Assessing COVID-19 Pandemic-Induced Air Quality Improvements: Insights from Marienplatz in Stuttgart, Germany

This study provides a comprehensive assessment of the impacts of COVID-19 pandemic-induced lockdowns on urban air quality at Marienplatz in Stuttgart, Germany, from 2018 to 2022. Utilizing high-resolution temporal datasets and advanced analytical techniques, including meteorological normalization and Shapley Additive Explanations (SHAP), the research disentangles the effects of emission reductions from meteorological variability on key atmospheric pollutants (CO, NO, NO2, O3, PM2.5, PM10). The findings reveal that the lockdown phases resulted in pronounced and significant reductions in primary traffic-related pollutants, with CO and NO concentrations declining by more than 50% relative to pre-pandemic baselines. In contrast, secondary pollutants, notably ozone, exhibited substantial increases (up to 50%), attributable to altered photochemical regimes and reduced NOx titration, as confirmed by Ox-NOx relationship analyses and photochemical sensitivity diagnostics. Particulate matter trends revealed limited short-term response, indicating persistent contributions from non-traffic sources such as residential heating and regional transport. Meteorologically normalized trends and SHAP analyses further confirmed that emission reductions, rather than meteorological fluctuations, were the primary drivers of the observed improvements in air quality. These insights highlight the transient and pollutant-specific nature of air-quality responses to abrupt emission reductions and provide critical scientific evidence to inform the design of robust, multi-sectoral urban air quality management and climate adaptation strategies in the post-pandemic era.