The 24 hour AQI is a prediction of what the 24 hour AQI average will be for the current day. The prediction is based on a weighted average of the last 12 hours of data, with the most recent hours being weighted more heavily.
Oregon 24 Hour Air Quality Index (AQI) Map
The current air quality is displayed above using the Air Quality Index (AQI). As seen in the table below, the AQI is a numbered and color coded way to report the daily air quality. The AQI is not a specific unit of measurement, rather it is scaled indication of general air quality. The AQI in Lane county is calculated for two major pollutants regulated by the Clean Air Act: ground-level ozone and particulate matter (PM2.5). For each of these pollutants the US EPA has established national air quality standards to protect public health.
Air Quality Index
Levels of Health Concern
When the AQI is in this range:
..air quality conditions are:
...as symbolized by this color:
Unhealthy for Sensitive Groups
151 to 200
201 to 300
301 to 500
The current AQI represents the amount of pollution in the air using a weighted average of the last twelve hours and is a forecast of the current days average pollution level. The actual AQI level for any given day is based on the 24 hour average of the pollution levels for that day and can be found here or by selecting the "AQI for the Last 45 Days" link on the left side of this page.