The Fengyun-3 HIRAS Constellation: Achieving 8-Times-Daily Global Monitoring of Atmospheric Gases

Thermal infrared hyperspectral remote sensing from satellites is one of the key techniques for monitoring gas component concentrations in the atmosphere. With the successful launch of FY-3H in late 2025, the Hyperspectral Infrared Atmospheric Sounder-I (HIRAS-I) onboard China’s Fengyun (FY)-3D together with the HIRAS-II onboard FY-3 E/F/H series of meteorological satellites (hereafter referred to as the HIRAS constellation) enables up to eight times daily global monitoring of various trace gases. In this study, we present global spatial distributions of three key atmospheric species, carbon monoxide (CO), formic acid (HCOOH), and ammonia (NH₃) retrieved from HIRAS constellation spectra using our established optimal estimation retrieval framework. The hotspots and diurnal variations of these species can be effectively captured by the HIRAS constellation. The observed CO diurnal cycles are further compared against ground‑based Xianghe TCCON observations, showing good agreement. These high‑frequency satellite measurements provide a valuable observational constraint for reducing uncertainties in source/sink estimates and for improving our understanding of atmospheric transport and chemical transformation processes.