What is the EPA 'Action Level' for indoor radon concentrations?

The EPA recommends that homeowners take active mitigation steps if radon levels are measured at or above $4.0 \text{ pCi/L}$ (picocuries per liter).

How does the source of Radon-222 differ from that of Carbon Monoxide?

Radon-222 is a naturally occurring gas produced by the radioactive decay of uranium in soil and rocks. In contrast, Carbon Monoxide is a human-made pollutant resulting from the incomplete combustion of fossil fuels in appliances or vehicles.

Compare the detection methods for Radon-222 versus Volatile Organic Compounds (VOCs).

Radon-222 is odorless and tasteless, requiring specific radioactive testing kits (like alpha-track detectors) to identify. Some VOCs may have distinct chemical odors, though both generally require specialized sensors for accurate measurement in indoor environments.

What is the difference between the health effects of Radon-222 and Asbestos?

While both cause lung disease and cancer, Radon-222 causes damage via alpha radiation that mutates DNA. Asbestos is a physical fiber that causes mechanical scarring (asbestosis) and specific cancers like mesothelioma through physical irritation of tissues.

Why is it a mistake to assume a home is safe from radon just because it is a new construction?

Radon levels depend on the underlying geology (uranium content in soil) rather than the age of the building. Even new, well-sealed homes can trap radon gas that enters through the foundation or well water if radon-resistant techniques weren't used.

What is the misconception regarding 'smelling' a radon leak?

Many people confuse radon with natural gas (which has added mercaptan for smell). Radon is a noble gas and is completely odorless, meaning a resident can never 'smell' a leak; only a scientific test can confirm its presence.

Why is opening a window only a temporary solution for high radon levels?

While opening windows increases ventilation and dilutes the gas, it does not stop the source of the gas entering from the soil. Once the window is closed, the pressure differential will continue to draw radon into the home, causing levels to rise again.

Define Radon-222 in the context of environmental science.

Radon-222 is a radioactive, colorless, and odorless noble gas that results from the natural decay of uranium in the earth's crust and is classified as a primary indoor air pollutant.

What is 'Sub-slab Depressurization'?

It is a radon mitigation technique that uses a fan and PVC pipe to create a vacuum beneath the house's foundation, suctioning the gas out and venting it into the atmosphere above the roof.

How does alpha radiation from radon cause lung cancer?

Alpha particles are heavy and highly ionizing; when inhaled, they strike lung tissue cells and cause double-strand breaks in DNA, leading to mutations that can eventually become cancerous.

Radon-222 Gas | College Board AP Environmental Science

Revision Notes

College Board

Environmental Science

Unit 7: Atmospheric Pollution

Radon-222 Gas

Summary

Radon-222 is a naturally occurring, radioactive noble gas produced by the decay of uranium in the Earth's crust. It represents a significant indoor air quality concern because it is undetectable by human senses and is a leading cause of lung cancer due to the emission of alpha particles that damage respiratory tissue.

1. Definition & Core Concepts

Radon-222 is a radioactive isotope of the noble gas radon, characterized by being completely colorless, odorless, and tasteless, making it impossible to detect without specialized equipment.
It is a naturally occurring substance produced through the radioactive decay chain of uranium, which is found in varying concentrations in rocks, soil, and groundwater globally.
Because it is a noble gas, it is chemically inert and does not bind to other elements, allowing it to migrate easily through porous soil and enter the atmosphere or building structures.

2. Underlying Principles of Accumulation

Radon enters buildings primarily through soil gas infiltration, where the gas moves from the high-pressure environment of the soil into the lower-pressure environment of a building's interior.
This pressure differential is often caused by the 'stack effect,' where warm air rising inside a home creates a slight negative pressure at the base of the structure, effectively drawing radon in through foundation cracks.
Geological factors play a major role; areas with high concentrations of granite, shale, and phosphate rock typically exhibit higher levels of radon gas production.

Diagram showing a house structure with radon gas (red squiggles) rising from uranium-rich soil and infiltrating the basement through the foundation due to pressure differences.

3. Methods of Entry and Exposure

Foundation Cracks: Radon penetrates through microscopic gaps in floor slabs, construction joints, and wall cavities that are in direct contact with the earth.
Well Water: In homes using private wells, radon can dissolve into the groundwater and be released into the air as an aerosol when water is agitated during showering or dishwashing.
Basements and Crawl Spaces: These areas are most vulnerable because they have the largest surface area in contact with the soil and often suffer from poor ventilation, allowing gas concentrations to build up.

4. Health Impacts: The Mechanism of Damage

5. Mitigation & Management Techniques

6. Exam Strategy & Tips