The public-health group ranked the pollution levels of U.S. cities and counties based on air quality measurements that state and local agencies reported to the U.S. Environmental Protection Agency between 2005 and 2007.
Overall, the report found that air pollution at times reaches unhealthy levels in almost every major city and that 186.1 million people live in those areas. The number is much higher than last year's figure of about 125 million people because recent changes to the federal ozone standard mean more counties recognize unhealthy levels of pollution.
Health effects from air pollution include changes in lung function, coughing, heart attacks, lung cancer and premature death.
"Six out of 10 Americans right now as we speak live in areas where the air can be dirty enough to send people to the emergency room, dirty enough to shape how kids' lungs develop and even dirty enough to kill," said Janice E. Nolen, the association's assistant vice president on national policy and advocacy.
Cities including Los Angeles, New York, Atlanta, Charlotte, Philadelphia, Washington D.C. and Baltimore have seen improvements in air quality over the last decade, the report said.
The Los Angeles-Long Beach-Riverside region of Southern California remained the metropolitan area with the highest levels of ozone pollution, as it has in each of the past 10 reports. Other metropolitan areas considered to have the most ozone pollution included Houston-Baytown-Huntsville and Dallas-Fort Worth in Texas.
The areas with the most short-term particle pollution or soot were Pittsburgh-New Castle, Pa.; and the California areas of Fresno-Madera, Bakersfield and Los Angeles-Long Beach-Riverside.
The cleanest metro area in all categories was Fargo, N.D.
The rankings in the "State of the Air Report" were based on ozone pollution levels produced when heat and sunlight come into contact with pollutants from power plants, cars, refineries and other sources.
The lung association also studied short-term and year-round levels of particle pollution, which is made up of a mix of tiny solid and liquid particles in the air.
On Tuesday, a separate study showed that exposure to air pollution both early and late in pregnancy may have a .
Air pollution, especially pollution from car exhaust, was linked to smaller birth weight in the study even after researchers controlled for known risk factors.