Pollution Characteristics And Oxidatin Potential Of Fine Particules In Background Station Of Yangtze River Delta (Lin'an)

Atmospheric fine particles(PM_2.5)play a reverse impact on both air quality and human health,which is the primary pollutant in the Yangtze River Delta(YRD)region currently.Thus,characteristics,sources,and health toxicity of PM_2.5 are essential to make precise regional emission-control strategies.In this study,the source apportionment and the oxidation potential(OP)of PM_2.5were studiedon the basis of in-situ observation results and model simulation at Lin`an Regional Background Station(Lin'an site,119°44?E,30°18?N).We collected filtersmples from March 2018 to February 2019 in Lin'an site.The seasonal variation of chemical components of PM_2.5 were studied by quantitatively measuring the daily concentrations of water-soluble ions.Organic carbon compounds(OM)were the most important chemical components of PM_2.5in all seasons,with the contribution of 18%,33%,40%and 21%in spring,summer,autumn and winter,respectively.Nitrate had the most significant seasonal variation,with the contribution of 14%,5%,7%and 18%in spring,summer,autumn and winter,respectively.As PM_2.5 concentration increased,the proportion of the secondary inorganic salt aerosols(SIA)in PM_2.5 also increased.We quantified the contributions of the transmission from 41 cities in the YRD to Lin'an by using the Community Multiscale Air Quality(CMAQ)model.The transmission of PM_2.5pollution between cities in the YRD was obvious,and there was a general rule of“the closer the distance,the greater the contribution”.Moreover,sulfate mainly came from long-distance transport outside the YRD.Both the primary particles and secondary organic aerosols in Lin'an were mainly generated in Hangzhou,with a contribution of 49.9%and 69.6%,respectively.Other nearby cities also had an important impact on the air quality of Lin'an.For example,Huzhou,Ningbo and Jiaxing can contribute 10%,6%and 4%to PM_2.5 of Lin'an,respectively.However,the contribution of sulfate from Hangzhou was only 12.5%to Lin'an,while it can reach up to 54.5%from regions outside the YRD.The oxidation potential of PM_2.5 in Lin'an was measured by DTT method,and the correlation between chemical components of PM_2.5 and OP^DTT was established.In 2018,the annual average of DTT_v was 0.94±0.37 nmol·min^-1·ug^-1.The DTT_v in all seasonal showed positive linear correlation with PM_2.5,in which winter(1.163?0.370 nmol·min^-1·ug^-1)>spring(1.010?0.268 nmol·min^-1·ug^-1)>autumn(0.934?0.342 nmol·min^-1·ug^-1)>summer(0.638?0.255 nmol·min^-1·ug^-1).The water-soluble organic carbon(WSOC)was the main contributor to the OP of PM_2.5.In addition,Mg²⁺in spring,NO₃^-and SO₄^2-in summer,K⁺,SO₄^2-and Na⁺also largely affected the OP of PM_2.5 in Lin'an in different seasons.According to the above characteristics and rules,we provided recommendations on formulating regional air pollution control strategies.It is recommended to dynamically adjust the scope of joint prevention and control.In spring,summer or autumn,the focus should be on pollution control in neighboring cities within 100 km.However,source emissions should be controlled on a larger scale,including the eastern Jiangxi in summer,including the border areas between Jiangsu-Anhui-Shandong-Henan and the North China Plain in winter.Air pollution control action in winter and spring(November to next April),needs to be strengthened.In particular,it is necessary to reduce the emissions of volatile organic compounds,vehicle non-exhaust,fireworks,ammonia and dust.In addition,it is suggested to attach great importance to the study of the relationship between PM_2.5 components and human health,and timely remind the public to take health protection measures.These results enhance the understanding of the characteristics,formation,transport,and health effects of PM_2.5,which can provide an important scientific reference for the government to make relevant control strategies.