A Satellite Data-Driven Framework to Rapidly Quantify Air Basin-Scale NO x Emission and Its Application to the Po Valley during the COVID-19 Pandemic

Abstract. The evolving nature of the COVID-19 pandemic necessitates timely estimates of the resultant perturbations to anthropogenic emissions. Here we present a novel framework based on the relationships between observed column abundance and wind speed to rapidly estimate the air-basin-scale NO x emission rate and apply it at the Po Valley in Italy using OMI and TROPOMI NO 2 tropospheric column observations. The NO x chemical lifetime is retrieved together with the emission rate and found to be 15–20 h in winter and 5–6 h in summer. A statistical model is trained using the estimated emission rates before the pandemic to predict the trajectory without COVID-19. Compared with this business-as-usual trajectory, the real emission rates show three distinctive drops in March 2020 ( −42 % ), November 2020 ( −38 % ), and March 2021 ( −39 % ) that correspond to tightened COVID-19 control measures. The temporal variation of pandemic-induced NO x emission changes qualitatively agrees with Google and Apple mobility indicators. The overall net NO x emission reduction in 2020 due to the COVID-19 pandemic is estimated to be 22 % .