Accumulation of air pollutants by a Spruce Forest in Eastern Belgium

In the course of a 20 mo sampling campaign, 29 ions and elements were determined in rain water which had been collected under trees and in clearings of a spruce forest. Comparing deposition rates between these two locations gives information as to the filtering capacity of tree foliage towards air pollutants. This filtering capacity depends on the gas reactivity and on the particle diameter while pollutant accumulation rates closely depend upon meteorological conditions, mainly rainfall and duration of dry periods. Therefore, pollutant accumulation by trees should be studied on the basis of well-defined meteorological events rather than on the basis of fixed time sampling intervals, which tend to mask the strong effect of precipitation events.