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CFC-11, CFC-12 and HCFC-22 ground-based remote sensing FTIR measurements at Reunion Island and comparisons with MIPAS/ENVISAT data
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  • Source:
    Atmospheric Measurement Techniques, 9(11), 5621-5636.
Filetype[PDF-4.08 MB]

  • Description:
    Profiles of CFC-11 (CCl3F), CFC-12 (CCl2F2) and HCFC-22 (CHF2Cl) have been obtained from Fourier transform infrared (FTIR) solar absorption measurements above the Saint-Denis (St Denis) and Maido sites at Reunion Island (21 degrees S, 55 degrees E) with low vertical resolution. FTIR profile retrievals are performed by the well-established SFIT4 program and the detail retrieval strategies along with the systematic/random uncertainties of CFC-11, CFC-12 and HCFC-22 are discussed in this study. The FTIR data of all three species are sensitive to the whole troposphere and the lowermost stratosphere, with the peak sensitivity between 5 and 10 km. The ground-based FTIR data have been compared with the collocated Michelson Interferometer for Passive Atmospheric Sounding (MIPAS/ENVISAT) data and found to be in good agreement: the observed mean relative biases and standard deviations of the differences between the smoothed MIPAS and FTIR partial columns (6-30 km) are (-4.3 and 4.4 %), (-2.9 and 4.6 %) and (-0.7 and 4.8 %) for CFC-11, CFC-12 and HCFC-22, respectively, which are within the combined error budgets from both measurements. The season cycles of CFC-11, CFC-12 and HCFC-22 from FTIR measurements and MIPAS data show a similar variation: concentration is highest in February-April and lowest in August-October. The trends derived from the combined St Denis and Maido FTIR time series are -0.86 +/- 0.12 and 2.84 +/- 0.06% year(-1) for CFC-11 and HCFC-22, respectively, for the period 2004 to 2016, and -0.76 +/- 0.05% year(-1) for CFC-12 for 2009 to 2016. These measurements are consistent with the trends observed by the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Division's (GMD) Halocarbons & other Atmospheric Trace Species Group (HATS) measurements at Samoa (14.2 degrees S, 170.5 degrees W) for CFC-11 (-0.87 +/- 0.04% year(-1)), but slightly weaker for HCFC-22 (3.46 +/- 0.05 %) year(-1) and stronger for CFC-12 (-0.60 +/- 0.02% year(-1)).
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