What factor increases suction on soil, leading to an increased risk of radon infiltration?

Cold outdoor temperatures significantly increase suction on the soil, which can lead to a higher risk of radon infiltration into structures. When outdoor temperatures drop, the air inside a building often becomes warmer, creating a pressure differential known as the stack effect. This effect leads to air being pulled from the soil into the interior of the structure to replace the rising warm air. As the cold air settles, it exerts a lower pressure, which essentially draws more air (and potentially radon gas) from the surrounding soil.

Radon gas, which is naturally occurring and originates from the decay of uranium in the soil, can be sucked into foundations, cracks, or other openings in the building. Thus, during colder months or in colder climates, the risk increases because of this enhanced suction effect.

Other factors such as higher indoor temperatures, low humidity levels, or high atmospheric pressure do not create the same scenario for increased soil suction in relation to radon gas infiltration. Higher indoor temperatures might reduce the density of air slightly but do not create as significant a differential as the contrasting cold outdoor temperatures do. Similarly, low humidity levels and high atmospheric pressure do not directly influence the movement of radon from the soil into a building in the same way as colder outdoor conditions do.