Size Distribution And Pollution Characterization Of Atmospheric Particulate Matter (PM) In Taiyuan

In recent years, atmospheric haze pollution becomes more and more serious. Particulate matter, especially the inorganic salts and carbon aerosol in fine particle were the main factors that caused the visibility degradation and haze formation. Taiyuan was one of most polluted cities in China, but c urrently related researches on the size distribution and chemical compositions of atmospheric particulate matter in Taiyuan have not been reported. In this study, PM10 size-segregated particle samples were collected with five-stage air sampler(TH-235, USA) in Taiyuan from July 2014 to April 2015 to perform a detailed characterization of nine water-soluble ions(WSIs), OC and EC. Atmospheric particulate matter(PM10) size composition,the concentration levels of WSIs, OC and EC, size distribution, seasonal variation, extinction contribution and potential sources were discussed and estimated finally. The results were of great significance to learn the main factors controlling atmospheric haze formation in Taiyuan, and provide a scientific evidence for formulat ion and implementation of air quality improvement policies.(1)The daily average concentration of PM10 was 173.7 ?g/m/3, which exceeded Grade II standard value(150 ?g�m-3) according to China National Ambient Air quality Standard(GB3095-2012). PM10 levels varied seasonally, and were 199.1 and 194.2 ?g/m3 in winter and spring, respectively, which were both much higher than that in summer. The size-segregated PM10 particle showed a bimodal distribution with one mode peak in the fine-particle size range(0~0.95 ?m) and another mode peak in the coarse-particle size range(3.0~7.2 ?m). Fine particle(<1.5 ?m) were the main component of PM10, accounting for 53 %, 61 % and 72 % in summer, winter and spring, respectively.(2)The daily average concentration of WSIs in PM10 was 47.5 ?g/m3, and seasonal trend was winter>summer>spring. SO42-, NO3- and NH4+ were the main water soluble ions and accounted for 66~80 % of the total WSIs. SO42-, K+, NH4+ and Cl- showed a unimodal distribution at <0.95 ?m in all samples, while Ca2+ and Mg2+ showed a bimodal distribution at <0.95 ?m and 3.0~7.2 ?m. In addition, NO3- showed a unimodal particle size distribution at <0.95 ?m in winter and spring, and a bimodal particle size distribution at <0.95 ?m and 3.0-7.2 ?m in summer. F- had a unimodal size distribution in summer with the peak at 3.0-7.2 ?m, and a bimodal distribution at <0.95 ?m and 3.0~7.2 ?m in winter and spring.(3)The daily average concentration of OC and EC in PM10 were 18.9 ?g/m3 and 8.4 ?g/m3, respectively. OC and EC showed a bimodal pattern with one dominated peak in the fine-particle size range(<0.95 ?m) and another minor peak in the coarse-particle size range(3.0~7.2 ?m). OC concentration in PM1.5 accounted for 63.8 %?81.6 % and 66.1 % of the OC in PM10, and EC concentration in PM1.5 accounted for 58.2 %?78.3 % and 68.5% of the EC in PM10 in summer, winter and spring in Taiyuan, respectively. The daily average concentration of SOC was 11.1 ?g/m3 with highest level in winter, and showed a unimodal size distribution at <0.95 ?m. SOC level in PM0.95 accounted for 62 %~85 % of SOC in PM10.(4)The result estimated by IMPROVE model showed that OM contributed the most to atmospheric extinction coefficient(27 %), followed by(NH4)2SO4(23 %), EC(18 %), NH4NO3(12 %), coarse mass(10 %), NO2(6 %) and clean air(4 %). The extinction contributions of different components varied with the seasons. In summer and spring, the higher contributors were inorganics including(NH4)2SO4 and NH4NO3, accounting for 48% and 32 %, respectively, while in winter OM contributed the most(37 %).(5)The PCA and PMF model analys is were used to study the sources of PM10 in Taiyuan. The result indicated that the PM10 were mainly emitted by coal combustion and secondary sources, and soil dust, road dust, diesel and biomass burning also cannot been ignored.