What does it mean when an Air Quality Advisory is issued?

An Air Quality Advisory is issued by the Environmental Protection Agency and local air-quality agencies when the outdoor air in your area is unhealthy. These agencies rely on a tool called the Air Quality Index (AQI).

The AQI is a measure of the concentrations of five major air pollutants: low-level atmospheric ozone (formed when certain other air pollutants react with sunlight), particulate matter (from vehicles, power plants, forest fires, and stirred-up dust), carbon monoxide (mostly from vehicles), sulfur dioxide (produced when sulfur-containing fuels such as coal and oil are burned), and nitrogen dioxide (mainly from internal combustion engines burning fossil fuels).

Depending on the aggregate levels of these pollutants in the air, the AQI can be as low as zero and as high as 500. Communities aim to keep their AQI at 100 or below; below 50 is optimal for health.

If your community issues an advisory, you may need to modify your activities for the day. An AQI between 50 and 100 is considered acceptable for all but a small percentage of people who are unusually sensitive to pollution. An AQI between 100 and 150 due to ozone or particle pollution may affect older people, those with heart or lung disease, and individuals who are active outdoors. Above 150, air quality can cause airway inflammation and respiratory distress (even in healthy individuals) and, in susceptible people, can provoke or worsen an asthma attack. At these levels, stay indoors—especially if you plan to exercise.

Anything above 201 is considered very unhealthy or hazardous for everyone. You can find your daily local air quality report at AirNow. Some weather apps on mobile phones also provide air quality information.