Study On The Temporal And Spatial Distribution Of Aerosols And Pollutants In The Coastal Areas Of Jiangsu And The Impact Of Typhoon

The ocean and land atmospheres are interconnected and unified.For making overall plans for ocean and land air pollution prevention and control,it is necessary to take the coastal areas as the key point and pay attention to the interactive effects of land and ocean atmospheres.Among them,the monitoring of aerosols,nitrogen dioxide（NO₂）,and sulfur dioxide（SO₂）over long time series and in the extreme weather is highly significant to enhance the air quality in coastal areas.Most studies focus on spatial and temporal distribution characteristics of aerosols and polluted gases over a single region of land and ocean rather than generalized analyze their comparison and relation.The spatiotemporal distribution patterns and potential source areas of Aerosol Optical Depth（AOD,2000～2020）,NO₂,and SO₂ concentrations（2005～2020）over land and ocean in Jiangsu Province were identified based on long-time MODIS and OMI data in this study.The results show that the average AOD over land in Jiangsu Province from2000 to 2020 is 1.57 times that of the ocean,whereas the average NO₂ and SO₂ concentrations over land in Jiangsu Province from 2005 to 2020 are 1.93 and 1.47 times that of the ocean,respectively.On an interannual time scale,the correlation coefficients of varitation of NO₂and SO₂ concentrations and the anthropogenic emissions of NO_x and SO₂ over land of Jiangsu Province are 0.63 and 0.87,and the concentration of ocean air pollutants gradually decreased from offshore to far offshore.These indicate that anthropogenic activities from land strongly influence air quality over both ocean and land.Driven by the China’s air quality control policy,the AOD over land and ocean in Jiangsu Province decreased by 0.003/a during 2000to 2020,the SO₂ concentrations on ocean and land decreased by 0.011 DU/a and 0.023 DU/a during 2005 to 2020.During 2005 to 2000,the NO₂ concentrations decreased by 0.005 DU/a over land but increased by 0.0004 DU/a over ocean,indicating that pollution control for coastal cities and major ports should be improved in the future.The potential sources analysis shows that aerosols and polluted gases over the coastal area of Jiangsu Province are mainly transmitted by the neighboring provinces（Jiangsu,Anhui,Henan,Shandong amd Zhejiang Province）and the surrounding ocean（the Yellow Sea and the East China Sea）.Monitoring air pollutants in extreme weather,such as typhoons,is helpful to understand the air quality under this condition.Most of the typhoon studies analyzed single typhoon in Southeast China,and there is still no comprehensive analysis of the impacts of typhoon on air pollutants in Jiangsu Province.Therefore,this study analyzed the extent and degree of typhoon effects on aerosol particles with aerodynamic diameters of less than 2.5μm(PM_2.5),NO₂ and SO₂ concentrations in Jiangsu Province based on typhoon cases during 2015 to 2020,combined with ERA5 meteorology and ground air quality monitoring data in Jiangsu Province.The conclusions are as follows:（1）The extent of typhoon effects on PM_2.5,NO₂and SO₂ concentrations can be judged by the local wind speed and precipitation.Typhoons significantly affected PM_2.5 and SO₂ concentrations when the local wind speed is higher than3 m/s and precipitation is present,or when the wind speed is higher than 2 m/s and precipitation is higher than 1 mm/h.The typhoon significantly affected NO₂ concentrations when the local wind speed is higher than 3 m/s.（2）The influence degrees of wind speed and precipitation are different.The correlation coefficients of PM_2.5,NO₂ and SO₂ concentrations with local wind speed mostly ranged from–0.3 to–0.8,and those with precipitation mostly ranged from–0.3 to 0,indicating that local wind speed was the main driver of PM_2.5,NO₂ and SO₂ concentrations decrease in Jiangsu Province during the typhoon period.（3）PM_2.5,NO₂,and SO₂ concentrations increase at some monitoring stations before and after the typhoon transit.Before the typhoon transit,PM_2.5,NO₂,and SO₂ concentrations increase at inland stations under the influence of near-surface pollution air masses from southern Jiangsu and surrounding areas;during the typhoon transit,the airflow is circulating under the action of typhoon vortex,which is facilitative to the accumulation of local pollutants;after the typhoon transit,the wind speed and boundary layer height decrease in Jiangsu Province,which hindered the diffusion of PM_2.5,NO₂ and SO₂.This study will strengthen the understanding of the spatiotemporal distribution of aerosol and polluted gases over long time series and in extreme weather.It can provide reliable data for land-sea integration to deepen coastal air pollution prevention in Jiangsu Province.