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

June 28, 2023 — Canadian wildfire smoke pushed Chicago metro AQI past 240 (Very Unhealthy), the worst single-day reading in the city's monitored history.

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?

June 28, 2023 — Canadian wildfire smoke pushed Chicago metro AQI past 240 (Very Unhealthy), the worst single-day reading in the city's monitored history.

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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