.; Benedict, K. B.; Schwandner, F.
M.; Li, Y.; Clarisse, L.; Hurtmans, D. R.; Van Damme, M.; Clerbaux, C.;
Coheur, P. F.; Philip, S.; Martin, R. V.; Pye, H. O. T. Atmospheric ammonia
and particulate inorganic nitrogen over the United States. Atmos. Chem.
Phys. 2012, 12, 10295– 10312, DOI: 10.5194/acp-12-10295-2012
[Crossref], [CAS], Google Scholar
15
Atmospheric ammonia and particulate inorganic nitrogen over the United
States
Heald, C. L.; Collett, J. L., Jr.; Lee, T.; Benedict, K. B.; Schwandner, F.
M.; Li, Y.; Clarisse, L.; Hurtmans, D. R.; Van Damme, M.; Clerbaux, C.;
Coheur, P.-F.; Philip, S.; Martin, R. V.; Pye, H. O. T.
Atmospheric Chemistry and Physics (2012), 12 (21), 10295-10312CODEN:
ACPTCE; ISSN:1680-7316. (Copernicus Publications)
We use in situ observations from the Interagency Monitoring of PROtected
Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring
Project, 11 surface site campaigns as well as IR Atm. Sounding
Interferometer (IASI) satellite measurements with the GEOS-Chem model to
investigate inorg. aerosol loading and atm. ammonia concns. over the United
States. IASI observations suggest that current ammonia emissions are
underestimated in California and in the springtime in the Midwest. In
California this underestimate likely drives the underestimate in nitrate
formation in the GEOS-Chem model. However in the remaining continental
United States we find that the nitrate simulation is biased high
(normalized mean bias > = 1.0) year-round, except in Spring (due to the
underestimate in ammonia in this season). None of the uncertainties in
precursor emissions, the uptake efficiency of N2O5 on aerosols, OH concns.,
the reaction rate for the formation of nitric acid, or the dry deposition
velocity of nitric acid are able to explain this bias. We find that
reducing nitric acid concns. to 75 % of their simulated values corrects the
bias in nitrate (as well as ammonium) in the US. However the mechanism for
this potential redn. is unclear and may be a combination of errors in
chem., deposition and sub-grid near-surface gradients. This "updated"
simulation reproduces PM and ammonia loading and captures the strong
seasonal and spatial gradients in gas-particle partitioning across the
United States. We est. that nitrogen makes up 15-35 % of inorg. fine PM
mass over the US, and that this fraction is likely to increase in the
coming decade, both with decreases in sulfur emissions and increases in
ammonia emissions.
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16. 16
Saylor, R.; Myles, L.; Sibble, D.; Caldwell, J.; Xing, J. Recent trends in
gas-phase ammonia and PM2.5 ammonium in the Southeast United States. J. Air
Waste Manage. Assoc. 2015, 65, 347– 357, DOI: 10.1080/10962247.2014.992554
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16
Recent trends in gas-phase ammonia and PM2.5 ammonium in the Southeast
United States
Saylor, Rick; Myles, LaToya; Sibble, Daryl; Caldwell, Jason; Xing, Jia
Journal of the Air & Waste Management Association (2015), 65 (3),
347-357CODEN: JAWAFC; ISSN:1096-2247. (Taylor & Francis Ltd.)
Ammonia measurements from the Southeastern Aerosol Research and
Characterization (SEARCH) study network were analyzed for trends over 9 yr
(2004-2012) of observations. Total ammonia concns., defined as the sum of
gas-phase ammonia and fine particle ammonium, were found to be decreasing
by 1-4% yr-1 and were qual. consistent with ammonia emission ests. for the
SEARCH states of Alabama, Georgia, Mississippi, and Florida. On the other
hand, gas-phase ammonia mixing ratios were found to be slightly rising or
steady over the region, leading to the observation that the gas-phase
fraction of total ammonia has steadily increased over 2004-2012 as a result
of declining emissions of the strong acid precursor species sulfur dioxide
(SO2) and nitrogen oxides (NOx) and consequent reduced partitioning of
ammonia to the fine particle phase. Because gas-phase ammonia is removed
from the atm. more rapidly than fine particle ammonium, an increase in the
gas-phase fraction of total ammonia may result in shifted deposition
patterns as more ammonia is deposited closer to sources rather than
transported downwind in fine particles. Addnl. long-term measurements and
modeling studies are needed to det. if similar transitions of total ammonia
to the gas phase are occurring outside of the Southeast and to assess if
these changes are impacting plants and ecosystems near major ammonia
sources. Unusually high ammonia concns. obsd. in 2007 in the SEARCH
measurements are hypothesized to be linked to emissions from wildfires that
were much more prevalent across the Southeast during that year due to
elevated temps. and widespread drought. Although wildfires are currently
estd. to be a relatively small fraction (3-10%) of total ammonia emissions
in the Southeast, the projected increased incidence of wildfires in this
region as a result of global climate change may lead to this source's
increased importance over the rest of the 21st century. Implications:
Ammonia concns. from the Southeastern Aerosol Research and Characterization
study (SEARCH) network are analyzed over the 9-yr period 2004-2012. Total
ammonia (gaseous ammonia + PM2.5 ammonium) concns. declined at a rate of
1-4% yr-1, consistent with U. S. Environmental Protection Agency (EPA)
emission ests. for the Southeast United States, but the fraction of ammonia
in the gas phase has risen steadily (+1-3% yr-1) over the time period.
Declining emissions of SO2 and NOx resulting from imposed air quality
regulations have resulted in decreased atm. strong acids and less ammonia
partitioning to the particle phase, which may impact the amt. and overall
pattern of ammonia deposition.
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17. 17
Lawal, A. S.; Guan, X.; Liu, C.; Henneman, L. R. F.; Vasilakos, P.;
Bhogineni, V.; Weber, R. J.; Nenes, A.; Russell, A. G. Linked Response of
Aerosol Acidity and Ammonia to SO2 and NOx Emissions Reductions in the
United States. Environ. Sci. Technol. 2018, 52, 9861– 9873, DOI:
10.1021/acs.est.8b00711
[ACS Full Text ], [CAS], Google Scholar
17
Linked Response of Aerosol Acidity and Ammonia to SO2 and NOx Emissions
Reductions in the United States
Lawal, Abiola S.; Guan, Xinbei; Liu, Cong; Henneman, Lucas R. F.;
Vasilakos, Petros; Bhogineni, Vasudha; Weber, Rodney J.; Nenes, Athanasios;
Russell, Armistead G.
Environmental Science & Technology (2018), 52 (17), 9861-9873CODEN: ESTHAG;
ISSN:0013-936X. (American Chemical Society)
Large redns. of sulfur and nitrogen oxide emissions in the United States
have led to considerable improvements in air quality, though recent
analyses in the Southeastern United States have shown little response of
aerosol pH to these redns. This study examines the effects of reduced
emissions on the trend of aerosol acidity in fine particulate matter
(PM2.5), at a nationwide scale, using ambient concn. data from three
monitoring networks-the Ammonia Monitoring Network (AMoN), the Clean Air
Status and Trends network (CASTNET) and the Southeastern Aerosol Research
and Characterization Network (SEARCH), in conjunction with thermodn.
(ISORROPIA-II) and chem. transport (CMAQ) model results. Sulfate and
ammonium experienced similar and significant decreases with little change
in pH, neutralization ratio (f = [NH4+]/2[SO42-] + [NO3-]), or nitrate. Oak
Grove, MS was the only SEARCH site showing statistically significant pH
changes in the Southeast region where small increases in pH (0.003-0.09 pH
units/yr) were obsd. Of the five regions characterized using CASTNET/AMoN
data, only California exhibited a statistically significant, albeit small
pH increase of +0.04 pH units/yr. Furthermore, statistically insignificant
(α = 0.05) changes in ammonia were obsd. in response to emission and PM2.5
speciation changes. CMAQ simulation results had similar responses, showing
steady ammonia levels and generally low pH, with little change from 2001 to
2011.
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18. 18
Hansen, D. A.; Edgerton, E. S.; Hartsell, B. E.; Jansen, J. J.; Kandasamy,
N.; Hidy, G. M.; Blanchard, C. L. The Southeastern Aerosol Research and
Characterization Study: Part 1─Overview. J. Air Waste Manage. Assoc. 2003,
53, 1460– 1471, DOI: 10.1080/10473289.2003.10466318
[Crossref], [PubMed], [CAS], Google Scholar
18
The Southeastern Aerosol Research and Characterization Study: part 1 -
overview
Hansen, D. Alan; Edgerton, Eric S.; Hartsell, Benjamin E.; Jansen, John J.;
Kandasamy, Navaneethakrishnan; Hidy, George M.; Blanchard, Charles L.
Journal of the Air & Waste Management Association (2003), 53 (12),
1460-1471CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
A review. This paper presents an overview of a major, long-term program for
tropospheric gas and aerosol research in the southeastern USA. Building on
three existing ozone-focused research sites begun in mid-1992, the
Southeastern Aerosol Research and Characterization Study (SEARCH) was
initiated in mid-1998 as a 7-yr observation and research program with a
broader focus, including aerosols and an expanded geog. coverage in the
Southeast. The monitoring network comprises four urban-rural (or
urban-suburban) site pairs at locations along the coast of the Gulf of
Mexico and inland, including two moderately sized and two major urban areas
(Pensacola, Florida; Gulfport, Mississippi; Atlanta, Georgia; and
Birmingham, Alabama). The sites are equipped with an extensive suite of
instruments for measuring particulate matter (PM), gases relevant to
secondary O3 and the prodn. of secondary aerosol particles, and surface
meteorol. The measurements taken to date have added substantially to the
knowledge about the temporal behavior and geog. variability of tropospheric
aerosols in the Southeast. Details are presented in four papers to follow.
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19. 19
Edgerton, E. S.; Hartsell, B. E.; Saylor, R. D.; Jansen, J. J.; Hansen, D.
A.; Hidy, G. M. The Southeastern Aerosol Research and Characterization
Study: Part II. Filter-Based Measurements of Fine and Coarse Particulate
Matter Mass and Composition. J. Air Waste Manage. Assoc. 2005, 55, 1527–
1542, DOI: 10.1080/10473289.2005.10464744
[Crossref], [PubMed], [CAS], Google Scholar
19
The Southeastern Aerosol Research and Characterization Study: part II.
Filter-based measurements of fine and coarse particulate matter mass and
composition
Edgerton, Eric S.; Hartsell, Benjamin E.; Saylor, Rick D.; Jansen, John J.;
Hansen, D. Alan; Hidy, George M.
Journal of the Air & Waste Management Association (2005), 55 (10),
1527-1542CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
The Southeastern Aerosol Research and Characterization Study (SEARCH) was
implemented in 1998-1999 to provide data and analyses for the investigation
of the sources, chem. speciation, and long-term trends of fine particulate
matter (PM2.5) and coarse particulate matter (PM10-2.5) in the Southeastern
United States. This work is an initial anal. of 5 years (1999-2003) of
filter-based PM2.5 and PM10-2.5 data from SEARCH. We find that annual PM2.5
design values were consistently above the National Ambient Air Quality
Stds. (NAAQS) 15 μg/m3 annual std. only at monitoring sites in the two
largest urban areas (Atlanta, GA, and North Birmingham, AL). Other sites in
the network had annual design values below the std., and no site had daily
design values above the NAAQS 65 μg/m3 daily std. Using a particle compn.
monitor designed specifically for SEARCH, we found that volatilization
losses of nitrate, ammonium, and org. carbon must be accounted for to
accurately characterize atm. particulate matter. In particular, the federal
ref. method for PM2.5 underestimates mass by 3-7% as a result of these
volatilization losses. Org. matter (OM) and sulfate account for ∼60% of
PM2.5 mass at SEARCH sites, whereas major metal oxides (MMO) and
unidentified components ("other") account for ≥80% of PM10-2.5 mass.
