Air Quality Forecast

Sunday, July 21

Sun

Mon

Tue

Wed

Thu

Northern Zone

PM 2.5

OZONE

Coast and Central Bay

PM 2.5

Eastern Zone

PM 2.5

OZONE

South Central Bay

OZONE

Santa Clara Valley

OZONE

Last Updated: Sunday, July 21 at 9:59 AM

Air Quality Index

0-50

Good (G)

51-100

Moderate (M)

101-150

Unhealthy for Sensitive Groups (USG)

151-200

Unhealthy (U)

201-300

Very Unhealthy (VH)

301-500

Hazardous (H)

Pollutant

Ozone

Ground-level ozone, commonly called "smog," is the major summertime cause of poor air quality in the Bay Area.

PM 2.5

Microscopically small mixtures of solid particles or liquid droplets that are emitted directly into the air.

Air Quality Forecast and Spare the Air Alerts

Air is almost always on the move, and pollution can easily drift from one reporting zone to another. This is particularly true in the Bay Area, which forms a single air basin, and where winds can blow pollution from one location into neighboring valleys.

That is why a Spare the Air Alert is called for the entire Bay Area when air quality is forecast to be unhealthy in any one of the five reporting zones: North Counties, Coast and Central Bay, Eastern Zone, South Central Bay, and Santa Clara Valley.

Reporting zones are different from county lines: they are defined by air current patterns and geographic features that lead to shared air quality within certain areas.

The Air District issues a daily forecast that predicts air pollution levels for the coming five-day period. The forecast uses the U.S. EPA's Air Quality Index to indicate how healthy or unhealthy those air pollution levels are expected to be.

A Spare the Air Alert is called when air quality is forecast to be unhealthy, or above 100 in the AQI, in any one of the reporting zones. An alert may span over two days if air quality is expected to remain unhealthy for prolonged periods.

If air quality is unhealthy in the Bay Area, it is almost always because of two kinds of air pollutants: Ozone and fine particulate matter, or PM2.5.

The daily forecast is available by signing up for email ‌AirAlerts or calling the Air District’s 24-hour, toll-free information line (1-800-HELP AIR).

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Air Quality Forecast

0-50

Good (G)

51-100

Moderate (M)

101-150

Unhealthy for Sensitive Groups (USG)

151-200

Unhealthy (U)

201-300

Very Unhealthy (VH)

301-500

Hazardous (H)

Air Quality Forecast and Spare the Air Alerts

San Francisco Bay Area Air Quality Status

5-Day Air Quality Forecast

Air Quality Forecast

Forecast Reporting Zones

Northern Zone

Coast and Central Bay

Eastern Zone

South Central Bay

Santa Clara Valley

0-50

Good (G)

51-100

Moderate (M)

101-150

Unhealthy for Sensitive Groups (USG)

151-200

Unhealthy (U)

201-300

Very Unhealthy (VH)

301-500

Hazardous (H)

Air Quality Forecast and Spare the Air Alerts

San Francisco Bay Area
Air Quality Status