United States: EPA Releases Revised Ozone NAAQS

On October 1, the Environmental Protection Agency issued a prepublication version of a final rule establishing a new National Ambient Air Quality Standard (NAAQS) for ozone. The final rule lowers the primary and secondary standard from 75 to 70 parts per billion. Once published, the rule will take effect 60 days from the publication date. This regulation has major implications for the regulated community and state regulators.


The NAAQS are the foundation for one of the main air quality regulation regimes under the federal Clean Air Act. Pursuant to the Clean Air Act, EPA must establish primary and secondary NAAQS for certain pollutants, the "emissions of which ... cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare." 42 U.S.C. § 7408(a)(1)(A). Once NAAQS are set for these "criteria pollutants," EPA must also periodically review the standards every five years and revise them if needed. Primary NAAQS are set at levels requisite to protect the public health and allow for "an adequate margin of safety." Id. § 7409(b)(1). Secondary NAAQS are set at levels "requisite to protect the public welfare from any known or anticipated adverse effects." Id. § 7409(b)(2). Ozone is one of six regulated "criteria pollutants" under the NAAQS program. (The others are nitrogen oxides, sulfur dioxides, lead, carbon monoxide, and particulate matter.)

As part of its implementation of the Clean Air Act, EPA has divided the country into air quality regions. EPA designates each air quality control region as being "in attainment" of a standard, as "nonattainment," or as "unclassifiable." The regulation of air pollutants depends on the classification of the respective air quality region, and stricter obligations attach to nonattainment areas than those that are in attainment with the NAAQS or that are unclassifiable.

Under the Clean Air Act, states are primarily responsible for attaining and maintaining the standards for those regions within their borders. They do this by formulating and submitting to EPA for its approval their State Implementation Plans (SIPs), which lay out their plans for reaching the standards, including controls imposed on individual sources of the pollutant in question. If a state does not submit a timely SIP, or if EPA does not approve a state's SIP, EPA will directly impose a Federal Implementation Plan (FIP), under which the federal agency takes over implementation and enforcement authority for a given pollutant standard in a given state until that state submits and obtains approval of a compliant SIP.

The Revised Ozone NAAQS

The current primary and secondary ozone NAAQS are set at 75 parts per billion (ppb). This figure represents a limit on the annual fourth-highest daily maximum eight-hour concentration, averaged over three years. The EPA, based on consideration of health data, recent scientific studies, and risk analyses, found that these standards were not sufficient to protect human health and welfare. Accordingly, in December 2014 EPA proposed lowering the current primary and secondary ozone NAAQS from 75 ppb to a range of 65 to 70 ppb.

The new rule sets both primary and secondary ozone NAAQS to 70 ppb. The new rule retains the same averaging time (eight-hour) and form (annual fourth-highest daily maximum, averaged over three years) as the existing standard. Thus, the revised standards would be met at an ambient air monitoring site when the three-year average of the annual fourth-highest daily maximum eight-hour average ozone concentration is less than or equal to 70 ppb.

The new ozone rule also addresses data handling at monitoring sites. Under the rule, EPA will permit monitoring sites with two or more ozone monitoring instruments operating simultaneously to combine data into a single site-level data record for determining compliance with the NAAQS. EPA also provides a process that would allow the Regional Administrator to approve "site combinations," or to combine data across two nearby monitors for the purpose of calculating a valid design value. This new rule codifies one of EPA's existing practices, and it was unanimously supported.

The rule also contains a revised method of validating monitoring data to calculate an eight-hour average. Once the rule becomes effective, a daily maximum value will be considered valid if eight-hour averages are available for at least 13 of the 17 consecutive moving eight-hour periods in a day, or if the daily maximum value is greater than the level of the NAAQS. According to EPA, this is designed to eliminate "double counting" exceedances of the NAAQS based on overlapping eight-hour periods from two consecutive days under the previous ozone NAAQS.

Implementation and Impact of the New Ozone NAAQS

EPA will now submit the final rule to the Office of the Federal Register for publication. The rule takes effect 60 days after it appears in the Register, which for large and complex rules of this sort typically occurs several weeks or months after EPA releases the prepublication version. If the revised standards require any changes in a state's basic implementation programs, the state has three years to submit any necessary SIP revisions to EPA for federal approval. Further SIP revisions may become necessary if and when one or more of a state's air quality regions are reclassified as "nonattainment" with respect to the new, more stringent standards.

