Significant Increase in Ammonia Emissions in China: Considering Nonagricultural Sectors Based on Isotopic Source Apportionment.

Isotopic source apportionment results revealed that nonagricultural sectors are significant sources of ammonia (NH3) emissions, particularly in urban areas. Unfortunately, nonagricultural sources have been substantially underrepresented in the current anthropogenic NH3 emission inventories (EIs). Here, we propose a novel approach to develop a gridded EI of nonagricultural NH3 in China for 2016 using a combination of isotopic source apportionment results and the emission ratios of carbon monoxide (CO) and NH3. We estimated that isotope-corrected nonagricultural NH3 emissions were 4370 Gg in China in 2016, accounting for an increase in the total NH3 emissions from 7 to 31%. As a result, compared to the original NH3 EI, the annual emissions of total NH3 increased by 35%. Thus, in comparison to the simulation driven by the original NH3 EI, the WRF-Chem model driven by the isotope-corrected NH3 EI has reduced the model biases in the surface concentrations and dry deposition flux of reduced nitrogen (NHx = gaseous NH3 + particulate NH4+) by 23 and 31%, respectively. This study may have wide-ranging implications for formulating targeted strategies for nonagricultural NH3 emissions controls, making it facilitate the achievement of simultaneously alleviating nitrogen deposition and atmospheric pollution in the future.

High-Resolution PM2.5 Emissions and Associated Health Impact Inequalities in an Indian District.

Health and livelihood impacts from ambient air pollution among populations in developing countries are disproportional. These disparities are often overlooked due to a lack of information on microlevel emission data, especially in smaller cities and rural areas. The current work in an Indian district, Saharanpur, proposes the use of novel data sets to estimate microlevel emissions from air-polluting infrastructure sectors in urban and rural areas for use in pollutant transport models. Health impacts estimated based on the surface PM2.5 concentration suggest that the rate of premature deaths is 158 (95% CI: 122-163) and 143 (95% CI: 65-151) deaths per 100 000 people in urban and rural areas, respectively. Sixty-eight percent of the 6372 (95% CI: 3321-6987) annual premature deaths occurs in rural areas. Depicting higher contribution-exposure disparities among socioeconomic groups, the study observed that compared to their contribution to air pollution, low socioeconomic status (SES) groups in the region experience 6,7, 7, and 26% more premature deaths from PM2.5 exposure for industries, household cooking fuel burning, open waste burning, and transportation, respectively. The majority of disability-adjusted life years (DALYs) in the study domain are observed in economically weaker worker categories. Reduced income due to the loss of these life years will significantly impact these groups due to their dependence on daily wages for basic life necessities. Microlevel pollution mitigation policies with a focus on these inequalities are critical for promoting environmental equity and justice.

Transport Pathways of Nitrate Formed from Nocturnal N2O5 Hydrolysis Aloft to the Ground Level in Winter North China Plain.

Particulate nitrate (NO3-) has currently become the major component of fine particles in the North China Plain (NCP) during winter haze episodes. However, the contributions of formation pathways to ground NO3- in the NCP are not fully understood. Herein, the NO3- formation pathways were comprehensively investigated based on model simulations combined with two-month field measurements at a rural site in the winter NCP. The results indicated that the nocturnal chemistry of N2O5 hydrolysis aloft could contribute evidently to ground NO3- at the rural site during the pollution episodes with high aerosol water contents, achieving the contribution percentages of 25.2-30.4% of the total. In addition to the commonly proposed vertical mixing of breaking nocturnal boundary layer in the early morning, two additional transport pathways (frontal downdrafts and downslope mountain breezes) in the nighttime were found to make higher contributions to ground NO3-. Considering the dominant role (69.6-74.8%) of diurnal chemistry in NO3- formation, reduction of NOx emissions in the daytime may be an effective control measure for reducing regional NO3- in the NCP.

Vapor isotopic evidence for the worsening of winter air quality by anthropogenic combustion-derived water.

