LOS ANGELES, CA -  Morning traffic fills the SR2 freeway in Los Angeles, California. The nation's second largest city, Los Angeles, has again been ranked the worst in the nation for ozone pollution and fourth for particulates by the American Lung Association in it's annual air quality report card. Ozone is a component of smog that forms when sunlight reacts with hydrocarbon and nitrous oxide emissions. Particulates pollution includes substances like dust and soot. 

Scientists and clean air advocates are well aware that fine particles in the air, known as PM2.5, are correlated with deaths from cardiovascular disease. 

“You can see days where we have higher pollution, and they’ve already tracked that to more hospital admissions for heart disease, heart attacks," said Angela Johnson Meszaros, general counsel for Physicians for Social Responsibility - Los Angeles. "That kind of thing, we already knew.”

A study out this month in the journal "Environmental Research" may shed light on something that wasn't as well known — the mechanism by which particulate matter causes the disease.

Fine particles are released by vehicles, wood burning, power plants and other industrial sources and are capable of embedding deep within lungs. 

Scientists with the California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment studied data from 3,000 women over a five-year period and found that long-term exposure to PM2.5 was strongly linked with increased levels of C-reactive proteins (CRP). The proteins are indicators of inflammation, which is tied to heart disease and stroke. 

The study also identified that smokers and people with diabetes, lower incomes, high blood pressure and those undergoing hormone therapy are more vulnerable to PM2.5. At the same time, the impacts seem to be lessened by certain medications and moderate alcohol consumption. 

“These are significant findings that might help us develop better approaches to reducing risks associated with PM2.5 exposure,” said Dr. John Balmes, a professor of medicine at the University of California, San Francisco, and member of the California Air Resources Board. 

Where is the PM2.5?

Meszaros said that in general the Southern California's Inland Empire is most inundated with PM2.5, a result of winds pushing the pollution inland from the ocean.

“If you look generally at the particulate maps, what you’ll see is the San Bernardino/Riverside areas are going to be red, red, red; and the coastal areas are going to be green, green, green,” Meszaros said. 

Tina Cox, a spokeswoman with the South Coast Air Quality Management District, said that within Los Angeles County last year, the City of Compton had the highest levels of PM2.5, followed by Burbank.