During the summer of 2001, Maine recorded 17 days in which smog levels were high enough to cause health risks, according to Environmental Protection Agency data released Tuesday. That was an increase from 2000 of two days, an upward trend that was seen across New England.

High levels of ground-level ozone, also known as smog, are caused by a combination of heat, sunshine and air pollution, so the recent drought has exacerbated air quality problems.

Breathing smog can be dangerous for those with breathing problems, and has been cited as a potential cause of asthma and respiratory infections.

Many areas in New England suffered more days this year with temperatures above 90 degrees, than any other summer in the past two decades, the regional EPA office in Boston said.

High energy use during the drought also led to increased ozone levels, because of the air pollution created in energy production. Seven of New England’s 10 highest electricity days on record occurred during July and August 2002 – all on high ozone days.

Preliminary EPA data show that 43 dangerous ozone days occurred in one or more New England states during 2002. In Maine, the tally was 17 days, up from 15 in 2001.

Ozone data here are collected from May through September at more than a dozen research sites scattered from Ashland to Kittery.

Connecticut led New England with 36 bad air days in 2002. Maine came in fourth, with its air quality rating worse than both New Hampshire’s and Vermont’s.

In recent years, ozone levels have increased with heat, but long-term averages indicate that smog levels are slowly decreasing.

“When we look at air quality conditions a generation ago, we can feel proud of the advances,” Robert Varney of the New England EPA office said in a prepared statement.

“A summer like this one, however, reminds us that our efforts to pursue cleaner cars and fuels and our commitment to reducing power plant emissions and conserving energy in our daily lives must continue,” Varney said.