As many as 24,000 deaths annually in California are linked to chronic exposure to fine particulate pollution, triple the previous official estimate of 8,200, according to state researchers.
The revised figures are based on a review of new research across the nation about the hazards posed by microscopic particles, which sink deep into the lungs.
"Our report concludes these particles are 70% more dangerous than previously thought, based on several major studies that have occurred in the last five years," said Bart Croes, chief researcher for the California Air Resources Board. Croes will present his findings at a board meeting in Fresno this morning.
The studies, including one by USC tracking 23,000 people in greater Los Angeles, and another by the American Cancer Society monitoring 300,000 people across the United States, have found rates of heart attacks, strokes and other serious disease increase exponentially after exposure to even slightly higher amounts of metal, dust or other fragments from tailpipes and smokestacks.
It is difficult to attribute individual deaths to particulate pollution, Croes conceded, but he said long-term studies that account for smoking, obesity and other risks have increasingly zeroed in on fine particulate pollution as a killer.
"There's no death certificate that says specifically someone died of air pollution, but cities with higher rates of air pollution have much greater rates of death from cardiovascular diseases," he said.
Californians exposed to high levels of fine particulates had their lives cut short on average by 10 years, the board staff found.
Researchers also found that when particulates are cut even temporarily, death rates fall.
"When Dublin imposed a coal ban, when Hong Kong imposed reductions in sulfur dioxide, when there was a steel mill strike in Utah . . . they saw immediate reductions in deaths," Croes said.
More measures will be needed, air board officials said, including eventually lowering the maximum permissible levels of soot statewide. California already has the lowest thresholds in the world, at 12 micrograms per cubic meter, but researchers say no safe level of exposure has been found. More regulations are being drafted, including one requiring cleaner heavy-duty trucks.
"We must work even harder to cut short these life-shortening emissions," Air Resources Board Chairwoman Mary Nichols said in a statement.
Clean air advocates said they would be watching closely.
"These numbers are shocking; they're incredible," said Tim Carmichael, senior policy director for the Coalition for Clean Air, a statewide group. He and others said the board must strengthen a soot clean-up plan submitted to them by the San Joaquin Valley Air Pollution Control District. A hearing and vote on the plan is scheduled for today.
Numerous Central Valley public health groups wrote Nichols this week, urging bans on the use of industrial equipment on bad air days, tougher controls on boilers and crop drying equipment, and other action. The economic cost attributed to premature deaths and illnesses linked to particulate exposure in the Central Valley has been estimated at $3 billion a year, and $70 billion statewide, according to separate studies. Those figure are expected to be revised upward based on the new report.
"We must clean up the air. We cannot afford further delay," the group wrote.
Agricultural and construction industry groups have fought such provisions, saying that they could cripple the region's economy, but have not publicly complained about the plan as proposed. Board spokesman Leo Kay said that given the new mortality findings, "I certainly don't expect a rubber-stamp approval."