Abstract
Abstract. Since the Montreal Protocol on Substances that Deplete the Ozone Layer and its amendments came into effect, growth rates of the major ozone depleting substances (ODS), particularly CFC-11, -12 and -113 and CH3CCl3, have declined markedly, paving the way for global stratospheric ozone recovery. Emissions have now fallen to relatively low levels, therefore the rate at which this recovery occurs will depend largely on the atmospheric lifetime of these compounds. The first ODS measurements began in the early 1970s along with the first lifetime estimates calculated by considering their atmospheric trends. We now have global mole fraction records spanning multiple decades, prompting this lifetime re-evaluation. Using surface measurements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the National Oceanic and Atmospheric Administration Global Monitoring Division (NOAA GMD) from 1978 to 2011, we estimated the lifetime of CFC-11, CFC-12, CFC-113 and CH3CCl3 using a multi-species inverse method. A steady-state lifetime of 45 yr for CFC-11, currently recommended in the most recent World Meteorological Organisation (WMO) Scientific Assessments of Ozone Depletion, lies towards the lower uncertainty bound of our estimates, which are 544861 yr (1-sigma uncertainty) when AGAGE data were used and 524561 yr when the NOAA network data were used. Our derived lifetime for CFC-113 is significantly higher than the WMO estimates of 85 yr, being 10999121 (AGAGE) and 10997124 (NOAA). New estimates of the steady-state lifetimes of CFC-12 and CH3CCl3 are consistent with the current WMO recommendations, being 11195132 and 11295136 yr (CFC-12, AGAGE and NOAA respectively) and 5.044.925.20 and 5.044.875.23 yr (CH3CCl3, AGAGE and NOAA respectively).
Highlights
Earth System Sciences surements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the National Oceanic and Atmospheric Administration Global Monitoring Division (NOAA GMD) from 1978 to 2011, we estimated the lifetime of CFC11, CFC-12, CFC-113 and CH3CCl3 using a multi-species inverse method
Atmospheric Lifetime Experiment (ALE), and subsequent projects, the Global Atmospheric Gases Experiment (GAGE) and Advanced Global Atmospheric Gases Experiment (AGAGE, Prinn et al, 2000) used automated gas chromatograph with an electron capture detector (GC-ECD) systems to monitor CFC mole fractions at five background locations across the globe, and measurements are ongoing today. These data sets have primarily been used for emissions estimation in more recent years (e.g. Cunnold et al, 1994), emissions derived using a chemical transport model and the ALE/GAGE/AGAGE measurements have been compared to inventory estimates to investigate the feasibility of particular lifetime estimates
We find that an uncertainty function that begins at around 1.5 % in the 1970s and 1980s that drops to 0.3 % from 2000 fits the AGAGE-NOAA differences well for CFC-11 and 12, whereas relatively constant uncertainties of around 0.3 % and 1 % fit the differences between the two networks for CFC-113 and CH3CCl3
Summary
Earth System Sciences surements from the Advanced Global Atmospheric Gases Experiment (AGAGE) and the National Oceanic and Atmospheric Administration Global Monitoring Division (NOAA GMD) from 1978 to 2011, we estimated the lifetime of CFC11, CFC-12, CFC-113 and CH3CCl3 using a multi-species inverse method. ALE, and subsequent projects, the Global Atmospheric Gases Experiment (GAGE) and Advanced Global Atmospheric Gases Experiment (AGAGE, Prinn et al, 2000) used automated GC-ECD systems to monitor CFC mole fractions at five background locations across the globe, and measurements are ongoing today These data sets have primarily been used for emissions estimation in more recent years (e.g. Cunnold et al, 1994), emissions derived using a chemical transport model and the ALE/GAGE/AGAGE measurements have been compared to inventory estimates to investigate the feasibility of particular lifetime estimates (e.g. a lifetime of 26 yr for CFC-113 was found to be largely inconsistent with estimated release rates in Fraser et al, 1996). This is because our technique requires robust emissions estimates, which do not appear to be available for some important ozone-depleting gases such as CCl4 (e.g. Xiao et al, 2010; Montzka et al, 2011b)
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