Radiative impact of long-lived halocarbons and their atmospheric trends, derived from 15 years of IASI/Metop measurements

In addition to being harmful to the ozone layer (for chlorinated and brominated compounds), halocarbons are also potent greenhouse gases. Their monitoring is therefore essential. Here we exploit measurements from the infrared satellite sounder IASI which offers the potential to robustly assess trends in the atmospheric abundances of trace gases owing to the stability and the consistency of the measurements made by three successive instruments over a period of more than 15 years. Despite their weak spectral signatures, we have recently reported the detection of eight long-lived halocarbons in IASI spectra: CFC-11, CFC-12, HCFC-22, HCFC-142b, HFC-134a, CF₄, SF₆ and CCl₄.

In this work we exploit the available record of continuous IASI measurements to (1) determine the temporal evolution in atmospheric abundance of these species (2) quantify their radiative impact for the first time. We calculate their global radiative forcing based on integration over specific bands of IASI spectrally resolved fluxes (Whitburn et al., 2020^[1]). Our results are validated with ground-based measurement networks and other remote sensors data. We conclude by assessing the usefulness of IASI and follow-on missions to contribute to the global monitoring of CFCs and their substitutes.

^[1] Whitburn, S. et al. Spectrally resolved fluxes from IASI data: retrieval algorithm for clear-sky measurements. J. Clim. 33, 6971—6988 (2020).