Detecting and assessing trends of CFCs and substitutes from IASI measurements
Résumé
The first Infrared Atmospheric Sounding Instrument (IASI) on the Metop satellites suite has achieved
more than 13 years of continuous operation. The instrument stability and the consistency between the
different instruments on the successive Metop (A, B and C) is remarkable and offer the potential to
investigate trends in the concentration of various species better than with any other previous or current
hyperspectral IR sounder. The low noise of IASI radiances is also such that even weakly absorbing
species can be identified, on single or at least on averaged spectra. In this work, we apply the so-called
whitening transformation on IASI spectra, and show that it allows removing most of the climatological
background from spectra, leaving a residual that contains those spectral signatures that depart from
normality. These can subsequently be attributed to changes in the abundance of trace species. By
exploiting the first decadal record of IASI measurements, this method allows to (1) detect and monitor
halogenated compounds regulated by the Montreal protocol (CFCs) or used as substitutes (HCFCs,
HFCs), as well as fluorinated compounds (CF?, SF?) and potentially short-lived chlorine species, for
which substantial emissions are suspected (2) give a first assessment of the trend evolution of these
species over the 2008-2017 period covered by IASI on Metop-A. This is done by targeting various
geographical areas on the globe and examining the remote oceanic and continental source regions
separately. The trend evolution in the different chemical species, either negative or positive, is validated
against what is observed from ground-based measurement networks. We will conclude by assessing the
usefulness of IASI and follow-on mission to contribute to global measurements of ozone depleting
substances.