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© Author(s) 2018. This work is distributed under
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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Aug 2018

Research article | 02 Aug 2018

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This discussion paper is a preprint. A revision of the manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP).

Synergistic effect of water-soluble species and relative humidity on morphological changes of aerosol particles in Beijing mega-city during severe pollution episodes

Xiaole Pan1, Baozhu Ge1, Zhe Wang1,2, Yu Tian1,3, Hang Liu1,3, Lianfang Wei1, Siyao Yue1,3, Itsushi Uno2, Hiroshi Kobayashi4, Tomoaki Nishizawa5, Atsushi Shimizu5, Pingqing Fu1,3,7, and Zifa Wang1,3,6 Xiaole Pan et al.
  • 1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
  • 2Research Institute for Applied Mechanics, Kyushu University, Kasuga, 816-8580, Japan
  • 3University of Chinese Academy of Sciences, Beijing,100049, China
  • 4University of Yamanashi, Yamanashi, 400–0016, Japan
  • 5National Institute for Environmental Studies, Ibaraki, 305-8506, Japan
  • 6Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 7Institute of Surface-Earth System Science, Tianjin University, Tianjin, 300072, China

Abstract. Depolarization ratio (δ) of backscattered light from aerosol particle is an applicable parameter for real-time distinguishing spherical and non-spherical particles, which has been widely adopted by ground-based Lidar observation and satellite remote sensing. From November 2016 to February of 2017, it consecutively suffered from numbers of severe air pollution at Beijing with daily averaged mass concentration of PM2.5 (aerodynamic diameter less than 2.5μm) larger than 150μg/m3. We preformed concurrent measurements of water-soluble chemical species and depolarization properties of aerosol particles on the basis of a continuous dichotomous Aerosol Chemical Speciation Analyzer (ACSA-14) and a bench-top optical particle counter with a polarization detection module (POPC). We found that δ value of ambient particles generally decrease as mass concentration of PM2.5 increased at unfavorable meteorological condition. Ratio of mass concentration of nitrate (NO3) to that of sulfate (SO42−) in PM2.5 was 1.5±0.6, indicating of great importance of NOx in the formation of heavy pollution. Mass concentration of NO3 in PM2.5 (fNO3) was generally an order of magnitude higher than that in coarse mode (cNO3) with a mean fNO3/cNO3 ratio of 14±10. Relatively high allocation (fNO3/cNO3=5) of NO3 in coarse mode could be partially attributed to hygroscopic growth/coagulation of nitrate-rich fine mode particles under higher relative humidity condition. As a result, δ values of particles with Dp=2μm (δDp=2) and 5μm (δDp=5) decreased evidently as the mass fraction of water-soluble species (NO3 and SO42−) increase in both PM2.5 and PM2.5–10, respectively. In particular, due to synergistic effect of RH, δDp=5 value could decrease by 50% as mass fraction of NO3 in PM2.5–10 increased from 8% to 23%. It suggested that alteration of non-sphericity of mineral dust particles was evident owing to coating with pollutants and heterogeneous reactions on the surface of the particle during heavy pollution period. This study brings the attention to great variability of morphological changes of aerosol particles along the transport, which have great complex effects in evaluating their climate and health effect.

Xiaole Pan et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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