唐山市大气PM2.5 季节污染特征及来源分析

Seasonal Characteristics and Sources of PM2.5 in Tangshan

为深入了解唐山市大气PM2.5污染成因与来源,采用在线观测设备于2017年9月1日—2018年8月31日连续监测了唐山市PM2.5及其水溶性离子和碳质组分(OC、EC)的质量浓度变化,为大气污染防治提供决策依据。结果表明,监测期间PM2.5日均质量浓度为14—310μg·m−3,平均值为58.9μg·m−3,监测期间日均浓度超标率为22%。唐山市PM2.5浓度季节变化特征为:冬季(63μg·m−3)>秋季(61μg·m−3)>春季(59μg·m−3)>夏季(45μg·m−3)。PM2.5中Fe含量比例高于Ca、Zn和Pb;OC和EC质量浓度比例冬季高于其他3个季节;水溶性离子以SO42−、NO3−和NH4+为主,春、夏、秋、冬季总浓度占PM2.5浓度的比例分别为61.2%、79.6%、54.15%、42.9%;NH4+浓度夏季最高,冬季最低,可能由于夏季NH3挥发释放相对较高,且空气相对湿度较大,NH3通过气-液非均相反应产生较多的NH4+。PMF结果表明,燃煤、燃油、机动车尾气和二次反应是唐山PM2.5的主要来源。后向轨迹聚类结果表明,夏季气团大部分主要来自相对清洁的内陆地区和海洋地区;春季和秋季气团主要来自中东地区的长程传输和山东西南部地区的短程传输;冬季气团主要由相对清洁的地区经长程传输过来,而唐山市冬季PM2.5污染最严重,一定程度反映了冬季受本地污染排放的影响。

To understand the characteristics and sources of PM2.5 in Tangshan,the mass concentration of PM2.5 and its water-soluble ions,trace metals and carbon components including organic carbon(OC)and element carbon(EC)were monitored continuously from September 1,2017 to August 31,2018.Results showed that the daily average concentration of PM2.5 during the monitoring period ranged from 14 to 310μg·m−3 with the mean value of 58.9μg·m−3.The over standard rate of daily average concentration was 22%.The highest PM2.5 level was observed in winter(63μg·m−3),followed by autumn(61μg·m−3),spring(59μg·m−3),and summer(45μg·m−3).The proportion of Fe in PM2.5 was higher than that of Ca,Zn and Pb.The proportion of OC and EC in winter was higher than that in other seasons.SO42−,NO3−and NH4+were the three main water-soluble ion components,which contributed to 61.2%,79.6%,54.2%and 42.9%of the PM2.5 concentration,in spring,summer,autumn and winter,respectively.The concentration of NH4+was highest in summer whereas lowest in winter,probably due to the relatively high release of NH3 in summer and the relative humidity.The PMF analysis results showed that the main sources of PM2.5 in Tangshan were coal and oil combustion,vehicle exhaust and secondary reactions.Backward trajectories showed that the air masses in summer were mainly originated from clean inland and oceanic areas,and the air masses in spring and autumn came from the Middle East through long-distance transport and southwest of Shandong Province.The air masses in winter were originated from clean areas through long-distance transport.The highest PM2.5 concentration in winter suggested that the emissions caused by local heating activities should contribute significantly to air pollution in winter in Tangshan.