The headline is a blend of every live source below, weighted by trust (reference monitors over community sensors over the model) and proximity. Offline sensors are dropped. History and forecast come from the model; the 24-hour value is the EPA index averaged over the last day.
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42
US Air Quality Index
Good
Balanced across 6 live sources · PM2.5 driving
0 Good150300500 Hazardous
9924-hour official (EPA)
17This hour (model)
Right now, for you
Great air. Enjoy normal outdoor activity.
Improving, down from 147 (Sensitive) 6h ago· PM2.5 driving
Cleanest next 18h
11 AM–1 PM · AQI ~34 (Good)
Worst next 18h
3 AM–5 AM · AQI ~86 (Moderate)
🔥 A wildfire is upwind (nearest 3 mi NE); smoke is a likely cause.
EPA AirNow: (Discussion Issued 7/17/26 12:45pm)
The Illinois Environmental Protection Agency has issued a Chicago area Air Pollution Action Day for Saturday July 18th. This is in addition to the ongoing Purple Forecast Air Pollution Action Day in effect today July 17th for all 6 Chicago area forecast sectors and Rockford.
A Chicago area Air Pollution Action Day is declared when weather conditions are such that widespread ozone and or particulate levels are expected to be at or above the Unhealthy for Sensitive Groups (USG) category.
While the ongoing Action Day criteria for Rockford will be allow to expire, the lack of reaching action day criteria does not mean that the Rockford sector or other AQI forecast sectors can’t be downgraded to a USG AQI forecast. Criteria for the extra Action Day headline outside of Chicago falls under the criteria of a Red AQI forecast or forecast of USG for all or nearly all Illinois AQI forecast sectors.
Today smoke/PM2.5 levels are decreasing and verifying well against smoke model guidance. Unfortunately, that guidance also depicts a varying degree of smoke returning to Northern IL tomorrow afternoon and progressing towards Central IL Sunday. Expectations of reaching USG for the 24-hour average on Saturday are questionable but reaching USG or higher on NowCast hourly readings the latter half of Saturday seems likely, leading in part to the decision to continue with USG or higher forecasts for some areas. Smoke will have to continue to be monitored, and forecasts assessed for the possibility of wildfire smoke impacts throughout the coming weekend.
AQI Category Guidance
Unhealthy - Sensitive groups: Avoid long or intense outdoor activities. Consider rescheduling or moving activities indoors. Everyone else: Reduce long or intense activities. Take more breaks during outdoor activities.
Very Unhealthy - Sensitive groups: Avoid all physical activity outdoors. Reschedule to a time when air quality is better or move activities indoors. Everyone else: Avoid long or intense activities. Consider rescheduling or moving activities indoors. Note: If you don't have an air conditioner, staying inside with the windows closed may be dangerous in extremely hot weather. If you are hot, go someplace with air conditioning or check with your local government to find out if cooling centers are available in your community.
Note, NowCast AQI readings may show categories higher than the daily forecast to help identify periods of higher 1-hour PM2.5/smoke. For a description of the differences between daily AQI forecasts and NowCast AQI, visit https://www.airnow.gov/aqi/aqi-basics/using-air-quality-index/ .
🔥
23 active fire detections within 100 mi
Nearest is 3 mi NE. 2 detections are upwind, a likely source of any smoke.
A balanced score across every live reading, then each source on its own. Community sensors run hot during smoke; the model is the smooth regional picture.