Which environmental factor contributes to higher radon concentrations in homes?

The influence of heavy rainfall on radon concentrations in homes can be attributed to the way water movement affects radon gas, which originates from the decay of uranium found in soil and rock. When heavy rainfall occurs, the saturation of the soil can lead to the displacement of radon gas. As water fills the spaces in the soil, it can push radon closer to the surface and increase the likelihood of it entering buildings through cracks and other openings in the foundation.

This phenomenon is particularly relevant because homes often experience changes in pressure due to weather conditions. When external air pressure decreases, such as during or just after heavy rainfall, it can create a vacuum effect that draws radon gas into the building. Additionally, wet soil can also create a barrier that reduces radon's initial escape to the atmosphere, subsequently funneling more of it into homes.

In contrast, dry soil conditions are less likely to promote the movement of radon gas toward the surface, while humidity doesn't have a direct correlation with radon entry into buildings. Extreme temperatures, while affecting air pressure in some cases, do not directly link to the concentration levels of radon in the same way heavy rainfall does. Therefore, heavy rainfall is the most significant environmental factor among the options presented that contributes to higher