How many times higher can VOC levels be indoors than outdoors?

• A. 10x
• B. 5x
• C. 2x
• D. 3x

Answer: (B)

Indoor VOC levels tend to be higher because there are continuous emissions from indoor sources—furniture, flooring, paints, cleaning products, and office supplies—while outdoor air carries a much larger, more diluting volume that reduces concentrations. Outdoor air is also constantly mixed and dispersed by wind and sunlight, which helps keep VOCs lower on a comparative basis. In typical buildings with standard ventilation, the indoor environment can have VOC concentrations that are several times (often around five times) higher than outdoors, reflecting the balance between ongoing indoor sources and the dilution that outdoor air provides.

The other options describe lower or extreme multipliers that aren’t the general expectation for most indoor environments. So the best answer here is about five times higher.