杭州市大气颗粒物消光组分的粒径分布特征研究

2010年8月在杭州市朝晖、云栖、杭钢和下沙4个点位采集了不同粒径大气颗粒物样品,并对其主要消光组分的粒径分布特征进行了分析,包括SO42-、NO3-、NH4+、OC和EC等.同时在朝晖点位对多种气态污染物和多个气象要素进行了同步观测,以评估杭州市能见度下降的影响因素.结果表明:PM2.5、RH、SO2和NO2均与能见度呈一定负相关关系.4个监测点位颗粒物浓度变化均呈双峰型,峰值出现在0.4~0.7μm和9.0~10μm粒径段.以3.3μm为粗细颗粒的分界线,不同监测点位PM10中粗、细颗粒所占比例均等.水溶性离子消光组分的浓度大小顺序为:SO42->NH4+>NO3-. SO42-、NO3-和NH4+均显单峰结构,SO42-和NH4+的峰值出现在0.4~1.1μm的粒径段,NO3-峰值出现在5.8~10μm粒径段.OC显单峰结构,峰值出现在0.4~0.7μm粒径段;EC显双峰结构,峰值出现在0.4~0.7μm和2.1~3.3μm范围内.因而,要解决杭州的能见度问题,应减少细颗粒物,尤其是粒径<1.1μm的颗粒物的污染. NO3-、SO42-、OC和EC对杭州市颗粒物消光能力相对贡献率之比为2.2%:13.7%:29.8%:43.8%.因此要有效控制杭州市大气能见度的降低趋势, 首要的就是控制EC的主要排放源,即机动车尾气的排放.

Size distributions of extinction components in Hangzhou atmospheric particles.

Samples of atmospheric particles were collected in August at four monitoring stations(Yunqi,Zhaohui,Hanggang,Xiasha)in Hangzhou City.Size distributions of the main extinction components were quantified,including SO42-,NO3-,NH4+,OC and EC.Meanwhile,a wide range of gaseous pollutants and meteorological elements were observed simultaneously on Zhaohui station in order to assess the influence factors of visibility degradation.PM2.5,RH,SO2 and NO2 were negatively correlated with visibility.The peaks of particles concentration appeared in the size of 0.4~0.7μm and 9.0~10μm.SO42-,NO3-,NH4+ and OC exhibited the single modal.The peaks of SO42-and NH4+ were in the size of 0.4~1.1μm,while the peak of NO3-appeared in the size of 5.8~10μm and the peak of OC was in 0.4~0.7μm.EC exhibited the bi-modal and the peaks were in 0.4~0.7μm and 2.1~3.3μm.In order to solve the visibility problem of Hangzhou,the fine particles,especially the size that less than 1.1μm should be reduced primarily.EC was the dominant extinction component in this study and the pollution sources of EC,such as vehicle exhausts should be primarily controlled in Hangzhou to improve the visibility and reduce the haze days.