Observing Air Quality in Asia from Geostationary Earth Orbit at High Spatiotemporal Resolution - GEMS

Diurnal variation of air quality over Asia have been observed by the Geostationary Environment Monitoring Spectrometer (GEMS) for the first time from a geostationary Earth orbit (GEO) since its launch in February 2020. GEMS has provided column amounts of atmospheric pollutants (O₃, NO₂, SO₂, HCHO, CHOCHO, and aerosols) to capture their diurnal variations with the UV–visible spectrometer at 0.6 nm spectral resolution and sophisticated retrieval algorithms. Details of the GEMS mission are presented, including calibrations, results, validations, and case studies including volcanic eruption, dusts, and urban pollution. L2 algorithms have been updated for version 2 and the products were released on November 30, 2022. In version 2, there are noticeable improvements in trace gases from updated AMF and the separation of stratospheric/tropospheric components. Ongoing calibration/validation activities including the 2022 GMAP/SIJAQ campaign and international CAL/VAL team works are critical to diagnose and improve the overall data quality. The GEMS retrievals indicate good agreements from the validation campaign, but still require further improvement in L1 processing. We start testing improvements for L1 processing including BTDF correction. Faster sampling rates at higher spatial resolution increase the probability of finding cloud-free pixels, leading to more observations of aerosols and trace gases than has been possible from LEO. GEMS will be joined by NASA’s Tropospheric Emissions: Monitoring of Pollution (TEMPO) this year and ESA’s Sentinel-4 to form a GEO AQ satellite constellation in late 2024, respectively, as recognized by the Committee on Earth Observation Satellites (CEOS).