Anthropogenic NOx emissions of China, the US and Europe from 2019 to 2022 inferred from TROPOMI observations

Anthropogenic nitrogen oxide (NOx) emissions are closely associated with human activities. In recent years, global human activity patterns have changed significantly owing to the COVID-19 epidemic and international energy crisis. However, their effects on NOx emissions are not yet fully understood. In this study, we developed a two-step inversion framework using NO2 observations from the TROPOMI satellite and the GEOS-Chem global atmospheric chemical transport model, and inferred global anthropogenic NOx emissions from 2019 to 2022, focusing on China, the United States (U.S.), and Europe. Our results indicated an 1.68% reduction in NOx emissions in 2020 and a 5.72% rebound in 2021 across all regions. China rebounded faster than the others, surpassing its 2019 levels by July 2020. In 2022, emissions declined in all regions, driven mainly by the Omicron variant, energy shortages, and clean energy policies. Our findings provide valuable insights for the development of effective future emission management strategies.