Anthropogenic combustion-derived water (CDW) may accumulate in an airshed due to stagnant air, which may further enhance the formation of secondary aerosols and worsen air quality. Here we collected three-winter-season, hourly resolution, water-vapor stable H and O isotope compositions together with atmospheric physical and chemical data from the city of Xi'an, located in the Guanzhong Basin (GZB) in northwestern China, to elucidate the role of CDW in particulate pollution. Based on our experimentally determined water vapor isotope composition of the CDW for individual and weighted fuels in the basin, we found that CDW constitutes 6.2% of the atmospheric moisture on average and its fraction is positively correlated with [PM2.5] (concentration of particulate matter with an aerodynamic diameter less than 2.5 µm) as well as relative humidity during the periods of rising [PM2.5]. Our modeling results showed that CDW added additional average 4.6 µg m-3 PM2.5 during severely polluted conditions in the GZB, which corresponded to an average 5.1% of local anthropogenic [PM2.5] (average at ∼91.0 µg m-3). Our result is consistent with the proposed positive feedback between the relative humidity and a moisture sensitive air-pollution condition, alerting to the nontrivial role of CDW when considering change of energy structure such as a massive coal-to-gas switch in household heating in winter.

Impact of coronavirus-driven reduction in aerosols on precipitation in the western United States.

Among the many impacts of COVID-19, the pandemic led to improved air quality conditions in the countries under quarantine due to the shutdown of industries, drastically reduced traffic, and lockdowns. Meanwhile, the western United States, particularly the coastal areas from Washington to California, received much less precipitation than normal during early 2020. Is it possible that this reduction in precipitation was driven by the reduced aerosols due to the coronavirus? Here we show that the reduction in aerosols resulted in higher temperatures (up to ∼0.5 °C) and generally lower snow amounts but cannot explain the observed low precipitation amounts over this region. In addition to an assessment of the effects of the coronavirus-related reduction in aerosols on precipitation across the western United States, our findings also provide basic information on the potential impacts different mitigation efforts aimed at reducing anthropogenic aerosols would have on the regional climate.

Exploring drivers of the aggravated surface O3 over North China Plain in summer of 2015-2019: Aerosols, precursors, and meteorology.

Continuous aggravated surface O3 over North China Plain (NCP) has attracted widely public concern. Herein, we evaluated the effects of changes in aerosols, precursor emissions, and meteorology on O3 in summer (June) of 2015-2019 over NCP via 8 scenarios with WRF-Chem model. The simulated mean MDA8 O3 in urban areas of 13 major cities in NCP increased by 17.1%∼34.8%, which matched well with the observations (10.8%∼33.1%). Meanwhile, the model could faithfully reproduce the changes in aerosol loads, precursors, and meteorological conditions. A relatively-even O3 increase (+1.2%∼+3.9% for 24-h O3 and +1.0%∼+3.8% for MDA8 O3) was induced by PM2.5 dropping, which was consistent with the geographic distribution of regional PM2.5 reduction. Meanwhile, the NO2 reduction coupled with a near-constant VOCs led to the elevated VOCs/NOx ratios, and then caused O3 rising in the areas under VOCs-limited regimes. Therein, the pronounced increases occurred in Handan, Xingtai, Shijiazhuang, Tangshan, and Langfang (+10.7%∼+13.6% for 24-h O3 and +10.2%∼+12.2% for MDA8 O3); while the increases in other cities were 5.7%∼10.5% for 24-h O3 and 4.9%∼9.2% for MDA8 O3. Besides, the meteorological fluctuations brought about the more noticeable O3 increases in northern parts (+12.5%∼+13.5% for 24-h O3 and +11.2%∼+12.4% for MDA8 O3) than those in southern and central parts (+3.2%∼+9.3% for 24-h O3 and +3.7%∼+8.8% for MDA8 O3). The sum of the impacts of the three drivers reached 16.7%∼21.9%, which were comparable to the changes of the observed O3. Therefore, exploring reasonable emissions-reduction strategies is essential for the ozone pollution mitigation over this region.

Four year long simulation of carbonaceous aerosols in India: Seasonality, sources and associated health effects.

