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The development of chemical transport models with advanced physics and chemical schemes could improve air-quality forecasts. In this study, the China Meteorological Administration Unified Atmospheric Chemistry Environment (CUACE) model, a comprehensive chemistry module incorporating gaseous chemistry and a size-segregated multicomponent aerosol algorithm, was coupled to the Weather Research and Forecasting (WRF) framework with chemistry (WRF-Chem) using an interface procedure to build the WRF/CUACE v1.0 model. The latest version of CUACE includes an updated aerosol dry deposition scheme and the introduction of heterogeneous chemical reactions on aerosol surfaces. We evaluated the WRF/CUACE v1.0 model by simulating PM 2.5 , O3 , NO2 , and SO2 concentrations for January, April, July, and October (representing winter, spring, summer and autumn, respectively) in 2013, 2015, and 2017 and comparing them with ground-based observations. Secondary inorganic aerosol simulations for the North China Plain (NCP), Yangtze River Delta (YRD), and Sichuan Basin (SCB) were also evaluated. The model captured well the variations of PM 2.5 , O3 , and NO2 concentrations in all seasons in eastern China. However, it is difficult to accurately reproduce the variations of air pollutants over SCB, due to its deep basin terrain. The simulations of SO2 were generally reasonable in the NCP and YRD with the bias at -15.5 % and 24.55 %, respectively, while they were poor in the Pearl River Delta (PRD) and SCB. The sulfate and nitrate simulations were substantially improved by introducing heterogeneous chemical reactions into the CUACE model (e.g., change in bias from -95.0 % to 4.1 % for sulfate and from 124.1 % to 96.0 % for nitrate in the NCP). Additionally, The WRF/CUACE v1.0 model was revealed with better performance in simulating chemical species relative to the coupled Fifth-Generation Penn State/NCAR Mesoscale Model (MM5) and CUACE model. The development of the WRF/CUACE v1.0 model represents an important step towards improving air-quality modeling and forecasts in China. [ABSTRACT FROM AUTHOR]

Abstract Fine particulate matter (PM 2.5) pollution in Eastern China (EC) has raised concerns due to its adverse effects on air quality, climate, and human health. This study investigated the long-term variation trend in satellite-derived PM 2.5 concentrations and how it was related to pollutant emissions and meteorological parameters over EC and seven regions of interest (ROIs) during 1998–2016. Over EC, the annual mean PM 2.5 increased before 2006 due to the enhanced emissions of primary PM 2.5 , NO x and SO 2 , but decreased with the reduced SO 2 emissions after 2006 evidently in response to China's clean air policies. In addition, results from statistical analyses indicated that in the North China Plain (NCP), Northeast China (NEC), Sichuan Basin (SCB) and Central China (CC) planetary boundary layer height (PBLH) was the dominant meteorological driver for the PM 2.5 decadal changes, and in the Pearl River Delta (PRD) wind speed is the leading factor. Overall, the variation in meteorological parameters accounted for 48% of the variances in PM 2.5 concentrations over EC. The population-weighted PM 2.5 over EC increased from 36.4 μg/m3 in 1998–2004 (P1) to 49.4 μg/m3 in 2005–2010 (P2) then decreased to 46.5 μg/m3 in 2011–2016 (P3). In the NCP and NEC, the percentages of the population living above the World Health Organization (WHO) Interim Target-1 (IT-1, 35 μg/m3) have risen steadily over the past 20 yr, reaching maxima of 97.3% and 78.8% in P3, respectively, but decreases of ∼30% from P2 to P3 were found for the SCB and PRD. Graphical abstract Image 1 Highlights • The joint effect of emission and meteorological determined the decadal trend of PM 2.5 • The changes in meteorological parameters explained 48% of the variances in PM 2.5. • Planetary boundary layer height was the dominant driver for the decadal changes of PM 2.5 • Eastern China has experienced slight decreases in the population-weighted mean PM 2.5 over the past 10 year. The joint effect of emissions and meteorological determined the decadal trend in PM 2.5. The decadal variation in meteorological parameters accounted for 48% of the variances in PM 2.5 concentrations over Eastern China. Eastern China has experienced slight decreases in the population-weighted mean PM 2.5 over the past 10 year. [ABSTRACT FROM AUTHOR]

