Development of A Multilayer Biochemical Dry Deposition model

A multi-layer biochemical dry deposition model has been developed to study gaseous exchanges between the atmosphere and biosphere. A biochemical stomatal conductance model was chosen based on comparisons of four different existing stomatal conductance schemes. A new cuticle conductance model was derived based on membrane passive transport theory and Fick's first law. The biochemical stomatal conductance scheme describes photosynthesis and respiration and their coupling with stomatal conductance for both sunlit and shaded leaves. Various aspects of the photosynthetic process in both C3 and C4 plants are considered in the model, such as the efficiency of the photosynthetic enzyme system, the amount of photosynthetically active radiation and the capacity of the leaf to export or utilize the products of photosynthesis. The cuticle conductance scheme accounts for the effects of diffusivity, solubility of specific gases in the cuticle membrane, as well the thickness of the cuticle membrane on cuticle conductance. In addition, a normalized soil water stress factor was applied to potential photosynthesis to account for plant response to both drought and waterlogging stresses. The model can account for the direct, indirect and tightly coupled effects of environmental factors on stomatal regulation of gaseous exchanges between plants and their environment. The biochemical dry deposition model was tested against eddy correlation data from six field experiments. It is shown that the model is able to estimate water vapor, carbon dioxide and ozone fluxes correctly, and the model results match well with measurements made in the field. The model is for use in the nationwide dry deposition network--CASTNet, and will assist in detecting total pollutant loadings to major ecosystems.