What does active soil depressurization (ASD) primarily do?

Active soil depressurization (ASD) primarily functions to reduce radon levels in a structure by creating a pressure differential that prevents radon gas from entering the indoor environment. It works by establishing a lower pressure area beneath the building compared to the pressure in the surrounding soil. This pressure differential causes the radon gas, which is naturally emitted from the ground, to be drawn away from the home's foundation, thus directing it outside instead of allowing it to infiltrate the indoor air.

This method is particularly effective because radon is a heavy gas that tends to accumulate in low-pressure areas. By lowering the pressure beneath the building with a fan system, ASD effectively reverses the natural airflow patterns, promoting the movement of radon from the soil into the designated exhaust pathway rather than into the living space.

While the other options present possible benefits associated with indoor air quality, they do not accurately capture the primary function of ASD in radon mitigation. For instance, increasing indoor air pressure would counteract the depressurization effect needed to control radon levels, and decreasing humidity levels or providing ventilation does not directly address the mechanism by which radon is managed through ASD.