Members of the Board of Environmental Protection will hold a public hearing this Thursday on a proposal to remove nine Maine counties from a list of locations that fail to meet federal standards for ground-level ozone.

The U.S. Environmental Protection Agency has designated the following midcoast and Portland-area counties as being in “nonattainment” of national ambient air quality standards for ozone: Hancock, Waldo, Knox, Lincoln, Kennebec, Androscoggin, Sagadahoc, Cumberland and York.

The federal government calculates ozone levels by averaging air quality measurements over eight-hour blocks of time taken during the past three years. The standard for ozone is 80 parts per billion.

Staff with the state Department of Environmental Protection said last month that the nine counties all meet the federal threshold.

They credited the improvement to a variety of factors, including tougher state emissions standards and a drop in air pollution blowing into Maine from other states.

Removing the counties from the nonattainment list, DEP officials said, would help send a message that Maine is moving in the right direction on air pollution issues.

Groups in other states have also successfully used a region’s failing grade on ground-level ozone to block or delay development projects.

Ozone, while needed to filter harmful ultraviolet rays in the upper atmosphere, can cause respiratory problems when inhaled, especially by the very young and elderly. Ground-level ozone forms when pollutants in vehicle exhaust, smokestack emissions and other fumes react chemically with sunlight.

The BEP will hear public comments on the re-designation proposal at 9:30 a.m. Thursday, July 6, at a conference room of the Holiday Inn-Ground Round near the Augusta Civic Center.

The board is tentatively scheduled to vote on the proposal on Aug. 3. If approved by the board, the proposal will be sent to EPA officials for consideration.

Officials have cautioned that re-designation as an attainment area does not mean that the region’s air quality is always healthy. Many Maine counties – especially those in the southern and coastal areas – will likely continue to experience dangerously high ozone levels on some hot summer days.

Maine’s official forecasts for ground-level ozone may be found at: http://www.maine.gov/dep/air/ozone/