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

Atmospheric SO 2 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 SO 2 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 SO 2 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 SO 2 retrievals. The accuracy of FY-3F/OMS SO 2 retrievals was evaluated by comparing them with the DOAS and COvariance-Based Retrieval Algorithm (COBRA) SO 2 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 SO 2 retrievals exhibit good stability over clean oceanic regions (with a precision of approximately 0.15 DU), successfully capture volcanic SO 2 plumes, and effectively detect the elevated SO 2 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 SO 2 retrievals. This study is the first to present SO 2 retrievals from FY-3F/OMS observations, which is crucial for a comprehensive understanding of OMS's capability in SO 2 retrievals.