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. 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.
- Daily AQI - is used for reporting daily air quality and is based on the National Ambient Air Quality Standards (NAAQS) for fine particles (PM2.5, PM10) which is a 24-hour average, midnight to midnight, and for ozone (O3) which is the maximum 8-hour average. The daily AQI is reported to EPA and is used for demonstrating compliance with the NAAQS.
- Current AQI - uses EPA's NowCast calculation to report current conditions versus daily averages. The NowCast was developed so people can take timely action to reduce their exposure to high levels of air pollution when conditions are rapidly changing. This is particularly effective when air quality deteriorates rapidly like during wildfires and dust storms. A NowCast formula exists for ozone as well.
- Why not report a one hour AQI? Reporting one hour of data would have no context in terms of health related recommendations since a one-hour health standard doesn't exist for PM or ozone. Air pollution health standards are reviewed every five years. Learn more about the review process here.
Sometimes the Current AQI reports “green/good” air quality for PM2.5 (smoke), even when I can see or smell wildfire smoke. Why?It could be for a couple reasons:1. Weather determines how the smoke will spread and where it will be carried by the wind. The smoke may remain near the ground or rise to considerable heights. When the smoke stays high in the sky, the air may appear hazy but air quality measurements near the ground, where we breathe, may show only low levels of pollutants. In these situations, the reported AQI may be in the low risk range (good to moderate), despite the visible smoke. Learn more about wildfire smoke here.2. The AQI is updated every hour. Smoke from wildfires can cause air quality to rapidly decline in between the hourly reports, so be sure to take precautions if you smell smoke and check the AQI each hour.