Limited data suggest that much of the unidentified mass in PM10-2.5 may be
OM. For paired comparisons of urban-rural sites, differences in PM2.5 mass
are explained, in large part, by higher OM and black carbon at the urban
site. For PM10 higher urban concns. are explained by higher MMO and
"other.". Annual means for PM2.5 and PM10-2.5 mass and major components
demonstrate substantial declines at all of the SEARCH sites over the
1999-2003 period (10-20% in the case of PM2..5, dominated by 14-20%
declines in sulfate and 11-26% declines in OM, and 14-25% in the case of
PM10-2.5, dominated by 17-30% declines in MMO and 14-31% declines in
"other"). Although declining national emissions of sulfur dioxide and
anthropogenic carbon may account for a portion of the obsd. declines,
addnl. investigation will be necessary to establish a quant. assessment,
esp. regading trends in local and regional emission, primary carbon
emissions, and meteorol.
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20. 20
Edgerton, E. S.; Hartsell, B. E.; Saylor, R. D.; Jansen, J. J.; Hansen, D.
A.; Hidy, G. M. The Southeastern Aerosol Research and Characterization
Study, Part 3: Continuous Measurements of Fine Particulate Matter Mass and
Composition. J. Air Waste Manage. Assoc. 2006, 56, 1325– 1341, DOI:
10.1080/10473289.2006.10464585
[Crossref], [PubMed], [CAS], Google Scholar
20
The Southeastern Aerosol Research and Characterization Study, part 3:
continuous measurements of fine particulate matter mass and composition
Edgerton, Eric S.; Hartsell, Benjamin E.; Saylor, Rick D.; Jansen, John J.;
Hansen, D. Alan; Hidy, George M.
Journal of the Air & Waste Management Association (2006), 56 (9),
1325-1341CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
Deployment of continuous analyzers in the Southeastern Aerosol Research and
Characterization Study (SEARCH) network began in 1998 and continues today
as new technologies are developed. Measurement of fine particulate matter
(PM2.5) mass is performed using a dried, 30 °C tapered element oscillating
microbalance (TEOM). TEOM measurements are complemented by observations of
light scattering by nephelometry. Measurements of major constituents
include: SO42- via redn. to SO2; NH4+ and NO3- via resp. catalytic oxidn.
and redn. to NO, black carbon (BC) by optical absorption, total carbon by
combustion to CO2, and org. carbon by difference between the latter two
measurements. Several illustrative examples of continuous data from the
SEARCH network are presented. A distinctive composite annual av. diurnal
pattern is obsd. for PM2.5 mass, nitrate, and BC, likely indicating the
influence of traffic-related emissions, growth, and break up of the
boundary layer and formation of ammonium nitrate. Examn. of PM2.5
components indicates the need to better understand the continuous compn. of
the unmeasured "other" category, because it contributes a significant
fraction to total mass during periods of high PM2.5 loading. Selected
episodes are presented to illustrate applications of SEARCH data. An SO2
conversion rate of 0.2%/h is derived from an observation of a plume from a
coal-fired power plant during early spring, and the importance of local,
rural sources of NH3 to the formation of ammonium nitrate in particulate
matter (PM) is demonstrated.
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21. 21
Zheng, G.; Su, H.; Wang, S.; Pozzer, A.; Cheng, Y. Impact of non-ideality
on reconstructing spatial and temporal variations of aerosol acidity with
multiphase buffer theory. Atmos. Chem. Phys. 2021, 2021, 47– 63, DOI:
10.5194/acp-22-47-2022
[Crossref], Google Scholar
There is no corresponding record for this reference.
22. 22
Fountoukis, C.; Nenes, A. ISORROPIA II: a computationally efficient
thermodynamic equilibrium model for
K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosols. Atmos. Chem. Phys. 2007,
7, 4639– 4659, DOI: 10.5194/acp-7-4639-2007
[Crossref], [CAS], Google Scholar
22
ISORROPIA II: a computationally efficient thermodynamic equilibrium model
for K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosols
Fountoukis, C.; Nenes, A.
Atmospheric Chemistry and Physics (2007), 7 (17), 4639-4659CODEN: ACPTCE;
ISSN:1680-7316. (Copernicus Publications)
This study presents ISORROPIA II, a thermodn. equil. model for the
K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosol system. A comprehensive
evaluation of its performance is conducted against water uptake
measurements for lab. aerosol and predictions of the SCAPE2 thermodn.
module over a wide range of atmospherically relevant conditions. The two
models agree well, to within 13% for aerosol water content and total PM
mass, 16% for aerosol nitrate and 6% for aerosol chloride and ammonium.
Largest discrepancies were found under conditions of low RH, primarily from
differences in the treatment of water uptake and solid state compn. In
terms of computational speed, ISORROPIA II was more than an order of
magnitude faster than SCAPE2, with robust and rapid convergence under all
conditions. The addn. of crustal species does not slow down the thermodn.
calcns. (compared to the older ISORROPIA code) because of optimizations in
the activity coeff. calcn. algorithm. Based on its computational rigor and
performance, ISORROPIA II appears to be a highly attractive alternative for
use in large scale air quality and atm. transport models.
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23. 23
Clegg, S. L.; Pitzer, K. S.; Brimblecombe, P. Thermodynamics of
multicomponent, miscible, ionic solutions. Mixtures including unsymmetrical
electrolytes. J. Phys. Chem. 1992, 96, 9470– 9479, DOI:
10.1021/j100202a074
[ACS Full Text ], [CAS], Google Scholar
23
Thermodynamics of multicomponent, miscible, ionic solutions. Mixtures
including unsymmetrical electrolytes
Clegg, Simon L.; Pitzer, Kenneth S.; Brimblecombe, Peter
Journal of Physical Chemistry (1992), 96 (23), 9470-9CODEN: JPCHAX;
ISSN:0022-3654.
Model equations for the excess Gibbs energy and solvent and solute activity
coeffs. (given previously for sym. salt systems) are developed for mixts.
contg. an indefinite no. of ions of arbitrary charge, over the entire
concn. range. The equations are expressed on a mole fraction basis and
comprise a Debye-Hueckel term extended to include the effects of unsym.
mixing and a Margules expansion carried out to the four suffix level. The
model is tested by using activity coeff. and salt soly. data data for the
systems H-(Al,Mg,Ca,Sr)-Cl-H2O, H-(La,Ca)-NO3-H2O, Na-Mg-Cl-SO4-H2O,
Mg-Ca-K-Cl-H2O, and Na-K-Mg-So4-H2O at 298.15 K. Thermodn. properties of
quaternary aq. solns. are predicted using only parameters detd. from binary
and ternary mixts. Salt solubilities in both systems involving HNO3 are
satisfactorily represented from aq. salt soln. to pure liq. HNO3.
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24. 24
Wexler, A. S.; Clegg, S. L. Atmospheric aerosol models for systems
including the ions H+, NH4+, Na+, SO42–, NO3–, Cl–, Br–, and H2O. J.
Geophys. Res.: Atmos. 2002, 107, ACH 14-1– ACH 14-14, DOI:
10.1029/2001JD000451
[Crossref], Google Scholar
There is no corresponding record for this reference.
25. 25
Friese, E.; Ebel, A. Temperature Dependent Thermodynamic Model of the
System H+–NH4+–Na+–SO42––NO3––Cl––H2O. J. Phys. Chem. A 2010, 114, 11595–
11631, DOI: 10.1021/jp101041j
[ACS Full Text ], [CAS], Google Scholar
25
Temperature Dependent Thermodynamic Model of the System
H+-NH4+-Na+-SO42--NO3--Cl--H2O
Friese, Elmar; Ebel, Adolf
Journal of Physical Chemistry A (2010), 114 (43), 11595-11631CODEN: JPCAFH;
ISSN:1089-5639. (American Chemical Society)
A thermodn. model of the system H+-NH4+-Na+-SO42--NO3--Cl--H2O is
parametrized and used to represent activity coeffs., equil. partial
pressures of H2O, HNO3, HCl, H2SO4, and NH3, and satn. with respect to 26
solid phases (NaCl(s), NaCl·2H2O(s), Na2SO4(s), Na2SO4·10H2O(s),
NaNO3·Na2SO4·H2O(s), Na3H(SO4)2(s), NaHSO4(s), NaHSO4·H2O(s),
NaNH4SO4·2H2O(s), NaNO3(s), NH4Cl(s), NH4NO3(s), (NH4)2SO4(s),
(NH4)3H(SO4)2(s), NH4HSO4(s), (NH4)2SO4·2NH4NO3(s), (NH4)2SO4·3NH4NO3(s),
H2SO4·H2O(s), H2SO4·2H2O(s), H2SO4·3H2O(s), H2SO4·4H2O(s), H2SO4·6.5H2O(s),
HNO3·H2O(s), HNO3·2H2O(s), HNO3·3H2O(s), and HCl·3H2O(s)). The enthalpy of
formation of the complex salts NaNH4SO4·2H2O(s) and Na2SO4·NaNO3·H2O(s) is
calcd. The model is valid for temps. .ltorsim. 263.15 up to 330 K and
concns. from infinite diln. to satn. with respect to the solid phases. For
H2SO4-H2O solns. the degree of dissocn. of the HSO4- ion is represented
near the exptl. uncertainty over wide temp. and concn. ranges. The
parametrization of the model for the subsystems H+-NH4+-NO3--SO42--H2O and
H+-NO3--SO42--Cl--H2O relies on previous studies, which are only partly
adjusted to new data. For these systems the model is applicable to temps.
below 200 K, dependent upon liq.-phase compn., and for the former system
also to supersatd. solns. Values for the model parameters are detd. from
literature data for the vapor pressure, osmotic coeff., emf, degree of
dissocn. of HSO4-, and the dissocn. const. of NH3 as well as measurements
of calorimetric properties of aq. solns. like enthalpy of diln., enthalpy
of soln., enthalpy of mixing, and heat capacity. The high accuracy of the
model is demonstrated by comparisons with exptl. detd. mean activity
coeffs. of HCl in HCl-Na2SO4-H2O solns., soly. measurements for the
quaternary systems H+-Na+-Cl--SO42--H2O, Na+-NH4+-Cl--SO42--H2O, and
Na+-NH4+-NO3--SO42--H2O as well as vapor pressure measurements of HNO3,
HCl, H2SO4, and NH3.
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26. 26
Hennigan, C. J.; Izumi, J.; Sullivan, A. P.; Weber, R. J.; Nenes, A. A
critical evaluation of proxy methods used to estimate the acidity of
atmospheric particles. Atmos. Chem. Phys. 2015, 15, 2775– 2790, DOI:
10.5194/acp-15-2775-2015
[Crossref], [CAS], Google Scholar
26
A critical evaluation of proxy methods used to estimate the acidity of
atmospheric particles
Hennigan, C. J.; Izumi, J.; Sullivan, A. P.; Weber, R. J.; Nenes, A.
