The Clark County Department of Air Quality (DAQ) is currently evaluating ozone levels in the Las Vegas Valley Nonattainment (NA) Zone, with the potential for redesignation in 2024 from moderate NA to serious NA under the 2015 8-hour ozone National Ambient Air Quality Standard (NAAQS). The Las Vegas Valley Nonattainment Zone includes the portion of Clark County that lies in hydrographic area 212 (HA 212).
Ozone NAAQS, Nonattainment Classification, and the Impending EPA Reclassification in the Las Vegas Valley
The ozone NAAQS is a pivotal health-based standard mandated by the Clean Air Act (CAA) to safeguard air quality. NA areas are classified based on their design value, reflecting the extent to which the NAAQS is exceeded in that area.
After the revision of the 8-hour ozone NAAQS from 0.075 to 0.07 ppm in 2015, the Las Vegas Valley received an initial designation in 2018 as a marginal NA area, representing the lowest ozone NA classification, with a deadline to attain the 2015 ozone NAAQS by 2021. In 2021, DAQ submitted 17 demonstrations of exceptional events, aiming to exclude 28 instances of ozone exceedances that occurred in 2018 and 2020. These exceedances were attributed to wildfire smoke or stratospheric intrusions. These demonstrations were not approved by EPA, and the final rule, released on January 5, 2023, reclassified the Las Vegas Valley as a moderate NA area under the 2015 ozone NAAQS (88 FR 775) and mandated that the region achieve compliance by August of 2024.
Reaching the ozone standard by the August 2024 deadline is unlikely, and it’s anticipated that the Environmental Protection Agency (EPA) will reclassify the Las Vegas Valley from a moderate to a serious NA status shortly thereafter. The Clark County Department of Environment & Sustainability (DES) will need to prepare and submit a State Implementation Plan (SIP) in accordance with the Clean Air Act’s criteria for areas classified as serious NA.
Permitting Impacts of Ozone Nonattainment Classifications
The change in NA classification will have serious permitting impacts for sources in the area. The table below summarizes the permitting impacts associated with different ozone NA classifications:
| Nonattainment Classification | Major Source Threshold VOC or NOX (tpy)* | Significant Emission Rate VOC or NOX (tpy) | Emission Offset Ratios | Comply with Lowest Achievable Emission Rates for Major Sources? (Y/N) |
| Marginal or Moderate | 100 | 40 | 1.1:1 (moderate)
1.15:1 (marginal) | N (marginal)
Y (moderate) |
| Serious | 50 | 25** | 1.2:1 | Y |
* Major source thresholds for both New Source Review and Title V programs.
**This limit is no reflective of current DAQ rules and a rulemaking process for CCAQR Section 12.3 will be required to update this regulation to be consistent with 40 CFR Part 51 Subpart I. |
As shown in the table, a redesignation to serious NA would significantly impact permitting for sources located in the Las Vegas Valley. Implications include:
- New stationary sources will be subject to the 50 tpy major source thresholds for NOX and VOC.
- Existing minor sources with potential-to-emit (PTE) exceeding 50 tpy NOX or VOC, will be re-classified to major sources under Title V. This may mean additional monitoring, recordkeeping, and reporting requirements added to existing permits.
- Existing Prevention of Significant Deterioration (PSD) sources which plan to expand are subject to the Nonattainment New Source Review (NA-NSR) program requirements if emission increases exceed the Significant Emission Rate (SER) for NOX or VOC.
- As shown in the table above the SER is likely to move downwards and be less than the SER for purposes of PSD evaluations.
- Major source NA-NSR permitting would involve compliance with Lowest Achievable Emission Rates (LAER) and generation of emission offsets such as Mobile Emission Reduction Credits (MERCs).
Stay Informed and Seek Guidance
Trinity Consultants has extensive experience supporting strategic planning for stationary sources located in NA areas facing redesignation. Trinity is well-versed in NA-NSR permitting across multiple jurisdictions. Trinity will be hosting a webinar in the next few months regarding permitting implications of this change in NA status. Stay up to date on the latest webinar information on Trinity’s
website.
If you have questions regarding the potential Las Vegas Valley redesignation to serious NA and its impact on your facility’s future projects, please reach out to Trinity’s
Reno office or call
775.242.3200.
