Q&A on Review and Revision of the National Ambient Air Quality Standard for Ozone

Editor’s Note: Here are answers to some questions about the recent announcement by the U.S. Environmental Protection Agency regarding a proposed revision to the National Ambient Air Quality Standard (NAAQS) for ozone from Dr. H. Christopher Frey, Distinguished University Professor at North Carolina State University and chair of the EPA’s Clean Air Scientific Advisory Committee.

The answers provided here are Dr. Frey’s personal views, and they do not represent any official position of EPA or the EPA Clean Air Scientific Advisory Committee (CASAC).

What is a NAAQS?

The NAAQS are the National Ambient Air Quality Standards.  These are national standards that are intended to protect the public from adverse health effects from exposure to common yet harmful air pollutants. There are also national air quality standards to protect the “public welfare” against other types of damage from air pollution, such as damage to ecological systems.

More specifically, Section 108 of the Clean Air Act requires the EPA Administrator to identify and list certain air pollutants that, in the Administrator’s “judgment, cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare” and “the presence of which in the ambient air results from numerous or diverse mobile or stationary sources.” Furthermore, these standards must “accurately reflect the latest scientific knowledge.”

How does the EPA Administrator make decisions about a NAAQS aimed at protecting public health?

The Clean Air Act states that NAAQS must be set based on the “judgment of the Administrator” to allow “an adequate margin of safety” and to be “requisite to protect the public health.” The term “margin of safety” has been interpreted (by EPA and federal courts) to be intended to address uncertainties and to provide a reasonable degree of protection, but not necessarily provide zero risk to all individuals.  In making decisions regarding the “adequate margin of safety,” EPA typically takes into account the nature and severity of the health effects, the size of the sensitive populations at risk, and the kind and degree of uncertainties.

Dr. Chris Frey
Dr. Chris Frey

Does EPA take cost into account when setting a NAAQS?

No. It is illegal for EPA to take cost into account when setting a NAAQS.  The Clean Air Act specifies that the NAAQS must be set to protect public health and public welfare (e.g., ecological impact). In Whitman v. American Trucking Associations in 2001, the U.S. Supreme Court ruled that in setting a NAAQS, the EPA may not consider the costs of implementing the standards.

What is ozone?

Unlike oxygen, which contains two oxygen atoms, ozone contains three oxygen atoms. Ozone is much more chemically reactive and for this reason it can cause adverse effects when it comes into contact with the human respiratory system. It can also cause problems for other living systems, such as plants.

Where does ozone come from?

Ozone is formed in the atmosphere as a result of other air pollutants, particularly nitrogen oxides and organic compounds. Nitrogen oxides are emitted from combustion of fuels by power plants, cars and many other sources. Organic compounds are emitted by combustion and also from evaporation of fuels, solvents, paints, and other types of coatings. For example, when you smell “gasoline” at the gas station, you are smelling organic compounds. Nitrogen oxides and organic compounds react in the presence of sunlight to produce ozone.

Why is ozone a problem?

Ozone causes damage to human health. Exposure to ozone for relatively short periods of time (e.g., 8 hours) at high enough levels leads to reduction in lung function, pulmonary inflammation, respiratory symptoms and illness, and premature mortality. People with asthma, children, the elderly, and outdoor workers are among groups of people who are either particularly exposed to ozone, more likely to suffer adverse effects, or combinations of both. The scientific evidence supporting these findings includes clinical studies, epidemiologic studies and toxicological studies.

What is CASAC?

CASAC is the Clean Air Scientific Advisory Committee. CASAC provides independent advice to the EPA Administrator on technical bases for National Ambient Air Quality Standards (NAAQS). CASAC was established under the Clean Air Act (CAA) amendments of 1977. In particular, Section 109(d)(2) of the Clean Air Act requires that an independent scientific review committee “shall recommend to the Administrator any new… standards and revisions of existing criteria and standards as may be appropriate.”

CASAC is comprised of seven members appointed by the EPA Administrator. These members include experts from outside the EPA in topics such as air quality, health effects, ecological effects and risk assessment methods. The seven-member CASAC is supported by panels for each NAAQS review that are augmented with additional experts. The Ozone Review Panel is composed of the seven members of CASAC plus 13 additional experts representing a wide range of disciplines needed to assess the scientific basis of the NAAQS.

CASAC is subject to the Federal Advisory Committee Act (FACA), which means that CASAC members and panelists are subject to a variety of ethics rules, and CASAC must conduct its work in public.

What was CASAC’s advice to EPA on the current NAAQS for ozone?

With regard to the standard to protect human health, CASAC concluded that there is “adequate scientific evidence to recommend a range of levels for a revised primary ozone standard from 70 ppb to 60 ppb.” In its June 26, 2014 letter to the EPA Administrator, CASAC advised that “based on the scientific evidence, a level of 70 ppb provides little margin of safety for the protection of public health, particularly for sensitive subpopulations” and further stated that “Although a level of 70 ppb is more protective of public health than the current standard, it may not meet the statutory requirement to protect public health with an adequate margin of safety.” Thus, CASAC advised the Administrator “to set the level of the standard lower than 70 ppb within a range down to 60 ppb.”

CASAC also provides advice on revising the NAAQS for welfare effects. CASAC identified key types of damage to ecosystems from exposure to ozone including “adverse welfare effects related to ecosystem services, food and fiber products from crops, and damage to resource use from foliar injury.” CASAC recommended that EPA adopt a new “indicator” for estimating ecosystem exposure to ozone based on a typical plant growing season. Specifically, CASAC recommended use of an index known as “W126” which is based on ambient ozone levels in each day of a three-month period between 8 a.m. and 8 p.m., and to set the standard at a level of the W126 index between 7 ppm-hours to 15 ppm-hours.

