The Bay Area Air Quality Management District has issued a Spare the Air Alert for today because of a high-pressure system producing clear skies, light winds and high inland temperatures.
This is the fifth such alert so far in 2015, according to air district officials.
The hot weather is expected to result in smoggy conditions throughout the region, according to air district executive director Jack Broadbent.
"Motor vehicle exhaust is the number one source of smog-forming pollution, so we're asking Bay Area residents to share rides, take transit, bike or walk to help keep pollution levels down," Broadbent said in a statement.
Smog can cause throat irritation, congestion and chest pain. It can also trigger asthma by inflaming the lining of the lungs, and exacerbate other respiratory conditions such as bronchitis or emphysema, according to air district officials.
Nearly 40 percent of smog pollution in the Bay Area comes from passenger vehicles, air district officials said.