Observationally-derived Fractional Release Factors, Ozone Depletion Potentials, and Stratospheric Lifetimes of Four Long-Lived CFCs: CFC-13 (CClF3), CFC-114 (C2Cl2F4), CFC-114a (CF3CCl2F), and CFC-115 (C2ClF5)

Short Summary: The greater the stratospheric lifetime of chlorofluorocarbons (CFCs), the longer they will deplete ozone. This paper investigates four longer-lived CFCs, and discovers two of them have much shorter lifetimes than previously believed. Demonstrating emissions of these compounds are higher than assumed, to account for their abundance. Unusually this paper uses stratospheric whole-air samples, rather than models or lab-based experiments, to derive policy-relevant metrics for these compounds.

Abstract: The longer an Ozone Depleting Substance (ODS) remains in the stratosphere, the longer it will be available for the process of ozone depletion. We present improved policy-relevant parameters: Fractional Release Factors (FRFs), Ozone Depletion Potentials (ODPs), and stratospheric lifetimes, for four understudied long-lived chlorofluorocarbons (CFCs): CFC-13 (CClF₃), CFC-114 (CClF₂CCClF₂), CFC-114a (CCl₂FCF₃), and CFC-115 (C₂ClF₅). Previous estimates for the stratospheric lifetimes of these compounds were derived using model and laboratory-based kinetic studies. This study instead uses stratospheric observational data, and correlations between FRFs and lifetimes, to semi-empirically and independently determine the steady-state stratospheric lifetimes of these compounds.

Our newly derived stratospheric lifetime estimates are 366 (290–439) years for CFC-13 (264 years shorter than previous estimates), 208 (171–250) years for CFC-114 (similar to previous estimates), 84 (74–95) years for CFC-114a (23 years shorter), and 404 (321–489) years for CFC-115 (260 years shorter). For CFC-13 and CFC-115 this is outside the uncertainty ranges of previously published estimates. This suggests that these two compounds may have had greater emissions than previously thought, in order to account for their abundance. We calculated FRFs and ODPs for the four CFCs of interest: CFC-13 (FRF=0.07, ODP=0.44), CFC-114 (FRF=0.12, ODP=0.52), CFC-114a (FRF=0.31, ODP=0.54), and CFC-115 (FRF=0.06, ODP=0.28). Providing new and updated lifetimes, FRFs and ODPs for these compounds, will help improve future estimates of their tropospheric emissions and their potential to damage the stratospheric ozone layer.