Source Attribution Analysis of an Ozone Concentration Increase Event in the Main Urban Area of Xi’an Using the WRF-CMAQ Model

Abstract

The significant increase in ambient ozone (O3) levels across China highlights the urgent need to investigate the sources and mechanisms driving regional O3 events, particularly in densely populated urban areas. This study focuses on Xi’an, located in northwestern China on the Guanzhong Plain near the Qinling Mountains, where the unique topography contributes to pollutant accumulation. Urbanization and industrial activities have significantly increased pollutant emissions. Utilizing the Weather Research and Forecasting–Community Multiscale Air Quality Model (WRF-CMAQ), we analyzed the contributions of specific regional and industrial sources to rising O3 levels, particularly during an atypical winter event characterized by unusually high concentrations. Our findings indicated that boundary conditions were the primary contributor to elevated O3 levels during this event. Notably, Xianyang and Baoji accounted for 30% and 22% of the increased O3 levels in Xi’an, respectively. Additionally, residential sources and transportation accounted for 31% and 28% of the O3 increase. Within the Xi’an metropolitan area, Baqiao District (18–27%) and Weiyang District (23–30%) emerged as leading contributors. The primary industries contributing to this rise included residential sources (28–37%) and transportation (35–43%). These insights underscore the need for targeted regulatory measures to mitigate O3 pollution in urban settings.

Keywords

• O₃
• WRF-CMAQ
• source apportionment
• regional transport