Wet processes, including aqueous-phase chemistry, wet scavenging, and wet surface uptake during dry deposition, are important for global modeling of aerosols and aerosol precursors. In this study, we ...improve the treatments of these wet processes in the Goddard Earth Observing System with chemistry (GEOS-Chem) v12.6.0, including pH calculations for cloud, rain, and wet surfaces, the fraction of cloud available for aqueous-phase chemistry, rainout efficiencies for various types of clouds, empirical washout by rain and snow, and wet surface uptake during dry deposition. We compare simulated surface mass concentrations of aerosols and aerosol precursors with surface monitoring networks over the United States, European, Asian, and Arctic regions, and show that model results with updated wet processes agree better with measurements for most species. With the implementation of these updates, normalized mean biases (NMBs) of surface nitric acid, nitrate, and ammonium are reduced from 78 %, 126 %, and 45 % to 0.9 %, 15 %, and 4.1 % over the US sites, from 107 %, 127 %, and 90 % to −0.7 %, 4.2 %, and 16 % over European sites, and from 121 %, 269 %, and 167 % to −21 %, 37 %, and 86 % over Asian remote region sites. Comparison with surface measured SO2, sulfate, and black carbon at four Arctic sites indicated that those species simulated with the updated wet processes match well with observations except for a large underestimate of black carbon at one of the sites. We also compare our model simulation with aircraft measurement of nitric acid and aerosols during the Atmospheric Tomography Mission (ATom)-1 and ATom-2 periods and found a significant improvement of modeling skill of nitric acid, sulfate, and ammonium in the Northern Hemisphere during wintertime. The NMBs of these species are reduced from 163 %, 78 %, and 217 % to −13 %, −1 %, and 10 %, respectively. The investigation of impacts of updated wet process treatments on surface mass concentrations indicated that the updated wet processes have strong impacts on the global means of nitric acid, sulfate, nitrate, and ammonium and relative small impacts on the global means of sulfur dioxide, dust, sea salt, black carbon, and organic carbon.
Cloud water acidity affects the atmospheric chemistry of
sulfate and organic aerosol formation, halogen radical cycling, and trace
metal speciation. Precipitation acidity including post-depositional ...inputs
adversely affects soil and freshwater ecosystems. Here, we use the GEOS-Chem model of atmospheric chemistry to simulate the global distributions of
cloud water and precipitation acidity as well as the total acid inputs to
ecosystems from wet deposition. The model accounts for strong acids
(H2SO4, HNO3, and HCl), weak acids (HCOOH, CH3COOH,
CO2, and SO2), and weak bases (NH3 as well as dust and sea salt aerosol
alkalinity). We compile a global data set of cloud water pH measurements for
comparison with the model. The global mean observed cloud water pH is 5.2±0.9, compared to 5.0±0.8 in the model, with a range from 3 to
8 depending on the region. The lowest values are over East Asia, and the highest
values are over deserts. Cloud water pH over East Asia is low because of
large acid inputs (H2SO4 and HNO3), despite NH3 and dust
neutralizing 70 % of these inputs. Cloud water pH is typically 4–5 over
the US and Europe. Carboxylic acids account for less than 25 % of
cloud water H+ in the Northern Hemisphere on an annual basis but
25 %–50 % in the Southern Hemisphere and over 50 % in the southern
tropical continents, where they push the cloud water pH below 4.5.
Anthropogenic emissions of SO2 and NOx (precursors of
H2SO4 and HNO3) are decreasing at northern midlatitudes, but
the effect on cloud water pH is strongly buffered by NH4+ and
carboxylic acids. The global mean precipitation pH is 5.5 in GEOS-Chem, which is
higher than the cloud water pH because of dilution and below-cloud scavenging
of NH3 and dust. GEOS-Chem successfully reproduces the annual mean
precipitation pH observations in North America, Europe, and eastern Asia.
Carboxylic acids, which are undetected in routine observations due to
biodegradation, lower the annual mean precipitation pH in these areas by 0.2
units. The acid wet deposition flux to terrestrial ecosystems taking into
account the acidifying potential of NO3- and NH4+ in
N-saturated ecosystems exceeds 50 meqm-2a-1 in East Asia and the
Americas, which would affect sensitive ecosystems. NH4+ is the
dominant acidifying species in wet deposition, contributing 41 % of the
global acid flux to continents under N-saturated conditions.
