Characteristics and source apportionment of volatile organic compounds pollution in the urban area of Xianyang City

Ozone (O3) has become a primary impediment to further improvements in air quality in many Chinese cities. A deep analysis of O3 precursor emission sources and formation mechanisms is therefore important. In this study, we investigated the characteristics of volatile organic compounds (VOCs) in Xianyang City, located on the Fenwei Plain. Positive matrix factorization (PMF) was used to apportion VOC sources, and the atmospheric box model (AtChem-MCM) was employed to examine the O3 formation processes, assess O3 formation sensitivity, and identify its primary sources. The results revealed that the average concentration of VOCs during the sampling period was (78.79 ± 57.83) µg·m−3. Alkanes were the most abundant group (27.21 µg·m−3, 34.53%), followed by oxygenated VOCs (26.81%), halogenated hydrocarbons (15.05%), alkenes (11.26%), aromatics (10.02%), and acetylenes (2.31%). PMF results indicated that petrochemical production-related sources contributed the most to VOCs (28.40%) during the summer, followed by combustion sources (18.64%), industrial sources (17.69%), motor vehicle emissions (16.31%), biogenic sources (10.36%), and solvent usage (8.60%). The budget analysis of O3 showed an average daytime net O3 formation rate ($P_{{\mathrm{O}}_3} $) of 64.29 µg·m−3·h−1, with a peak of 100.08 µg·m−3·h−1 between 10:00 and 12:00. The reaction RO2· + NO was identified as the predominant formation pathway. Sensitivity analysis using the relative incremental reactivity coefficient method showed that daytime O3 formation in Xianyang was jointly controlled by NOX and VOCs. The formation of O3 was sensitive to industrial sources, motor vehicle emissions, and solvent use. Source apportionment of O3 indicated that petrochemical production-related sources (23.76%) and industrial sources (22.11%) were the largest contributors, followed by motor vehicle emissions (16.98%), solvent use (16.35%), and combustion sources (12.87%). These findings suggest that strengthening the control of emissions from petrochemical production, industrial activities, and motor vehicles is crucial for mitigating summer O3 pollution in Xianyang.