Re-evaluation of the lifetimes of the major CFCs and CH<sub>3</sub>CCl<sub>3</sub> using atmospheric trends

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).

Recent increases in the atmospheric growth rate and emissions of HFC-23 (CHF<sub>3</sub>) and the link to HCFC-22 (CHClF<sub>2</sub>) production

“…The model uses an annually repeating, monthly varying hydroxyl radical (OH) field from Spivakovsky et al (2000), which has been adjusted to match the observed trend in methyl chloroform (e.g. Rigby et al, 2013). For the gases in this paper, potential variations in OH concentration (e.g.…”

“…The firn air measurements were included in the inversion, with the age spectra from the firn model used to relate the firn measurements to high-latitude atmospheric mole fractions Vollmer et al, 2016). A 12-box model of atmospheric transport and chemistry was used to simulate baseline mole fractions, which assumed that the atmosphere was divided into four zonal bands (90-30 • N, 30-0 • N, 0-30 • S and 30-90 • S) and at 500 and 200 hPa vertically (Cunnold et al, 1994;Rigby et al, 2013). The model uses an annually repeating, monthly varying hydroxyl radical (OH) field from Spivakovsky et al (2000), which has been adjusted to match the observed trend in methyl chloroform (e.g.…”

Atmospheric histories and emissions of chlorofluorocarbons CFC-13 (CClF<sub>3</sub>), ΣCFC-114 (C<sub>2</sub>Cl<sub>2</sub>F<sub>4</sub>), and CFC-115 (C<sub>2</sub>ClF<sub>5</sub>)

“…Boxes are also separated at altitudes represented by 500 and 200 hPa. Model transport parameters and stratospheric photolytic loss vary seasonally and repeat interannually (Rigby et al, 2013). For the CFCs analyzed here, loss in the atmosphere is dominated by photolytic destruction in the stratosphere.…”

“…Similar to the study by Vollmer et al (2016) for halons, the present analysis uses a firn air model to characterize the age of the CFCs in the firn air samples , the AGAGE 12-box model to relate atmospheric mole fractions to surface emissions (Rigby et al, 2013), two inversion approaches to estimate hemispheric emissions, and a Lagrangian transport model to study regional emissions of CFC-115 in northeastern Asia. …”

“…The AGAGE box model was originally created by Cunnold et al (1983) and has since been rewritten and modified (Cunnold et al, 1994(Cunnold et al, , 1997Rigby et al, 2013;Vollmer et al, 2016). In the current version of the model, the atmosphere is divided into four zonal bands, separated at the Equator and at the 30 • latitudes, thereby creating boxes of similar air masses.…”