In his study, we use a combination of multivariate statistical methods to understand the relationships of PM2.5 with local meteorology and synoptic weather patterns in different regions of China ...across various timescales. Using June 2014 to May 2017 daily total PM2.5 observations from ∼ 1500 monitors, all deseasonalized and detrended to focus on synoptic-scale variations, we find strong correlations of daily PM2.5 with all selected meteorological variables (e.g., positive correlation with temperature but negative correlation with sea-level pressure throughout China; positive and negative correlation with relative humidity in northern and southern China, respectively). The spatial patterns suggest that the apparent correlations with individual meteorological variables may arise from common association with synoptic systems. Based on a principal component analysis of 1998–2017 meteorological data to diagnose distinct meteorological modes that dominate synoptic weather in four major regions of China, we find strong correlations of PM2.5 with several synoptic modes that explain 10 to 40 % of daily PM2.5 variability. These modes include monsoonal flows and cold frontal passages in northern and central China associated with the Siberian High, onshore flows in eastern China, and frontal rainstorms in southern China. Using the Beijing–Tianjin–Hebei (BTH) region as a case study, we further find strong interannual correlations of regionally averaged satellite-derived annual mean PM2.5 with annual mean relative humidity (RH; positive) and springtime fluctuation frequency of the Siberian High (negative). We apply the resulting PM2.5-to-climate sensitivities to the Intergovernmental Panel on Climate Change (IPCC) Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections to predict future PM2.5 by the 2050s due to climate change, and find a modest decrease of ∼ 0.5 µg m−3 in annual mean PM2.5 in the BTH region due to more frequent cold frontal ventilation under the RCP8.5 future, representing a small “climate benefit”, but the RH-induced PM2.5 change is inconclusive due to the large inter-model differences in RH projections.
PM2.5 during severe winter haze in Beijing, China, has reached levels as high as 880 μg/m3, with sulfur compounds contributing significantly to PM2.5 composition. This sulfur has been traditionally ...assumed to be sulfate, although atmospheric chemistry models are unable to account for such large sulfate enhancements under dim winter conditions. Using a 1‐D model, we show that well‐characterized but previously overlooked chemistry of aqueous‐phase HCHO and S(IV) in cloud droplets to form a S(IV)‐HCHO adduct, hydroxymethane sulfonate, may explain high particulate sulfur in wintertime Beijing. We also demonstrate in the laboratory that methods of ion chromatography typically used to measure ambient particulates easily misinterpret hydroxymethane sulfonate as sulfate. Our findings suggest that HCHO and not SO2 has been the limiting factor in many haze events in Beijing and that to reduce severe winter pollution in this region, policymakers may need to address HCHO sources such as transportation.
Plain Language Summary
Air pollution in Beijing is especially severe in winter, when concentrations of tiny particles in the air can reach concentrations over 20 times greater than the safe level recommended by the World Health Organization. In these severe pollution episodes, observations show that a large portion of the particles is made up of sulfur. Scientists have assumed that this sulfur is in the form of sulfate; however, computer simulations of air pollution chemistry have been unable to explain such high sulfate concentrations. We show with a simple computer simulation that a large portion of the sulfur in these haze episodes may, instead of sulfate, actually be a molecule called hydroxymethane sulfonate, which is formed by a chemical reaction in cloud droplets of dissolved formaldehyde with dissolved sulfur dioxide. We also show in laboratory experiments that the machines typically used for determining the chemical composition of particles easily misinterpret hydroxymethane sulfonate as sulfate. Importantly, the chemistry that produces hydroxymethane sulfonate is usually limited by formaldehyde, implying that reductions in sulfur dioxide would be ineffective at reducing severe haze. Instead, focusing future emissions reductions on formaldehyde emissions may be an effective way to curtail severe winter haze in the Beijing area.
