The alert is being issued due to the expected combination of hot temperatures and exhaust from motor vehicles, the district said.
A ban on wood burning is in place, and the district encourages Bay Area residents to drive less and conserve energy.
Vehicle exhaust, gas vapors, industrial emissions and household chemicals contain volatile components that react with sunlight and oxygen at high temperatures to form ground-level ozone, according to the district.
Breathing ozone can lead to throat irritation, congestion and chest pain and can trigger or worsen asthma, bronchitis and emphysema.
Air district officials urge residents to bike to work or around town, take public transit, telecommute, carpool and avoid using aerosol spray cleaners, paints and hairsprays.
For more tips on how to spare the air, visit www.baaqmd.gov.