The number of deaths from breathing sooty smog in California may be more than twice as high as previously estimated, based on a recent University of Southern California study that examined the risk of such deaths in the Los Angeles basin.

A team of researchers headed by Michael Jerrett, associate professor of preventive medicine, found two to three times greater risk of mortality from heart attacks, lung cancer and other serious illness tied to chronic exposure to fine particulate matter than previous studies.

The study looked at specific soot measurements and deaths in hundreds of neighborhoods – rather than relying on citywide annual averages used in the past – and detected the largest increased risks in the Inland Empire, the area east of Los Angeles, Jerrett said.

Currently, state officials estimate 9,000 Californians die annually from diseases caused or aggravated by air pollution, more than half of them in Southern California.