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Pollution Characteristics of Water-Soluble Ions in Aerosols in Urban Area in Beibei of Chongqing

Category: Aerosol and Atmospheric Chemistry

Accepted Manuscripts
DOI: 10.4209/aaqr.2017.11.0500
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Yanpei Li1, Qingju Hao1, Tianxue Wen2, Dongsheng Ji2, Zirui Liu2, Yuesi Wang2, Xiaoxi Li1, Xinhua He1, Changsheng Jiang 1

  • 1 Key Laboratory of Eco-environments in Three Gorges Reservoir Region (Ministry of Education), College of Resources and Environment, Southwest University, Chongqing 400715, China
  • 2 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Highlights

Droplet-mode SO42– in spring and autumn was mainly from in-cloud processes.
SO42– had condensation and droplet modes in summer from oxidation of SO2.
Temperature and photochemical reaction were the dominant factors affecting NO3 formation.
Secondary transformation processes were the major source of the water-soluble ions.
The degree of oxidation of sulfate was considerably greater than nitrate in each season.


Abstract

To investigate the pollution characteristics of water-soluble ions in aerosols in the urban area in Beibei Suburb of Chongqing, the graded aerosol samples were continuously collected by cascade impactor (Andersen) from March 2014 to February 2015. Water-soluble ions, including Na+, NH4+, K+, Mg2+, Ca2+, F, Cl, NO3 and SO42– in different particle size ranges (< 0.43, 0.43–0.65, 0.65–1.10, 1.10–2.10, 2.10–3.30, 3.30–4.70, 4.70–5.80, 5.80–9.00 and 9.00–100 µm) were measured by ion chromatography. The results showed that SO42– mainly distributed in the droplet mode in spring and autumn from in-cloud processes. While SO42– had both condensation and droplet modes in summer from the oxidation of SO2. NH4+ and SO42– were mainly presented in the form of NH4HSO4 in aerosols. Except for summer, NO3 mostly existed in the form of NH4NO3 in fine particles and Ca(NO3)2 in coarse particles. Na+ was single-peaked in spring and summer, and double-peaked in autumn and winter. Fine-mode K+ showed single-peak distribution in each season. The existent form of Cl was KCl in fine mode, and CaCl2 in coarse mode. Mg2+ mainly distributed in coarse particles, which showed a bimodal pattern distribution in spring and summer. Ca2+ was mainly existed in coarse modes, whose concentration increased with increasing particle size. Mg2+, Ca2+ and F were mainly appeared in coarse particles, and other ions were mainly distributed in fine particles. The emissions from motor vehicle exhaust, combustion process, soil sources and construction dust were the major sources of the water-soluble ions in this area. SOR (sulfur oxidation ratios) was the highest in summer and the lowest in winter, but NOR (nitrogen oxidation ratios) in winter was higher than other seasons. SOR value of condensation-mode (0.43–0.65 µm) was greater than 0.10 only in summer. SOR was considerably higher than NOR at the same particle sizes in the whole year.

Keywords

Water-soluble ions Fine mode Coarse mode Size distribution


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