Key Points
Chemistry models have been unable to explain high levels of observed particulate sulfur, usually interpreted as sulfate, during Beijing winter haze events
Typical measurement systems for ambient particulates easily misinterpret hydroxymethane sulfonate (HMS) as sulfate
HMS may comprise a large portion of particulate sulfur during extreme haze, implying that HCHO, rather than SO2, would be a limiting factor for such events
Hydroxymethanesulfonate (HMS) has recently been
identified as an abundant organosulfur compound in aerosols during winter
haze episodes in northern China. It has also been detected in other regions
...although the concentrations are low. Because of the sparse field
measurements, the global significance of HMS and its spatial and seasonal
patterns remain unclear. Here, we modify and add to the implementation of
HMS chemistry in the GEOS-Chem chemical transport model and conduct multiple
global simulations. The model accounts for cloud entrainment and
gas–aqueous mass transfer within the rate expressions for heterogeneous
sulfur chemistry. Our simulations can generally reproduce quantitative HMS
observations from Beijing and show that East Asia has the highest HMS
concentration, followed by Europe and North America. The simulated HMS shows
a seasonal pattern with higher values in the colder period. Photochemical
oxidizing capacity affects the competition of formaldehyde with oxidants
(such as ozone and hydrogen peroxide) for sulfur dioxide and is a key factor
influencing the seasonality of HMS. The highest average HMS concentration
(1–3 µg m−3) and HMS ∕ sulfate molar ratio (0.1–0.2) are found in
northern China in winter. The simulations suggest that aqueous clouds act as
the major medium for HMS chemistry while aerosol liquid water may play a
role if its rate constant for HMS formation is greatly enhanced compared to
cloud water.
Geostationary satellite measurements of aerosol optical depth (AOD) over East Asia from the Geostationary Ocean Color Imager (GOCI) and Advanced Himawari Imager (AHI) instruments can augment surface ...monitoring of fine particulate matter (PM2.5) air quality, but this requires better understanding of the AOD–PM2.5 relationship. Here we use the GEOS-Chem chemical transport model to analyze the critical variables determining the AOD–PM2.5 relationship over East Asia by simulation of observations from satellite, aircraft, and ground-based datasets. This includes the detailed vertical aerosol profiling over South Korea from the KORUS-AQ aircraft campaign (May–June 2016) with concurrent ground-based PM2.5 composition, PM10, and AERONET AOD measurements. The KORUS-AQ data show that 550 nm AOD is mainly contributed by sulfate–nitrate–ammonium (SNA) and organic aerosols in the planetary boundary layer (PBL), despite large dust concentrations in the free troposphere, reflecting the optically effective size and high hygroscopicity of the PBL aerosols. We updated SNA and organic aerosol size distributions in GEOS-Chem to represent aerosol optical properties over East Asia by using in situ measurements of particle size distributions from KORUS-AQ. We find that SNA and organic aerosols over East Asia have larger size (number median radius of 0.11 µm with geometric standard deviation of 1.4) and 20 % larger mass extinction efficiency as compared to aerosols over North America (default setting in GEOS-Chem). Although GEOS-Chem is successful in reproducing the KORUS-AQ vertical profiles of aerosol mass, its ability to link AOD to PM2.5 is limited by under-accounting of coarse PM and by a large overestimate of nighttime PM2.5 nitrate. The GOCI–AHI AOD data over East Asia in different seasons show agreement with AERONET AODs and a spatial distribution consistent with surface PM2.5 network data. The AOD observations over North China show a summer maximum and winter minimum, opposite in phase to surface PM2.5. This is due to low PBL depths compounded by high residential coal emissions in winter and high relative humidity (RH) in summer. Seasonality of AOD and PM2.5 over South Korea is much weaker, reflecting weaker variation in PBL depth and lack of residential coal emissions.
Tropospheric reactive gaseous chlorine (Cly) impacts the atmosphere's oxidation capacity with implications for chemically reduced gases such as methane. Here we use Greenland ice‐core records of ...chlorine, sodium, and acidity, and global model simulations to show how tropospheric Cly has been impacted by anthropogenic emissions since the 1940s. We show that anthropogenic contribution of nonsea‐salt chlorine significantly influenced total chlorine and its trends after the 1940s. The modeled regional 170% Cly increase from preindustrial to the 1970s was driven by acid displacement from sea‐salt‐aerosol, direct emission of hydrochloric acid (HCl) from combustion, and chemical reactions driven by anthropogenic nitrogen oxide (NOx) emissions. Since the 1970s, the modeled 6% Cly decrease was caused mainly by reduced anthropogenic HCl emissions from air pollution mitigation policies. Our findings suggest that anthropogenic emissions of acidic gases and their emission control strategies have substantial impacts on Cly with implications for tropospheric oxidants, methane, and mercury.
