Physics Colloquium: Advances in halocarbon emissions modeling, with impacts on the ozone layer and climate

Prof. Megan Lickley, Georgetown University

Abstract: Chlorofluorocarbons and their replacement chemicals are potent greenhouse gases whose production is regulated under the Montreal Protocol. These halocarbons are contained in equipment such as air conditioners, fire extinguishers, and foams and continue to be emitted after production has ceased. These ‘banks’ within equipment and applications are thus potential sources of future emissions, and must be carefully accounted for in order to evaluate ongoing compliance with the Montreal Protocol. Quantifying bank emissions versus nascent emissions has been limited by large uncertainties in bank size as well as uncertainties in atmospheric lifetimes. In this talk I will present a probabilistic Bayesian model of halocarbon banks and emissions, incorporating the widest range of constraints to date. I will show how jointly considering production and emissions of multiple gases can reduce uncertainty in lifetimes and ultimately better constrain banks, production and emissions estimates. I apply this model to the suite of the major banked chemicals regulated under the Montreal Protocol. I will show that if atmospheric lifetime and prior assumptions are accurate, banks are very likely larger than previous international assessments suggest, and that production has very likely been higher than reported.