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 NO₂ concentration 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 NO₂ densities due to the lockdown measures. Our results revealed that there was an evident decrease of global NO₂ in 2020, especially in China, Europe, and USA. The global mean NO₂ densities decreased approximately 2.1 and 3.9 μmol/m² in the first and second waves of the epidemic. While in the Northern Hemisphere, NO₂ densities decreased 6.6 μmol/m² on 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 NO₂ concentration, which therefore the largest contributor in the first wave decreases of global average NO₂ densities. 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.