Air Quality Forecast

Wednesday, December 4
Wed
Thu
Fri
Sat
Sun
Northern Zone
60
PM 2.5
62
PM 2.5
M
PM 2.5
G
PM 2.5
G
PM 2.5
Coast and Central Bay
60
PM 2.5
75
PM 2.5
M
PM 2.5
M
PM 2.5
G
PM 2.5
Eastern Zone
64
PM 2.5
71
PM 2.5
M
PM 2.5
M
PM 2.5
G
PM 2.5
South Central Bay
64
PM 2.5
68
PM 2.5
G
PM 2.5
G
PM 2.5
G
PM 2.5
Santa Clara Valley
79
PM 2.5
79
PM 2.5
M
PM 2.5
M
PM 2.5
M
PM 2.5
Last Updated: Wednesday, December 4 at 10:05 AM

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).

Bay Area Air Quality Management District
375 Beale Street, Suite 600
San Francisco, CA 94105
1-800-HELP AIR | (415) 749-4900
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