India's air quality is in a dismal state, with many studies ascribing it to PM2.5. Most of these corroborate that carbonaceous aerosol (CA) constitute significant fraction of PM2.5. However, investigations on the effect of long-term meteorological or emission changes on PM2.5 and its components, and their associated health effects are rare. In this work, WRF-Chem simulations for three seasons over four years (2016-2019) were carried out to cogitate the spatial and temporal changes in PM2.5 and its components in India. Model predicted PM2.5 concentrations were in good agreement with the ground-based observations for 25 cities. PM2.5 was highest in winter and lowest in pre-monsoon. PM2.5 reduced by ∼8% in Indo-Gangetic Plain (IGP) but increased by ∼38% and ∼130% in south and northeast India, respectively, from 2016 to 2019. IGP witnessed three times higher average PM2.5 concentrations than south India. No significant interannual change in CA contributions was observed, however, it peaked in the winter season. Other inorganics (OIN) were the major component of PM2.5, contributing more than 40%. Primary organic aerosol (POA) fractions were higher in north India, while secondary inorganic aerosol (SIA) dominated south India. Transport and residential sectors were the chief contributors to CA across India. Biomass burning contributed up to ∼23% of PM2.5 in regions of IGP during post-monsoon, with CA fractions up to 50%. Associations between PM2.5 and its components with daily inpatient admissions from a tertiary care centre in Delhi showed that PM2.5 and OIN had lower associations with daily hospital admissions than CA. Every 10 µg/m3 increase in POA, black carbon (BC), and secondary organic aerosol (SOA) were associated with ∼1.09%, ∼3.07% and ∼4.93% increase in the risk of daily hospital admissions. This invigorates the need for more policies targeting CA rather than PM2.5 to mitigate associated health risks, in India.

Response of aerosol composition to the clean air actions in Baoji city of Fen-Wei River Basin.

The implementation of air pollution control measures could alter the compositions of submicron aerosols. Identifying the changes can evaluate the atmospheric responses of the implemented control measures and provide more scientific basis for the formulation of new measures. The Fen-Wei River Basin is the most air polluted region in China, and thereby is a key area for the reduction of emissions. Only limited studies determine the changes in the chemical compositions of submicron aerosols. In this study, Baoji was selected as a representative city in the Fen-Wei River Basin. The compositions of submicron aerosols were determined between 2014 and 2019. Organic fractions were determined through an online instrument (Quadrupole Aerosol Chemical Speciation Monitor, Q-ACSM) and source recognition was performed by the Multilinear Engine (ME-2). The Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) was also employed to evaluate the contributions of emissions reduction and meteorological conditions to the changes of submicron aerosol compositions. The results indicate that the mass concentrations of submicron aerosols have been substantially decreased after implementation of air pollution control measures. This was mainly attributed to the emission reductions of sulfur dioxide (SO2) and primary organic aerosol (POA). In addition, the main components that drove the pollution episodes swapped from POA, sulfate, nitrate and less-oxidized organic (LO-OOA) in 2014 to nitrate and more-oxidized OOA (MO-OOA) in 2019. Due to the changes of chemical compositions of both precursors and secondary pollutants, the pollution control measures should be modernized to focus on the emissions of ammonia (NH3), nitrogen oxides (NOx) and volatile organic compounds (VOCs) in this region.

Contribution of local and surrounding area anthropogenic emissions to a high ozone episode in Zhengzhou, China.

This study analyzed an ozone pollution episode that occurred in the summer of 2020 in Zhengzhou, the provincial capital of Henan, China, and quantified the contribution of local and surrounding area anthropogenic emissions to this episode based on the Weather Research and Forecasting with Chemistry (WRF/Chem) model. Simulation results showed that the WRF/Chem model is well suited to simulate the ozone concentrations in this area. In addition, four simulation scenarios (removing the emissions from the northern Zhengzhou, southwestern Zhengzhou, Zhengzhou local and southeastern Zhengzhou) were conducted to explore the specific contributions of local emissions and emissions from surrounding areas within Henan to this ozone pollution episode. We found that contributions from the northern, local, southwestern, and southeastern regions were 6.1%, 5.9%, 1.7%, and 1.5%, respectively. The northern and local emissions of Zhengzhou (only emissions from Zhengzhou) were prominent contributors within the simulation areas. In other words, during this episode, most of the ozone pollution in Zhengzhou appeared to be transported in from regions outside Henan Province.

