Atmosphere‐biosphere trace gas exchanges simulated with a single‐column model

The exchange of oxidized nitrogen species (NOx) between the biosphere and atmosphere is controlled by complex interactions between emissions, dry deposition, (photochemical) chemical transformations, and turbulent exchanges, all varying with height within the canopy. We have developed a multilayer atmosphere‐biosphere trace gas exchange model to study the role of canopy interactions in the net atmosphere‐biosphere NOx exchange flux on a global scale. We evaluate this model, implemented in a single‐column chemistry and meteorological model, for a selection of ecosystems by comparison with observations. The modeled and observed ozone and oxidized nitrogen concentrations and fluxes are generally in reasonable agreement if we constrain our model with site‐specific surface and meteorological parameters. The sensitivity of atmosphere‐biosphere trace gas exchange to nocturnal turbulent exchange appears to be large. A comparison of the NOx fluxes calculated by the traditional big leaf approach and the atmosphere‐biosphere model is presented. For sites that are exposed to relatively large anthropogenic emission fluxes, the big‐leaf approach and biosphere model calculate similar NOx fluxes, which confirms the applicability of the big‐leaf approach for polluted regions. However, for relatively pristine sites, differences between the NOx fluxes of the biosphere model and the big leaf approach are significant. This underscores the importance of an explicit representation of the biosphere processes for those locations where the NO soil emissions flux is comparable to or exceeds the anthropogenic emissions.