High area temperatures have prompted a Spare the Air alert for Sunday by the Bay Area Air Quality Management District.
The alerts are issued when weather forecasts indicate there will be high levels of smog in the air.
Residents are asked to drive less during summer Spare the Air days by carpooling, taking public transportation, bicycling or walking to their destinations.
Smog can cause throat irritation, congestion, chest pain, asthma, inflame the lungs and make existing lung conditions worse. Young children, seniors and those with respiratory and heart conditions are particularly at risk to the effects of smog.
Sunday's Spare the Air alert is the fourth issued in the summer season. Three were issued on consecutive days during a heat wave last month.