南京北郊早春霾污染过程及硫酸盐形成研究

Investigation of haze pollution and the formation of sulfate in early spring in northern suburbs of Nanjing

对2016年3月南京北郊PM_(2.5)进行采样分析,通过样品中的水溶性离子(Na^+、NH_4^+、K^+、Ca^(2+)、Mg^(2+)、Cl^-、NO_3^-、SO_4^(2-))和碳质组分(OC、EC),探讨霾污染的特征、来源及硫酸盐形成机制.结果表明,采样期间南京北郊PM_(2.5)平均浓度(103.22±48.5)μg/m^3.污染天二次硫酸盐的形成与NO_2对SO_2的氧化相关性较强,而O_3的氧化作用影响较小;清洁天则相反.污染天,具有酸度缓冲作用的矿物粉尘使得气溶胶颗粒物总体呈弱碱性,而碱性环境下又更利于二次硫酸盐的形成.南京北郊早春二次污染严重,SOC主要由大气中碳氢化合物与O_3发生光氧化反应生成.污染天主要排放源为机动车尾气排放,其次是生物质和煤炭燃烧;清洁天主要排放源为煤炭燃烧和扬尘,机动车尾气影响较小.

To investigate the characteristics and sources of haze pollution and the formation mechanism of sulfate the northern suburb of Nanjing,PM2.5 samples were collected in March 2016,and the concentrations of water-soluble ions(Na^+,NH4^+,K^+,Ca^2+,Mg^2+,Cl^-,NO3^-and SO4^2-)and carbonaceous components(OE and EC)were measured.The average concentration of PM2.5 during the sampling period was(103.22±48.5)μg/m3.In contrast to clean days,the formation of secondary sulphate in the polluted days was much stronger related to the oxidation of SO2 by NO2 than the oxidation with O3.The mineral dust could serve as buffered agent and kept the aerosol in weakly alkaline state during polluted days,which was preferred for the secondary sulfate formation.In this work,the secondary organic carbon(SOC)in PM2.5 was mainly formed from the photooxidation of hydrocarbons with O3.The main sources of PM2.5 components in polluted days were motor vehicle emissions,followed by biomass and coal combustion.In clean days,the bulk components were mainly contributed by coal combustion and dust emission with little influences from motor vehicle exhaust.