城市快速路近路区域冬季碳气溶胶的分布特征与来源解析

Distribution characteristics and source apportionment of carbonaceous aerosol in the area beside urban expressway during winter

2019年12月6-13日,在枫生快速近路区域,在距离快速路不同水平距离设置4个采样点,距离快速路同一水平距离不同垂直高度设置5个采样点,采集PM_(2.5)样品;采用碳分析仪测定有机碳(OC)和元素碳(EC),讨论分析碳气溶胶的分布特征,运用主成分分析法对PM_(2.5)的来源进行解析。结果表明:采样期间,枫生快速近路区域,大气PM_(2.5)中OC和EC的质量浓度为8.3~20.5、2.5~5.4μg·m^(-3),比南昌非快速路旁区域的OC、EC质量浓度高,反映机动车尾气对PM_(2.5)中碳组分的贡献;距快速路不同水平距离4个采样点的PM_(2.5)中OC、EC的质量浓度,随着与快速路水平距离的增加,呈递减趋势;距快速路同一水平距离不同垂直高度5个采样点的PM_(2.5)中OC在不同高度采样点呈“W”型分布特征,而EC随着高度上升,质量浓度逐渐降低;垂直方向上,PM_(2.5)中OC组分的质量浓度并没有随着高度的上升呈现单一渐减的趋势,反映OC的分布不仅受一次排放影响,同时受气象条件和二次生成的影响。主成分分析源解析结果显示,研究区域PM_(2.5)的主要来源为汽油、柴油车尾气(56.1%)、煤炭/生物质燃烧混合源(25.4%)和特定柴油车排放源(14.8%),受机动车尾气(70.9%)排放影响大。

From December 6th to December 13th,2019,in the area beside Feng Sheng expressway,several sampling sites were set to collect PM_(2.5)samples with different horizontal distances from the expressway at the same height and with different vertical heights at the same horizontal distance.Organic carbon(OC)and elemental carbon(EC)in PM_(2.5)were determined by carbon analyzer.The distribution characteristics of carbonaceous aerosols were discussed.The source of PM_(2.5)was analyzed and apportioned by principal component analysis(PCA)method.The results showed that the mass concentration range of OC and EC in PM_(2.5)were 8.3-20.5 and 2.5-5.4μg·m^(-3),respectively.The concentrations of OC and EC in the study area were higher than those of non-express roadside area in Nanchang,reflecting the contribution of vehicle exhaust to carbon components in PM_(2.5).The concentrations of OC and EC in PM_(2.5)at four sampling points at different horizontal distances from expressways decreased with the increasing of horizontal distances from expressways.In the PM_(2.5)sampling points at the same horizontal distance and different vertical heights of the expressway,OC showed a W-shaped distribution at the sampling points at different heights,while EC concentration decreased gradually with the increasing of height.Vertically,the concentration of OC component in PM_(2.5)did not decrease with the increasing of height,indicating that the distribution of OC is not only affected by primary emission,but also by meteorological conditions and secondary generation.PCA results showed that the main sources of PM_(2.5)in the study area were the exhaust emission sources of gasoline and diesel vehicles(56.1%),coal/biomass combustion mixed sources(25.4%)and specific diesel vehicle emissions(14.8%).PM_(2.5)in the area beside urban expressway was mainly affected by vehicle exhaust emissions(70.9%).