[Source Apportionment of Ambient VOCs in Qingdao Based on Photochemical Loss Correction]

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).