天津市区夏冬季环境空气PM2.5中碳组分污染特征及来源研究

Character and source analysis of carbonaceous aerosol in PM_(2.5) during summer-winter period,Tianjin urban area

为了明确天津市区环境受体PM_(2.5)中碳组分的污染特征及来源,本研究分别于2016年2月(冬季)和8月(夏季)在天津市区设置6个采样点位同步采集PM_(2.5)样品,采用热光反射法测定样品中各个碳组分(OC1~OC4、EC1~EC3和OP(裂解碳))的含量,并计算得到OC、EC、CharEC和Soot-EC,以定性识别大气颗粒物中碳组分的来源.结果表明,夏季PM_(2.5)中OC平均浓度为(7.5±3.0)μg·m-3,占PM_(2.5)的11.7%±4.1%;而冬季相比于夏季OC的浓度和占比均有增加,分别为(13.1±7.0)μg·m-3和13.9%±2.8%.夏季和冬季EC浓度分别为(4.0±1.8)μg·m-3、(4.3±2.4)μg·m-3,占PM_(2.5)的6.1%±2.0%和4.6%±1.2%.OC与EC的相关性在夏季(r=0.83,p<0.01)和冬季(r=0.96,p<0.01)均显著,而冬季CharEC与OC(r=0.94,p<0.01)、EC(r=0.98,p<0.01)相关性明显高于夏季(OC:r=0.44,p<0.01;EC:r=0.45,p<0.01).PM_(2.5)中OC/EC平均值在夏季和冬季分别为1.9和3.0,估算得到夏季SOC为(2.6±1.4)μg·m-3,占OC的33.5%±13.6%;冬季为(3.5±2.5)μg·m-3,占OC的26.6%±12.0%.夏季Char-EC/Soot-EC为6.5,高于冬季(4.9),并且空间差异性显著(t检验,p<0.05).正定矩阵因子模型(PMF)解析结果表明,天津市区大气PM_(2.5)中碳组分主要有4类来源:燃煤及生物质排放混合源、柴油车、汽油车、道路尘,对夏季PM_(2.5)中碳组分分担率分别为35.4%、16.4%、20.5%、14.4%;对冬季碳组分分担率分别为41.3%、15.5%、18.1%、16.3%.可见,燃煤和机动车是天津市区PM_(2.5)中碳组分的主要来源.

To indentify the characteristics and sources of carbonaceous fractions in PM2.5,the ambient PM2.5 samples were collected at six sites in Tianjin urban area in February and August,2016. The OC1 ~ OC4,EC1 ~ EC3 and OP（ pyrolytic carbon） were analyzed using the thermal/optical reflection protocol,and then OC,EC,Char-EC and Soot-EC were calculated as well. Results indicated that the average OC concentration in winter was（ 13.1±7.0）μg·m^-3,and accounted for 13.9%±2.8% of PM2.5 mass,higher than that in summer（（ 7.5±3.0） μg·m^-3,11.7%±4.1%）.The average concentrations of EC in summer and winter were（ 4.0±1.8） μg·m^-3 and（ 4.3±2.4） μg·m^-3,respectively,and accounted for 6.1%±2.0% and 4.6%±1.2% of PM2.5 mass,respectively. Correlations between OC and EC were significant in winter（ r = 0. 96,p 0. 01） and summer（ r = 0. 83,p 0. 01）. While the correlationcoefficients between Char-EC and OC,and between Char-EC and EC were higher in winter than those in summer.The OC/EC in summer and winter were1.9 and 3.0,respectively. The SOC concentration were estimated to be（ 2.6±1.4） μg·m^-3 in summer and（ 3.5±2.5） μg·m^-3 in winter,accounting for33.5% ±13.6% and 26.6% ±12.0% of OC mass,respectively. The Char-EC/Soot-EC in summer（ 6.5） was apparently higher than in winter（ 4.9）,and there was significantly spatial heterogeneity for the Char-EC/Soot-EC（ t-test,p0.05）. Results of Positive Matrix Factorization（ PMF） analysis suggested that the coal combustion/biomass burning,diesel vehicle exhaust,gasoline vehicle exhaust and road dust were major sources of carbonaceous materials in Tianjin urban area. Contributions of these sources to carbonaceous materials in summer were up to 35. 4%,12. 4%,16. 5%,22. 4%,respectively,while those in winter were 41.3%,10.3%,13.0%,26.4%,respectively. The coal combustion and motor vehicles were the main sources of carbonaceous materials in Tianjin urban area.