上海城区典型污染过程VOCs特征及臭氧潜势分析

Characteristics of Ambient VOCs and Their Role in O_3 Formation:A Typical Air Pollution Episode in Shanghai Urban Area

利用在线气相色谱-氢火焰离子化(GC-FID)监测系统对上海市城区典型污染前、污染中和污染后的55种挥发性有机物(VOCs)进行了自动连续监测,分析了各个阶段VOCs(C2～C12)体积分数、物种变化特征.结果表明上海市城区典型污染前VOCs平均体积分数为27×10-9;污染中VOCs体积分数迅速增加,比污染前高3倍,达到87×10-9;具体以烷烃最高(35.2×10-9)、芳香烃次之(30.0×10-9)、烯烃最低(21.6×10-9);用最大臭氧生成潜势量(ΦOFP)对不同污染阶段污染VOCs大气活性进行了评估,结果表明不同污染阶段VOCs的ΦOFP均呈现污染前<污染后<污染中的变化特征.污染前期的ΦOFP依次是芳香烃(53.0%)>烯烃(36.1%)>烷烃(11.7%);污染中期的ΦOFP依次是芳香烃(54.7%)>烯烃(36.7%)>烷烃(9.8%);污染后期ΦOFP则依次是烯烃(52.7%)>芳香烃(36.0%)>烷烃(13.2%).具体关键活性物种主要包括甲苯、间、对二甲苯、1,3-丁二烯、乙烯、丙烯等芳香烃和烯烃物种,具体以烯烃C2～C4为主,芳香烃C6～C8为主.不同污染阶段O3与ΦOFP之间存在典型的非线性负相关关系,并且ΦOFP转化为O3的量均小于20%,说明臭氧浓度仍有很大上升空间;这对定量评估大气中VOCs对臭氧的影响具有重要意义.

The concentration,speciation and chemical reactivity of ambient volatile organic compounds（VOCs） in shanghai city were analyzed and measured by using online gas chromatography with flame ionization detection systems（GC-FID）during a typical air pollution episode（from Oct.30th to Nov.2nd,2010） and 55 kinds of VOCs were detected.The results show that averaged concentrations of VOCs was 27×10-9 before the episode,and then dramatically increased by 3 times（87 ×10-9）in the episode than the former,the main components were alkanes（35.2 ×10-9）,aromatics（30.0 ×10-9）,alkenes（21.6 ×10-9）.Furthermore,the maximum ozone formation potential（ΦOFP） is analyzed and showed that ΦOFP（in the episode） ΦOFP（after the episode） ΦOFP（before the episode）.Before the episode,the percent of ΦOFP for aromatics 53.0%,alkenes 36.1% and alkanes 11.7%;in the episode,the percent of ΦOFP for aromatics 54.7%,alkenes 36.7% and alkanes 9.8%;after the episode,the percent of ΦOFP for alkenes 52.7%,aromatics 36.0%and alkanes 13.2%.Alkenes（C2-C4）and aromatics（C6-C8）are the main components for the ozone formation,namely toluene,m,p-xylene,1,3-butadiene,propene,ethene et al.In addition,the relationship is negative and nonlinear between the O3 and ΦOFP.And efficiencies of ΦOFP formed into O3 are below 20.0% in different stage of episode.This is very important and meaningful for the quantitative evaluate the influence of VOCs towards O3.