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Seasonal Characteristics of Sulfate and Nitrate in Size-segregated Particles in Ammonia-poor and -rich Atmospheres in Chengdu, Southwest China

Category: Aerosol and Atmospheric Chemistry

Volume: 19 | Issue: 12 | Pages: 2697-2706
DOI: 10.4209/aaqr.2019.07.0368
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To cite this article:
Li, Q., Yang, Z., Li, X., Ding, S. and Du, F. (2019). Seasonal Characteristics of Sulfate and Nitrate in Size-segregated Particles in Ammonia-poor and -rich Atmospheres in Chengdu, Southwest China. Aerosol Air Qual. Res. 19: 2697-2706. doi: 10.4209/aaqr.2019.07.0368.

Qinkai Li1,2, Zhou Yang3, Xiaodong Li 1,2, Shiyuan Ding1,2, Feng Du4

  • 1 Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China
  • 2 Tianjin Key Laboratory of Earth Critical Zone Science and Sustainable Development in Bohai Rim, Tianjin University, Tianjin 300072, China
  • 3 College of Tourism and Geographical Sciences, Tongren University, Tongren 565300, China
  • 4 State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, China

Highlights

  • An NH3-poor atmosphere was observed at Chengdu during 2012–2013.
  • NO3 linearly related with NH4+/SO42– in both NH3-poor and -rich atmosphere.
  • NO3 formed more efficiently than SO42– during cold and NH3-rich atmosphere in winter.

Abstract

In order to determine the seasonal characteristics of water-soluble inorganic ions (WSIIs) in aerosols in urban atmospheres, size-segregated particulate matter (PM) samples were collected over a one-year period from February 2012 to January 2013 in a typical urban location, Chengdu in Southwest China, using an Andersen cascade impactor sampler. The PM mass concentrations, particularly the fine fraction, peaked during winter, and the WSIIs were more enriched in the fine fraction (21.7%) than the coarse fraction (9.2%). The sums of the equivalent ratios of cations (Na+, NH4+, K+, Mg2+, and Ca2+) to anions (SO42–, NO3, Cl, and F) indicated that the fine particles (0.86) were more acidic than the coarse ones (1.60). The average NH4+/SO42– molar ratio (A/S) in the fine fraction (1.79) was much higher during winter than the other three seasons (< 1.5), implying a generally NH3-poor atmosphere in Chengdu; hence, the NO3 in the fine particles was principally formed through homogeneous reactions involving ammonia and nitric acid during winter, whereas it was heterogeneously formed during the other three seasons. Significant positive correlations were observed between the A/S and NO3 molar concentrations during spring and winter; therefore, the formation of particle-phase NO3 may be accelerated by increased A/S in both NH3-poor and -rich atmospheres. Moreover, the A/S and NO3/SO42– molar ratios displayed negative and positive correlations during spring and winter, respectively, suggesting that the variation in atmospheric NH4+ (or NH3) during winter affected the formation of NO3 more strongly than that of SO42–, whereas more SO42– than NO3 was formed in the NH3-poor atmosphere during spring, when most of the NO3 in the aerosols would be expected to form via heterogeneous reactions.

Keywords

Size-segregated particles Sulfate Nitrate Ammonium Chengdu


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