Deposition rates measured for atmospheric aerosol particles in a beech and spruce forest (Solling)

It could be shown that naturally occurring radionuclides being used as tracers not only are a reasonable solution, but also offer advantages (time resolution, continuous measurements) over other methods in determinations of the turbulent diffusion coefficient (radon, thoron), determinations of the deposition rate of aerosol particles (daughter products of radon and thoron of short half-lives) and assessments of the mean retention time of aerosol particles in the atmosphere. The activity concentrations measured for the inert gases radon and thoron in and above forested land showing a simple geometrical pattern are to a large extent determined by climatic conditions. As a result of the daily variations in turbulent exchange the maximum and minimum values for the daily activity concentrations of radon show considerable scatter, usually differing by one or two orders of magnitude. This obvious relationship permitted general weather situations to be described solely on the basis of radon activity concentrations. The distinctions thus made between individual weather conditions found confirmation in the relevant metereological charts. From the concentration gradients of radioactive inert gases it is possible to calculate absolute turbulent diffusion coefficients that are in reasonable agreement with values obtained on the basis of simple metereological methods. The measurement of deposition rates using daughter products of radon with short half-lives offered the expected basic advantages in that it ensured high time resolution in determinations of activity deposited directly on the biomass. It could thus be avoided that the amount of activity deposited was entirely attributed to that portion of radioactive aerosol particles being bound to aerosol, which is an error commonly made in such studies. The activity originating from unbound amounts of radon daughter products was systematically taken into account. (orig./KW)