承德市PM_(2.5)中碳质组分的季节分布特征及来源解析

Seasonal Variation and Source Apportionment of Carbonaceous Species in PM_(2.5) in Chengde

为研究承德市PM_(2.5)中碳质组分的季节变化及污染来源,于2019年1、4、7和10月采集大气PM_(2.5)样品,测定碳质组分浓度.通过有机碳(OC)与元素碳(EC)比值、总碳质气溶胶(TCA)及二次有机碳(SOC)的估算,分析碳质组分的变化特征;结合后向轨迹和主成分分析(PCA)方法,分析污染来源.结果表明,采样期间PM_(2.5)、OC和EC的平均质量浓度分别为(31.26±21.39)、(13.27±8.68)和(2.80±1.95)μg·m^(-3).PM_(2.5)的季节变化趋势为:冬季[(47.68±30.37)μg·m^(-3)]>秋季[(28.72±17.12)μg·m^(-3)]>春季[(26.59±15.32)μg·m-3]>夏季[(23.17±8.38)μg·m^(-3)],与总碳(TC)、OC和EC季节变化趋势一致,冬季(R2=0.85)的OC与EC来源较一致;OC/EC值得出4个季节均受到交通和燃煤源排放的影响,且冬季受烟煤排放影响显著.TCA的平均浓度为(21.38±13.68)μg·m^(-3),占PM_(2.5)比例达68.39%,二次转化率(SOC/OC)为:春季(54.09%)>秋季(37.64%)>夏季(32.91%)>冬季(25.43%).后向轨迹模拟结果表明,春季和夏季气团携带的污染物浓度相对较低,秋季污染物的传输通道为西南方向,冬季为西北方向,主成分分析(PCA)表明,承德市PM_(2.5)削减的关键是控制机动车尾气、燃煤和生物质燃烧源的排放.

In order to study the seasonal variations and pollution sources of carbonaceous species in PM_(2.5)in Chengde,the concentration of these components was determined in atmospheric PM_(2.5)samples collected in January,April,July,and October 2019.The change in carbonaceous species were analyzed based on the estimation of the ratio of organic carbon(OC)to elemental carbon(EC),total carbonaceous aerosol(TCA),and secondary organic carbon(SOC).The source of these pollutants was determined by means of the backward trajectory and principal component analysis(PCA).The results showed that the mean mass concentrations of PM_(2.5),OC,and EC during the sampling period were(31.26±21.39)μg·m^(-3),(13.27±8.68)μg·m^(-3),and(2.80±1.95)μg·m^(-3),respectively.The seasonal variations of PM_(2.5)were:winter[(47.68±30.37)μg·m^(-3)]>autumn[(28.72±17.12)μg·m^(-3)]>spring[(26.59±15.32)μg·m^(-3)]>summer[(23.17±8.38)μg·m^(-3)],consistent with the trend of total carbon(TC),OC,and EC.The source of OC and EC during winter(R2=0.85)was similar.Based on the ratio of OC/EC,all four seasons were affected by traffic and coalburning source emissions,and the most affected season by bituminous coal emissions was winter.The average concentration of TCA was(21.38±13.68)μg·m^(-3),which accounted for 68.39%of PM_(2.5).The order of secondary conversion rate(SOC/OC)was:spring(54.09%)>autumn(37.64%)>summer(32.91%)>winter(25.43%).The results of the backward trajectory simulation show that the pollutant concentrations carried by air masses are relatively low in spring and summer,and the transport channels of pollutants are southwest in autumn and northwest in winter.The results of the PCA showed that the key to reducing PM_(2.5)in Chengde is to control emissions from vehicle exhausts,and coal and biomass combustion sources.