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[Display omitted] Aerosol ammonium (NH 4 +), mainly produced from the reactions of ammonia (NH 3) with acids in the atmosphere, has significant impacts on air pollution, radiative forcing, and human health. Understanding the source and formation mechanism of NH 4 + can provide scientific insights into air quality improvements. However, the sources of NH 3 in urban areas are not well understood, and few studies focus on NH 3 /NH 4 + at different heights within the atmospheric boundary layer, which hinders a comprehensive understanding of aerosol NH 4 +. In this study, we perform both field observation and modeling studies (the Community Multiscale Air Quality, CMAQ) to investigate regional NH 3 emission sources and vertically resolved NH 4 + formation mechanisms during the winter in Beijing. Both stable nitrogen isotope analyses and CMAQ model suggest that combustion-related NH 3 emissions, including fossil fuel sources, NH 3 slip, and biomass burning, are important sources of aerosol NH 4 + with more than 60% contribution occurring on heavily polluted days. In contrast, volatilization-related NH 3 sources (livestock breeding, N-fertilizer application, and human waste) are dominant on clean days. Combustion-related NH 3 is mostly local from Beijing, and biomass burning is likely an important NH 3 source (∼15%–20%) that was previously overlooked. More effective control strategies such as the two-product (e.g., reducing both SO 2 and NH 3) control policy should be considered to improve air quality. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic lockdowns led to a sharp drop in socio-economic activities in China in 2020, including reductions in fossil fuel use, industry productions, and traffic volumes. The short-term impacts of lockdowns on China's air quality have been measured and reported, however, the changes in anthropogenic emissions have not yet been assessed quantitatively, which hinders our understanding of the causes of the air quality changes during COVID-19. Here, for the first time, we report the anthropogenic air pollutant emissions from mainland China by using a bottom-up approach based on the near-real-time data in 2020 and use the estimated emissions to simulate air quality changes with a chemical transport model. The COVID-19 lockdown was estimated to have reduced China's anthropogenic emissions substantially between January and March in 2020, with the largest reductions in February. Emissions of SO 2 , NO x , CO, non-methane volatile organic compounds (NMVOCs), and primary PM 2.5 were estimated to have decreased by 27 %, 36 %, 28 %, 31 %, and 24 %, respectively, in February 2020 compared to the same month in 2019. The reductions in anthropogenic emissions were dominated by the industry sector for SO 2 and PM 2.5 and were contributed to approximately equally by the industry and transportation sectors for NO x , CO, and NMVOCs. With the spread of coronavirus controlled, China's anthropogenic emissions rebounded in April and since then returned to the comparable levels of 2019 in the second half of 2020. The provinces in China have presented nearly synchronous decline and rebound in anthropogenic emissions, while Hubei and the provinces surrounding Beijing recovered more slowly due to the extension of lockdown measures. The ambient air pollution presented much lower concentrations during the first 3 months in 2020 than in 2019 while rapidly returning to comparable levels afterward, which have been reproduced by the air quality model simulation driven by our estimated emissions. China's monthly anthropogenic emissions in 2020 can be accessed from 10.6084/m9.figshare.c.5214920.v2 (Zheng et al., 2021) by species, month, sector, and province. [ABSTRACT FROM AUTHOR]

As urban air pollution becomes a severe environmental and societal issue globally, there is an increasing need on making air quality forecasts to prevent health and capital loss. Currently, most of the studies only provide air pollution forecasts on single or multiple sites, rather than citywide information. Due to complex urban structure and spatial transportation of air pollutants, the distribution of citywide air quality can be highly varying, which makes it extremely challenging to make accurate forecasts. Here, we address this challenge by exploring the potential of combining the dense air quality monitoring data with the deep learning technique. By using the fine-granular PM 2.5 concentrations data collected from 417 micro monitoring stations in Lanzhou City, China, we proposed an end-to-end method to predict future citywide PM 2.5 concentrations at 500 m × 500 m × 1 h resolution. This method consists of a spatio-temporal transformation component and a spatio-temporal prediction component, of which the former is responsible for converting PM 2.5 concentration data into spatial-maps, while the spatio-temporal prediction network (i.e., Air-PredNet in our study) based on ConvLSTM in the latter is responsible for capturing the spatio-temporal characterizations in the spatial-map sequences and finally generating citywide air quality forecasts. The results show that our method can accurately predict the spatial distribution and variations of PM 2.5 concentration with an RMSE of 2.12 μg/m3 for 1-h prediction and an RMSE of 4.09 μg/m3 for 6-h prediction. In addition, we also proved the robustness of Air-PredNet based on the prediction performance for O 3 and NO 2. Our results demonstrate the potential and feasibility of dense monitoring data combined with advanced data science methods for citywide urban air quality forecast, which supports the urban atmospheric environment fine management and decision-making. [Display omitted] • This study combines dense monitoring data with deep learning on air quality forecasts. • The model can forecast citywide air quality at 500m × 500m × 1h resolution. • The collected air quality information is converted into dense spatial maps. • Using spatial-map sequences to predict spatial-map sequences. • Model performance is improved by feature fusion and lightweight model design. [ABSTRACT FROM AUTHOR]

Increasing emissions from road transportation endanger China’s objective to reduce national greenhouse gas (GHG) emissions. The unconstrained growth of vehicle GHG emissions are mainly caused by the insufficient improvement of energy efficiency (kilometers traveled per unit energy use) under current policies, which cannot offset the explosion of vehicle activity in China, especially the major southern provinces. More stringent polices are required to decline GHG emissions in these provinces, and thereby help to constrain national total emissions. In this work, we make a provincial-level projection for vehicle growth, energy demand and GHG emissions to evaluate vehicle GHG emission trends under various policy options in China and determine the way to constrain national emissions. Through sensitivity analysis of various single policies, we propose an integrated policy set to assure the objective of peak national vehicle GHG emissions be achieved around 2030. The integrated policy involves decreasing the use of urban light-duty vehicles by 25%, improving fuel economy by 25% by 2035 comparing 2020, and promoting electric vehicles and biofuels. The stringent new policies would allow China to constrain GHG emissions from road transport sector around 2030. This work provides a perspective to understand vehicle GHG emission growth patterns in China’s provinces, and proposes a strong policy combination to constrain national GHG emissions, which can support the achievement of peak GHG emissions by 2030 promised by the Chinese government. [ABSTRACT FROM AUTHOR]

By analyzing the pollutant concentrations over the urban area and over the rural area of the city of Lanzhou, Gansu Province, China, the relationships between the daytime inversion intensity and the pollutant concentration in the atmospheric boundary layer (ABL) are studied with the consideration of wind speed and direction, potential temperature, specific humidity profiles, pollutant concentration in the ABL, the surface temperature, and global radiation on the ground. It was shown that the daytime inversion is a key factor in controlling air pollution concentration. A clear and positive feedback process between the daytime inversion intensity and the air pollutants over the city was found through the analysis of influences of climatic and environmental factors. The mechanisms by which the terrain and air pollutants affect the formation of the daytime inversion are discussed. The solar radiation as the essential energy source to maintain the inversion is analyzed, as are various out-forcing factors affecting the inversion and air pollutants. At last, a physical frame of relationships of air pollution with daytime inversion and the local and out-forcing factors over Lanzhou is built. [ABSTRACT FROM AUTHOR]

