Why Ozone Nonattainment Classifications Matter

Ozone nonattainment classifications are part of the EPA’s framework for enforcing the Clean Air Act and protecting public health. Ground-level ozone, a key component of smog, is formed when volatile organic compounds (VOCs) and nitrogen oxides (NO_X) react in sunlight.

When an area fails to meet the National Ambient Air Quality Standards (NAAQS) for ozone, it is designated as a nonattainment area and subject to increasingly stringent requirements based on the severity of the pollution. These classifications—Marginal, Moderate, Serious, Severe, and Extreme—determine the regulatory obligations for both state agencies and local facilities.

Northern Wasatch Front: Judicial Stay Granted Amid Reclassification to Serious Nonattainment

On December 9, 2024, the EPA reclassified the Northern Wasatch Front ozone nonattainment area from “Moderate” to “Serious” after determining the region failed to meet the 2015 ozone NAAQS of 70 ppb by the required deadline. The 2015 NAAQS is met when the 3-year average of the annual fourth highest daily maximum 8-hour average ambient ozone concentration (i.e., the Design Value [DV]) does not exceed 70 parts per billion (ppb) at each ambient air quality monitoring site within the area.

This reclassification, effective January 8, 2025, imposes stricter permitting and emissions control requirements on facilities.

Key requirements under the Serious classification include:

• Implementation of Reasonably Available Control Technology (RACT) for all sources emitting ≥50 tons per year (tpy) of VOC or NO_X.
• Reduced major source thresholds (MSTs) from 100 tons per year (tpy) to 50 tpy for ozone precursors – NO_X and VOCs.
• 18% Reasonable Further Progress (RFP) over 6 years.
• Emissions offsets at a 1.2:1 ratio for new major sources and major modifications.

Utah challenged this reclassification, citing international emissions under Clean Air Act Section 179B, but the EPA dismissed these claims and issued the rule without public comment, invoking the Administrative Procedure Act’s “good cause” exemption.

In response, Utah filed a petition for judicial review, and a judicial stay was granted, temporarily halting the enforcement of the Serious classification. This stay provides a brief reprieve for facilities, delaying the implementation of stricter permitting and offset requirements. However, the stay is temporary, and the EPA’s classification could be overturned; facilities should prepare for compliance in anticipation of the stay being lifted.

Uinta Basin: Judicial Stay Granted Amid Reclassification to Moderate Nonattainment

On December 16, 2024, the EPA finalized its decision to reclassify the Uinta Basin from “Marginal” to “Moderate” nonattainment for the 2015 ozone NAAQS. This decision was based on the Basin’s failure to meet the standard by the attainment deadline, despite the State of Utah and the Ute Indian Tribe requesting a second extension of the attainment date for the Uinta Basin, Utah marginal nonattainment area under the 2015 ozone NAAQS. As noted above, attainment is achieved when a DV does not exceed 70 ppb at each monitoring site in the area. This rule was made to be effective on January 15, 2025.

In response, the State of Utah and other stakeholders filed a request for administrative reconsideration and a judicial stay. The EPA agreed to reconsider the reclassification and committed to providing status updates to the courts every 120 days.

On May 22, 2025, a judicial stay was granted, effectively pausing the implementation of the Moderate nonattainment requirements. As a result, the Utah Division of Air Quality (UDAQ) has halted all work on the Moderate State Implementation Plan (SIP) and is awaiting further direction from the EPA.

This stay provides temporary regulatory relief for facilities in the Uinta Basin. Until the EPA completes its reconsideration or the courts issue a final ruling, facilities are not required to comply with the more stringent Moderate classification requirements, including:

• RACT requirements for sources emitting ≥100 tpy of VOC or NO_X.
• 15% RFP over 6 years.
• Emissions offsets at a 1.15:1 ratio for new major sources and modifications.

Facilities should remain vigilant, as the stay is temporary. Depending on the outcome of the EPA’s reconsideration, the Moderate classification could be reinstated.

Impact on Your Facility

With judicial stays now granted for both the Northern Wasatch Front and the Uinta Basin, facilities in these ozone nonattainment areas are temporarily shielded from the immediate implementation of more stringent air quality requirements. However, this relief is both temporary and conditional, pending EPA reconsideration and further court rulings.

What This Means for Your Facility:

• No Immediate SIP Compliance Required: Facilities are not currently required to meet Serious classification requirements for the Northern Wasatch Front or the Moderate nonattainment requirements for the Uinta Basin. These reclassifications include requirements such as RACT implementation and VOC reduction plans.
• Permitting Flexibility: New or modified sources are not yet subject to the lower MSTs or higher offset ratios that would apply under the reclassifications.
• Planning Window: Facilities have a limited window to assess emissions, evaluate potential control technologies, and prepare for compliance scenarios in the event the stays are lifted.

Next Steps

If your facility operates in either the Northern Wasatch Front or the Uinta Basin, it is critical to begin preparing for the new compliance obligations in the event the stays are lifted. Preparation may include the following:

• Review your current emissions inventory and permitting status.
• Evaluate whether your facility meets the new thresholds for RACT and offset requirements.
• Prepare for potential SIP-driven changes, including new control technologies or operational adjustments.

If you would like to discuss these new regulatory updates for Utah and how they may impact your facility, please contact Trinity’s Salt Lake City office or call 385.509.4478.