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Pollution Properties of Water-Soluble Secondary Inorganic Ions in Atmospheric PM2.5 in the Pearl River Delta Region

Category: Aerosol and Atmospheric Chemistry

Volume: 15 | Issue: 5 | Pages: 1737-1747
DOI: 10.4209/aaqr.2014.12.0333
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Dingli Yue1, Liuju Zhong 1, Tao Zhang1, Jin Shen1, Yan Zhou1, Limin Zeng2, Huabin Dong3, Siqi Ye1

  • 1 Guangdong Environmental Monitoring Center, State Environmental Protection Key Laboratory of Regional Air Quality Monitoring, Guangzhou 510308, China
  • 2 Peking University, State Key Joint Laboratory of Environmental Simulation and Pollution Control, Beijing 100871, China
  • 3 Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Highlights

Interaction of secondary inorganic ions and their gaseous precursors was discussed.
SO42–, NO3 and NH4+ totally contributed 46.0% (summer)–64.3% (winter) to PM2.5.
NH3 was abundant and NH4+ in PM2.5 can totally balance SO42– and NO3.
High HNO3 concentration put an evidence for strong atmospheric oxidizing property.
Strong oxidizing property and NH3 played crucial roles in fine particle pollution.


Abstract

Based on the online observation of PM2.5 mass concentration, its water-soluble inorganic ions, and their gaseous precursors during August of 2013 to March of 2014 at the atmospheric supersite in the Pearl River Delta (PRD) region, the inter-action of the secondary compositions and their precursors was discussed, and the pollution properties of the secondary inorganic ions were revealed. During the whole measurement period, the average concentrations of SO42–, NO3 and NH4+ were 16.6 µg m–3, 9.0 µg m–3 and 10.2 µg m–3, respectively, with total contribution to PM2.5 of 55.8%, indicating the significant role of secondary transformation in PM2.5 pollution. The seasonal average total contributions of SO42–, NO3 and NH4+ to PM2.5 varied from 46.0% to 64.3%, lowest in summer and highest in winter. The contributions of SO42– and NH4+ to PM2.5 were relatively stable; while those of NO3 in different seasons were distinct, even dominating PM2.5 in some pollution cases in winter. NH3 was abundant with an annual average concentration of 15.2 µg m–3, facilitating the neutralization of H2SO4 and HNO3 with the average [NH4+]/(2[SO42–] + [NO3]) equivalent charge ratio of 1.1. The maximum daily peak concentration of HNO3 was as high as 18.6 µg m–3, providing an evidence for the strong oxidizing property of the atmosphere in the PRD region. The theoretical equilibrium constant (Ke) of NH4NO3 is always lower than the observed concentration product (Km = [NH3] × [HNO3]) in spring and winter with higher HNO3 concentrations; while in over 60% of the time during summer and autumn, mainly during daytime, Ke was higher. In general, the strong oxidizing property and NH3 played important roles in the fine particle pollution in the PRD region.

Keywords

PM2.5 Water-soluble inorganic ions Secondary transformation Gas-particle conversion


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