When the days turn hot and humid, Dr. Scott Morin’s Biddeford practice fills up with people complaining of symptoms from chronic obstructive pulmonary disease, a common respiratory illness. That’s when ozone levels climb highest, and air pollution is at its worst.

People may feel the strongest effects if they live in Cumberland, York, and Hancock counties, which have the highest levels of air pollution in the state, according to a report released Wednesday by the American Lung Association. However, overall air pollution levels in Maine and nationally have eased since the 1990s, the report found.

The lung association issued letter grades for each county across the country, based on ozone levels and other measures of air quality. For ozone, York and Hancock counties received a D and Cumberland received a C, while Bangor and much of the rest of the state earned A grades.

Bangor’s air quality was among the best in the nation, ranked the fourth-cleanest in overall air quality compared with other metropolitan areas. Salinas, California, has the cleanest air in the country, according to the report. In addition to ozone, the report measured long-term and short-term exposure to particle air pollution.

“It’s really striking to think that [Portland and Bangor] are 150 miles apart and the air quality is so different,” Morin said.

The reason: Pollution travels to Maine from the coal plants in the Midwest and the densely populated eastern seaboard, reaching southern and coastal Maine but not as far as Bangor.

“The wind patterns carry the pollution to Maine from states south and west of us. If we took every car off the road, we would still have pollution because we’re breathing everyone else’s air,” said Carol Kelly, with the American Lung Association.

The winds tend to hug the coast, which is why Hancock County ended up with a D grade for ozone, while inland areas received A grades, Kelly said.

Morin, a pulmonologist who operates an outpatient practice with Southern Maine Health Center, said the high ozone levels in the summer make it noticeably worse for patients with respiratory problems, and he tells his patients to stay indoors on the days when ozone levels spike.

“You can really feel it in the air when you breathe,” Morin said. “Air quality can definitely be a trigger.”

Emily Figdor, director of Environment Maine, an advocacy group, said Acadia National Park can have “smoggy” days of low visibility.

“These grades are of grave concern,” Figdor said. “Air pollution is the cause of so many health problems.”

Figdor said compared to 20 years ago, air pollution levels have improved, due to better air quality standards. But she said scientists are finding that air pollution can cause health problems at levels that were previously considered safe. For instance, the Environmental Protection Agency is currently reviewing the safe ozone standard, now set at 75 parts per billion, to determine whether the standard should be reduced to 60 parts per billion.

Figdor said Maine should pursue incentives for alternative energy, such as solar panels and wind power, and look for ways to improve energy efficiency to reduce pollution from regional power plants.

The wind industry has been investing in Maine, with several operating wind farms and proposals to build four additional wind farms.

Joe Lawlor can be contacted at 791-6376 or at:

jlawlor@pressherald.com

Twitter: @joelawlorph