AQI provides a simple, uniform way to report daily air pollution concentrations, to tell the public about ways to reduce air pollution associated with these concentrations and to describe some general precautionary steps that can be taken. AQI is a reporting tool that converts the pollutant concentrations measured in a community’s air to a simple number on a scale of 0 to 500. Intervals on the AQI scale are related to the potential health effects of the daily measured concentrations of five major pollutants: ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2) and particulate matter (PM10) and (PM2.5). The intervals and the terms describing the air quality levels are:
Understanding the AQI
The purpose of the AQI is to help you understand what local air quality means to your health. To make it easier to understand, the AQI is divided into six categories:
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When the AQI is in this range: |
...air quality conditions are: |
...as symbolized by this color: |
| 0 to 50 |
Good |
Green |
| 51 to 100 |
Moderate |
Yellow |
| 101 to 150 |
Unhealthy for Sensitive Groups |
Orange |
| 151 to 200 |
Unhealthy |
Red |
| 201 to 300 |
Very Unhealthy |
Purple |
| 301 to 500 |
Hazardous |
Maroon |
Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:
- “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.
The AirData Web site gives you access to air pollution data for the entire United States.
The AQI tells you how clean the air is and whether it will affect your health. EPA, state and local agencies work together to report current and forecast conditions for ozone and particle pollution. AIRNow forecasts next-day air quality.
