The Evolution of CFC Lifetimes in the Context of Emission Monitoring

The recent indirect detection of CFC-11 emissions prompts continued monitoring of atmospheric CFC concentrations and improvement of emission inversion models. In particular, changes to stratospheric circulation and mixing, which impact the lifetime of these compounds, will need to be considered when inverting emission from observations. The destruction of a given CFC in its "critical zone" of photolytic destruction depends on the mass flux into the critical zone, as well as the mixing rate of CFC-rich tropical air with depleted extratropical air. An increase in the mass flux through the photolytic zone, which is consistent with model projections of enhanced stratospheric circulation, would increase CFC destruction and decrease CFC lifetimes, while changes to the morphology of the circulation or an increase in mixing between the tropics and extratropics could decrease destruction by redirecting CFC-rich air away from the critical zone. Here, we evaluate the extent to which surface and satellite observations of CFC concentrations can improve our understanding of the transport of CFCs through the stratosphere. By focusing on the flux of CFCs into and out of the critical zone, we explore the sensitivity of total atmospheric lifetime to plausible changes to stratospheric transport. These results are framed in the context of future CFC emission monitoring and compliance with the Montreal Protocol.