Which are examples of indoor air pollutant sources?

• A. Natural sources (uranium) only
• B. Human-made sources only (insulation, VOCs from furniture, carpet, paneling; formaldehyde from building materials, furniture, upholstery, and carpeting; and lead from paints)
• C. Natural sources (uranium), human-made sources (VOCS, formaldehyde, lead), and combustion (vehicles) - radon, mold, dust
• D. Outdoor sources only

Answer: (C)

Indoor air quality is influenced by a mix of sources: natural, human-made, and combustion-related. Naturally occurring elements like uranium in the soil lead to radon, a gas that can seep into buildings and accumulate. Moisture problems inside buildings foster mold, another natural indoor pollutant. Human-made sources are common indoors as well—VOCs released from paints, furniture, carpets, and paneling; formaldehyde from building materials and upholstery; and lead from old paints. Combustion processes, such as heating, cooking, and penetrating vehicle exhaust, introduce additional pollutants indoors. Because indoor air pollutants come from all these categories, the statement that includes natural sources (radon), human-made sources (VOCs, formaldehyde, lead), and combustion-related sources (vehicles) best captures indoor pollutant sources, including examples like radon, mold, and dust. The other options miss one or more of these categories (natural, human-made, or combustion).