- Conference Proceedings Paper
Abstract: Halogenated greenhouse gases (such as HCFCs, HFCs, PFCs, and SF6) have global warming potentials thousands to tens of thousands of times greater than carbon dioxide on a per kilogram basis. Estimating the emissions of these gases on a global scale is challenging since direct measurements are unavailable. Instead, they are inferred using measured global atmospheric concentrations and knowledge of their lifetimes. The ocean uptake for halogenated species can impact their lifetimes, but this process has been assumed to be largely negligible in the past. Further, reaction with hydroxyl radicals (OH) is a major atmospheric loss pathway for HCFCs and HFCs. Emission estimations usually assume OH is constant over time, but recent chemistry-climate models suggest OH increased after 1980, implying underestimated emissions. Here, we use a coupled atmosphere-ocean model to explore how the inferred lifetimes and emissions of certain HCFCs, HFCs, PFCs, and SF6 can be affected by ocean processes and time-varying OH. We show that by including the ocean uptake, the lifetimes are shortened by 2 – 15% for HCFCs and HFCs, and 20 – 40% for PFC-14 and SF6. Certain HCFCs and HFCs can be further destroyed in the ocean due to microbial activity; this could lead to up to an another 8 – 25% decrease in their lifetimes. We also show that increases in modeled OH imply an additional underestimation in HCFC and HFC emissions by ~10% near their respective peak emissions. These species are considered under the Montreal Protocol and its amendments and the Paris Agreement. Evaluating the success of these global agreements requires accurate knowledge of contributions to global warming from these gases and consideration of these processes.