Air Quality Index
The Air Quality Index (AQI) was developed for citizens unfamiliar with all the National Ambient Air Quality Standards (NAAQS) for various air pollutants, and as a way to compare pollutant levels to each other. At low levels, the AQI is essentially just the percent of the standard for any particular pollutant. However, when the air quality is worse than the standard, the computation of the AQI is more complex. For practical purposes, it is enough to know that an AQI value of 100 means that the air quality was right at the maximum value allowed by the standard.
Technically, the AQI is computed daily from midnight to midnight for certain specified sites and pollutants. The highest AQI value is selected from among all these values, and is reported as "the AQI" for that day for the region. In order to give timely data, we report the highest AQI value which as occurred "today" as opposed to reporting a midnight to midnight value.
The AQI is the latest version of the Pollution Standards Index (PSI), however, they are not exactly the same. Although they are very close, you can not validly compare an old PSI value with the new AQI value. If you are an air pollution history afficionado, you will remember that years ago the PSI index started out as a variation of the AQI, and now we're back to the AQI again!
| Air Quality |
Air Quality Index |
Protect Your Health |
|---|---|---|
Good |
0-50 |
No health impacts are expected when air quality is in this range. |
Moderate |
51-100 |
Unusually sensitive people should consider limiting prolonged outdoor exertion. |
Unhealthy for |
101-150 |
Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion. |
Unhealthy |
151-200 |
Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion. |
Very |
201-300 |
Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should limit outdoor exertion |
AQI Data
The AQI data on our main "Air Quality" page are updated only twice each weekday. The "AM" AQI represents the highest AQI value which as occured as of about 10:40 today, and the "PM" AQI is the highest AQI value so far today as of about 3:40 PM.
To view the highest AQI which has occurred so far today, CLICK HERE. These are the highest average AQI values since midnight. They are automatically updated hourly around 36 minutes after the hour.