The Tropospheric Emissions: Monitoring POllution (TEMPO) instrument (see Smithsonian Institute, EO Portal, or WMO Oscar) is supposed to measure air pollution over North America from a geostationary orbit. It is in that sense comparable to Copernicus Sentinel-4 Ultraviolet, Visible, Near-infrared (UVN) (to be launched on EUMETSATs Meteosat Third Generation (MTG)-S in 2023) or GEO-Kompsat 2 Geostationary Environment Monitoring Spectrometer (GEMS). UVN and GEMS are confirmed to happen but I can't find a recent firm status on TEMPO. Does TEMPO have a confirmed platform? Apparently, the instrument has been built and delivered to NASA. The last I've seen is an unconfirmed proposal for it to fly on a commercial satellite in 2022, but this is scarce on details.
NO₂ from TROPOMI. Source: Smithsonian Institute, © KNMI/IASB/ESA/SAO.