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

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.