Seasonal characteristics, formation mechanisms and source origins of PM2.5 in two megacities in Sichuan Basin, China
Huanbo Wang1,2, Mi Tian1, Yang Chen1, Guangming Shi1, Yuan Liu1, Fumo Yang1,2,3,4, Leiming Zhang5, Liqun Deng6, Jiayan Yu7, Chao Peng1, and Xuyao Cao11Research Center for Atmospheric Environment, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing, 400714, China 2Chongqing University, Chongqing, 400044, China 3Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China 4Yangtze Normal University, Chongqing, 408100, China 5Environment and Climate Change Canada, Toronto, Canada 6Sichuan Academy of Environmental Sciences, Chengdu, 610041, China 7Chongqing Environmental Monitoring Center, Chongqing 401147, China
Received: 20 Mar 2017 – Accepted for review: 08 Apr 2017 – Discussion started: 10 Apr 2017
Abstract. To investigate the characteristics of PM2.5 and its major chemical components, formation mechanisms, and geographical origins in the two biggest cities, Chengdu (CD) and Chongqing (CQ) in Sichuan Basin, the most densely populated basin in China, daily PM2.5 samples were collected simultaneously at one urban site in each city from October 2014 to July 2015. Annual mean concentrations of PM2.5 were 67.0 ± 43.4 and 70.9 ± 41.4 μg m−3 at CD and CQ, respectively. Secondary inorganic aerosols (SNA) and organic matter (OM) accounted for 41.1 % and 26.1 %, respectively, of PM2.5 mass at CD, and 37.4 % and 29.6 % at CQ. Seasonal variations of PM2.5 and its major chemical components were significant, usually with the highest values in winter and the lowest in summer. SNA and OM were 1.7–3.4 times higher on polluted days than on clean days at both sites, whereas their percentage contributions to PM2.5 varied differently among the components and between the two sites. Gas-phase oxidation probably played an important role on the formation of secondary aerosols when PM2.5 mass varied in the range of 75–150 μg m−3, while heterogeneous transformation was likely the major mechanism on the heavy polluted days. Geographical regions causing high PM2.5 were identified to mainly distribute within the basin at both sites based on potential source contribution function (PSCF) analysis.
Wang, H., Tian, M., Chen, Y., Shi, G., Liu, Y., Yang, F., Zhang, L., Deng, L., Yu, J., Peng, C., and Cao, X.: Seasonal characteristics, formation mechanisms and source origins of PM2.5 in two megacities in Sichuan Basin, China, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-258, in review, 2017.