In two recent studies, lead by Empa, unexpected atmospheric trend reversals were found for the hydrochlorofluorocarbons (HCFCs) HCFC-31 (CH2ClF) and HCFC-133a (CF3CH2Cl). The two compounds, which have no end-user applications, have been measured continuously in the atmosphere at European (Mace Head and Jungfraujoch) and Australian (Cape Grim) stations using AGAGE measurement technologies. Complementary measurements from Antarctica and from archived air in canisters allowed to reconstruct their atmospheric histories over the past ~15 years. The measurements show increasing abundance in the atmosphere until about 2012, but after that, the concentrations start to decline again. When combining these measurements with the AGAGE 12-box model, it reveals a sharp reversal in their global emissions as well. The sources of these compounds are still not fully known but most likely, HCFC-31 is an intermediate process agent in the production of the refrigerant HFC-32, and HCFC-133a is an intermediate in the production of the refrigerant HFC-134a. Given that the world-wide productions of these two compounds is continuing to increase, it is a puzzle as to why HCFC-31 and HCFC-133a are declining in the atmosphere.
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First observations, trends, and emissions of HCFC-31 (CH2ClF) in the global atmosphere. Schoenenberger, F. et al. (2015), Geophysical Research Letters 42, 7817–7824.
Abrupt reversal in emissions and atmospheric abundance of HCFC-133a (CF3CH2Cl). Vollmer, M.K. et al. (2015), Geophysical Research Letters 42, 8702–8710.