Bay Area air district officials issued a third straight Spare the Air alert for Saturday (Sept. 14) and expanded an air quality advisory for possible smoke drifting from Northern California wildfires.

A combination of light winds, high temperatures and vehicle exhaust will continue to cause elevated concentrations of ozone, or smog, Bay Area Air Quality District officials said.

Smoke, mostly at higher elevations, may drift to the region from the Walker Fire in Plumas County and other Northern California wildfires, the air district said.

Saturday's alert is the 15th Spare the Air alert this year.

While air quality is expected to exceed federal standards for ozone, the wildfire smoke in the region is not expected to exceed the federal standard for fine particulates, the air district said Friday.

"In the Bay Area, the best thing we can do to reduce harmful air pollution and greenhouse gases is to drive less," said Jack Broadbent, executive officer of the district.

The alerts are issued when ozone pollution is forecast to reach unhealthy levels.

When an air alert is issued, outdoor exercise should be done only in the early morning hours when ozone concentrations are lower, according to the air district.