Air Quality Index
The AQI is an index for reporting daily air quality. It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. 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 national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain sensitive groups of people, then for everyone as AQI values get higher.
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:
|Air Quality Index Levels of Health Concern||Numerical
|Good||0 to 50||Air quality is considered satisfactory, and air pollution poses little or no risk.|
|Moderate||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 who are unusually sensitive to air pollution.|
|Unhealthy for Sensitive Groups||101 to 150||Members of sensitive groups may experience health effects. The general public is not likely to be affected.|
|Unhealthy||151 to 200||Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.|
|Very Unhealthy||201 to 300||Health alert: everyone may experience more serious health effects.|
|Hazardous||301 to 500||Health warnings of emergency conditions. The entire population is more likely to be affected.|
Note: Values above 500 are considered Beyond the AQI. Follow recommendations for the "Hazardous category." Additional information on reducing exposure to extremely high levels of particle pollution is available here.
We provide two AQIs: A Current AQI (reflects near real-time conditions) and a daily AQI.
The Current Air Quality Index was developed so that people can take timely action to reduce their exposure to high levels of air pollution when conditions are rapidly changing.
This is different than the health-based standard for fine particle pollution, which is calculated using a 24 hour average, midnight to midnight. The 24 hour average is then reported as the day’s Air Quality Index. The reason a 24 hour period must be used for this calculation is because current science about air pollution exposure and health effects is based on a 24 hour timeframe.
To better reflect real-time conditions, the Current Air Quality Index is computed from the most recent 12 hours of data. The calculation uses longer averages during periods of stable air quality and shorter averages when air quality is quickly changing. This is particularly effective when events occur that make air quality deteriorate rapidly, like wildfires and dust storms. Learn more about PM
A similar calculation is used to report ozone. The only difference is that an 8-hour average is used. Learn more about ozone
- The daily Air Quality Index for each day is reported to EPA and it is what cooresponds to the health standard, which is a 24 hour standard for PM and an 8-hour standard for ozone. The official AQI is reported each month. Five year summary 2013-2017.
- Days when the AQI was over moderate for PM2.5 since 1999, when PM2.5 monitoring began shortly after new national health standards were established. (Spokane Clean Air has been measuring for larger particles since the standards were established in 1971.) A daily AQI for PM2.5 over 100 is an exceedance of the health-based, national ambient air quality standard.