Abstract: In-situ aircraft measurements of aerosols and clouds of 7 flights during the period from July to September of 2008 are analyzed in Beijing, China. The measured aerosol concentrations indicated that the Beijing region was highly polluted by aerosol particles. The impact of heavy aerosol particle loadings on cloud formation is studied. The microphysical characters of clouds (including number concentrations of cloud droplets (Nc), cloud droplet radius (Rc), liquid water content (LWC)), and number concentrations of aerosol particles (Na) were measured during the experiments. The aircraft measurements indicated that under high aerosol particle conditions, large number of cloud droplets was formed with small size of droplets. By contrast, under low aerosol particle conditions, the formation of cloud droplets was limited by the number of Na. In this case, small number of cloud droplets was formed with large size of droplets. The number concentrations of cloud droplets were sensitivity to LWC under high aerosol particle conditions. With low LWC value (<0.1gm−3), the Nc was slowly increased with the Na. For example, the cloud droplets were increased from 200 to 300cm−3, while aerosol particles were increased from 1000 to 6000cm−3, indicating that a large amount of aerosol particles were unchanged under low LWC condition. By contrast, with high LWC value (>0.5gm−3), the activation of aerosol particles to become cloud droplets was significantly enhanced. For example, the cloud droplets were increased from 700 to 1900cm−3, while aerosol particles were increased from 1000 to 6000cm−3, suggesting that a large amount of aerosol particles were converted to cloud droplets when there were enough LWC for supporting such conversions. This study also suggests that the Rc was also very sensitivity to the LWC values. The increase in the LWC values led to significant increase in the size of cloud droplets. [Copyright &y& Elsevier]

Abstract: Direct emissions of air pollutants from the cement industry in China were estimated by developing a technology-based methodology using information on the proportion of cement produced from different types of kilns and the emission standards for the Chinese cement industry. Historical emissions of sulfur dioxide (SO2), nitrogen oxides (NO X ), carbon monoxide (CO), particulate matter (PM) and carbon dioxide (CO2) were estimated for the years 1990–2008, and future emissions were projected up to 2020 based on current energy-related and emission control policies. Compared with the historical high (4.36Tg of PM2.5, 7.16Tg of PM10 and 10.44Tg of TSP in 1997), PM emissions are predicted to drop substantially by 2020, despite the expected tripling of cement production. Certain other air pollutant emissions, such as CO and SO2, are also predicted to decrease with the progressive closure of shaft kilns. NO X emissions, however, could increase because of the promotion of precalciner kilns and the rapid increase of cement production. CO2 emissions from the cement industry account for approximately one eighth of China’s national CO2 emissions. Our analysis indicates that it is possible to reduce CO2 emissions from this industry by approximately 12.8% if advanced energy-related technologies are implemented. These technologies will bring co-benefits in reducing other air pollutants as well. [ABSTRACT FROM AUTHOR]

Abstract: In this study, aerosol vertical distributions of 17 in-situ aircraft measurements during 2005 and 2006 springs are analyzed. The 17 flights are carefully selected to exclude dust events, and the analyses are focused on the vertical distributions of aerosol particles associated with anthropogenic activities. The results show that the vertical distributions of aerosol particles are strongly affected by weather and meteorological conditions, and 3 different types of aerosol vertical distributions corresponding to different weather systems are defined in this study. The measurement with a flat vertical gradient and low surface aerosol concentrations is defined as type-1; a gradual decrease of aerosols with altitudes and modest surface aerosol concentrations is defined as type-2; a sharp vertical gradient (aerosols being strongly depressed in the PBL) with high surface aerosol concentrations is defined as type-3. The weather conditions corresponding to the 3 different aerosol types are high pressure, between two high pressures, and low pressure systems (frontal inversions), respectively. The vertical mixing and horizontal transport for the 3 different vertical distributions are analyzed. Under the type-1 condition, the vertical mixing and horizontal transport were rapid, leading to strong dilution of aerosols in both vertical and horizontal directions. As a result, the aerosol concentrations in PBL (planetary boundary layer) were very low, and the vertical distribution was flat. Under the type-2 condition, the vertical mixing was strong and there was no strong barrier at the PBL height. The horizontal transport (wind flux) was modest. As a result, the aerosol concentrations were gradually reduced with altitude, with modest surface aerosol concentrations. Under the type-3 condition, there was a cold front near the region. As a result, a frontal inversion associated with weak vertical mixing appeared at the top of the inversion layer, forming a very strong barrier to prevent aerosol particles being exchanged from the PBL height to the free troposphere. As a result, the aerosol particles were strongly depressed in the PBL height, producing high surface aerosol concentrations. The measured vertical aerosol distributions have important implications for studying the effects of aerosols on photochemistry. The J[O3] values are reduced by 11%, 48%, and 50%, under the type-1, type-2, and type-3 conditions, respectively. This result reveals that atmospheric oxidant capacity (OH concentrations) is modestly reduced under the type-1 condition, but is significantly reduced under the type-2 and type-3 conditions. This result also suggests that the effect of aerosol particles on surface solar flux is an integrated column effect, and detailed vertical distributions of aerosol particles are very important for assessing the impacts of aerosol on photochemistry. [Copyright &y& Elsevier]

In this study, air pollutants, including ozone (O3), nitrogen oxides (NO x =NO+NO2), carbon monoxides (CO), sulfur dioxide (SO2), and volatile organic compounds (VOCs) measured in the Yangtze River Delta (YRD) region during several air flights between September/30 and October/11 are analyzed. This measurement provides horizontal and vertical distributions of air pollutants in the YRD region. The analysis of the result shows that the measured O3 concentrations range from 20 to 60ppbv. These values are generally below the US national standard (84ppbv), suggesting that at the present, the O3 pollutions are modest in this region. The NO x concentrations have strong spatial and temporal variations, ranging from 3 to 40ppbv. The SO2 concentrations also have large spatial and temporal variations, ranging from 1 to 35ppbv. The high concentrations of CO are measured with small variations, ranging from 3 to 7ppmv. The concentrations of VOCs are relatively low, with the total VOC concentrations of less than 6ppbv. The relative small VOC concentrations and the relative large NO x concentrations suggest that the O3 chemical formation is under a strong VOC-limited regime in the YRD region. The measured O3 and NO x concentrations are strongly anti-correlated, indicating that enhancement in NO x concentrations leads to decrease in O3 concentrations. Moreover, the O3 concentrations are more sensitive to NO x concentrations in the rural region than in the city region. The ratios of Δ[O3]/Δ[NO x ] are −2.3 and −0.25 in the rural and in the city region, respectively. In addition, the measured NO x and SO2 concentrations are strongly correlated, highlighting that the NO x and SO2 are probably originated from same emission sources. Because SO2 emissions are significantly originated from coal burnings, the strong correlation between SO2 and NO x concentrations suggests that the NO x emission sources are mostly from coal burned sources. As a result, the future automobile increases could lead to rapid enhancements in O3 concentrations in the YRD region. [Copyright &y& Elsevier]

As the problem of urban environment and air pollution continues to intensify, the public has developed a very strong perception of the surrounding environment. With this growing perception, their emotions and satisfaction about the environment may also be greatly affected. This article explores the main factors that affect the public's environmental satisfaction with two main novelties. The first is to develop a data acquisition platform. Based on socially aware computing and a participatory sensing method, the public's subjective environmental satisfaction is measured by quantifying the collected sensing data. The second is to establish a multiple regression model and a correlation model to analyze the relationship between public's environmental satisfaction and atmospheric environmental factors, and to compare the influence of each factor. Lanzhou City was taken as a case study, and a total of 33505 data points was acquired over a year of experiment. The experimental results show: (1) Air pollution in Lanzhou affects public environmental satisfaction more strangely than meteorological factors. (2) There is a negative correlation between public environmental satisfaction and different air pollutants in Lanzhou. (3) PM 2.5 , PM 10 and NO 2 are the main influencing factors of the public's environmental satisfaction in Lanzhou. Overall, our study demonstrates a viable method for capturing public environmental satisfaction and identifying probable drivers of it, and our results provide important information for policy makers to prioritize areas that can more effectively improve public satisfaction. Image 1 • Several novel techniques including big data and participatory sensing were applied. • A model of public environmental satisfaction was built that effectively collected and processed data. • A multiple regression model was combined with Pearson's correlation analysis to identify influencing factors. • Experimental results can provide empirical evidence for environmental governance. [ABSTRACT FROM AUTHOR]

