北京市郊区夏季臭氧重污染特征及生成效率

Pollution Characteristics and Production Efficiency of Ozone in Summertime at Rural Site in Beijing

为研究北京郊区夏季O_3(臭氧)重污染过程特征及O_3生成的光化学敏感性,基于2016年夏季在北京郊区开展的针对O_3及其相关污染物的强化观测试验(7月23日—8月31日,共计40 d),分析了观测期间O_3浓度[以φ(O_3)计]变化特征、O_3重污染过程主控因素与O_3敏感性化学特征.结果表明:观测期间φ(O_3)超标时有发生,最大小时φ(O_3)为151.1×10^(-9),其中有15 d的φ(O_3)最大8 h滑动平均值(O_3-max-8h)超过了GB 3095—2012《环境空气质量标准》二级标准限值,占观测天数的37.5%;不同O_3重污染过程成因有所不同,城市烟羽传输的污染物对郊区O_3重污染过程影响显著(观测期间臭氧重污染过程:过程1,7月27—29日;过程3,8月9—11日;过程4,8月16日;过程5,8月21—24日),区域光化学污染对郊区O_3重污染过程也有贡献(观测期间O_3重污染过程2:8月4—6日);结合后向气流轨迹进一步辅助说明了不同重污染过程中O_3的来源不同.研究还发现,观测区域存在反"周末效应"现象,说明观测区域周末受人为影响较为明显;基于观测数据计算的OPE(O_3生成效率)分析了O_3光化学敏感性表明,在有OPE值的22 d内NO_x控制区和VOCs控制区出现的概率(41%)相等,即观测区域O_3对NO_x和VOCs均敏感;此外还发现,在O_3重污染过程中光化学敏感性会随其反应进程发生改变,由NO_x控制区逐渐转变为VOCs控制区.

In order to study the pollution characteristics and formation sensitivities of ozone,concentration characteristics,severe pollution episodes and formation sensitivity of ozone were studied based on measurements of ozone and other trace gases conducted in summer 2016（July 23-August 31,40 days） at a rural site in Beijing.The results showed that elevated ozone levels were observed frequently during the observation period;the maximum hourly φ（O3） was 151.1×10^-9.Compared with the National Ambient Air Quality Standard（GB 3095-2012） for ozone（O3-max-8 h）,15 days（about 37.5% of the sampling days） exceeded the guideline value.Five typical heavy O3 pollution episodes were selected;in case 1（7.27-7.29）,case 3（8.9-8.11）,case 4（8.16） and case 5（8.21-8.24）,the urban plumewastransported to the observed areas,contributing to high concentrations of ozone.In addition,regional transport of ozone also led to elevated concentrations（e.g.,case 2,8.4-8.6）.Backward trajectory analysis also demonstrated the above results.In addition,antiweekend effects were also found.Ozone concentrations were higher on weekdays than on weekends,which indicated that ozone formation was controlled by titration of NOx.Ozone production efficiency calculated by monitoring data showed that ozone formation was dominated by both NOx-sensitive and VOC-sensitive（41%）.Furthermore,in the heavy ozone pollution episodes,ozone formation gradually transferred from being NOx-sensitive to VOCs-sensitive.