People with heart failure, chronic obstructive pulmonary disease, diabetes, and inflammatory diseases such as rheumatoid arthritis face a higher risk of death when exposed to particulate air pollution -- commonly known as soot -- for one year or more, a new study suggests.

According to the study findings, a fairly brief increase in particulate air pollution boosts the risk of death by 27 percent to 32 percent among some patients with diabetes, chronic obstructive pulmonary disease and congestive heart failure. And people with diseases like rheumatoid arthritis face a similar risk.

"Air pollution significantly increases risks in a relatively short period of time," said study lead author Joel Schwartz, a professor of environmental epidemiology at the Harvard School of Public Health. "These people are dying within a year or two of pollution concentrations going up," he added.

Schwartz and his colleagues examined hospital records for Medicare patients in 34 U.S. cities from 1985 to 1999 to find patients who had been admitted for treatment of a number of diseases. Then, they followed the patients for as long as 15 years to see if they lived or died.

The researchers also examined the annual air pollution levels of particulate matter, which is made up of tiny particles that can easily travel into the lungs.

The researchers reported their findings Monday at the American Thoracic Society meeting in San Diego.

According to the study, each time particulate matter levels increased by 10 micrograms per cubic meter over two years, the risk of dying went up by 32 percent for those with diabetes and 28 percent for those with chronic obstructive pulmonary disease.

The risk of death rose by 27 percent for those with congestive heart failure and 22 percent for people with inflammatory diseases, which include rheumatoid arthritis and lupus.

The higher risks of death appeared to be linked to higher air pollution levels in the previous two years before the patients died, suggesting the pollution acts quickly, Schwartz said.

In cases when pollution levels fell, the death rates returned to expected levels within two years.

Could there be some other factor besides air pollution at play?

It's possible, Schwartz said, but studies that used different methods have shown similar results.

Dr. Norman Edelman, chief medical officer of the American Lung Association, said the new study was consistent with previous research that suggested the dangers of particulate matter. "It's a powerful study," he said, indicating "it doesn't take years and years to see an effect."

Why is this type of air pollution so hazardous to health?

"The answer is not in," Edelman said. But it appears that the particles in soot activate the immune system, which releases chemicals that harm the body. Those who are already at ill are at increased risk, he said.