How did CASAC reach that conclusion?

The process by which CASAC developed its scientific and policy advice regarding the NAAQS for ozone is lengthy. In general, the process includes preparation by EPA staff of a sequence of detailed technical reports which are reviewed by CASAC in an iterative multi-year process. Based on this review process, both EPA staff and CASAC develop recommendations to the Administrator regarding whether the current NAAQS is adequate and, if not, regarding how the NAAQS should be revised. CASAC concluded its review of the ozone NAAQS with advice delivered to the Administrator in a June 26,2014 letter regarding recommendations for revising the ozone NAAQS. The key steps in CASAC’s review process include the following:

  • In December 2009, CASAC provided comments to the EPA Administrator on a draft plan from EPA regarding how EPA proposed to conduct the scientific review of the ozone NAAQS (EPA-CASAC-10-004).
  • In June 2011, CASAC provided comments to the EPA Administrator regarding EPA’s draft plan for how it would conduct exposure and risk assessments for human health and for public welfare adverse effects (EPA-CASAC-11-008).
  • In August 2011, CASAC provided a detailed review of the EPA’s first draft of the Integrated Science Assessment (ISA) for Ozone (EPA-CASAC-11-009).
  • In March 2012, CASAC provided a detailed review of EPA’s second draft of the Integrated Science Assessment (EPA-CASAC-12-004). CASAC was not satisfied with this second draft and recommended that EPA provide a third draft of the ISA for further review.
  • In November 2012, CASAC provided a detailed review of the third draft of the Integrated Science Assessment and concluded that, with completion of the recommended revisions, “the ISA will serve as a scientifically sound foundation for the risk and exposure assessment and policy assessment documents for the ozone National Ambient Air Quality Standards (NAAQS) review.”
  • Also in November 2012, CASAC provided a detailed review of EPA’s draft exposure and risk assessments for both human health and public welfare adverse effects.  CASAC found that these first drafts were “works in progress.”
  • Also in November 2012, CASAC provided a detailed review of the EPA’s first draft of the Policy Assessment (PA), which contains EPA staff recommendations for consideration by the Administrator.  CASAC found that “that the PA needs substantial improvement.”
  • After a significant gap in time, CASAC received and reviewed second drafts of the risk and exposure assessments for human health and public welfare, and of the policy assessment.  In a series of letters to the Administrator completed in June 2014 to July 2014, CASAC provided detailed review of the second draft exposure and risk assessments and provided its scientific and policy advice regarding the ozone NAAQS for human health and public welfare.

Thus, the CASAC review process for the current review of the ozone standard spanned nearly five years, from 2009 to 2014, and resulted in 10 separate reports from CASAC to the EPA Administrator during that time period.

All of CASAC’s deliberations took place in public meetings that were announced in the Federal Register.  Public comments were invited at all meetings. Several of the meetings were conducted face-to-face in the Research Triangle Park, NC, area, while others were conducted by teleconference.

Is EPA required to act on CASAC’s advice?

The Clean Air Act gives the Administrator discretion to make decisions regarding the NAAQS. The Clean Air Act requires that an independent scientific panel provide advice regarding the NAAQS to the Administrator, but does not specifically require that the Administrator follow the advice. In practice, if the Administrator does not follow CASAC advice, a reason for the departure from CASAC advice is typically included as part of the final rule. A 2013 decision by the U.S. Court of Appeals for the D.C. Circuit implies that CASAC should clearly distinguish scientific advice from policy advice, and that the burden on EPA to justify departures from CASAC advice is stronger with regard to scientific rather than policy issues. However, CASAC is not precluded from offering policy advice. In the most recent review cycles for each pollutant regulated under the NAAQS, there are examples in which the Administrator followed CASAC’s advice and examples in which the Administrator did not. CASAC does not and cannot set the NAAQS. Only the Administrator can set a NAAQS.

The Administrator’s proposed rule is consistent with CASAC advice for the public health standard, but deviates from CASAC advice for the public welfare standard. For the public welfare standard, the Administrator is considering a range of W126 values outside the range recommended by CASAC and is proposing to set the public welfare standard at the same level as the public health standard, rather than to follow CASAC’s advice to use the biologically relevant W126 index.

How often do EPA and CASAC review a NAAQS?

The Clean Air Act requires that “at 5-year intervals… the Administrator shall complete a thorough review of … the national ambient air quality standards… and shall make such revisions in such criteria and standards and promulgate such new standards as may be appropriate.” The review schedule for a NAAQS is set by EPA. The schedule for the current review cycle for the ozone standard slipped. In April 2014, the Northern District of California of U.S. District Court ordered EPA to issue its proposed decision on revising the ozone standard by Dec. 1, 2014 and to finalize the rule by Oct. 1, 2015.

Does the NAAQS change every five years?

Not necessarily. CASAC will recommend revisions to an existing NAAQS if there is scientific evidence to warrant such a recommendation. In the previous review cycle for the ozone standard, completed in 2008, CASAC regarded that the NAAQS for human health should have been set between 60 ppb and 70 ppb, and the EPA Administrator at that time chose to set the standard at 75 ppb. The scientific evidence in the most recent scientific review is stronger and more complete than in the previous review. CASAC’s current recommendation is that the standard should be less than 70 ppb and as low as 60 ppb, which is similar to the recommendation from the previous review cycle. Thus, had the standard been set within the range recommended by CASAC in the previous review cycle, it is possible that little to no change would be countenanced in the current review cycle.

In the case of the NAAQS for lead, the most recent CASAC review concluded that the current standard for lead is adequate and recommended that no revision be made. Thus, it is clearly not the case that a 5-year review cycle implies that a standard must change every 5 years.

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