A SIMPLE EMPIRICAL-MODEL TO ESTIMATE ANNU AL DRY DEPOSITION OF ATMOSPHERIC POLLUTANTS IN NEEDLES OF SPRUCE AND PINE

A large set of field data for leaf conductance and climate for Picea a bies and Pinus sylvestris is used to parametrize an empirical model fo r stomatal uptake of gaseous pollutants such as SO2 in exposed tree cr owns. The model predicts diffusion and uptake of SO2 in needles on a d aily and seasonal basis. Key driving parameters are the temperature mi nima of the previous nights or the soil temperatures and actual quantu m flux density and vapor pressure deficit. Routines are applied to acc ount for time dependend responses of stomata during the day and for ch anging weather conditions. As an example, we present the simulated ann ual SO2 deposition for Tyrol (Austria) and Hessen (Germany). It became apparent that annual acid deposition in needles can induce substantia l cation demand in spruce, although official critical values of ambien t concentrations may not have been surpassed. It is suggested to accom plish routine documentations of ambient gaseous pollutant concentratio ns with simulated effective doses at the tissue level. Such comparison s may reveal critical periods that would be overlooked by just conside ring ambient atmospheric concentrations and neglecting biological dete rminants of dry deposition of gaseous pollutants.