ESTIMATION OF DRY DEPOSITION IN THE BORNHOVED LAKE DISTRICT WITH A RESISTANCE MODEL

Dry deposition of gaseous air pollutants is an important input pathway of acidifying and eutrophying compounds to various ecosystems. However, it cannot be measured on a routine basis under many circumstances. For monitoring purposes, inferential methods based on measured air concentrations and electrical resistance analogy models have been developed. In this paper, the application of such a model system to the Bornhoved Lakes research area, model tests, modelling results and a comparison, taking SO2 deposition as an example, with an independent method to estimate dry deposition to forest canopies (net throughfall) are presented. The turbulent and quasi-laminar boundary layer resistances are modelled according to micrometeorological theory and by using empirical similarity functions, respectively. Surface resistances are estimated with a modular partial resistance model system after Wesely (Atmospheric Environment 23 (1989) 1293-1304). The temporal behavior is shown to be realistic. However, the computed SO2 deposition rates to a beech canopy are much lower than the SOx dry deposition as determined by net throughfall. Possible reasons for this discrepancy due to model weaknesses concerning the effects of, e.g., surface wetness and complex terrain on dry deposition are discussed, as well as the advantages of the resistance analogue model.