Chicago, IL Air Quality Index (AQI)
AirNow NowCastChicago (Cook Co.)12 min agoAQS-170313103
NowCast Trend — Past 12 Hours
PM2.5 · AQIAirNow NowCastChicago (Cook Co.)12 min agoAQS-170313103
3-Day AQI Forecast
Forecasts combine AirNow model output with NOAA HYSPLIT smoke transport. Accuracy degrades beyond 48 hours. Always check the latest before outdoor plans.
Smoke Days This Year
Days with AQI > 100 (USG or worse) at any monitor in Chicago
Health Guidance — Unhealthy for Sensitive Groups
Reduce or reschedule strenuous activity.
Unusually sensitive may feel effects.
Sensitive groups should limit time outside.
About Smoke Season in Chicago
Chicago sits in the transport corridor for wildfire smoke from the western United States and, increasingly, Canada. June through September is the primary smoke season, with episodes most common when high-pressure systems build over the northern Rockies, steering surface winds eastward.
The 2023 Canada wildfires — the largest on record — sent PM2.5 concentrations in Chicago above 200 µg/m³ for more than 48 hours. Climate models project the number of high-smoke days to double by 2050 across the Northeast.
The best protection is a HEPA air purifier sized for your space (see our purifier calculator) and an N95 or KN95 respirator for essential outdoor activity during smoke events.
Frequently Asked Questions
What does AQI measure?
The Air Quality Index (AQI) is a standardized scale from 0–500 that translates complex pollutant concentrations into a single number. We report the 2024 EPA standard which updated PM2.5 breakpoints to better reflect current science.
What is NowCast?
NowCast is EPA's algorithm for computing a real-time AQI from the most recent 12 hours of hourly monitor data. It weights recent hours more heavily, so the displayed AQI responds quickly to changing conditions.
How often does the data update?
AirNow publishes hourly monitor data each hour. WildfireWindow fetches and displays the latest available reading, typically within 5 minutes of publication.
What are PM2.5 particles?
PM2.5 refers to fine particulate matter 2.5 microns or smaller in diameter — about 1/30th the width of a human hair. These particles penetrate deep into the lungs and can enter the bloodstream, making them particularly hazardous.