European Soil NOx Emissions Derived From Satellite NO2 Observations

We introduce an innovative method to distinguish soil nitrogen oxides (NOx = NO + NO2) emissions from satellite-based total NOx emissions. To evaluate the approach, we compare the deviation between the tropospheric NO2 concentration observed by satellite and two atmospheric composition model simulations driven by the newly estimated soil NOx emissions and the Copernicus Atmosphere Monitoring Service (CAMS) inventory. The estimated average soil NOx emissions in Europe are 1.7 kg N ha−1 yr−1 in 2019, and the annual soil NOx emissions are approximately 1.7 times larger than that of the CAMS inventory. The discrepancy originates mainly from the forests, which would mean that the soil NOx emissions over forest areas in Europe are currently underestimated by the CAMS inventory. The model evaluation indicates that the simulations driven by DECSO-soil emissions performed significantly better than using CAMS-soil. Overall, the simulated RMSE% of DECSO-soil is lower than that of CAMS-soil, approximately 6% lower in spring and 2% lower in autumn. Our method can easily be extended to other regions in the world despite having monthly variations that are very different from those in Europe.