中国典型沿海城市冬季PM_(2.5)中碳组分的污染特征及来源解析

Pollution characteristics and sources analysis of carbon components in PM_(2.5) in winter at typical coastal cities of China

为研究中国典型沿海城市冬季PM_(2.5)中碳组分的污染特征及来源,于2018年12月5日—2019年1月30日分别在天津(TJ)、上海(SH)和青岛(QD)同步采集PM_(2.5)样品。结果表明,天津、上海和青岛PM_(2.5)的平均浓度分别为(116.96±66.93)、(31.21±25.62)、(74.93±54.60)μg·m^(-3),OC和EC的空间分布均为天津(18.69±7.95)μg·m^(-3)和(4.98±2.08)μg·m^(-3)>青岛(16.45±8.94)μg·m^(-3)和(2.01±1.04)μg·m^(-3)>上海(7.28±3.11)μg·m^(-3)和(1.05±1.25)μg·m^(-3)。3个站点的OC和EC均呈现较好的相关性,表明OC和EC具有相似的来源;OC/EC比值范围在2.37—7.53、5.47—46.41和4.77—13.36之间,证明各采样点均存在二次有机碳(SOC)的生成;采用最小R^(2)法(MRS)估算SOC浓度,得到3个采样点SOC的平均质量浓度为(5.09±4.68)、(3.90±1.65)、(4.21±4.31)μg·m^(-3),分别占OC总量的27.2%、55.8%和19.5%,其中上海的SOC在OC中的占比最大,说明上海二次有机碳污染较为严重,这主要归因于冬季严重污染源排放和有利的二次转化气象条件,而天津和青岛的碳组分主要来自污染源的直接排放。主成分分析(PCA)结果发现,天津PM_(2.5)中碳组分主要来源于道路尘、生物质燃烧和机动车尾气,上海PM_(2.5)中碳组分主要来源于生物质燃烧、道路扬尘和机动车尾气。青岛PM_(2.5)中碳组分主要来源于道路扬尘、机动车尾气。后向轨迹聚类分析表明,来自西北方向的气团对天津的影响较大,PM_(2.5)和碳组分的浓度值最大;而对上海而言,主要受北方气溶胶经过海面又传输回上海的气团的影响;青岛站点主要受华北地区污染物和本地排放源的影响。

To investigate the pollution characteristics and sources of carbonaceous species in PM_(2.5),samples were collected at three sites simultaneously from Dec.5,2018 to Jan.30,2019 in Tianjin(TJ),Shanghai(SH)and Qingdao(QD).The result showed that the average mass concentrations of PM_(2.5) were(116.96±66.93),(31.21±25.62)μg·m^(-3) and(74.93±54.60)μg·m^(-3).The spatial distribution of OC and EC shows the order of TJ(18.69±7.65)μg·m^(-3),(4.98±2.08)μg·m^(-3)>QD(16.45±8.94)μg·m^(-3),(2.01±1.04)μg·m^(-3)>SH(7.28±3.11)μg·m^(-3),(1.05±1.25)μg·m^(-3).The good correlation between OC and EC indicated the similar OC and EC sources.The OC/EC ratios were 2.37—7.53,5.47—46.41 and 4.77—13.36 at TJ,SH and QD,respectively,showing that SOC exists at all sampling sites.The SOC concentration was estimated by MRS(minimum r squared method).The average mass concentrations of SOC at three sampling sites were(5.09±4.68),(3.90±1.65)and(4.21±4.31)μg·m^(-3),accounting for 27.2%,55.8%and 19.5%of the OC,respectively.Among them,the secondary carbonaceous pollution in SH is the most serious,and which is caused by severe pollution emissions and favorable meteorological conditions benefitting the secondary organic carbon formation,while carbon components in TJ and QD mainly comes from the primary emission.PCA analysis shows that the carbon components of PM_(2.5) at TJ are mainly from coal combustion,biomass combustion and motor vehicle exhaust,while at SH they are mainly from biomass combustion,road dust and motor vehicle exhaust.The carbon components at QD mainly come from road dust,motor vehicle exhaust and diesel vehicle exhaust.The backward trajectory analysis shows that the air mass from the northwest has a great influence on TJ,and the concentrations of PM_(2.5) and carbon components are the largest,while for the sties at SH and QD,the concentrations of carbon components and PM_(2.5) originating from the air mass in the middle of Hebei Province are the highest,indicating that the two cities are more affected by the transport of the surrounding areas.