Diurnal and seasonal variations of atmospheric methane innorthern Finland

摘要

Methane concentrations were monitored at a continental site in Lapland,located in the zone of boreal forests and wetlands.The one-year-long record showed monthly meanvariation of about 40 ppb.High concentrations were observed during winter and summer.Elevated concentrations together with weak mixing conditions in summer indicated signs oflocal or regional sources of methane in boreal wetlands.During July-August the average diurnalcycle was nearly 20 ppb.Examination of back-trajectories showed that during summer easternair flows often carried high concentrations indicating sources of methane in northwesternSiberia.During winter high concentrations became more evident in southern air flows.Simultaneous increase in other compounds (e.g.CO2,Nox,Nox) suggested emissions of anthropogenicorigin.X)