Vertical Diffusion in the Lower Atmosphere Using Aircraft Measurements of 222Rn

Abstract

Vertical profiles of 222Rn concentrations measured from 3 to 6 September 1995 in the northeastern United States, using a new radon instrument designed for aircraft measurements, are presented. A vertical diffusion model was employed to simulate the distributions of 222Rn concentrations by using time-dependent profiles of vertical eddy diffusivity in the lower atmosphere. To determine these profiles, O?Brien?s simple formulation was applied using the diurnal changes of the boundary layer height and surface fluxes. The model-calculated profiles of the 222Rn concentrations were then compared with the aircraft measurements of 222Rn. Model simulations were also calculated using different values of the vertical eddy diffusivity above the boundary layer. Using the value of kz above the boundary layer equal to 10% of its maximum boundary layer value in the model resulted in the best vertical profiles of the calculated 222Rn compared with the measurements within the boundary layer. From aircraft measurement data of the naturally occurring radionuclide 222Rn, the vertical mixing processes in the lower atmosphere were studied. These data will be useful for model validations.