Check the AQI for Chicago at 8 a.m. on a smoky July morning, then walk through your kitchen at noon. The fine particles you saw in that 8 a.m. reading are already settling on your counters. The Illinois air quality index measures outdoor air. It also tells you what is about to be in your house.
We’ve tracked Illinois conditions year-round since 2023, the summer the Canadian smoke first showed up in serious volume. The numbers on this page come from the U.S. EPA, AirNow, the Illinois EPA, and the American Lung Association. The recommendations come from the same playbook we run in our own homes when an alert hits.
TL;DR QUICK ANSWERS
Live air quality index AQI map now today in Illinois
Illinois AQI swings wider than most states. Chicago, Aurora, Joliet, and Naperville post Moderate-to-Unhealthy numbers on a typical summer ozone day or during any active smoke event, while Springfield and Peoria usually stay cleaner. The 30 seconds it takes to check before you open the windows is the most useful thing you’ll do all morning.
- For the most current readings across the state, check this real-time air quality map Illinois residents can read by zip code or city.
- Illinois AQI peaks in summer (ozone and heat) and during the wildfire smoke incursions that have hit the state every year since 2023.
- Indoor PM2.5 typically settles at 30 to 70 percent of the outdoor reading in a standard home with closed windows, per U.S. EPA infiltration research.
- Once the outdoor AQI crosses 101, sensitive groups should act first: close windows, switch HVAC to recirculate, and run a HEPA purifier.
- The state’s worst air quality almost always shows up in the Chicago metro. Downstate cities run cleaner on most days.
TOP TAKEAWAYS
- The Air Quality Index is the U.S. EPA’s 0-to-500 scale for reporting daily air pollution, with color tiers running from Good (green, 0–50) to Hazardous (maroon, 301+).
- Outdoor PM2.5 infiltrates closed homes at roughly 30 to 70 percent, so a Moderate outdoor day still puts measurable fine particles into your living room.
- The action you take indoors should scale with the outdoor number. Higher AQI means more aggressive filtration and sealing.
- Sensitive groups should act one tier earlier than the general population, per EPA guidance. That includes people with asthma, COPD, or heart disease, plus children, older adults, and pregnant individuals.
Why outdoor AQI matters inside your Illinois home
Indoor air is not separate air. PM2.5 particles, the ones small enough to reach deep into your lungs, slip through window frames, door seals, attic gaps, and HVAC intakes. In a standard home with windows closed, indoor PM2.5 typically settles at 30 to 70 percent of outdoor concentrations, according to U.S. EPA infiltration research. So a Moderate AQI of 75 outside can mean 25 to 50 µg/m³ of fine particles inside your living room, hours after the outdoor reading climbed.
The lag matters. Indoor concentrations rise more slowly than outdoor concentrations, but they also fall more slowly. A four-hour smoke event in your neighborhood can keep your indoor air elevated long after the outdoor air clears.
Where to read live numbers right now
For live state conditions, AirNow Illinois lets you search by city or zip code and returns the current AQI in the EPA color tier next to it. The U.S. EPA uses six tiers: Good (0–50), Moderate (51–100), Unhealthy for Sensitive Groups (101–150), Unhealthy (151–200), Very Unhealthy (201–300), and Hazardous (301+).
The tier matters more than the exact number. Once the outdoor reading crosses 101, sensitive groups should already be taking indoor action. At 151, that goes for everyone.
Illinois city by city: where conditions vary
Conditions vary across the state. A Moderate day in Chicago can be a clean day in Champaign, and wind patterns over Lake Michigan can shift pollution loads within hours.
Chicago AQI today
Chicago routinely posts the state’s highest AQI readings. The American Lung Association’s State of the Air report has ranked the Chicago metro among the most ozone-polluted in the country, with traffic on the Dan Ryan and Eisenhower expressways, industrial sources in the southeast neighborhoods, and lake-effect transport all contributing. A neighborhood-level Chicago air quality map, like the one AirNow publishes, can show how readings differ between Logan Square and the South Side on the same afternoon.
