大气环境科学实验室知识库

      近年来，我国大气挥发性有机物（ VOCs 和臭氧 O 3 污染问题 日益凸显VOCs 和 O 3 浓度升高 对城市或区域的空气质量、生态系统以及 全球 气候 变化有直接或间接影响 。 目前有关 VOCs 和 O 3 的研究 主要 集中在京津冀、长三角、珠三角以及中西部大城市， 而我国幅员辽阔，不同地区 VOCs 和 O 3 污染差异很大，东部沿海城市 威海 与 西部地区 乌鲁木齐 O 3 问题日益凸显 。威海市 2014 至 2017年 O 3 呈上升趋势，其中 2017 年 5~ 10 月 O 3 浓度 较 2016 年同期 上升 12.18%12.18%；近年来， 乌鲁木齐夏季 O 3 作 为首要污染物的天数和其浓度呈 上升 趋势 且 VOCs和 O 3 研究仍 缺乏 。因此，本文 利用 SUMMA 罐采样 三级冷阱预浓缩 GC/FID/MS分析系统， 率先 研究威海和乌鲁木齐 城市 大气 VOCs 组成 特征和 来源， 结合 后向轨迹 模型 探讨 不团气团来向 的 VOCs 组成特征， 并 利用基于观测的 模型 OBM对威海 O 3 生成的典型化学过程及敏感性作了初步研究， 并 取得了一定认识， 主要 结果如下：
      威海市山大（ SD ）和临港 LG 站点 非甲烷总烃（ TNMHCs 的平均浓度相当，分别为 10.45±7.50×10 9 v/v 和 9.33±7.16×10 9 v/v 其 组成占比 从高到低均是烷烃、烯烃、芳香烃和乙炔； SD 和 LG 站点 早 7 时 NMHCs 浓度 均大于午间13 时 C2 C3 烃类、 乙苯和二甲苯日变化趋势相同，受相 似排放源（机动车排放）影响，不同时期 （工作日、周末和节假日）机动车排放对大气中 NMHCs 影响不同，中秋假期表现出 NMHCs 浓度的增加 。 甘泉堡（ GQP 站点 总挥发性有机物的平均浓度为 62.34±41.01×10 9 v/v 其组成占比从高到低依次是烷烃、 含氧有机物 、 炔烃 、 卤代烃 、 芳香烃 和 烯烃 。
      后向轨迹模型聚类分析结果表明，SD 站点西南方向烯烃、芳香烃和炔烃占比 最高 ，西北转西南方向 气团烷烃占比最高 北 西 北 和西南方向气团受机动车排放的影响较大，各个方向气团受液化石油气使用、工业溶剂和工业活动影响不可忽视； 相比海洋气团 ，陆地气团会明显提高该地区 NMHCs 的浓度 。 GQP 站点以正北气团（ 68%68%）和正东气团 27%27%）为主，西北气团的烷烃占比 最低， 但其炔烃占比 最高 ；正东气团 TNMHCs 的平均浓度最高，为 28.13×10 9 v/v 。
      正定矩阵因子分析模型（PMF 输出结果表明，在 SD 和 L G 站点 溶剂使用和挥发 及 机动车排放源 对 NMHCs 的 贡献 大于 50%50%；在 GQP 站点 工业过程和汽车尾气排放对 VOCs 的贡献最为明显，分别 为 31.67% 和 24.42% 。
      OBM模拟结果表明， LG 站点属 VOCs 控制区， SD 站点 5 月属 VOCs 控制区， 9 月属 NOx 和 VOCs 共同控制区；控制人为源的烯烃和芳香烃对控制威海O 3 污染最为有效 SD 和 LG 站点日平均 臭氧净生成速率 𝑃(𝑂3)𝑛𝑒𝑡分别为 7.64×109 /h 和 3.02×10 9 /h ，白天 SD 站点 O 3 浓度主要受本地光化学过程的影响，而光化学生成和区域输入共同导致 LG 站点 O 3 浓度的变化，因此控制 O 3 污染要区域联防联控。
 

