Global NO₂ Dynamics During the COVID-19 Pandemic: A Comparison Between Two Waves of the Coronavirus

Nitrogen dioxide (NO2) as one of the key pollutants in the atmosphere, is an important trace gas of traffic emissions or industrial activities. The coronavirus disease (COVID-19) epidemic preventions have significantly reduced the emissions of NO2, which provided an opportunity to disentangling the contributions to global emissions in major epidemic regions. Here, we quantified the influences of lockdown measures on the NO2concentration at a global scale during the two waves of the COVID-19 epidemic, and disentangled the relative contributions of the major epidemic regions (i.e., China, Europe, and USA) on the global NO2densities due to the lockdown measures. Our results revealed that there was an evident decrease of global NO2in 2020, especially in China, Europe, and USA. The global mean NO2densities decreased approximately 2.1 and 3.9 μmol/m2in the first and second waves of the epidemic. While in the Northern Hemisphere, NO2densities decreased 6.6 μmol/m2on average during the first stage of the epidemic, and a slight increase (i.e., 1.7 μmol/m2) in the second wave of the epidemic. The magnitudes and durations of the second wave were much smaller than the first wave of the coronavirus infections. The strict lockdown measures implemented in China significantly decreased the NO2concentration, which therefore the largest contributor in the first wave decreases of global average NO2densities. Intervention at an early stage would be beneficial to the preventions of epidemic situation. Our study could provide references for economic loss assessments and economic recovery strategies during the stages ofpost-pandemic.