Source Apportionment Of Secondary Inorganic Aerosols During Extreme Fine Particulate Matter Pollution Events Over Yantze River Delta Of China In Winter

Extreme fine particulate matter(PM_2.5)pollution episodes have occurred frequently over Yangtze River Delta（YRD）of China in recent years.Elevated levels and fractions of secondary inorganic aerosols（SNA）sulfate,nitrate and ammonium are the characteristic of PM_2.5 pollution episodes.It is essential for source apportionment analysis of SNA to guarantee the pollution control strategies effectively and scientifically.In this work,the WRF-CMAQ models were applied to reproduce PM_2.5pollution events during January 2015 over YRD,focusing on key cities Shanghai,Nanjing and Hangzhou.Based on CMAQ-IPR process rate analysis technology,relatively important formation and removal processes of SNA at surface layer and upper levels in episodes were identified.Source apportionment method CMAQ-ISAM was conducted to quantify the dominant sources of SNA during pollution periods.The results of this study will provide the strong theoretical support for control policymaking through the whole process analysis of SNA from the origin of sources to receptors in detail.In this study,air quality condition during January,2015 over Yangtze River Delta was reproduced in relatively high accuracy through localized parameters adjustment in models.According to simulation results,adverse meteorological factors,low wind speed(<2 m·s^-1),planetary boundary layer（<600 m）and precipitation,were usually accompanied with PM_2.5pollution episodes.And rainfall was beneficial to high mass concentration PM_2.5 decreased.SNA were the largest composition in PM_2.5,accounting for 53.43%of total mass concentration.Process analysis results indicated that aerosol process such as homogeneous nucleation,gas to particle conversion were the main formation processes and vertical transportation from land surface to upper levels was the primary removal process for nitrate and ammonium.For sulfate,mass concentration increase and decrease were influenced by physical transportation significantly.Long range transportation from outside region of YRD was the main source of sulfate and nitrate with average percentage of 55.97%and 63.71%separately.Besides,industry process from Jiangsu province was the second contribution of sulfate in Shanghai with average percentage of 16.87%.But for Nanjing and Hangzhou,local industry process was the largest source of sulfate with percentage of 18.21%and 13.43%after boundary transportation.Meanwhile,industry process and power plant in Jiangsu province and transportation in Shanghai were the key regional sources over YRD to nitrate in Shanghai with percentage of 5.26%,5.30%and 5.38%.Industry process in Nanjing was the first contribution to nitrate of Nanjing over YRD region with average percentage of 4.08%.Industry process and power plant in Hangzhou with percentage of 7.01%and 4.43%were the main sources of nitrate of Hangzhou.As for ammonium,local volatile and transportation sectors were the dominant sources for Shanghai with percentage of 82.99%.Similarly,local volatile sector was the first source for ammonium in Nanjing accounting for 70.40%mass concentration.For Hangzhou,native volatile,transportation and agriculture sectors were the crux sources of ammonium with average percentage of 70.61%.