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Serious Area PM2.5 State Implementation Plan (SIP) Development (2017-2019)

The Serious PM2.5 SIP Development is very much an iterative process. The technical foundation of any SIP involves numerous emissions inventories, air quality modeling assumptions, potential emission controls, and ever-fluctuating design values recorded throughout the air monitoring network. The PM2.5 Implementation Rule is very prescriptive about how these numbers must fit together to comprise an approvable plan. Various components are compiled early in the process only to be pieced together with other components later in the process. Corrections and adjustment to the various pieces is almost always necessary – even right up to the very end. Nothing appearing in these Serious PM2.5 SIP development pages during the process of SIP development is to be regarded as a final product. The UDAQ is making this DRAFT work available for public review in an effort to ensue transparency throughout the SIP development process. We encourage the public to review and provide feedback on these intermediary products with the understanding that they are not yet final.


EPA designated three areas of the state as nonattainment areas for the 2006 24-hour PM2.5 standard on December 14, 2009.

In 2013, a D.C. Circuit Court of Appeals ruling against EPA interpretation of the Clean Air Act (CAA) required the agency to publish a new schedule for PM2.5.State Implementation Plan (SIP) submissions. Utah had to resubmit its three PM2.5 plans and demonstrate that each area would either attain the standard by December 31, 2015, or that it would be impracticable to do so even after applying all reasonable control measures.

In the wake of the decision by the D.C. Circuit, EPA issued a deadline rule that helped clarify the additional planning requirements included in Subpart 4 of the CAA. The rule indicated that all PM2.5 nonattainment areas would be initially classified as Moderate Areas. It then specified a deadline of December 31, 2014, for SIP submission and required Utah’s Moderate Areas to demonstrate attainment of the 2006 24-hour PM2.5 standard by December 31, 2015, or alternatively, demonstrate that attainment by that date would be impracticable.

The Division of Air Quality (DAQ) completed the Moderate Area SIPs for all three areas on time and submitted them to EPA.

On May 10, 2017, the EPA administrator issued a final rule to reclassify the Salt Lake City and Provo nonattainment areas from Moderate to Serious for the 2006 24-hour PM2.5 National Ambient Air Quality Standard (NAAQS). Under new SIP Requirement Rules issued by the EPA in August 2016 for Serious areas, new SIP revisions for Serious nonattainment areas must be completed by December 31, 2017, and demonstrate attainment of the PM2.5 standard by December 31, 2019.

Attainment of the standard does not mean the area is reclassified to attainment status. The EPA must act to redesignate an area from nonattainment to attainment status. The CAA outlines requirements that a nonattainment area must satisfy for redesignation to occur:

  1. attainment of the standard;
  2. fully approved attainment SIP;
  3. improvement in air quality is due to permanent and enforceable emissions reductions;
  4. the state has met requirements applicable to the area under CAA Section 110 and part D; and
  5. a fully approved maintenance plan.

All regulatory requirements for redesignation have been met for all three areas, with the maintenance plan being the core requirement for redesignating areas to attainment.

What’s New?

On April 28, 2017, the EPA Administrator signed a final action to reclassify the Salt Lake and Provo PM2.5 nonattainment areas from Moderate to Serious. The final action was published in the Federal Register on May 10, 2017. EPA indicated it will address the Logan area in a subsequent rulemaking.

Revisions to the SIPs and maintenance plans have been submitted to EPA. The plans demonstrate continued attainment of the standard through 2035 with an intermediate year check in 2026. Eight years after redesignation, the Division is required to submit a maintenance plan revision demonstrating attainment for the second ten-year maintenance period. EPA finalized redesignation of the Logan, UT-ID nonattainment area to attainment on June 18, 2021. The Logan area is now in the first ten-year maintenance period. In November of 2020, the EPA proposed to redesignate the Salt Lake City and Provo PM2.5 nonattainment areas to attainment. EPA received adverse comments on the proposal, and EPA and the Division continue to work through how to address the adverse comments so that the areas can be redesignated to attainment.

Serious Area Requirements

Nonattainment areas reclassified as Serious Areas must meet more stringent SIP requirements than Moderate Areas. The new Serious Area plans will differ from the Moderate Area plans in the following respects:

  1. Updated emissions inventories
    These emission inventories include a base year (2014) and an attainment year which must be identified in the plan. The attainment year could be as early as 2019 or as late as 2024.
  2. Evaluation and adoption of control measures for direct PM2.5 and its precursors
    The Division of Air Quality (DAQ) will evaluate direct PM2.5 and four precursors: sulfur dioxide (SO2), nitrogen oxides, (NOx), volatile organic compounds (VOCs), and ammonia (NH3). DAQ will evaluate whether it is appropriate to require emission controls at sources of ammonia. A similar analysis in the Moderate Area SIP concluded it would not result in lower concentrations of PM2.5.
  3. Application of Best Available Control Technology (BACT)
    The Serious Area SIPs will require implementation of control strategies that meet Best Available Control Technology (BACT). The Moderate Area SIPs required Reasonably Available Controls (RACT) rather than BACT. DAQ will reevaluate the RACT control measures approved in the Moderate Area SIPs to determine if they meet the BACT criteria. BACT and RACT benchmarks are very similar, and it is likely that many of the existing RACT controls will meet BACT. In some cases, however, existing control measures will need to be upgraded to meet BACT. DAQ will also continue to look for uncontrolled emissions sources. BACT controls are required on area and mobile sources in addition to point sources.
  4. Attainment demonstration date
    If DAQ finds that it is impracticable to model attainment of the PM2.5 standard by 2019, it will have to request an extension of the attainment date. If this occurs, the necessary level of controls would rise from BACT to Most Stringent Measures (MSM). MSM would achieve the most stringent emissions reductions from among those control measures which are either included in any SIP for any other NAAQS, or that have been achieved in practice in any state and can feasibly be implemented in the nonattainment area. Even if the air-quality model indicates that it is possible to attain the standard by 2019, sources in the nonattainment areas could still be required to apply MSM if the air monitoring data does not support a showing of attainment by the end of 2019.
  5. Failure to attain
    If a Serious Area fails to attain the NAAQS by the applicable attainment date, DAQ must submit a new attainment plan within one year that will achieve at least five percent annual reductions in direct PM2.5 or any PM2.5 plan precursor. The plan must also include any additional reductions needed to demonstrate expeditious attainment by no later than five years.

Important Documents

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