Enhanced summertime background ozone by anthropogenic emissions – Implications on ozone control policy and health risk assessment

Quantifying background ozone (O₃-BG) is critical for emission control policy development due to its significant contribution to the overall O₃ levels. However, O₃-BG is still hard to monitor because of the universal existence of human activities and the complex interactions between anthropogenic and biogenic emissions. Here, we used a source-oriented chemical transport model to assess O₃-BG with (O₃-BG-anth) and without (O₃-BG-ult) the presence of anthropogenic emissions. Results show that anthropogenic emissions enhance O₃-BG-anth compared to that derived from biogenic emissions alone (O₃-BG-ult). The enhancement increases with increasing O₃ levels because anthropogenic emissions generally increase abundance of OH and HO₂ radicals, raising atmospheric oxidation capacity. Sensitivity analysis demonstrates that anthropogenic NO_x abatement could have the co-benefit of reducing biogenic O₃, leading to more effective O₃ pollution control. In contrast, reducing anthropogenic VOCs increases the production of biogenic O₃, which is not beneficial to overall O₃ reduction. Our findings provide valuable information for developing emission control policy and risk assessment.