Tropospheric NO2 retrieval algorithm for geostationary satellite instruments: application to GEMS

Abstract

In this study, we develop an advanced retrieval algorithm for tropospheric nitrogen dioxide (NO2) from the geostationary satellite instruments and apply it to Geostationary Environment Monitoring Spectrometer (GEMS) observations. Overall, the algorithm follows previous heritage for the polar orbiting satellites, but several improvements are implemented to account for specific features of geostationary satellites. The retrieved DLR GEMS tropospheric NO2 columns show good capability to capture hotspot signals at the scale of city clusters and describe spatial gradients from city centers to surrounding areas. Diurnal variations of tropospheric NO2 columns over Asia are well described through hourly sampling of GEMS. Evaluation of DLR GEMS tropospheric NO2 columns against TROPOMI v2.4 and GEMS v2.0 operational products show overall good agreement. The uncertainty of DLR GEMS tropospheric NO2 vertical columns varies based on observation scenarios. This retrieval algorithm can be easily adapted to other geostationary satellite instruments, such as TEMPO and Sentinel-4, enabling hourly monitoring and analysis across each continent in the future.