CO2 emission inventory provides fundamental data for climate research and emission mitigation. Currently, most global CO2 emission inventories were developed with energy statistics from International Energy Agency (IEA) and were available at country level with limited source categories. Here, as the first step toward a high-resolution and dynamic updated global CO2 emission database, we developed a data-driven approach to construct seamless and highly-resolved energy consumption data cubes for 208 countries/territories, 797 sub-country administrative divisions in 29 countries, 42 fuel types, and 52 sectors, with the fusion of activity data from 24 international statistics and 65 regional/local statistics. Global CO2 emissions from fossil fuel combustion and cement production in 1970–2021 were then estimated with highly-resolved source category (1,484 of total) and sub-country information (797 of total). Specifically, 73% of global CO2 emissions in 2021 were estimated with sub-country information, providing considerably improved spatial resolution for global CO2 emission accounting. With the support of detailed information, the dynamics of global CO2 emissions across sectors and fuel types were presented, representing the evolution of global economy and progress of climate mitigation. Remarkable differences of sectoral contribution were found across sub-country administrative divisions within a given country, revealing the uneven distribution of energy and economic structure among different regions. Our estimates were generally consistent with existing databases at aggregated level for global total or large emitters, while large discrepancies were observed for middle and small emitters. Our database, named the Multi-resolution Emission Inventory model for Climate and air pollution research (MEIC) is publicly available through http://meicmodel.org.cn with highly-resolved information and timely update, which provides an independent carbon emission accounting data source for climate research. [ABSTRACT FROM AUTHOR]

Clean air policies in China have substantially reduced particulate matter (PM2.5) air pollution in recent years, primarily by curbing end-of-pipe emissions. However, reaching the level of the World Health Organization (WHO) guidelines may instead depend upon the air quality co-benefits of ambitious climate action. Here, we assess pathways of Chinese PM2.5 air quality from 2015 to 2060 under a combination of scenarios that link global and Chinese climate mitigation pathways (i.e. global 2°C- and 1.5°C-pathways, National Determined Contributions (NDC) pledges and carbon neutrality goals) to local clean air policies. We find that China can achieve both its near-term climate goals (peak emissions) and PM2.5 air quality annual standard (35 μg/m3) by 2030 by fulfilling its NDC pledges and continuing air pollution control policies. However, the benefits of end-of-pipe control reductions are mostly exhausted by 2030, and reducing PM2.5 exposure of the majority of the Chinese population to below 10 μg/m3 by 2060 will likely require more ambitious climate mitigation efforts such as China's carbon neutrality goals and global 1.5°C-pathways. Our results thus highlight that China's carbon neutrality goals will play a critical role in reducing air pollution exposure to the level of the WHO guidelines and protecting public health. [ABSTRACT FROM AUTHOR]

Exposure to fine particulate matter (PM2.5) is known to harm public health. In China, after implementation of aggressive emissions control measures under the Action Plan of Air Pollution Prevention and Control (2013–2017), air quality has significantly improved. In this work, we investigated changes in PM2.5 exposure and the associated health impacts in China for the period 2013–2017. We used an optimal estimator of PM2.5 combining in-situ observations, satellite measurements, and simulations from a chemical transport model to derive the spatial and temporal variations in PM2.5 exposure, and then used well-developed exposure-response functions to estimate the premature deaths attributable to PM2.5 exposure. We found that national population-weighed annual mean PM2.5 concentrations decreased from 67.4 µg m−3 in 2013 to 45.5 µg m−3 in 2017 (32% reduction). This rapid decrease in PM2.5 pollution led to a 14% reduction in premature deaths due to long-term exposure. We estimated that, during 2013–2017, the premature deaths attributable to long-term PM2.5 exposure decreased from 1.2 million (95% CI: 1.0, 1.3; fraction of total mortality: 13%) in 2013 to 1.0 million (95% CI: 0.9, 1.2; 10%) in 2017. Despite the rapid decrease in annual mean PM2.5 concentrations, health benefits associated with reduced long-term exposure were limited, because for many cities, the PM2.5 levels remain at the portion where the exposure-response function is less steeper than that at the low-concentration end. We also found that the deaths associated with acute exposure decreased by 61% during 2013–2017 due to rapid reduction in the number of heavily polluted days. Our results confirm that clean air policies in China have mitigated the air pollution crisis; however, continuous emissions reduction efforts are required to protect citizens from air pollution. [ABSTRACT FROM AUTHOR]

The authors discuss clean air strategy for China. They mention that the country have to overcome two major factors to meet the country's ambitious air quality policy such as the increase in fossil-fuel usage and the decentralized system of environmental enforcement. They state that China needs to promote development concerning the constrained fossil-fuel use instead of using more energy to ensure economic growth.

Cities in Northeast China, e.g., Harbin, were brought to the forefront of air pollution control by a national-level policy promulgated in 2021, i.e., the Circular on Further Promoting the Pollution Prevention and Control Battle (the FP3CB Circular) which aimed at eliminating heavy or severe air pollution events. In this study, we explored the response of Harbin aerosol to the FP3CB Circular, based on observational results from two campaigns conducted during 2020–2021 and 2021–2022. A clear decreasing trend was identified for the impact of domestic biomass burning between the two winters, presumably driven by the clean heating actions. The 2021–2022 winter was also characterized by reduced formation of secondary organic aerosol but enhanced production of nitrate, which could be attributed to the less humid conditions but higher temperatures, respectively, compared to the 2020–2021 winter. The overall effect of these changes was a decrease in the contribution of organic species to wintertime aerosol in Harbin. In addition, the number of heavy or severe pollution days rebounded in the 2021–2022 winter compared to 2020–2021 (5 vs. 3), indicating that the emissions of primary particles and gaseous precursors must be further reduced to achieve the ambitious goals of the FP3CB Circular. [Display omitted] ● Biomass burning impacts decreased in the 2021–2022 winter compared to 2020–2021. ● SOA formation was reduced in the 2021–2022 winter, accompanied with decreased RH. ● NOR was enhanced in the 2021–2022 winter, driven by increased temperatures. ● OA contribution to aerosol mass decreased in the 2021–2022 winter. ● Heavy pollution days rebounded in the 2021–2022 winter despite clean air actions. [ABSTRACT FROM AUTHOR]

Abstract: Strong economic growth in China has fueled development of cities where increase in energy demand and transportation lead to severe air pollution. The cities contribute also a significant share of the national greenhouse gas emissions. We identify strong synergies between air quality and climate relevant measures that would allow improving cost-efficiency of air pollution policies. In order to help local policy makers to identify viable and efficient solutions, we developed a city-scale emission model (GAINS-City) based on the Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model developed by the International Institute for Applied Systems Analysis (IIASA, Austria). The GAINS-City model relies on a technology-based approach to evaluate the co-benefits of various policies. This approach allows for estimation of emission reductions of several pollutants (including SO2, NO X , PM) and CO2 for individual policies and support evaluation of co-benefits. In addition, a reduction index, an integrated rank of the individual reductions potential, was defined to recommend the priority of policies implementation. The approach will have great potential to be applied in many large cities with local input data and/or minor structure modifications. We conducted a case study in Beijing to demonstrate the model features. Based on the technology-based evaluation approach, policy packages were designed and implemented in policy scenarios. The emissions under three scenarios (Baseline, Air Quality, and Strict Air Quality) in base year (2005) and future years (2020 and 2030) were estimated. The results indicate a significant reduction potential. In 2030, implementation of Air Quality and Strict Air Quality scenarios could result in reductions of 39–48% of SO2 emissions, 38–42% of NO X emissions, 37–55% of PM2.5 emissions and 5–22% of CO2 emissions respectively, compared with the Baseline scenario. The results demonstrated air quality policies and measures could also have co-benefits of reducing CO2 emissions. However, there is no significant difference of reductions between the two policy scenarios, which indicates the limited further reduction potential in the stricter air quality case. This calls for a wider application of cleaner technologies, such as IGCC and CCS, and more aggressive air quality measures by neighboring provinces to control regional air pollution. [Copyright &y& Elsevier]

