First results of SO ₂ columns from FY-3F/OMS instrument observations

Abstract. Atmospheric SO2 has a significant impact on the urban environment and on global climate. Remote sensing provides an unprecedented tool for the continuous and real-time monitoring of atmospheric SO2 from volcanic eruptions and anthropogenic emissions. The Ozone Monitoring Suite (OMS) onboard the Chinese FENGYUN-3F (FY-3F) satellite launched in August 2023 is a new hyperspectral UV-VIS instrument in the FY-3 family of satellites, aiming to obtain information about atmospheric trace gases. In this study, we use the OMS Nadir (OMS-N) top-of-atmosphere (TOA) measurements and Differential Optical Absorption Spectroscopy (DOAS) inversion to for the first time retrieve global SO2 columns from these measurements. Based on the characteristics of the OMS instrument and the performance of its L1 data, specific schemes including solar spectrum selection, spectral soft calibration, and background offset correction were developed to effectively reduce along-track stripes and across-track asymmetry found in the raw OMS SO2 retrievals. The accuracy of FY-3F/OMS SO2 retrievals was evaluated by comparing them with the DOAS and COvariance-Based Retrieval Algorithm (COBRA) SO2 products from the TROPOspheric Monitoring Instrument (TROPOMI) onboard Copernicus Sentinel-5 Precursor (Sentinel-5P) over three typical areas: clean oceanic regions, volcanic eruption regions, and anthropogenic emission regions. The results indicate that the OMS SO2 retrievals exhibit good stability over clean oceanic regions (with a precision of approximately 0.15 DU), successfully capture volcanic SO2 plumes, and effectively detect the elevated SO2 columns from anthropogenic emissions in regions such as the Middle East, Eastern India, and Northern Russia. Detector non-uniformity and Air mass factor (AMF) uncertainty remains the primary error source of this first version of OMS SO2 retrievals. This study is the first to present SO2 retrievals from FY-3F/OMS observations, which is crucial for a comprehensive understanding of OMS's capability in SO2 retrievals.