# The Relationship between Radon and Geology: Sources, Transport and Indoor Accumulation
## 2 The Origin of Radon
### Rocks and Soil Migration Factors
#### 2.2.3 Pressure  
Pressure differences in the soil and rocks can also drive the movement of radon. In general, radon tends to migrate from areas of high pressure to areas of low pressure [50]. For example, the gas pressure in the subsurface may be higher than atmospheric pressure, which causes radon to move towards the surface [51]. Pressure differences can also occur due to natural geological features such as faults, fractures, and other openings in the rock,  
\begin{table}
\begin{tabular}{l c} \hline \hline
**Lithologies** & **Porosity (\%)** \\ \hline Arenaceous marl & 24.54–31.74 \\ Basalt & 3.06 \\ Gneiss & 1.21 \\ Granite & 2.70 \\ Limestone & 2.00–12.09 \\ Marlite & 15.45–19.03 \\ Sandstones & 11.95–24.94 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Porosity of several lithologies (adapted from [44]).  
which can create areas of high or low pressure that affect the movement of radon [52]. The movement of radon through these pathways can be enhanced by factors such as soil moisture, temperature, and the concentration of other gases in the subsurface [53]. The migration of radon through soil and rock can be complex and difficult to predict, highlighting the importance of using multiple techniques to assess radon concentration and movement in different geological settings [54]. These interactions were comprehensively discussed by [PERSON] and [PERSON] (1997) who used the value of signal processing to interpret diurnal and semidiurnal variations in atmospheric pressure and radon concentration in soil gases [55]. The authors found that these variations could be used to estimate soil gas transport parameters, potentially providing meaningful insights into the real gas velocity. Their investigation identified two peaks in the power spectral density (PSD) of atmospheric pressure at 12 and 24 h intervals, a pattern that seems to be common on the surface of the Earth. These pressure changes allowed the researchers to calculate three soil gas transport parameters: tortuosity, the ratio of intrinsic permeability to effective porosity (the portion of porosity involved in gas transport), and the pressure gradient. The parameters k and n could be independently established when the surface gas flux was simultaneously monitored. This reliable assessment of transport parameters is made possible by the robust and representative method, which provides important details about the depth of radon sources and the time it takes for information to reach the surface when radon bursts take place at deep levels. Given that radon is present in all soils and that detecting its concentration simply calls for passive sensors that do not obstruct the rising gas column, its use as a soil gas tracer is particularly appropriate. Data on gas flux gathered in Andalusia, Spain, in connection with mineral exploration was used by the authors to test their methodology. It was discovered that the full set of transport characteristics could help interpret observed radon outbursts, which curiously, were linked to local seismic activity. Thus, their work demonstrates the potential of this method for geological research and hazard prediction.