Analysis of chaotic behavior of indoor Radon Concentrations

Indoor ²²²Rn concentration are influenced by several factores which may change with time, thereby causing temporal fluctuations of radon concentrations in rooms. Different chaos based measurements (fractal analyses) were applied to radon time series in three different rooms (kitchen, working room, radiation laboratory) in Austria to determine the degree of chaotic behavior, to predict fluctuations in the future, and to investigate correlation's with meteorological parameters. Our fractal analyses of these indoor radon time series demonstrated that indoor ²²²Rn concentrations do indeed exhibit features which are characteristic of chatoic systems. The computed fractal dimensions, such as Hurst exponent, Lyapunov exponent, capacity dimension, embedding dimension and attractor dimension, provided estimates of the degree of chaotic behavior, such as low dimensional chaos for the kitchen, high dimensional chaos for the working room and chaos with additive noise for the radiation laboratory. Application of a nonlinear prediction algorithm revealed that the predictability of radon time series is restricted to approximately three relative time steps into the future and into the past, e.g. monthly radon measurements cannot be reliably extrapolated beyound a period of three months. If the similarity of fractal dimensions between radon concentrations and meteorological parameters is used as a measure of the degree of correlation, our analyses suggest a strong correlation between radon concentrations and negative pressure differences.