Maize yield reduction and economic losses caused by ground-level ozone pollution with exposure- and flux-response relationships in the North China Plain.

Ground-level ozone (O3) has negative effects on agricultural crops. Maize is an important grain crop in China. The North China Plain (NCP) serves as the major crops' production area of China and experiences severe ozone pollution. Using the ground-level ozone simulated by an atmospheric chemistry transport model (WRF-Chem), we quantified the yield reduction and economic losses of maize during 2015-2018 over NCP based on exposure-response AOT40 (accumulation of hourly O3 concentration exceed 40 ppb) and flux-response POD6 (phytotoxic dose of ozone over 6 nmol m-2 s-1). Results showed that the ozone concentration, AOT40, and POD6 clearly increased from 2015 to 2018 in growing season of maize over NCP. The four-year annual mean ozone concentration, AOT40, and POD6 were 0.055 ppm, 18.02 ppm h, and 5.02 mmol m-2, respectively. At county level, the relative loss of maize yield (MRYL) based on AOT40 and POD6 had clearly spatio-temporal differences in NCP. The average MRYLs of AOT40 and of POD6 from 2015 to 2018 were 10.4% and 21.4%, respectively, and these reductions were associated with 2399 million and 5637 million US dollars, respectively. This study suggests that surface ozone increased the yield losses of maize, and indicates that further reductions in ozone concentrations can enhance the food security in China.

Spatiotemporal variation in soil degradation and economic damage caused by wind erosion in Northwest China.

Wind erosion causes significant dust emissions in northwest China, resulting in large amounts of soil organic matter and nutrient losses. It has a significant impact on air quality, climate change, vegetation growth, and economic growth at the regional scale. In this work, the Weather Research Forecasting with Chemistry atmospheric chemical transport model was used to simulate the temporal and spatial processes of dust emissions in northwest China from 1980 to 2015. The temporal and spatial variation characteristics of the loss of soil organic matter and nutrients (total nitrogen and total phosphorus) due to dust emissions, and the economic damage from wind erosion, were simulated and calculated. Spatial patterns of soil organic matter and nutrient losses are consistent with dust emission rates across the research region. The average annual dust emissions were approximately 65.17 million tons, with losses of soil organic matter, total nitrogen, and total phosphorus resulting from dust emissions of 531,494 tons, 30,754 tons, and 37,095 tons, respectively. In addition, the average annual economic loss caused by wind erosion was 309.25 million yuan in northwest China during the entire study period. This research is valuable for understanding the role of wind erosion on the carbon and nutrient cycles and the mechanism of soil degradation in northwest China and estimating the economic impacts of wind erosion.

Changes of air pollutants and simulation of a heavy pollution process during COVID-19 in Shenyang.

During COVID-19, Shenyang implemented strict household isolation measures, resulting in a sharp reduction in anthropogenic emission sources, providing an opportunity to explore the impact of human activities on air pollution. The period from January to April of 2020 was divided into normal period, blockade period and resumption period. Combined with meteorological and pollutant data, mathematical statistics and spatial analysis methods were used to compare with the same period of 2015-2019. The results showed that PM2.5, PM10, NO2 and O3 increased by 32.6%, 13.2%, 4.65% and 22.7% in the normal period, among which the western area changed significantly. During the blockade period, the concentration of pollutants decreased by 35.79%, 35.87%, 32.45% and -4.84%, of which the central area changed significantly. During the resumption period, the concentration of pollutants increased by 21.8%, 8.7%, 5.7% and -6.3%, and the area with the largest change was located in the western. During the blockade period, a heavy pollution occurred with PM2.5 as the main pollutant. The WRF-Chem model and the HYSPLIT model were used to reproduce the pollution occurrence process. The result showed that winds circulated as zonal winds during the pollution process at high altitudes. These winds were controlled by straight westerly and weak northwesterly airflows in front of the high pressure, and the ground was located behind the warm low pressure. Weather conditions were relatively stable. Thus, high temperatures (average > 10 ℃), high humidity (40%-60%) and slow wind (2 m/s) conditions prevailed for a long time in the Shenyang area. The unfavorable meteorological conditions lead to the occurrence of pollution. The backward trajectory showed that the potential source areas were concentrated in the urban agglomeration around Shenyang, and sporadic contributions came from North Korea.

