Testing the CO2M NO2 Retrieval Algorithm using TROPOMI Spatial Zoom Data

The future Copernicus Anthropogenic CO2 Monitoring Mission (CO2M) will provide CO2 data at a high resolution of 2x2 km2 with unprecedented accuracy and precision. In addition to bands in the near-infrared and shortwave infrared, the CO2I spectrometer on board of CO2M also contains a visible band for the retrieval of NO2 tropospheric columns. NO2 observations will be performed to aid the detection and identification of CO2 emission plumes, as NO2 is co-emitted during combustion processes and acts as a tracer of CO2. Due to its relatively low tropospheric background value and biospheric influence, local enhancements of tropospheric NO2 are better detectable than those of CO2 and allow for more accurate CO2 emission estimates. Furthermore, this NO2 product will be very valuable for air quality applications, especially emission source quantification.To fully exploit the high resolution of the NO2 measurements, five times higher than the operational resolution of the TROPOMI instrument onboard Sentinel 5P, improvements on multiple aspects of the air-mass correction in the tropospheric NO2 retrieval algorithm are considered: (1) anisotropic surface treatment at high spatial resolution using MODIS-like products, (2) effective cloud/aerosol parameter retrieval as a scattering layer using co-registered cloud information provided by the on-board cloud imager instrument (CLIM) and the measured O2-O2 and O2-A absorption bands and (3) high resolution NO2 a-priori profiles from the CAMS global/regional model forecasts.The TROPOMI instrument produced a limited data set during the commissioning phase, where measurements were performed with increased spatial sampling of 2.4x1.8 km2. This data set captures typical scenes showing NO2 emission plumes at a similar spatial resolution as the planned CO2M measurements, allowing for the CO2M NO2 retrieval algorithm to be tested on real data. These TROPOMI zoom data are processed with the new prototype algorithm for CO2M and impacts of the improvements are quantified.