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Characteristics of Water-Soluble Inorganic Components and Acidity of PM2.5 in a Coastal City of China

Category: Aerosol and Atmospheric Chemistry

Volume: 17 | Issue: 9 | Pages: 2152-2164
DOI: 10.4209/aaqr.2016.11.0513
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Xin Wu1,2,3, Junjun Deng1,2, Jinsheng Chen 1,2, Youwei Hong1,2, Lingling Xu1,2, Liqian Yin1,2, Wenjiao Du1,2,3, Zhenyu Hong1,2,3, Nanzhen Dai1,2,4, Chung-Shin Yuan5

  • 1 Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 2 Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
  • 3 University of Chinese Academy of Sciences, Beijing 100049, China
  • 4 College of Environment and Resources, Fuzhou University, Fuzhou 350116, China
  • 5 Institute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan

Highlights

Contributions and concentrations of sea-salt aerosol acidity were quantified.
Acidity of PM2.5 in harbor site in summer was the highest.
Poor ammonium in PM2.5 mainly combined with sulfate as the form of NH4HSO4.


Abstract

To investigate the characteristics of water-soluble inorganic ions (WSIIs) of PM2.5 and aerosol acidity in a coastal city, 352 samples were collected at four sites representing four functional zones (FJ: living town; XY: industrial area; TZ: scenery areas; HR: harbor) in Xiamen, China in 2015–2016. Mass concentrations of PM2.5, nine WSIIs, total acidity and in-situ acidity of aerosol/non-sea-salt aerosol were measured. Overall, the mean mass concentrations of PM2.5 in the study area in spring, summer, autumn and winter were 57.5 ± 22.3, 28.1 ± 12.6, 46.8 ± 18.3 and 62.4 ± 22.1 µg m–3, respectively. WSIIs accounted for 36%–56% of PM2.5 at four sites. Secondary ions (non-sea-salt SO42–, NO3 and NH4+) contributed more than 74% to total WSIIs. Neutralization degree distributions indicated that 79.5% of PM2.5 was acidic. Total acidity and in-situ acidity both showed obvious seasonal variations, exhibited the peak values of 193.20 and 130.17 nmol m–3 at HR site in summer. Sea-salt contributed 2.58%–17.74% to acidity in four seasons. The normalized ammonium concentration ([NH4+]/[SO42–]) and normalized nitrate concentration ([NO3]/[SO42–]) showed greater correlation coefficients after eliminating the ammonium-poor data points (greater than 0.66), especially at HR site. NH4HSO4 was the major form of WSIIs in PM2.5 and the formation of aqueous HNO3 could enhance aerosol acidity.

Keywords

Water-soluble inorganic ions Secondary ions Sea-salt aerosol acidity Coastal city


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