What is the Air Quality Index (AQI)?

The AQI is a numeric, color-coded index for reporting daily air quality. It indicates how clean or polluted air is and what associated health effects may be of concern. The AQI focuses on health effects that may be experienced within a few hours or days after breathing polluted air.

The U.S. Environmental Protection Agency (EPA) calculates the AQI for five major air pollutants regulated by the federal Clean Air Act: ground-level ozone; particle pollution (also known as particulate matter); carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, the EPA has established national air quality standards to protect public health.

A green or "good" AQI is 0 to 50. Air quality is considered satisfactory, and air pollution poses little or no risk.

A yellow or “moderate” AQI is 51 to 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people. For example, people who are unusually sensitive to ozone may experience respiratory symptoms.

An orange or “unhealthy for sensitive groups” AQI is 101 to 150. Although the general public is not likely to be affected at this AQI range, people with lung disease, older adults, and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults, and children are at greater risk from the presence of particles in the air.

A red or “unhealthy” AQI is 151 to 200. Everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects.

A purple or “very unhealthy” AQI is 201 to 300. This would trigger a health alert, signifying that everyone may experience more serious health effects.

A maroon or “hazardous” AQI is greater than 300. This would trigger a health warning of emergency conditions. The entire population is more likely to be affected.

For more information on AQI and its impacts on