1. Empa, Institute of Materials Science and Technology, Ueberlandstrasse 129, 8600 Duebendorf, Switzerland
2. Climate Research, Met Office, FitzRoy Road, Exeter EX1 3PB, UK
3. School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 1TS, UK
4. School of Earth and Atmospheric Sciences, Georgia Institute of Technology, 221 Bobby Dodd Way, Atlanta, Georgia 30332-0340, USA
5. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
6. Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0244, USA
7. Atmospheric Research, Commonwealth Scientific and Industrial Research Organisation, PMBI, Aspendale, Victoria 3195, Australia

Correspondence to: Stefan Reimann¹ Correspondence and requests for materials should be addressed to S.R. (Email: stefan.reimann@empa.ch).

Abstract

Methyl chloroform (CH₃CCl₃, 1,1,1,-trichloroethane) was used widely as a solvent before it was recognized to be an ozone-depleting substance and its phase-out was introduced under the Montreal Protocol¹. Subsequently, its atmospheric concentration has declined steadily^{2, 3, 4} and recent European methyl chloroform consumption and emissions were estimated to be less than 0.1 gigagrams per year^{1, 5}. However, data from a short-term tropospheric measurement campaign (EXPORT) indicated that European methyl chloroform emissions could have been over 20 gigagrams in 2000 (ref. 6), almost doubling previously estimated global emissions^{1, 4}. Such enhanced emissions would significantly affect results from the CH₃CC1₃ method of deriving global abundances of hydroxyl radicals (OH) (refs 7–12)—the dominant reactive atmospheric chemical for removing trace gases related to air pollution, ozone depletion and the greenhouse effect. Here we use long-term, high-frequency data from Mace Head, Ireland and Jungfraujoch, Switzerland, to infer European methyl chloroform emissions. We find that European emission estimates declined from about 60 gigagrams per year in the mid-1990s to 0.3–1.4 and 1.9–3.4 gigagrams per year in 2000–03, based on Mace Head and Jungfraujoch data, respectively. Our European methyl chloroform emission estimates are therefore higher than calculated from consumption data^{1, 5}, but are considerably lower than those derived from the EXPORT campaign in 2000 (ref. 6).

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