上海市某化工区夏季典型光化学过程VOCs特征及活性研究

本研究基于夏季某化工区外5 km处观测点O_3及VOCs在线观测结果,分析了VOCs污染及光化学反应活性特征.结果显示,西南风向的VOCs平均体积分数为63.9×10~(-9)±28.6×10~(-9),高于其他风向42%(45.0×10~(-9)±28.0×10~(-9)),不同主导风向下的VOCs特征具有一定的相似性,均以烯烃、卤代烃和烷烃为主要组分,说明化工园区局地排放和累积对观测点VOCs影响较大.主要VOCs物种的日变化都具有夜间体积分数累积增多,白天逐步降低的特征;但是异戊二烯呈现日变化较小的特征,显示其受到人为源和天然源的双重影响.西南风向的臭氧生成潜势(Ozone Formation Potential,OFP)为242.1×10~(-9),远高于其他风向的OFP(174.1×10~(-9)),而平均MIR(Maximum Increment Reactivity)则较为接近;烯烃在VOCs总OFP中的贡献比例均在70%以上,其次是芳香烃.使用乙苯和间/对二甲苯的比值来表征气团光化学反应进程,计算得到观测点西南风向VOCs消耗量为(51.7×10~(-9)±38.8×10~(-9)),烯烃和卤代烃是最主要VOCs消耗组分.

Characteristics and chemical reactivity of VOCs during a typical photochemical episode in summer at a chemical industrial area

The concentration, speciation and photochemistry reactivity of VOCs at a site 5 km southeast of a chemical industrial area in summer were continuously measured and analyzed. The results showed that the mixing ratio of VOCs was (63.9×10^-9±28.6×10^-9) under southwesterly wind, higher than 45.0×10^-9±28.0×10^-9 under the other wind directions. VOCs characteristics were similar under different wind directions, mainly consisting of alkenes, halogenated hydrocarbons and alkanes. Most VOCs species exhibited diurnal variations with increased concentrations in nighttime and reduced concentrations in daytime. The diurnal variation of isoprene was less significant, indicating that its sources could be derived from both anthropogenic and biogenic emissions. The OFP (Ozone Formation Potential) of VOCs was 242.1×10^-9 under southwesterly wind, much higher than 174.1×10^-9 under other wind directions. By contrast, the average values of the MIR (Maximum Increment Reactivity) were comparable under different wind directions. Alkenes contributed over 70% to OFP, followed by aromatic hydrocarbons. The ratio of ethylbenzene to m/p-xylene was used as an indicator for photochemical processing. The chemical loss of VOCs was 51.7×10^-9±38.8×10^-9 under southwesterly wind. Alkenes and halogenated hydrocarbons contributed the most to the chemical loss of VOCs.