Radon cannot be reduced with which of the following devices?

The concept of radon reduction focuses on the methods that can effectively lower indoor radon levels. Radon is a radioactive gas that can accumulate in homes, particularly in areas with poor ventilation or a foundation below ground level. The correct answer indicates that none of the devices listed (humidifiers, electrostatic precipitators, or ionizers) are effective in reducing radon levels.

Humidifiers work by adding moisture to the air and do not address the radon gas itself; thus, they do not contribute to radon reduction. Electrostatic precipitators are designed to remove particles from the air, particularly pollutants and allergens, but they do not interact with gaseous substances like radon. Similarly, ionizers may help to reduce particulate matter in the air but have no effect on radon gas concentrations. These devices primarily focus on particulate air quality and lack the mechanism needed to mitigate radon specifically.

Therefore, understanding that radon reduction typically involves methods like sub-slab depressurization or increased ventilation illustrates why none of the listed devices serve that purpose, confirming that the correct answer is that none of them can effectively reduce radon levels.