Suburbs and downstate
Suburban Cook, DuPage, Lake, and Will counties usually mirror Chicago’s pattern, with PM2.5 spikes tied to commuter traffic. Rockford and the Fox River Valley carry a different mix, leaning industrial with less ozone, while downstate cities like Springfield, Peoria, Champaign, and Bloomington run cleaner on most days. Spring agricultural burns and winter inversions are the main exceptions.
What’s driving Illinois readings
Illinois PM2.5 levels today
Fine particulate matter, particles 2.5 microns and smaller, is the pollutant most consistently linked to respiratory and cardiovascular problems. The main Illinois sources are familiar: vehicle exhaust, industrial emissions, residential wood burning, and any combustion process. The U.S. EPA’s 24-hour standard for PM2.5 is 35 µg/m³. Any full day above that line puts sensitive groups at elevated risk.
Illinois ozone levels today
Ground-level ozone forms when sunlight and heat react with nitrogen oxides and volatile organic compounds from vehicles and industry. Illinois ozone season runs roughly May through September, with peak readings between 2 and 7 p.m. on hot, sunny days. Kids playing outside and outdoor workers feel it first: chest tightness, coughing, and reduced lung function.
Illinois wildfire smoke air quality
Canadian wildfire smoke reached Chicago in heavy concentrations in June 2023, pushing AQI readings into the Hazardous tier for days. The pattern has repeated each summer since. Illinois air quality forecasters now treat northern-hemisphere smoke as a regular summer variable rather than a freak event, and smoke can travel hundreds of miles aloft to settle into the Great Lakes region with the right wind pattern. For deeper coverage of how smoke affects what you breathe at home, see our guide to wildfire smoke and your indoor air.
Reading the Illinois air pollution forecast
Most of tomorrow’s air is knowable today. AirNow publishes next-day forecasts for the major Illinois metros, giving you 24 hours to plan: when to open the windows, when to keep them closed, when to skip the morning run, and when to swap in a fresh HVAC filter.
Illinois air quality alerts sensitive groups
The U.S. EPA defines sensitive groups as people with asthma, COPD, or cardiovascular disease; older adults; children; pregnant individuals; and people who work or exercise outdoors. When the state issues an alert at AQI 101 to 150, those individuals should already be moving indoors, sealing the house, and turning on filtration. The general population can wait until AQI 151.
If you or someone in your household has a respiratory condition, talk with your physician about a personalized air-quality action plan. The Illinois Department of Public Health publishes guidance specific to asthma and chronic respiratory disease management during air quality events.
“After tracking Illinois conditions across three wildfire smoke seasons, what stands out is this: the households that breathe easiest aren’t the ones with the most expensive purifiers. They’re the ones who check the outdoor numbers by 7 a.m. and adjust the home accordingly. The data is free. Most people just don’t think to look.”
ESSENTIAL RESOURCES
Bookmark these. They’re the same sources we rely on when verifying claims for IndoorAirWise coverage of Illinois conditions.
AirNow.gov. National live AQI and next-day forecasts, searchable by zip code. The home base for daily air quality checking.
AirNow AQI Basics. The official EPA explainer for how the AQI scale, color tiers, and health categories actually work.
Illinois EPA Air Quality Program. State-level monitoring network, attainment status, and current advisories.
American Lung Association State of the Air. Annual report card on ozone and particle pollution, with city and county grades for Illinois metros.
CDC Wildfire Smoke Guidance. Federal health guidance for protecting yourself and your household during smoke events.
U.S. EPA Indoor Air Quality. Foundational guidance on indoor pollutants, infiltration, ventilation, and remediation.
IDPH Asthma Program. Illinois-specific asthma resources, management plans, and air-quality response guidance.
