The Air Quality Index

Indoor air quality can be affected by outdoor air pollution. The EPA calculates outdoor air pollution with a measuring tool called the Air Quality Index. This takes into account five major pollutants, the level of those pollutants in the air, and how your health could be damaged or affected by breathing that level of polluted air.

The Air Quality Index is a sort of yardstick, measured in levels from zero to 500, with corresponding colors for each level from "good" to "very unhealthy". A measurement of 50 is thought to be good, with few pollutants. Pollutant levels under 100 are generally considered to be "satisfactory". Anything beyond 100 begins to enter the danger zone, first to those with sensitivities, then to the general public.