Air quality is considered satisfactory, and air pollution poses little or no risk.

Air quality is acceptable, however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.

Air quality is not good for members of sensitive groups, while others may be less affected.

Everyone may begin to experience health effects. Members of sensitive groups may experience more serious health effects.

Air quality is very harmful and considerably affects everyone. Members of sensitive groups are advised against going out.

Air quality is at a hazardous level that severely affects everyone, especially the respiratory and cardiovascular systems. People are advised to close their windows.