Mecklenburg and 15 other North Carolina counties might violate new ozone standards the Environmental Protection Agency proposed Wednesday.
The EPA proposed a national standard between 65 and 70 parts per billion, and will take comment on a level as low as 60 ppb. The current standard of 75 ppb was set in 2008.
Mecklenburg would be the only county in North Carolina to violate a standard at the upper end of the proposed range, based on readings from the past three years, the state Division of Air Quality says. Sixteen counties, including Mecklenburg, Union, Lincoln and Rowan, would break a limit at the low end of the range.
If the EPA dropped the standard to 60 ppb, 29 counties would be in violation.
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Ozone is an irritating gas whose primary ingredients come from motor vehicles and industries, including power plants. Health advocates are cheering the EPA’s new proposal, while industry groups say it will drive up business costs.
The federal government gives state and local governments years to correct air-quality problems. But continued violations could lead to a loss of federal highway grants and new emission limits for businesses.
The number of North Carolina counties affected by the new ozone standard could be higher or lower than the initial projections.
If a recent trend of lower ozone readings continues, fewer counties might be in violation. “We expect that trend to continue, although the weather can always influence levels in a given year,” said Tom Mather of the state air-quality division.
North Carolina logged the lowest ozone readings on record this year, with no daily violations of the current standard.
But because the EPA counts as violators all the counties in a single metropolitan area, the total could be much higher.
Mecklenburg, the state’s smoggiest county, now meets the current ozone standard but hasn’t been formally designated as in compliance. A request for that designation is expected to go to the EPA in December or January.
Federal law requires the agency to review the standard every five years. The final standards on the current review will be issued by October 2015.
The EPA says studies show that ozone levels below the current standard can harm the respiratory system, aggravate asthma and is linked to premature death from respiratory and heart conditions.
At the same time, ozone levels are dropping. State and federal rules on power plants and vehicle emissions reduced average levels by one third between 1980 and 2013, the EPA says.
Areas that violate the new standards would have between 2020 and 2037 to meet the new standards, depending on the severity of local conditions.