北京混合功能区夏冬季细颗粒物组分特征及来源比较

于2014年8月和12月,选择北京某城市混合功能区,分别手工采集一个月的环境空气PM2.5样品,实验室方法测定滤膜中的元素碳/有机碳、9种可溶性离子、16种无机元素等20余种化学组分,采用CMB模型对夏冬两季PM2.5来源进行分析.结果表明,夏季PM2.5日均质量浓度为73μg/m3,低于《环境空气质量标准》,而冬季平均值为111μg/m3,高于夏季和标准限值.冬季OC和EC浓度均高于夏季,且OC/EC比值升高,OC和EC呈线性相关,提示二者有相同来源.NO3-、SO42-、NH4+是北京混合功能区3种主要可溶性离子,且夏季生成量较高;冬季Cl-显著升高与燃煤排放有关.Si、Ti、Fe、Zn、Al等元素质量浓度在0.1~10μg/m3浓度水平,Pb、Cu、Mn、Cr、Ba、Sb等在10~102ng/m3浓度水平,V、Ni、Co、Mo、Cd等在0.1~10ng/m3浓度水平.且冬季各个元素浓度均高于夏季.CMB模型初步解析结果表明,夏季和冬季颗粒物的来源变化明显,夏季二次硫酸盐、机动车和二次硝酸盐贡献率居前三位,而冬季则为燃煤、机动车和扬尘.

Characterization and source apportionment of PM2.5 in mixed function area during summer and winter,Beijing

Air particulate matter samples from mixed function area in Beijing were collected during Aug. and Dec. 2014. The chemical components consisted of organic carbon (OC) and elemental carbon (EC), 9 water-soluble ions, and 16elements in PM_2.5 were analyzed. The chemical mass balance (CMB) method had been applied to identify the source of PM_2.5. The results showed that the average daily mass concentration of PM_2.5in summer was 73μg/m³, which was lower than the relevant Chinese air quality standards. While in winter, the average daily mass concentration was 111μg/m³, which was much higher than summer and the standards. The concentrations of OC and EC, and OC/EC ratio in winter were higher than in summer. And a linear correlation was identified between the OC and EC due to the same source apportionment. The secondary ions such as sulphate (SO₄^2-), nitrite (NO₃^-) and ammonium (NH₄⁺) were the most important compounds in the particles of this area, because they accounted for a large fraction of PM_2.5 especially in summer. The concentration of chloride ion (Cl^-) was increased in winter due to the coal combustion. The concentrations of Si, Ti, Fe, Zn and Al were in the range of 0.1~10μg/m³; Pb, Cu, Mn, Cr, Ba and Sb 10~10²ng/m³; V, Ni, Co, Mo and Cd 0.1~10ng/m³. The contents of all the elements were higher in winter than in summer. The results of the source apportionment showed that the major contributions of PM_2.5 were second sulfate, motor vehicle exhausts and second nitrite in summer, while coal combustion, motor vehicle exhausts and raise dust in winter.