Profiles of the Natural Contaminant Radon 222 as a Measure of the Vertical Diffusivity

Abstract

The concentrations of atmospheric pollutants are affected to a large extent by the intensity of the vertical transport that is governed by the daily variations of the eddy diffusion. This presentation is a report on a study of the vertical eddy diffusion based upon profiles of the natural contaminant Radon 222. The temporal and spacial variations in Radon 222 concentrations are affected by vertical transport and advection, radioactive decay and Radon 222 emanation from the ground. A number of investigations concerning the use of Radon 222 as a tracer in the study of the vertical transport are reported in the literature. These studies were carried out from both analytical and experimental viewpoints. Among the authors who have treated this subject are Israel (1951), Malakhov (1959), Jacobi and Andre (1963), Wilkening (1970), Birot and Andre (1970), and Roffman (1971). Hosler (1969) derived average vertical diffusion coefficients for thermal inversion and unstable convective periods based upon Radon 222 profiles. It is the purpose of this paper to show that averaging of Radon 222 concentrations over a long period of time is insufficient to represent changes in the vertical diffusivity when thermal inversion dissipates and convection due to ground heating is initiated and that the eddy diffusion coefficient changes by a factor of 20 or more during this period.