南京北郊大气气溶胶中水溶性有机碳(WSOC)的污染特征

摘要

对南京北郊2014年1~11月的大气气溶胶进行采样分析,研究了其中水溶性有机碳(WSOC)的污染特征.WSOC在PM2.5,PM10和TSP中的年平均浓度分别为5.90±3.38、6.93±3.79、7.34±3.91μg/m3,80%以上的WSOC集中在PM2.5中.PM2.5中WSOC冬季浓度最高,夏季浓度次之,与冬夏季较强的二次转化过程有关;春季粗粒径段浓度较高,受到土壤来源颗粒物的影响;秋季浓度最低.春秋季PM2.5中WSOC浓度夜晚高于白天,受夜间不利扩散条件的影响较大;但冬夏季却是白天高于夜晚,与白天较强的光化学反应有关.降水对各个粒径的WSOC都有清除作用,对PM2.5的清除效率最高;四个季节比较,夏季清除效率最高,达到54.9%.霾发生时,随着霾污染等级的加重,PM2.5中WSOC浓度逐渐增加,从非霾天的3.84μg/m3升高到重度霾天的11.23μg/m3,增加了近4倍,在细粒子中的比例也增大,霾天稳定的天气条件有利于二次有机污染物的生成.%The atmospheric particles collected during January to November 2014 at a northern suburban site of Nanjing was analyzed and focused on the characterization of water-soluble organic carbon (WSOC) in the samples. The annual mean concentrations of WSOC in PM2.5, PM10 and TSP were determined to be 5.90 ± 3.38, 6.93 ± 3.79, 7.34 ± 3.91μg /m3 respectively, and more than 80% of WSOC was concentrated in PM2.5 samples. The WSOC concentration in PM2.5 was highest in winter following by summer, which was likely related to the strong secondary production during these two seasons; the WSOC concentration was relatively higher in coarse particles during spring, likely due to influences from soil-derived particles; in autumn, the WSOC concentration was the lowest. During spring and autumn, it was also found that the PM2.5 WSOC concentration was higher during nighttime, probably owing to the atmospheric conditions during nighttime unfavorable for pollutant dispersion; on the other hand, the concentration was higher during daytime in winter and summer, suggesting the stronger photochemical production of WSOC during these two seasons. The scavenging effect due to precipitation influenced the WSOC concentrations in particles across all size ranges, but was most efficient for PM2.5, which can reach an maximum of 54.9% during summer. The PM2.5 WSOC concentration also increased significantly with the increase of pollution level, on average nearly 4times from 3.84μg/m3 in non-hazy days to 11.23μg/m3 in heavily polluted days; the mass fraction of WSOC in fine mode particles increased in hazy days as well, suggesting that stagnant atmospheric conditions during hazy days promoted the formation of secondary organic pollutants.