Plain Language Summary
Greenland ice cores preserve information from past atmospheres and provide information on how human activities have changed the composition of the atmosphere. While ice‐core chlorine mainly originates from deposited sea‐salt particles in the air, we found that emissions from human activities also influence ice‐core chlorine. Using six Greenland ice cores and global model simulations, we show that the observed increasing trend in nonsea‐salt chlorine during the 1940s–1970s was caused by enhanced human emissions of acidic gases and the resulting chemical reactions involving atmospheric sea‐salt particles, and the observed decrease after the 1970s is largely attributed to air pollution control strategies that are widely applied in North America and Europe.
Key Points
Greenland ice‐core records showed nonsea‐salt chlorine increased from the 1940s to 1970s, and decreased leveled off afterward
Historical simulations by a global model qualitatively capture the observed trends when only considering changes in anthropogenic emissions
Modeled trends are driven by anthropogenic emissions of sulfur dioxide, nitrogen oxides, and coal combustion‐emitted hydrochloric acid
Rural economic growth is a crucial matter to be concerned because most of the Indonesian population lives in rural areas. On the other hand, rural economic growth so far is still far behind with ...economic growth in urban areas. This lag needs to find a solution in order to provide a multiplier effect on the sustainability of development, such as reducing urbanization flows, equal distribution of urban and rural population income, etc. One solution that can be pursued is by empowering youth organizations (Karang Taruna) as an effort for economic sustainability in the countryside. However, the empowerment of these Karang Taruna is faced with a bitter reality, namely the problem of unemployment. Nationally, in 2016 according to BPS records the open unemployment rate reached 5.50 percent. However, there was a decline in 2017 to 5.33%. Madura Island, especially Bangkalan and Sampang Regencies have the same problem. This phenomenon of high unemployment in productive age is certainly a separate social problem in society. On the other hand today the existence of Karang Taruna as a youth organization that actually serves to help solve the problem of unemployment, especially among young people (productive) still tends to be barren. On this basis, this study aims to find a solution to overcome unemployment among young people through youth empowerment. This study uses a qualitative research design with depth interviews with selected respondents to obtain the required data. The results obtained from this study are the need for organizational management as a concrete step to address the challenges of the problem of youth organization in addition to the need to grow and develop professional cadets of youth organizations.
Sulfur compounds are an important constituent of particulate matter, with impacts on climate and public health. While most sulfur observed in particulate matter has been assumed to be sulfate, ...laboratory experiments reveal that hydroxymethanesulfonate (HMS), an adduct formed by aqueous phase chemical reaction of dissolved HCHO and SO2, may be easily misinterpreted in measurements as sulfate. Here we present observational and modeling evidence for a ubiquitous global presence of HMS. We find that filter samples collected in Shijiazhuang, China, and examined with ion chromatography within 9 days show as much as 7.6 μg m−3 of HMS, while samples from Singapore examined 9–18 months after collection reveal ~0.6 μg m−3 of HMS. The Shijiazhuang samples show only minor traces of HMS 4 months later, suggesting that HMS had decomposed over time during sample storage. In contrast, the Singapore samples do not clearly show a decline in HMS concentration over 2 months of monitoring. Measurements from over 150 sites, primarily derived from the IMPROVE network across the United States, suggest the ubiquitous presence of HMS in at least trace amounts as much as 60 days after collection. The degree of possible HMS decomposition in the IMPROVE observations is unknown. Using the GEOS‐Chem chemical transport model, we estimate that HMS may account for 10% of global particulate sulfur in continental surface air and over 25% in many polluted regions. Our results suggest that reducing emissions of HCHO and other volatile organic compounds may have a co‐benefit of decreasing particulate sulfur.
