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

摘要

The samples of water-soluble inorganic ions (WSIs), including anions (F~-, Cl, S0_4~(2-), NO_3~-) and cations (NH4_4~, K~+, Na~+, Ca~(2+), Mg~(2+)) in 8 size-segregated particle matter (PM), were collected using a sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0 urn) from October 2008 to September 2009 at five sites in both polluted and background regions of a coastal city, Xiamen. The results showed that paniculate matters in the fine mode (PM2.1, Dp<2.1 um) comprised large part of mass concentrations of aerosols, which accounted for 45.56-51.27%, 40.04-60.81%, 42.02-60.81%, and 40.46-57.07% of the total paniculate 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 ugm~(-3) (winter), respectively, which accounted for 57.30±6.51% of the PM_(2.1), mass concentrations. Secondary pollutants of NH4", SO_4~(2-)and NO_3~- were the dominant contributors of WSIs, which suggested that pollutants from anthropogenic activities, such as SO-2, NOx were formed in aerosols by photochemical reactions. The size distributions of Na~+, Cl~-, SO_4~(2-) and NO_3~-were bimodal, peaking at 0.43-0.65 um and 3.3-5.8 urn. Although some ions, such as NH4" presented bimodal distributions, the coarse mode was insignificant compared to the fine mode. Ca~(2+) and Mg~(2+) exhibited unimodal distributions at all sampling sites, peaking at 2.1-3.3 μm, while K~+ having a bimodal distributions with a major peak at 0.43-0.65 μm and a minor one at 3.3-4.7 μm, 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.