The Sichuan and Chongqing regions suffer from severe haze weather in winter due to the unfavourable atmospheric diffusion conditions. Reanalysis and precipitation datasets were applied in this study to calculate and distinguish air stagnation events using a developed criterion, and the impacts of the occurrence of air stagnation events on air quality were analysed in combination with the PM 2.5 concentration data for the winters of 2013–2016. The highest occurrence frequency of air stagnation events was observed in 2013, and the lowest, 2015. The meteorological conditions during winter in the Sichuan Basin were inclined to form unfavourable atmospheric diffusion conditions, and the occurrence frequency of air stagnation days was up to 76.6% on average during the four winters. The effects of air stagnation events on air quality were most obvious in the western and southern Sichuan Basin. The mean concentrations of PM 2.5 during air stagnation days were higher by 41.9% than those during non-air stagnation days. The PM 2.5 concentrations were adjusted using the favourable atmospheric diffusion conditions in 2015 as a baseline to quantify the PM 2.5 contribution to the improvement of air quality in the other years, which revealed that the level of PM 2.5 in the Sichuan and Chongqing regions was declining at a rate of approximately 10.7% overall during the winters of 2013–2016, implying that the air pollutant reduction measures have been highly effective. Furthermore, the occurrence frequency of air stagnation days and events were increased in recent ten years of 2007–2016, with linear slopes of 0.61 yr −1 and 0.26 yr −1 , respectively. The study revealed that the government might face a greater challenge in improving the air quality over winter and should pay more attention to reduction of pollutant emission in areas of Chengdu, Chongqing and cities in the south of the Sichuan Basin. [ABSTRACT FROM AUTHOR]

This study used the MERRA-2 reanalysis dataset and ground-based and satellite observational data to comprehensively analyze a typical dust storm event in east Asia on 2–7 May 2017 which engulfed most of China as well as ocean and Japan, and explore the accuracy and comprehensiveness of the MERRA-2 dataset in the analysis of dust processes. The results of comparison show that the description of the spatiotemporal distribution and evolution of the dust aerosols in the dust event using the MERRA-2 data is consistent with the data of AERONET, National Urban Air Quality Real-time Publishing Platform and Hamawari-8. Gobi Deserts was the most influential source area of this dust event with the highest emissions reaching 1.9 × 106 μg/m3. The vertical motion of the atmosphere can lift dust from the source area above 500 hPa. There were low-pressure troughs at 500 and 850 hPa and the winds behind and in front of the trough led to the high-altitude, long-distance transport of dust. Dust gradually affected the northwest China, north China, northeast China, and even the ocean and Japan on 2–7 May. This study demonstrates that although there is some uncertainty about the source of dust emission in the MERRA-2 model, the data accurately simulated the evolution of the dust event and analyze it comprehensively, while the accuracy of simulating the long-term evolution of dust requires further evaluation. [ABSTRACT FROM AUTHOR]

Aerosol microphysical and optical properties as well as aerosol direct radiative effect (ADRE) were measured at a few ground sites to investigate aerosol optical‐radiative characteristics in northeastern China. Bimodal size distributions showed a dominance of fine mode particles at Shenyang, a megacity, and more impacts from larger particles at Fushun and Dalian, industrial and coastal sites, respectively. High aerosol optical depths at 440 nm in July (0.67–1.25) were ascribed to hygroscopic effects or cloud processing. Single scattering albedos at 440 nm show strong to moderate absorption at the urban and industrial sites (0.84–0.86) and weaker absorption at the coastal and rural sites (0.92–0.94). The single scattering albedo wavelength dependence implied influences of dust at the urban, industrial, and coastal regions (shorter wavelengths) and biomass emissions at the rural site (longer wavelengths). Absorptive aerosol optical depths at the urban and industrial sites were ~2.5 and 3.7 times higher than at the coastal and rural sites. Large negative ADREs at the bottom of the atmosphere at the urban and industrial sites implied strong surface cooling and the larger ADREs at the top of the atmosphere at the coastal site indicated more cooling of the Earth‐atmosphere system. The main aerosol types at the urban and industrial sites were mixed absorbing particles, while weakly‐absorbing fine mode particles dominated the coastal and rural sites. This study provides new information on the aerosol distributions and potential regional climate effects of aerosols in northeastern China. Key Points: High AODs in July were ascribed to hygroscopic effects in Northeast ChinaThe SSA440 nm show strong to slight absorption over the study regionThere is stronger surface cooling effect at the urban and industrial sites [ABSTRACT FROM AUTHOR]

The role of PM 2.5 (particles with aerodynamic diameters ≤ 2.5 µm) deposition in air quality changes over China remains unclear. By using the three-year (2013, 2015, and 2017) simulation results of the WRF/CUACE v1.0 model from a previous work (Zhang et al., 2021), a non-linear relationship between the deposition of PM 2.5 and anthropogenic emissions over central-eastern China in cold seasons as well as in different life stages of haze events was unraveled. PM 2.5 deposition is spatially distributed differently from PM 2.5 concentrations and anthropogenic emissions over China. The North China Plain (NCP) is typically characterized by higher anthropogenic emissions compared to southern China, such as the middle-low reaches of Yangtze River (MLYR), which includes parts of the Yangtze River Delta and the Midwest. However, PM 2.5 deposition in the NCP is significantly lower than that in the MLYR region, suggesting that in addition to meteorology and emissions, lower deposition is another important factor in the increase in haze levels. Regional transport of pollution in central-eastern China acts as a moderator of pollution levels in different regions, for example by bringing pollution from the NCP to the MLYR region in cold seasons. It was found that in typical haze events the deposition flux of PM 2.5 during the removal stages is substantially higher than that in accumulation stages, with most of the PM 2.5 being transported southward and deposited to the MLYR and Sichuan Basin region, corresponding to a latitude range of about 24°N-31°N. [Display omitted] [ABSTRACT FROM AUTHOR]

