Vertical diffusion in the lower atmosphere using aircraft measurements of Rn-222

Vertical profiles of Rn-222 concentrations measured from 3 to 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 Rn-222 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 Rn-222 concentrations were then compared with the aircraft measurements of Rn-222. Model simulations were also calculated using different values of the vertical eddy diffusivity above the boundary layer. Using the value of k(z) 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 Rn-222 compared with the measurements within the boundary layer. From aircraft measurement data of the naturally occurring radionuclide Rn-222, the vertical mixing processes in the lower atmosphere were studied. These data will be useful for model validations.