NOx Emissions Reduction and Rebound in China Due to the COVID-19 Crisis

During the COVID-19 lockdown (24 January–20 March) in China low air pollution levels were reported in the media as a consequence of reduced economic and social activities. Quantification of the pollution reduction is not straightforward due to effects of transport, meteorology, and chemistry. We have analyzed the NO_x emission reductions calculated with an inverse algorithm applied to daily NO₂ observations from TROPOMI onboard the Copernicus Sentinel-5P satellite. This method allows the quantification of emission reductions per city and the analysis of emissions of maritime transport and of the energy sector separately. The reductions we found are 20–50% for cities, about 40% for power plants, and 15–40% for maritime transport depending on the region. The reduction in both emissions and concentrations shows a similar timeline consisting of a sharp reduction (34–50%) around the Spring festival and a slow recovery from mid-February to mid-March.