CARBON-MONOXIDE AND METHANE OVER CANADA - JULY-AUGUST 1990

Carbon monoxide (CO) and methane (CH4) were measured in the 0.15- to 6 -km portion of the troposphere over subarctic and boreal landscapes of midcontinent and eastern Canada during July-August 1990. In the mid-c ontinent region, Arctic air entering the region was characterized by r elatively uniform CO concentrations (86-108 parts per billion by volum e (ppbv)) and CH4 concentrations (1729-1764 ppbv). Local biomass burni ng and long-range transport of CO into the area from industrial/urban sources and distant fires did frequently produce enhanced and variable concentrations. Emissions of CH4 from the Hudson Bay lowlands was the primary source far enhanced and variable concentrations, especially a t altitudes of 0.15-1 km. In eastern Canada, most of the observed vari ability in CO and CH4 was similar in origin to the phenomena described for the midcontinent region. However, unexpectedly low concentrations of CO (51 ppbv) and CH4 (1688 ppbv) were measured in the midtroposphe re on several flights. Combined meteorological and chemical data indic ated that the low CO-CH4( )events were the result of long-range transp ort of tropical Pacific marine air to subarctic latitudes.