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. On a Spare the Air day, Bay Area residents are asked through radio and television announcements to reduce their driving, refrain from using gas-powered gardening equipment and curb other air polluting activities such as painting and aerosol spray can usage. People especially sensitive to smog are advised to limit their time outdoors.