郴州市大气PM2.5碳组分污染特征及其来源分析

为研究郴州市PM_2.5中碳组分的污染特征及来源，于2016年7月-2017年4月分4个季度典型时段采集郴州市环境大气中的PM_2.5，测定了样品中OC（有机碳）和EC（元素碳）的质量浓度，对碳气溶胶污染水平、时空分布、SOC（二次有机碳）以及OC和EC相关性等特征进行了分析，并分析了碳组分的来源.结果表明:郴州市ρ（PM_2.5）年均值为（40.2±19.0）μg/m3，ρ（OC）、ρ（EC）占比分别为15.7%和7.2%；ρ（OC）与ρ（EC）相关性分析显示二者来源较为一致，但春季、夏季差异相对较大；ρ（SOC）全年估算值为1.84 μg/m3，占ρ（OC）的29.11%，夏季较高的温度和较低的相对湿度导致夏季ρ（SOC）的估算偏低.结合碳组分丰度分析、PCA（主成分分析）和PMF（正矩阵因子分解分析）结果发现，燃煤/道路尘、机动车排放和生物质燃烧对PM_2.5中TC（总碳）的影响最为明显，贡献率分别为49.25%~56.71%、19.79%~25.36%和9.35%~13.69%.反向轨迹聚类结果显示，广东珠三角区域的汽油车排放、道路尘和生物质燃烧对郴州市PM_2.5中碳组分有较大的影响，而燃煤和柴油车的贡献主要来源于本地.研究显示，郴州市PM_2.5中碳组分污染较为严重，应重点加强本地燃煤和柴油车的控制. 

Characteristics and Sources of Carbonaceous Species in Atmospheric PM2.5 in Chenzhou City

The characteristics and sources of carbonaceous species in PM_2.5 were investigated in this study. PM_2.5 samples were collected in Chenzhou City during typical periods of 4 seasons from July 2016 to April 2017. The concentrations of OC (organic carbon) and EC (elemental carbon) in PM_2.5 were determined, and the characteristics of OC and EC were further discussed in detail, including the pollution levels, the temporal and spatial distributions of OC and EC, SOC (secondary organic carbon) and relationships of OC and EC. Results showed that the average mass concentration of PM_2.5 in Chenzhou City was (40.2±19.0) μg/m3, meanwhile the concentrations of OC and EC accounted for 15.7% and 7.2%, respectively. Despite non-significant correlation in spring and summer, the correlation between OC and EC was significant on the whole. The concentration of SOC was 1.84 μg/m3, accounting for 29.11% of OC, and the SOC content in summer was underestimated because of the high temperature and low humidity. According to the percentages of eight carbon fractions in PM_2.5 and the results of PCA and the PMF model, it can be concluded that coal combustion/road dust (49.25%-56.71%), vehicle exhaust (19.79%-25.36%) and biomass burning (9.35%-13.69%) were the three main sources of total carbon in PM_2.5 in Chenzhou City. Moreover, based on the results of the backward trajectory model, the gasoline vehicle exhaust, road dust and biomass burning of the Pearl River Delta and Guangdong have great influence on the carbon composition of PM_2.5 in Chenzhou City, while the coal combustion and diesel vehicle exhaust were mostly derived from local sources. The results showed that carbonaceous pollution is serious in Chenzhou City and the control of carbonaceous pollution should be focused on coal combustion and diesel vehicles.