Emanated products as a probe of atmospheric transport

Abstract

Atmospheric transport of radon, thoron and their decay products is analysed in the light of the Richardson diffusion theory, replacing the length scale by a time scale. It is shown that the mean operation involved in the usual procedure of parameterisation of eddy diffusion must be related to the isotopic mean life, and its relation to spectra of atmospheric turbulence. There are cases where the conventional parameterisation of eddy diffusion is inconsistent and contradictory. For example the case of the thoron distribution which generally must be treated by Richardson formalism.

The conventional methods are shown to be reasonable for interpretation of radon222 and Pb212 profiles, provided this is done carefully. It is shown that the vertical transport due to the mean wind cannot be neglected, as sometimes it is a dominant factor. A criterion for estimating the relative importance of advection and eddy diffusion is derived. Application of this criterion establish that in the free atmosphere radon transport is generally dominated by advection. This result is demonstrated by semi-uniform numerical model.

For a practical application it seemed that the radon could be a promising tool for the study of the large scale (synoptic) vertical wind and of divergent regimes.