Division Links

PM2.5 Moderate Area State Implementation Plans (SIPs) (2009-2014)

In 2006, the Environmental Protection Agency (EPA) tightened the 24-hour PM2.5 standard from 65µg/m3 (microgram per cubic meter) to 35µg/m3. While the state was in attainment under the previous 24-hour standard, all or parts of seven Utah counties did not meet the new 24-hour PM2.5 standard.

Utah continues to attain the 2006 annual PM2.5 standard (15µg/m3) at all locations.


The Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for air pollutants that impact human health and the environment. The EPA set NAAQS for six pollutants:

  • Carbon Monoxide
  • Lead
  • Nitrogen Dioxide
  • Ozone
  • Particulate Matter (PM10 and PM2.5
  • Sulfur Dioxide

Under the CAA, EPA reviews, and if necessary, revises the NAAQS every five year. In 2006, the EPA tightened the 24-hour PM2.5 standard from 65 µg/m3 cubic meters to 35 µg/m3. Seven Utah counties did not meet this new 24-hour standard. The state, however, remained in attainment for the annual PM2.5 standard.


When the EPA designates areas as nonattainment for air quality standards, the CAA requires states to develop State Implementation Plans (SIPs) to attain the standards. The SIP serves to:

  • Demonstrate that the State has a program in place to implement new or revised NAAQS.
  • Identify the emissions control requirements the State will rely upon to attain and/or maintain the NAAQS.

The health-based National Ambient Air Quality Standards (NAAQS) regulate concentrations of PM2.5. Fine particulates are subject to two standards: a 24-hour standard of 35µg/m3 and an annual standard of 12µg/m3.

Utah meets the annual standard in all areas of the state. Salt Lake and Davis Counties and parts of Utah, Weber, Box Elder, Tooele, and Cache counties exceed the 24-hour standard at times during the winter. The EPA designated these areas as nonattainment and combined the seven counties into three nonattainment areas (Salt Lake, Provo, and Logan for purposes of SIP development.

State Implementation Process

After the EPA designated areas along the Wasatch Front and Cache County as nonattainment for PM2.5, the Division of Air Quality (DAQ) initiated a multi-year process to develop a State Implementation Plan to reduce current PM2.5 emissions and bring fine particulate levels below the standard. Through the SIP development process, the Division:

  1. identified the sources of emissions through emission inventories;
  2. developed a model to mimic atmospheric conditions; and,
  3. tested possible emission reduction strategies.

DAQ used emissions data to understand the types and quantity of emissions emitted into the atmosphere. DAQ scientists used a computer model developed by the EPA and National Oceanic and Atmospheric Administration to replicate conditions during high pollution days and to test emission reduction strategies. DAQ asked for recommendations on emission control strategies from stakeholders, industry, and working groups. Once DAQ identified the most promising emission controls, scientists ran them through the model to ascertain their potential for successfully reducing PM2.5 pollution to meet the NAAQS.

The Division looked at emission reductions in three categories:

  • Area Sources
  • Mobile Sources
  • Point Sources

DAQ proposed control strategies in the SIPS for each source category to bring the nonattainment areas into compliance with the NAAQs.

Area Designations and SIP Call

After the EPA announces a new or revised National Ambient Air Quality Standard (NAAQS), it determines whether the state is attaining the standard, not attaining the standard, or contains areas that may be unclassifiable. EPA must make these designations within two years after setting or revising the standard and take into account initial recommendations made by the governor. EPA designated three areas of the state as nonattainment areas for the 2006 24-hour PM2.5 standard on December 14, 2009.

Moderate SIP Goals and Deadlines

Once these three areas were designated as nonattainment, the Clean Air Act required Utah to control fine-particle pollution and prepare State Implementation Plans (SIPs) plans detailing how and when the 24-hour PM2.5 standard would be met. Those SIPs were due to EPA by December 14, 2012, three years after the agency’s final designation. Nonattainment areas had to meet the new standard by 2014, although EPA could grant extensions of the attainment date for up to five additional years for areas with more severe PM2.5 problems and where emission-control measures are not available or feasible.

Stakeholder Process

In 2009, the Division of Air Quality (DAQ) began a three-year process to develop SIPs that would bring fine-particulate levels to or below the standard.

