Facility-scale quantification and monitoring of ammonia (NH₃) emissions using ASTER multispectral thermal infrared observations

Abstract. Ammonia (NH₃) is an important atmospheric pollutant affecting air quality, ecosystems, and climate, but current satellite observations remain limited in their ability to resolve individual emission sources. Hyperspectral thermal infrared sounders such as the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS) provide broad spatial coverage and high spectral sensitivity, but their kilometer‑scale footprints limit direct facility‑scale source attribution. Here, we investigate whether high‑spatial‑resolution multispectral thermal infrared imaging can detect NH₃ 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 inversion. The method exploits the differential sensitivity of ASTER bands 13 and 14 to NH₃ absorption in the ν₂ band near 930–970 cm⁻¹ and retrieves NH₃ column enhancements at 90 m spatial resolution. Surface emissivity is taken from a long‑term ASTER emissivity climatology, while scene‑level emissivity products are used diagnostically to identify plume‑related band behavior. Sensitivity tests show that NH₃ absorption remains measurable after convolution with the ASTER spectral response functions, but retrieval performance depends strongly on thermal contrast between the surface and the NH₃‑bearing layer.

The retrieval is applied to ASTER observations over three industrial NH₃ point sources: Khor Al Zubair, Tolyatti, and Piesteritz. Khor Al Zubair provides the clearest demonstration, with repeated source‑connected plume structures under favorable arid conditions. Tolyatti and Piesteritz show that detection is also possible in more heterogeneous environments, although only under suitable thermal contrast and surface conditions. Source‑rate estimates derived with the Integrated Mass Enhancement method are interpreted as instantaneous effective estimates for successful plume scenes, not as annual mean emissions or continuous facility‑average emissions. Where independent constraints are available, ASTER‑derived source‑rate statistics are consistent in magnitude with published satellite and airborne estimates.

These results demonstrate that multispectral thermal infrared imagers can provide high‑resolution information on NH₃ plume structure and source location, complementing coarse‑resolution hyperspectral satellite observations. The approach is best suited for large, persistent sources and episodic plume mapping rather than routine monitoring, because ASTER sampling is limited by revisit frequency, cloud cover, and thermal contrast. The framework supports retrospective analysis of archival ASTER scenes and informs future high‑resolution thermal infrared imaging concepts for NH₃ point‑source detection.