Different contributions of meteorological conditions and emission reductions to the ozone pollution during Shanghai’s COVID-19 lockdowns in winter and spring

Shanghai experienced the COVID-19 lockdowns (LCD) in the winter of 2020 and the spring of 2022, respectively. In this paper, the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) modeling system was used to simulate ozone (O₃) in Shanghai, and the contributions of meteorological conditions and emission reductions to the increases of the ground-level O₃ concentrations in Shanghai during the two LCD periods were analyzed. The relationships between O₃ concentrations and meteorological factors were quantified by the multiple linear regression model (MLR). The results showed that the increases in the concentrations of daily maximum 8-h moving average O₃ (MDA8 O₃) were caused by both meteorological changes and emission reductions, but their relative contributions to O₃ concentrations were different in winter and spring. Unfavorable meteorological conditions and the emission reductions during the 2020 winter LCD period increased MDA8 O₃ by 2.2 μg/m³ (2.2%) and 2.8 μg/m³ (2.8%), respectively, relative to the same period in the previous year. On the other hand, the meteorological conditions during the 2022 spring LCD period increased MDA8 O₃ by 7.9 μg/m³ (6.6%), while the emission reductions only increased MDA8 O₃ by 1.1 μg/m³ (0.9%). The O₃ formation in Shanghai urban areas was under the VOC-limited conditions during two lockdowns in winter and spring. Therefore, the VOCs emission reductions were more effective for the control of O₃ in Shanghai urban areas. The results emphasized the complex relationship between emission reductions, meteorological conditions and short-term O₃ changes.