Using multi-satellite observations to constrain ammonia emissions and unlock their potential over open water

Reducing uncertainty in ammonia ([Formula: see text]) emissions, particularly those over open water, which have largely been unexplored, remains a key challenge. This study refines 2019 [Formula: see text] emissions over the south-central United States (SCUS) using inverse modeling technique with Cross-track Infrared Sounder (CrIS) data and assesses its impact on inorganic [Formula: see text]. We also present a novel assessment of [Formula: see text] emissions constrained by Infrared Atmospheric Sounding Interferometer (IASI) and CrIS datasets both individually and combined. For the first time, we demonstrate the potential of refining [Formula: see text] emissions over open water using satellite data, specifically over the northwestern Gulf of Mexico (NWGOM). Annual posterior NH₃ emissions exceeded prior estimates over SCUS by 1.43 GgNa^-1 (2.5-fold), raising average concentrations by 2.9 ppb (3.4-fold), particularly in Texas, New Mexico, and Oklahoma, and increasing levels of particulate ammonium (1.26-fold), sulfate (1.01-fold), and nitrate (2-fold). Combined IASI/CrIS outperformed individual datasets when compared with surface measurements. Over NWGOM, average [Formula: see text] concentrations increased significantly by 1.4 ppb, predominantly driven by biological nitrogen fixation. This study highlights the potential of satellite data to refine [Formula: see text] emissions over open water and emphasizes the role of multi-satellite datasets and high-resolution regional inverse modeling in improving air quality forecasts and global emission estimates.