Atmospheric Chemistry and Physics (2015), 15 (5), 2775-2790CODEN: ACPTCE;
ISSN:1680-7324. (Copernicus Publications)
Given significant challenges with available measurements of aerosol
acidity, proxy methods are frequently used to est. the acidity of atm.
particles. In this study, four of the most common aerosol acidity proxies
are evaluated and compared: (1) the ion balance method, (2) the molar ratio
method, (3) thermodn. equil. models, and (4) the phase partitioning of
ammonia. All methods are evaluated against predictions of thermodn. models
and against direct observations of aerosol-gas equil. partitioning acquired
in Mexico City during the Megacity Initiative: Local and Global Research
Objectives (MILAGRO) study. The ion balance and molar ratio methods assume
that any deficit in inorg. cations relative to anions is due to the
presence of H+ and that a higher H+ loading and lower cation/anion ratio
both correspond to increasingly acidic particles (i.e., lower pH). Based on
the MILAGRO measurements, no correlation is obsd. between H+ levels
inferred with the ion balance and aerosol pH predicted by the thermodn.
models and NH3-NH+4 partitioning. Similarly, no relationship is obsd.
between the cation/anion molar ratio and predicted aerosol pH. Using only
measured aerosol chem. compn. as inputs without any constraint for the gas
phase, the E-AIM (Extended Aerosol Inorgs. Model) and ISORROPIA-II
thermodn. equil. models tend to predict aerosol pH levels that are
inconsistent with the obsd. NH3-NH+4 partitioning. The modeled pH values
from both E-AIM and ISORROPIA-II run with gasCaerosol inputs agreed well
with the aerosol pH predicted by the phase partitioning of ammonia. It
appears that (1) thermodn. models constrained by gas + aerosol measurements
and (2) the phase partitioning of ammonia provide the best available
predictions of aerosol pH. Furthermore, neither the ion balance nor the
molar ratio can be used as surrogates for aerosol pH, and previously
published studies with conclusions based on such acidity proxies may need
to be reevaluated. Given the significance of acidity for chem. processes in
the atm., the implications of this study are important and far reaching.
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27. 27
Guo, H.; Xu, L.; Bougiatioti, A.; Cerully, K. M.; Capps, S. L.; Hite, J.
R., Jr.; Carlton, A. G.; Lee, S. H.; Bergin, M. H.; Ng, N. L.; Nenes, A.;
Weber, R. J. Fine-particle water and pH in the southeastern United States.
Atmos. Chem. Phys. 2015, 15, 5211– 5228, DOI: 10.5194/acp-15-5211-2015
[Crossref], [CAS], Google Scholar
27
Fine-particle water and pH in the southeastern United States
Guo, H.; Xu, L.; Bougiatioti, A.; Cerully, K. M.; Capps, S. L.; Hite, J.
R., Jr.; Carlton, A. G.; Lee, S.-H.; Bergin, M. H.; Ng, N. L.; Nenes, A.;
Weber, R. J.
Atmospheric Chemistry and Physics (2015), 15 (9), 5211-5228CODEN: ACPTCE;
ISSN:1680-7324. (Copernicus Publications)
Particle water and pH are predicted using meteorol. observations (relative
humidity (RH), temp. (T)), gas/particle compn., and thermodn. modeling
(ISORROPIA-II). A comprehensive uncertainty anal. is included, and the
model is validated. We investigate mass concns. of particle water and
related particle pH for ambient fine-mode aerosols sampled in a relatively
remote Alabama forest during the Southern Oxidant and Aerosol Study (SOAS)
in summer and at various sites in the southeastern US during different
seasons, as part of the Southeastern Center for Air Pollution and
Epidemiol. (SCAPE) study. Particle water and pH are closely linked; pH is a
measure of the particle H+ aq. concn. and depends on both the presence of
ions and amt. of particle liq. water. Levels of particle water, in turn,
are detd. through water uptake by both the ionic species and org. compds.
Thermodn. calcns. based on measured ion concns. can predict both pH and
liq. water but may be biased since contributions of org. species to liq.
water are not considered. In this study, contributions of both the inorg.
and org. fractions to aerosol liq. water were considered, and predictions
were in good agreement with measured liq. water based on differences in
ambient and dry light scattering coeffs. (prediction vs. measurement: slope
= 0.91, intercept = 0.5 μg m-3, R2 = 0.75). ISORROPIA-II predictions were
confirmed by good agreement between predicted and measured ammonia concns.
(slope = 1.07, intercept = -0.12 μg m-3, R2 = 0.76). Based on this study,
org. species on av. contributed 35% to the total water, with a
substantially higher contribution (50 %) at night. However, not including
contributions of org. water had a minor effect on pH (changes pH by 0.15 to
0.23 units), suggesting that predicted pH without consideration of org.
water could be sufficient for the purposes of aq. secondary org. aerosol
(SOA) chem. The mean pH predicted in the Alabama forest (SOAS) was 0.94 ±
0.59 (median 0.93). pH diurnal trends followed liq. water and were driven
mainly by variability in RH; during SOAS nighttime pH was near 1.5, while
daytime pH was near 0.5. pH ranged from 0.5 to 2 in summer and 1 to 3 in
the winter at other sites. The systematically low pH levels in the
southeast may have important ramifications, such as significantly
influencing acid-catalyzed reactions, gas-aerosol partitioning, and
mobilization of redox metals and minerals. Particle ion balances or molar
ratios, often used to infer pH, do not consider the dissocn. state of
individual ions or particle liq. water levels and do not correlate with
particle pH.
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28. 28
Nah, T.; Guo, H.; Sullivan, A. P.; Chen, Y.; Tanner, D. J.; Nenes, A.;
Russell, A.; Ng, N. L.; Huey, L. G.; Weber, R. J. Characterization of
aerosol composition, aerosol acidity, and organic acid partitioning at an
agriculturally intensive rural southeastern US site. Atmos. Chem. Phys.
2018, 18, 11471– 11491, DOI: 10.5194/acp-18-11471-2018
[Crossref], [CAS], Google Scholar
28
Characterization of aerosol composition, aerosol acidity, and organic acid
partitioning at an agriculturally intensive rural southeastern US site
Nah, Theodora; Guo, Hongyu; Sullivan, Amy P.; Chen, Yunle; Tanner, David
J.; Nenes, Athanasios; Russell, Armistead; Ng, Nga Lee; Huey, L. Gregory;
Weber, Rodney J.
Atmospheric Chemistry and Physics (2018), 18 (15), 11471-11491CODEN:
ACPTCE; ISSN:1680-7324. (Copernicus Publications)
The implementation of stringent emission regulations has resulted in the
decline of anthropogenic pollutants including sulfur dioxide (SO2),
nitrogen oxides (NOx), and carbon monoxide (CO). In contrast, ammonia (NH3)
emissions are largely unregulated, with emissions projected to increase in
the future. We present real-time aerosol and gas measurements from a field
study conducted in an agriculturally intensive region in the southeastern
US during the fall of 2016 to investigate how NH3 affects particle acidity
and secondary org. aerosol (SOA) formation via the gas-particle
partitioning of semi-volatile org. acids. Particle water and pH were detd.
using the ISORROPIA II thermodn. model and validated by comparing predicted
inorg. HNO3-NO3- and NH3-NHC4 gas-particle partitioning ratios with
measured values. Our results showed that despite the high NH3 concns. (av.
8.1±5.2 ppb), PM1 was highly acidic with pH values ranging from 0.9 to 3.8,
and an av. pH of 2.2±0.6. PM1 pH varied by approx. 1.4 units diurnally.
Measured particle-phase water-sol. org. acids were on av. 6% of the total
non-refractory PM1 org. aerosol mass. The measured oxalic acid gas-particle
partitioning ratios were in good agreement with their corresponding
thermodn. predictions, calcd. based on oxalic acid's physicochem.
properties, ambient temp., particle water, and pH.
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31. 31
Shi, W.; Ou, Y.; Smith, S. J.; Ledna, C. M.; Nolte, C. G.; Loughlin, D. H.
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Projecting state-level air pollutant emissions using an integrated
assessment model: GCAM-USA
Shi, Wenjing; Ou, Yang; Smith, Steven J.; Ledna, Catherine M.; Nolte,
Christopher G.; Loughlin, Daniel H.
Applied Energy (2017), 208 (), 511-521CODEN: APENDX; ISSN:0306-2619.
(Elsevier Ltd.)
Integrated Assessment Models (IAMs) characterize the interactions among
human and earth systems. IAMs typically have been applied to investigate
future energy, land use, and emission pathways at global to continental
scales. Recent directions in IAM development include enhanced technol.
detail, greater spatial and temporal resoln., and the inclusion of air
pollutant emissions. These developments expand the potential applications
of IAMs to include support for air quality management and for coordinated
environmental, climate, and energy planning. Furthermore, these IAMs could
help decision makers more fully understand tradeoffs and synergies among
policy goals, identify important cross-sector interactions, and, via
scenarios, consider uncertainties in factors such as population and
economic growth, technol. development, human behavior, and climate change.
A version of the Global Change Assessment Model with U. S. state-level
resoln. (GCAM-USA) is presented that incorporates U. S.-specific emission
factors, pollutant controls, and air quality and energy regulations.
Resulting air pollutant emission outputs are compared to U. S.
Environmental Protection Agency 2011 and projected inventories. A Quality
Metric is used to quantify GCAM-USA performance for several pollutants at
the sectoral and state levels. This information provides insights into the
types of applications for which GCAM-USA is currently well suited and
highlights where addnl. refinement may be warranted. While this anal. is
specific to the U. S., the results indicate more generally the importance
of enhanced spatial resoln. and of considering national and sub-national
regulatory constraints within IAMs.
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Ou, Y.; West, J. J.; Smith, S. J.; Nolte, C. G.; Loughlin, D. H. Air
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Air pollution control strategies directly limiting national health damages
in the US
Ou, Yang; West, J. Jason; Smith, Steven J.; Nolte, Christopher G.;
Loughlin, Daniel H.
Nature Communications (2020), 11 (1), 957CODEN: NCAOBW; ISSN:2041-1723.
(Nature Research)
Abstr.: Exposure to fine particulate matter (PM2.5) from fuel combustion
significantly contributes to global and US mortality. Traditional control
strategies typically reduce emissions for specific air pollutants and
sectors to maintain pollutant concns. below stds. Here we directly set
national PM2.5 mortality cost redn. targets within a global human-earth
system model with US state-level energy systems, in scenarios to 2050, to
identify endogenously the control actions, sectors, and locations that most
cost-effectively reduce PM2.5 mortality. We show that substantial health
benefits can be cost-effectively achieved by electrifying sources with high
primary PM2.5 emission intensities, including industrial coal, building
biomass, and industrial liqs. More stringent PM2.5 redn. targets expedite
the phaseout of high emission intensity sources, leading to larger declines
in major pollutant emissions, but very limited co-benefits in reducing CO2
emissions. Control strategies limiting health damages achieve the greatest
emission redns. in the East North Central and Middle Atlantic states.
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* Figures
* References
* Support Info
* ABSTRACT
High Resolution Image
Download MS PowerPoint Slide
FIGURE 1
Figure 1. Comparison of multiphase buffer theory and the pioneering W16
concept model in explaining aerosol acidity variations in SE-US. Over the
last decade in SE-US, SO42– has decreased substantially while the total
ammonia is roughly constant, and thus the TA/TS ratios have increased.
