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

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.