This paper presents the first development and evaluation of a reduced-complexity air quality model for China. In this study, the reduced-complexity Intervention Model for Air Pollution over China (InMAP-China) is developed by linking a regional air quality model, a reduced-complexity air quality model, an emission inventory database for China, and a health impact assessment model to rapidly estimate the air quality and health impacts of emission sources in China. The modeling system is applied over mainland China for 2017 under various emission scenarios. A comprehensive model evaluation is conducted by comparison against conventional Community Multiscale Air Quality (CMAQ) modeling system simulations and ground-based observations. We found that InMAP-China satisfactorily predicted total PM 2.5 concentrations in terms of statistical performance. Compared with the observed PM 2.5 concentrations, the mean bias (MB), normalized mean bias (NMB) and correlations of the total PM 2.5 concentrations are - 8.1 µ g m -3 , - 18 % and 0.6, respectively. The statistical performance is considered to be satisfactory for a reduced-complexity air quality model and remains consistent with that evaluated in the USA. The underestimation of total PM 2.5 concentrations was mainly caused by its composition, primary PM 2.5. In terms of the ability to quantify source contributions of PM 2.5 concentrations, InMAP-China presents similar results to those based on the CMAQ model, with variation mainly caused by the different treatment of secondary inorganic aerosols in the two models. Focusing on the health impacts, the annual PM 2.5 -related premature mortality estimated using InMAP-China in 2017 was 1.92 million, which was 250 000 deaths lower than estimated based on CMAQ simulations as a result of the underestimation of PM 2.5 concentrations. This work presents a version of the reduced-complexity air quality model over China that provides a powerful tool to rapidly assess the air quality and health impacts associated with control policy and to quantify the source contribution attributable to many emission sources. [ABSTRACT FROM AUTHOR]

Abstract: Rural vehicles (RVs) could contribute significantly to air pollutant emissions throughout Asia due to their considerable population, extensive usage, and high emission rates, but their emissions have not been measured before and have become a major concern for the accuracy of regional and global emission inventories. In this study, we measured CO, HC, NOx and PM emissions of RVs using a combined on-board emission measurement system on real roads in China. We also compared the emission levels of the twenty RVs to those of nineteen Euro II light-duty diesel trucks (LDDTs) that we measured for previous studies. The results show that one-cylinder RVs have lower distance-based emission factors compared to LDDTs because of their smaller weight and engine power, but they have significantly higher fuel-based PM emission factors than LDDTs. Four-cylinder RVs have equivalent emission levels to LDDTs. Based on the emission factors and the activity data obtained, we estimate that the total emissions of RVs in China in 2006 were 1049 Gg of CO, 332 Gg of HC, 933 Gg of NOx, and 54 Gg of PM, contributing over 40% to national on-road diesel CO, NOx, and PM emissions. As RVs are a significant contributor to national emissions, further research work is needed to improve the accuracy of inventories at all levels, and the government should strengthen the management of RVs to facilitate both policy making and research work. [Copyright &y& Elsevier]

Abstract: With the help of regression analysis, the relationships were detected between aerosol''s contribution to apparent reflectance (ACR) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) on board Terra and hourly PM10 mass concentration measured at 30 ground-based locations in Beijing for the August of 2003 and 2004. It was shown that there was a good correlation between the ACR and PM10 (linear correlation coefficient, R=0.56). On the basis of this relationship, spatial distribution and possible sources of PM10 derived from MODIS were analyzed and two frequently heavily-polluted regions were found, namely downtown of the city and the district near Xishan Mountain. These two regions coincidently are also urban heat island centers. The foundings of this paper will be greatly useful for environmental monitoring and urban planning for Beijing, especially for the 2008 Olympic game to be held in Beijing. [Copyright &y& Elsevier]

China is rapidly developing as evidenced by enhanced urbanization and industrialization and greatly increased energy consumption. However, these have brought Chinese cities a variety of urban air pollution problems in recent decades. During the 1970s, black smoke from stacks became the characteristic of Chinese industrial cities; in the 1980s, many southern cities began to suffer serious acid rain pollution; and recently, the air quality in large cities has deteriorated due to nitrous oxides (NOx), carbon monoxide (CO), and photochemical smog, which are typical of vehicle pollution. Some cities now have a mixture of these. Urban air pollution influences both the health of citizens and the development of cities. To control air pollution and protect the atmospheric environment, the Chinese government has implemented a variety of programs. This paper first reviews the current status of air quality in Chinese cities, especially key cities, then describes the characteristics of some major urban air pollutants, including total suspended particles (TSP), respirable particles 10 microns or less in diameter (PM10), very fine particles 2.5 microns or less in diameter (PM2.5), sulfur dioxide (SO2), acid rain, NOx, and photochemical smog. Two specific topics, SO2 and acid rain control and vehicle emission control, are used to illustrate the actions that the government has taken and future plans. Finally, a case study of the Chinese capital, Beijing, is presented with a discussion of its main air pollution problems, recently implemented control measures and their effects, and future strategies for urban air quality improvement. [ABSTRACT FROM AUTHOR]

Background: Exposure to air pollution, a leading contributor to the global burden of disease, can cause economic losses. Driven by clean air policies, the air quality in China, one of the most polluted countries, has improved rapidly since 2013. This has enabled a unique, quasi-experiment to assess the economic impact of air pollution empirically.Methods and Findings: Using a series of nation-scale longitudinal surveys in 2011, 2013, and 2015, we first examined the questionnaire-based medical expenditure changes before and after the policy intervention for air pollution. Using a state-of-the-art estimator of the historical concentration of particulate matters with diameter less than 2.5 μm (particulate matter (PM)2.5), we further quantified the association between household medical expenditure and PM2.5 using mixed-effect models of the repeated measurements from 26,511 households in 126 cities. Regression models suggest a robust linear association between reduced PM2.5 and saved medical expenditures, since the association did not vary significantly across models with different covariate adjustments, subregions, or subpopulations. Each 10 μg/m3 reduction in PM2.5 was associated with a saving of 251.6 (95% CI: 30.8, 472.3; p-value = 0.026) Yuan in per capita annual medical expenditure. However, due to limitations in data quality (e.g., self-reported expenditures), and imperfect control for unmeasured confounders or impact from concurrent healthcare reform in China, the causality underlying our findings should be further confirmed or refuted.Conclusion: In this study, we observed that compared with the PM2.5 reduction in 2013, the PM2.5 reduction in 2017 was associated with a saving of 552 (95% CI: 68, 1036) Yuan / (person × year), or approximately 736 billion Yuan (equivalent to 111 billion US dollar) per year nationally, which is equivalent to approximately 1% of the national gross domestic product of China. [ABSTRACT FROM AUTHOR]

With rapid economic growth and urbanization, the Yangtze River Delta (YRD) region in China has experienced serious air pollution challenges. In this study, we analyzed the air pollution characteristics and their relationship with emissions and meteorology in the YRD region during 2014–2016. In recent years, the concentrations of all air pollutants, except O 3 , decreased. Spatially, the PM 2.5 , PM 10 , SO 2 , and CO concentrations were higher in the northern YRD region, and NO 2 and O 3 were higher in the central YRD region. Based on the number of non-attainment days (i.e., days with air quality index greater than 100), PM 2.5 was the largest contributor to air pollution in the YRD region, followed by O 3 , PM 10 , and NO 2. However, particulate matter pollution has declined gradually, while O 3 pollution worsened. Meteorological conditions mainly influenced day-to-day variations in pollutant concentrations. PM 2.5 concentration was inversely related to wind speed, while O 3 concentration was positively correlated with temperature and negatively correlated with relative humidity. The air quality improvement in recent years was mainly attributed to emission reductions. During 2014–2016, PM 2.5 , PM 10 , SO 2 , NO x , CO, NH 3 , and volatile organic compound (VOC) emissions in the YRD region were reduced by 26.3%, 29.2%, 32.4%, 8.1%, 15.9%, 4.5%, and 0.3%, respectively. Regional transport also contributed to the air pollution. During regional haze periods, pollutants from North China and East China aggravated the pollution in the YRD region. Our findings suggest that emission reduction and regional joint prevention and control helped to improve the air quality in the YRD region. Unlabelled Image [ABSTRACT FROM AUTHOR]