      In recent years,air pollution of VOCs and ozone in China has become more and more prominent and enhanced concentration of VOCs and ozone would have a direct or indirect impact on the air quality, ecosystem and global climate change At present ,the reseaches on V OCs and ozone mostly condu c ted in Beijing Tianjin Hebei, Yangtze River Delta, the Pearl River D elta and metropolitan cities in Midwest H o wev er, China has a vast territory and VOCs and ozone pollution varies greatly in different areas and the current situation of VOCs and O 3 pollut ion in coastal and western cities such as Weihai and Urumqi, is not well understood. O 3 concentration in Weihai was on the rise from 2014 to 2017, and from May to October 2017 increased by 12.18% compared with that over the same period in 2016. I n recent years the days and concentrations of O 3 as the primary pollutant were on the rise in Urumqi The knowledg e on VOCs and O 3 is still lacking, and futher reseach is needed. Therefore, in this study, composition characteristics and source attr ibution of VOCs in Weihai and U rumqi were performed by using SUMMA sampling and GC FID/MS analysis system coupled with a three stage preconcentration . B ackward trajectory was used to discuss the composition characteristics of VOCs under the different air masses . Meanwhile, the typical chemical process and the sensitivity of ozone formation in Weihai were preliminarily studied by using the observation based model ( OBM). The main results are as The average concentration of total NMHCs (TNMHCs at S handa (SD) and Lingang ( in Weihai were 10.45±7.50×10 9 v/v and 9.33±7.16×10 9 v/v, respectively,and the highest concentration was alkanes, followed by alkene s, aromatics and alkynes .
      The concentrations of NMHCs at 7 A M were greater than those at 13 PM , and C2 C3 hydrocarbons ethylbenzene and xylene showed the same change trend , indicating the influences of similar emission source The contribution of vehicle emissions to NMHCs was differe nt among working days, weekends and holidays. Note that significant
elevated NMHCs concentrations were observed in the Mid Autumn festival holiday. The average concentration
of total VOCs at Ganquanpu ( GQP in Urumqi was 62.34 41.01 × 10 9 v/v. The order of VOCs components was as follows: alkanes,oxygen ed organic compounds, alkynes, halogenated hydrocarbons , aromatic s , alkenes         Combined with the backward trajectory model, it was found that the composition characteristics of NMHCs were significantly different under the different air masses . The proportions of alkenes, aromatics and alkynes in southwest direction were slightly high er than those in the other five directions, and the proportions of alkane in northwest southwest direction were the highest, followed by that in northwest direction. The air masses in southwest and north north west directions were greatly affected by vehicle emissions, while the air masses in six directions were affected by the use of LPG, industrial solvents and industrial activities. Compared with marine air masses, the land air mass at the SD site significantly increased the local NMHCs concentration, indicating the influence of local land emissions. At GQP, air mass were mainly from the northwest (68%) and the e ast (27%), while the northwest air mass ha d a slightly lower proportion of alkanes tha n that from the w e st and the north air mass, and the proport ion of alkynes wa s much higher than that of the e ast and north air mass. The average concentration of TNMHCs in the e ast air mass wa s the highest, with 28.13 ×10 9 v/v .

      PMF(Positive Matrix model results showed that at SD and LG solvent use and evaporation, and the vehicle emissi on contributed to more than 50% At GQP, industrial processes and automobile exhaust emissions contributed largely to VOCs during the observation period, reaching to 31.67% and 24.42% respectively.

       Results of OBM simulation indicated tha t LG was controlled by VOCs during whole observation period; SD was mainly control ed by VOCs in May, but jointly controlled by NOx and VOCs in September. The control of anthropogenic alkenes and aromatic hydrocarbons was the most effective in controlling O 3 pollution. The daily average of net O 3 formation rate 𝑃(𝑂3)𝑛𝑒𝑡 were respectively 7. 64 x 10 9 /h and 3.02 x 10 9 /h at SD and LG . Lo cal O 3 production at SD not only sustained its in situ ozone but
also exported horizontally and vertically , and at LG both the local O3 photochemical formation and regional input merely sustained O3 concentration in the daytime.Therefore controlling O3 pollution in Weihai needed inter regional prevention and control.