长三角典型城市臭氧污染特征及VOCs来源解析

Analysis of Variation Characteristics and Source of Atmospheric Ozone Pollution in the Yangtze River Delta Region

为了解长三角区域臭氧(O_(3))污染特征及来源成因,利用2021年5−10月长三角区域典型城市上海市、南京市和合肥市的挥发性有机物(VOCs)及常规连续在线观测数据,识别对O_(3)生成贡献较大的VOCs组分,并对比O_(3)污染日和非污染日VOCs组分体积分数的变化,同时结合正交矩阵因子分析模型探究VOCs来源解析。结果表明:①上海市、南京市和合肥市O_(3)日最大8 h滑动平均浓度的第90百分位数分别为163、185和163μg/m^(3),超标天数分别为20、42和20 d,VOCs平均体积分数分别为12.93×10^(-9)±8.61×10^(-9)、14.45×10^(-9)±7.56×10^(-9)和15.60×10^(-9)±8.12×10^(-9),3个城市VOCs均以烷烃为主,上海市VOCs中芳香烃、南京市VOCs中烯烃以及合肥市VOCs中炔烃占比较突出。②南京市和合肥市的臭氧生成潜势(OFP)月变化均呈先降后升的趋势,上海市变化不明显。上海市和合肥市VOCs中芳香烃对O_(3)生成贡献最大,贡献率在40%以上,南京市VOCs中烯烃(40.1%)和芳香烃(35.9%)对O_(3)生成贡献较突出。③3个城市O_(3)浓度日变化均呈单峰分布,在污染日12:00之前O_(3)生成速率和生成量均显著高于非污染日,其前体物VOCs体积分数和NO_(2)浓度呈相似的双峰分布特征。从示踪组分来看,O_(3)污染日上海市机动车尾气源和工业排放源、南京市机动车尾气源和溶剂使用源、合肥市汽油挥发源等均有所增加。④机动车尾气源和工业排放源为3个城市VOCs的主要贡献源,此外上海市的石化化工源、南京市的溶剂使用源以及合肥市的汽油挥发源和燃烧源对夏季VOCs的贡献不容忽视。研究显示,较高的前体物浓度和较快的前体物消耗速率是O_(3)超标的重要原因,长三角区域大气VOCs管控应重点关注机动车尾气源和工业源的排放。

From May to October 2021,volatile organic compounds(VOCs)and conventional continuous online observation data were monitored in typical cities such as Shanghai,Nanjing and Hefei in the Yangtze River Delta region to understand the characteristics and sources of ozone(O_(3))pollution.The VOCs components that contribute significantly to O_(3) production were identified,and the changes in VOCs component concentrations were compared between ozone polluted and non-polluted days.The positive matrix decomposition model was used to explore the source apportionment of VOCs.The results showed that:(1)The 90^(th) percentile of daily maximum 8-hour average ozone concentration in Shanghai,Nanjing,and Hefei was 163,185 and 163μg/m^(3),respectively.The number of days exceeding the standard were 20 days,42 days and 20 days,respectively.The average volume fraction of VOCs were 12.93×10^(-9)±8.61×10^(-9),14.45×10^(-9)±7.56×10^(-9) and 15.60×10^(-9)±8.12×10^(-9),respectively.The VOCs in all three cities were dominated by alkanes,among which aromatic hydrocarbons in Shanghai,olefins in Nanjing,and alkynes in Hefei account for prominent proportions.(2)The monthly variations of ozone generation potential(OFP)in Nanjing and Hefei showed a trend of first decreasing and then increasing,while the variation in Shanghai was not significant;aromatic hydrocarbons in VOCs in Shanghai and Hefei contributed the most to ozone generation,accounting for above 40% each.Olefins and aromatic hydrocarbons in Nanjing made significant contributions to ozone generation.(3)The daily variation of ozone in the three cities showed a unimodal distribution.The ozone generation rate and amount before 12:00 on polluted days were significantly higher than those on non-polluted days.The precursors VOCs and NO_(2) showed similar bimodal distributions.From the perspective of tracer components,Shanghai′s solvent coatings and industrial emissions,Nanjing′s motor vehicle exhaust and solvent coatings,and Hefei′s gasoline volatilization all increased on ozone pollution days.(4)Motor vehicle exhaust and industrial emissions were the main sources of VOCs in the three cities.In addition,the contributions of Shanghai petrochemical and chemical industry sources,Nanjing solvent use sources,and Hefei gasoline volatilization and combustion sources to VOCs in summer cannot be ignored.The results show that higher precursor concentrations and faster precursor consumption rate are important reasons for excessive ozone levels.The sources of atmospheric VOCs control in the Yangtze River Delta region should focus on vehicle exhaust and industrial source emissions.