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

Abstract

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.