SEASONAL TRENDS AND LOCAL INFLUENCES ON NONMETHANE HYDROCARBON CONCENTRATIONS IN THE CANADIAN BOREAL FOREST

Mixing ratios of nommethane hydrocarbons, both biogenic and anthropoge nic, have been monitored year-round at several sites in the boreal for ests of Saskatchewan and Ontario. Seasonal patterns in hydrocarbon mix ing ratios are explained by the wintertime effect of the Arctic air ma ss and die summertime increase in photochemical processing at all site s. Summertime differences in hydrocarbon distributions between sites a re indicative of the density of anthropogenic sources and the oxidativ e capacity of the atmosphere in the region. Consideration of hydrocarb on mixing ratios and OH reaction rate constants suggests that the biog enic hydrocarbon isoprene may limit the oxidative capacity of the atmo sphere in boreal regions. The observed temperature dependence of the i soprene mixing ratio suggests that the ambient isoprene concentration is strongly influenced by the emission rate.