San Francisco–Oakland, CA Air Quality & Smog

Dominant pollutants, when smog is worst, notable historical episodes, and local agency resources for San Francisco–Oakland, CA — 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

PM2.5 (wildfire season — Aug-Oct), ozone (mostly low — fog and marine influence).

Seasonal pattern: when smog is worst

The Bay Area's normal air quality is excellent — consistent marine influence keeps the basin ventilated. The exception is wildfire season. The Bay was the global poster city for wildfire smoke during the 2020 Glass Fire / SCU Lightning Complex when the sky turned orange and AQI exceeded 200 for weeks.

A recent or notable event

September 9, 2020 — wildfire smoke from multiple Sierra and North Bay fires combined with marine layer to turn the Bay Area sky deep orange; AQI exceeded 250 across most of the region.

Local agencies and resources

BAAQMD runs both the regulatory monitor network and the regional Spare the Air alert program.

• Bay Area Air Quality Management District (BAAQMD)
• California Air Resources Board (CARB)

How to check air quality in San Francisco–Oakland

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 San Francisco–Oakland-specific advisories and alerts that go beyond the federal AirNow feed, check the agency pages above directly.

Common questions about San Francisco–Oakland air quality

Why does San Francisco–Oakland have air-quality and smog problems?

The Bay Area's normal air quality is excellent — consistent marine influence keeps the basin ventilated. The exception is wildfire season. The Bay was the global poster city for wildfire smoke during the 2020 Glass Fire / SCU Lightning Complex when the sky turned orange and AQI exceeded 200 for weeks.

What are the main air pollutants in San Francisco–Oakland?

San Francisco–Oakland's dominant pollutants are PM2.5 (wildfire season — Aug-Oct), ozone (mostly low — fog and marine influence). The AQI on any given day is usually driven by whichever of these is highest.

Has San Francisco–Oakland had a major air-quality or smog event?

September 9, 2020 — wildfire smoke from multiple Sierra and North Bay fires combined with marine layer to turn the Bay Area sky deep orange; AQI exceeded 250 across most of the region.

How can I check San Francisco–Oakland'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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