Variability of radon distribution in the atmospheric surface layer over the land of middle latitudes

The variability of radon distribution in the surface atmosphere is investigated by numerical modeling of radon turbulent transport, based on the data of continuous field natural observations. The boundary conditions, including the radon flux from the surface and radon volumetric activity variation near the surface, were set according to the observations. Variations of turbulent diffusion coefficient altitude profiles were calculated by the observations of wind velocity pulsations at two altitudes made synchronously on the same location. The altitude profiles of radon volumetric activity typical for the atmospheric surface layer over the land of middle latitudes are obtained. It is shown that the radon volumetric activities at any altitudes vary concurrently, but the near-surface radon volumetric activity are greater than one at 10 m. The relative difference between them varies from 10 % (near local midnight) to 120 % (near local midday). The most considerable increase of the radon volumetric activity gradient occurs below 2 m. (paper)