RADON - Radon indoor and soil gas variability

Project RADON - Radon indoor and soil gas variability – joint experimental assessment  (PTDC/CTE-GIX/110325/2009) - is a research project funded by FCT.

This project aims to investigate the physical mechanisms influencing radon variability and its migration into indoor environments by means of the synergy of adequate experimental, data analysis and modelling techniques. 

The main steps of the RADON project comprise 
1) setting-up a multi-parametric experimental station in a dwelling undisturbed by human activity, 
2) simultaneously acquire high-quality experimental data on indoor and soil radon concentrations as well as on environmental parameters 
3) analyse the acquired data with advanced data analysis techniques, and 
4) implement a numerical model of radon migration.

Executive Summary

Radon is a naturally occurring radioactive noble gas generated within mineral grains of uranium bearing rocks by alpha decay from radium. Radon can move from the solid grains into the air or water-filled pores of the media and further migrate via diffusion and/or advection to the atmosphere. The exhalation of radon from porous media (rocks, soils,...) to the atmosphere poses a potential health hazard, since inhalation of its short-lived decay products is well known to have adverse health effects, particularly in poorly ventilated dwellings located in areas of high radon potential (as is the case of large areas in Portugal).

Understanding the temporal variability of indoor radon concentrations is hindered by the spatially and temporally complex interplay between diffusive and advective transport processes. Radon generation and migration is determined by the local geology (radium content of the solid source, tectonic features), water saturation, as well as pressure and temperature gradients influencing radon migration processes. Meteorological effects (rainfall, temperature, winds,...) induce pressure differences and changes in water saturation and therefore are also though to influence radon migration. However, the role of meteorological factors in indoor radon concentrations and corresponding variability patterns is still poorly understood. Furthermore, the influence of temperature on radon emanation and transport is also an open issue. Stack effects can explain radon mobility in air, but do not account for temperature-driven transport within the porous medium.

This project aims to investigate the physical mechanisms influencing radon variability and its migration into indoor environments by means of the synergy of adequate experimental, data analysis and modelling techniques. Considering that most experimental studies conducted so far on indoor radon were performed in habited dwellings, with passive and low-sensitivity sensors, for short periods of time, and often addressing only indoor radon and not radon in the geological environment (soil/bedrock), this project aims to contribute to a better quantification and understanding of the simultaneous variability of radon in indoor and soil air by setting-up a unique radon monitoring experimental station in a undisturbed dwelling located in a high radon prone area near the old uranium mine of Urgeiriça (central Portugal). The objective is to use very sensitive and robust gamma- and alpha solid-state sensors, adequate for high resolution and continuous long-term radon monitoring, in order to acquire simultaneously experimental data on both indoor and soil radon concentrations. The radon measurements will be complemented with concurrent outdoor meteorological measurements (air and soil temperature, atmospheric pressure, humidity, rainfall and winds) and indoor measurements of air temperature, pressure and humidity, as well as with CO2 measurements. In order to have a rigorous quantitative assessment of the temporal variability of radon concentrations and environmental parameters, the experimental data will be analysed using advanced data analysis techniques appropriate for the description of non-stationary and non-linear features. As a tool for the interpretation of the experimental results, a physical numerical model for radon migration combining radon generation, decay, diffusion and advection will be implemented and further extended to include thermal diffusion in its formulation.

Quantifying and understanding radon variability in indoor air is not only relevant for assessing potential health hazards from exposure to radon gas, but also highly relevant from the point of view of geophysics, since a better understanding of radon generation and transport processes is important for most geophysical applications of radon, either as a tracer, seismic precursor, or atmospheric proxy.