上海市城区春节和“五一”节期间大气挥发性有机物的组成特征

挥发性有机物(VOCs)是对流层臭氧和二次有机气溶胶等二次污染生成过程的关键前体物.研究VOCs的浓度水平、组成特征和反应活性对揭示复合型大气污染的形成机制具有重要意义.本研究利用在线气相-氢离子火焰法测量了2009年春节和"五一"节期间上海市城区大气中56种VOCs.结果表明,上海市城区大气受机动车尾气排放源影响明显,VOCs浓度日变化特征呈双峰状,与上下班交通高峰基本吻合.大气中VOCs平均体积分数为(28.39±18.35)×10-9;各组分百分含量依次为:烷烃46.6%,芳香烃27.0%,烯烃15.1%,乙炔11.2%.用OH消耗速率和臭氧生成潜势(OFP)评估了VOCs大气化学反应活性,结果表明,上海市城区大气VOCs化学反应活性与VOCs体积浓度相关性良好;VOCs活性与乙烯相当,平均化学反应活性较强;OH消耗速率贡献最大的物种是烯烃51.2%和芳香烃31.8%;OFP贡献最大的物种是芳香烃53.4%和烯烃30.2%;对臭氧生成贡献最大的关键活性物种为丙烯、乙烯、甲苯、二甲苯以及丁烯类物质.

Characterization of volatile organic compounds (VOCs) around the Chinese Spring Festival and International Labour Day in the urban area of Shanghai,China

Volatile organic compounds(VOCs) have been recognized as important precursors in the production of tropospheric ozone and secondary organic aerosol.Studies on the concentration,speciation,and chemical reactivity of VOCs are necessary to further understand the formation process of atmospheric pollution.Gas chromatography with flame ionization detection(GC/FID) was employed to monitor VOCs in the urban area of Shanghai during Chinese Spring Festival(from Jan.19th to Feb.7th,2009) and the International Labor Day(from Apr.23rd to Jun.5th,2009) and 56 kinds of VOCs were detected.Two peaks in the morning and evening were observed in the diurnal profile of VOCs,consistent with the rush hours,suggesting that the atmosphere in the urban area of Shanghai was mainly affected by vehicle emissions.The average mixing ratio of VOCs in the urban area of Shanghai was(28.39 ± 18.35) × 10^-9.The major components of the VOCs were alkanes(46.6%),aromatics(27.0%),alkenes(15.1%),and acetylene(11.2%).The OHradical loss rate and the ozone formation potential were applied to access the chemical reactivity of VOCs.There was a significantly positive correlation between the mixing ratio and the chemical reactivity.The chemical reactivity of the atmosphere in the urban area of Shanghai was similar to that of ethylene.The alkenes and aromatics were the dominant species for the chemical reactivity.For the OHradical loss rate,the alkenes andaromatics accounted for 51.2% and 31.8%,respectively;and for the ozone formation potential,they accounted for 30.2% and 53.4%,respectively.Considering individual compounds,propylene,ethylene,toluene,xylenes,and butenes were the most important contributors to ozone formation in the atmosphere in the urban area of Shanghai.