Pioneering Air Quality Monitoring over East and Southeast Asia with the Geostationary Environment Monitoring Spectrometer (GEMS)

The Geostationary Environment Monitoring Spectrometer (GEMS) onboard the Geostationary Korea Multi-Purpose Satellite-2B (GEO-KOMPSAT-2B) satellite, launched in February 2020, represents a pioneering milestone in air quality monitoring across East and Southeast Asia.GEMS provides hourly data on atmospheric pollutants, including nitrogen dioxide (NO 2 ), sulfur dioxide (SO 2 ), ozone (O 3 ), volatile organic compounds such as formaldehyde (HCHO) and glyoxal (CHOCHO), as well as aerosols, all with high spatial resolution.The Environmental Satellite Center (ESC) of the National Institute of Environmental Research (NIER) is responsible for processing, retrieving, and distributing GEMS data, offering critical insights into the transport and spatial distribution of these pollutants.GEMS data has been instrumental in analyzing significant air pollution events, such as episodes of elevated particulate matter, wildfires, and volcanic eruptions.Additionally, ongoing research projects led by ESC are focused on developing novel application techniques, including satellite data fusion, top-down emissions estimation, and nighttime pollutant detection.GEMS operates as part of a global geostationary constellation, alongside the United States' Tropospheric Emissions: Monitoring of Pollution (TEMPO) and Europe's Sentinel-4, enhancing both the spatial and temporal coverage of air pollutants and facilitating data sharing for quality assurance.Looking ahead, ESC aims to expand its environmental monitoring capabilities by launching a constellation of microsatellites dedicated to greenhouse gas monitoring, together with the next generation of GEMS, which will continue its air quality monitoring missions.This paper presents an overview of GEMS operations, data products, and applications while outlining future strategies for enhancing air quality monitoring and supporting environmental policies aimed at clean air and climate mitigation.