Air quality becomes more of a concern during the hot, hazy summer months. The Air Quality Index, or AQI, tells you how clean or polluted the air is. It also indicates what health effects might be a concern for you, focusing on effects you may experience within a few hours or days of breathing polluted air.
The AQI is calculated for the five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide. The Environmental Protection Agency has established national air quality standards for each of these pollutants. Ground-level ozone and airborne particles pose the greatest threat to health in this country.
Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern.
An AQI value of 100 generally corresponds to the level the EPA has set to protect public health. AQI values below 100 are satisfactory - but when values are over 100, air quality is considered unhealthy. As the values rise, the risk groups expand from sensitive individuals to the public at large. On a "bad air" day, affected groups should limit activity and stay indoors.
To make the AQI easier to understand, it is divided into six categories:
- Good: The AQI value for your community is between 0 and 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
- Moderate: The AQI for your community is between 51 and 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.
- Unhealthy for Sensitive Groups: When AQI values are between 101 and 150, members of sensitive groups may experience health effects. This means they are likely to be affected at lower levels than the general public. For example, people with lung disease are at greater risk from exposure to ozone, while people with either lung disease or heart disease are at greater risk from exposure to particle pollution. The general public is not likely to be affected when the AQI is in this range.
- Unhealthy: Everyone may begin to experience health effects when AQI values are between 151 and 200. Members of sensitive groups may experience more serious health effects.
- Very Unhealthy: AQI values between 201 and 300 trigger a health alert, meaning everyone may experience more serious health effects.
- Hazardous: AQI values over 300 trigger health warnings of emergency conditions. The entire population is more likely to be affected.
Each AQI category has been assigned a different color for quick recognition. (See chart below.)