Relationship between CO2 Flux and CO2 Concentration at a Boreal Forest

On the diurnal time scale, eddy correlation CO₂ flux measurements have footprints of about 1 km², while CO₂ concentration measurements have footprints of the order of 1000 km². Therefore it is necessary to understand the relationship between the CO₂ flux and concentration measurements to scale up the small scale flux measurements to the regional scale concentration measurements. In this study, we examined the flux-concentration relationship in the atmospheric boundary layer (ABL) at a boreal forest site in Saskatchewan, Canada; using a combination of flux measurements, aircraft profile concentration measurements, and coupled biosphere-atmosphere model. The results suggest that in the night time with typically low wind speed, the CO₂ concentration in the shallow stably stratified ABL is dominated by the local CO₂ flux. While the daytime CO₂ concentration in the deep well-mixed ABL is strongly influenced by atmospheric transport, and the atmospheric transport is driven by mesoscale and synoptic scale processes. Therefore, understanding of the mesoscale and synoptic scale atmosphere-biosphere interaction is important in the flux-concentration relationship.