Characteristics And Sources Of Organic Aerosol Of Fine Particulate Matter In A Typical Coal

Particulate matter（PM）dominated air pollution despite of improving PM pollution in recent years.It is reported that organic aerosol（OA）was the major part of PM in China.The key to air pollution control was investigation of OA sources and formation processes.In this study,wintertime fine PM(PM_2.5)was measured in an urban site of Jinzhong city using time of flight-aerosol chemical speciation monitor（TOF-ACSM）,and chemical composition of PM_2.5 and formation mechanisms of secondary organic aerosol（SOA）were explored.The variation of PM_2.5 chemical composition during COVID-19epidemic was analyzed to investigate the effect of the pollution reduction measures on PM_2.5 control.The main conclusions were as followed:（1）The average concentration of non-refractory PM_2.5(NR-PM_2.5)was101.3±92.4μg m^-3 in winter.OA was the major part of NR-PM_2.5 followed by sulfate,ammonia,nitrate,and chloride,on average accounting for 35%,26%,19%,19%,and 3%,respectively.The mass concentration of PM_2.5 and contribution of primary OA（POA）was at high level in northern China.（2）Source apportionment using multilinear engine（ME-2）showed OA was composed of vehicle exhaust（HOA,8%）,coal combustion OA（CCOA,12%）,biomass burning OA（BBOA,17%）,cooking OA（COA,6%）,non-coal industrial OA（NCIOA,4%）,and SOA including less oxidized SOA（LO-OOA,22%）and more oxidized SOA（MO-OOA,31%）,which indicated SOA dominated OA of PM_2.5.OA was mainly from local area and the southwest and southeast of Shanxi Province were potential geographical origins of HOA,CCOA,and COA.（3）BBOA and CCOA were the principal OA before pollution,while SOA became the dominant OA during pollution and diffusion.SOA formation was associated with aquas-phase processes in winter.The increasing temperature could facilitate formation of MO-OOA,and LO-OOA formed primarily by aquas-phase processes.（4）During COVID-19 lockdown,the concentration of NR-PM_2.5decreased by 52.8%and reduction rates of SO₂,NO₂,and CO were 25-50%.The reduction rate of PM_2.5 compositions ranged from 48.6%for nitrate and organic aerosol（OA）to 79.7%for chloride.Sulfate and OA contributed the largest part of NR-PM_2.5 reduction and contribution was about 30%for each one.The result of source apportionment showed that POA decreased by 48.5%and more than 60%for POA reduction was explained by CCOA and HOA.（5）Local emissions governed the formation of secondary inorganic compositions combined with air mass back-trajectories cluster analysis.The emission reduction measures resulted in reduced SOA and POA and contributed 50-91%to air quality improvement,which highlighted the predominant role of regional-joint emission reductions in improving air in Taiyuan basin.