Spare the Air program
Spare the Air is a program established by the Bay Area Air Quality Management District in 1991 to combat air pollution during the summer in the San Francisco Bay Area, the season when clear skies, hot temperatures, lighter winds, and a strong temperature inversion combine and trap air pollutants near the ground. Spare the Air days are declared for days in which levels of ground-level ozone (a constituent of smog) are predicted to exceed the EPA's federal health-based standard of 84 ppb, or an air quality index over 100.