A SEMIPHENOMENOLOGICAL MODEL FOR STOMATAL GAS-TRANSPORT

Ordinary diffusion of gases from (or into) a sub-stomatal cavity throu gh a stomatal pore into (or from) the ambient air is considered. The f ormulation of molar flux densities for trace components (CO2 and e.g. gaseous pollutants) is based on the use of the effective diffusion coe fficient and the coupling between transport of water vapour is include d. System geometry is simplified and the semiphenomenological, analyti cal molar flux expressions are presented in terms of the concentration difference between the cavity and the ambient air. The correction fac tors for the influence of a steady wind and the interference between p ores are derived. The interference is found to be important once stoma ta were not almost closed. The wind reduces the interference. The dire ct effect of water vapour diffusion on the transport of trace gases is shown to be marginal.