Methane mole fraction and [delta]13C above and below the trade wind inversion at Ascension Island in air sampled by aerial robotics

• Published in: Geophysical research letters Vol. 43; no. 22; p. 11,893
• Main Authors: Brownlow, R, Lowry, D, Thomas, R M, Fisher, R E, France, J L, Cain, M, Richardson, T S, Greatwood, C, Freer, J, Pyle, J A, MacKenzie, A R, Nisbet, E G
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-11-2016
• Subjects: Air masses; Air sampling; Atmosphere; Boundary layer; Boundary layers; Emissions; Fractions; Geophysics; Methane; Trade winds; Tropical environments; Wetland agriculture
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL071155

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 2700m 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 [delta]13C was observed compared to the air below. Back trajectories indicate that lofted CH4 emissions from Southern Hemisphere Africa have bulk [delta]13CCH4 signatures similar to background, suggesting mixed emissions from wetlands, agriculture, and biomass burning. The campaigns illustrate the usefulness of unmanned aerial system sampling and Ascension's value for atmospheric measurement in an understudied region.