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UTAH 

State Implementation Plan

Control Measures for Area and Point Sources, Fine Particulate Matter, 

PM2.5 SIP for the Logan, UT-ID Nonattainment Area

Section IX. Part A.23

Adopted by the Utah Air Quality Board

December 3, 2014
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Acronyms ................................................................................................................................ 3

Table of Contents ................................................................................................................ 5

List of Figures .......................................................................................................................7

List of Tables ........................................................................................................................ 8
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Acronyms

BACT Best Available Control Technology

CAA Clean Air Act

CFR Code of Federal Regulations

CMAQ Community Multiscale air Quality

CTG Control Techniques Guideline documents

DAQ Utah Division of Air Quality (also UDAQ)

EPA Environmental Protection Agency

FRM Federal Reference Method

MACT Maximum Available Control Technology

MATS Model Attainment Test Software

MPO Metropolitan Planning Organization

μg/m3 Micrograms Per Cubic Meter

Micron One Millionth of a Meter

NAAQS National Ambient Air Quality Standards

NESHAP National Emissions Standards for Hazardous Air Pollutants

NH3 Ammonia

NOx Nitrogen Oxides

NSPS New Source Performance Standard

NSR New Source Review

PM Particulate Matter

PM10 Particulate Matter Smaller Than 10 Microns in Diameter

PM2.5 Particulate Matter Smaller Than 2.5 Microns in Diameter
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RACM Reasonably Available Control Measures

RACT Reasonably Available Control Technology

RFP Reasonable Further Progress

SIP State Implementation Plan

SMOKE Sparse Matrix Operator Kernal Emissions

SO2 Sulfur Dioxide

SOx Sulfur Oxides

TSD Technical Support Document

VOC Volatile Organic Compounds

UAC Utah Administrative Code

WRF Weather Research and Forecasting 
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TABLE OF CONTENTS

Chapter 1 – INTRODUCTION AND BACKGROUND..................................................................10

1.1 Fine Particulate Matter.................................................................................................................... 10

1.2 Health and Welfare Impacts of PM2.5 .............................................................................................. 10

1.3 Fine Particulate Matter in Utah....................................................................................................... 11

1.4 2006, NAAQS for PM2.5 .................................................................................................................... 11

1.5 PM2.5 Nonattainment Areas in Utah................................................................................................ 11

1.6 PM2.5 Precursors.............................................................................................................................. 13

Chapter 2 – REQUIREMENTS FOR 2006, PM2.5 PLAN REVISIONS ............................................15

2.1 Requirements for Nonattainment SIPs ............................................................................................ 15

2.2 PM2.5 SIP Guidance ........................................................................................................................... 16

2.3 Summary of this SIP Proposal........................................................................................................... 16

Chapter 3 – Ambient Air Quality Data ..................................................................................17

3.1 Measuring Fine Particle Pollution in the Atmosphere ..................................................................... 17

3.2 Utah’s Air Monitoring Network........................................................................................................ 17

3.3 Annual PM2.5 – Mean Concentrations.............................................................................................. 18

3.4 Daily PM2.5 – Averages of 98th Percentiles and Design Values...................................................... 19

3.5 Composition of Fine Particle Pollution – Speciated Monitoring Data.............................................. 20

3.6 PM2.5 Saturation Studies................................................................................................................... 23

3.7 PCAP Study ....................................................................................................................................... 23

3.8 Ammonia (NH3) Studies.................................................................................................................... 24

Chapter 4 – EMISSION INVENTORY DATA .............................................................................25

4.1 Introduction...................................................................................................................................... 25

4.2 The 2008 Emissions Inventory.......................................................................................................... 26

4.3 Characterization of Utah’s Airsheds................................................................................................. 26

Chapter 5 – ATTAINMENT DEMONSTRATION .......................................................................29

5.1 Introduction..................................................................................................................................... 29

5.2 Photochemical Modeling................................................................................................................. 29

