上海市大气挥发性有机物化学消耗与臭氧生成的关系

本研究基于夏季上海3个不同功能站点臭氧(O3)及其前体物的观测结果,分析了上海不同地区O3及其前体物的污染特征及空间差异;采用参数化的方法估算了VOCs的大气化学消耗水平.结果表明,观测期间上海市区VOCs浓度约为20×10-9,高于西部郊区的17×10-9;两个地区VOCs最大增量反应活性(以O3/VOCs计)的平均值比较接近,约为5.0mol·mol-1.但是,市区VOCs的大气消耗水平(4.0×10-9)不足西部郊区VOCs消耗水平(8.3×10-9)的一半,这是西部郊区O3污染更重的重要原因;东部沿海郊区O3浓度的变化主要是由于区域输送.不同地区VOCs消耗水平与O3生成浓度的比值接近,说明不同地区VOCs消耗生成O3的效率接近;烯烃和芳香烃是最主要的VOCs消耗物种,二者对VOCs消耗量的总贡献高达90%.VOCs的消耗水平在正午达到最大,夜间消耗水平最低,日分布曲线与O3生成的日变化曲线相似,但O3峰值出现时间略晚于VOCs消耗水平峰值出现的时间.

Chemical Loss of Volatile Organic Compounds and Its Impact on the Formation of Ozone in Shanghai

The spatial characterization of ozone (O₃) and its precursors was studied based on the field measurements in urban and rural areas of Shanghai during the summer of 2014. The chemical loss of volatile organic compounds (VOCs) was estimated by the parameterization method. The mixing ratio of VOCs was 20×10^-9 in urban area and 17×10^-9 in the west rural area during the measurements. The average values of the maximum incremental reactivity were comparable in urban and rural areas, namely 5.0 mol ·mol^-1 (O₃/VOCs). By contrast, the chemical loss of VOCs was 8.3×10^-9 in west rural area, which was two times as that in urban area. The more chemical loss of VOCs was probably one of the important reasons leading to the higher O₃ concentration in west rural area. The regional transport might be important reason of the variation of O₃ in the eastern coastal rural area. The chemical loss of VOCs showed good agreement with the local formation of O₃ in both urban and rural areas, suggesting a similar efficiency of O₃ formation from the chemical loss of VOCs. Among the chemical loss, aromatics and alkenes are the dominant VOC species of the atmospheric chemistry which accounts for more than 90%. The diurnal profile of VOC chemical loss matched well with the production of O₃ with one-hour postponement.