Carbonyl Compound Reduction Mitigates Ozone Pollution: Lessons from Pollution Control during the 19th Asian Games in Hangzhou, China

This study conducted comprehensive field measurements of ozone and related species during the 19th Asian Games conducted in Hangzhou, China (September 11 to October 15, 2023), to assess the effectiveness of ozone pollution control measures during the Pre-Games, During-Games, and Post-Games phases. The observational results show a notable decrease in O3 concentrations during the Games compared to the Pre-Games period. An observation-based chemical box model revealed a significant reduction in ROx radical and ozone formation rates by 42.0% and 47.2%, respectively, during the Games. The weakened photolysis of HCHO and other carbonyls was identified as the primary contributing pathway, accounting for 64.7% of the total decline in P(ROx). Despite a significant rebound in the concentrations of atmospheric nitrous acid and halogen radical precursors, it still cannot counteract the reduction in ozone formation. Source apportionment of HCHO across different phases indicated a significant reduction in primary HCHO emissions during the Games. In addition, changes in meteorological conditions, such as decreased solar radiation and lower temperatures, also contributed to the decline in atmospheric oxidation capacity during the Games. In the Post-Games period, the O3 concentrations decreased continuously despite the rebound of anthropogenic emissions, which is mainly attributed to the meteorological changes. These findings highlight the importance of carbonyl compounds, particularly formaldehyde, in O3 formation and atmospheric oxidation capacity in urban areas, and provide new insights for improving air quality.