GEMS geostationary satellite investigation of the processes driving atmospheric pollutant diurnal and seasonal variations over Asia

Hourly observations were the main motivator for going to geostationary Earth orbit (GEO) to make satellite atmospheric composition measurements. The South Korean GEO-KOMPSAT-2/GEMS instrument realizes this capability over Asia with operational tracking of atmospheric pollutant diurnal variations. In this paper we discuss quantitative measures to characterize the diurnal variation of nitrogen dioxide (NO2) and formaldehyde (HCHO) as seen by GEMS and contrast these with the view obtained at the single overpass time of a low-Earth orbiting (LEO) satellite such as S5-P/TROPOMI. We use 3D atmospheric chemical transport model analysis to investigate how seasonal factors affect the pollutant diurnal emissions, meteorology, transport and chemistry processes at different spatial scales and contrast several metropolitan and background regions where air quality and human exposure are dependent on different sector emissions. Considering LEO infrared retrievals of carbon monoxide (CO) from TROPOMI also helps differentiate combustion sources such as fires. The satellite column retrievals are also compared with ground-based Pandora sun spectrometer observations and aircraft measurements taken during the 2023 ASIA-AQ aircraft field campaign.