Low European methyl chloroform emissions inferred from long-term atmospheric measurements

Methyl chloroform in the balance Use of the solvent methyl chloroform is being phased out under the Montreal Protocol because of its ozone-depleting properties. Its atmospheric concentrations are declining, but recent studies have come to conflicting conclusions about trends in European emissions. Estimates range from less than 100,000 kg per year to over 20 million kg per year, the latter more than doubling previous global estimates. A new study evaluates these estimates based on data from Mace Head in Ireland and Jungfraujoch, Switzerland. The results do not support the recent unexpectedly high estimates, but with emission estimates from 60 million kg per year in the mid-1990s to up to 3.4 million kg per year from 2000 to 2003, they are higher than the latest consumption-based figures. The authors speculate that if these figures are correct, unrecorded methyl chloroform sources must exist, suggesting under-reporting of emissions by industry or of consumption by the Montreal Protocol reporting process. Methyl chloroform (CH 3 CCl 3 , 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 Protocol 1 . 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 CH 3 CC1 3 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 c