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Volume 17, issue 11 | Copyright

Special issue: Regional transport and transformation of air pollution in...

Atmos. Chem. Phys., 17, 7277-7290, 2017
https://doi.org/10.5194/acp-17-7277-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 16 Jun 2017

Research article | 16 Jun 2017

Insight into winter haze formation mechanisms based on aerosol hygroscopicity and effective density measurements

Yuanyuan Xie1, Xingnan Ye1,2, Zhen Ma1, Ye Tao1, Ruyu Wang1, Ci Zhang1, Xin Yang1,2, Jianmin Chen1,2, and Hong Chen1 Yuanyuan Xie et al.
  • 1Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention (LAP), Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China
  • 2Institute of Atmospheric Sciences, Fudan University, Shanghai 200433, China

Abstract. We characterize a representative particulate matter (PM) episode that occurred in Shanghai during winter 2014. Particle size distribution, hygroscopicity, effective density, and single particle mass spectrometry were determined online, along with offline analysis of water-soluble inorganic ions. The mass ratio of SNAPM1. 0 (sulfate, nitrate, and ammonium) fluctuated slightly around 0.28, suggesting that both secondary inorganic compounds and carbonaceous aerosols contributed substantially to the haze formation, regardless of pollution level. Nitrate was the most abundant ionic species during hazy periods, indicating that NOx contributed more to haze formation in Shanghai than did SO2. During the representative PM episode, the calculated PM was always consistent with the measured PM1. 0, indicating that the enhanced pollution level was attributable to the elevated number of larger particles. The number fraction of the near-hydrophobic group increased as the PM episode developed, indicating the accumulation of local emissions. Three banana-shaped particle evolutions were consistent with the rapid increase of PM1. 0 mass loading, indicating that the rapid size growth by the condensation of condensable materials was responsible for the severe haze formation. Both hygroscopicity and effective density of the particles increased considerably with growing particle size during the banana-shaped evolutions, indicating that the secondary transformation of NOx and SO2 was one of the most important contributors to the particle growth. Our results suggest that the accumulation of gas-phase and particulate pollutants under stagnant meteorological conditions and subsequent rapid particle growth by secondary processes were primarily responsible for the haze pollution in Shanghai during wintertime.

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Urban air pollution is one of the greatest environmental concern in 21st century. In this paper, we trace temporal evolutions of aerosol hygroscopicity and effective density during a representative particulate matter episode, which provide a strong support on that severe haze pollution can be formed in highly polluted areas by the initial accumulation of gas-phase and particulate pollutants under stagnant meteorological conditions and subsequent rapid particle growth by secondary processes.
Urban air pollution is one of the greatest environmental concern in 21st century. In this paper,...
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