PORTLAND – Maine has experienced more smoggy days this summer than in any period since 1995 and likely will break the state record, the Environmental Protection Agency reported.

On Thursday, ozone levels reached an unhealthful level in southern and midcoast Maine for the 12th day this summer, the EPA said.

In 2000, only three days were deemed unhealthful ozone days.

On Friday, intense heat forced the temporary closure of the visitors center at Acadia National Park. The outside temperature was 90 degrees but the apparent temperature inside was 107, according to Betty Lyle, the visitors center supervisor. The apparent temperature is a combination of the relative humidity and the air temperature, she said. The center lacks air conditioning.

Ozone was a problem in much of the state.

Ground-level ozone, or smog, is a colorless gas that forms when chemicals found in motor vehicle exhaust and industrial emissions combine in the heat of summer.

Although ozone in the Earth’s upper atmosphere protects against the sun’s ultraviolet rays, high ground-level ozone concentrations are considered unhealthful. Smog makes breathing hard for people with asthma and other respiratory conditions.

“If we continue to get hot weather from the south and west, chances are we’ll have more ozone smog days,” said Judy Berk, spokesperson for the Natural Resources Council of Maine.

The EPA said even healthy people are at risk of lung damage and other problems when ozone levels are high.

In addition to heat, air currents that bring polluted air from the Midwest make Maine and the rest of New England the “tailpipe of the nation in terms of high pollution,” Berk said.

The high ozone levels are just one anomaly in a summer of strange weather patterns.

June 2001 was the warmest June in about 130 years, despite nights that dipped as low as 41 degrees.

Meanwhile, July average temperatures were below normal, although on seven days temperatures soared to the 90s. Many days saw both bright sunshine and rain.

Water temperatures have been lower than usual for about three weeks due to south-southwest winds, and a riptide Wednesday caused dangerous conditions along beaches in Cumberland and York counties.