Comment on “Tracking Ethane From Space Over a Large US Oil and Gas Region” by Francoeur et al.

Recent studies have established the ability to detect atmospheric ethane from space using thermal infrared observations from the Cross-track Infrared Sounder (CrIS). Francoeur et al. (2025; https://doi.org/10.1029/2025GL115286) compare temporal changes in ethane spectral signals over the Permian Basin with emission changes inferred previously from CrIS for the same region. The spectral signals and the previously-estimated emissions do not change at the same relative rate, and the authors ascribe this apparent disparity to potential impacts from interferences and radiative transfer uncertainties. Here we show that spectral signals should not be expected to change in a 1:1 manner with emissions due to the regional ethane background and because, in the thermal infrared, signal: column sensitivity drops when higher emissions cause a greater fraction of the atmospheric column to be located near the ground. We agree with Francoeur et al. (2025, https://doi.org/10.1029/2025GL115286) regarding both the value and challenges associated with space-borne thermal infrared ethane measurements.