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Published Online May 3, 2001
Science DOI: 10.1126/science.1058673

Research Articles

Submitted on December 28, 2000
Accepted on April 17, 2001

Evidence for Substantial Variations of Atmospheric Hydroxyl Radicals in the Past Two Decades

R. G. Prinn 1, J. Huang 1, R. F. Weiss 2, D. M. Cunnold 3, P. J. Fraser 4, P. G. Simmonds 5, A. McCulloch 5, C. Harth 2, P. Salameh 2, S. O'Doherty 5, R. H. J. Wang 3, L. Porter , B. R. Miller 2

1 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA.
3 Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA.
4 Atmospheric Research, Commonwealth Scientific and Industrial Research Organization, Aspendale, Victoria, Australia.
5 School of Chemistry, University of Bristol, Bristol, UK.

The hydroxyl radical (OH) is the dominant oxidizing chemical in the atmosphere. It destroys most air pollutants, and many gases involved in ozone depletion and the greenhouse effect. Global measurements of 1,1,1-trichloroethane (methyl chloroform, CH3CCl3) provide an accurate method for determining the global and hemispheric behavior of OH. Measurements show that CH3CCl3 levels rose steadily from 1978 to reach a maximum in 1992 and then decreased rapidly to levels in 2000 lower than the levels when measurements began in 1978. Analysis of these observations shows that OH levels in the southern hemisphere are on average about 14 ±35% higher than in the northern hemisphere, and global average OH levels rose 15 ±22% between 1979 and 1989 and then subsequently decreased to levels in 2000 about 10 ±24% below 1979 values. These variations imply important and unexpected gaps in current understanding of the capability of the atmosphere to cleanse itself.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)