However, the pH is roughly the same. (a) W16 concept model attributed this
stable pH to the conversions in (NH4)2SO4/NH4HSO4 ratios, (10) while (b)
multiphase buffer theory explained it as the multiphase NH4+/NH3 buffering
effect. (1) Note that the amount of sulfate shown in (b) indicate the charge
equivalent concentrations.
High Resolution Image
Download MS PowerPoint Slide
FIGURE 2
Figure 2. Buffering capacity curve for US scenario. The inputs are based on
average summertime SEARCH data at the CTR site. Here, the influence of NVCs
is not considered (see Section 5), while NH3(g) is included. In panel (c),
the left Y axis correspond to β shown by the shaded areas, while the right Y
axis correspond to the pH shown by the filled black circles. As the NH3(g)
measurements are missing in 2011, it was assumed to be the average of NH3(g)
in 2010 and 2012 (the hollow circle in Figure 2c). The black dashed line
indicates the fitted annual pH trends for reference. The result shown here is
based on the ISORROPIA model, while that based on the E-AIM model is shown in
Figure S2. Although the detailed pH values predicted by these two models can
differ by ±0.3 units, both models indicate the same variations in the
dominant buffering regimes. Note that the pH jump in 2008 is likely related
to minor bugs in the ISORROPIA algorithm (see Figure S3).
High Resolution Image
Download MS PowerPoint Slide
FIGURE 3
Figure 3. Potential influence of organic acids in the buffer capacities in
SE-US. (a) Example buffering capacity curve based on the average summer 2016
conditions at the CTR site. (b) Annual trends in ISORROPIA-predicted pH and
ideal pKa* of major organic acids in summer SE-US. The total (gas + particle)
concentrations of the three investigated organic acids, HCOOH, CH3COOH, and
(COOH)2, are based on the observation in an agriculturally intensive rural
SE-US site in fall 2016, (28) which is near the CTR site. These
concentrations are expected to be satisfactory as an order-of-magnitude
estimation of the concentrations in the summer CTR site.
High Resolution Image
Download MS PowerPoint Slide
FIGURE 4
Figure 4. Explanations for the decreasing trend of ammonium-to-sulfate molar
ratios RSO4, where RSO4 = ([NH4+] – [NO3–])/[SO42–]tot. (a) Observed trend of
TA/TS, RSO4, and NVCs/TS in SEARCH-CTR site in summer 2004 to 2016. (b)
Simulated trend with decreasing SO42–, assuming constant NH3(g) of 0.23 μg
m–3 (decadal mean of CTR site). (c) Simulated variation of the difference
between the corrected ratios, RSO4,f, and RSO4 with sulfate and gas-phase
NH3. Simulation in panels (b) and (c) reproduced settings in Figure 2 of
Weber et al.10, i.e., assuming a constant Na+ = 0.03 μg m–3, total HNO3 =
0.08 μg m–3, total HCl = 0.02 μg m–3, temperature of 298 K, and RH at 73.8%.
High Resolution Image
Download MS PowerPoint Slide
FIGURE 5
Figure 5. Predicted future U.S. pH trends. (a) “Ref” scenario is based on Shi
et al., (31) while (b) “US50” scenario is more stringent as assumed in Ou et
al. (32) The shaded area indicates the NH3 buffered pH ranges (i.e., the
ammonia pKa*,ni ± 1).
High Resolution Image
Download MS PowerPoint Slide
* REFERENCES
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This article references 32 other publications.
1. 1
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Advancement of Science)
Aerosol acidity largely regulates the chem. of atm. particles, and
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ISSN:1680-7324. (Copernicus Publications)
Acidity, defined as pH, is a central component of aq. chem. In the atm.,
the acidity of condensed phases (aerosol particles, cloud water, and fog
droplets) governs the phase partitioning of semivolatile gases such as
HNO3, NH3, HCl, and org. acids and bases as well as chem. reaction rates.
It has implications for the atm. lifetime of pollutants, deposition, and
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as well as ambient ammonia. Historical measurements indicate that cloud
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knowledge on the acidity of atm. condensed phases, specifically particles
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ISSN:0001-4842. (American Chemical Society)
Atm. aerosols and fine particulate matter (PM2.5) are strongly affecting
human health and climate in the Anthropocene, i.e., in the current era of
globally pervasive and rapidly increasing human influence on planet
Earth. Poor air quality assocd. with high aerosol concns. is among the
leading health risks worldwide, causing millions of attributable excess
deaths and years of life lost every year. Besides their health impact,
aerosols are also influencing climate through interactions with clouds
and solar radiation with an estd. neg. total effective radiative forcing
that may compensate about half of the pos. radiative forcing of carbon
dioxide but exhibits a much larger uncertainty. Heterogeneous and
multiphase chem. reactions on the surface and in the bulk of solid,
semisolid, and liq. aerosol particles have been recognized to influence
aerosol formation and transformation and thus their environmental
effects. However, atm. multiphase chem. is not well understood because of
its intrinsic complexity of dealing with the matter in multiple phases
and the difficulties of distinguishing its effect from that of gas phase
reactions. Recently, research on atm. multiphase chem. received a boost
from the growing interest in understanding severe haze formation of very
high PM2.5 concns. in polluted megacities and densely populated regions.
State-of-the-art models suggest that the gas phase reactions, however,
are not capturing the high concns. and rapid increase of PM2.5 obsd.
during haze events, suggesting a gap in our understanding of the chem.
mechanisms of aerosol formation. These haze events are characterized by
high concns. of aerosol particles and high humidity, esp. favoring
multiphase chem. In this Account, we review recent advances that we have
made, as well as current challenges and future perspectives for research
on multiphase chem. processes involved in atm. aerosol formation and
transformation. We focus on the following questions: what are the key
reaction pathways leading to aerosol formation under polluted conditions,
what is the relative importance of multiphase chem. vs. gas-phase chem.,
and what are the implications for the development of efficient and
reliable air quality control strategies. In particular, we discuss
advances and challenges related to different chem. regimes of sulfate,
nitrate, and secondary org. aerosols (SOAs) under haze conditions, and we
synthesize new insights into the influence of aerosol water content,
aerosol pH, phase state, and nanoparticle size effects. Overall, there is
increasing evidence that multiphase chem. plays an important role in
aerosol formation during haze events. In contrast to the gas phase
photochem. reactions, which are self-buffered against heavy pollution,
multiphase reactions have a pos. feedback mechanism, where higher
particle matter levels accelerate multiphase prodn., which further
increases the aerosol concn. resulting in a series of record-breaking
pollution events. We discuss perspectives to fill the gap of the current
understanding of atm. multiphase reactions that involve multiple phys.
and chem. processes from bulk to nanoscale and from regional to global
scales. A synthetic approach combining lab. expts., field measurements,
instrument development, and model simulations is suggested as a roadmap
to advance future research.
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Ulrich; Su, Hang
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ISSN:2375-2548. (American Association for the Advancement of Science)
Fine-particle pollution assocd. with winter haze threatens the health of
more than 400 million people in the North China Plain. Sulfate is a major
component of fine haze particles. Record sulfate concns. of up to ∼300 μg
m-3 were obsd. during the Jan. 2013 winter haze event in Beijing.
State-of-the-art air quality models that rely on sulfate prodn.
mechanisms requiring photochem. oxidants cannot predict these high levels
because of the weak photochem. activity during haze events. We find that
the missing source of sulfate and particulate matter can be explained by
reactive nitrogen chem. in aerosol water. The aerosol water serves as a
reactor, where the alk. aerosol components trap SO2, which is oxidized by
NO2 to form sulfate, whereby high reaction rates are sustained by the
high neutralizing capacity of the atm. in northern China. This mechanism
is self-amplifying because higher aerosol mass concn. corresponds to
higher aerosol water content, leading to faster sulfate prodn. and more
severe haze pollution.
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6. 6
Li, W.; Xu, L.; Liu, X.; Zhang, J.; Lin, Y.; Yao, X.; Gao, H.; Zhang, D.;
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Nenes, Athanasios; Shi, Zongbo
Science Advances (2017), 3 (3), e1601749/1-e1601749/6CODEN: SACDAF;
ISSN:2375-2548. (American Association for the Advancement of Science)
It has long been hypothesized that acids formed from anthropogenic
pollutants and natural emissions dissolve iron (Fe) in airborne
particles, enhancing the supply of bioavailable Fe to the oceans.
However, field observations have yet to provide indisputable evidence to
confirm this hypothesis. Single-particle chem. anal. for hundreds of
individual atm. particles collected over the East China Sea shows that
Fe-rich particles from coal combustion and steel industries were coated
with thick layers of sulfate after 1 to 2 days of atm. residence. The Fe
in aged particles was present as a "hotspot" of (insol.) iron oxides and
throughout the acidic sulfate coating in the form of (sol.) Fe sulfate,
which increases with degree of aging (thickness of coating). This
provides the "smoking gun" for acid iron dissoln., because iron sulfate
was not detected in the freshly emitted particles and there is no other
source or mechanism of iron sulfate formation in the atm.
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7. 7
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We examined the respiratory health effects of exposure to acidic air
pollution among 13,369 white children 8 to 12 years old from 24
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a two-stage logistic regression model to analyze the data, adjusting for
the potential confounding effects of sex, history of allergies, parental
asthma, parental education, and current smoking in the home. Children
living in the community with the highest levels of particle strong
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confidence interval (CI) 1.11-2.48] to report at least one episode of
bronchitis in the past year compared to children living in the
least-polluted community. Fine particulate sulfate was also associated
with higher reporting of bronchitis (OR = 1.65; 95% CI 1.12-2.42). No
other respiratory symptoms were significantly higher in association with
any of the air pollutants of interest. No sensitive subgroups were
identified. Reported bronchitis, but neither asthma, wheeze, cough, nor
phlegm, were associated with levels of particle strong acidity for these
children living in a nonurban environment.
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8. 8
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Freedman, Miriam Arak; Ott, Emily-Jean E.; Marak, Katherine E.
Journal of Physical Chemistry A (2019), 123 (7), 1275-1284CODEN: JPCAFH;
ISSN:1089-5639. (American Chemical Society)
PH is one of the most basic chem. properties of aq. soln., but its
measurement in nanoscale aerosol particles presents many challenges. The
pH of aerosol particles is of growing interest in the atm. chem.
community because of its demonstrated effects on heterogeneous chem. and
human health, as well as potential effects on climate. The authors have
shown that phase transitions of aerosol particles are sensitive to pH,
focusing on systems that undergo liq.-liq. phase sepn. Currently, aerosol
pH is calcd. indirectly from knowledge of species present in the gas and
aerosol phases through the use of thermodn. models. From these models,
ambient aerosol is expected to be highly acidic (pH ∼ 0-3). Direct
measurements have focused on model systems due to the difficulty of this
measurement. This area is one in which phys. chemists should be
encouraged to contribute because of the potential consequences for
aerosol processes in the environment.
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9. 9
Zheng, G. J.; Duan, F. K.; Su, H.; Ma, Y. L.; Cheng, Y.; Zheng, B.;
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Zhang, Q.; Huang, T.; Kimoto, T.; Chang, D.; Poschl, U.; Cheng, Y. F.;
He, K. B.
