Characterization of ambient volatile organic compounds, source apportionment, and the ozone-NO<sub>x</sub>-VOC sensitivities in a heavily polluted megacity of central China: Effect of sporting events and the emission reductions

Abstract. Abstract: The implementation of strict emission control during the 11th National Minority Games (NMG) in September 2019 provided a valuable opportunity to assess the impact of such emission controls on the characteristics of VOCs and other air pollutants. Here, we investigated the characteristics of VOCs and the O3-NOx-VOCs sensitivity comprehensively in Zhengzhou before, during, and after the NMG by delivering field measurements combined with the WRF (Weather Research and Forecasting)-CMAQ (Community Multi-scale Air Quality) model simulations. The average mixing ratios of VOCs during the control periods were 34 ppbv, and cut down by about 16% before and after emission reduction. The ozone precursors (NOx) also decreased significantly during the control period; however, the ozone pollution was severe during the entire observation period. Positive Matrix Factorization analysis indicated seven major sources of ambient VOCs, including coal combustion, biomass burning, vehicle exhausts, industrial processes, biogenic emissions, solvent utilization and liquefied petroleum gas (LPG). The results show that the major source emissions, such as coal combustion and solvent utilization, were significantly reduced during the control period. As for ozone formation potential (OFP), the value during the control period was 183 μg/m3, which was 0.23 and 0.17 times lower than those before and after control period, respectively. Solvent utilization and combustion controls were the most important measures taken to reduce OFP during NMG period. Through control policies, it can effectively reduce carcinogenic risk. However, non-cancer risks of ambient VOC exposures were all exceeding the safe level (hazard quotient = 1) during the sampling periods, and emphasis on the reduction of acrolein emissions was needed. In addition, the WRF/CMAQ model simulation indicated that O3 formation was controlled by VOCs in Zhengzhou. The results of the Empirical Kinetic Modelling Approach showed that the NOx reduction in Zhengzhou might led to higher ozone pollution. It is suggested that reduction ratios of the precursors (VOCs : NOx) is more than 2, which can effectively alleviate ozone pollution.