Facility-scale quantification and monitoring of ammonia (NH 3 ) emissions using ASTER multispectral thermal infrared observations

Ammonia (NH 3 ) is an important atmospheric pollutant affecting air quality, ecosystems, and climate. Hyperspectral thermal infrared sounders such as IASI and CrIS combine broad coverage with high spectral sensitivity, but their kilometer-scale footprints limit facility-scale source attribution. Here we test whether high-spatial-resolution multispectral thermal infrared imaging can detect NH 3 plumes at facility scale. We develop a physically based retrieval framework for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), combining radiative transfer calculations with lookup table (LUT) inversion. The method exploits the differential sensitivity of ASTER bands 13 and 14 to NH 3 absorption in the ν 2 band near 930–970 cm −1 , retrieving NH 3 column enhancements at 90 m spatial resolution with surface emissivity prescribed from a long-term ASTER emissivity climatology. NH 3 absorption remains measurable after convolution with the ASTER spectral response functions, but retrieval performance depends strongly on thermal contrast between the surface and the NH 3 -bearing layer. The retrieval is applied to three industrial NH 3 point sources: Khor Al Zubair, Tolyatti, and Piesteritz. Khor Al Zubair yields repeated source-connected plumes under favorable arid conditions; Tolyatti and Piesteritz show that detection is also possible in more heterogeneous environments. Source rates derived with the Integrated Mass Enhancement method are instantaneous estimates for individual detected scenes rather than annual mean emissions, with detected-scene medians of 56.6, 27.1, and 6.0 kt yr −1 at the three sites. These agree in order of magnitude with published satellite and airborne estimates, and at Khor Al Zubair to within a few per cent of the CrIS estimate once the differing NH 3 lifetime assumptions are placed on a common basis. The reported uncertainties are dominated by the assumed effective wind speed and are not a complete error budget. Multispectral TIR imagers can therefore resolve NH 3 plume structure and source location, complementing coarse-resolution sounders. Sampling is limited by revisit frequency, cloud cover and thermal contrast, so the approach suits episodic mapping of large, persistent sources and retrospective analysis of the ASTER archive.