Determination of Total Column of Trichlorofluoromethane in the Atmosphere Considering the Effect of Amorphous Water Ice Precipitation on the Spectrometer Detector

A ground-based spectroscopic method for determining the trichlorofluoromethane (CCl₃F) content from measurements of IR spectra of solar radiation using an IFS-125HR Fourier spectrometer (FTIR method) is considered. A detector based on mercury–cadmium–tellurium (HgCdTe), which is used for measurements in the CCl₃F absorption spectral region, was cooled by liquid N₂. An amorphous ice film grew on the detector crystal as the vacuum in the metal Dewar flask gradually deteriorated during cooling. The spectral absorption band of amorphous ice at liquid N₂ temperature overlapped the CCl₃F absorption band. The variability of the ice film thickness added additional uncertainty to the estimates of the CCl₃F atmospheric content. A technique has been developed to estimate the thickness of the ice film, to account for its spectral absorption in the algorithm for solving the inverse problem, and to eliminate this uncertainty. The technique was applied to measuring the atmospheric concentration of CCl₃F in 2017–2019 over the NDACC St. Petersburg station. The results were compared with those obtained earlier using a technique in which the thickness of the ice film was treated as an unknown parameter adjusted during solution of the inverse problem. Previously obtained CCl₃F atmospheric contents were refined using the proposed technique. The difference reached 10%.