南京市PM2.1中有机碳和元素碳污染特征及影响因素

采用DRI Model 2001A热/光碳分析仪测定了2011年南京市区(南师)和郊区工业区(南化)大气气溶胶细粒子(PM2.1)中有机碳(OC)和元素碳(EC)的含量,并对两地的OC、EC污染特征进行了评价,分析了细粒子中含碳物质的来源.结果显示,在PM2.1中,南京市市区OC、EC的年平均浓度分别为12.79,3.18μg/m3,郊区工业区分别为13.44,3.74μg/m3,工业区污染更加严重.市区和工业区冬春季OC、EC含量较高且冬季OC、EC相关性较高,这与冬季燃煤量增加,并且受内陆西风及逆温的影响,污染物集中在南京市上空不易扩散有关;夏季两地OC、EC含量及相关性均达到最低,可能由于夏季降雨频繁,加上台风作用,稀释和清除了部分污染物.应用OC/EC比值法对市区和郊区工业区二次有机碳(SOC)含量进行了估算,两地均是夏季SOC占TOC比例最高,分别为46.63%、45.65%,SOC主要来自于光化学反应,可见在光照充裕、辐射强烈的夏季更加有助于SOC的生成.

Pollution characteristics and influencing factors of organic and elemental carbon in PM2.1 in Nanjing

The concentrations of organic carbon (OC) and elemental carbon (EC) in aerosol fine particles (PM2.1) collected in Nanjing Normal University representing urban area and in Nanjing College of Chemical Technology standing for suburban industrial area were analyzed using DRI Model 2001A Thermal Optical Carbon Analyzer. The pollution characteristics of OC and EC in the two sites were evaluated, and the sources of carbonaceous materials in PM2.1 were analyzed. The results showed that the annual average concentrations of OC and EC were 12.79μg/m3 and 3.18μg/m3 respectively in urban area, and 12.79μg/m3 and 3.18μg/m3 respectively in suburban industrial area, indicating that pollution in industrial area was more serious than in urban area. The concentrations of OC and EC in winter and spring were obviously higher compared with those in summer, either for urban area or for suburban industrial area, which was the same as the case of correlation between OC and EC. The higher concentrations of OC and EC in winter and spring were resulted from the increased coal combustion and the unfavorable transport conditions of air pollutants affected by inland west wind in Nanjing. However, in summer, some air pollutants could be diluted and removed via frequent rainfall and typhoon. For the urban and suburban areas, the ratio of second organic carbon (SOC) in total organic carbon (TOC), estimated by OC/EC ratio method, were 46.63% and 45.65% respectively, which was the highest in summer among the four seasons. This implies that high temperature and strong radiation were benefical to SOC generation through photochemical reaction.