Air Quality Forecast

Tuesday, October 4
Mon
Tue
Wed
Thu
Fri
Northern Zone
41
OZONE
38
OZONE
G
OZONE
G
OZONE
G
OZONE
Coast and Central Bay
46
PM2.5
46
PM2.5
G
PM2.5
M
PM2.5
M
PM2.5
Eastern Zone
45
OZONE
44
OZONE
G
OZONE
M
OZONE
M
OZONE
South Central Bay
43
OZONE
40
OZONE
G
OZONE
G
OZONE
G
OZONE
Santa Clara Valley
48
OZONE
42
OZONE
M
OZONE
M
OZONE
M
OZONE
Last Updated Monday, October 3 at 10:12 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).