Perfluorocarbons in the global atmosphere: tetrafluoromethane, hexafluoroethane, and octafluoropropane

We present atmospheric baseline growth rates from the 1970s to the present for the longlived, strongly infrared-absorbing perfluorocarbons (PFCs) tetrafluoromethane (CF4), hexafluoroethane (C2F6), and octafluoropropane (C3F8) in both hemispheres, measured with improved accuracies (∼1–2%) and precisions (<0.3%, or <0.2 ppt (parts per trillion dry air mole fraction), for CF4; <1.5%, or <0.06 ppt, for C2F6; <4.5%, or <0.02 ppt, for C3F8) within the Advanced Global Atmospheric Gases Experiment (AGAGE). Pre-industrial background values of 34.7±0.2 ppt CF4 and 0.1±0.02 ppt C2F6 were measured in air extracted from Greenland ice and Antarctic firn. Anthropogenic sources are thought to be primary aluminum production (CF4, C2F6, C3F8), semiconductor production (C2F6, CF4, C3F8) and refrigeration use (C3F8). Global Correspondence to: J. Mühle ([email protected]) emissions calculated with the AGAGE 2-D 12-box model are significantly higher than most previous emission estimates. The sum of CF4 and C2F6 emissions estimated from aluminum production and non-metal production are lower than observed global top-down emissions, with gaps of ∼6 Gg/yr CF4 in recent years. The significant discrepancies between previous CF4, C2F6, and C3F8 emission estimates and observed global top-down emissions estimated from AGAGE measurements emphasize the need for more accurate, transparent, and complete emission reporting, and for verification with atmospheric measurements to assess the emission sources of these long-lived and potent greenhouse gases, which alter the radiative budget of the atmosphere, essentially permanently, once emitted. Published by Copernicus Publications on behalf of the European Geosciences Union. 5146 J. Mühle et al.: Perfluorocarbons in the global atmosphere Table 1. Lifetimes and global warming potentials of CF4, C2F6, and C3F8. Lifetime Global Warming Potential (GWP) Formula Name years 100-yr horizon 100-yr horizon 500-year horizon (SARa) (AR4b) (AR4) CF4 PFC-14 50 000 6500 7390 11 200 C2F6 PFC-116 10 000 9200 12 200 18 200 C3F8 PFC-218 2600 7000 8830 12 500 a IPCC Second Assessment Report; b IPCC Fourth Assessment Report.