LAUSR

Abstract PM 2.5 samples were collected in urban area in Taiyuan for four seasons from August 2009 to April 2010. The Water-soluble inorganic ions (WSI, including F − , Cl − , NO 3 − , SO 4 2 − , Na + , NH 4 + , K + , Mg 2 + , and Ca 2 + ) were analyzed by ion chromatography. The daily PM 2.5 levels in the field samples varied from 49.90 to 477.93 μg/m 3 with the mean of 209.54 μg/m 3 , which all largely exceeded the PM 2.5 24-hour limitation value of 35 μg/m 3 in Environmental Protection Administration of United States and 75 μg/m 3 in Ministry of Environmental Protection of China. The WSI average concentration was 68.86 μg/m 3 and accounted for about 32.86% of PM 2.5 . As the most abundant anion and cation, SO 4 2 − and NH 4 + were 43.53 and 14.78 percent of WSI, respectively. PM 2.5 in Taiyuan was acidic by the micro-equivalents concentration methods but nearly neutral in autumn, and the chemical forms of WSI were mainly NH 4 HSO 4 , (NH 4 ) 2 SO 4 and NH 4 NO 3 . PM 2.5 and WSI levels showed obvious seasonal variation and were the highest in winter in all samples. PM 2.5 , SO 4 2 − , and some coal-related ions such as NH 4 + and Cl − were higher in winter than other seasons, which mainly attributed to more coal combustion for power and indoor heating supply. The ratio analysis showed that Mg 2 + and Ca 2 + were not only from soil dust, but also from coal combustion and industry emission. Biomass burning such as the cornstalk and tree branches led to the highest K + emission in autumn and summer. Wind had a regular influence on the PM 2.5 and WSI, and would transport the soil dust mainly from the northwest and also lead to re-suspension of dust in the air when the wind speed was high. Furthermore, the dustpan topography easily helped the pollutants to concentrate in Taiyuan city, and some coal coking industries might contribute to high PM 2.5 and WSI in Taiyuan.