Monitoring ammonia point sources over East Asia from the Geostationary Interferometric Infrared Sounder (GIIRS) on board China's FengYun-4 satellite

Atmospheric ammonia (NH3) is a reactive nitrogen compound that affects air quality and threatens public health. Real-time monitoring of atmospheric NH3 variations using satellite measurements will provide a reliable scientific basis for evaluating emission management strategies for anthropogenic sources. As the world's first geostationary hyperspectral infrared sounder, the Geostationary Interferometric Infrared Sounder (GIIRS) on board the FengYun-4 series of satellites provides an important advance to monitor NH3 total columns with day/night measurements at a 2-hour temporal resolution and a spatial resolution of 12 km at nadir. Using GIIRS NH3 retrievals, this study focused on the analysis of industrial and agricultural NH3 point sources over East Asia and in particular the diurnal cycle of these point sources. The identified point sources are first compared with estimates from the Emissions Database for Global Atmospheric Research (EDGAR) and similar hyperspectral infrared satellites, such as IASI and CrIS. The diurnal variations of NH3 point sources are further compared with simulations from chemical transport model such as GEOS-Chem. The findings demonstrate the unique capability of FY-4B/GIIRS in identifying NH3 point sources and capturing their temporal changes over East Asia, offering critical insights beyond the capabilities of current low-Earth orbit (LEO) instruments.