Wet and Dry Deposition of Atmospheric Trace Elements in Forest Areas

Abstract

Vet and dry deposition rates of the elements SO₄ ⁻, NO₃ ⁻, Cl⁻, Pb, Mn, Fe and Cd estimated for the period of April 1983 to April 1985 at 5 different measuring sites, most of them located in the state of Hesse, are presented, In accordance to earlier investigations, wet deposition is found to be the dominant sink for the elements SO₄ ⁻, NO₃ ⁻, Cl⁻, Pb and Cd, Mn and Fe are affected by dry deposition to a large extent, No pronounced differences of total deposition have been found, comparing three sampling sites in forest areas with the other two sites within the sampling network. The importance of “episodes” of wet deposition is shown at one station for SO₄ ⁻. Up to 40% of the annual wet deposition of SO₄ ⁻ is associated with only 10% of the annual rainfall-events. Dry deposition processes that take place in the canopy of forest stands lead to an enhancement of element concentrations in the throughfall. The ratio of different elements in precipitation below and above the canpoy suggests a functional dependence on the mass median diameter of the corresponding aerosol particles.