Atmospheric Chemistry and Physics (2015), 15 (6), 2969-2983CODEN: ACPTCE;
ISSN:1680-7324. (Copernicus Publications)
Extreme haze episodes repeatedly shrouded Beijing during the winter of
2012-2013, causing major environmental and health problems. To better
understand these extreme events, we performed a model-assisted anal. of
the hourly observation data of PM2.5 and its major chem. compns. The
synthetic anal. shows that (1) the severe winter haze was driven by
stable synoptic meteorol. conditions over northeastern China, and not by
an abrupt increase in anthropogenic emissions. (2) Secondary species,
including orgs., sulfate, nitrate, and ammonium, were the major
constituents of PM2.5 during this period. (3) Due to the dimming effect
of high loading of aerosol particles, gaseous oxidant concns. decreased
significantly, suggesting a reduced prodn. of secondary aerosols through
gas-phase reactions. Surprisingly, the observational data reveals an
enhanced prodn. rate of secondary aerosols, suggesting an important
contribution from other formation pathways, most likely heterogeneous
reactions. These reactions appeared to be more efficient in producing
secondary inorgs. aerosols than org. aerosols resulting in a strongly
elevated fraction of inorgs. during heavily polluted periods. (4)
Moreover, we found that high aerosol concn. was a regional phenomenon.
The accumulation process of aerosol particles occurred successively from
cities southeast of Beijing. The apparent sharp increase in PM2.5 concn.
of up to several hundred μgm-3 per h recorded in Beijing represented
rapid recovery from an interruption to the continuous pollution
accumulation over the region, rather than purely local chem. prodn. This
suggests that regional transport of pollutants played an important role
during these severe pollution events.
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10. 10
Weber, R. J.; Guo, H.; Russell, A. G.; Nenes, A. High aerosol acidity
despite declining atmospheric sulfate concentrations over the past 15
years. Nat. Geosci. 2016, 9, 282– 285, DOI: 10.1038/ngeo2665
[Crossref], [CAS], Google Scholar
10
High aerosol acidity despite declining atmospheric sulfate concentrations
over the past 15 years
Weber, Rodney J.; Guo, Hongyu; Russell, Armistead G.; Nenes, Athanasios
Nature Geoscience (2016), 9 (4), 282-285CODEN: NGAEBU; ISSN:1752-0894.
(Nature Publishing Group)
Particle acidity affects aerosol concns., chem. compn. and toxicity.
Sulfate is often the main acid component of aerosols, and largely dets.
the acidity of fine particles under 2.5 μm in diam., PM2.5. Over the past
15 years, atm. sulfate concns. in the southeastern United States have
decreased by 70%, whereas ammonia concns. have been steady. Similar
trends are occurring in many regions globally. Aerosol ammonium nitrate
concns. were assumed to increase to compensate for decreasing sulfate,
which would result from increasing neutrality. Here we use obsd. gas and
aerosol compn., humidity, and temp. data collected at a rural
southeastern US site in June and July 2013 (ref. 1), and a thermodn.
model that predicts pH and the gas-particle equil. concns. of inorg.
species from the observations to show that PM2.5 at the site is acidic.
PH buffering by partitioning of ammonia between the gas and particle
phases produced a relatively const. particle pH of 0-2 throughout the 15
years of decreasing atm. sulfate concns., and little change in particle
ammonium nitrate concns. We conclude that the redns. in aerosol acidity
widely anticipated from sulfur redns., and expected acidity-related
health and climate benefits, are unlikely to occur until atm. sulfate
concns. reach near pre-anthropogenic levels.
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11. 11
West, J. J.; Ansari, A. S.; Pandis, S. N. Marginal PM25: Nonlinear
Aerosol Mass Response to Sulfate Reductions in the Eastern United States.
J. Air Waste Manage. Assoc. 1999, 49, 1415– 1424, DOI:
10.1080/10473289.1999.10463973
[Crossref], [PubMed], [CAS], Google Scholar
11
Marginal PM2.5: nonlinear aerosol mass response to sulfate reductions in
the eastern United States
West, J. Jason; Ansari, Asif S.; Pandis, Spyros N.
Journal of the Air & Waste Management Association (1999), 49 (12),
1415-1424CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
Redns. in airborne sulfate concn. may cause inorg. fine particulate
matter (PM2.5) to respond nonlinearly, as nitric acid gas may transfer to
the aerosol phase. Where this occurs, redns. in sulfur dioxide (SO2)
emissions will be much less effective than expected at reducing PM2.5. As
a measure of the efficacy of redns. in sulfate concn. on PM2.5, we define
marginal PM2.5 as the local change in PM2.5 resulting from a small change
in sulfate concn. Using seasonal-av. conditions and assuming thermodn.
equil., we find that the conditions for PM2.5 to respond nonlinearly to
sulfate redns. are common in the eastern United States in winter,
occurring at half of the sites considered, and uncommon in summer, due
primarily to the influence of temp. Accounting for diurnal and
intraseasonal variability, we find that seasonal-av. conditions provide a
reasonable indicator of the time-averaged PM2.5 response. These results
indicate that redns. in sulfate concn. may be up to 50% less effective at
reducing the annual-av. PM2.5 than if the role of nitric acid is
neglected. Further, large redns. in sulfate will also cause an increase
in aerosol nitrate in many regions that are the most acidic.
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12. 12
Pinder, R. W.; Adams, P. J.; Pandis, S. N. Ammonia Emission Controls as a
Cost-Effective Strategy for Reducing Atmospheric Particulate Matter in
the Eastern United States. Environ. Sci. Technol. 2007, 41, 380– 386,
DOI: 10.1021/es060379a
[ACS Full Text ], [CAS], Google Scholar
12
Ammonia Emission Controls as a Cost-Effective Strategy for Reducing
Atmospheric Particulate Matter in the Eastern United States
Pinder, Robert W.; Adams, Peter J.; Pandis, Spyros N.
Environmental Science & Technology (2007), 41 (2), 380-386CODEN: ESTHAG;
ISSN:0013-936X. (American Chemical Society)
Current regulation aimed at reducing inorg. atm. fine particulate matter
(PM2.5) is focused on redns. in SO2 and NOx ≡ NO + NO2; however, controls
on these pollutants are likely to increase in cost and decrease in
effectiveness in the future. A supplementary strategy is redn. in NH3
emissions, yet an evaluation of controls on ammonia has been limited by
uncertainties in emission levels and in the cost of control technologies.
We use state of the science emission inventories, an emission-based
regional air quality model, and an explicit treatment of uncertainty to
est. the cost-effectiveness and uncertainty of ammonia emission redns. on
inorg. particulate matter in the Eastern USA. Since a paucity of data on
agricultural operations precludes a direct calcn. of the costs of ammonia
control, we calc. the ammonia savings potential, defined as the min. cost
of applying SO2 and NOx emission controls in order to achieve the same
redn. in ambient inorg. PM2.5 concn. as obtained from a 1 ton decrease in
ammonia emissions. Using 250 scenarios of NH3, SO2, and NOx emission
redns., we calc. the least-cost SO2 and NOx control scenarios that
achieve the same redn. in ambient inorg. PM2.5 concn. as a decrease in
ammonia emissions. We find that the lower-bound ammonia savings potential
in the winter is $8,000/ton NH3; therefore, many currently available
ammonia control technologies are cost-effective compared to current
controls on SO2 and NOx sources. Larger redns. in winter inorg.
particulate matter are available at lower cost through controls on
ammonia emissions.
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13. 13
Tsimpidi, A. P.; Karydis, V. A.; Pandis, S. N. Response of Inorganic Fine
Particulate Matter to Emission Changes of Sulfur Dioxide and Ammonia: The
Eastern United States as a Case Study. J. Air Waste Manage. Assoc. 2007,
57, 1489– 1498, DOI: 10.3155/1047-3289.57.12.1489
[Crossref], [CAS], Google Scholar
13
Response of inorganic fine particulate matter to emission changes of
sulfur dioxide and ammonia: the Eastern United States as a case study
Tsimpidi, Alexandra P.; Karydis, Vlassis A.; Pandis, Spyros N.
Journal of the Air & Waste Management Association (2007), 57 (12),
1489-1498CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
A three-dimensional chem. transport model (PMCAMx) was used to
investigate changes in fine particle (PM2.5) concns. in response to
changes in sulfur dioxide (SO2) and ammonia (NH3) emissions during July
2001 and Jan. 2002 in the eastern United States. A uniform 50% redn. in
SO2 emissions was predicted to produce an av. decrease of PM2.5 concns.
by 26% during July but only 6% during Jan. A 50% redn. of NH3 emissions
leads to an av. 4 and 9% decrease in PM2.5 in July and Jan., resp. During
the summer, the highest concn. of sulfate is in South Indiana (12.8 μg /
m-3), and the 50% redn. of SO2 emissions results in a 5.7 μg / m-3(44%)
sulfate decrease over this area. During winter, the SO2 emissions redn.
results in a 1.5 μg/m-3 (29%) decrease of the peak sulfate levels (5.2
μg/m-3) over Southeast Georgia. The max. nitrate and ammonium concns. are
predicted to be over the Midwest (1.9 μg/m-3 in Ohio and 5.3 μg/m-3 in
South Indiana, resp.) in the summer whereas in the winter these concns.
are higher over the Northeast (3 μg/m-3 of nitrate in Connecticut and 2.7
μg/m-3 of ammonium in New York). The 50% NH3 emissions redn. is more
effective for controlling nitrate, compared with SO2 redns., producing a
1.1 μg/m-3 nitrate decrease over Ohio in July and a 1.2 μg/m-3 decrease
over Connecticut in Jan. Ammonium decreases significantly when either SO2
or NH3 emissions are decreased. However, the SO2 control strategy has
better results in July when ammonium decreases, up to 2 μg/m-3 (37%), are
predicted in South Indiana. The NH3 control strategy has better results
in Jan. (ammonium decreases up to 0.4 μg/m-3 in New York). The spatial
and temporal characteristics of the effectiveness of these emission
control strategies during the summer and winter seasons are discussed.
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14. 14
Pinder, R. W.; Gilliland, A. B.; Dennis, R. L. Environmental impact of
atmospheric NH3 emissions under present and future conditions in the
eastern United States. Geophys. Res. Lett. 2008, 35, L12808, DOI:
10.1029/2008GL033732
[Crossref], [CAS], Google Scholar
14
Environmental impact of atmospheric NH3 emissions under present and
future conditions in the eastern United States
Pinder, R. W.; Gilliland, A. B.; Dennis, R. L.
Geophysical Research Letters (2008), 35 (12), L12808/1-L12808/6CODEN:
GPRLAJ; ISSN:0094-8276. (American Geophysical Union)
Recent regulations require large-scale emission redns. of NOx and SO2 in
the eastern United States. These emission changes will alter the
partitioning of ammonia between the gas and particle phases. Furthermore,
ammonia emissions are expected to increase in the future. How will these
changes impact the contribution of ammonia to inorg. particulate matter
and nitrogen deposition We use a chem. transport model and emission
scenarios representing years 2001, 2010, and 2020 to est. the future
change of the sensitivity of iPM2.5 to ammonia emission redns. and change
in nitrogen deposition to ecosystems. We find that during winter
conditions, particulate matter concns. in several locations in the
Midwestern US continue to have significant sensitivity to NH3 emissions.
In addn., the total nitrogen deposition near NH3 emission sources
increases 10-40%.
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15. 15
Heald, C. L.; Collett, J. L., Jr.; Lee, T.; Benedict, K. B.; Schwandner,
F. M.; Li, Y.; Clarisse, L.; Hurtmans, D. R.; Van Damme, M.; Clerbaux,
C.; Coheur, P. F.; Philip, S.; Martin, R. V.; Pye, H. O. T. Atmospheric
ammonia and particulate inorganic nitrogen over the United States. Atmos.
