Global atmospheric concentrations and source strength of ethane

Abstract

Ethane (C₂H₆), like other gaseous hydrocarbons, contributes significantly to the chemistry of the lower atmosphere, chiefly through reactions with the OH (hydroxyl) radical, an important tropospheric oxidizing agent. We present here a study of the variation in C₂H₆ concentration between northern and southern latitudes over 3 years, together with a new estimate of its source strength. Ethane concentrations vary from 0.07 to 3 p.p.b.v. (parts per 10⁹ by volume) in air samples collected in remote surface locations in the Pacific (latitude 71° N–47° S) in all four seasons between September 1984 and June 1985. Earlier remote measurements have generally shown concentrations in the 0.3–3.0 p.p.b.v. range, but coverage over a wide latitude range in the Southern Hemisphere has been limited to single trips^1–5. The variations are consistent with southerly transport from sources located chiefly in the Northern Hemisphere, further modified by seasonal variations in the strength of the reaction of C₂H₆ with OH radicals. These global data can be combined with concurrent data for CH₄ (refs 6, 7) and the laboratory reaction rates⁸ of each with OH to provide an estimate of 3 months as the average atmospheric lifetime for C₂H₆ and 13±3 Mtons for its annual atmospheric release.