https://doi.org/10.1140/epjst/e2015-02404-1
Regular Article
Intrinsic vs. spurious long-range memory in high-frequency records of environmental radioactivity
Critical re-assessment and application to indoor 222Rn concentrations from Coimbra, Portugal
1 Research Domain IV – Transdisciplinary Concepts & Methods, Potsdam Institute for Climate Impact Research, Telegrafenberg A31, 14473 Potsdam, Germany
2 Department of Electronics Engineering, Piraeus University of Applied Sciences, 250 Thivon & P. Ralli, 12244 Aigaleo, Athens, Greece
3 INESC TEC – INESC Technology and Science, Campus da FEUP, Rua Dr. Roberto Frias, 4200-464 Porto, Portugal
4 Instituto Dom Luiz, University of Lisbon, Campo Grande, Edificio C8, 1749-016 Lisbon, Portugal
5 Faculty of Economics, University of Porto, Rua Dr. Roberto Frias, 4200-464 Porto, Portugal
6 CEMUC – Department of Earth Sciences, University of Coimbra, 3030-790 Coimbra, Portugal
a e-mail: reik.donner@pik-potsdam.de
Received: 15 March 2015
Revised: 23 April 2015
Published online: 10 June 2015
The presence or absence of long-range correlations in the environmental radioactivity fluctuations has recently attracted considerable interest. Among a multiplicity of practically relevant applications, identifying and disentangling the environmental factors controlling the variable concentrations of the radioactive noble gas radon is important for estimating its effect on human health and the efficiency of possible measures for reducing the corresponding exposition. In this work, we present a critical re-assessment of a multiplicity of complementary methods that have been previously applied for evaluating the presence of long-range correlations and fractal scaling in environmental radon variations with a particular focus on the specific properties of the underlying time series. As an illustrative case study, we subsequently re-analyze two high-frequency records of indoor radon concentrations from Coimbra, Portugal, each of which spans several weeks of continuous measurements at a high temporal resolution of five minutes.Our results reveal that at the study site, radon concentrations exhibit complex multi-scale dynamics with qualitatively different properties at different time-scales: (i) essentially white noise in the high-frequency part (up to time-scales of about one hour), (ii) spurious indications of a non-stationary, apparently long-range correlated process (at time scales between some hours and one day) arising from marked periodic components, and (iii) low-frequency variability indicating a true long-range dependent process. In the presence of such multi-scale variability, common estimators of long-range memory in time series are prone to fail if applied to the raw data without previous separation of time-scales with qualitatively different dynamics.
© EDP Sciences, Springer-Verlag, 2015