STATISTICS
Indoor air can be 2 to 5 times more polluted than outdoor air, even in homes with no obvious pollution source. Source: U.S. EPA Report on the Environment, Indoor Air Quality.
Americans spend roughly 90 percent of their time indoors, where pollutant concentrations are often higher than typical outdoor levels. Source: U.S. EPA, The Inside Story: A Guide to Indoor Air Quality.
The Chicago metropolitan area consistently ranks among the most ozone-polluted U.S. metros in the American Lung Association’s annual report card. Source: American Lung Association, State of the Air Most Polluted Cities.
FINAL THOUGHTS AND OPINION
The point of checking the air quality index in your part of Illinois isn’t to worry. It’s to know. When you know the outdoor reading, you can make a 15-second decision: open the windows or close them, swap the HVAC filter or wait, run the air purifier or save the energy. None of these are heroic moves. They’re small calibrations that add up over a year of breathing, and they cost almost nothing once the habit is built.
Three years of covering Illinois conditions have shifted our view. The state has moved past the point where outdoor air quality is a once-a-year news story. Summer smoke days, ozone alerts, and inversion-driven PM2.5 spikes are now a regular feature of the calendar. The households doing this well aren’t the wealthiest. They’re the ones who have built one habit (check the number before the day starts) and one workflow (know what to do when the number is bad). That’s the whole game.
FREQUENTLY ASKED QUESTIONS
What is the air quality in Illinois today?
Illinois air quality varies by city and by hour. Chicago, Aurora, and Joliet often see Moderate-to-Unhealthy readings during summer ozone days or active smoke events, while Springfield, Peoria, and Champaign typically run cleaner. Check AirNow or the Illinois EPA dashboard for the live number nearest you.
Is the air quality bad in Chicago right now?
Chicago’s AQI changes hourly. Summer afternoons during ozone season and any day with active wildfire smoke transport are the highest-risk windows. The American Lung Association consistently ranks Chicago among the most ozone-polluted U.S. metros, so a Moderate-or-worse summer reading is typical, not unusual.
How do I check air quality in my Illinois zip code?
Go to airnow.gov, enter your zip code in the search bar, and the page returns the nearest monitoring station’s current AQI plus its EPA color tier. The free AirNow mobile app does the same and can push alerts when readings cross a threshold you set.
What causes poor air quality in Illinois?
The main drivers are summer ozone (formed from vehicle and industrial emissions plus sunlight), PM2.5 from traffic and combustion, wildfire smoke transported from Canada and the western U.S., and winter temperature inversions that trap pollutants near the ground.
Does outdoor air pollution affect my indoor air?
Yes. Per U.S. EPA infiltration research, indoor PM2.5 typically settles at 30 to 70 percent of outdoor concentrations in a standard home with closed windows. The cleaner you keep the indoor environment through filtration, recirculation, and sealing, the smaller that ratio becomes.
When is air quality worst in Illinois?
Two windows. Summer afternoons between roughly 2 and 7 p.m. when ozone peaks, and any day during an active wildfire smoke event regardless of season. Winter inversions also push PM2.5 higher for short stretches, usually mornings during cold, calm weather.
What AQI level is unsafe for sensitive groups?
AQI 101 to 150 is the Unhealthy for Sensitive Groups tier per U.S. EPA. People with asthma, COPD, or cardiovascular disease, along with older adults, children, and pregnant individuals, should reduce outdoor exposure at that level. The general population enters the unhealthy zone at AQI 151.
Build a 30-second morning habit
Three steps, in this order, every morning before you start the day:
- Check airnow.gov or your AirNow app for your zip code.
- If the AQI is above 100, close the windows and switch your HVAC to recirculate.
- If the AQI is above 150, run a HEPA purifier in the room where you’ll spend the most time today.
To pair this habit with the longer-term work, our MERV 13 filter guide explains which filter rating actually catches what’s coming in, and our winter HVAC efficiency guide walks the home audit room by room.