The lower ozone NAAQS standards will have a significant impact on the regulated community. As EPA indicated, the rule will impose billions of dollars each year in compliance costs. Here are a few potential developments:

  • The reduction of the ozone NAAQS means that some regions that are in attainment with the 75 ppb standards may not be in attainment with the 70 ppb standard. Those regions will accordingly be subject to reclassification as nonattainment. A reclassification will place heavy burdens on new business development and existing operators. Until an area is formally designated with respect to the revised ozone NAAQS, the New Source Review provisions applicable to the area's current designation apply.
  • Specifically, sources in areas newly designated as nonattainment may need to apply Reasonably Available Control Technology (RACT) measures to reduce their emission of ozone precursors. Additionally, sources in these areas that wish to expand operations will need to obtain offsets of their increased emissions. Because offsets can be difficult or impossible to obtain in some areas, including in newly designated areas, redesignation as nonattainment (or redesignation to a more restricted nonattainment category) can severely limit economic growth in a given area.
  • If a new source is capable of being constructed in a nonattainment area, the source will need to employ control technology with the Lowest Available Emission Rate (LAER) rather than the Best Available Control Technology (BACT). This can impose tremendous costs on industry as a LAER analysis requires use of the most stringent emission limitation that is achieved in practice for a source category or that is contained in a SIP – a standard significantly more rigid than a case-by-case BACT analysis.
  • An increased number of nonattainment areas may also lead to an increased number of major source or major modification permitting. The permitting thresholds for major sources and major modifications are lower in nonattainment areas than they are in attainment areas. Accordingly, the lower NAAQS standard is likely to increase the permitting burden on existing and future sources.
  • The revised ozone NAAQS will impact permitting requirements under the Prevention of Significant Deterioration (PSD) program, requiring new major sources to demonstrate compliance with the 70 ppb ozone NAAQS. Projects currently pending review under the PSD program will receive the benefit of a grandfathering provision precluding them from having to demonstrate compliance with the revised standard if:
  1. the reviewing authority has formally determined that the application is complete on or before the signature date of the revised ozone NAAQS, or
  2. the reviewing authority has published a notice of a draft permit or preliminary determination before the effective date of the revised ozone NAAQS.

The EPA, however, granted state regulatory agencies discretion as to whether or not to adopt grandfathering provisions.

  • Given EPA's delegation of authority to state regulatory agencies, any industrial firm whose operations cause the emission of ozone or its precursors will need to closely follow the actions taken by the state in which it operates in response to this new rule. As the states prepare their SIP revisions, new controls and limitations may be imposed on these firms' operations.
  • In addition to controlling pollution for the air quality regions within their own borders, states have certain obligations under the Clean Air Act to prevent emissions that contribute to a downwind state's failure to attain air standards. Therefore, even if an industrial firm operates in a region that will be in attainment even with the revised standards, the more stringent standard may require a state to place limits on that firm's emissions to account for interstate pollution issues.

Once the final rule is published in the Federal Register, parties who wish to challenge it in the D.C. Circuit Court of Appeals will have 60 days to do so. Potential challenges to this rule by environmental advocates, industry, and/or states may prevent regulatory certainty until such challenges are resolved by the courts, which can take years.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

To print this article, all you need is to be registered on Mondaq.com.

Click to Login as an existing user or Register so you can print this article.

In association with
Related Video
Up-coming Events Search
Font Size:
Mondaq on Twitter
Register for Access and our Free Biweekly Alert for
This service is completely free. Access 250,000 archived articles from 100+ countries and get a personalised email twice a week covering developments (and yes, our lawyers like to think you’ve read our Disclaimer).
Email Address
Company Name
Confirm Password
Mondaq Topics -- Select your Interests
 Law Performance
 Law Practice
 Media & IT
 Real Estate
 Wealth Mgt
Asia Pacific
European Union
Latin America
Middle East
United States
Worldwide Updates
Check to state you have read and
agree to our Terms and Conditions

Terms & Conditions and Privacy Statement

Mondaq.com (the Website) is owned and managed by Mondaq Ltd and as a user you are granted a non-exclusive, revocable license to access the Website under its terms and conditions of use. Your use of the Website constitutes your agreement to the following terms and conditions of use. Mondaq Ltd may terminate your use of the Website if you are in breach of these terms and conditions or if Mondaq Ltd decides to terminate your license of use for whatever reason.

Use of www.mondaq.com

You may use the Website but are required to register as a user if you wish to read the full text of the content and articles available (the Content). You may not modify, publish, transmit, transfer or sell, reproduce, create derivative works from, distribute, perform, link, display, or in any way exploit any of the Content, in whole or in part, except as expressly permitted in these terms & conditions or with the prior written consent of Mondaq Ltd. You may not use electronic or other means to extract details or information about Mondaq.com’s content, users or contributors in order to offer them any services or products which compete directly or indirectly with Mondaq Ltd’s services and products.


Mondaq Ltd and/or its respective suppliers make no representations about the suitability of the information contained in the documents and related graphics published on this server for any purpose. All such documents and related graphics are provided "as is" without warranty of any kind. Mondaq Ltd and/or its respective suppliers hereby disclaim all warranties and conditions with regard to this information, including all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement. In no event shall Mondaq Ltd and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use or performance of information available from this server.

The documents and related graphics published on this server could include technical inaccuracies or typographical errors. Changes are periodically added to the information herein. Mondaq Ltd and/or its respective suppliers may make improvements and/or changes in the product(s) and/or the program(s) described herein at any time.


