杭州市不同高度大气PM2.5的污染特征研究

A study on pollution characteristics of atmospheric PM_(2.5) in different heights in Hangzhou

为研究杭州市大气PM_(2.5)的污染特征,评估本地污染源和外来污染源对PM_(2.5)的影响,于2013年10月10日至11月2日对杭州市主城区两个不同高度的采样点进行采样,并定量分析大气PM_(2.5)中的化学成分。结果表明,采样期间20、84m高度的大气PM_(2.5)日均质量浓度分别为(80.5±28.9)、(80.3±29.3)μg/m3,不同高度的PM_(2.5)浓度及其化学成分无明显差异;PM_(2.5)主要成分质量分数按如下排序:SO_4^(2-)>有机碳(OC)>NO_3^->NH_4^+>元素碳(EC);大气PM_(2.5)中二次粒子SO_4^(2-)、NO_3^-、NH_4^+平均质量浓度总和约为39.0μg/m3,二次转化是杭州市大气PM_(2.5)的主要来源,SO_4^(2-)、NO_3^-、NH_4^+贡献率为48%左右;20、84 m高度的大气PM_(2.5)中OC分别为(15.6±5.1)、(14.8±4.7)μg/m3,EC分别为(4.6±1.8)、(4.6±1.6)μg/m3,OC/EC(质量比)约为3.3。采样期间,杭州市大气PM_(2.5)在近地面垂直方向上分布较为均匀,表明杭州市大气PM_(2.5)受外来污染源的影响较小。而在本地污染源中,杭州市大气PM_(2.5)主要受到生物质燃烧、机动车尾气、燃煤和餐饮油烟等来源的影响,地面扬尘的作用不明显。

In order to study the pollution characteristics of PM2.5 in Hangzhou and the effects of local and external pollution sources on PM2.5,the samples were collected by the small-volume samplers at different heights （ 2 0 m in Zhaohui site and 84 m in Kexie site） in Hangzhou from October 10th to November 2rd,2013. The concentrations and chemical compositions of PM2.5 were obtained. The results showed that mass concentrations of PM2.5 at 20 and 84 m were （80.5 ± 28.9） and （80.3 ± 29.3）μg/m^3 , respectively. No significant difference appeared in PM2.5 concentrations and their chemical compositions between different heights. The material balance analysis indicated that the mass fractions of major chemical species in PM2.5 were in the following order： SO4 〉 OC〉 NO3 〉 NH4^±〉 EC. Secondary ions of SO4 ,NO3 and NH4^± were the major ions, totally contributing 39.0 μg/m^3 to the PM2 .5 . Mass concentrations of OC at 20 and 84 m were （15.6 ± 5.1） and （14.8 ± 4.7） μg/m^3 , and those of EC （4 .6 ± 1 .8 ） and （4 . 6 ± 1 . 6 ）μg/m^3. OC/EC （mass fraction） was 3.3. The atmospheric PM2 5 in Hangzhou was evenly distributed, suggesting that the external sources of PM2.5 in Hangzhou was little. In the local sources,the atmospheric PM2.5 in Hangzhou was mainly influenced by biomass burning, vehicle exhaust, coal and cooking fumes, etc. The impact of dust on atmospheric PM2 5 was not obvious.