Bay Area residents are encouraged to find other ways of getting around Saturday as the area's air quality is expected to be unhealthy because of heat and light winds, Bay Area Air Quality Management District officials said.
The warning was issued as the air district's 16th Spare the Air smog alert for 2016.
Light winds, heat and motor vehicle exhaust will combine to make the air unhealthy, especially for young children, seniors and people with respiratory and heart problems.
District officials said the single most effective way for people to improve air quality is to drive less or drive electric vehicles that do not pollute.
"As you make plans for the weekend, consider events and activities you can walk or bike to, instead of driving," air district executive officer Jack Broadbent said in a statement.
Broadbent also said the best time of the day to be outside Saturday is in the morning or evening when temperatures are lower.
Smog can irritate throats, cause congestion, chest pain, trigger asthma, inflame the lining of the lungs and make bronchitis and emphysema worse, district officials said. Long-term exposure to smog can damage the lungs.
Residents are encouraged to walk, bike, carpool or take transit Saturday and every day.
More information about Spare the Air Alerts, including when alerts have been issued, can be found www.sparetheair.org. Residents can also call (800) HELP-AIR, visit Spare the Air on Facebook or Twitter or download the Spare the Air app to find out when an alert has been issued.