北京大气PM2.5中微量元素的浓度变化特征与来源

为了解北京大气细粒子中微量元素的污染水平和来源,在车公庄和清华园进行了连续1年、每周1次的PM_2.5采样和全样品分析.微量元素浓度的周变化大,尤以冬季为甚,相邻2周最大相差达1.6倍;但除冬季的平均浓度较高之外,其季节变化并不显著.微量元素的富集因子在春季最低,反映了频繁发生的沙尘天气的影响.Se、Br和Pb的浓度比来自于北京A层土壤中的含量要高出约1000～8000倍,表明它们主要来自于人为污染.其中Se的富集度最高,反映了北京细粒子来自于燃煤污染的特征.Pb的年均浓度(0.31μg·m^-3)虽然未超过WHO的年均标准,但与洛杉矶和布里斯班相比处于较高的水平;与Br、Se的比较分析表明,燃煤可能是Pb除机动车排放之外的另一个重要来源.

Characteristics and Sources of Trace Elements in Ambient PM2.5 in Beijing

To understand concentration levels and sources of trace elements in PM2.5(particulate matter with aerodynamic diameters less than 2.5 microns) concentration and composition in the ambient air of Beijing, weekly samples were simultaneously collected for one year in Chegongzhuang and Qinghuayuan. Trace elements exhibited similar significant weekly variations. The strongest weekly shift occurred in winter, which reached as high as a factor of 1.6 for two consecutive weeks. No obvious seasonal pattern was found for trace elements except for that their average concentrations were much higher in winter. The EFs of trace elements were lowest in spring, probably due to frequent dust storms resulting in reduced contribution of anthropogenic sources and increased contribution of soil dust. The ambient concentrations of Se, Br, and Pb were about 1000-8000 times higher than those expected from the crustal soil in Beijing. Se was most enriched in PM2.5, reflecting the characteristics of fine particles from coal burning in Beijing. The annual mean concentration of Pb of 0.31 microgram.m-3 did not exceeded the WHO annual standard, but was at very high level compared to those measured in Los Angles and Brisbane. Comparison analysis of Pb with Br and Se shows that coal burning is probably another major source of Pb in PM2.5 other than vehicle emission.