DAQ employed an inclusive public involvement process to assist the agency in SIP development. More than 100 participants from each of the seven nonattainment counties met several times during the SIP development process to provide ideas and recommendations for emission-control strategies that would complement community needs.

Initial reductions resulting from workgroup recommendations reduced PM2.5 levels to within a few micrograms of the standard. DAQ spent another year identifying controls beyond these recommendations to bring areas into attainment.

Subpart 1 Moderate Area SIPs

A SIP for the Logan nonattainment area was completed on time in December 2012. SIPs for the Salt Lake City and Provo nonattainment areas were completed a year later in January 2014. Each of these SIPs demonstrated attainment, but only by 2019, making use of the 5-year extension afforded by the CAA.

Subpart 1 SIP Control Measures

Emission control measures adopted into the Moderate Area SIPs included the following:

  • Twenty-three new area-source rules projected to reduce over 15,000 tons of annual emissions
  • Source-specific point source controls projected to reduce 4,600 tons of annual emissions
  • A new Inspection/Maintenance (I/M) program in Cache County

Area Sources

Area Sources are smaller, localized emission sources. These sources include small businesses and manufacturers, home and commercial heating, food preparation, and printing services. The Air Quality Board approved 23 new area source rules to reduce area source emissions. Costs to install area source controls ranged between $3,000 and $10,000 per ton. New area source rules reduced emissions from:

  • Commercial Cooking
  • Consumer Products
  • Printing and Publishing
  • Painting and Degreasing
  • Wood Stoves and Boilers

Point Sources

Large manufacturing (point) sources were required to reduce their emissions through the installation of Reasonably Available Control Technology (RACT) under the SIP. Costs to install point-source controls ranged between $30,000 and $100,000 per ton. Utah’s oil refineries saw the largest emissions reductions from the required application of state-of-the-art emissions controls. When fully implemented, these controls will reduce annual emissions by over 2,000 tons per year from current emission rates. The permitting process and previous SIPs have regularly controlled emissions from point sources. Additional emission controls imposed by the Salt Lake and Provo PM2.5 SIPs were projected to result in 4,600 fewer tons per year emitted from point sources along the Wasatch Front.

Mobile Sources

Vehicles contribute almost half of the emissions that lead to the formation of PM2.5 during winter inversions, so reducing mobile source emissions in nonattainment areas is a priority. The combination of Tier 2 federal fleet standards and local transportation plans to reduce trips and vehicle miles travelled (VMTs) are projected to result in up to a 50 percent reduction in vehicle emissions by 2019. (The Serious Area SIPs will continue to rely on Tier 2, as well as a shift to Tier 3 fleet standards). Transportation plans and programs within the Salt Lake nonattainment area were required to conform with the emission budgets in the Moderate Area SIPs to ensure that transportation activities did not interfere with air-quality progress.

Court Decision

As the Subpart 1 SIPs for Salt Lake City and Provo were nearing completion, the D.C. Circuit Court of Appeals found that EPA had incorrectly interpreted the Clean Air Act when determining how to implement the NAAQS for PM2.5. The January 4, 2013 court ruling held that the EPA should have implemented the PM2.5 NAAQS based on Clean Air Act (CAA) Subpart 1 and Subpart 4 of Part D, Title 1. EPA had (incorrectly) required states to develop their SIPs based only on Subpart 1. Utah was therefore required to supplement its three SIPs to address the additional requirements of Subpart 4. Subpart 4 introduces a classification scheme among nonattainment areas in which areas can be either Moderate or Serious. All areas are to be classified, initially, as Moderate.

In the wake of the decision by the D.C. Circuit, EPA issued a deadline rule that helped clarify the additional requirements. The rule specified a deadline of December 31, 2014, for SIP submission and required the nonattainment 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.

Subpart 4 Moderate Area SIPs

DAQ spent the summer of 2014 revising all three SIPs to meet the moderate area planning requirements of Subpart 4. On December 3, 2014, the Air Quality Board (AQB) approved PM2.5 SIPs that met the moderate area planning requirements of both Subparts 1 and 4, Part D, of Title 1, of the Clean Air Act. A separate SIP was adopted for each of Utah’s three nonattainment areas (illustrated in the map, above).