We use 2005–2016 observations of formaldehyde (HCHO) columns over China from the OMI, GOME‐2, and SCIAMACHY satellite instruments to evaluate long‐term trends in emission inventories of volatile organic compounds (VOCs) that affect air quality. The observations show large increases over 2005–2016 in the North China Plain (+1.1 ± 0.5% a−1 relative to 2005) and the Yangtze River Delta region (+1.5 ± 0.4% a−1 relative to 2005), consistent with the trend of anthropogenic VOC emissions in the Multi‐resolution Emission Inventory for China (MEIC). Unlike other pollutants, VOC emissions have not been decreasing in recent years. An exception is the Huai River Basin in rural eastern China where the satellite data show rapidly decreasing VOC emissions since the early 2010s that appear to reflect bans on agricultural fires. Plain Language Summary: Satellite observations of formaldehyde can detect emissions of volatile organic compounds (VOCs), which are of concern for air quality. Here we use 2005–2016 satellite observations of formaldehyde over China to infer trends in VOC emissions. We find increases of 13% in the North China Plain and 18% in the Yangtze River Delta. Unlike other pollutants, emissions of VOCs in China have not decreased in recent years. An exception is in rural areas where post‐2010 restrictions on crop burning to improve air quality have resulted in sharp decreases of VOC emissions. Key Points: 2005 to 2016 satellite observations of formaldehyde show increases in Chinese anthropogenic emissions of volatile organic compoundsThe increases are largest in the North China Plain and Yangtze River Delta and are consistent with the MEIC emission inventoryDecreases are observed in rural eastern China since the early 2010s that appear due to new restrictions on crop burning [ABSTRACT FROM AUTHOR]

Abstract Air pollution is one of the most harmful consequences of China's rapid economic development and urbanization. Particularly in the Beijing-Tianjin-Hebei (BTH) regions, particulate matter concentrations have consistently exceeded the national air quality standards. Over the last years, China implemented ambitious measures to reduce emissions from the power, industry and transportation sectors, with notable success during the 11th and 12th Five Year Plan (FYP) periods. However, such strategies appear to be insufficient to reduce the ambient PM 2.5 concentration below the National Air Quality Standard of 35 μg m−3 across the BTH region within the next 15 years. We find that a comprehensive mitigation strategy for the residential sector in the BTH region would deliver substantial air quality benefits. Beyond the already planned expansion of district heating and natural gas distribution in urban centers and the foreseen curtailment of coal use for households, such a strategy would redirect some natural gas from power generation units towards the residential sector. Rural households would replace biomass for cooking by liquid petroleum gas (LPG) and electricity, and substitute coal for heating by briquettes. Jointly, these measures could reduce the primary PM 2.5 and SO 2 emissions by 28% and 11%, respectively, and the population-weighted PM 2.5 concentrations by 13%, i.e., from 68 μg m−3 to 59 μg m−3. We estimate that such a strategy would reduce premature deaths attributable to ambient and indoor air pollution by almost one third. Graphical abstract Unlabelled Image Highlights • Air quality and health benefits from a comprehensive mitigation strategy in the residential sector were estimated. • Compared to the baseline, the residential mitigation scenario will result in 28% and 11% lower PM 2.5 and SO 2 emissions. • The population weighted PM 2.5 concentration will decrease by 13% compared to the baseline. • The health impacts will be reduced by almost one third, with the majority delivered from eliminating solid fuel use for cooking. [ABSTRACT FROM AUTHOR]

Abstract There exist substantial differences in top-of-atmosphere direct radiative forcing of aerosols due to a region's economic production (RF p) and consumption (RF c), in the context of economic globalization, trade and globalizing air pollution. Yet an explicit systematic analysis of all socioeconomic and atmospheric factors determining the RF difference is lacking. Here, we evaluate five socioeconomic (population, per capita output, emission intensity) and atmospheric (chemical efficiency and radiative efficiency) factors that determine a region's RF p , RF c and their difference. We consider the RF of secondary inorganic aerosols, primary organic aerosols and black carbon by 10 regions worldwide in 2007. The population size varies by a factor of nine across the regions, and per capita output by 40 times from both production- and consumption-based perspectives. The cross-regional spread reaches a factor of 181 (species dependent) for production-based emission intensity and a factor of 96 for consumption-based intensity. From one region to another, production-based chemical efficiency changes within a factor of 5 and consumption-based efficiency within a factor of 3.5. Radiative efficiency varies slightly across the regions (within 2) from both production- and consumption-based perspectives. Although socioeconomic factors are often a greater driver for the difference between a source region's RF p and RF c , the atmospheric factors are also important for many source regions and species. Our results contribute to regional attribution of climate change and establishment of effective international collaborative mitigation strategies. Highlights • Multiple factors differentiate a region's aerosol RF c from its RF p. • Socioeconomic factors usually play a greater role for most regions and species. • Atmospheric factors are also important for some regions and species. • Our study is relevant to regional attribution of aerosol radiative forcing. [ABSTRACT FROM AUTHOR]

The increasingly high frequency of heavy air pollution in most regions of China signals the urgent need for the transition to an environmentally friendly production performance by socioeconomic sectors for the sake of people's health and sustainable development. Focusing on CO 2 and major air pollutants, this paper presents a comprehensive environmental efficiency index based on evaluating the environmental efficiency of major socioeconomic sectors, including agriculture, power, industry, residential and transportation, at the province level in China in 2010 based on a slack-based measure DEA model with non-separable bad output and weights determined by the coefficient of variation method. In terms of the environment, 5, 16, 6, 7 and 4 provinces operated along the production frontier for the agricultural, power, industrial, residential and transportation sectors, respectively, in China in 2010, whereas Shanxi, Heilongjiang, Ningxia, Hubei and Yunnan showed lowest efficiency correspondingly. The comprehensive environmental efficiency index varied from 0.3863 to 0.9261 for 30 provinces in China, with a nationwide average of 0.6383 in 2010; Shanghai ranked at the top, and Shanxi was last. Regional disparities in environmental efficiency were identified. A more detailed inefficiency decomposition and benchmarking analysis provided insight for understanding the source of comprehensive environmental inefficiency and, more specifically, the reduction potential for CO 2 and air pollutants. Some specific research and policy implications were uncovered from this work. [ABSTRACT FROM AUTHOR]

We developed a high-resolution Beijing-Tianjin-Hebei (BTH) regional air pollutants emission inventory for the year 2013. The inventory was established using a bottom-up approach based on facility-level activity data obtained from multiple data sources. The estimates from the BTH 2013 emission inventory show that the total emissions of SO 2 , NO X , PM 2.5 , PM 10 , CO, NMVOC, NH 3 , BC, and OC were 2,305, 2,686, 1,090, 1,494, 20,567, 2,207, 623, 160, and 254 Gg, respectively. The industry sector is the largest emissions source for SO 2 , NO X , PM 2.5 , PM 10 , CO, and NMVOC in the BTH region, contributing 72.6%, 43.7%, 59.6%, 64.7%, 60.3%, and 70.4% of the total emissions, respectively. Power plants contributed 11.8% and 23.3% of the total SO 2 and NO X emissions, respectively. The transportation sector contributed 28.9% of the total NO X emissions. Emissions from the residential sector accounted for 31.3%, 21.5%, 46.6% and 71.7% of the total PM 2.5 , NMVOC, BC and OC emissions, respectively. In addition, more than 90% of the total NH 3 emissions originate from the agriculture sector, with 44.2% from fertilizer use and 47.7% from livestock. The spatial distribution results illustrate that air pollutant emissions are mainly distributed over the eastern and southern BTH regions. Beijing, Tianjin, Shijiazhuang, Tangshan and Handan are the major contributors of air pollutants. The major NMVOC species in the BTH region are ethylene, acetylene, ethane and toluene. Ethylene is the biggest contributor in Tianjin and Hebei. The largest contributor in Beijing is toluene. There is relatively low uncertainty in SO 2 and NO X emission estimates, medium uncertainty in PM 2.5 , PM 10 and CO emission estimates, and high uncertainties in VOC, NH 3 , BC and OC emission estimates. The proposed policy recommendations, based on the BTH 2013 emission inventory, would be helpful to develop strategies for air pollution control. [ABSTRACT FROM AUTHOR]

