The diurnal evolution of 222Rn and its progeny in the atmospheric boundary layer during the Wangara experiment
- 1European Commission – DG Joint Research Centre, Institute for Environment and Sustainability, 21020 Ispra, Italy
- 2Atmospheric Science Group – Department of Geosciences and Wind Science and Engineering Research Center, Texas Tech University, USA
Abstract. The diurnal atmospheric boundary layer evolution of the 222Rn decaying family is studied using a state-of-the-art large-eddy simulation model. In particular, a diurnal cycle observed during the Wangara experiment is successfully simulated together with the effect of diurnal varying turbulent characteristics on radioactive compounds initially in a secular equilibrium. This study allows us to clearly analyze and identify the boundary layer processes driving the behaviour of 222Rn and its progeny concentrations. An activity disequilibrium is observed in the nocturnal boundary layer due to the proximity of the radon source and the trapping of fresh 222Rn close to the surface induced by the weak vertical transport. During the morning transition, the secular equilibrium is fast restored by the vigorous turbulent mixing. The evolution of 222Rn and its progeny concentrations in the unsteady growing convective boundary layer depends on the strength of entrainment events.