database of ineffective reduction ratio-20230318

Ground-level ozone (O3) pollution has shifted from being a scientific topic to a governmental imperative in China. Shanghai, as a representative of mega cities, is also facing the challenge of O3 pollution constraining the continued improvement of urban air quality. In order to curb the spread of coronavirus disease 2019 (COVID-19), Shanghai has adopted extremely strict control measures during the period of April and May 2022 (CLP-22). The concentrations of precursor pollutants such as VOCs and NO2 have decreased by nearly 50%, however, O3 concentrations have increased by more than 20%. Considering the scale of urbanization, the particularity of lockdown period and the stringency of lockdown measures, O3 rise during CLP-22 in Shanghai was further investigated utilizing ground-level observed data, an observation-based model, and a chemical transport model. The increase in O3 was mainly attributable to ineffective VOCs and NOx reduction ratios and adverse meteorological conditions. The model results suggest that the higher VOCs reduction, the more effective in decreasing the daily maximum 8-hour moving average (MDA8) O3 concentration under the same total reduction percentage of VOCs and NOx emissions, whereas higher NOx reductions than VOCs may lead to O3 increases, especially in urban areas. This indicates that simple one-fits-all control measures such as short-term lockdown strategies may not achieve control targets for both primary and secondary pollutants. Only well-designed strategies with reasonable control of VOCs to NOx ratios and active VOC species can mitigate O3 pollution.