Chem. Phys. 2012, 12, 10295– 10312, DOI: 10.5194/acp-12-10295-2012
[Crossref], [CAS], Google Scholar
15
Atmospheric ammonia and particulate inorganic nitrogen over the United
States
Heald, C. L.; Collett, J. L., Jr.; Lee, T.; Benedict, K. B.; Schwandner,
F. M.; Li, Y.; Clarisse, L.; Hurtmans, D. R.; Van Damme, M.; Clerbaux,
C.; Coheur, P.-F.; Philip, S.; Martin, R. V.; Pye, H. O. T.
Atmospheric Chemistry and Physics (2012), 12 (21), 10295-10312CODEN:
ACPTCE; ISSN:1680-7316. (Copernicus Publications)
We use in situ observations from the Interagency Monitoring of PROtected
Visual Environments (IMPROVE) network, the Midwest Ammonia Monitoring
Project, 11 surface site campaigns as well as IR Atm. Sounding
Interferometer (IASI) satellite measurements with the GEOS-Chem model to
investigate inorg. aerosol loading and atm. ammonia concns. over the
United States. IASI observations suggest that current ammonia emissions
are underestimated in California and in the springtime in the Midwest. In
California this underestimate likely drives the underestimate in nitrate
formation in the GEOS-Chem model. However in the remaining continental
United States we find that the nitrate simulation is biased high
(normalized mean bias > = 1.0) year-round, except in Spring (due to the
underestimate in ammonia in this season). None of the uncertainties in
precursor emissions, the uptake efficiency of N2O5 on aerosols, OH
concns., the reaction rate for the formation of nitric acid, or the dry
deposition velocity of nitric acid are able to explain this bias. We find
that reducing nitric acid concns. to 75 % of their simulated values
corrects the bias in nitrate (as well as ammonium) in the US. However the
mechanism for this potential redn. is unclear and may be a combination of
errors in chem., deposition and sub-grid near-surface gradients. This
"updated" simulation reproduces PM and ammonia loading and captures the
strong seasonal and spatial gradients in gas-particle partitioning across
the United States. We est. that nitrogen makes up 15-35 % of inorg. fine
PM mass over the US, and that this fraction is likely to increase in the
coming decade, both with decreases in sulfur emissions and increases in
ammonia emissions.
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16. 16
Saylor, R.; Myles, L.; Sibble, D.; Caldwell, J.; Xing, J. Recent trends
in gas-phase ammonia and PM2.5 ammonium in the Southeast United States.
J. Air Waste Manage. Assoc. 2015, 65, 347– 357, DOI:
10.1080/10962247.2014.992554
[Crossref], [CAS], Google Scholar
16
Recent trends in gas-phase ammonia and PM2.5 ammonium in the Southeast
United States
Saylor, Rick; Myles, LaToya; Sibble, Daryl; Caldwell, Jason; Xing, Jia
Journal of the Air & Waste Management Association (2015), 65 (3),
347-357CODEN: JAWAFC; ISSN:1096-2247. (Taylor & Francis Ltd.)
Ammonia measurements from the Southeastern Aerosol Research and
Characterization (SEARCH) study network were analyzed for trends over 9
yr (2004-2012) of observations. Total ammonia concns., defined as the sum
of gas-phase ammonia and fine particle ammonium, were found to be
decreasing by 1-4% yr-1 and were qual. consistent with ammonia emission
ests. for the SEARCH states of Alabama, Georgia, Mississippi, and
Florida. On the other hand, gas-phase ammonia mixing ratios were found to
be slightly rising or steady over the region, leading to the observation
that the gas-phase fraction of total ammonia has steadily increased over
2004-2012 as a result of declining emissions of the strong acid precursor
species sulfur dioxide (SO2) and nitrogen oxides (NOx) and consequent
reduced partitioning of ammonia to the fine particle phase. Because
gas-phase ammonia is removed from the atm. more rapidly than fine
particle ammonium, an increase in the gas-phase fraction of total ammonia
may result in shifted deposition patterns as more ammonia is deposited
closer to sources rather than transported downwind in fine particles.
Addnl. long-term measurements and modeling studies are needed to det. if
similar transitions of total ammonia to the gas phase are occurring
outside of the Southeast and to assess if these changes are impacting
plants and ecosystems near major ammonia sources. Unusually high ammonia
concns. obsd. in 2007 in the SEARCH measurements are hypothesized to be
linked to emissions from wildfires that were much more prevalent across
the Southeast during that year due to elevated temps. and widespread
drought. Although wildfires are currently estd. to be a relatively small
fraction (3-10%) of total ammonia emissions in the Southeast, the
projected increased incidence of wildfires in this region as a result of
global climate change may lead to this source's increased importance over
the rest of the 21st century. Implications: Ammonia concns. from the
Southeastern Aerosol Research and Characterization study (SEARCH) network
are analyzed over the 9-yr period 2004-2012. Total ammonia (gaseous
ammonia + PM2.5 ammonium) concns. declined at a rate of 1-4% yr-1,
consistent with U. S. Environmental Protection Agency (EPA) emission
ests. for the Southeast United States, but the fraction of ammonia in the
gas phase has risen steadily (+1-3% yr-1) over the time period. Declining
emissions of SO2 and NOx resulting from imposed air quality regulations
have resulted in decreased atm. strong acids and less ammonia
partitioning to the particle phase, which may impact the amt. and overall
pattern of ammonia deposition.
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17. 17
Lawal, A. S.; Guan, X.; Liu, C.; Henneman, L. R. F.; Vasilakos, P.;
Bhogineni, V.; Weber, R. J.; Nenes, A.; Russell, A. G. Linked Response of
Aerosol Acidity and Ammonia to SO2 and NOx Emissions Reductions in the
United States. Environ. Sci. Technol. 2018, 52, 9861– 9873, DOI:
10.1021/acs.est.8b00711
[ACS Full Text ], [CAS], Google Scholar
17
Linked Response of Aerosol Acidity and Ammonia to SO2 and NOx Emissions
Reductions in the United States
Lawal, Abiola S.; Guan, Xinbei; Liu, Cong; Henneman, Lucas R. F.;
Vasilakos, Petros; Bhogineni, Vasudha; Weber, Rodney J.; Nenes,
Athanasios; Russell, Armistead G.
Environmental Science & Technology (2018), 52 (17), 9861-9873CODEN:
ESTHAG; ISSN:0013-936X. (American Chemical Society)
Large redns. of sulfur and nitrogen oxide emissions in the United States
have led to considerable improvements in air quality, though recent
analyses in the Southeastern United States have shown little response of
aerosol pH to these redns. This study examines the effects of reduced
emissions on the trend of aerosol acidity in fine particulate matter
(PM2.5), at a nationwide scale, using ambient concn. data from three
monitoring networks-the Ammonia Monitoring Network (AMoN), the Clean Air
Status and Trends network (CASTNET) and the Southeastern Aerosol Research
and Characterization Network (SEARCH), in conjunction with thermodn.
(ISORROPIA-II) and chem. transport (CMAQ) model results. Sulfate and
ammonium experienced similar and significant decreases with little change
in pH, neutralization ratio (f = [NH4+]/2[SO42-] + [NO3-]), or nitrate.
Oak Grove, MS was the only SEARCH site showing statistically significant
pH changes in the Southeast region where small increases in pH
(0.003-0.09 pH units/yr) were obsd. Of the five regions characterized
using CASTNET/AMoN data, only California exhibited a statistically
significant, albeit small pH increase of +0.04 pH units/yr. Furthermore,
statistically insignificant (α = 0.05) changes in ammonia were obsd. in
response to emission and PM2.5 speciation changes. CMAQ simulation
results had similar responses, showing steady ammonia levels and
generally low pH, with little change from 2001 to 2011.
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18. 18
Hansen, D. A.; Edgerton, E. S.; Hartsell, B. E.; Jansen, J. J.;
Kandasamy, N.; Hidy, G. M.; Blanchard, C. L. The Southeastern Aerosol
Research and Characterization Study: Part 1─Overview. J. Air Waste
Manage. Assoc. 2003, 53, 1460– 1471, DOI: 10.1080/10473289.2003.10466318
[Crossref], [PubMed], [CAS], Google Scholar
18
The Southeastern Aerosol Research and Characterization Study: part 1 -
overview
Hansen, D. Alan; Edgerton, Eric S.; Hartsell, Benjamin E.; Jansen, John
J.; Kandasamy, Navaneethakrishnan; Hidy, George M.; Blanchard, Charles L.
Journal of the Air & Waste Management Association (2003), 53 (12),
1460-1471CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
A review. This paper presents an overview of a major, long-term program
for tropospheric gas and aerosol research in the southeastern USA.
Building on three existing ozone-focused research sites begun in
mid-1992, the Southeastern Aerosol Research and Characterization Study
(SEARCH) was initiated in mid-1998 as a 7-yr observation and research
program with a broader focus, including aerosols and an expanded geog.
coverage in the Southeast. The monitoring network comprises four
urban-rural (or urban-suburban) site pairs at locations along the coast
of the Gulf of Mexico and inland, including two moderately sized and two
major urban areas (Pensacola, Florida; Gulfport, Mississippi; Atlanta,
Georgia; and Birmingham, Alabama). The sites are equipped with an
extensive suite of instruments for measuring particulate matter (PM),
gases relevant to secondary O3 and the prodn. of secondary aerosol
particles, and surface meteorol. The measurements taken to date have
added substantially to the knowledge about the temporal behavior and
geog. variability of tropospheric aerosols in the Southeast. Details are
presented in four papers to follow.
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19. 19
Edgerton, E. S.; Hartsell, B. E.; Saylor, R. D.; Jansen, J. J.; Hansen,
D. A.; Hidy, G. M. The Southeastern Aerosol Research and Characterization
Study: Part II. Filter-Based Measurements of Fine and Coarse Particulate
Matter Mass and Composition. J. Air Waste Manage. Assoc. 2005, 55, 1527–
1542, DOI: 10.1080/10473289.2005.10464744
[Crossref], [PubMed], [CAS], Google Scholar
19
The Southeastern Aerosol Research and Characterization Study: part II.
Filter-based measurements of fine and coarse particulate matter mass and
composition
Edgerton, Eric S.; Hartsell, Benjamin E.; Saylor, Rick D.; Jansen, John
J.; Hansen, D. Alan; Hidy, George M.
Journal of the Air & Waste Management Association (2005), 55 (10),
1527-1542CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
The Southeastern Aerosol Research and Characterization Study (SEARCH) was
implemented in 1998-1999 to provide data and analyses for the
investigation of the sources, chem. speciation, and long-term trends of
fine particulate matter (PM2.5) and coarse particulate matter (PM10-2.5)
in the Southeastern United States. This work is an initial anal. of 5
years (1999-2003) of filter-based PM2.5 and PM10-2.5 data from SEARCH. We
find that annual PM2.5 design values were consistently above the National
Ambient Air Quality Stds. (NAAQS) 15 μg/m3 annual std. only at monitoring
sites in the two largest urban areas (Atlanta, GA, and North Birmingham,
AL). Other sites in the network had annual design values below the std.,
and no site had daily design values above the NAAQS 65 μg/m3 daily std.
Using a particle compn. monitor designed specifically for SEARCH, we
found that volatilization losses of nitrate, ammonium, and org. carbon
must be accounted for to accurately characterize atm. particulate matter.
