TRANSPORT AND FATE OF REACTIVE TRACE GASES IN RED SPRUCE NEEDLES .2. INTERPRETATIONS OF FLUX EXPERIMENTS USING GAS-TRANSPORT THEORY

A mathematical description of the multicomponent transport of gaseous species into needles of conifer trees is presented. Detailed physiology of the stomatal zone is taken into account, and diffusion through the atmospheric boundary layer, wax-filled antechamber, stomata, and substomatal cavity are described starting from the fundamental equations for multicomponent gas diffusion. The model was used to analyze the results from two sets of exposure experiments in which red spruce saplings were exposed to gas-phase H2O2 or to a combination of H2O2, SO2, and O3. Model calculations indicate that the wax-filled antechamber may provide a porous zone in which water can condense, thus protecting the sensitive inner tissues below the stomata from exposure to water-soluble, toxic, trace gases (such as SO2 and H2O2). The model was found to be sensitive to the accuracy of measurements of leaf temperature, dewpoint temperature of the chamber inlet and exit air, and gas flow rate and may provide some insight into the role of atmospheric pollutants in forest decline.