Methane mole fraction and δ13C above and below the trade wind inversion at Ascension Island in air sampled by aerial robotics

Rebecca Brownlow, David Lowry, Rick Thomas, Rebecca Fisher, James France, Michelle Cain, Thomas Richardson, Colin Greatwood, Jim Freer, John Pyle, Euan Nisbet

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Ascension Island is a remote South Atlantic equatorial site, ideal for monitoring tropical background CH4. In September 2014 and July 2015, octocopters were used to collect air samples in Tedlar bags from different heights above and below the well-defined Trade Wind Inversion (TWI), sampling a maximum altitude of 2700 meters above mean sea-level. Sampling captured both remote air in the marine boundary layer below the TWI, and also air masses above the TWI that had been lofted by convective systems in the African tropics. Air above the TWI was characterized by higher CH4 but no distinct shift in δ13C was observed compared to the air below. Back-trajectories indicate that lofted methane emissions from southern hemisphere Africa have bulk δ13CCH4 signatures similar to background, suggesting mixed emissions from wetlands, agriculture and biomass burning. The campaigns illustrate the usefulness of UAS sampling, and Ascension’s value for atmospheric measurement in an understudied region.
Original languageEnglish
Pages (from-to)11893-11902
Number of pages10
JournalGeophysical Research Letters
Issue number22
Early online date5 Nov 2016
Publication statusPublished - 28 Nov 2016

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