An assessment of health effects due to ozone and particulate matter (PM10) suggests that each of the 12 million residents of the South Coast Air Basin of California experiences ozone-related symptoms on an average of up to 17 days each year and faces an increased risk of death in any year of 1/10,000 as a result of elevated PM10 exposure. The estimated annual economic value of avoiding these effects is nearly $10 billion. Attaining air pollution standards may save 1600 lives a year in the region.