What do the Marginal, Slight, Enhanced, Moderate, and High risk categories for severe weather mean?

DETROIT Its a hot holiday weekend in Michigan, but air quality for much of the state is at a moderate level of concern. The U.S. AQI (Air Quality Index) is how the EPA reports air quality. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. Air quality is acceptable.