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 Standard (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. These designations are based on the most recent three years of air quality monitoring data, state recommendations, and other relevant technical information. If an area does not meet the standard, the state must submit a plan detailing how the area will achieve attainment of the NAAQS, in accordance with the Clean Air Act (CAA). This plan must include both regulatory and non-regulatory control measures to achieve the standard by the designated attainment 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). The area was required to achieve attainment by August 3, 2021. To meet this deadline, the Las Vegas Valley needed to demonstrate that its O₃ design value, based on 2018-2020 air quality data, was equal to or less than 0.070 parts per million (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. DAQ requested that EPA exclude these events from the 2018-2020 design value calculation. On July 22, 2022, EPA proposed not to approve these demonstrations and determined that the Las Vegas Valley failed to meet its attainment deadline, 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 O₃ NAAQS (88 FR 775), setting a new attainment deadline of August 3, 2024. On October 18, 2023, EPA issued a final rule determining that the Las Vegas Valley had failed to submit the required moderate nonattainment plan by the submission deadline (88 FR 71757). In November 2024, DAQ submitted an attainment plan to meet the planning requirements for moderate nonattainment areas and resolve EPA's finding of failure to submit. The plan addresses the following required 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

Key requirements for a Moderate Attainment SIP are outlined in CAA Section 182(b) and include:

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

Moderate Attainment SIP Development

Developing a Moderate Attainment SIP is an iterative process. The timeline below outlines the key stages of its development. To ensure broad public involvement, DAQ engaged both industry representatives and clean air advocates throughout the stakeholder process. Public meetings were held to provide updates on regulatory timelines, outline DAQ’s planned actions to meet moderate classification requirements, and offer opportunities for public questions. Click here to view details on stakeholder workshops. 

Click here to view common acronyms and abbreviations used in the attainment development process.