Study On The Impact Of Changes In Asian Anthropogenic Aerosol And Its Precursor Emissions On The East Asian Summer Monsoon Since The “Ten Measures??

Due to the implementation of policies aimed at reducing emissions,the emissions of anthropogenic aerosol（AA）precursors in China have significantly decreased in recent years,which has changed the spatial distribution pattern of AA emission changes in Asia,and has an important impact on the circulation and precipitation of the East Asian Summer Monsoon（EASM）.This study uses the CAM6,which is the atmospheric module of Community Earth System Model CESM2.1.1（Community Earth System Model 2.1.1）to examine the responses of EASM to the AA emission reduction over East Asia,as well as the dipole changes in AA emissions caused by AA emission reduction over East Asia and the increase of AA emission over South Asia during 2013-2017.This study shows that the emission of AA precursors in East Asia decreased in 2013-2017,especially in eastern China.The anthropogenic emissions of sulfur dioxide（SO₂）decreased by1-15 g m^-2 year^-1,the anthropogenic emissions of primary particulate matter（POM）decreased by 0.1-0.6 g m^-2 year^-1,the anthropogenic emissions of black carbon（BC）aerosol decreased by 0.03-0.3 g m^-2 year^-1,and the anthropogenic emissions of secondary organic aerosol gas（SOAG）decreased by 0.01-0.1 g m^-2 year^-1.AA emission reduction led to+1.59（±0.97）W m^-2 effective radiation forcing（ERF）over the central and eastern China（25°-40°N,105°-122.5°E）,and increased the surface temperature by 0.09（±0.07）°C.This warming increased the sea-land thermal contrast between China and it’s surrounding oceans,thus strengthening the western Pacific subtropical high.The airflow on the west side of the western Pacific subtropical high strengthened the southerly winds in the east-central region of China by 0.25（±0.22）m s^-1,and brought more warm and wet water vapor from the sea,thus increasing the rainfall rate by0.32（±0.16）mm day^-1.The emission of AA precursors in South Asia increased in the summer of 2013-2017,especially in the Indo-Gangetic Plain（IGP）region（25°-35°N,70°-90°E）.The anthropogenic emission of SO₂ increased by 0.5-5 g m^-2 year^-1,POM increased by 0.1-0.3 g m^-2 year^-1,BC aerosol increased by 0.01-0.1 g m^-2 year^-1,and SOAG increased not significantly.The reduction of AA emissions in East Asia and the increase of AA emissions in South Asia in 2013-2017formed dipole pattern of AA emissions change.Dipole changes in AA emissions from East Asia and South Asia increased the ERF over the central and eastern regions of China by+3.39（±0.89）W m^-2,the surface temperature increased by 0.20（±0.08）°C,and the rainfall decreased by 0.07（±0.16）mm day^-1.It is due to the westward shift of the strengthened western Pacific subtropical high,linked to the increase in BC in South Asia.Based on multiple EASM indices,the reductions in aerosol emissions from East Asia alone increased the EASM strength by almost 5%,and the dipole changes in AA emissions increased the EASM by 5%-15%during2013-2017,revealing an important role of South Asian aerosols in changing the East Asian climate.