In particular, the federal ref. method for PM2.5 underestimates mass by
3-7% as a result of these volatilization losses. Org. matter (OM) and
sulfate account for ∼60% of PM2.5 mass at SEARCH sites, whereas major
metal oxides (MMO) and unidentified components ("other") account for ≥80%
of PM10-2.5 mass. Limited data suggest that much of the unidentified mass
in PM10-2.5 may be OM. For paired comparisons of urban-rural sites,
differences in PM2.5 mass are explained, in large part, by higher OM and
black carbon at the urban site. For PM10 higher urban concns. are
explained by higher MMO and "other.". Annual means for PM2.5 and PM10-2.5
mass and major components demonstrate substantial declines at all of the
SEARCH sites over the 1999-2003 period (10-20% in the case of PM2..5,
dominated by 14-20% declines in sulfate and 11-26% declines in OM, and
14-25% in the case of PM10-2.5, dominated by 17-30% declines in MMO and
14-31% declines in "other"). Although declining national emissions of
sulfur dioxide and anthropogenic carbon may account for a portion of the
obsd. declines, addnl. investigation will be necessary to establish a
quant. assessment, esp. regading trends in local and regional emission,
primary carbon emissions, and meteorol.
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20. 20
Edgerton, E. S.; Hartsell, B. E.; Saylor, R. D.; Jansen, J. J.; Hansen,
D. A.; Hidy, G. M. The Southeastern Aerosol Research and Characterization
Study, Part 3: Continuous Measurements of Fine Particulate Matter Mass
and Composition. J. Air Waste Manage. Assoc. 2006, 56, 1325– 1341, DOI:
10.1080/10473289.2006.10464585
[Crossref], [PubMed], [CAS], Google Scholar
20
The Southeastern Aerosol Research and Characterization Study, part 3:
continuous measurements of fine particulate matter mass and composition
Edgerton, Eric S.; Hartsell, Benjamin E.; Saylor, Rick D.; Jansen, John
J.; Hansen, D. Alan; Hidy, George M.
Journal of the Air & Waste Management Association (2006), 56 (9),
1325-1341CODEN: JAWAFC; ISSN:1096-2247. (Air & Waste Management
Association)
Deployment of continuous analyzers in the Southeastern Aerosol Research
and Characterization Study (SEARCH) network began in 1998 and continues
today as new technologies are developed. Measurement of fine particulate
matter (PM2.5) mass is performed using a dried, 30 °C tapered element
oscillating microbalance (TEOM). TEOM measurements are complemented by
observations of light scattering by nephelometry. Measurements of major
constituents include: SO42- via redn. to SO2; NH4+ and NO3- via resp.
catalytic oxidn. and redn. to NO, black carbon (BC) by optical
absorption, total carbon by combustion to CO2, and org. carbon by
difference between the latter two measurements. Several illustrative
examples of continuous data from the SEARCH network are presented. A
distinctive composite annual av. diurnal pattern is obsd. for PM2.5 mass,
nitrate, and BC, likely indicating the influence of traffic-related
emissions, growth, and break up of the boundary layer and formation of
ammonium nitrate. Examn. of PM2.5 components indicates the need to better
understand the continuous compn. of the unmeasured "other" category,
because it contributes a significant fraction to total mass during
periods of high PM2.5 loading. Selected episodes are presented to
illustrate applications of SEARCH data. An SO2 conversion rate of 0.2%/h
is derived from an observation of a plume from a coal-fired power plant
during early spring, and the importance of local, rural sources of NH3 to
the formation of ammonium nitrate in particulate matter (PM) is
demonstrated.
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21. 21
Zheng, G.; Su, H.; Wang, S.; Pozzer, A.; Cheng, Y. Impact of non-ideality
on reconstructing spatial and temporal variations of aerosol acidity with
multiphase buffer theory. Atmos. Chem. Phys. 2021, 2021, 47– 63, DOI:
10.5194/acp-22-47-2022
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22. 22
Fountoukis, C.; Nenes, A. ISORROPIA II: a computationally efficient
thermodynamic equilibrium model for
K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosols. Atmos. Chem. Phys.
2007, 7, 4639– 4659, DOI: 10.5194/acp-7-4639-2007
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22
ISORROPIA II: a computationally efficient thermodynamic equilibrium model
for K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosols
Fountoukis, C.; Nenes, A.
Atmospheric Chemistry and Physics (2007), 7 (17), 4639-4659CODEN: ACPTCE;
ISSN:1680-7316. (Copernicus Publications)
This study presents ISORROPIA II, a thermodn. equil. model for the
K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosol system. A comprehensive
evaluation of its performance is conducted against water uptake
measurements for lab. aerosol and predictions of the SCAPE2 thermodn.
module over a wide range of atmospherically relevant conditions. The two
models agree well, to within 13% for aerosol water content and total PM
mass, 16% for aerosol nitrate and 6% for aerosol chloride and ammonium.
Largest discrepancies were found under conditions of low RH, primarily
from differences in the treatment of water uptake and solid state compn.
In terms of computational speed, ISORROPIA II was more than an order of
magnitude faster than SCAPE2, with robust and rapid convergence under all
conditions. The addn. of crustal species does not slow down the thermodn.
calcns. (compared to the older ISORROPIA code) because of optimizations
in the activity coeff. calcn. algorithm. Based on its computational rigor
and performance, ISORROPIA II appears to be a highly attractive
alternative for use in large scale air quality and atm. transport models.
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23. 23
Clegg, S. L.; Pitzer, K. S.; Brimblecombe, P. Thermodynamics of
multicomponent, miscible, ionic solutions. Mixtures including
unsymmetrical electrolytes. J. Phys. Chem. 1992, 96, 9470– 9479, DOI:
10.1021/j100202a074
[ACS Full Text ], [CAS], Google Scholar
23
Thermodynamics of multicomponent, miscible, ionic solutions. Mixtures
including unsymmetrical electrolytes
Clegg, Simon L.; Pitzer, Kenneth S.; Brimblecombe, Peter
Journal of Physical Chemistry (1992), 96 (23), 9470-9CODEN: JPCHAX;
ISSN:0022-3654.
Model equations for the excess Gibbs energy and solvent and solute
activity coeffs. (given previously for sym. salt systems) are developed
for mixts. contg. an indefinite no. of ions of arbitrary charge, over the
entire concn. range. The equations are expressed on a mole fraction basis
and comprise a Debye-Hueckel term extended to include the effects of
unsym. mixing and a Margules expansion carried out to the four suffix
level. The model is tested by using activity coeff. and salt soly. data
data for the systems H-(Al,Mg,Ca,Sr)-Cl-H2O, H-(La,Ca)-NO3-H2O,
Na-Mg-Cl-SO4-H2O, Mg-Ca-K-Cl-H2O, and Na-K-Mg-So4-H2O at 298.15 K.
Thermodn. properties of quaternary aq. solns. are predicted using only
parameters detd. from binary and ternary mixts. Salt solubilities in both
systems involving HNO3 are satisfactorily represented from aq. salt soln.
to pure liq. HNO3.
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24. 24
Wexler, A. S.; Clegg, S. L. Atmospheric aerosol models for systems
including the ions H+, NH4+, Na+, SO42–, NO3–, Cl–, Br–, and H2O. J.
Geophys. Res.: Atmos. 2002, 107, ACH 14-1– ACH 14-14, DOI:
10.1029/2001JD000451
[Crossref], Google Scholar
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25. 25
Friese, E.; Ebel, A. Temperature Dependent Thermodynamic Model of the
System H+–NH4+–Na+–SO42––NO3––Cl––H2O. J. Phys. Chem. A 2010, 114, 11595–
11631, DOI: 10.1021/jp101041j
[ACS Full Text ], [CAS], Google Scholar
25
Temperature Dependent Thermodynamic Model of the System
H+-NH4+-Na+-SO42--NO3--Cl--H2O
Friese, Elmar; Ebel, Adolf
Journal of Physical Chemistry A (2010), 114 (43), 11595-11631CODEN:
JPCAFH; ISSN:1089-5639. (American Chemical Society)
A thermodn. model of the system H+-NH4+-Na+-SO42--NO3--Cl--H2O is
parametrized and used to represent activity coeffs., equil. partial
pressures of H2O, HNO3, HCl, H2SO4, and NH3, and satn. with respect to 26
solid phases (NaCl(s), NaCl·2H2O(s), Na2SO4(s), Na2SO4·10H2O(s),
NaNO3·Na2SO4·H2O(s), Na3H(SO4)2(s), NaHSO4(s), NaHSO4·H2O(s),
NaNH4SO4·2H2O(s), NaNO3(s), NH4Cl(s), NH4NO3(s), (NH4)2SO4(s),
(NH4)3H(SO4)2(s), NH4HSO4(s), (NH4)2SO4·2NH4NO3(s), (NH4)2SO4·3NH4NO3(s),
H2SO4·H2O(s), H2SO4·2H2O(s), H2SO4·3H2O(s), H2SO4·4H2O(s),
H2SO4·6.5H2O(s), HNO3·H2O(s), HNO3·2H2O(s), HNO3·3H2O(s), and
HCl·3H2O(s)). The enthalpy of formation of the complex salts
NaNH4SO4·2H2O(s) and Na2SO4·NaNO3·H2O(s) is calcd. The model is valid for
temps. .ltorsim. 263.15 up to 330 K and concns. from infinite diln. to
satn. with respect to the solid phases. For H2SO4-H2O solns. the degree
of dissocn. of the HSO4- ion is represented near the exptl. uncertainty
over wide temp. and concn. ranges. The parametrization of the model for
the subsystems H+-NH4+-NO3--SO42--H2O and H+-NO3--SO42--Cl--H2O relies on
previous studies, which are only partly adjusted to new data. For these
systems the model is applicable to temps. below 200 K, dependent upon
liq.-phase compn., and for the former system also to supersatd. solns.
Values for the model parameters are detd. from literature data for the
vapor pressure, osmotic coeff., emf, degree of dissocn. of HSO4-, and the
dissocn. const. of NH3 as well as measurements of calorimetric properties
of aq. solns. like enthalpy of diln., enthalpy of soln., enthalpy of
mixing, and heat capacity. The high accuracy of the model is demonstrated
by comparisons with exptl. detd. mean activity coeffs. of HCl in
HCl-Na2SO4-H2O solns., soly. measurements for the quaternary systems
H+-Na+-Cl--SO42--H2O, Na+-NH4+-Cl--SO42--H2O, and Na+-NH4+-NO3--SO42--H2O
as well as vapor pressure measurements of HNO3, HCl, H2SO4, and NH3.
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26. 26
Hennigan, C. J.; Izumi, J.; Sullivan, A. P.; Weber, R. J.; Nenes, A. A
critical evaluation of proxy methods used to estimate the acidity of
atmospheric particles. Atmos. Chem. Phys. 2015, 15, 2775– 2790, DOI:
10.5194/acp-15-2775-2015
[Crossref], [CAS], Google Scholar
26
A critical evaluation of proxy methods used to estimate the acidity of
atmospheric particles
Hennigan, C. J.; Izumi, J.; Sullivan, A. P.; Weber, R. J.; Nenes, A.