Halogens Enhance Haze Pollution in China.

Severe and persistent haze events in northern China, characterized by high loading of fine aerosol especially of secondary origin, negatively impact human health and the welfare of ecosystems. However, current knowledge cannot fully explain the formation of this haze pollution. Despite field observations of elevated levels of reactive halogen species (e.g., BrCl, ClNO2, Cl2, HBr) at several sites in China, the influence of halogens (particularly bromine) on haze pollution is largely unknown. Here, for the first time, we compile an emission inventory of anthropogenic bromine and quantify the collective impact of halogens on haze pollution in northern China. We utilize a regional model (WRF-Chem), revised to incorporate updated halogen chemistry and anthropogenic chlorine and bromine emissions and validated by measurements of atmospheric pollutants and halogens, to show that halogens enhance the loading of fine aerosol in northern China (on average by 21%) and especially its secondary components (∼130% for secondary organic aerosol and ∼20% for sulfate, nitrate, and ammonium aerosols). Such a significant increase is attributed to the enhancement of atmospheric oxidants (OH, HO2, O3, NO3, Cl, and Br) by halogen chemistry, with a significant contribution from previously unconsidered bromine. These results show that higher recognition of the impact of anthropogenic halogens shall be given in haze pollution research and air quality regulation.

Impacts of COVID-19 on air quality in mid-eastern China: An insight into meteorology and emissions.

The coronavirus disease (COVID-19) spread rapidly worldwide in the first half of 2020. Stringent national lockdown policies imposed by China to prevent the spread of the virus reduced anthropogenic emissions and improved air quality. A weather research and forecasting model coupled with chemistry was applied to evaluate the impact of meteorology and emissions on air quality during the COVID-19 outbreak (from January 23 to February 29, 2020) in mid-eastern China. The results show that air pollution episodes still occurred on polluted days and accounted for 31.6%-60.5% of the total number of outbreak days in mid-eastern China from January 23 to February 29, 2020. However, anthropogenic emissions decreased significantly, indicating that anthropogenic emission reduction cannot completely offset the impact of unfavorable meteorological conditions on air quality. Favorable meteorological conditions in 2019 improved the overall air quality for a COVID-19 outbreak in 2019 instead of 2020. PM2.5 concentrations decreased by 4.2%-29.2% in Beijing, Tianjin, Shijiazhuang, and Taiyuan, and increased by 6.1%-11.5% in Jinan and Zhengzhou. PM2.5 concentrations increased by 10.9%-20.5% without the COVID-19 outbreak of 2020 in mid-eastern China, and the frequency of polluted days increased by 5.3%-18.4%. Source apportionment of PM2.5 during the COVID-19 outbreak showed that industry and residential emissions were the dominant PM2.5 contributors (32.7%-49.6% and 26.0%-44.5%, respectively) followed by agriculture (18.7%-24.0%), transportation (7.7%-15.5%), and power (4.1%-5.9%). In Beijing, industrial and residential contributions to PM2.5 concentrations were lower (32.7%) and higher (44.5%), respectively, than in other cities (38.7%-49.6% for industry and 26.0%-36.2% for residential). Therefore, enhancing regional cooperation and implementing a united air pollution control are effective emission mitigation measures for future air quality improvement, especially the development of new technologies for industrial and cooking fumes.

Impact of biomass burnings in Southeast Asia on air quality and pollutant transport during the end of the 2019 dry season.

