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Characteristics, Formation Mechanisms and Potential Transport Pathways of PM2.5 at a Rural Background Site in Chongqing, Southwest China

Category: Aerosol and Atmospheric Chemistry

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DOI: 10.4209/aaqr.2019.01.0010
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Chao Peng1,2, Mi Tian 1,7, Yang Chen1, Huanbo Wang1, Leiming Zhang3, Guangming Shi1,4, Yuan Liu1, Fumo Yang 1,4,5, Chongzhi Zhai6

  • 1 Research Center for Atmospheric Environment, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
  • 2 University of Chinese Academy of Sciences, Beijing 100049, China
  • 3 Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto, Ontario, Canada
  • 4 National Engineering Research Center for Flue Gas Desulfurization, College of Architecture and Environment, Sichuan University, Chengdu 610065, China
  • 5 Institute of New Energy and Low-carbon Technology, Sichuan University, Chengdu 610065, China
  • 6 Chongqing Academy of Environmental Science, Chongqing 401147, China
  • 7 School of Urban Construction and Environmental Engineering, Chongqing University, Chongqing 400044, China


  • Chemical characteristics of PM2.5 were investigated at a rural background site.
  • Photochemical reactions and transport led to high SO42– concentrations in summer.
  • The role of NO3 formation was highlighted for the dramatic increase of PM2.5.
  • Ammonium-rich condition promoted NO3 formation under low temperature.


Daily PM2.5 samples were collected at a rural background station (JinYun) located in Chongqing across four consecutive seasons from October 2014 to July 2015. Major water-soluble inorganic ions (WSII), organic carbon (OC) and elemental carbon (EC) were analyzed, and their chemical characteristics, transport pathways and potential source regions were investigated. The annual average of PM2.5 concentrations was 56.2 ± 31.0 μg m-3, of which secondary inorganic aerosol (SNA) and carbonaceous aerosols accounted for 41.0% and 29.4%, respectively. Higher concentrations and contributions of SO42- were observed in summer than autumn and spring, likely caused by the secondary transformation of SO2 to SO42-. In addition, transportation from the urban area of Chongqing (Yubei) also played an important role for the elevated SO42- levles in summer. Aqueous-phase reactions played important roles for the accumulation of PM2.5 during pollution period in winter. However, on an annual basis homogeneous gas-phase reaction might dominate the NO3- formation. Aerosol environment was ammonium-rich and NH4+ formation promoted the production of NO3- under lower temperature. Carbonaceous content, of which 81.0%–84.6% was organic carbon, was higher in winter than that in other seasons. Primary organic carbon (POC) represented 50.0%–77.2% of the total OC. Analysis using potential source contribution function (PSCF) suggests the site was mainly affected by regional pollutant sources, e.g., the southwestern and northern areas of Chongqing.


PM2.5 Rural background site Chemical transformation Potential transport pathways

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