A round of scorching temperatures forecast for the Bay Area over the next two days, combined with wildfire smoke and vehicle fumes, prompted air district officials to issue a Spare the Air alert for Sunday.
High temperatures for Sunday are expected to top 100 in some areas and the National Weather Service has issued a heat advisory for Sunday and Monday.
In addition, a Red Flag Warning is in effect from Saturday night through Monday morning due to dry conditions and gusty winds.
Northerly winds will carry smoke from the August Complex and North Complex blazes to parts of the region, exacerbating smog, or ozone pollution, levels.
"High inland temperatures mixed with wildfire smoke and vehicle exhaust are creating an unhealthy breathing environment," said Jack Broadbent, executive officer of the Bay Area Air Quality Management District.
"If we all drive less, we can help reduce harmful ozone pollution and protect the health of Bay Area residents."
Sunday's Spare the Air Alert is the 35th declared so far this year.
Smog can cause throat irritation, congestion, chest pain, trigger asthma, inflame the lining of the lungs and worsen bronchitis and emphysema, air district officials said.
During a Spare the Air alert, outdoor exercise should take place only in the early morning, when smog levels are lower.
When smoke reaches unhealthy levels, residents should stay inside if possible with windows and doors closed until it subsides, if temperatures allow.
When it's too hot, residents are urged to visit an air-cooling center or other building that provides filtered air.
Multiple cooling centers will be open in Santa Clara County, including at the Mitchell Park Community Center's El Palo Alto room at 3700 Middlefield Road, from 10 a.m. to 6 p.m. on Sunday and Monday. A list of cooling centers and safety tips from the county can be found here.