Mondaq Ltd requires you to register and provide information that personally identifies you, including what sort of information you are interested in, for three primary purposes:

  • To allow you to personalize the Mondaq websites you are visiting.
  • To enable features such as password reminder, newsletter alerts, email a colleague, and linking from Mondaq (and its affiliate sites) to your website.
  • To produce demographic feedback for our information providers who provide information free for your use.

Mondaq (and its affiliate sites) do not sell or provide your details to third parties other than information providers. The reason we provide our information providers with this information is so that they can measure the response their articles are receiving and provide you with information about their products and services.

If you do not want us to provide your name and email address you may opt out by clicking here .

If you do not wish to receive any future announcements of products and services offered by Mondaq by clicking here .

Information Collection and Use

We require site users to register with Mondaq (and its affiliate sites) to view the free information on the site. We also collect information from our users at several different points on the websites: this is so that we can customise the sites according to individual usage, provide 'session-aware' functionality, and ensure that content is acquired and developed appropriately. This gives us an overall picture of our user profiles, which in turn shows to our Editorial Contributors the type of person they are reaching by posting articles on Mondaq (and its affiliate sites) – meaning more free content for registered users.

We are only able to provide the material on the Mondaq (and its affiliate sites) site free to site visitors because we can pass on information about the pages that users are viewing and the personal information users provide to us (e.g. email addresses) to reputable contributing firms such as law firms who author those pages. We do not sell or rent information to anyone else other than the authors of those pages, who may change from time to time. Should you wish us not to disclose your details to any of these parties, please tick the box above or tick the box marked "Opt out of Registration Information Disclosure" on the Your Profile page. We and our author organisations may only contact you via email or other means if you allow us to do so. Users can opt out of contact when they register on the site, or send an email to unsubscribe@mondaq.com with “no disclosure” in the subject heading

Mondaq News Alerts

In order to receive Mondaq News Alerts, users have to complete a separate registration form. This is a personalised service where users choose regions and topics of interest and we send it only to those users who have requested it. Users can stop receiving these Alerts by going to the Mondaq News Alerts page and deselecting all interest areas. In the same way users can amend their personal preferences to add or remove subject areas.


A cookie is a small text file written to a user’s hard drive that contains an identifying user number. The cookies do not contain any personal information about users. We use the cookie so users do not have to log in every time they use the service and the cookie will automatically expire if you do not visit the Mondaq website (or its affiliate sites) for 12 months. We also use the cookie to personalise a user's experience of the site (for example to show information specific to a user's region). As the Mondaq sites are fully personalised and cookies are essential to its core technology the site will function unpredictably with browsers that do not support cookies - or where cookies are disabled (in these circumstances we advise you to attempt to locate the information you require elsewhere on the web). However if you are concerned about the presence of a Mondaq cookie on your machine you can also choose to expire the cookie immediately (remove it) by selecting the 'Log Off' menu option as the last thing you do when you use the site.

Some of our business partners may use cookies on our site (for example, advertisers). However, we have no access to or control over these cookies and we are not aware of any at present that do so.

Log Files

We use IP addresses to analyse trends, administer the site, track movement, and gather broad demographic information for aggregate use. IP addresses are not linked to personally identifiable information.


This web site contains links to other sites. Please be aware that Mondaq (or its affiliate sites) are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of these third party sites. This privacy statement applies solely to information collected by this Web site.

Surveys & Contests

From time-to-time our site requests information from users via surveys or contests. Participation in these surveys or contests is completely voluntary and the user therefore has a choice whether or not to disclose any information requested. Information requested may include contact information (such as name and delivery address), and demographic information (such as postcode, age level). Contact information will be used to notify the winners and award prizes. Survey information will be used for purposes of monitoring or improving the functionality of the site.


If a user elects to use our referral service for informing a friend about our site, we ask them for the friend’s name and email address. Mondaq stores this information and may contact the friend to invite them to register with Mondaq, but they will not be contacted more than once. The friend may contact Mondaq to request the removal of this information from our database.


This website takes every reasonable precaution to protect our users’ information. When users submit sensitive information via the website, your information is protected using firewalls and other security technology. If you have any questions about the security at our website, you can send an email to webmaster@mondaq.com.

Correcting/Updating Personal Information

If a user’s personally identifiable information changes (such as postcode), or if a user no longer desires our service, we will endeavour to provide a way to correct, update or remove that user’s personal data provided to us. This can usually be done at the “Your Profile” page or by sending an email to EditorialAdvisor@mondaq.com.

Notification of Changes

If we decide to change our Terms & Conditions or Privacy Policy, we will post those changes on our site so our users are always aware of what information we collect, how we use it, and under what circumstances, if any, we disclose it. If at any point we decide to use personally identifiable information in a manner different from that stated at the time it was collected, we will notify users by way of an email. Users will have a choice as to whether or not we use their information in this different manner. We will use information in accordance with the privacy policy under which the information was collected.

How to contact Mondaq

You can contact us with comments or queries at enquiries@mondaq.com.

If for some reason you believe Mondaq Ltd. has not adhered to these principles, please notify us by e-mail at problems@mondaq.com and we will use commercially reasonable efforts to determine and correct the problem promptly.