Evidence of continuing methylchloroform emissions from the United States

[1] 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.