At the end of the dry season, March and April in Southeast Asia (SEA), agricultural refuse burnings occur over the region, mainly in the countries of Myanmar, Thailand, Laos, Cambodia and Vietnam, in preparation for the wet rice plantation. In this study, the impact of biomass burnings at the height of the burning period in March 2019 in mainland SEA on air quality and pollutant transport is modelled using the Weather Research Forecast WRF-Chem air quality model with emission input from the National Center for Atmospheric Research (NCAR) Fire Emission Inventory from NCAR (FINN). FINN is derived from satellite remote sensing data and species emission factors. A simulation of the dispersion of pollutants from biomass burnings from 13 to 19 March 2019, when the burnings was most intense, was performed. Validation of the model prediction using observed meteorological and pollutant data such as AOD measurements on ground from AERONET (Aerosol Robotic Network) and data from MODIS and CALIPSO satellites is carried out at various sites in the region. The results show that impact on air quality was most pronounced in Thailand and Laos but the effect of biomass burnings in mainland SEA at the end of the dry season is widespread in terms of pollutant dispersion and population exposure over the whole region and beyond. It is also shown that the transport of pollutants from biomass burnings in SEA to southern China, Taiwan and beyond is facilitated by the Truong Son mountain range, when under westerly wind, acting as a launching pad to uplift the pollutant plumes to higher altitude which then can be dispersed widely and transported farther from the biomass burning sources in Thailand and Laos.

Association of retreating monsoon and extreme air pollution in a megacity.

The world's top ranked mega city Delhi is known for deteriorated air quality. However, the analysis of air pollution data of 5 years (2014-2018) reveals that years 2016 and 2017, which were marked by an unusual delayed withdrawal of monsoon, witnessed an unprecedented extreme levels of toxic PM2.5 particles (≤2.5 µm in diameter) touching a peak level of ∼760 µg/m3 (24 hr average), immediately after the monsoon retreat, surpassing WHO standards by ∼30 time and Indian national standards by ∼12 times, jeopardising lives of its citizens. However, the normal monsoon withdrawal years do not show such extreme levels of pollution. The high resolution WRF-Chem model along with meteorological data are used in this work to understand that how the delayed monsoon withdrawal and associated vagarious anti-cyclonic circulation resulted in trapping externally generated pollutants ceaselessly under colder conditions, leading to historic air quality crisis in landlocked mega city in these selected years. The sensitivity analysis confirmed that when WRF-chem model forced the climatology of normal monsoon year (2015) to simulate the pollution scenario of 2016 and 2017 for the above time period, the crisis subsided. Present findings suggest that such unusual monsoon patterns are on the hook to spur extreme pollution events in recent time.

Quantifying the impact of particle matter on mortality and hospitalizations in four Brazilian metropolitan areas.

Air quality management involves investigating areas where pollutant concentrations are above guideline or standard values to minimize its effect on human health. Particulate matter (PM) is one of the most studied pollutants, and its relationship with health has been widely outlined. To guide the construction and improvement of air quality policies, the impact of PM on the four Brazilian southeast metropolitan areas was investigated. One-year long modeling of PM10 and PM2.5 was performed with the WRF-Chem model for 2015 to quantify daily and annual PM concentrations in 102 cities. Avoidable mortality due to diverse causes and morbidity due to respiratory and circular system diseases were estimated concerning WHO guidelines, which was adopted in Brazil as a final standard to be reached in the future; although there is no deadline set for its implementation yet. Results showed satisfactory representation of meteorology and ambient PM concentrations. An overestimation in PM concentrations for some monitoring stations was observed, mainly in São Paulo metropolitan area. Cities around capitals with high modelled annual PM2.5 concentrations do not monitor this pollutant. The total avoidable deaths estimated for the region, related to PM2.5, were 32,000 ± 5,300 due to all-cause mortality, between 16,000 ± 2,100 and 51,000 ± 3,000 due non-accidental causes, between 7,300 ± 1,300 and 16,700 ± 1,500 due to cardiovascular disease, between 4,750 ± 900 and 10,950 ± 870 due ischemic heart diseases and 1,220 ± 330 avoidable deaths due to lung cancer. Avoidable respiratory hospitalizations were greater for PM2.5 among 'children' age group than for PM10 (all age group) except in São Paulo metropolitan area. For circulatory system diseases, 9,840 ± 3,950 avoidable hospitalizations in the elderly related to a decrease in PM2.5 concentrations were estimated. This study endorses that more restrictive air quality standards, human exposure, and health effects are essential factors to consider in urban air quality management.

A WRF-Chem model-based future vehicle emission control policy simulation and assessment for the Beijing-Tianjin-Hebei region, China.

