北京冬季雾霾天气下颗粒物及其化学组分的粒径分布特征研究

Characteristics of mass and chemical species size distributions of particulate matter during haze pollution in the winter in Beijing

为认识雾霾天气下颗粒物及其化学组分的粒径分布特征,利用13级低压撞击采样器采集北京城区冬季一次典型雾霾天气下的大气颗粒物,采用离子色谱和元素碳/有机碳分析仪分析了PM10中不同粒径的水溶性离子、元素碳和有机碳组分,获得了颗粒物及其化学成分的粒径分布特征.结果表明,不同天气下颗粒物质量浓度大小为:雾霾>多云>雪天>晴天,4种天气下PM2.5/PM10均大于74%,说明冬季污染主要是由细颗粒物污染引起.SO2-4、NO-3、NH+4、Cl-、Ca2+是最主要的水溶性离子.SO2-4、NO-3、NH+4在0.76μm出现单峰;Ca2+和Mg2+在0.31和5.13~8.09μm出现双峰,主要分布在粗模态;Cl-和K+在0.76和5.13μm出现双峰,主要分布在细粒径段.OC、EC也富集于细粒子,显单峰结构.随污染程度增加,二次无机离子及碳组分浓度均显著增加,SO2、NO2的表观转化率(SOR、NOR)以及OC/EC在灰霾期间都远远高于二级良,可见二次无机源及有机源是污染的主要来源.在空气流动性差的灰霾持续期,机动车尾气排放的EC等一次污染物贡献增加.分析NO-3/SO2-4的粒径分布发现,机动车尾气对爱根核模态及凝结模态的亚微米模态(<1μm)贡献大于固定源,机动车尾气排放对大气污染的贡献已十分凸显.此外,燃煤污染的区域输送对污染的形成也有重要贡献,重污染期间土壤扬尘的贡献较小.

To investigate characteristics of chemical species and their size distributions of particulate matters( PM) during the haze events,the PM samples were collected by a Dekati low pressure impactor during the winter haze / fog events in Beijing. The concentrations of water-soluble ions,and organic and elemental carbon were quantified. The PM mass concentrations under different weather conditions were compared. The ratio of PM2.5/ PM10 was over 74% in all weather conditions,implying that fine particles predominated over the severe haze pollution. SO2-4,NO-3,NH+4,Cl-,and Ca2+were the most abundant water-soluble ions. Distinct size distributions were found for different ions. SO2-4,NO-3,and NH+4peaked at 0.76 μm. Ca2+and Mg2+both peaked at 0.31 μm and 5.13 ~ 8.09 μm,but were mainly in the coarse mode. Cl-and K+both peaked at 0.76 μm and 5.13 μm,but were mainly in the fine mode. OM and EC also dominated in the fine mode. The concentrations of secondary inorganic ions and carbonaceous matters increased apparentlyduring haze pollution. Meanwhile,SOR,NOR,and OC / EC were higher during the haze events,suggesting that the formation of secondary inorganic and organic aerosols played a dominant role for haze pollution. During the haze extention period,the contribution of primary emissions from vehicle exhaust increased. For submicron aerosols,the contribution from mobile sources was greater than stationary sources based on the analysis of the size distributions for the ratio of NO-3to SO2-4concentrations. Regional transport of coal-burning pollutants played a significant role in the formation of heavy pollution,while dust had small effects.