Stratospheric Lifetimes of CFC-11 and CFC-12 from Envisat MIPAS
Hoffmann, Lars; Hoppe, Charlotte; Lehmann, Catrin; Müller, Rolf; Spang, Reinhold
Forschungszentrum Jülich, GERMANY
Monitoring the global distribution of chlorofluorocarbons like CFC-11 and CFC-12 is important for many reasons. The chlorine released by photolytic decomposition plays a major role in ozone depletion both in the upper stratosphere and in the polar regions. In addition, CFCs and most of their replacements are strong infrared absorbers, and they contribute significantly to the anthropogenic greenhouse effect. Continuous measurements of photochemically long-lived trace gases such as CFC-11 or CFC-12 are useful to validate transport in atmospheric models. Furthermore, tracer-tracer relations of long-lived trace gases are frequently examined to study dynamical processes like mixing events.
CFCs originate from anthropogenic activity in the troposphere and are removed by photolytic decomposition and reaction with atomic oxygen in the stratosphere. Their trends are controlled by the balance of sinks and sources. The "stratospheric lifetime" is one particular measure of the global loss rate for CFCs. The loss rates are crucial in determining the Ozone Depletion Potentials (ODPs) and the Greenhouse Warming Potentials (GWPs) of CFCs. The lifetimes of many long-lived compounds, including CFC-11 and CFC-12, are currently being reassessed within a SPARC initiative.
The ratio of the stratospheric lifetimes of two CFCs can be determined based on the tracer-tracer correlation method. This method relates the slope of the relation between two long-lived tracer to the ratio of their fluxes through the tropopause. Here, we apply the method to zonal mean climatologies of CFC-11 and CFC-12 obtained from Envisat MIPAS, to provide new estimates of their relative stratospheric lifetimes. To validate the results, the same approach is applied on global climatologies from other satellite experiments (ACE, CRISTA-1, and HIRDLS) and simulation results from a chemical transport model (EMAC/CLaMS).