BAR HARBOR — Much of what passes for fog and clouds along the Maine coast in summer is actually a vast blanket of pollution that stretches from the Gulf of Mexico to northern Maine, air quality researchers say.

In pollution-free air, mountains 100 miles away should be visible from certain heights, but visibility is commonly limited to 30 miles and sometimes to half that distance in Maine.

Clayton Maybee of the state Department of Environmental Protection said warm, humid air masses drifting in from industrial centers in the South and West bring chemical pollutants from coal-burning plants and industries.

Maybee is coordinating a joint state and federal study of the impact of air pollution on the scenic qualities of Acadia National Park.

He contends that a combination of sulfates from oil- and coal-powered electric plants and nitrates from automobile emissions engulfs the park landscape in a gray, chemical smog.

His research supports the findings of a new study commissioned by the U.S. Environmental Protection Agency, which reports a cloak of murky sulfate pollution everywhere east of the Mississippi River.

Since the growth of the industrial age in the late 1800s, much of the air has been clogged with white flakes of industrial chemicals, each about one-millionth of a meter wide. Light reflecting off these flakes interferes with natural clarity of the air, making distant objects appear to be shrouded in a haze.

Alan Van Arsdale, a researcher for the Northeast States for Coordinated Air Use Management, says the decline in New England visibility has been tracked for more than a century by an observatory in Blue Hill, Mass.

Observers since the 1880s have stepped outside three times daily to determine if they could see three distant mountains, he said.

In the beginning, all three mountains could be seen regularly. But now only one is visible, and sometimes none can be seen, Van Arsdale said.

He said the primary culprit is sulfur dioxide, a colorless gas emitted by industrial and power-generating boilers. Sulfur, a component of coal and fuel oil, turns to gas in the burning process, and the gas gradually changes to particles of sulfate in the atmosphere.