Distribution Characteristics of Water-soluble Ions in Size-segregated Particulate Matters in Taiyuan

Abstract

The distributions of size-segregated particles (PM10) and water-soluble ions (WSIs) in Taiyuan were studied from July 2014 to April 2015 by TE-235 aerosol sampling and ion chromatography analyzing. As the results shown, the daily PM10 level was 173.7 μg·m^-3, which exceeded the Grade Ⅱ limitation value in the Ambient Air Quality Standard (150 μg·m^-3, GB 3095-2012). PM10 levels varied seasonally, and its were 199.1 and 194.2 μg·m^-3 in winter and spring, respectively, which were much higher than those in summer. The PM10 size-segregated was bimodal distribution for the range of 0-0.95 and 3.0-7.2 μm. The concentration of WSIs was the highest in winter, followed by summer and spring. SO4^2-, NO3^- and NH4⁺ were the main water soluble ions and accounted for 66% to 80% of the total WSIs. SO4^2-, K⁺, NH4⁺ and Cl^- showed a unimodal distribution at <0.95 μm in all samples, while Ca²⁺ and Mg²⁺ showed a bimodal distribution at <0.95 μm and 3.0-7.2 μm. NO3^- showed a unimodal size distribution at <0.95 μm in winter and spring, compared with a bimodal distribution at <0.95 μm and 3.0-7.2 μm in summer. By the correlation analysis, PM10 and WSIs decreased with the increase of wind speed in summer and winter other than in spring for the road-dust re-suspension by strong wind. Based on the ratio analysis of NO3^-/SO4^2- and Mg²⁺/Ca²⁺, coal combustion was the main source of NO3^- and SO4^2-, while Mg²⁺ and Ca²⁺ were mainly from the dust and coal combustion.