What primarily causes air pressure differences that can affect radon levels indoors?

Indoor/outdoor temperature differences and mechanical equipment are primary factors that impact air pressure differences, which can significantly influence radon levels indoors. Differences in temperature between the inside of a building and the outside can create pressure variations due to the natural tendency of air to move from areas of high pressure to low pressure. When outdoor air is cooler than indoor air, it creates a negative pressure that can draw radon-laden air from the soil into the home.

Mechanical equipment, such as heating, ventilation, and air conditioning (HVAC) systems, can also impact air pressure. These systems can create areas of positive or negative pressure within a structure, further affecting how air, including radon, moves through the building. For instance, if a furnace or exhaust fan operates, it can create a pull that draws air from the foundation into the basement or living areas.

The other choices represent factors that might have some influence on radon levels, but they do not primarily create the air pressure differences responsible for indoor radon accumulation. For example, while humidity levels and wind speed can relate to air quality, they do not directly cause the pressure changes essential for driving radon from the ground into a building. Altitude and weather patterns might influence overall radon levels in the