天津市郊夏季的臭氧变化特征及其前体物VOCs的来源解析

本文利用天津市南开大学津南校区大气环境综合观测站的臭氧及其前体物（VOCs和NO_x）、气象参数等在线监测仪器，获取了2018年夏季（6~8月）小时分辨率的数据信息；分析臭氧及其前体物的相互关系及变化特征；根据光化学年龄计算出VOCs的初始浓度对其日间（06：00~24：00）VOCs体积分数的光化学损耗进行修正；将初始体积分数和直接监测的VOCs体积分数分别纳入PMF模型进行人为源的来源解析.结果表明，夏季天津O₃的平均体积分数为（41.3±25.7）×10^-9，而VOCs的平均体积分数为（13.9±12.3）×10^-9，其中烷烃的平均体积分数（7.0±6.8）×10^-9明显高于其它VOCs物种.烷烃中浓度较高的物种分别为丙烷和乙烷，占总烷烃浓度贡献的47%.夏季O₃的生成潜势（OFP）平均值为52.1×10^-9，其中烯烃的OFP值最高，对于TVOCs臭氧生成潜势的贡献达到57%.VOCs日间光化学损耗量计算结果表明，烯烃日间损耗占VOCs损耗总量的75%.基于初始浓度解析的VOCs来源分别为：化工排放和溶剂使用（25%）、机动车尾气（22%）、燃烧源（19%）、天然气和液化石油气（19%）和汽油挥发（15%）.相比于直接将监测浓度纳入PMF解析的结果，化工排放和溶剂使用贡献百分占比下降4%，机动车尾气贡献百分占比下降5%.利用PMF源解析结果结合OFP分析不同源类对臭氧污染的相对贡献，基于初始体积分数数据的结果显示，贡献最高源类为化工排放和溶剂使用（26%）.与利用直接监测数据的解析结果相比，化工排放和溶剂使用的OFP值降低7%，天然气和液化石油气的OFP值明显降低13%.

Characteristics of Ozone and Source Apportionment of the Precursor VOCs in Tianjin Suburbs in Summer

From June to August 2018, a 1-hr resolution concentration dataset of ozone and its gaseous precursors (volatile organic compounds(VOCs) and NO_x), and meteorological parameters were synchronously monitored by online instruments of the Nankai University Air Quality Research Supersite. The relationships and variation characteristics between ozone and its precursors were analyzed. According to the photochemical age, the initial concentrations of VOCs were calculated, and the photochemical loss of the concentration of VOCs during the daytime (06:00-24:00) was corrected. The initial and directly monitored concentrations of VOCs were incorporated into the PMF model for source apportionment. The results indicated that the mean concentration of O₃ in Tianjin in summer was (41.3±25.7)×10^-9, while that of VOCs was (13.9±12.3)×10^-9. The average concentration of alkane (7.0±6.8)×10^-9 was clearly higher than that of other VOC species. The species with high concentrations of alkanes were propane and ethane, accounting for 47% of the total alkane concentration. The average ozone formation potential (OFP) in summer was 52.1×10^-9, and the OFP value of alkene was the highest and its contribution reached 57%. During the daytime, alkene loss accounted for 75% of the total VOC loss. The major sources of VOCs that were calculated based on the initial concentration data were the chemical industry and solvent usage (25%), automobile exhaust (22%), combustion source (19%), LPG/NG (19%), and gasoline volatilization (15%), respectively. Compared with the apportionment results based on directly monitored concentrations, the contribution of the chemical industry and solvent usage decreased by 4%, while automobile exhaust decreased by 5%. By combining the results of PMF apportionment and the OFP model to analyze the relative contributions of emission sources to ozone formation, and we found that the highest contribution source of ozone was the chemical industry and solvent usage (26%) in summer. Compared with the analysis results based on the directly monitored concentrations, the OFP values of the chemical industry and solvent usage decreased by 7%, while that of NG/LPG apparently decreased by 13%.