太原市冬季灰霾期间大气细颗粒物化学成分特征

研究了太原市灰霾发生期间大气PM2.5质量浓度和化学成分变化规律.采样时间为2011年12月27日16:00~2012年1月3日04:00,使用TH-150C中流量大气PM2.5采样器(采样膜为直径90mm的石英纤维滤膜)在山西大学环境科学研究所5层楼顶每隔4h采样一次,得到灰霾样品34个,非灰霾样品5个.采样期间对大气PM2.5质量浓度进行实时监测.结果表明:灰霾期间(初起、进展、鼎盛、减弱4个阶段)大气PM2.5平均浓度达(692±272)μg/m3,是非灰霾期间(即灰霾消失阶段) (54±12)μg/m3的12.8倍;在灰霾发生期间,大气PM2.5中Hg、Pb、As等重金属污染物、OC以及水溶性无机离子SO42-、NO3－、NH4+、K+、Cl－、F－浓度呈现相似的变化趋势,即在灰霾初起、进展阶段不断增加,在灰霾鼎盛期达到最大值,随后随着灰霾的减弱和消失而不断下降,最终降到一个较低的水平;而与燃煤关系不大的Zn元素、Ca2+、Mg2+等在灰霾各个时期浓度变化较小.以上结果说明冬季灰霾天气使太原市大气PM2.5浓度显著上升,并增加PM2.5中重金属、有机物和二次气溶胶含量,使其化学成分发生改变,同时也反映了冬季燃煤和生物质燃烧对太原市大气PM2.5的化学组成影响大于交通源和土壤扬尘.

Investigation of chemical compositions of atmospheric fine particles during a wintertime haze episode in Taiyuan City

The aim of this study is to investigate the mass concentration and chemical compositions of atmospheric fine particulate matter (PM2.5) at different stage during a typical urban haze episode in Taiyuan, Shanxi Province, China. The PM2.5 samples were collected every four hours at a five-story building in Shanxi University using a medium-volume PM2.5 impactor at a flow rate of 100L/min from 4p.m. on Dec. 27, 2011 to 4a.m. on Jan. 3, 2012 when a typical haze event occurred. Overall 39 samples were obtained at different haze stages, namely infancy, development, peak, decay, and disappearance. The mass concentrations of ambient PM2.5 were measured and the heavy metals, water-soluble ions, and organic carbon (OC) and elemental carbon (EC) in all samples were detected, respectively. Results showed that during the haze event, the mean concentration of ambient PM2.5 was (692±272)μg/m3 (about 12.8 times higher than that when haze disappeared) and the levels of OC, Hg, As, Pb, NH4+, SO42－, NO3－, Cl－, F－, and K+ were significantly elevated while the levels of Zn, Ca2+, and Mg2+ were increased slightly. It indicated that secondary aerosols and organic matter had been formed abundantly and suggested that coal and biomass combustion contributed more to the haze formation than traffic vehicles, soil, and construction dust. It was concluded that coal and biomass burning in winter in Taiyuan was the main factor responsible for the elevation of atmospheric PM2.5 concentration and made more influences on modification of PM2.5 in compositions when haze occurred.