武汉市城区大气PM_(2.5)的碳组分与源解析

Carbonaceous species composition and source apportionment of PM_(2.5) in urban atmosphere of Wuhan

大气细颗粒物(PM2.5)和碳组分(OC,EC)是影响大气能见度、气候变化以及人体健康的重要污染物,研究大气颗粒物及其中碳组分的污染特征及各类典型污染源对大气细颗粒物及碳组分的贡献,对于认识区域和城市大气污染状况,控制细颗粒物的污染,具有重要意义。2011年7月至2012年2月,利用大流量PM2.5采样器采集武汉市大气细颗粒物样品并对其碳组分进行测定。武汉市城区大气中PM2.5、OC和EC的质量浓度平均值分别为(127±48.7)、(19.4±10.5)和(2.9±1.48)μg·m-3。其PM2.5的浓度处于我国主要城市的中等偏高水平,而OC、EC的浓度则属中等偏下水平,但均高于国外城市。武汉市大气PM2.5质量浓度的季节性变化呈现出秋季>冬季>夏季的趋势,是气象因素和污染源排放综合影响的结果。OC浓度和EC浓度具有较好的相关性(r2=0.69),表明二者存在来源联系。OC/EC的比值为6.7,指示武汉市大气中OC和EC的来源受汽车尾气排放和生物质燃烧的共同影响。SOA的平均质量浓度值为12.5μg·m-3约占PM2.5平均质量浓度的9.8%,表明SOA对武汉市城区大气PM2.5具有重要贡献。结合PM2.5所含的水溶性离子、微量元素组成,利用正矩阵因子分析(PMF)模型对武汉市城区大气PM2.5来源进行解析,结果表明,其主要来源及贡献率分别为机动车源(27.1%)、二次硫酸盐和硝酸盐(26.8%)、工厂排放(26.4%)和生物质燃烧(19.6%)。

Fine particles （PM2.5） and carbonaceous aerosol （OC, EC） are important pollutants due to their adverse effects on visibility, climate change, and human health. To identify the regional pollution condition and develop effective control strategies s to manage and maintain the urban air quality, it is important to study the characteristics of fine particles and carbonaceous aerosol and the relative contributions of typical emission sources to fine particles and carbonaceous aerosol. Wuhan city is a highly industrialized city in Central China. 24 hrs air samples were collected consecutively by a Hi-Volume PM2.5 air sampler every three days from July 2011 to February 2012, to determine the carbonaceous species compositions and potential sources of PM2.5 in urban atmosphere of Wuhan. The average concentrations of PM2.~, OC and EC in the urban air were （127.1±48.7）, （19.4±10.5） and （2.9±1.48） μg·m-3, respectively. The concentration of PM2.5 was relatively higher compared to other major cities in China, while the OC and EC concentrations were lower. However, the concentrations of PM2.5, OC and EC were much higher than reported values of cities in other countries in the world. The PM2.5 concentrations showed the highest in autumn, followed by winter and spring due to the combined effects of meteorological factors and source emissions. A significant correlations （r2=0.69） between OC and EC was found in the PM2.5 of the urban air, indicating potential similar OC and EC sources. The average ratio of OC/EC was 6.7, suggesting that the main sources of OC and EC were vehicle emission and biomass burning. Average level of secondary organic aerosol （SOA） was 12.5 μg·m-3, accounting for 9.8% of PM2.s concentrations. The result of positive matrix factor （PMF） analysis suggested four source categories had contributed to the PM2.5 in the urban air, i.e. vehicle emission （27.1%）, secondary sulfate and nitrate aerosol （26.8%）, industrial emission （26.4%）, and biomass burning emission （19.6%）, respectively.