Atmospheric Removal of Airborne Metals by Wet and Dry Deposition

Abstract

At 13 sites of different air quality in the Federal Republic of Germany dry and wet deposition was determined separately. Over the period summer 1979 to summer 1981 chemical analyses were performed for lead, cadmium, manganese and iron by atomic absorption spectrometry. Mass balances of wet and dry deposition rates show the different significance of both removal pathways. Elements bound on large aerosol particles (Mn and Fe) are removed from the atmosphere preferentially by dry deposition, whereas elements bound on submicron particles are removed by wet deposition.

To qualify both removal processes deposition velocities and washout factors are calculated. Characteristic deposition velocities of the metals confirm the sedimentation as the dominant mechanism. Characteristic washout factors are in the range from 100 to 5000. A correlation between deposition velocities and washout factors demonstrates that dry deposition and wet removal are most efficient for metals bound on large particles. Nevertheless, wet deposition is the main removal process for submicron particles.