A "Spare the Air" alert declared for Labor Day has been extended through Sept. 4.
Residents are encouraged to drive less and reduce their emissions of ozone-forming pollutants, including curtailing use of lawnmowers and other devices using internal combustion engines.
The Spare the Air alert, which was called by the Bay Area Air Quality Management District, will be the first since Aug. 7, but the district's air quality advisory for smoke has been in effect all weekend. The Bay Area again may experience smoke pollution from regional wildfires.
Spare the Air alerts are called when ozone pollution can reach unhealthy levels. Ozone is created when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, trains and other sources react chemically in the presence of sunlight, creating a whole new harmful pollutant.