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Science 13 November 1987:
Vol. 238. no. 4829, pp. 945 - 950
DOI: 10.1126/science.238.4829.945
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Articles

Atmospheric Trends in Methylchloroform and the Global Average for the Hydroxyl Radical

R. PRINN 1, D. CUNNOLD 2, R. RASMUSSEN 3, P. SIMMONDS 4, F. ALYEA 2, A. CRAWFORD 3, P. FRASER 5, and R. ROSEN 6

1 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139.
2 School of Geophysical Sciences, Georgia Institute of Technology, Atlanta, GA 30332.
3 Institute of Atmospheric Sciences, Oregon Graduate Center, Beaverton, OR 97005.
4 Department of Geochemistry, University of Bristol, Bristol, BF8-1TS, United Kingdom.
5 Division of Atmospheric Research, Commonwealth Scientific and Industrial Research Organization, Aspendale, 3195 Victoria, Australia.
6 Atmospheric and Environmental Research, Inc., Cambridge, MA 02139.

Frequent atmospheric measurements of the anthropogenic compound methylchloroform that were made between 1978 and 1985 indicate that this species is continuing to increase significantly around the world. Reaction with the major atmospheric oxidant, the hydroxyl radical (OH), is the principal sink for this species. The observed mean trends for methylchloroform are 4.8, 5.4, 6.4, and 6.9 percent per year at Aldrigole (Ireland) and Cape Meares (Oregon), Ragged Point (Barbados), Point Matatula (American Samoa), and Cape Grim (Tasmania), respectively, from July 1978 to June 1985. These measured trends, combined with knowledge of industrial emissions, were used in an optimal estimation inversion scheme to deduce a globally averaged methylchloroform atmospheric lifetime of 6.3 (+ 1.2, -0.9) years (1sgr uncertainty) and a globally averaged tropospheric hydroxyl radical concentration of (7.7 ± 1.4) x 105 radicals per cubic centimeter (1sgr uncertainty). These 7 years of gas chromatographic measurements, which comprise about 60,000 individual calibrated real-time air analyses, provide the most accurate estimates yet of the trends and lifetime of methylchloroform and of the global average for tropospheric hydroxyl radical levels. Accurate determination of hydroxyl radical levels is crucial to understanding global atmospheric chemical cycles and trends in the levels of trace gases such as methane.

Submitted on June 2, 1987
Accepted on September 1, 1987


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