Chicago ? Long-term exposure to the air pollution in some of America’s biggest metropolitan areas significantly raises the risk of dying from lung cancer and is about as dangerous as living with a smoker, a study of a half-million people found.

The study echoes previous research and provides the strongest evidence yet of the health dangers of the pollution levels found in many big cities and even some smaller ones, according to the researchers from Brigham Young University and New York University.

The risk is from what scientists call combustion-related fine particulate matter  soot emitted by cars and trucks, coal-fired power plants and factories.

The study appears in today’s Journal of the American Medical Assn.

It involved 500,000 adults who enrolled in 1982 in an American Cancer Society survey on cancer prevention. The researchers examined participants’ health records through 1998 and analyzed data on annual air pollution averages in the more than 100 cities in which participants lived.

The researchers first took into account other risk factors for heart and lung disease such as cigarettes, diet, weight and occupation.

Lung cancer death rates were compared with average pollution levels, as measured in micrograms per cubic meter of air. The researchers found that the number of lung cancer deaths increased 8 percent for every increase of 10 micrograms. Other heart- and lung-related causes of death increased 6 percent for every 10-microgram increase.

Allen Dearry, a scientist at the National Institute of Environmental Health Sciences, which funded the study, called it “the best epidemiologic evidence that we have so far that that type of exposure is associated with lung cancer death.”

The JAMA study did not list data from individual cities in which the participants lived. Researchers said the study was designed to examine the overall health risk posed by fine particulate matter in the United States  not compare pollution levels in various cities.

Thurston said the lung cancer risks were comparable to those faced by nonsmokers who live with smokers and are exposed long-term to secondhand cigarette smoke. Such risks have been estimated at 16 percent to 24 percent higher than those faced by people living with nonsmokers, Thurston said.

In the early 1980s, when the study began, some major cities had air pollution levels of 25 to 30 micrograms per cubic meter, which would confer a more than 20 percent increased risk of lung cancer mortality, said C. Arden Pope III, an environmental epidemiologist at Brigham Young University and a co-leader of the JAMA study.

The Environmental Protection Agency set average annual limits at 15 micrograms per cubic meter in 1997, when it tightened its standards to include fine particulate matter  pollutants measuring less than 2.5 micrometers. That is about 1/28th the width of a human hair.

That regulation followed another study by Pope linking fine particulate pollution and lung cancer that included many of the same participants as the JAMA study.

Pope said the new study doubles the follow-up time and does a better job of taking other risk factors into account, to address criticism from industry groups who challenged the earlier study and sued the EPA over the 1997 regulations. The Supreme Court last year upheld the way the EPA set those standards.

Industry challenges to the standards are ongoing, said Jayne Brady, spokeswoman for the Edison Electric Institute, which represents most of the nation’s major electric utilities, including operators of many coal-powered plants.

Despite those challenges, Brady said, “We are trying to do everything we can to reduce emissions.”