Which of the following is NOT one of the four radon transport mechanisms?

The correct answer identifies that the stack effect is not considered one of the primary mechanisms for radon transport. Radon, a naturally occurring radioactive gas, can move through soil and structures via several established mechanisms.

Emanation refers to the process by which radon gas is released from soil or building materials. This occurs when radium in the soil or materials decays and produces radon, allowing it to escape into the air or enter buildings through cracks and openings.

Diffusion involves the movement of radon gas from areas of higher concentration to lower concentration. This is driven by the natural tendency of gases to equalize their concentration in different areas, allowing radon to migrate from the ground into structures.

Advection is the process where radon gas is carried along with the movement of air. It can occur when air flows through the soil, pulling radon gas along with it into buildings, which can significantly affect indoor radon levels.

While the stack effect is related to air movement within buildings due to temperature differences, it is centered around the displacement of indoor air rather than the specific transport mechanisms of radon itself. Therefore, stating that it is not one of the four primary mechanisms of radon transport is accurate.