Aerosols are important atmospheric constituents with significant impacts on both regional air quality and the global climate and environment. Aerosol effects on radiation, clouds and precipitation are strongly related to the optical properties of aerosols, which vary considerably in space and time. This study reviewed the current understanding of the optical and radiative properties of aerosols and aerosol effects in China, and presented future research prospects. The Chinese aerosol remote sensing network (CARSNET) has been developed and expanded to include >80 stations across China. An internationally recognized radiometric calibration and data processing method has been developed to provide high-quality observational data of key optical properties. Ground lidars are used to provide information on the vertical aerosol optical properties on the spatiotemporal scales. The spatio-temporal distribution and evolution of aerosols are also analyzed using multi-satellite observations. Particle type and component content information are derived from aerosol component retrieval algorithm. Given the advantages of aerosol assimilation reanalysis products in terms of temporal resolution and spatial coverage, such information can more accurately characterize the climatological impact of aerosol optical properties and aerosol–climate interactions. Measurements obtained using the above methods can quantitatively reveal the influence of aerosol direct radiation effects in different regions, and support the exploration of the potential mechanisms of aerosol impacts on weather and climate from the perspective of ground-based remote sensing, which will help to guide the direction of future research. [ABSTRACT FROM AUTHOR]

Atmospheric aerosol levels are high in different regions of China. Changes in atmospheric stability and mixing layer height (MLH) may affect the vertical aerosol distribution during pollution events. Here, we continuous studied the spatiotemporal distribution of MLH in China over 2000–2013 to characterize the regional-scale properties of atmospheric boundary layers. MLH was larger in the Southern Coastal and Southeastern China (1241.5 ± 73.5 and 632.7 ± 61.8 m, respectively), but lower in Eastern and Southwestern China (518.1 ± 63.6 and 462.7 ± 88.5 m, respectively). We divided the monitoring stations into 11 regions; these regions could be classified into three types with an increasing linear trend (95% confidence level), with a decreasing linear trend (95% confidence level), and with fluctuation changes. In all regions, MLH was higher in spring and summer than in autumn and winter. The spatial distribution of the diurnal MLH increased significantly at 1400 BJT (Beijing time) in all regions, with the strongest radiation being noted during the daytime. Higher levels of PM 2.5 with corresponding lower MLH were noted during winter, indicating that lower MLH could confine the pollutant diffusion to near the surface. By contrast, in spring, higher MLH could be potentially due to the dynamic condition. In general, the poor air quality days occurred more frequently in winter than in other seasons. As the air quality worsened, most MLH showed a decreasing trend in almost all regions. This work provides information that aids in further understanding not only MLH distribution in China but also specific PM–MLH interaction to facilitate regional atmospheric environment monitoring and prediction. • Greater MLH was found in Southern and lower MLH in Southwestern China. • The annual MLH with increasing/declining/fluctuating trends were found. • Interaction between PM and MLH contributed to the regional air quality. [ABSTRACT FROM AUTHOR]

The reduction of traffic flow in downtown areas during the Chinese National Day holiday and the fireworks during the Spring Festival provide a unique opportunity for investigating the impact of urban anthropogenic activities on aerosol optical properties during these important Chinese festivals in Beijing. The National Day in 2014 and 2015 and Spring Festival in 2015 and 2016 were selected as study periods. The aerosol optical depth (AOD) at 440 nm increased over the all holiday periods and the average AODs during the 2015 National Day, 2015 Spring Festival and 2016 Spring Festival were about 81%, 21% and 36% higher than the background levels, respectively. The average AOD in 2014 National Day holiday was lower than background level partly influenced by precipitation event. The absorption AOD (AAOD) at 440 nm showed consistent variations with the AOD and the average AAODs during the 2015 National Day, 2015 Spring Festival and 2016 Spring Festival holidays were about 75%, 19% and 23% higher than the background level, respectively. The mean values of single scattering albedo were greater than the background level during the Spring Festival holidays, whereas the values during the National Day holiday in 2015 were lower partly due to the reduction of vehicular emissions in downtown areas. Fine- and coarse-mode particle volumes during pollution periods in holidays were ~ 0.04–0.25 μm 3 and ~ 0.03–0.15 μm 3 larger than background level, respectively. The results of potential source contribution function and concentration-weighted trajectory analyses identified the areas south of Beijing as the main source regions of PM 2.5 and were responsible for the extremely high PM 2.5 concentrations in Beijing during the holiday periods. The findings of this study may aid understanding the effects of human activities on aerosol optical properties over Beijing area and contribute to improving regional air quality. [ABSTRACT FROM AUTHOR]