新疆奎独乌区域冬季大气重污染过程PM2.5组成特征及来源解析

为研究新疆奎独乌（奎屯、独山子、乌苏）区域冬季大气重污染过程的PM_2.5污染特征及其成因，于2015年2月4-10日在奎屯、独山子和乌苏三地开展PM_2.5样品采集，并对其中的元素、水溶性离子及碳组分进行测试，分析不同污染水平下PM_2.5中化学组分的变化规律.结果表明，采样期间奎独乌区域ρ（PM_2.5）日均值均超过GB 3095-2012《环境空气质量标准》二级标准（75 μg/m3），2月9日ρ（PM_2.5）最高（298.58 μg/m3），超标2.98倍.通过比较PM_2.5载带化学组分质量百分比发现，随着污染等级加剧，SO₄2-、NO₃-质量百分比呈逐渐增加的趋势，严重污染时SO₄2-、NO₃-质量百分比分别较轻度污染时增长11.7%、5.5%；NH₄+、碳组分及元素组分质量百分比则呈下降趋势，严重污染较轻度污染时分别下降0.7%、9.5%、2.4%；结合采样期间静稳及高湿的气象条件，说明此次重污染由本地污染物累积及二次颗粒物生成所致.随着污染水平的加重，SOR（硫氧化率）及NOR（氮氧化率）的值也在随之增大，说明污染越重大气二次转化程度越高，进一步验证了二次颗粒物是导致此次重污染的原因之一.对不同污染等级PM_2.5进行质量重构发现，PM_2.5中主要组分均为硫酸盐和OM（有机物），硫酸盐和OM的质量百分比分别在23.0%~34.7%、16.4%~28.7%之间，说明此次重污染过程的主要污染源为燃煤及机动车尾气. 

Chemical Composition and Source Apportionment of PM2.5 during a Winter Air Pollution Episode in the Kui-Du-Wu Area of Xinjiang Uygur Autonomous Region

To understand the chemical composition and source apportionment of PM_2.5 during a winter air pollution episode, ambient PM_2.5 samples were collected in Kuitun, Dushanzi and Wusu cities from February 4th to February 10th, 2015. Chemical composition (i.e., mass concentrations, elements, water soluble ions and carbonaceous species) of PM_2.5 were analyzed. The results showed that high concentrations of PM_2.5 were observed during the sampling period, exceeding the Ambient Air Quality Standards (GB 3095-2012). The PM_2.5 concentration on February 9th was the highest at 298.58 μg/m3, which was 2.98 times higher than the standard (75 μg/m3). The ratio of SO₄2- and NO₃- in PM_2.5 mass showed increasing trends with the aggravation of air quality, while the ratio of NH₄+, carbonaceous species and elements showed decreasing trends. The percentages of SO₄2- and NO₃- increased by 11.7% and 5.5% between slight pollution and severe pollution, respectively, while the percentage of NH₄+, carbon and elements decreased by 0.7%, 9.5% and 2.4% between slight pollution and severe pollution, respectively. Combined with stagnant atmosphere, low wind speed ( < 1.8 m/s) and high relative humidity (55%-85%) during the sampling period, we concluded that this air pollution episode was mainly caused by local air pollution accumulation and formation of secondary aerosols. The values of SOR and NOR increased with the pollution level going up, indicating that secondary transformation rate was promoted under severe pollution. Mass closure was used to discuss the relative contributions of the major compositions in the PM_2.5. The chemical species were divided into the following eight categories:mineral dust (MIN), trace elements (TE), organic matter (OM), EC, sulfate, nitrate, ammonium and others. The mass reconstruction of PM_2.5 showed that sulfate and organic matter (OM) were the dominant components, accounting for 23.0%-34.7% and 16.4%-28.7% of PM_2.5 mass, respectively, which indicated that major sources of PM_2.5 in the study area were coal combustion and vehicle exhaust.