天津市郊夏季VOCs化学特征及其时间精细化的来源解析

夏季为环境空气中臭氧污染事件的频发时期,针对挥发性有机化合物(VOCs)及其臭氧生成潜势(OFP)的时间精细化的来源解析研究,对有效地进行臭氧污染防控具有非常重要的作用.利用2019年夏季(6～8月)天津市郊区点位监测的小时分辨率VOCs在线数据,分析臭氧污染事件和非臭氧污染时期环境受体中VOCs及其OFP的变化特征,并利用正定矩阵因子分解(PMF)模型进行精细化的来源解析研究.结果表明,夏季环境受体中VOCs平均体积分数为24.42×10-9,臭氧污染事件中的VOCs平均体积分数为27.72×10-9,较非臭氧污染时期增加15.69％.夏季总VOCs(TVOCs)的OFP为87.92×10-9,其中烯烃的OFP最高,对TVOCs的OFP的贡献达58.28％.臭氧污染事件中TVOCs的OFP为102.68×10-9,较非臭氧污染时期增加19.59％.臭氧污染事件中VOCs的来源分别为石化工业及汽油挥发(29.44％)、柴油车尾气(23.52％)、液化石油气及汽油车尾气(22.00％)、天然气及燃烧(13.41％)、溶剂使用(6.14％)和植物排放(5.49％).相比于非臭氧污染时期,液化石油气及汽油车尾气和柴油车尾气分别增长4.84％和5.29％.石化工业及汽油挥发和植物排放的贡献均表现为08:00开始上升,11:00达到最高,这与太阳辐射增强和温度不断上升密切相关.液化石油气及汽油车尾气和柴油车尾气均具有明显的早晚高峰特征,并在夜间(00:00～06:00)保持较高贡献水平.根据PMF结果并结合OFP的计算方法,解析了不同源类对臭氧生成潜势的 贡献.石化工业及汽油挥发(31.01％)和柴油车尾气(36.64％)是较高贡献源类,相比非臭氧污染时期分别增加了 1.74％和8.27％;并且石化工业及汽油挥发贡献率在臭氧污染事件发生过程的上升阶段显著增加,而在下降阶段明显下降.

Chemical Characteristics and Source Apportionment with Temporal Refinement for VOCs in Tianjin Suburb in Summer

Summer is a period with frequent ozone pollution events in the air. It is very important to identify the source apportionment of ambient volatile organic compounds (VOCs) and their ozone formation potential (OFP) to effectively prevent and control ozone pollution. The hourly resolution VOC online data for Tianjin Suburb during the summer of 2019 (June to August) were applied to analyze the variation characteristics of ambient VOCs and their OFP during ozone pollution events and non-ozone pollution periods, and the refined source apportionment of the ambient VOCs and their OFP was carried out by using the positive matrix factorization (PMF) model. The results showed that the mean volume fraction of ambient VOCs in summer was 24.42×10^-9. The average volume fraction of ambient VOCs in ozone pollution events was 27.72×10^-9, 15.69% higher than that in the non-ozone pollution period. The OFP of total VOCs (TVOCs) in summer was 87.92×10^-9, of which olefin was the highest, contributing 58.28% to the OFP of TVOCs. The OFP of TVOCs in the ozone pollution events was 102.8×10^-9, increased 19.59% compared to the non-ozone pollution period. The contributing sources of ambient VOCs in ozone pollution events were the petrochemical industry and gasoline volatilization (29.44%), diesel vehicle exhaust (23.52%), liquefied petroleum gas (LPG)/gasoline vehicle exhaust (22.00%), natural gas/combustion (13.41%), solvent use (6.14%), and plant emissions (5.49%). Compared with that in the non-ozone pollution period, LPG/gasoline vehicle exhaust and diesel vehicle exhaust increased by 4.84% and 5.29%, respectively. The contribution of the petrochemical industry and gasoline volatilization as well as plant emissions began to increase at 8:00 and reached the highest at 11:00, which was closely related to the increase in solar radiation and ambient temperature. Both LPG/gasoline vehicle exhaust and diesel vehicle exhaust showed obvious morning and evening peaks and maintained a high contribution level at night (00:00-06:00). Combining the PMF results and the OFP method, the contributions of different sources to the OFP were analyzed. The petrochemical industry and gasoline volatilization (31.01%) and diesel vehicle exhaust (36.64%) were the highest contributors during ozone pollution events, which increased by 1.74% and 8.27%, respectively, compared with those during the non-ozone pollution period. Additionally, its contribution percentage significantly increased during the rising stage of ozone pollution events and clearly decreased in the declining stage.