5.3 Domain/Grid Resolution.................................................................................................................. 29

5.4 Episode Selection............................................................................................................................. 30
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5.5 Meteorological Data........................................................................................................................ 33

5.6 Photochemical Model Performance Evaluation.............................................................................. 34

5.7 Summary of Model Performance .................................................................................................... 41

5.8 Modeled Attainment Test ............................................................................................................... 42

5.9 Air Quality as of the Attainment Date............................................................................................. 43

Chapter 6 – CONTROL MEASURES ........................................................................................44

6.1 Introduction..................................................................................................................................... 44

6.2 Utah Stakeholder Workgroup Efforts.............................................................................................. 44

6.3 Identification of Measures .............................................................................................................. 45

6.4 Existing Control Measures............................................................................................................... 46

6.5 SIP Controls...................................................................................................................................... 52

6.6 Reasonably Available Control Measures (RACM/RACT).................................................................. 53

Chapter 7 – TRANSPORTATION CONFORMITY ......................................................................60

7.1 Introduction...................................................................................................................................... 60

7.2 Consultation ..................................................................................................................................... 60

7.3 Regional Emission Analysis.............................................................................................................. 61

7.4 Transportation Conformity PM2.5 Components............................................................................... 62

7.5 Interim PM2.5 Conformity Test......................................................................................................... 62

7.6 Transportation Conformity PM2.5 Budgets ...................................................................................... 63

Chapter 8 – REASONABLE FURTHER PROGRESS ....................................................................64

8.1 Introduction..................................................................................................................................... 64

8.2 Moderate Area Planning Requirements.......................................................................................... 64

8.3 RFP for the Logan, UT-ID Nonattainment Area ............................................................................... 65

8.4 Milestones for the Logan, UT-ID Nonattainment Area ................................................................... 67

Chapter 9 – CONTINGENCY MEASURES.................................................................................68

9.1 Background...................................................................................................................................... 68

9.2 Contingency Measures and Implementation Schedules for the Nonattainment Area................... 68

9.3 Conclusions...................................................................................................................................... 69
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List of Figures

Figure 1.1, Nonattainment Areas for the 2006, PM2.5 NAAQS ................................................................... 12

Figure 3.1, Utah’s PM2.5 Air Monitoring Network ...................................................................................... 18

Figure 3.2, Composite Wintertime PM2.5 Speciation Profiles..................................................................... 22

Figure 5.1: Northern Utah photochemical modeling domain.................................................................... 30

Figure 5.2: Hourly PM2.5 concentrations for January 11-20, 2007 ............................................................ 31

Figure 5.3: Hourly PM2.5 concentrations for February 14-19, 2008 ........................................................... 32

Figure 5.4: 24-hour average PM2.5 concentrations for December-January, 2009-10. ............................... 33

Figure 5.5: UDAQ monitoring network...................................................................................................... 34

Figure 5.6: Spatial plot of CMAQ modeled 24-hr PM2.5 (μg/m3) for 2010 Jan. 03..................................... 35

Figure 5.7: 24-hr PM2.5 time series (Hawthorne). Observed 24-hr PM2.5 (blue trace) and CMAQ 

modeled 24-hr PM2.5 (red trace). ............................................................................................................. 36

Figure 5.8: 24-hr PM2.5 time series (Ogden). Observed 24-hr PM2.5 (blue trace) and CMAQ modeled 24-

hr PM2.5 (red trace)..................................................................................................................................... 37

.................................................................................................................................................................... 37

Figure 5.9: 24-hr PM2.5 time series (Lindon). Observed 24-hr PM2.5 (blue trace) and CMAQ modeled 24-

hr PM2.5 (red trace)..................................................................................................................................... 37

Figure 5.10: 24-hr PM2.5 time series (Logan). Observed 24-hr PM2.5 (blue trace) and CMAQ modeled 24-

hr PM2.5 (red trace)..................................................................................................................................... 38

