Analysis Of The Optical Properties And Transport Characteristics Of Atmospheric Aerosols In Typical Regions Of China

Aerosols can have a significant impact on climate change by adjusting the radiative energy balance of the earth-atmosphere system through direct,semi-direct and indirect effects.The vertical distribution of different aerosols has significantly different effects on the thermal structure and stability of the atmosphere,which is still one of the most important factors affecting the uncertainty in the estimation of aerosol radiative forcing.In addition,the transport and local emissions of aerosols significantly affect their distribution characteristics and pose a serious hazard to the atmospheric environment and human health.Therefore,the study of the vertical distribution,trends,transport characteristics and anthropogenic emission contributions of aerosols is of great scientific importance for assessing the climate effects of aerosols.Based on CALIOP and ground-based pollutant monitoring data in China,this paper obtains the spatial and temporal distribution,vertical characteristics and seasonal variations of aerosols in typical regions of China from June 2006 to December 2020.Analyses the transport pathways of aerosols in different regions using the HYSPLIT model.Using historically similar meteorological fields,the background concentrations of air pollutants were obtained by linear fitting,then the influence of local anthropogenic emissions was assessed to quantify the contribution of some anthropogenic activities to air pollutants.The main conclusions are as follows:（1）The vertical distribution of aerosols has significant regional and seasonal differences.The aerosol extinction coefficient（AEC）is highest in Guanzhong Plain（GZ）and Central China（CC）regions,with high values(>0.35 km^-1)mainly in the 0-2km above mean sea level（AMSL）and largest in winter,and aerosols are mainly regular fine particles.Large values of AEC(>0.2 km^-1)are distributed over 1-3 km in the Taklamakan（TD）,with the largest AEC in spring and mainly irregular coarse particles.AEC is lowest in the Tibet Plateau region（TP）,with less seasonal variation,and aerosol particles are coarse and irregular.（2）The main types of aerosols in different regions and their distribution heights significantly influence the trends of aerosol optical depth（AOD）in that region.The frequency of polluted dust is greatest in Beijing-Tianjin-Hebei（BTH）,CC and Cheng-Yu District（CY）,and the significant decrease in 0-2 km AOD leads to a significant trend in total AOD.Weaker trends in AOD in the TD and TP are influenced by aerosols distributed at 2-4 km and 4-6 km,especially dust.（3）Significant differences in aerosol sources and transport pathways between regions.The trajectories of aerosols show that regions with high anthropogenic emissions,such as BTH,Yangtze River Delta（YRD）,CY and GZ,have transport from the Mongolian Plateau and Northern India,in addition to transport of dust from the TD,Alashan and Ordos Plateau（AOP）.Anthropogenic aerosols in the TD,AOP mainly come from the Iranian and Xinjiang.TP’s aerosols are mainly from the Iranian,northern India and TD.The lengths of dust,polluted dust and polluted continental aerosol trajectories become significantly shorter in summer,indicating that summer is not conducive to the transport of such aerosols.The transport trends of the different aerosols vary considerably and have an impact on the regional AOD.（4）Although the long-range transport activities have an important impact on the distribution of air pollutants,but the impact of local emissions cannot be ignored.During the COVID-19 outbreak at the end of 2019,the Chinese government undertook stringent control measures that could be used to study the impact of widespread anthropogenic emission controls on air pollutants in China.During the period of strictest control of the pandemic（Per.2）,PM₁₀decreased by 23.9%in the BTH and PM_2.5decreased by 16.5%in the YRD.In addition,NO₂was the most responsive air pollutant during the pandemic,the concentration of NO₂in the YRD decreased by 30.66%in Per.2.The rate of decline for most pollutants slowed down during the beginning of resumption of work（Per.3）.However,the Wuhan region was late release of the pandemic control,so its NO₂dropped by 48.17%in this period.