ABSTRACT
Ozone was one of the major pollutants affecting the environmental air quality in China. The accurate apportionment of key sources and their contributions of ambient ozone and its precursor VOCs played an important role in the effective prevention and control of ozone pollution. Therefore, this study utilized the photochemical-age-based parameterization method to estimate the initial concentrations of ambient VOCs data collected from January 1 to February 28, 2021 in Jiaozhou, Qingdao and corrected the photochemical losses of ambient VOC species. The positive matrix factorization(PMF) and ozone formation potential(OFP) models were used to conduct source apportionment of ambient VOCs and their OFPs so as to provide data support for the prevention and control of ozone pollution in Qingdao. The results showed that the average values of ambient ρ(TVOCs) and OFP in Qingdao during the study period were 65.9 µg·m-3 and 176.7 µg·m-3, respectively. Propane had the highest concentration(12.4 µg·m-3) and percentage(18.9%), whereas m/p-xylene had the highest OFP(24.6 µg·m-3) and percentage(13.9%). The mean initial concentration of TVOCs during the study was 153.1 µg·m-3, and its photochemical loss rate reached 63.8%. Alkenes were the VOC species with the highest photochemical loss rate(92.1%), and the photochemical loss rate of isoprene reached 98.6%, which was substantially higher than that of other VOC species. According to the source apportionment results of initial concentrations(IC-PMF), liquefied petroleum gas(24.2%), solvent use(17.8%), natural gas and petrochemical-related enterprises(16.6%), gasoline volatilization(13.2%), combustion and gasoline vehicle emissions(12.2%), biogenic emissions(8.6%), and diesel vehicle emissions(7.4%) were the main contributing sources of the ambient VOCs in Jiaozhou. Compared with the apportioned results of IC-PMF, the contribution of biogenic emissions was underestimated by 38.9% in the apportioned results based on observed concentrations(OC-PMF), and the contribution of natural gas and petrochemical-related enterprises was underestimated by 28.5%, and the underestimations of their contributions were substantially higher than those of other sources. Compared with that before the Spring Festival, the contribution of gasoline volatilization to ambient VOCs increased markedly during the Spring Festival, whereas the contributions of solvent use, combustion, and gasoline vehicle emissions to ambient VOCs increased most significantly after the Spring Festival. The main contributing sources of ambient ozone during the study period were solvent use(31.3%), natural gas and petrochemical-related enterprises(16.1%), biogenic emissions(14.5%), and combustion and gasoline vehicle emissions(13.2%). The primary contributors of ambient ozone in different Spring Festival periods showed substantial differences. Before the Spring Festival, solvent use had the highest contribution(71.1 µg·m-3), and gasoline volatilization was the highest contributor during the Spring Festival(34.4 µg·m-3), whereas biogenic emissions after the Spring Festival were the highest contributor(39.1 µg·m-3).
ABSTRACT
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 93.8 µg·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 246.3 µg·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 16.4 µg·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 38.0 µg·m-3and 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.