Excess mortality (ΔMort) in China due to exposure to ambient fine particulate matter with aerodynamic diameter ≤2.5 μm (PM2.5) was determined using an ensemble prediction of annual average PM2.5 in 2013 by the community multiscale air quality (CMAQ) model with four emission inventories and observation data fusing. Estimated ΔMort values due to adult ischemic heart disease, cerebrovascular disease, chronic obstructive pulmonary disease, and lung cancer are 0.30, 0.73, 0.14, and 0.13 million in 2013, respectively, leading to a total ΔMort of 1.3 million. Source-oriented CMAQ modeling determined that industrial and residential sources were the two leading sources of ΔMort, contributing to 0.40 (30.5%) and 0.28 (21.7%) million deaths, respectively. Additionally, secondary ammonium ion from agriculture, secondary organic aerosol, and aerosols from power generation were responsible for 0.16, 0.14, and 0.13 million deaths, respectively. A 30% ΔMort reduction in China requires an average of 50% reduction of PM2.5 throughout the country and a reduction by 62%, 50%, and 38% for the Beijing-Tianjin-Hebei, Jiangsu-Zhejiang-Shanghai, and Pearl River Delta regions, respectively. Reducing PM2.5 to the CAAQS grade II standard of 35 μg m-3 would only lead to a small reduction in mortality, and a more stringent standard of <15 μg m-3 would be needed for more remarkable reduction of ΔMort. [ABSTRACT FROM AUTHOR]

Emissions of the fine particulate matters (diameter of 2.5 μm or less) caused by both the primary particle emissions and the precursor emission sources such as sulfur dioxide and nitrogen oxides, have contributed significantly to poor urban air quality in China, and have attracted tremendous public attention over the past few years. This study provides an interdisciplinary study to investigate the key contributors driving air pollution emissions changes in China from 1997 to 2012, by applying the Logarithmic Mean Divisia Index method. The decomposition results are presented in both multiplicative and additive approaches to show the relative and absolute contribution of each factor in affecting emission changes. Changes in total particulate matter emissions are attributed to variations in primary particle, sulfur dioxide and nitrogen oxides emissions. It is manifested that the economic growth effect and energy intensity effect have always been the two key drivers in affecting the changes in air pollutant emissions over the period. The effects of emission efficiency, production structure and population growth contribute less significantly to overall emission changes, and the impacts of different factors vary among different pollutants. Since current strategies and policies in combatting particulate matter emissions are inefficient, this paper provides a guideline for the Chinese Government to deal with the air pollution problem for sustainable development in China. [ABSTRACT FROM AUTHOR]

Particulate air pollution has had a significant impact on human health in China and it is associated with cardiovascular and respiratory diseases and high mortality and morbidity. These health impacts could be translated to reduced labor availability and time. This paper utilized a supply-driven input-output (I-O) model to estimate the monetary value of total output losses resulting from reduced working time caused by diseases related to air pollution across 30 Chinese provinces in 2007. Fine particulate matter (PM 2.5 ) pollution was used as an indicator to assess impacts to health caused by air pollution. The developed I-O model is able to capture both direct economic costs and indirect cascading effects throughout inter-regional production supply chains and the indirect effects greatly outnumber the direct effects in most Chinese provinces. Our results show the total economic losses of 346.26 billion Yuan (approximately 1.1% of the national GDP) based on the number of affected Chinese employees (72 million out of a total labor population of 712 million) whose work time in years was reduced because of mortality, hospital admissions and outpatient visits due to diseases resulting from PM 2.5 air pollution in 2007. The loss is almost the annual GDP of Vietnam in 2010. The proposed modelling approach provides an alternative method for health-cost measurement with additional insights on inter-industrial and inter-regional linkages along production supply chains. [ABSTRACT FROM AUTHOR]

BACKGROUND: Three decades of rapid economic development is causing severe and widespread PM2.5 (particulate matter ≥ 2.5 µm) pollution in China. However, research on the health impacts of PM2.5 exposure has been hindered by limited historical PM2.5 concentration data. OBJECTIVES: We estimated ambient PM2.5 concentrations from 2004 to 2013 in China at 0.1° resolution using the most recent satellite data and evaluated model performance with available ground observations. METHODS: We developed a two-stage spatial statistical model using the Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6 aerosol optical depth (AOD) and assimilated meteorology, land use data, and PM2.5 concentrations from China's recently established ground monitoring network. An inverse variance weighting (IVW) approach was developed to combine MODIS Dark Target and Deep Blue AOD to optimize data coverage. We evaluated model-predicted PM2.5 concentrations from 2004 to early 2014 using ground observations. RESULTS: The overall model cross-validation R2 and relative prediction error were 0.79 and 35.6%, respectively. Validation beyond the model year (2013) indicated that it accurately predicted PM2.5 concentrations with little bias at the monthly (R² = 0.73, regression slope = 0.91) and seasonal (R² = 0.79, regression slope = 0.92) levels. Seasonal variations revealed that winter was the most polluted season and that summer was the cleanest season. Analysis of predicted PM2.5 levels showed a mean annual increase of 1.97 µg/m³ between 2004 and 2007 and a decrease of 0.46 µg/m³ between 2008 and 2013. CONCLUSIONS: Our satellite-driven model can provide reliable historical PM2.5 estimates in China at a resolution comparable to those used in epidemiologic studies on the health effects of long-term PM2.5 exposure in North America. This data source can potentially advance research on PM2.5 health effects in China. [ABSTRACT FROM AUTHOR]

The Xi'an City and the surrounding area (the Guan-Zhong—GZ region) in western China have been suffering severe air pollutions during wintertime in recent years. In-situ black carbon (BC) measurement combined with a regional dynamical and chemical model (WRF-Chem model) is used to investigate the formation of a haze episode occurred from Jan. 3rd to Jan. 13th 2013. The results show that the measured BC concentrations exhibit a large day-to-day variability. The impacts of synoptic weather systems, local meteorological parameters and mountain effect on the BC variability are studied. Because the GZ region is surrounded by two major mountains, the Loess Plateau in the north and the Qinling Mountains in the south, especially the peak of the Qinling Mountains higher than 3000 m, we particularly analyze the effects of the Qinling Mountains on the BC pollution. The analysis shows that the BC pollution in Xi'an City and the GZ region is strongly affected by the synoptic weather systems, local meteorological winds and the Qinling Mountains. Under a typical northeast wind condition, winds are blocked by the Qinling Mountains, and BC particles are trapped at the foothill of the mountains, resulting in high BC concentrations in the city of Xi'an. Under a typical east wind condition, BC particles are transported along a river valley and the foothill of the Qinling Mountains. In this case, the mountain-river valley plays a role to accelerate the east wind, resulting in a reduction of the BC pollution. Under a typical calm wind condition, the BC particles are less diffused from their source region, and there is a mountain breeze from the Qinling Mountains to the city of Xi'an, and BC particles accumulate in the city, especially in the north side of the city. This study illustrates that while locating between complicated terrain conditions, such as the GZ region, the mountains play very important roles for the formation of hazes in the region. [ABSTRACT FROM AUTHOR]

