An approach to retrieve information on the carbonyl fluoride (COF<sub>2</sub>) vertical distributions above Jungfraujoch by FTIR multi-spectrum multi-window fitting

Abstract

Abstract. We present an original multi-spectrum fitting procedure to retrieve volume mixing ratio (VMR) profiles of carbonyl fluoride (COF 2 ) from ground-based high resolution Fourier transform infrared (FTIR) solar spectra. The multi-spectrum approach consists of simultaneously combining, during the retrievals, all spectra recorded consecutively during the same day and with the same resolution. Solar observations analyzed in this study with the SFIT-2 v3.91 fitting algorithm correspond to more than 2900 spectra recorded between January 2000 and December 2007 at high zenith angles, with a Fourier Transform Spectrometer operated at the high-altitude International Scientific Station of the Jungfraujoch (ISSJ, 46.5 • N latitude, 8.0 • E longitude, 3580 m altitude), Switzerland. The goal of the retrieval strategy described here is to provide information about the vertical distribution of carbonyl fluoride. The microwindows used are located in the ν 1 or in the ν 4 COF 2 infrared (IR) absorption bands. Averaging kernel and eigenvector analysis indicates that our FTIR retrieval is sensitive to COF 2 inversion between 17 and 30 km, with the major contribution to the retrieved information always coming from the measurement. Moreover, there was no significant bias between COF 2 partial columns, total columns or VMR profiles retrieved from the two bands. For each wavenumber region, a complete error budget including all identified sources has Correspondence to: P. Duchatelet (p.duchatelet@ulg.ac.be) been carefully established. In addition, comparisons of FTIR COF 2 17-30 km partial columns with KASIMA and SLIM-CAT 3-D CTMs are also presented. If we do not notice any significant bias between FTIR and SLIMCAT time series, KASIMA COF 2 17-30 km partial columns are lower of around 25%, probably due to incorrect lower boundary conditions. For each times series, linear trend estimation for the 2000-2007 time period as well as a seasonal variation study are also performed and critically discussed. For FTIR and KASIMA time series, very low COF 2 growth rates (0.4±0.2%/year and 0.3±0.2%/year, respectively) have been derived. However, the SLIMCAT data set gives a slight negative trend (−0.5±0.2%/year), probably ascribable to discontinuities in the meteorological data used by this model. We further demonstrate that all time series are able to reproduce the COF 2 seasonal cycle, which main seasonal characteristics deduced from each data set agree quite well.

Satellite observations of stratospheric carbonyl fluoride

“…As mentioned in the Introduction, there is evidence that the atmospheric abundance of COF 2 is increasing with time (Duchatelet et al, 2009;Brown et al, 2011). Although the atmospheric abundances of COF 2 source gases such as CFC-12 and CFC-113 are currently decreasing, HCFC-22 and the minor HFC contributors are still on the increase.…”

“…HF is removed from the stratosphere by slow transport to, and rainout in, the troposphere, or by upward transport to the mesosphere, where it is destroyed by photolysis (Duchatelet et al, 2010). The recent stratospheric fluorine inventory for -2009(Brown et al, 2014 indicates a year-on-year increase of HF and total fluorine.…”

“…Recent studies indicate that its atmospheric abundance is increasing (Duchatelet et al, 2009;Brown et al, 2011). The main sources of COF 2 are the atmospheric degradation of CFC-12 (CCl 2 F 2 ) and CFC-113 (CF 2 ClCFCl 2 ), which are both now banned under the Montreal Protocol, and HCFC-22 (CHF 2 Cl), the most abundant HCFC and classed as a transitional substitute under the Montreal Protocol.…”

“…Previously, vertical profiles of COF 2 in the atmosphere have been determined from measurements taken by the Atmospheric Trace MOlecule Spectroscopy (ATMOS) instrument which flew four times on NASA space shuttles between 1985 and 1994 (Rinsland et al, 1986;Zander et al, 1994). Additionally, there have been several studies into the seasonal variability of COF 2 columns above Jungfraujoch using ground-based Fourier transform infrared (FTIR) solar observations (Mélen et al, 1998;Duchatelet et al, 2009). The use of satellite remotesensing techniques allows the measurement of COF 2 atmospheric abundances with global coverage, and the investigation more fully of COF 2 trends, and seasonal and latitudinal variability.…”

Global stratospheric fluorine inventory for 2004–2009 from Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measurements and SLIMCAT model simulations

“…The reaction path for a particular compound is determined by the number of fluorine atoms in the molecule. The source gas molecule will first be broken down into CF 2 Cl and will then follow the following path (Tressaud, 2006): (Duchatelet et al, 2009;Brown et al, 2011).…”