Air quality alerts were issued just before noon Monday for much of the Chicago metropolitan area, covering both Illinois and northwest Indiana counties, and are expected to remain in effect through Tuesday evening. State environmental agencies and the National Weather Service warned that weather conditions could raise ozone and fine particulate levels into the range that poses extra risk for sensitive people.
Who’s included and why
The advisory covers these Illinois counties: McHenry, Lake, Kane, DuPage, Kendall, Grundy, Cook and Will; and these northwest Indiana counties: Lake, Porter, Newton and Jasper. The Illinois Environmental Protection Agency and the Indiana Department of Environmental Management issued an Air Pollution Action Day for Tuesday because forecasts indicated persistent conditions that can increase ground-level ozone and particulate concentrations.
| Region | Included counties (examples) |
|---|---|
| Illinois suburbs & Chicago | Cook, DuPage, Lake, Will, Kane, McHenry, Kendall, Grundy |
| Northwest Indiana | Lake, Porter, Newton, Jasper |
Health guidance and air measurements
Officials described an Action Day as a response to expected air-pollution levels reaching or exceeding the Unhealthy for Sensitive Groups threshold on the Air Quality Index for multiple days. As the National Weather Service put it:
“An 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 category of the Air Quality Index for multiple days.”
At about 12:30 p.m. Monday, Chicago's reported air quality index was in the moderate range, with PM2.5 (fine particulate) reading about 64. For context, the source notes that PM2.5 values above 100 enter the Unhealthy for Sensitive Groups category.
Practical steps for residents
Health officials asked certain groups—particularly people with asthma or other pulmonary conditions, active children and older adults—to limit prolonged outdoor exertion while the advisory is in force. They also asked everyone to take simple actions to lower emissions and reduce pollutant buildup across the region.
- Walk, bike, carpool or use public transportation when possible.
- Avoid drive-throughs and try to combine errands into a single trip.
- Delay refueling and the use of gasoline-powered lawn equipment until after 7 p.m.
- Turn off vehicle engines if idling for more than 30 seconds.
- Conserve electricity—turn off lights and set air conditioners to 75°F or higher where feasible.
Weather context and outlook
Local meteorologists noted a stretch of warm weather across the Chicago area, with temperatures expected in the 80s and 90s through the work week. Those conditions—hotter air and sunlight—contribute to formation of ground-level ozone and can keep pollutants from dispersing, factors that helped prompt the Action Day declaration.
Residents with chronic respiratory conditions or families caring for young children should monitor symptoms, follow doctors’ recommendations for inhaler or medication use, and check local air-quality updates before planning extended outdoor activities. The advisory will remain in effect through Tuesday evening unless agencies update it based on changing conditions.