Severe haze repeatedly shrouded Harbin during the winter of 2019–2020, making it one of the 10 most polluted cities in China for January of 2020. Here we explored the major drivers for the extreme atmospheric pollution events. Enhanced formation of secondary organic and inorganic aerosols was evident at higher pollution levels, accompanied with a sharp growth of aerosol water content (AWC) and a persistent increase of aerosol pH. Non-biomass burning (non-BB) combustion sources were inferred to be relatively stable during the measurement period. The elemental carbon mass apportioned to the non-BB sources exhibited an apparent increasing trend as aerosol concentrations became higher, pointing to the influence of unfavorable dispersion conditions. In addition, biomass burning (BB) emissions were found to be strengthened at higher aerosol concentrations. This trend was associated with a large drop of temperature, presumably indicating that the strengthened BB emissions were due to more intensive use of biomass for heating. In brief, the winter haze events in Harbin were caused by a synergy of three factors, i.e., enhanced secondary aerosol formation, unfavorable dispersion conditions and strengthened BB emissions. A semi-quantitative approach was developed to further estimate the relative importance of these drivers. Strengthened BB emissions were always less responsible for haze events compared to other factors, whereas the less severe and heavily polluted haze events were caused mainly by unfavorable dispersion conditions and enhanced secondary aerosol formation, respectively. This study provides observational evidences for efficient production of secondary species in aerosol water despite the frigid winter in Harbin, and thus highlights the need for effective control of gaseous precursors, both organic and inorganic. [Display omitted] • Harbin experienced the most polluted month in recent years during January of 2010. • Heterogeneous secondary aerosol formation was at play in the frigid atmosphere. • Heavily polluted episodes were mainly due to enhanced secondary aerosol formation. • Unfavorable meteorology was the dominant driver for less severe haze events. • Haze episodes had lower temperatures and stronger biomass burning emissions. [ABSTRACT FROM AUTHOR]

Severe haze hovered over Harbin during the heating season of 2019–2020, making it one of the ten most polluted Chinese cities in January of 2020. Here we focused on the optical properties and sources of brown carbon (BrC) during the extreme atmospheric pollution periods. Enhanced formation of secondary BrC (BrC sec) was evident as relative humidity (RH) became higher, accompanied with a decrease of ozone but concurrent increases of aerosol water content and secondary inorganic aerosols. These features were generally similar to the characteristics of haze chemistry observed during winter haze events in the North China Plain, and indicated that heterogeneous reactions involving aerosol water might be at play in the formation of BrC sec , despite the low temperatures in Harbin. Although BrC sec accounted for a substantial fraction of brown carbon mass, its contribution to BrC absorption was much smaller (6 vs. 28%), pointing to a lower mass absorption efficiency (MAE) of BrC sec compared to primary BrC. In addition, emissions of biomass burning BrC (BrC BB) were inferred to increase with increasing RH, coinciding with a large drop of temperature. Since both the less absorbing BrC sec and the more absorbing BrC BB increased as RH became higher, the MAE of total BrC were largely unchanged throughout the measurement period. This study unfolded the contrast in the source apportionment results of BrC mass and absorption, and could have implications for the simulation of radiative forcing by brown carbon. • Secondary BrC formation was enhanced at high RH despite low temperatures. • Secondary BrC accounted for 28% of brown carbon mass. • The contribution of secondary BrC to total brown carbon absorption was only 6%. • Though sources varied, total BrC had relatively constant optical properties. • BrC was inferred as an important contributor to aerosol absorption in Harbin. [ABSTRACT FROM AUTHOR]

Abstract: Following model evaluation in part I, this part II paper focuses on the process analysis and chemical regime analysis for the formation of ozone (O3) and particulate matter with aerodynamic diameter less than or equal to 10 μm (PM10) in China. The process analysis results show that horizontal transport is the main contributor to the accumulation of O3 in Jan., Apr., and Oct., and gas-phase chemistry and vertical transport contribute to the production and accumulation of O3 in Jul. Removal pathways of O3 include vertical and horizontal transport, gas-phase chemistry, and cloud processes, depending on locations and seasons. PM10 is mainly produced by primary emissions and aerosol processes and removed by horizontal transport. Cloud processes could either decrease or increase PM10 concentrations, depending on locations and seasons. Among all indicators examined, the ratio of provides the most robust indicator for O3 chemistry, indicating a VOC-limited O3 chemistry over most of the eastern China in Jan., NOx-limited in Jul., and either VOC- or NOx-limited in Apr. and Oct. O3 chemistry is NOx-limited in most central and western China and VOC-limited in major cities throughout the year. The adjusted gas ratio, AdjGR, indicates that PM formation in the eastern China is most sensitive to the emissions of SO2 and may be more sensitive to emission reductions in NOx than in NH3. These results are fairly consistent with the responses of O3 and PM2.5 to the reductions of their precursor emissions predicted from sensitivity simulations. A 50% reduction of NOx or AVOC emissions leads to a reduction of O3 over the eastern China. Unlike the reduction of emissions of SO2, NOx, and NH3 that leads to a decrease in PM10, a 50% reduction of AVOC emissions increases PM10 levels. Such results indicate the complexity of O3 and PM chemistry and a need for an integrated, region-specific emission control strategy with seasonal variations to effectively control both O3 and PM2.5 pollution in China. [Copyright &y& Elsevier]

Abstract: The U.S. EPA Models-3 Community Multiscale Air Quality (CMAQ) modeling system with the process analysis tool is applied to China to study the seasonal variations and formation mechanisms of major air pollutants. Simulations show distinct seasonal variations, with higher surface concentrations of sulfur dioxide (SO2), nitrogen dioxide (NO2), and particulate matter with aerodynamic diameter less than or equal to 10 μm (PM10), column mass of carbon monoxide (CO) and NO2, and aerosol optical depth (AOD) in winter and fall than other seasons, and higher 1-h O3 and troposphere ozone residual (TOR) in spring and summer than other seasons. Higher concentrations of most species occur over the eastern China, where the air pollutant emissions are the highest in China. Compared with surface observations, the simulated SO2, NO2, and PM10 concentrations are underpredicted throughout the year with NMBs of up to −51.8%, −32.0%, and −54.2%, respectively. Such large discrepancies can be attributed to the uncertainties in emissions, simulated meteorology, and deviation of observations based on air pollution index. Max. 1-h O3 concentrations in Jan. and Jul. at 36-km are overpredicted with NMBs of 12.0% and 19.3% and agree well in Apr. and Oct. Simulated column variables can capture the high concentrations over the eastern China and low values in the central and western China. Underpredictions occur over the northeastern China for column CO in Apr., TOR in Jul., and AODs in both Apr. and Jul.; and overpredictions occur over the eastern China for column CO in Oct., NO2 in Jan. and Oct., and AODs in Jan. and Oct. The simulations at 12-km show a finer structure in simulated concentrations than that at 36-km over higher polluted areas, but do not always give better performance than 36-km. Surface concentrations are more sensitive to grid resolution than column variables except for column NO2, with higher sensitivity over mountain and coastal areas than other regions. [Copyright &y& Elsevier]

