长沙市夏秋季VOCs特征及在臭氧生成中的作用研究

Characteristics of ambient VOCs and their role in ozone formation during summer and autumn in Changsha

为了解我国中部地区VOCs污染特征及对臭氧(O_(3))生成的影响,于2021年5—10月在湖南省长沙市主城区开展了VOCs在线监测,共计监测116种组分.测量结果显示:观测期间总VOCs平均体积分数为(23.09±9.97)×10^(-9),VOCs月均浓度呈“U”型变化,7月最低,10月最高,而VOCs日变化呈典型双峰型,受人为源活动影响显著;长沙市VOCs化学组成以含氧挥发性有机物(OVOCs)为主,其次是烷烃和卤代烃,而对臭氧生成潜势(OFP)有较大贡献的主要是OVOCs和芳香烃,二者合计占比达到68.3%,其中丙醛、乙醛、间/对-二甲苯、乙烯和甲苯是关键活性物种.OBM(基于观测的模型)模拟结果显示:长沙市5月、8月和9月臭氧生成属于协同控制区,6—7月属于VOCs控制区,而10月处于NO_(x)控制区.人为源VOCs中削减高碳醛类、烯烃类、烷烃类对臭氧防控最为有效.

The ground-level ozone(O_(3))concentration is continuously increasing in middle areas of China during recent years.Volatile organic compounds(VOCs)are important precursors in photochemical production of ozone,which is of great significance for O_(3) prevention and control.In order to clarify the characteristics of ambient VOCs and their role in ozone formation in China s middle areas,we conducted online VOCs observation in Changsha from May to October in 2021,monitoring 116 VOC species in total.The mean value of mixing ratios for measured VOCs was(23.09±9.97)×10^(-9).Monthly average concentration of VOCs in Changsha showed a“U”shape,with the lowest in July and the highest in October,while the diurnal variation of VOCs concentration showed a bimodal pattern,indicating the influence of human activities.OVOCs were the most abundant component of VOCs,followed by alkane and halo carbon.However,OVOCs and aromatics were the two largest contributors to ozone formation potential(OFP),with a cumulative contribution of 68.3%.Propionaldehyde,acetaldehyde,m/p-xylene,ethylene and toluene were the most important VOCs species to OFP.The observation-based model(OBM)showed that O_(3) formation in Changsha was in a transition regime in May,August,September and in a VOCs-limited regime from June to July,while in a NO_(x)-limited regime in October.For the anthropogenic VOCs,ALDP,OLEP and PARP should be given priority in emission control measures.