Revealing Diurnal Variations of Air Quality Observations in Asia from Geostationary Environment Monitoring Spectrometer (GEMS)

A new era of air quality observations from geostationary Earth orbit(GEO) has begun with the launch of Geostationary Environment Monitoring Spectrometer (GEMS) over Asia and Tropospheric Emission of Pollutants (TEMPO) over North America as the two components of geostationary air quality (AQ) constellation. GEMS has provided hourly observations of AQ over Asia from a GEO since November 2020. Column amounts of atmospheric pollutants (O3, NO2, SO2, HCHO, CHOCHO, and aerosols) have been provided to capture their diurnal variations with the UV–visible spectrometer at 0.6 nm spectral resolution and sophisticated retrieval algorithms. Details of the latest GEMS version 3 products are presented, including validations, calibration, and case studies of volcanic eruption, dusts, and urban pollution. In version 3, there are noticeable improvements in trace gases from updated AMF, the separation of stratospheric/tropospheric components, fitting window, spectroscopy etc. Calibration/validation activities including the ASIA-AQ, Pandora Asia network (PAN), PEGASOS, GMAP/SIJAQ, ACCLIP, and international CAL/VAL team works are critical to evaluate and improve the overall data quality. The GEMS retrievals indicate good agreements from the campaigns, but still require further improvements in L1 processing as well. We are improving L1 processor 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 have been possible from LEO. Planned ESA’s Sentinel-4 in 2025 will complete the GEO AQ satellite constellation with GEMS and TEMPO, as recognized by the Committee on Earth Observation Satellites (CEOS).