Atmospheric Chemistry and Physics (2015), 15 (5), 2775-2790CODEN: ACPTCE;
ISSN:1680-7324. (Copernicus Publications)
Given significant challenges with available measurements of aerosol
acidity, proxy methods are frequently used to est. the acidity of atm.
particles. In this study, four of the most common aerosol acidity proxies
are evaluated and compared: (1) the ion balance method, (2) the molar
ratio method, (3) thermodn. equil. models, and (4) the phase partitioning
of ammonia. All methods are evaluated against predictions of thermodn.
models and against direct observations of aerosol-gas equil. partitioning
acquired in Mexico City during the Megacity Initiative: Local and Global
Research Objectives (MILAGRO) study. The ion balance and molar ratio
methods assume that any deficit in inorg. cations relative to anions is
due to the presence of H+ and that a higher H+ loading and lower
cation/anion ratio both correspond to increasingly acidic particles
(i.e., lower pH). Based on the MILAGRO measurements, no correlation is
obsd. between H+ levels inferred with the ion balance and aerosol pH
predicted by the thermodn. models and NH3-NH+4 partitioning. Similarly,
no relationship is obsd. between the cation/anion molar ratio and
predicted aerosol pH. Using only measured aerosol chem. compn. as inputs
without any constraint for the gas phase, the E-AIM (Extended Aerosol
Inorgs. Model) and ISORROPIA-II thermodn. equil. models tend to predict
aerosol pH levels that are inconsistent with the obsd. NH3-NH+4
partitioning. The modeled pH values from both E-AIM and ISORROPIA-II run
with gasCaerosol inputs agreed well with the aerosol pH predicted by the
phase partitioning of ammonia. It appears that (1) thermodn. models
constrained by gas + aerosol measurements and (2) the phase partitioning
of ammonia provide the best available predictions of aerosol pH.
Furthermore, neither the ion balance nor the molar ratio can be used as
surrogates for aerosol pH, and previously published studies with
conclusions based on such acidity proxies may need to be reevaluated.
Given the significance of acidity for chem. processes in the atm., the
implications of this study are important and far reaching.
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27. 27
Guo, H.; Xu, L.; Bougiatioti, A.; Cerully, K. M.; Capps, S. L.; Hite, J.
R., Jr.; Carlton, A. G.; Lee, S. H.; Bergin, M. H.; Ng, N. L.; Nenes, A.;
Weber, R. J. Fine-particle water and pH in the southeastern United
States. Atmos. Chem. Phys. 2015, 15, 5211– 5228, DOI:
10.5194/acp-15-5211-2015
[Crossref], [CAS], Google Scholar
27
Fine-particle water and pH in the southeastern United States
Guo, H.; Xu, L.; Bougiatioti, A.; Cerully, K. M.; Capps, S. L.; Hite, J.
R., Jr.; Carlton, A. G.; Lee, S.-H.; Bergin, M. H.; Ng, N. L.; Nenes, A.;
Weber, R. J.
Atmospheric Chemistry and Physics (2015), 15 (9), 5211-5228CODEN: ACPTCE;
ISSN:1680-7324. (Copernicus Publications)
Particle water and pH are predicted using meteorol. observations
(relative humidity (RH), temp. (T)), gas/particle compn., and thermodn.
modeling (ISORROPIA-II). A comprehensive uncertainty anal. is included,
and the model is validated. We investigate mass concns. of particle water
and related particle pH for ambient fine-mode aerosols sampled in a
relatively remote Alabama forest during the Southern Oxidant and Aerosol
Study (SOAS) in summer and at various sites in the southeastern US during
different seasons, as part of the Southeastern Center for Air Pollution
and Epidemiol. (SCAPE) study. Particle water and pH are closely linked;
pH is a measure of the particle H+ aq. concn. and depends on both the
presence of ions and amt. of particle liq. water. Levels of particle
water, in turn, are detd. through water uptake by both the ionic species
and org. compds. Thermodn. calcns. based on measured ion concns. can
predict both pH and liq. water but may be biased since contributions of
org. species to liq. water are not considered. In this study,
contributions of both the inorg. and org. fractions to aerosol liq. water
were considered, and predictions were in good agreement with measured
liq. water based on differences in ambient and dry light scattering
coeffs. (prediction vs. measurement: slope = 0.91, intercept = 0.5 μg
m-3, R2 = 0.75). ISORROPIA-II predictions were confirmed by good
agreement between predicted and measured ammonia concns. (slope = 1.07,
intercept = -0.12 μg m-3, R2 = 0.76). Based on this study, org. species
on av. contributed 35% to the total water, with a substantially higher
contribution (50 %) at night. However, not including contributions of
org. water had a minor effect on pH (changes pH by 0.15 to 0.23 units),
suggesting that predicted pH without consideration of org. water could be
sufficient for the purposes of aq. secondary org. aerosol (SOA) chem. The
mean pH predicted in the Alabama forest (SOAS) was 0.94 ± 0.59 (median
0.93). pH diurnal trends followed liq. water and were driven mainly by
variability in RH; during SOAS nighttime pH was near 1.5, while daytime
pH was near 0.5. pH ranged from 0.5 to 2 in summer and 1 to 3 in the
winter at other sites. The systematically low pH levels in the southeast
may have important ramifications, such as significantly influencing
acid-catalyzed reactions, gas-aerosol partitioning, and mobilization of
redox metals and minerals. Particle ion balances or molar ratios, often
used to infer pH, do not consider the dissocn. state of individual ions
or particle liq. water levels and do not correlate with particle pH.
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28. 28
Nah, T.; Guo, H.; Sullivan, A. P.; Chen, Y.; Tanner, D. J.; Nenes, A.;
Russell, A.; Ng, N. L.; Huey, L. G.; Weber, R. J. Characterization of
aerosol composition, aerosol acidity, and organic acid partitioning at an
agriculturally intensive rural southeastern US site. Atmos. Chem. Phys.
2018, 18, 11471– 11491, DOI: 10.5194/acp-18-11471-2018
[Crossref], [CAS], Google Scholar
28
Characterization of aerosol composition, aerosol acidity, and organic
acid partitioning at an agriculturally intensive rural southeastern US
site
Nah, Theodora; Guo, Hongyu; Sullivan, Amy P.; Chen, Yunle; Tanner, David
J.; Nenes, Athanasios; Russell, Armistead; Ng, Nga Lee; Huey, L. Gregory;
Weber, Rodney J.
Atmospheric Chemistry and Physics (2018), 18 (15), 11471-11491CODEN:
ACPTCE; ISSN:1680-7324. (Copernicus Publications)
The implementation of stringent emission regulations has resulted in the
decline of anthropogenic pollutants including sulfur dioxide (SO2),
nitrogen oxides (NOx), and carbon monoxide (CO). In contrast, ammonia
(NH3) emissions are largely unregulated, with emissions projected to
increase in the future. We present real-time aerosol and gas measurements
from a field study conducted in an agriculturally intensive region in the
southeastern US during the fall of 2016 to investigate how NH3 affects
particle acidity and secondary org. aerosol (SOA) formation via the
gas-particle partitioning of semi-volatile org. acids. Particle water and
pH were detd. using the ISORROPIA II thermodn. model and validated by
comparing predicted inorg. HNO3-NO3- and NH3-NHC4 gas-particle
partitioning ratios with measured values. Our results showed that despite
the high NH3 concns. (av. 8.1±5.2 ppb), PM1 was highly acidic with pH
values ranging from 0.9 to 3.8, and an av. pH of 2.2±0.6. PM1 pH varied
by approx. 1.4 units diurnally. Measured particle-phase water-sol. org.
acids were on av. 6% of the total non-refractory PM1 org. aerosol mass.
The measured oxalic acid gas-particle partitioning ratios were in good
agreement with their corresponding thermodn. predictions, calcd. based on
oxalic acid's physicochem. properties, ambient temp., particle water, and
pH.
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29. 29
Atkins, P.; Jones, L. Chemical principles: The quest for insight;
Macmillan: New York, 2007.
Google Scholar
There is no corresponding record for this reference.
30. 30
Atkins, P. W.; De Paula, J.; Keeler, J. Atkins’ physical chemistry;
Oxford university press: Oxford, 2018.
Google Scholar
There is no corresponding record for this reference.
31. 31
Shi, W.; Ou, Y.; Smith, S. J.; Ledna, C. M.; Nolte, C. G.; Loughlin, D.
H. Projecting state-level air pollutant emissions using an integrated
assessment model: GCAM-USA. Appl. Energy 2017, 208, 511– 521, DOI:
10.1016/j.apenergy.2017.09.122
[Crossref], [PubMed], [CAS], Google Scholar
31
Projecting state-level air pollutant emissions using an integrated
assessment model: GCAM-USA
Shi, Wenjing; Ou, Yang; Smith, Steven J.; Ledna, Catherine M.; Nolte,
Christopher G.; Loughlin, Daniel H.
Applied Energy (2017), 208 (), 511-521CODEN: APENDX; ISSN:0306-2619.
(Elsevier Ltd.)
Integrated Assessment Models (IAMs) characterize the interactions among
human and earth systems. IAMs typically have been applied to investigate
future energy, land use, and emission pathways at global to continental
scales. Recent directions in IAM development include enhanced technol.
detail, greater spatial and temporal resoln., and the inclusion of air
pollutant emissions. These developments expand the potential applications
of IAMs to include support for air quality management and for coordinated
environmental, climate, and energy planning. Furthermore, these IAMs
could help decision makers more fully understand tradeoffs and synergies
among policy goals, identify important cross-sector interactions, and,
via scenarios, consider uncertainties in factors such as population and
economic growth, technol. development, human behavior, and climate
change. A version of the Global Change Assessment Model with U. S.
state-level resoln. (GCAM-USA) is presented that incorporates U.
S.-specific emission factors, pollutant controls, and air quality and
energy regulations. Resulting air pollutant emission outputs are compared
to U. S. Environmental Protection Agency 2011 and projected inventories.
A Quality Metric is used to quantify GCAM-USA performance for several
pollutants at the sectoral and state levels. This information provides
insights into the types of applications for which GCAM-USA is currently
well suited and highlights where addnl. refinement may be warranted.
While this anal. is specific to the U. S., the results indicate more
generally the importance of enhanced spatial resoln. and of considering
national and sub-national regulatory constraints within IAMs.
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32. 32
Ou, Y.; West, J. J.; Smith, S. J.; Nolte, C. G.; Loughlin, D. H. Air
pollution control strategies directly limiting national health damages in
the US. Nat. Commun. 2020, 11, 957, DOI: 10.1038/s41467-020-14783-2
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32
Air pollution control strategies directly limiting national health
damages in the US
Ou, Yang; West, J. Jason; Smith, Steven J.; Nolte, Christopher G.;
Loughlin, Daniel H.
Nature Communications (2020), 11 (1), 957CODEN: NCAOBW; ISSN:2041-1723.
(Nature Research)
Abstr.: Exposure to fine particulate matter (PM2.5) from fuel combustion
significantly contributes to global and US mortality. Traditional control
strategies typically reduce emissions for specific air pollutants and
sectors to maintain pollutant concns. below stds. Here we directly set
national PM2.5 mortality cost redn. targets within a global human-earth
system model with US state-level energy systems, in scenarios to 2050, to
identify endogenously the control actions, sectors, and locations that
most cost-effectively reduce PM2.5 mortality. We show that substantial
health benefits can be cost-effectively achieved by electrifying sources
with high primary PM2.5 emission intensities, including industrial coal,
building biomass, and industrial liqs. More stringent PM2.5 redn. targets
expedite the phaseout of high emission intensity sources, leading to
larger declines in major pollutant emissions, but very limited
co-benefits in reducing CO2 emissions. Control strategies limiting health
damages achieve the greatest emission redns. in the East North Central
and Middle Atlantic states.
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* vg1c00055_si_001.pdf (487.88 kb)
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