Man-made chlorofluorocarbons (CFCs) are the main reason for the Antarctic ozone “hole”. Under the Montreal Protocol, the production of these molecules has been regulated since 1990s. Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) were later used to replace CFCs. They are potent greenhouse gases, and their productions are also under regulation. It is important to understand all the loss pathways of these molecules to better estimate anthropogenic emissions and assess the global compliance to the Montreal Protocol.
The ocean uptake of these molecules was long been thought as a minor loss pathway. As anthropogenic emissions went down, natural losses become more important. We used a hierarchy of models to study the ocean uptake of CFCs, HCFCs, and HFCs and assess the impact on emission estimations.
Schematic illustrating the hierarchy of coupled atmosphere–ocean models used to simulate the oceanic uptake and outgassing of various halocarbons regulated under the Montreal Protocol.
Related Work
2023
GRL
On the Influence of Hydroxyl Radical Changes and Ocean Sinks on Estimated HCFC and HFC Emissions and Banks
Peidong Wang, Susan Solomon, Megan Lickley, Jeffery R. Scott, Ray F. Weiss, and Ronald G. Prinn
Abstract Hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are potent greenhouse gases regulated under the Montreal Protocol and its amendments. Emission estimates generally use constant atmospheric lifetimes accounting for loss via hydroxyl radical (OH) reactions. However, chemistry-climate models suggest OH increases after 1980, implying underestimated emissions. Further, HCFCs and HFCs are soluble in seawater and could be destroyed through in situ oceanic microbial activity. These ocean sinks are largely overlooked. Using a coupled atmosphere-ocean model, we show that increases in modeled OH imply underestimated HCFC and HFC emissions by 10% near their respective peak emissions. Our model results also suggest that oceanic processes could lead to up to an additional 10% underestimation in these halocarbon emissions in the 2020s. Ensuring global compliance to the Protocol and accurate knowledge of contributions to global warming from these gases therefore requires understanding of these processes.
@article{wang_influence_2023,title={On the {Influence} of {Hydroxyl} {Radical} {Changes} and {Ocean} {Sinks} on {Estimated} {HCFC} and {HFC} {Emissions} and {Banks}},volume={50},issn={0094-8276},number={18},urldate={2024-08-17},journal={Geophysical Research Letters},author={Wang, Peidong and Solomon, Susan and Lickley, Megan and Scott, Jeffery R. and Weiss, Ray F. and Prinn, Ronald G.},month=sep,year={2023},pages={e2023GL105472},}
2021
PNAS
On the effects of the ocean on atmospheric CFC-11 lifetimes and emissions
Peidong Wang, Jeffery R. Scott, Susan Solomon, John Marshall, Andrew R. Babbin, Megan Lickley, David W. J. Thompson, and 3 more authors
Proceedings of the National Academy of Sciences, Mar 2021
Manufactured CFC-11 is depleting the Antarctic ozone layer. CFC production has been strictly controlled by the Montreal Protocol, but emission estimates are very sensitive to choices of lifetimes, which are often assumed as constant over time. We employ a hierarchy of models to study the effect of the ocean on the time-dependent uptake and release of atmospheric CFC-11. The ocean is a sink for CFC-11 and significantly affects its total lifetime and hence the emission inferred from concentration data of past decades. This has not been explicitly included in international ozone assessments. We show that, as anthropogenic production ceases, ocean fluxes become more important, suggesting a need for further studies with high-resolution global models linking atmospheric chemistry and ocean processes. The ocean is a reservoir for CFC-11, a major ozone-depleting chemical. Anthropogenic production of CFC-11 dramatically decreased in the 1990s under the Montreal Protocol, which stipulated a global phase out of production by 2010. However, studies raise questions about current overall emission levels and indicate unexpected increases of CFC-11 emissions of about 10 Gg/yr after 2013 (based upon measured atmospheric concentrations and an assumed atmospheric lifetime). These findings heighten the need to understand processes that could affect the CFC-11 lifetime, including ocean fluxes. We evaluate how ocean uptake and release through 2300 affects CFC-11 lifetimes, emission estimates, and the long-term return of CFC-11 from the ocean reservoir. We show that ocean uptake yields a shorter total lifetime and larger inferred emission of atmospheric CFC-11 from 1930 to 2075 compared to estimates using only atmospheric processes. Ocean flux changes over time result in small but not completely negligible effects on the calculated unexpected emissions change (decreasing it by 0.4 ± 0.3 Gg/yr). Moreover, it is expected that the ocean will eventually become a source of CFC-11, increasing its total lifetime thereafter. Ocean outgassing should produce detectable increases in global atmospheric CFC-11 abundances by the mid-2100s, with emission of around 0.5 Gg/yr; this should not be confused with illicit production at that time. An illustrative model projection suggests that climate change is expected to make the ocean a weaker reservoir for CFC-11, advancing the detectable change in the global atmospheric mixing ratio by about 5 yr.
@article{wang_effects_2021,title={On the effects of the ocean on atmospheric {CFC}-11 lifetimes and emissions},volume={118},number={12},urldate={2024-08-17},journal={Proceedings of the National Academy of Sciences},author={Wang, Peidong and Scott, Jeffery R. and Solomon, Susan and Marshall, John and Babbin, Andrew R. and Lickley, Megan and Thompson, David W. J. and DeVries, Timothy and Liang, Qing and Prinn, Ronald G.},month=mar,year={2021},pages={e2021528118},}
