Abstract
Abstract. Estimates of the recovery time of stratospheric ozone heavily rely on the exact knowledge of the processes that lead to the decomposition of the relevant halogenated source gases. Crucial parameters in this context are fractional release factors (FRFs) as well as stratospheric lifetimes and ozone depletion potentials (ODPs). We here present data from the analysis of air samples collected between 2009 and 2011 on board research aircraft flying in the mid- and high-latitude stratosphere and infer the above-mentioned parameters for ten major source gases: CFCl3 (CFC-11), CF2Cl2 (CFC-12), CF2ClCFCl2 (CFC-113), CCl4 (carbon tetrachloride), CH3CCl3 (methyl chloroform), CHF2Cl (HCFC-22), CH3CFCl2 (HCFC-141b), CH3CF2Cl (HCFC-142b), CF2ClBr (H-1211), and CF3Br (H-1301). The inferred correlations of their FRFs with mean ages of air reveal less decomposition as compared to previous studies for most compounds. When using the calculated set of FRFs to infer equivalent stratospheric chlorine, we find a reduction of more than 20% as compared to the values inferred in the most recent Scientific Assessment of Ozone Depletion by the World Meteorological Organisation (WMO, 2011). We also note that FRFs and their correlations with mean age are not generally time-independent as often assumed. The stratospheric lifetimes were calculated relative to that of CFC-11. Within our uncertainties the ratios between stratospheric lifetimes inferred here agree with the values in recent WMO reports except for CFC-11, CFC-12 and CH3CCl3. Finally, we calculate lower ODPs than recommended by WMO for six out of ten compounds, with changes most pronounced for the three HCFCs. Collectively these newly calculated values may have important implications for the severity and recovery time of stratospheric ozone loss.
Highlights
2011 on board research aircraft flying in the mid- and highlatitude stratosphere and infer the above-mentioned parameters for ten major source gases: CFCl3 (CFC-11), CF2Cl2 (CFC-12), CF2ClCFCl2 (CFC-113), CCl4, CH3CCl3, CHF2Cl (HCFC22), CH3CFCl2 (HCFC-141b), CH3CF2Cl (HCFC-142b), CF2ClBr (H-1211), and CF3Br (H-1301)
If the data set used by Newman et al (2006) was influenced by mesospheric or even higher stratospheric air, this would lead to a modest shift of the fractional release factors (FRFs)–mean-age correlation similar to the observed difference
For CH3CCl3 and HCFC-142b we considered the maximum difference between our upper tropospheric and NOAA northern hemispheric (NH) mixing ratios
Summary
2011 on board research aircraft flying in the mid- and highlatitude stratosphere and infer the above-mentioned parameters for ten major source gases: CFCl3 (CFC-11), CF2Cl2 (CFC-12), CF2ClCFCl2 (CFC-113), CCl4 One of the most important observation-based studies of stratospheric lifetimes is that of Volk et al (1997), who used and further developed the theoretical framework of Plumb and Ko (1992) and Plumb (1996) to infer steady-state lifetimes of six important ozone-depleting halocarbons: CFCl3 (CFC-11), CF2Cl2 (CFC-12), CF2ClCFCl2 (CFC-113), CCl4 (carbon tetrachloride), CH3CCl3 (methyl chloroform), and CF2ClBr (H-1211) For this purpose they utilised the compact correlations that long-lived trace gases form with each other and with the mean ages of air (i.e. the mean stratospheric transit times). We compared our SF6 and CFC-11 mixing ratios during the seven 2010 Geophysica flights with in situ GCECD (Electron Capture Detector) measurements obtained by the High Altitude Gas Analyzer (HAGAR; see Werner et al, 2010, for details) with average 1 σ precisions of 1.3 % for SF6 and 1.9 % for CFC-11 Both data sets from the Geophysica flights are reported on the same NOAA calibration scales and showed very good agreement within their 1 σ measurement uncertainties
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