Using 2025 as the target year, we quantitatively assessed the reduction potentials of emissions of primary pollutants (including CO, HC, NOx, PM2.5 and PM10) under different vehicle control policies and the impacts of vehicle emission control policies in the BTH region on the regional PM2.5 concentration in winter and the surface ozone (O3) concentration in summer. Comparing the different scenarios, we found that (1) vehicle control policies will bring significant reductions in the emissions of primary pollutants. Among the individual policies, upgrading new vehicle emission standards and fuel quality in Beijing, Tianjin, and Hebei will be the most effective policy, with emission reductions of primary pollutants of 26.3%-54.7%, 38.0%-70.3% and 46.0%-81.6% in 2025, respectively; (2) for PM2.5 in winter, the Combined Scenario (CS) will lead to a reduction of 0.5-3.9 µg m-3 (3.5%-11.6%) for the monthly average PM2.5 concentrations in most areas. The monthly nitrate and ammonium concentrations would reduce by 5.8% and 5.3%, respectively, in the whole BTH region, indicating that vehicle emission control policies may play an important role in the reduction of PM2.5 concentrations in winter, especially for nitrate aerosols; and (3) for O3 concentrations in summer, vehicle emission control policies will lead to significant decreases. Under the CS scenario, the maximum reduction of monthly average O3 concentrations in the summer is approximately 3.6 ppb (5.9%). Most areas in the BTH region have a decrease of 15 ppb (7.5%) in peak values compared to the base scenario. However, in some VOC-sensitive areas in the BTH region, such as the southern urban areas, significant reductions in NOx may lead to increases in ozone concentrations. Our results highlight that season- and location-specific vehicle emission control measures are needed to alleviate ambient PM2.5 and O3 pollution effectively in this region due to the complex meteorological conditions and atmospheric chemical reactions.

Simulation of the impact of the emergency control measures on the reduction of air pollutants: a case study of APEC blue.

Serious air pollution motivates governments to take control measures. However, specific emission reduction effects of various temporary emission reduction policies are difficult to evaluate. During the Asia-Pacific Economic Cooperation meeting in Beijing in 2014, the Chinese government implemented a number of emergency emission control measures in the Beijing-Tianjin-Hebei area to maintain the air quality in this region. This gave us an opportunity to quantify the effectiveness of the emission reduction measures separately and identify the efficient policy combinations for the reduction of major pollutants. In this study, we evaluated the impacts of specific emission reduction measures on the concentrations of two major air pollutants (PM2.5 and O3) under eight policy scenarios using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). Comparing these scenarios, we found that the control policies against the primary PM2.5 emission achieved the most significant results. Meanwhile, all the emission control measures raised the ozone concentrations in different degrees, which might be partly attributed to the changes of PM2.5 concentration and the ratio of NOx and VOCs caused by the emission control measures. Our results suggest that, in VOC-sensitive areas like Beijing, emergency control measures focusing on primary PM2.5 emission could lead to significant PM2.5 reduction and relatively small ozone increase, and should be considered as a priority policy. Joint emission control at the regional scale is also important especially under unfavorable meteorological conditions.

Effect of potential HONO sources on peroxyacetyl nitrate (PAN) formation in eastern China in winter.

As an important secondary photochemical pollutant, peroxyacetyl nitrate (PAN) has been studied over decades, yet its simulations usually underestimate the corresponding observations, especially in polluted areas. Recent observations in north China found unusually high concentrations of PAN during wintertime heavy haze events, but the current model still cannot reproduce the observations, and researchers speculated that nitrous acid (HONO) played a key role in PAN formation. For the first time we systematically assessed the impact of potential HONO sources on PAN formation mechanisms in eastern China using the Weather Research and Forecasting/Chemistry (WRF-Chem) model in February of 2017. The results showed that the potential HONO sources significantly improved the PAN simulations, remarkably accelerated the ROx (sum of hydroxyl, hydroperoxyl, and organic peroxy radicals) cycles, and resulted in 80%-150% enhancements of PAN near the ground in the coastal areas of eastern China and 10%-50% enhancements in the areas around 35-40°N within 3 km during a heavy haze period. The direct precursors of PAN were aldehyde and methylglyoxal, and the primary precursors of PAN were alkenes with C > 3, xylenes, propene and toluene. The above results suggest that the potential HONO sources should be considered in regional and global chemical transport models when conducting PAN studies.