The diurnal evolution of 222-Rn and its progeny in the atmospheric boundary layer

Ground-based measurements and vertical distributions of radon and its daughters are used to benchmark regional and global circulation models. Regional surface fluxes of air pollutants and climatically sensitive compounds are often estimated by using the same data.

Despite many experimental studies in the literature, very few of them reported measurements of diurnal variation of radon and its daughters through the whole atmospheric boundary layer. Using a state-of-the-art large-eddy simulation, we studied the diurnal evolution of radon and its progeny. An observed diurnal cycle was successfully simulated. For the first time, the simulation included a first-order decaying system.

Both turbulent transport and transport asymmetry of the nuclide are important consequence of the entrainment of 'clean' air from the reservoir layer during the morning transition. These entrainment events are responsible for the collapse of the mixed layer concentrations. The evolution of the nuclide is directly related to radioactive decay contribution. Contribution in which turbulent mixing plays the major role. Turbulent transport affects the dispersion of 222-Rn and its progeny by acting preferentially on the radioactive decay.