Plain Language Summary
Sulfur molecules are a major part of the tiny particles in air that are both a significant cause of death worldwide and exert a large influence on climate. Scientists have previously assumed that the sulfur in particle air pollution is in the form of sulfate. However, recent work has shown that a different sulfur molecule called hydroxymethanesulfonate may be confused for sulfate in the machines used for determining the chemical composition of particles. By reanalyzing observations of particle chemical composition and conducting new observations we find a significant global presence of hydroxymethanesulfonate. Using a computer simulation of global air pollution chemistry, we find that hydroxymethanesulfonate may comprise more than one quarter of sulfur in particles in many polluted regions. The computer simulation also indicates that in multiple regions the formation of hydroxymethanesulfonate is controlled by levels of formaldehyde. Controlling emissions of formaldehyde or emissions of the volatile organic compounds that can create formaldehyde in the atmosphere can therefore have the added co‐benefit of also reducing the levels of sulfur in particle air pollution.
Key Points
New and reanalyzed observations suggest a ubiquitous global presence of hydroxymethanesulfonate (HMS) in particulate matter
GEOS‐Chem simulations suggest HMS may comprise over 25% of particulate sulfur in many polluted regions, especially in continental winter
Reductions of formaldehyde and other volatile organic compounds may have the co‐benefit of reducing particulate sulfur
Severe PM2.5 air pollution in China and the First Grand National Standard (FGNS), implemented in 2016 (annual PM2.5 concentration target of less than 35 µg m−3), necessitate urgent reduction ...strategies. This study applied the nested‐grid version of the Goddard Earth Observing System (GEOS) chemical transport model (GEOS‐Chem) to quantify 2000–2050 changes in PM2.5 air quality and related direct radiative forcing (DRF) in China, based on future emission changes under the representative concentration pathway (RCP) scenarios of RCP2.6, RCP4.5, RCP6.0, and RCP8.5. In the near term (2000–2030), a projected maximum increase in PM2.5 concentrations of 10–15 µg m−3 is found over east China under RCP6.0 and RCP8.5 and less than 5 µg m−3 under RCP2.6 and RCP4.5. In the long term (2000–2050), PM2.5 pollution clearly improves, and the largest decrease in PM2.5 concentrations of 15–30 µg m−3 is over east China under all RCPs except RCP6.0. Focusing particularly on highly polluted regions, we find that Beijing‐Tianjin‐Hebei (BTH) wintertime PM2.5 concentrations meeting the FGNS occur after 2040 under RCP2.6, RCP4.5, and RCP8.5, and summertime PM2.5 concentrations reach this goal by 2030 under RCP2.6 and RCP4.5. In Sichuan Basin (SCB), wintertime PM2.5 concentrations below the FGNS occur only in 2050 under RCP2.6 and RCP4.5, although future summertime PM2.5 will be well controlled. The difficulty in controlling future PM2.5 concentrations relates to unmitigated high levels of nitrate, although NOx and SO2 emissions show substantial reductions during 2020–2040. The changes in aerosol concentrations lead to positive aerosol DRF over east China (20°–45°N, 100°–125°E) by 1.22, 1.88, and 0.66 W m−2 in 2050 relative to 2000 under RCP2.6, RCP4.5, and RCP8.5, respectively. When considering both health and climate effects of PM2.5 over China, for example, PM2.5 concentrations averaged over east China under RCP4.5 (RCP2.6) decrease by 54% (43%) in 2050 relative to 2000, but at the cost of warming with DRF of 1.88 (1.22) W m−2. Our results indicate that it will be possible to mitigate future PM2.5 pollution in China, but it will likely take two decades for polluted regions such as BTH and SCB to meet the FGNS, based on all RCP scenarios. At the same time, the consequent warming effects from reduced aerosols are also significant and inevitable.
Key Points
Two decades will be needed for PM2.5 in key polluted regions to drop below 35 µg m−3 under all RCPs
Concentrations of PM2.5 fall by 38‐58% in 2050 relative 2000 over the four polluted areas under RCP2.6 and RCP4.5
Averaged over east China, changes in aerosols lead to positive DRF of 1.22 (1.88) W m−2 in 2050 relative 2000 under RCP2.6 (RCP4.5)
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