Long‐term trends in the concentrations of SF₆, CHClF₂, and COF₂ in the lower stratosphere from analysis of high‐resolution infrared solar occultation spectra

Abstract

Long-term trends in the concentrations of SF 6, CHCIF2 (CFC-22), and COF2 in the lower stratosphere have been derived from analysis of ca. 1980 and more recent infrared solar occultation spectra recorded near 32øN latitude at --•0.02-cm -1 resolution. Consistent sets of line parameters and spectral calibration methods have been used in the retrievals to minimize systematic error effects. Quoted error limits are 1 sigma estimated precisions. The SF 6 and CHCIF2 results are based on spectra recorded by balloon-borne interferometers in March 1981 and June 1988 and a comparison of these results with the Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment/Spacelab 3 measurements obtained in May 1985 near 30øN latitude. In the 13-18 km altitude range the mean measured SF 6 mixing ratio in parts per trillion by volume (pptv) increased from 1.17 +_ 0.21 in March 1981 to 2.02 +_ 0.20 pptv in June 1988, and the CHC1F 2 mixing ratio below 15 km altitude increased from 51 +_ 8 pptv in March 1981 to 102 +_ 10 pptv in June 1988. The CHC1F2 retrievals used new empirical CHCIF2 line parameters derived from 0.03-cm-1 resolution laboratory spectra recorded at six temperatures between 203 and 293 K' the derived mixing ratios are --•30% higher than obtained with earlier sets of line parameters, thereby removing a large discrepancy noted previously between IR and in situ measurements of CHCIF2. Assuming an exponential growth model for fitting the trends, SF 6 and CHC1F2 mean increase rates of 7.4% +_ 1.9% and 9.4% +_ 1.3% year -• are obtained, respectively which correspond to cumulative increases by factors of--• 1.7 and --•2.0 in the concentrations of these gases over the 7.2-year measurement period. Analysis of spectra recorded in October 1979 and April 1989 yields COF2 volume mixing ratios that are respectively 0.44 +_ 0.17 and 1.21 +_ 0.24 times the ATMOS/Spacelab 3 values, from which an average COF2 increase rate of 10.3 +_ 1.8% year -1 over this time period has been estimated. The present results are compared with previously reported observations and trends and with one-dimensional model calculations. The model calculated trends are in reasonably good agreement with the observations.

Diode Laser Jet Spectra and Analysis of the ν3 and ν8 Fundamentals of CHF2Cl

“…Chlorodifluoromethane (CHF 2 Cl, CFC 22) is mainly used in refrigeration, air conditioning, and fluoropolymer production (1). The atmospheric release rates grew from 53 × 10 9 g/yr (1975) to 95 · 10 9 g/yr in 1985 (1).…”

“…More recently infrared spectra have been obtained from the ground (3), from balloons (4), and from a space shuttle (ATMOS/Spacelab3) (1). Through the analysis of these infrared spectra a steady increase of the CFC 22 concentration in the troposhere from 1980 up to now has been observed (1,2,5). Reference (1) reports an increase from 51 ± 8 pptv (1981) up to 102 ± 10 pptv (1988), corresponding to increase rates of 9.4 ± 1.3%/yr from 1981 to 1988 (1) (cf.…”

“…The concentration of CHF 2 Cl in the atmosphere (troposphere and lower stratosphere) was measured initially by GC/MC techniques ( gas chromatography combined with mass spectrometry) on air samples (2). More recently infrared spectra have been obtained from the ground (3), from balloons (4), and from a space shuttle (ATMOS/Spacelab3) (1). Through the analysis of these infrared spectra a steady increase of the CFC 22 concentration in the troposhere from 1980 up to now has been observed (1,2,5).…”

“…It is well known that CHF 2 Cl contributes to ozone depletion and global warming (green house effect). The tropospheric lifetime, due to UV photolysis and oxidation by OH radicals (7), of CHF 2 Cl is about 10-30 years (1,2,(6)(7)(8); the most recent estimated lifetime is 15-20 years (9). The analysis of infrared tropospheric and stratospheric spectra is hindered by the lack of detailed spectroscopic knowledge (absorption cross sections, quantum assignments, line broadening parameters) even for the strongest bands in the atmospheric window (8-13 µm tational (and vibrational) cooling can be obtained by expanding seeded mixtures of CFC's in a supersonic jet, thus simplifying the absorption spectra.…”

“…The atmospheric release rates grew from 53 × 10 9 g/yr (1975) to 95 · 10 9 g/yr in 1985 (1). The concentration of CHF 2 Cl in the atmosphere (troposphere and lower stratosphere) was measured initially by GC/MC techniques ( gas chromatography combined with mass spectrometry) on air samples (2).…”