Background

On October 26, 2015, the U.S. Environmental Protection Agency (EPA) revised the primary and secondary ozone (O3) 8-hour National Ambient Air Quality Standards (NAAQS) from 0.075 parts per million (ppm) to 0.070 ppm. Within two years after setting or revising a NAAQS, EPA must designate areas as meeting (attainment) or not meeting (nonattainment) the standard. EPA’s final designations are based on the most recent three years of air quality monitoring data, recommendations from the state, and additional technical information. If an area is not meeting the standard, the state is required to prepare a SIP that identifies how the area will attain or maintain the NAAQS to comply with the provisions of the Clean Air Act (CAA). The SIP includes regulatory and non-regulatory control measures for reaching attainment by a specific deadline.

On June 4, 2018, EPA designated the Las Vegas Valley (HA 212) as a marginal nonattainment area for the 2015 O3 NAAQS effective August 3, 2018 (83 FR 25776) and the area was required to achieve attainment of the standard by August 3, 2021. To achieve attainment by this date, HA 212 was required to show that its O3 design value, based on 2018-2020 air quality data, was equal to or less than 0.070 ppm. In 2021, DAQ submitted 17 exceptional event demonstrations to exclude 28 ozone exceedances in 2018 and 2020 due to impacts from wildfire smoke or stratospheric intrusions and requested that EPA exclude the associated air quality data from the 2018-2020 design value calculation. On July 22, 2022, EPA proposed not to approve those demonstrations and to find that HA 212 failed to meet its attainment date based on a 2018-2020 design value of 0.074 ppm (87 FR 43764). On January 5, 2023, EPA issued a final rule reclassifying the Las Vegas Valley as a moderate nonattainment area for the 2015 ozone NAAQS (88 FR 775) and requiring the area to achieve attainment by August 3, 2024.

In November 2024, DAQ submitted an attainment SIP to address the planning requirements for areas classified as moderate nonattainment and resolve EPA's finding of failure to submit. The SIP includes the following elements: emission inventories, an attainment demonstration, nonattainment new source review, a 15% rate of progress, reasonably available control measures (RACM), reasonably available control technology (RACT), motor vehicle inspection and maintenance, contingency measures, and a motor vehicle emissions budget to ensure transportation conformity.

Key Requirements for Moderate Attainment SIPs

This new classification requires DAQ to submit an attainment SIP that meets the requirements for moderate areas established in CAA 182(b). Key requirements for moderate areas include:

• Baseline Emission Inventory*
• Emission Statements*
• Nonattainment New Source Review*
• Reasonably Available Control Technology (RACT) requirements
• Reasonably Available Control Measures (RACM)
• 15% Rate of Progress (ROP) requirements
• Attainment Demonstration with Modeling
• Contingency Measures
• Basic vehicle Inspection/Maintenance program

* = these requirements have already been met

Moderate Attainment SIP Development

Developing a Moderate Attainment SIP is an iterative process. The timeline below illustrates the development process. To ensure inclusive public involvement in the development of our attainment SIP, DAQ engaged both industry and clean air advocates in its stakeholder process. Public meetings were held to provide updates and information on regulatory timelines and the actions DAQ would take to meet the new requirements for a moderate classification and provide opportunities for questions. Details on stakeholder workshops are provided below.