Isotopic signatures of methane emissions from tropical fires, agriculture and wetlands: the MOYA and ZWAMPS flights

Euan G. Nisbet, Grant Allen, Rebecca E. Fisher, James L. France, James D. Lee, David Lowry, Marcos F. Andrade, Thomas J. Bannan, Patrick Barker, Prudence Bateson, Stéphane J.-B. Bauguitte, Keith N. Bower, Tim J. Broderick, Francis Chibesakunda, Michelle Cain, Alice E. Cozens, Michael C. Daly, Anita L. Ganesan, Anna E. Jones, Musa LambakasaMark F. Lunt, Archit Mehra, Isabel Moreno, Dominika Pasternak, Paul I. Palmer, Carl J. Percival, Joseph R. Pitt, Amber J. Riddle, Matthew Rigby, Jacob T. Shaw, Angharad C. Stell, Adam R. Vaughan, Nicola J. Warwick, Shona E. Wilde

Research output: Contribution to journalArticlepeer-review

Abstract

We report methane isotopologue data from aircraft and ground measurements in Africa and South America. Aircraft campaigns sampled strong methane fluxes over tropical papyrus wetlands in the Nile, Congo and Zambezi basins, herbaceous wetlands in Bolivian southern Amazonia, and over fires in African woodland, cropland and savannah grassland. Measured methane δ 13 C CH 4 isotopic signatures were in the range -55 to -49‰ for emissions from equatorial Nile wetlands and agricultural areas, but widely -60 ± 1‰ from Upper Congo and Zambezi wetlands. Very similar δ 13 C CH 4 signatures were measured over the Amazonian wetlands of NE Bolivia (around -59‰) and the overall δ 13 C CH 4 signature from outer tropical wetlands in the southern Upper Congo and Upper Amazon drainage plotted together was -59 ± 2‰. These results were more negative than expected. For African cattle, δ 13 C CH 4 values were around -60 to -50‰. Isotopic ratios in methane emitted by tropical fires depended on the C3: C4 ratio of the biomass fuel. In smoke from tropical C3 dry forest fires in Senegal, δ 13 C CH 4 values were around -28‰. By contrast, African C4 tropical grass fire δ 13 C CH 4 values were -16 to -12‰. Methane from urban landfills in Zambia and Zimbabwe, which have frequent waste fires, had δ 13 C CH 4 around -37 to -36‰. These new isotopic values help improve isotopic constraints on global methane budget models because atmospheric δ 13 C CH 4 values predicted by global atmospheric models are highly sensitive to the δ 13 C CH 4 isotopic signatures applied to tropical wetland emissions. Field and aircraft campaigns also observed widespread regional smoke pollution over Africa, in both the wet and dry seasons, and large urban pollution plumes. The work highlights the need to understand tropical greenhouse gas emissions in order to meet the goals of the UNFCCC Paris Agreement, and to help reduce air pollution over wide regions of Africa. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.

Original languageEnglish
Article number20210112
JournalPhilosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Volume380
Issue number2215
DOIs
Publication statusPublished - 24 Jan 2022

Keywords

  • African air pollution
  • African biomass burning
  • African wetlands
  • aircraft surveys
  • atmospheric methane
  • methane isotopes

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