Evidence of continuing methylchloroform emissions from the United States

We present measurements from three sites during 2001-2002 showing that methylchloroform emissions have continued in the U.S., despite the 1996 production ban under the Montreal Protocol. Available data from urban regions, if representative, suggest that 1997-2002 U.S. emissions declined exponentially from 18.5 to 3.0 Gg/yr. F-11 also showed evidence of ongoing emissions, whereas F-113 emissions have effectively ceased. Continuous in-situ measurements in urban regions provide an effective means of detecting ongoing emissions of banned compounds. Neglecting continuing emissions causes underestimates in tropospheric OH abundance derived from methylchloroform concentrations.