What is the most likely reason indoor radon fluctuates seasonally, showing higher levels in colder months?

What is the most likely reason indoor radon fluctuates seasonally, showing higher levels in colder months?

• A. Radon levels tend to increase in the colder months because of the difference in temperature inside and outside the home, which creates a vacuum pulling radon into the home at a higher rate.
• B. Radon production in the soil increases in the winter.
• C. Radon is released from home sources more during winter.
• D. Warmer weather causes radon to decay faster.

Answer: (A)

Radon indoors rises in winter mainly because of pressure differences created by heating and a more sealed house. When a home is heated, warm indoor air rises and escapes through the upper parts of the building, pulling in soil gas from beneath the foundation through cracks and openings. The soil continuously releases radon, but in winter the indoor-outdoor air pressure difference and reduced ventilation cause more of that soil gas to be drawn in and linger inside, boosting measured concentrations. Radon production in soil doesn’t noticeably increase in winter, and decay rate isn’t affected by temperature, so those factors don’t explain the seasonal rise. Radon from inside sources isn’t the major contributor; the primary source is soil gas entering the home.

Radon indoors rises in winter mainly because of pressure differences created by heating and a more sealed house. When a home is heated, warm indoor air rises and escapes through the upper parts of the building, pulling in soil gas from beneath the foundation through cracks and openings. The soil continuously releases radon, but in winter the indoor-outdoor air pressure difference and reduced ventilation cause more of that soil gas to be drawn in and linger inside, boosting measured concentrations. Radon production in soil doesn’t noticeably increase in winter, and decay rate isn’t affected by temperature, so those factors don’t explain the seasonal rise. Radon from inside sources isn’t the major contributor; the primary source is soil gas entering the home.