青岛市臭氧污染与非污染期间VOCs化学特征及来源解析

Chemical Characteristics and Source Apportionment for VOCs During the Ozone Pollution Episodes and Non-ozone Pollution Periods in Qingdao

青岛市夏季臭氧浓度水平高且污染事件频发,开展臭氧污染过程和非污染时期的挥发性有机物(VOCs)及其臭氧生成潜势(OFP)的精细化来源解析研究,对于有效降低沿海城市的大气臭氧污染,持续改善环境空气质量将会发挥重要的作用.因此,利用青岛市2020年夏季(6~8月)小时分辨率的在线VOCs监测数据,分析臭氧污染过程和非臭氧污染时期环境VOCs的化学特征,并通过正定矩阵因子分解(PMF)模型进行了环境VOCs及其OFP的精细化来源解析研究.结果表明,青岛市夏季环境ρ(TVOCs)平均值为93.8μg·m^(-3),臭氧污染过程相较于非臭氧污染时期TVOCs浓度上升了49.3%,其中芳香烃浓度增加最显著,增加了59.7%.夏季环境VOCs总的OFP达到246.3μg·m^(-3),臭氧污染过程相较于非臭氧污染时期环境VOCs的总OFP增加了43.1%;其中烷烃增加最多,增加了58.8%.间-乙基甲苯和2,3-二甲基戊烷是臭氧污染过程中OFP增加幅度最大的物种.青岛市夏季环境VOCs的主要贡献源为柴油车(11.2%)、溶剂使用(4.7%)、液化石油气及天然气(27.5%)、汽油车(8.9%)、汽油挥发(26.6%)、燃烧及石化相关企业排放(16.4%)和植物排放(4.8%).相较于非臭氧污染时期,臭氧污染过程中液化石油气及天然气浓度增加了16.4μg·m^(-3),是增加量最大的源类;而植物排放浓度增加了88.6%,是增加率最高的源类.另外,燃烧及石化相关企业排放是青岛市夏季OFP最大的贡献源,其OFP和贡献率分别达到38.0μg·m^(-3)和24.5%;其次为液化石油气及天然气以及汽油挥发.相较于非臭氧污染时期,臭氧污染过程中液化石油气及天然气、汽油挥发和溶剂使用对总OFP升高量的贡献率之和达到74.1%,是最主要的贡献源类.

The ambient concentration of ozone is high in Qingdao,and ozone pollution episodes occur frequently in summer.The refined source apportionment of ambient volatile organic compounds(VOCs)and their ozone formation potential(OFP)during ozone pollution episodes and non-ozone pollution periods can play an important role in effectively reducing air ozone pollution in coastal cities and continuously improving ambient air quality.Therefore,this study applied the online VOCs monitoring data with hourly resolution in summer(from June to August)in 2020 in Qingdao to analyze the chemical characteristics of ambient VOCs during the ozone pollution episodes and non-ozone pollution periods and conducted the refined source apportionment of ambient VOCs and their OFP using a positive matrix factorization(PMF)model.The results showed that the average mass concentration of ambient VOCs in Qingdao in summer was 93.8μg·m^(-3),and compared with that during the non-ozone pollution period,the mass concentration of ambient VOCs during the ozone pollution episodes increased by 49.3%,and the mass concentration of aromatic hydrocarbons increased by 59.7%.The total OFP of ambient VOCs in summer was 246.3μg·m^(-3).Compared with that in the non-ozone pollution period,the total OFP of ambient VOCs in the ozone pollution episodes increased by 43.1%;that of alkanes increased the most,reaching 58.8%.M-ethyltoluene and 2,3-dimethylpentane were the species with the largest increase in OFP and its proportion during the ozone pollution episodes.The main contributors of ambient VOCs in Qingdao in summer were diesel vehicles(11.2%),solvent use(4.7%),liquefied petroleum gas and natural gas(LPG/NG)(27.5%),gasoline vehicles(8.9%),gasoline volatilization(26.6%),emissions of combustion-and petrochemical-related enterprises(16.4%),and plant emissions(4.8%).Compared with that in the non-ozone pollution period,the contribution concentration of LPG/NG in the ozone pollution episodes increased by 16.4μg·m^(-3),which was the source category with the largest increase.The contribution concentration of plant emissions increased by 88.6%in the ozone pollution episodes,which was the source category with the highest increase rate.In addition,emissions from combustion-and petrochemical-related enterprises were the largest contributor to the OFP of ambient VOCs in summer in Qingdao,with its OFP and contribution proportion being 38.0μg·m^(-3) and 24.5%,respectively,followed by that of LPG/NG and gasoline volatilization.Compared with the non-ozone pollution period,the total contributions of LPG/NG,gasoline volatilization,and solvent use to the increase in OFP for ambient VOCs in the ozone pollution episodes were 74.1%,which were the main contribution source categories.