Air Quality Forecast

Monday, September 21
Mon
Tue
Wed
Thu
Fri
Northern Zone
57
PM 2.5
53
PM 2.5
M
PM 2.5
M
PM 2.5
M
PM 2.5
Coast and Central Bay
53
PM 2.5
42
PM 2.5
G
PM 2.5
G
PM 2.5
M
PM 2.5
Eastern Zone
74
OZONE
46
PM 2.5
G
PM 2.5
G
PM 2.5
M
OZONE
South Central Bay
50
PM 2.5
46
PM 2.5
G
PM 2.5
G
PM 2.5
M
PM 2.5
Santa Clara Valley
53
PM 2.5
50
PM 2.5
G
PM 2.5
G
PM 2.5
M
OZONE
Last Updated: Monday, September 21 at 10:12 AM

How the Forecast Affects 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. A Spare the Air Alert is called when air quality is forecast to be unhealthy in any one of the reporting zones. An alert may span over two days if air quality is expected to remain unhealthy.

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).