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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 2
Atmos. Chem. Phys., 18, 865–881, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 18, 865–881, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 24 Jan 2018

Research article | 24 Jan 2018

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 Cao1 Huanbo Wang et al.
  • 1Research Center for Atmospheric Environment, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing, 400714, China
  • 2School of Urban Construction and Environmental Engineering, Chongqing University, Chongqing, 400044, China
  • 3Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China
  • 4Coordinated Center of Excellence for Green Development in Wuling Region, Yangtze Normal University, Chongqing, 408100, China
  • 5Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto, Canada
  • 6Sichuan Academy of Environmental Sciences, Chengdu, 610041, China
  • 7Chongqing Environmental Monitoring Center, Chongqing, 401147, China

Abstract. To investigate the characteristics of PM2.5 and its major chemical components, formation mechanisms, and geographical origins in the two megacities, Chengdu (CD) and Chongqing (CQ), in Sichuan Basin of southwest China, daily PM2.5 samples were collected simultaneously at one urban site in each city for four consecutive seasons from autumn 2014 to summer 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 aerosol (SNA) and organic matter (OM) accounted for 41.1 and 26.1 % of PM2.5 mass at CD, and 37.4 and 29.6 % at CQ, respectively. Seasonal variations of PM2.5 and major chemical components were significant, usually with the highest mass concentration in winter and the lowest in summer. Daily PM2.5 concentration exceeded the national air quality standard on 30 % of the sampling days at both sites, and most of the pollution events were at the regional scale within the basin formed under stagnant meteorological conditions. The concentrations of carbonaceous components were higher at CQ than CD, likely partially caused by emissions from the large number of motorcycles and the spraying processes used during automobile production in CQ. Heterogeneous reactions probably played an important role in the formation of SO42−, while both homogeneous and heterogeneous reactions contributed to the formation of NO3. Geographical origins of emissions sources contributing to high PM2.5 masses at both sites were identified to be mainly distributed within the basin based on potential source contribution function (PSCF) analysis.

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