Impacts of meteorology and emission reductions on haze pollution during the lockdown in the North China Plain: Insights from six-year simulations

Abstract. Haze events across the North China Plain (NCP) during the COVID-19 lockdown have highlighted the complexities of air quality management in the face of reduced human activity. While previous studies have focused primarily on the atmospheric chemistry processes under anomalous weather conditions, interactions between air pollutants, atmospheric chemistry, and their responses to emissions and meteorological factors remain underexplored. Here, we utilized the WRF-Chem model to assess the impact of abrupt emission reductions and meteorological conditions on PM_2.5 levels across the NCP. By comparing simulations sensitive to meteorological conditions with climatology averaged over 2015–2019 and considering the sudden decrease in anthropogenic emissions due to the lockdown, we identified significant regional disparities. In the Northern NCP (NNCP), adverse meteorological conditions negated the benefits of emission reductions, leading to a net increase in PM_2.5 levels by 30 to 60 μg m^-3 during haze episodes. Conversely, the Southern NCP (SNCP) experienced a decrease in PM_2.5 levels attributed to favourable meteorological conditions combined with emission reductions, with decreases ranging from 20 to 40 μg m^-3 during the same periods. Our results highlight the critical role of meteorological conditions in modulating the effects of emission reductions, particularly in regions like the NNCP, where adverse weather can significantly counteract the benefits of reduced emissions. This study provides valuable insights into the complex interactions between emissions, meteorology, and air quality, underscoring the necessity of integrated approaches that address emissions and atmospheric dynamics.