Distributions, long term trends and emissions of four perfluorocarbons in remote parts of the atmosphere and firn air

J C Laube,W T Sturges,D E Oram,E Witrant,C Hogan,F S Mani,M J Newland,C E Reeves,T Röckmann,P Martinerie,C A M Brenninkmeijer,G P Mills,J Schwander,P J Fraser

doi:10.5194/acp-12-4081-2012

Abstract

Abstract. We report the first data set of atmospheric abundances for the following four perfluoroalkanes: n-decafluorobutane (n-C4F10), n-dodecafluoropentane (n-C5F12), n-tetradecafluorohexane (n-C6F14) and n-hexadecafluoroheptane (n-C7F16). All four compounds could be detected and quantified in air samples from remote locations in the Southern Hemisphere (at Cape Grim, Tasmania, archived samples dating back to 1978) and the upper troposphere (a passenger aircraft flying from Germany to South Africa). Further observations originate from air samples extracted from deep firn in Greenland and allow trends of atmospheric abundances in the earlier 20th century to be inferred. All four compounds were not present in the atmosphere prior to the 1960s. n-C4F10 and n-C5F12 were also measured in samples collected in the stratosphere with the data indicating that they have no significant sinks in this region. Emissions were inferred from these observations and found to be comparable with emissions from the EDGAR database for n-C6F14. However, emissions of n-C4F10, n-C5F12 and n-C7F16 were found to differ by up to five orders of magnitude between our approach and the database. Although the abundances of the four perfluorocarbons reported here are currently small (less than 0.3 parts per trillion) they have strong Global Warming Potentials several thousand times higher than carbon dioxide (on a 100-yr time horizon) and continue to increase in the atmosphere. We estimate that the sum of their cumulative emissions reached 325 million metric tonnes CO2 equivalent at the end of 2009.

Highlights

Perfluorocarbons (PFCs) are fully fluorinated hydrocarbons which have very long atmospheric lifetimes and very high Global Warming Potentials (GWPs) in the case of alkanes (IPCC, 2007; Bravo et al, 2010)
We report the first data set of atmospheric abundances for the following four perfluoroalkanes: n-decafluorobutane (n-C4F10), n-dodecafluoropentane (n-C5F12), n-tetradecafluorohexane (n-C6F14) and nhexadecafluoroheptane (n-C7F16)
This is the case for all four compounds reported here. n-C4F10 mixing ratios increased from 0.018±0.002 ppt in 1978 to 0.171±0.002 ppt at the end of 2010

Summary

Introduction

Perfluorocarbons (PFCs) are fully fluorinated hydrocarbons which have very long atmospheric lifetimes and very high Global Warming Potentials (GWPs) in the case of alkanes (IPCC, 2007; Bravo et al, 2010). The atmospheric sources of these previously reported compounds are entirely industrial and mainly attributed release from aluminium production, electronics manufacturing, fire protection and solvent applications (IPCC/TEAP, 2005; Muhle et al, 2010), except for CF4 which has been found to have been present in the atmosphere in pre-industrial times (e.g. Harnisch et al, 1996a; Worton et al, 2007). Emissions and usage have been reported for other perfluoroalkanes such as n-C4F10 and n-C5F12 These have been proposed and/or used as refrigerants, in air conditioning, as fire suppressants and in semiconductor manufacturing (Robin and Iikubo, 1992; Mazurin et al, 1994; IPCC/TEAP, 2005; EDGAR, 2010). It is likely that the GWP of n-C7F16 is between 8000 and 10 000 In addition these compounds have very long atmospheric lifetimes of 2,600 (n-C4F10), 4100 (n-C5F12), 3,100 (n-C6F14) and 3000 (n-C7F16) years (WMO, 2011). Discuss. on the same day as ours (Ivy et al, 2012)

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