Comments Show Split in State Support For EPA Proposal to Revise Ozone Standards

By Patrick Ambrosio

March 17 — Comments submitted by state environmental agencies show a lack of consensus for the Environmental Protection Agency proposal to set more stringent national ozone standards, with several state agencies urging the EPA to retain the current 75 parts per billion standard set in 2008.

State environmental agencies in Georgia, Indiana, Kentucky, Michigan and South Dakota asked the EPA to consider leaving the current standards in place for several reasons, including the lack of new research since the standards were last revised, multiple federal environmental regulations that will improve air quality even without a more stringent ozone standard and concerns about the standards approaching background levels in rural areas.

However, the National Association of Clean Air Agencies, which represents 42 state air agencies, and the Northeast States for Coordinated Air Use Management both filed comments in support of the EPA's proposal, citing a conclusion by the EPA's Clean Air Scientific Advisory Committee that there is adequate scientific evidence to justify a more stringent standard.

The EPA in November proposed (RIN 2060-AP38) to revise the current standards to somewhere in the range of 65 ppb to 70 ppb. The agency estimated its proposed rule could cost up to $16.6 billion annually in 2025, while providing up to $38 billion in annual benefits from reduced incidents of asthma, premature death and other health problems.

NACAA said in its comments that it supports the EPA's proposal, while NESCAUM, which represents eight northeastern state air agencies including New York and Massachusetts, said in its comments that even the 70 ppb level included in the agency's proposed rule may not be adequate to protect public health.

The public comment period on the proposal closed March 17. The agency is under a court-ordered deadline of Oct. 1 to finalize its decision on whether to revise or retain the standards, a regulatory time frame that bills introduced March 17 in the Senate and House seek to delay.

Concern About Background Levels

Several individual state agencies raised concerns about background ozone concentrations, which is the level of ozone in a given area that would exist absent any man-made emissions from inside the U.S.

Both naturally occurring emissions of volatile organic compounds, an ozone precursor that is emitted from tress and other natural sources, and emissions of VOCs and nitrogen oxides from other countries can contribute to background ozone concentrations that states cannot control, according to state agencies in South Dakota and Michigan.

The EPA's proposal to tighten the ozone standards will bring the standards closer or below background levels in many areas, according to the South Dakota Department of Environment and Natural Resources. The South Dakota comments reference 2014 monitoring data from six sites in the state that fall between 61 ppb and 68 ppb despite low emissions from industry, traffic and other man-made pollution sources in those areas.

States with low populations and “essentially zero” emissions of in-state ozone precursors will not be able to meet a more stringent ozone standard due to background levels and ozone transport issues, but will still need to spend significant resources trying to meet an unattainable standard, the South Dakota agency said.

Compliance Called ‘Nearly Impossible.'

The Michigan Department of Environmental Quality agreed that the EPA's proposal would make it “nearly impossible” for some states to come into compliance using available regulatory tools because of background ozone concentrations.

The Wyoming Department of Environmental Quality, which did not include a recommendation to retain the current standard in its comments, also raised concerns about background ozone issues. The EPA's ozone analysis largely ignored background ozone issues in the Western U.S. because it relied mostly on studies and models that focus on summertime ozone concentrations in urban areas.

Given the high contribution of background ozone to measured ozone concentrations in the West, the EPA's proposal would put an “undue responsibility” on many high-altitude, rural states to address ozone levels that are beyond their ability to control, according to the Wyoming DEQ.

Disagreement on Adequacy of Data 

One of the biggest differences in the state comments is whether the EPA's proposal to set a more stringent standard is justified based on available data.

NACAA said it supports the EPA's decision that the current standard is not adequate to protect public health.

“The serious threats to public exposure to ozone are well documented,” NACAA said.

NESCAUM cited the Clean Air Scientific Advisory Committee's conclusion that even a 70 ppb ozone standard may not provide a large enough margin of safety for public health, specifically for sensitive subpopulations including children. Studies have linked exposure to ozone levels of 70 ppb to lung function changes and cardiovascular effects, according to NESCUAM's comments.

“We expect EPA to uphold its legal obligation and set the ozone NAAQS at an appropriate level not exceeding the CASAC-recommended range that will protect public health with an adequate margin of safety,” NESCAUM said.

State air agencies in Georgia, Michigan and Indiana all disagreed that the science supports more stringent ozone standards. Those states all said there is uncertainty with the health studies cited by the EPA as justification for its proposal.

Additionally, the state agencies said that there has not been much new research since the last review of the ozone standards concluded in 2008, meaning that the EPA already considered those studies in setting the current standard.

Additional Reductions Expected 

Georgia and Kentucky's air regulatory agencies both noted that air quality will continue to improve even if the EPA does not revise the ozone standards in 2015. The Tier 3 motor vehicle and fuel standards, the cross-state air pollution rule, the proposed Clean Power plan, the 2012 mercury and air toxics standards for power plants and other federal rules all will directly or indirectly drive reductions in emissions of ozone precursors, the states said.

Michigan Gov. Rick Snyder (R), in a letter attached to the Michigan DEQ comments, said the EPA should evaluate the air quality impacts of all of those regulations before requiring industry to invest in additional pollution-control technology.

Eleven other governors, including potential 2016 Republican presidential candidate Gov. Scott Walker (Wis.), also have called on the EPA to retain the current standard. In a March 16 letter sent to EPA Administrator Gina McCarthy, the governors said the EPA should not impose a new ozone standard alongside other environmental regulations that are already lowering ozone emissions at a cost of billions of dollars.

“Piling on the additional burden and expense of a lower ozone standard simply isn’t necessary,” the governors said.

Push for Timely Guidance 

One area of agreement among state air agencies is the need for the EPA to publish its implementation rule soon after the potential final ozone standard.

Implementation rules, which establish attainment planning requirements, permitting requirements under the new source review program and other implementation requirements, are typically issued by the EPA several years after a national ambient air quality standard is revised. The final implementation rule for the 2008 ozone standards was only finalized in February 2015, a fact that several state agencies mentioned in their comments.

NACAA, NESCUAM and several individual state agencies all requested that the EPA issue the final implementation rule for the potential 2015 ozone standards as soon as possible after the standards are finalized. This would give states sufficient time to meet their regulatory obligations under a revised standard.

To contact the reporter on this story: Patrick Ambrosio in Washington at

To contact the editor responsible for this story: Larry Pearl at

All comments filed on EPA's proposal to revise the national ambient air quality standards for ozone are available at under Docket No. EPA-HQ-OAR-2008-0699.