Fine particles with aerodynamic diameters less than 1 μm (PM 1) often exert a greater threaten on human health, and thus it is highly imperative to accurately characterize the spatiotemporal variation of PM 1 concentrations and to assess the potential health risks. Our study attempted to predict the long-term full-coverage PM 1 concentrations across China during 2004–2018 using a stacking decision tree model based on satellite data, meteorological variables, and other geographical covariates. The result suggested that the stacking model captured strong prediction capability with a higher cross-validation (CV) R2 value (0.64), and the lower root-mean-square error (RMSE: 18.60 μg/m3) and mean absolute error (MAE: 11.96 μg/m3) compared with the individual model. The higher PM 1 concentrations were mainly concentrated on North China Plain (NCP), Yangtze River Delta (YRD), and Sichuan Basin due to intensive anthropogenic activities and poor meteorological conditions especially in winter. The annual mean PM 1 concentration in China exhibited a remarkable increase during 2004–2007 by 1.34 μg/m3/year (p < 0.05), followed by a gradual decrease during 2007–2018 by −1.61 μg/m3/year (p < 0.05). After 2013, the mean PM 1 concentration at the national scale experienced a dramatic decrease by −2.96 μg/m3/year (p < 0.05). The persistent increase of PM 1 concentration across China during 2004–2007 was mainly caused by the rapid increases of energy consumption and inefficient emission control measures, while the dramatic decrease since 2013 was attributed to increasingly strict control measures, particularly the implementation of the Air Pollution Prevention and Control Action Plan (the Action Plan). The long-term PM 1 estimates obtained here provide a key scientific basis and data support for epidemiological research and air pollution mitigation. • A stacking decision tree model was applied to estimate daily PM 1 level across China. • The stacking model captured strong prediction capability with a higher CV R2 value (0.64). • The mean PM 1 level over China experienced a rapid decrease by −2.96% μg/m3/year. [ABSTRACT FROM AUTHOR]

• Satellite-based PM 2.5 predictions at 1-km resolution during 2000–2018 were employed. • Clean air policies modified PM 2.5 spatial patterns and pollution-economic relation. • Urban areas showed higher PM 2.5 levels and greater PM 2.5 reduction than rural areas. • Stricter emission control led to greater decline in urban-rural PM 2.5 gap after 2013. To improve air quality, China has been implementing strict clean air policies since 2013. These policies not only substantially improved air quality but may also modify the spatial distribution of air pollution, since urban emission sources were under stricter control and some were moved to rural regions with lower air quality improvement targets and lacking of monitoring. Here, we predicted satellite-based monthly PM 2.5 concentrations during 2000–2018 at a 1-km resolution with complete spatial-temporal coverage to analyze changes in the spatial pattern of PM 2.5 pollution in China. We found that the PM 2.5 concentration in urban regions was higher than that in rural regions of the same city by an average of 3.3 μg/m3 during 2000–2018. This urban-rural disparity in PM 2.5 concentration significantly increased from 2.5 μg/m3 in 2000 and peaked in 2007 of 3.8 μg/m3, then it sharply declined by 49% during 2013–2018 with the implementation of clean air policies. This shrinkage in the urban-rural PM 2.5 gap was partly due to the 1.3 μg/m3 greater average decrease in the PM 2.5 level in the urban region than in the rural region of the same town during 2013–2018 on average. We also observed that cities that started monitoring earlier experienced greater decreases in the urban-rural PM 2.5 difference, and regions surrounding monitor showed significantly greater PM 2.5 decrease than regions far away from monitor during 2013–2018. Additionally, clean air policies modified the relationship between PM 2.5 concentrations and per capita gross domestic product (GDP), leading to a lower PM 2.5 level with the same per capita GDP after 2013. Emissions in rural and suburban regions should be considered to further improve air quality in China. [ABSTRACT FROM AUTHOR]

Isoprene, primarily emitted by vegetation, is considered to be the most important biogenicvolatile organic compound (BVOC) in the troposphere due to its abundant emission (∼40%of total VOCs globally) and high ozone (O3) formation potential. Once it is released to theatmosphere, isoprene is rapidly oxidised to form peroxy radicals (RO2), which can react withnitric oxide (NO) to form nitrogen dioxide (NO2), which when photolysed can form O3.However, a minor branch of the RO2 and NO reaction yields stable isoprene nitrates (INs)that temporarily terminate the O3 production by tying the active nitrogen into thenitrate functional group. The lifetimes of some of these nitrates are relatively long(days to weeks), so they can be transported and destroyed away from the source,releasing NO2 back to the atmosphere downwind. In other words, the formation of INscan change the O3 distribution. The role of INs in NOX (NO + NO2) recycling ispoorly understood, in part due to a lack of field measurement of the individualINs. Individual IN isomers derived through different isoprene initial-oxidation pathways (OHand NO3) were measured with a gas chromatography / mass spectrometry analytical systemin the summer of 2016 in Beijing as part of the Air Pollution and Human Health in aDeveloping Megacity (APHH-Beijing) programme. A regional chemistry transport model(Weather Research and Forecasting model coupled with Chemistry, WRF-Chem) has been setup to simulate the isoprene oxidation processes during the campaign period for most ofChina. Since existing chemical mechanisms coupled to WRF-Chem represent the INs aslumped organic nitrates, we developed a more explicit chemical mechanism with 7 INisomers by adding the Mainz Isoprene Mechanism (MIM2) and aspects of the MasterChemical Mechanism (MCM) to the Model for Ozone and Related chemical Tracers(MOZART-4) mechanism. The measurement data from Beijing have been used to evaluate and improve ourunderstanding of the production and loss of the INs. The modelled diel patterns of INsagree well with the observations, although there are discrepancies in the absoluteconcentrations. The impact of isoprene on O3, NOX, NOY and HOX in differentregimes across China is discussed in terms of the NOX-isoprene ratio as well as therole of isoprene derived organic nitrates in NOX recycling. The amount of NOXrecycled through the INs is quantified by using a tagging method. We also examinehow different treatments of isoprene and the INs in reduced mechanisms affect theresults, including the sensitivity of the formation of INs to the RO2 cross-reactions. [ABSTRACT FROM AUTHOR]

Poor air quality is an urgent issue for the modern world. Residents of megacities, such asBeijing, are particularly affected as high population density and rapid economic growthinevitably result in high levels of air pollution. Chinese cities regularly breach World HealthOrganisation (WHO) air quality guidelines, which are associated with severe health risksincluding cancer and cardiovascular disease. In 2010, 1.2 million premature deaths wereattributed to outdoor air pollution in China. Considerable efforts have been made to reduce atmospheric pollutant concentrations inChina within the past few years. Regulatory changes require the identification of thesources of air pollution and as such there is a pressing need for reliable measurementsof pollutant emissions. In comparison to concentration alone, the determinationof pollutant emission using the eddy-covariance technique requires fast-responsemeasurements. For the first time in Beijing, NOx and CO flux were observed in thisway as part of the 'Air Pollution and Human Health (APHH) in Beijing&#x2019; researchprogramme. During two field campaigns in November-December (winter) 2016 and May-June(summer) 2017, 5 Hz measurements of NOx and CO concentrations were made. Samplingtook place from a gas inlet co-located with a sonic anemometer at an elevation of 102 m on ameteorological tower in central Beijing. Analysis of the covariance between vertical windspeed and concentration enabled the calculation of emission flux, with an estimated footprintextent between 1 – 2 km upwind of the tower (which typically included some majorring roads and expressways). Observed 30-minute emissions were compared tomodified emissions estimates from the Multi-resolution Emission Inventory for China(MEIC). For both NOx and CO, calculated flux was almost entirely positive indicating emissiondominates over deposition as expected for an urban environment. The magnitude of theNOx flux was similar between the winter and summer campaigns, with an averagevalue of 3.8 ± 1 mg m−2 h−1 and 3.2 ± 0.8 mg m−2 h−1 respectively. CO fluxshowed considerably more variability between the two seasons with a measuredvalue of 28 ± 8 mg m−2 h−1 in the winter and 13 ± 4 mg m−2 h−1 in the summer.Analysis of diurnal variation in NOx and CO flux suggest that these species have adominant traffic source for both seasons. The variability in CO flux may be attributed toinefficiencies in engine combustion caused by cooler ambient temperatures in winter. [ABSTRACT FROM AUTHOR]

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 eventsTypical measurement systems for ambient particulates easily misinterpret hydroxymethane sulfonate (HMS) as sulfateHMS 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 [ABSTRACT FROM AUTHOR]