Global air quality responses to the COVID-19 pandemic
That uncertainty is due in part to the sensitivity of emissions, subsequent air pollution, and impact on human health to timing, location, natural variability, and policy. Using state-of-the-art observations, modeling, assimilation, and epidemiological tools, we explored the pollution pathways between emissions and concentrations and their potential impact on human health.
We find opposing responses in both aerosol and trace gas pollutants for the same reduction in precursor emissions. The sign and magnitude of these responses are a function of the emission distribution, the local photochemical regime of emissions, and the seasonality. In particular, the first lockdowns in China occurred during the late NH winter, while lockdowns on other continents subsequently occurred during the NH Spring and early Summer. These changes in photochemical regimes play a capital role in explaining the differing regional responses. We furthermore show that differential reductions in precursor emissions due to COVID-19 mitigation led to changes in chemical regimes and the relative efficacy of precursors in secondary pollution formation. These results show that the COVID-19 era represents a unique “scenario-of-opportunity” to test how future sectoral reductions could occur and thus may inform future pollution and climate mitigation strategies.