Figure 5.11: An example of the Salt Lake Valley at the end of a high PM2.5 episode. The lowest 

elevations of the Salt Lake Valley are still experiencing an inversion and elevated PM2.5 concentrations 

while the PM2.5 has been ‘cleared out’ throughout the rest of the valley. These ‘end of episode’ clear 

out periods are difficult to replicate in the photochemical model. ........................................................... 38
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Figure 5.12: The composition of observed and model simulated average 24-hr PM2.5 speciation 

averaged over days when an observed and modeled day had 24-hr concentrations > 35 μg/m3at the 

Hawthorne STN site.................................................................................................................................... 39

Figure 5.13: The composition of observed and model simulated average 24-hr PM2.5 speciation averaged 

over days when an observed and modeled day had 24-hr concentrations > 35 μg/m3at the Bountiful STN 

site. ............................................................................................................................................................. 40

Figure 5.14: The composition of observed and model simulated average 24-hr PM2.5 speciation averaged 

over days when an observed and modeled day had 24-hr concentrations > 35 μg/m3at the Lindon STN 

site. ............................................................................................................................................................. 40

Figure 5.15: The composition of model simulated average 24-hr PM2.5 speciation averaged over days 

when a modeled day had 24-hr concentrations > 35 μg/m3at the Logan monitoring site. No observed 

speciation data is available for Logan. ....................................................................................................... 41

Figure 5.16, Model Results for the Logan, UT-ID Nonattainment Area ..................................................... 42
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List of Tables

 

Table 3.1, PM2.5 Annual Mean Concentrations .......................................................................................... 19

Table 3.2, 24-hour PM2.5 Monitored Design Values................................................................................... 20

Table 4.1, Emissions Summary for 2010 (SMOKE). Emissions are presented in tons per average winter 

day. ............................................................................................................................................................. 27

Table 4.2, Emissions Summaries for the Logan, UT-ID Nonattainment Area; Baseline and Attainment Year 

(SMOKE). Emissions are presented in tons per average winter day. ........................................................ 28

Table 5.1, Modeled Concentrations (μg/m3) for the Salt Lake City, UT Nonattainment Area................... 43

Table 6.1, Tier 1 Emission Standards.......................................................................................................... 48

Table 6.2, Tier 2 Emission Standards.......................................................................................................... 50

Table 6.3 Area Source Strategy Screening.................................................................................................. 55

Table 6.4, Emissions Reductions from Area Source SIP Controls............................................................... 58

Table 7.1, Emissions Budgets for Transportation Conformity Purposes (EPA MOVES 2010a). Note: VOC 

emissions do not include refueling spillage and displacement vapor loss. Budgets are rounded to the 

nearest hundredth ton............................................................................................................................... 63

Table 8.1, Reasonable Further Progress in the Logan, UT-ID nonattainment area ................................... 66
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Chapter 1 – INTRODUCTION AND BACKGROUND

1.1 Fine Particulate Matter

According to EPA’s website, particulate matter, or PM, is a complex mixture of extremely small particles 

and liquid droplets. Particulate matter is made up of a number of components, including acids (such as 

nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

The size of particles is directly linked to their potential for causing health problems. EPA is concerned 

about particles that are 10 micrometers in diameter or smaller because those are the particles that 

generally pass through the throat and nose and enter the lungs. Once inhaled, these particles can affect 

the heart and lungs and cause serious health effects. Other negative effects are reduced visibility and 

accelerated deterioration of buildings. 

EPA groups particle pollution into two categories:

 "Inhalable coarse particles," such as those found near roadways and dusty industries, are larger 

than 2.5 micrometers and smaller than 10 micrometers in diameter. Utah has previously addressed 

inhalable coarse particles as part of its PM10 SIPs for Salt Lake and Utah Counties, but this fraction is 

not measured as PM2.5 and will not be a subject for this nonattainment SIP.