Subpart 4 allows for a demonstration that an area will attain the standard by the end of 2015, or alternately, that attainment is impracticable. The Logan PM2.5 SIP demonstrated attainment of the PM2.5 24-hour standard by the December 31, 2015, deadline. The SIPs for the Salt Lake City and Provo nonattainment areas demonstrated that attainment by 2015 was impractical. These analyses were consistent with the previously completed Subpart 1 SIPs for these areas that showed attainment would not be possible until the end of 2019. None of the emission-control strategies already adopted as part of the Subpart 1 SIPs were abandoned in preparing these impracticability demonstrations.

Logan PM2.5 SIP

The AQB adopted the Logan, UT-ID PM2.5 Nonattainment SIP on December 3, 2014. It includes area source control strategies and a new motor-vehicle emission inspection and maintenance (I/M) program to meet the PM2.5 NAAQS by the end of 2015.

The Logan area is now in the first ten-year maintenance period.

Salt Lake PM2.5 SIP

The AQB adopted the Salt Lake City, UT PM2.5 Nonattainment SIP on December 3, 2014. It includes new control measures affecting large stationary sources as well as smaller area sources to mitigate PM2.5 emissions, but does not predict attainment of the PM2.5 NAAQS by the end of 2015.

Provo PM2.5 SIP

The AQB adopted the Provo, UT PM2.5 Nonattainment SIP on December 3, 2014. It includes new control measures affecting large stationary sources as well as smaller area sources to mitigate PM2.5 emissions, but does not predict attainment of the PM2.5 NAAQS by the end of 2015.

Emission Limits and Operating Practices for Large Stationary Sources

As part of their emission-control strategy, the SIPs ensured that reasonably available control technology (RACT) was applied to large stationary sources within the PM2.5 nonattainment areas. For a Moderate Area PM2.5 SIP, these are sources that emit more than or equal to 100 tons-per-year (tpy) of PM2.5 or its precursors (SO2, NOx, and VOC). Large stationary sources were identified in the Salt Lake City and Provo nonattainment areas but not in the Logan area. The terms of these emission controls are made enforceable by including source-specific emission limits and operating practices in the SIP. These appear at Section IX Part H. Limits and practices specific to PM2.5 may be found in subsections 11, 12, and 13 of Part H. Subsections 1-4 pertain specifically to PM10.

SIP Submission

These three SIPs were submitted to EPA by the deadline specified in the rule. The emission control strategies in these SIPs were fundamentally the same as those previously adopted by the Board and have since been revised to reflect some of the EPA’s comments remaining from the SIP process.

Rulemaking for the SIP

The Air Quality Board adopted over twenty rules for the Moderate Area SIPs as part of the overall control strategy. These rules largely addressed area sources and targeted volatile organic compounds (VOC) emissions that contribute to the chemical formation of PM2.5 during winter months and ozone in the summer. EPA approved these into the Utah SIP on February 25, 2016.

Technical Support Documents

DAQ completed a Technical Support Document (TSD) for the three Subpart 4 Moderate Area SIPs. A TSD is not a part of the SIP, but is a companion piece that serves as the technical basis for the decisions made in the SIP. It describes the emissions inventories, modeling, and control strategies. Since all three nonattainment areas were included in the same air-quality modeling analysis, this TSD supports all three SIPs. To request a copy of a TSD on a CD, please contact Liam Thrailkill (lthrailkill@utah.gov(801) 536-4419.

Technical Information

SIP development is a complex process. The following fact sheets and technical support documents provide information about the PM2.5 problem in Utah, what causes it, what the SIP process will entail, the process grounding in federal rulemaking, etc. If you have questions please contact Rachel Chamberlain (rachelchamberlain@utah.gov), (801) 414-3390.

  • Air Pollution Modeling
    Fact Sheet: Working to clean Utah’s winter air.
  • PM2.5 Emission Inventory Preparation Plan
    Prepared January 13, 2011.
  • Utah’s Winter-Time Air Pollution
    Fact Sheet discussing where the pollution comes from and how it’s created.
  • Wintertime PM in Utah
    Utah’s winter PM2.5 problem.

Historic PM2.5 Development Information

In 2012, the Division produced a short informational video and companion booklet to provide the public with information about the PM2.5 moderate SIP development process. The video, booklet, and a fact sheet are linked below.


For more information or questions contact Rachel Chamberlain (rachelchamberlain@utah.gov), (801) 414-3390.

Last Updated:


Back to top