杭州无车日大气细颗粒物化学组成形成机制及光学特性

Chemical composition,formation mechanism and optical properties of atmospheric fine particles during the World Car Free Day in Hangzhou

在世界无车日期间对PM2.5化学组分、光学参数及气态污染物进行同步监测,评估机动车尾气排放对杭州市细颗粒物污染及能见度的影响.结果表明:管制期间NO2、NOx、CO和PM2.5浓度分别为45.0,50.8,1119,85.8μg/m3,比平日分别下降了17.5%、23.3%、20.6%和32.6%.管制期间PM2.5中OC、EC和二次无机组分浓度为8.58,4.29,25.95μg/m3,比管制前下降了13.8%、12.6%和15.7%,管制后则达到20.24,10.85,27.39μg/m3,上升了136.0%、152.7%和5.5%.管制期间较高的NO3-/PM2.5和NOR(0.15)表明PM2.5的形成更多受二次无机转化影响,管制后PM2.5中上升的OC、EC比例和较低的NOR(0.07)则说明PM2.5主要来自机动车排放的碳质组分的贡献.硫酸盐、硝酸盐、有机气溶胶和EC是最主要的消光组分,共解释了总消光系数的74.0%～89.7%.管制后,机动车排放的有机物和EC消光比例达到26.6%和24.6%,大气消光系数则达到438.7Mm-1,比管制期间上升了60.5%,表明机动车污染排放已成为影响杭州大气细颗粒物污染和能见度下降的重要因素.

Chemical components in PM2.5 and related optical parameters together with gaseous pollutants were simultaneously monitored during the World Car Free Day in Hangzhou to evaluate the influence of vehicle emissions on fine particle pollution and visibility. Concentrations of NO2, NOx, CO and PM2.5 were 45.0, 50.8, 1119 and 85.8μg/m^3 during control period with decrease of 17.5%, 23.3%, 20.6% and 32.6%, respectively, compared with the non-control period. Concentrations of OC, EC and secondary inorganic ions in PM2.5 were 8.58, 4.29 and 25.95μg/m^3 during control period, with corresponding decrease of 17.5%, 23.3%, 20.6% and 32.6%, respectively. While the species above increased to 20.24, 10.85 and 27.39μg/m^3 after the lifting of control measures, which increased by 136.0%, 152.7% and 5.5%, respectively. Higher NO3/PM2.5 and NOR ratios were observed during the control period, indicating PM2.5 was more dominated by secondary inorganic transformation. While the contribution of OC and EC to PM2.5 gradually dominated after control with the lower NOR （0.07）, suggesting that PM2.5 was mainly derived from carbonaceous aerosol emitted via vehicle emissions. Sulfates, nitrates, organic aerosol, and EC were the major extinction components and they could explain approximately 74.0%-89.7% of total extinction coefficient. The total extinction coefficient increased 60.5% to an extreme value of 438.7Mm-1 after the control period with 26.6% and 24.6% of the light extinction attributed to organic aerosol and EC, respectively. This study highlighted that vehicle emissions had a significant influence on fine particle pollution and visibility impairment in Hangzhou.