 "Fine particles," such as those found in smoke and haze, are 2.5 micrometers in diameter and 

smaller and thus denoted as PM2.5. These particles can be directly emitted from sources such as 

forest fires, or they can form when gases emitted from power plants, industries and automobiles 

react in the air. 

PM concentration is reported in micrograms per cubic meter or μg/m

3

. The particulate is collected on a 

filter and weighed. This weight is combined with the known amount of air that passed through the filter 

to determine the concentration in the air. 

1.2 Health and Welfare Impacts of PM2.5

Numerous scientific studies have linked particle pollution exposure to a variety of problems, including: 

 increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty breathing, 

for example;

 decreased lung function;

 aggravated asthma;

 development of chronic bronchitis;

 irregular heartbeat;

 nonfatal heart attacks; and

 premature death in people with heart or lung disease.
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People with heart or lung diseases, children and older adults are the most likely to be affected by 

particle pollution exposure. However, even if you are healthy, you may experience temporary symptoms 

from exposure to elevated levels of particle pollution.

1.3 Fine Particulate Matter in Utah 

Excluding wind-blown desert dust events, wild land fires, and holiday related fireworks, elevated PM2.5

in Utah occurs when stagnant cold pools develop during the winter season. 

The synoptic conditions that lead to the formation of cold pools in Utah’s nonattainment areas are: 

synoptic scale ridging, subsidence, light winds, snow cover (often), and cool to cold surface 

temperatures. These conditions occur during winter months, generally mid-November through early 

March.

During a winter-time cold pool episode, emissions of PM2.5 precursors react relatively quickly to elevate 

overall concentrations, and of course dispersion is very poor due to the very stable air mass. Episodes 

may last from a few days to tens of days when meteorological conditions change to once again allow for 

good mixing.

The scenario described above leads to exceedances and violations of the 24-hour health standard for 

PM2.5. In other parts of the year concentrations are generally low, and even with the high peaks 

incurred during winter, are well within the annual health standard for PM2.5.

1.4 2006, NAAQS for PM2.5

In September of 2006, EPA revised the (1997) standards for PM2.5. While the annual standard remained 

unchanged at 15 μg/m3, the 24-hr standard was lowered from 65 μg/m

3

to 35 μg/m

3

.

DAQ has monitored PM2.5 since 2000, and found that all areas within the state have been in compliance 

with the 1997 standards. At this new 2006 level, all or parts of five counties have collected monitoring 

data that is not in compliance with the 24-hr standard. 

In 2013, EPA lowered the annual average to 12 μg/m3. Monitoring data shows no instances of 

noncompliance with this revised standard.

1.5 PM2.5 Nonattainment Areas in Utah 

There are two distinct nonattainment areas for the 2006, PM2.5 standards residing entirely within the 

state of Utah. These are the Salt Lake City, UT, and Provo, UT nonattainment areas, which together 

encompass what is referred to as the Wasatch Front. A third nonattainment area is more or less 
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geographically defined by the Cache Valley which straddles the border between Utah and Idaho (the 

Logan, UT – ID nonattainment area.) Figure 1.1 below shows the geographic extent of these areas.

None of these three areas has violated the annual NAAQS for PM2.5. Without exception, the 

exceedances leading to 24-hr NAAQS violations are associated with relatively short-term meteorological 

occurrences.

Figure 1.1, Nonattainment Areas for the 2006, PM2.5 NAAQS

Each of these three areas was designated, by the EPA, based on the weight of evidence of the following 

nine factors recommended in its guidance and any other relevant information:

 pollutant emissions

 air quality data

 population density and degree of urbanization

 traffic and commuting patterns
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 growth

 meteorology

 geography and topography

 jurisdictional boundaries

 level of control of emissions sources

EPA also used analytical tools and data such as pollution roses, fine particulate composition monitoring 

data, back trajectory analyses, and the contributing emission score (CES) to evaluate these areas.

