A non-stationary model for sulphur aerosol depletion and deposition in a young spruce stand

A non-stationary partial differential equation (pde) of aerosol concentration in one space coordinate z (height above ground) is given. Submodels for the structure and aerodynamics of a young Norway spruce stand (height ~6 m) are developed from site-specific empirical data during a dry, stagnant summer period. The submodels and an empirical time series over 120 h for above-stand sulphur aerosol concentrations are used to quantify the pde and its upper boundary conditions. A simplified analysis indicates an uncertainty within one order of magnitude associated with this step. The pde-predictions of within-stand concentrations are within a factor of 2 of corresponding empirical concentration data. The associated deposition patterns show a diurnal variation and a complex z-dependency. Model improvements and further evaluation methods are suggested. The overall results suggest that estimates of aerosol deposition to forests based only on yearly and regional averages overlook strongly time and space dependent deposition patterns.