Distribution And Variation Of Hourly Aerosol Pollution Over Typical Urban Agglomerations In China Based On Himawari-8

Aerosol is one of the main components that disturb the radiation balance of the earth atmosphere system.Particles with diameter less than 2.5?m(PM2.5)are mainly distributed in the near surface atmosphere,which poses a serious threat to human health.Long term exposure to PM2.5 has a high risk of early death.As one of the most serious aerosol pollution regions in the world,it is necessary to monitor the overall distribution of aerosol pollution in urban agglomerations in central and eastern China with high precision.As the most important optical parameter of aerosols,aerosol optical depth(AOD)is an important parameter in the study of air pollution,which can indicate the pollution level to a certain extent.Japan launched a new generation of geostationary satellite Himawari-8/AHI(Advanced Himawari Imager)in 2016 to conduct high-frequency ground scanning observations in East Asia and provide hourly AOD products,as well as the latest reanalysis data MERRA-2(the Modern-Era Retrospective Analysis for Research and Applications,version 2)and CAMS(Copernicus Atmosphere Monitoring Service Reanalysis),makes it possible to obtain the hourly distribution of aerosols in China.However,it is still necessary to study the applicability of the three products in different situations.AOD data can be used to qualitatively understand the regional aerosol pollution level,but it is still unable to obtain accurate aerosol,especially the near surface PM2.5 concentration distribution,which also makes the current understanding of aerosol pollution distribution and change in China's urban agglomerations is not comprehensive.In order to solve the above problems,the accuracy of AHI,MERRA-2 and CAMS AOD products has been verified and evaluated based on the AERONET(AErosol RObotic NETwork)ground-based observation,and the differences of AOD performance under different time,place and pollution level are compared.Then,based on the AHI AOD data,an improved LME(Linear Mixed-effects)model considering regional and seasonal changes is constructed,and PM2.5 inversion of typical agglomerations in central and eastern China is realized.On this basis,we can capture the distribution characteristics and changes of aerosols in Central China(CCH),Beijing Tianjin Hebei(BTH),Yangtze River Delta(YRD)and Pearl River Delta(PRD),and analyze the impact of population exposure.The main contents and conclusions are as follows:(1)The V030 L3 AOD of AHI has higher accuracy than earlier data.Compared with reanalysis products,AHI has the highest correlation with ground observations(0.82).AHI is very reliable in central and eastern China with high aerosol pollution;however,MERRA-2 is the most suitable product in Northwest China.The accuracy of AODs showed diurnal and seasonal variations.The AHI AOD performed better in the morning,and reanalyssi AODs were the most consistent with the ground observation at noon.(2)Using AHI AOD,auxiliary meteorological parameters and ground cover information,by selecting independent variable factor combination,an improved regional and seasonal LME model was constructed to realize the inversion of PM2.5.Cross validation results show that the R~2of the improved seasonal LME model in CCH,BTH,YRD and PRD reaches 0.82,0.84,0.80 and 0.74,respectively.(3)Based on the high-precision PM2.5 inversion model and AHI AOD,the near surface PM2.5 concentrations of four urban agglomerations from July 2015 to June2020 were obtained.The central and northern CCH,central and southern BTH,central and northern YRD and area near Guangzhou have high aerosol pollution.PM2.5 level was low in spring and summer and high in autumn and winter.In CCH and YRD,the difference of PM2.5 concentration in winter and summer reached 20?g/m~3.The distribution of PM2.5 also showed an obvious diurnal variation,which showed high level in the morning and lower in the afternoon in the four regions.(4)Based on the time series analysis of PM2.5 concentration in each urban agglomeration area,the aerosol pollution level in the four regions has a decreasing trend in the past five years.The annual average PM2.5 concentration decline rates of CCH,BTH,YRD and PRD are 19.2,16.8,14.4 and 16.2?g/m~3,respectively.With the improvement of aerosol pollution,the areas of high-risk and ultra-high-risk exposure areas in the four typical urban agglomerations decreased,and the overall exposure risk tends to be better.