DNN model reveals sharp decline in PM_2.5 concentration in the Yangtze River Delta during COVID-19 lockdown and lift lockdown

The COVID-19 lockdown in early 2020 and subsequent lifting in late 2022 had a significant impact on air pollution levels in the Yangtze River Delta (YRD). Previous studies have not provided a clear understanding of the detailed spatiotemporal characteristics of PM_2.5 concentrations in various functional areas of cities during different periods before and after the outbreak of the epidemic. However, by employing a deep neural network (DNN) model and integrating satellite data, meteorological reanalysis, and PM_2.5 observations, established an estimation of high-resolution PM_2.5 distribution during the period from 2019 to 2022. The DNN model performed well (R² = 0.78). During the lockdown, PM_2.5 concentrations in 14 YRD cities were over 50% lower than in previous years. Interestingly, even after the lockdown was lifted, PM_2.5 levels remained relatively low due to reduced human activities caused by widespread infections. Found that PM_2.5 reductions varied across different intra-city functional regions during both the lockdown and lift lockdown periods. Overall, the changes in PM_2.5 levels during the 2022 lift lockdown were smaller than during the 2020 lockdown. These findings emphasize the need for tailored government policies to address COVID-19's impact on air pollution, considering diverse functional areas within the region.