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Nature 403, 295-298 (20 January 2000) | doi:10.1038/35002049

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A strong source of methyl chloride to the atmosphere from tropical coastal land

Y. Yokouchi1, Y. Noijiri1, L. A. Barrie2, D. Toom-Sauntry2, T. Machida1, Y. Inuzuka1, H. Akimoto3, H.-J. Li1,3, Y. Fujinuma1 & S. Aoki4

  1. National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba, Ibaraki 305-0053, Japan
  2. Atmospheric Environment Service, 4095, Dufferin St., Toronto, Ontario M3H 5T4, Canada
  3. Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1, Komaba, Meguro-ku , Tokyo 153-8904, Japan
  4. Center for Atmospheric and Oceanic Studies, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-0845, Japan

Correspondence to: Y. Yokouchi1 Correspondence and requests for materials should be addressed to Y.Y. (e-mail: Email: yokouchi@nies.go.jp).

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Methyl chloride (CH3Cl), the most abundant halocarbon in the atmosphere, has received much attention as a natural source of chlorine atoms in the stratosphere1, 2. The annual global flux of CH3 Cl has been estimated to be around 3.5 Tg on the grounds that this must balance the loss through reaction with OH radicals (which gives a lifetime for atmospheric CH3Cl of 1.5 yr)3, 4, 5. The most likely main source of methyl chloride has been thought to be oceanic emission2, 6, 7, 8, with biomass burning the second largest source9. But recent seawater measurements10 indicate that oceanic fluxes cannot account for more than 12% of the estimated global flux of CH3Cl, raising the question of where the remainder comes from. Here we report evidence of significant CH3Cl emission from warm coastal land, particularly from tropical islands. This conclusion is based on a global monitoring study and spot measurements, which show enhancement of atmospheric CH3Cl in the tropics, a close correlation between CH3Cl concentrations and those of biogenic compounds emitted by terrestrial plants, and OH-linked seasonality of CH3Cl concentrations in middle and high latitudes. A strong, equatorially located source of this nature would explain why the distribution of CH3Cl is uniform between the Northern and Southern hemispheres, despite their differences in ocean and land area.

  1. National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba, Ibaraki 305-0053, Japan
  2. Atmospheric Environment Service, 4095, Dufferin St., Toronto, Ontario M3H 5T4, Canada
  3. Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1, Komaba, Meguro-ku , Tokyo 153-8904, Japan
  4. Center for Atmospheric and Oceanic Studies, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-0845, Japan

Correspondence to: Y. Yokouchi1 Correspondence and requests for materials should be addressed to Y.Y. (e-mail: Email: yokouchi@nies.go.jp).