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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-511
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 02 Jul 2018

Research article | 02 Jul 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Variability of depolarization of aerosol particles in Beijing mega city: implication in interaction between anthropogenic pollutants and mineral dust particles

Yu Tian1,2, Xiaole Pan1, Tomoaki Nishizawa3, Hiroshi Kobayashi4, Itsushi Uno5, Xiquan Wang1, and Zifa Wang1,2,6 Yu Tian et al.
  • 1State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
  • 2University of Chinese Academy of Sciences, Beijing, 100049, China
  • 3National Institute for Environmental Studies, Tsukuba, Ibaraki, 305–8506, Japan
  • 4University of Yamanashi, Yamanashi, 400–0016, Japan
  • 5Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka, 816–8580, Japan
  • 6Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Science, Xiamen, 361021, China

Abstract. East Asia is suffering from a severe air pollution problem due to intensive emissions of anthropogenic pollutants and mineral dust aerosols. During transport, both Asian dust and pollutants undergo complex mixing processes, which result in great impacts on regional air quality, human health and climate. To characterize these mixing processes, we conducted long-term observations using an optical particle counter equipped with a polarization detection module (POPC) in the megacity of Beijing. Mass concentrations of PM2.5 (aerodynamic diameters of less than 2.5μm) and PM10 derived from POPC compared well with ground-based measurements. Based on size-resolved polarization measurements, anthropogenic pollutants, mineral dust and mixed-type mineral dust (dust particle with pollutant coatings) were well distinguished. We found that the depolarization ratio (DR, termed as the ratio of the intensity of the s-polarized signal to the intensity of the backward scattering signal [s/(s+p)]) for aerosol particles with optical diameters of <2.0μm has a pronounced seasonal variation trend, with a winter–spring high and a summer low pattern. Aerosols that originated from Mongolia and western China normally demonstrate non-spherical shapes, with a DR centred on 0.3, whereas the value for fine-mode particles was usually less than 0.1 due to the predominance of secondary water-soluble matter. In Beijing, the morphology of mineral dust changed obviously, particularly in humid conditions. Higher relative humidity accelerated the liquid phase reaction and promoted water absorption due to the coating of hygroscopic soluble compounds on the dust surface. This study also found that 48% of substandard air quality days featured high coarse-mode particles in the winter–spring time, which implies the great influence of heterogeneous processes on the surface of mineral dust on smog formation.

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Short summary
East Asian is characterized by severe anthropogenic pollution and dust storms due to fuel consumption and downwind location to dust sources. We studied the mixing states of dust and pollutants using an optical particle counter equipped with a polarization detection module (POPC), provide a deeper understanding of possible mechanisms of aerosols’ morphological change. In Beijing, the heterogeneous processes in mixture of dust and emitted pollutants has great influence of on smog formation.
East Asian is characterized by severe anthropogenic pollution and dust storms due to fuel...
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