Characterization of water-soluble inorganic ions in size-segregated aerosols in coastal city, Xiamen

Abstract

<p>The samples of water-soluble inorganic ions (WSIs), including anions (F^&minus;, Cl^&minus;, SO₄^2&minus;, NO₃^&minus;) and cations (NH₄⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺) in 8 size-segregated particle matter (PM), were collected using a sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0&nbsp;&mu;m) from October 2008 to September 2009 at five sites in both polluted and background regions of a coastal city, Xiamen. The results showed that particulate matters in the fine mode (PM_2.1, Dp&nbsp;&lt;&nbsp;2.1&nbsp;&mu;m) comprised large part of mass concentrations of aerosols, which accounted for 45.56&ndash;51.27%, 40.04&ndash;60.81%, 42.02&ndash;60.81%, and 40.46&ndash;57.07% of the total particulate mass in spring, summer, autumn, and winter, respectively. The water-soluble ionic species in the fine mode at five sampling sites varied from 15.33 to 33.82 (spring), 14.03 to 28.06 (summer), 33.47 to 72.52 (autumn), and 48.39 to 69.75&nbsp;&mu;g&nbsp;m^{&minus;&nbsp;3} (winter), respectively, which accounted for 57.30&nbsp;&plusmn;&nbsp;6.51% of the PM_2.1 mass concentrations. Secondary pollutants of NH₄⁺, SO₄^2&minus; and NO₃^&minus; were the dominant contributors of WSIs, which suggested that pollutants from anthropogenic activities, such as SO₂, NOx were formed in aerosols by photochemical reactions. The size distributions of Na⁺, Cl^&minus;, SO₄^2&minus; and NO₃^&minus; were bimodal, peaking at 0.43&ndash;0.65&nbsp;&mu;m and 3.3&ndash;5.8&nbsp;&mu;m. Although some ions, such as NH₄⁺ presented bimodal distributions, the coarse mode was insignificant compared to the fine mode. Ca²⁺ and Mg²⁺ exhibited unimodal distributions at all sampling sites, peaking at 2.1&ndash;3.3&nbsp;&mu;m, while K⁺ having a bimodal distributions with a major peak at 0.43&ndash;0.65&nbsp;&mu;m and a minor one at 3.3&ndash;4.7&nbsp;&mu;m, were used in most of samples. Seasonal and spatial variations in the size-distribution profiles suggested that meteorological conditions (seasonal patterns) and sampling locations (geographical patterns) were the main factors determining the formation of secondary aerosols and characteristics of size distributions for WSIs.</p><!-- articleText --