上海市PM_(2.5)中含碳物质的特征和影响因素分析

为了解上海市大气细颗粒物(PM2.5)中含碳物质的浓度及其影响因素,于2007年12月～2008年12月间在上海市的市区(徐家汇)和工业区(宝山)采样点分别采集了130多个PM2.5样品,应用DRI碳分析仪采用IMPROVE-TOR方法测定了样品中的有机碳(OC)、元素碳(EC)的含量.结果显示,OC和EC的季节平均浓度值冬季最高,夏季最低.上海市市区采样点PM2.5中OC和EC的年平均浓度为8.10μg.m-3和3.91μg.m-3,而工业区为11.91μg.m-3和4.69μg.m-3,高于市区;OC/EC比值在市区和工业区分别为2.01和2.42.OC和EC在4个季节都有较强的相关性(R2为0.52～0.87),其中冬季的相关性最高(R2为0.87,0.80),春季最低(R2为0.52,0.58),这与春季时上海的风向多变、污染物来源复杂有关.应用OC/EC比值法对二次有机碳(SOC)的含量进行了估算,SOC的年平均浓度在市区和工业区分别为2.72和5.07μg.m-3,占OC含量的30%左右,SOC对OC的贡献率夏季最高(约40%),这与夏季温度高、光照强烈有利于光化学反应进行的情况一致.降水对OC和EC的浓度有较明显的影响,冬季无降水天气的OC和EC平均浓度是雨雪天气时的2倍以上,而夏季有降水和无降水天气时OC和EC的浓度没有明显区别,这可能与夏季降水发生时大气稳定度较高有关.降水天气时OC/EC及SOC/OC比值明显降低.

Characteristics and Influencing Factors of Carbonaceous Aerosols in PM2,5in Shanghai, China

Organic carbon (OC) and elemental carbon (EC) in PM2.5 samples collected in urban (Xujiahui) and industrial (Baoshan) areas in Shanghai during 2007-2008 were analyzed with a DRI carbon analyzer using IMPROVE-TOR protocol. The results showed that the seasonal average concentrations of OC and EC were highest in the winter and lowest in the summer. The annual average concentrations of OC and EC were 8.10 and 3.91 microg x m(-3) at the urban sampling site, and 11.91 and 4.69 microg x m(-3) in the industrial area. The annual average OC/EC ratios at the two sites were 2.01 and 2.42, respectively. Strong correlations (R2 0.52-0.87) between OC and EC were found in all seasons, with the highest correlation coefficients in the winter ( R2 0.87 and 0.80) and the lowest in the spring (R2 0.52 and 0.58), indicating that the pollutant sources in spring was more complicated due to the varying wind directions. The annual average concentrations of secondary organic carbon (SOC) were 2.72 and 5.07 microg x m(-3) at the urban and industrial sites, accounting for about 30% of the total OC. The contribution of SOC to OC was the highest (about 40%) in the summer, in accordance with the high temperature and strong solar radiation in the summer. It was also found that precipitation had significant impact on the concentrations of OC and EC, especially in the winter. The average concentrations during periods without precipitation were two times higher than that during periods with precipitation in the winter, whereas no significant difference was found between the concentrations of OC and EC in the periods with and without precipitation in the summer, possibly due to the more stable atmospheric conditions during the periods with precipitation in comparison with those without precipitation. The OC/EC and SOC/OC ratios decreased significantly during precipitation.