Rates of heart attacks, strokes and potentially fatal blood clots in the leg increase after exposure to air pollution from traffic fumes. It alters the blood’s coagulation properties and heightens the risk of deep vein trombosis.

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.

A new research study based on the results of 60 studies worldwide and advice from a team of experts, including the World Health Organization, concluded that the microscopic particles are 70% more dangerously than previously thought, said Bart Croes, chief researcher for the California Air Resources Board. The study included one USC tracking 23,000 people in greater Los Angeles, and another by the American Cancer Society monitoring 300,000 people across the United States.

Researchers have found rates of heart attacks, strokes and other serious diseases increase exponentially after exposure to even slightly higher amounts of metal or dust.

“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,” Croes said.

Researchers found that when particulates are cut even for a short period of time, death rates fall. As an example, when Hong Kong imposed reductions in sulphur dioxide, or when Dublin imposed a coal ban, they saw immediate reductions in death rates.

“Particle pollution is a silent killer,” state Air Resources Board Chairwoman Mary Nichols was quoted as saying by the San Francisco Chronicle, after the board meeting in Fresno, where the Air Resources Board voted unanimously to approve the air cleanup plan, which aims to clean up the air by requiring large employers to encourage a portion of their workers carpool and by keeping families from using their fireplaces for up to 35 days each winter. The air cleanup plan relies on a draft state regulation that will curb emissions from diesel-powered trucks and buses, which the board is expected to make final in October, the Mercury News noted.

The plan requires final approval from the US Environmental Protection Agency.