Chicago, IL Air Quality & Smog

Dominant pollutants, when smog is worst, notable historical episodes, and local agency resources for Chicago, IL — plus how to check the current AQI. For real-time readings, the free Smog Report iOS app pulls live air quality from EPA AirNow.

Dominant pollutants

ozone (summer), PM2.5 (industrial + transport).

Seasonal pattern: when smog is worst

Ozone peaks on hot summer days, particularly along the lakeshore where stagnant lake-influenced air keeps NOₓ trapped. PM2.5 baseline elevated by industrial corridor activity along the Calumet River and I-90.

A recent or notable event

July 17, 2026 — a severe Canadian wildfire smoke event, fed by roughly 900 actively burning fires including 180+ in Ontario, pushed Chicago's AQI to 753 — "extremely hazardous," and briefly the worst air quality of any major city in the world, ahead of Detroit and New York. Beaches closed and outdoor events were cancelled. That eclipsed the previous record from June 28, 2023, when Canadian smoke pushed the metro AQI past 240. See the full 2026 wildfire smoke event guide for the regional picture.

Local agencies and resources

Illinois EPA runs the AirNow-feeding monitors. The Chicago Department of Public Health issues local advisories during smoke events.

• Illinois EPA
• City of Chicago Department of Public Health

How to check air quality in Chicago

The EPA's AirNow.gov publishes the canonical reading from the nearest regulatory monitor. For glanceable iPhone access — including widgets, Live Activities, Siri voice queries, and Apple Watch — install Smog Report. It's free, requires no account, and pulls from the same AirNow API.

For Chicago-specific advisories and alerts that go beyond the federal AirNow feed, check the agency pages above directly.

Common questions about Chicago air quality

Why does Chicago have air-quality and smog problems?

Ozone peaks on hot summer days, particularly along the lakeshore where stagnant lake-influenced air keeps NOₓ trapped. PM2.5 baseline elevated by industrial corridor activity along the Calumet River and I-90.

What are the main air pollutants in Chicago?

Chicago's dominant pollutants are ozone (summer), PM2.5 (industrial + transport). The AQI on any given day is usually driven by whichever of these is highest.

Has Chicago had a major air-quality or smog event?

July 17, 2026 — a severe Canadian wildfire smoke event pushed Chicago's AQI to 753, briefly the worst air quality of any major city in the world. That eclipsed the prior record from June 28, 2023, when Canadian smoke pushed the metro AQI past 240.

How can I check Chicago's air quality right now?

The EPA's AirNow.gov publishes the official reading from the nearest regulatory monitor. For live AQI on your iPhone — with home-screen widgets, Lock Screen Live Activities, Siri, and Apple Watch — the free Smog Report app pulls from the same AirNow feed. No account is required.

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