What factor is critical when measuring radon levels in relation to pressure differences?

The indoor air pressure relative to outdoor air pressure is a critical factor when measuring radon levels due to its impact on the movement of radon gas into a building. Radon is a naturally occurring radioactive gas that typically enters structures from the ground. If the indoor air pressure is lower than the outdoor air pressure, it can create a vacuum effect that draws radon-laden air into the home through cracks, gaps, and openings in the foundation. This means that monitoring and understanding the pressure dynamics within and outside the building is essential for assessing potential radon exposure.

While other considerations like the height of the building, ventilation, and construction materials can influence radon levels, they are not as directly related to the movement of radon gas as the pressure differential. For example, a building with poor ventilation might still show significant radon levels if the pressure difference allows radon to infiltrate. Similarly, while construction materials can affect radon levels, they do so in conjunction with the pressure difference that draws radon into living spaces. Therefore, the relationship between indoor and outdoor air pressure is paramount in understanding how radon can enter a home and, consequently, in effective mitigation strategies.