The U.S. Environmental Protection Agency announced Thursday that it will implement the 2008 federal eight-hour ozone standard of 0.075 parts per million (ppm), and in a preliminary statement listed Santa Barbara County as a probable nonattainment area with a classification of “marginal.”

The EPA announced it will issue final designations and classifications in mid-2012. Ground-level ozone is a principal component of smog.

“We have seen declining ozone levels in Santa Barbara County over the past decades,” District Director Dave Van Mullem said. “So our local air quality is improving, but the standards have changed as we learn more about the health effects caused by ozone.”

If the county’s final designation is nonattainment for ozone, there will be additional air quality planning requirements. The EPA noted that it expected many of the “marginal” areas to reach attainment by 2015, based on rules already in place.

“Santa Barbara County will strive to achieve attainment by 2015,” Van Mullem said.

Implementation of the 2008 ozone standard was delayed, and the county was considered in attainment of the previous federal eight-hour ozone standard of 0.08 ppm. The county is currently not in attainment of California’s eight-hour ozone standard of 0.070 ppm, and has issued a Clean Air Plan and associated control measures with the goal of attaining this standard.

Ground-level ozone is formed when nitrogen oxides and reactive organic gases react chemically in the presence of sunlight and heat. Ozone damages lungs and respiratory systems. It is known to harm lung development in children over time, has a role in causing early childhood asthma, and produces a range of respiratory symptoms in children and adults.

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— Mary Byrd is a public information officer for the Santa Barbara County Air Pollution Control District.