Mainers can breathe a little easier now that the 2007 ozone season is over.

The state exceeded the federal healthy air standard for ozone eight times between May and October. That's more than in the last three years combined and more than in any single year since 2002, when Maine had 15 high-ozone days. Maine had two bad-air days last year.

The U.S. Environmental Protection Agency released its preliminary end-of-ozone-season data for New England today. The region as whole saw an increase from 16 high-ozone days in 2006 to 26 days in 2007.

Ground-level ozone is a product of air pollution from cars, trucks and industrial smokestacks mixing together on hot, sunny days with little or no wind.

The EPA’s news release takes pains to point out that our air really is cleaner than it used to be and that hot weather was to blame for the increase in ozone this year.

It is true that Maine didn’t come anywhere close to breaking the record of 35 days set in 1988. But the numbers from this year don’t give a lot of confidence that Maine’s air is still getting cleaner rather than dirtier.

While southern New England may have had a hot summer, Maine certainly did not.

The temperature in Portland exceeded 90 degrees on six days this year, while the average is five days a year, according to the National Weather Service. (Interestingly, five of the six 90-degree days occurred in June and September.) The average temperature in Portland was 66.5 degrees Fahrenheit this summer, just slightly above the 66.3 degree long-term average.

Look here to see the historical ozone trend in Maine and New England. Go here to Maine’s ozone Web page.

If you found it a lot more comfortable to be indoors than out this week, it might not have been the heat. Or the humidity.

It might have been the ozone.

Apologies to the Chamber of Commerce, but the air in places like Acadia National Park, Port Clyde, Cape Elizabeth and Kennebunkport was anything but crisp and clean on Wednesday.

Pollution from tailpipes and smokestacks, a southwest wind and strong sunshine combined to make the air along the Maine coast potentially hazardous to your health. High ozone levels were detected Tuesday, and spread across the entire coastal region Wednesday before the weather shifted and cleared the air again.

The bad news is southern and midcoast Maine may soon reappear on a federal list of areas that don’t meet air quality standards for smog.

The good news is we could get cleaner air as a result.