While the general meteorological characteristics are identical between the Wasatch Front and Cache 

Valley, there are two important differences related to topography. First, the Cache Valley is a closed 

basin while the Wasatch Front has many large outlets that connect it to the larger Great Basin. The 

large outlets along the Wasatch Front provide the potential for greater advection of pollutants and for a 

potentially weaker cold pool. Second, the Cache Valley is a narrow (<20 km) valley bordered by 

extremely steep mountains. These topographical differences lead to faster forming, more intense, and 

more persistent cold pools in Cache Valley relative to the Wasatch Front. 

Because of these differences, the two Wasatch Front areas and the Cache Valley are designated as 

separate nonattainment areas; however, they have all been modeled together within the same 

modeling domain.

1.6 PM2.5 Precursors 

The majority of ambient PM2.5 collected during a typical cold-pool episode of elevated concentration is 

secondary particulate matter, born of precursor emissions. The precursor gasses associated with fine 

particulate matter are SO2, NOx, volatile organic compounds (VOC), and ammonia (NH3).

Clean Air Act Section 189(e) requires that the control requirements applicable in plans for major 

stationary sources of PM10 shall also apply to major stationary sources of PM10 precursors, except where 

the Administrator determines that such sources do not contribute significantly to PM10 levels which 

exceed the standard in the area.

As this paragraph now applies also to PM2.5 plans the following should be said about the way this plan is 

structured.

CAA Section 172 does not include any specific applicability thresholds to identify the size of sources that 

States and EPA must consider in the plan’s RACT and RACM analysis. In developing the emissions 

inventories underlying the SIP, the criteria of 40 CFR 51 for air emissions reporting requirements was 

used to establish a 100 ton per year threshold for identifying a sub-group of stationary point sources 

that would be evaluated individually. The control evaluations for each of these sources included PM2.5

as well as PM2.5 precursors. This principle was extended to the non-stationary source categories as well.
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When evaluating the cost per ton necessary to reduce emissions, consideration was given to the 

resulting PM2.5 concentrations. Through this process, reasonable controls were identified affecting 

PM2.5, SO2, NOx and VOC.

No such controls were identified for ammonia. Ammonia occurs in such abundance that PM2.5

concentrations are not sensitive to reductions in ammonia unless those reductions are very large. 

Within the stationary source category, there really were no significant amounts of ammonia to evaluate. 

The largest contributor to the ammonia inventory was the agricultural sector, and the maximum 

possible amount of ammonia reduction from that sector would still not be enough to affect a reduction 

in PM2.5. 

Additional information regarding control measures may be found in Chapter 6 as well as the Technical 

Support Document (TSD).
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Chapter 2 – REQUIREMENTS FOR 2006, PM2.5 PLAN REVISIONS

2.1 Requirements for Nonattainment SIPs

Section 110 of the Clean Air Act lists the requirements for implementation plans. Many of these 

requirements speak to the administration of an air program in general. Section 172 of the Act contains 

the plan requirements for nonattainment areas. Some of the more notable requirements identified in 

these sections of the Act that pertain to this SIP include:

 Implementation of Reasonably Available Control Measures (RACM) as expeditiously as 

practicable

 Reasonable Further Progress (RFP) toward attainment of the National Ambient Air Quality 

Standards by the applicable attainment date

 Enforceable emission limits as well as schedules for compliance

 A comprehensive inventory of actual emissions

 Contingency measures to be undertaken if the area fails to make reasonable further progress or 

attain the NAAQS by the applicable attainment date

On January 4, 2013, D.C. Circuit Court of Appeals found that EPA had incorrectly interpreted the Clean 

Air Act when determining how to implement the National Ambient Air Quality Standards (NAAQS) for 

PM2.5. The January 4, 2013 court ruling held that the EPA should have implemented the PM2.5 NAAQS 

based on both Clean Air Act (CAA) Subpart 1 (“Nonattainment Areas in General” of “Part D – Plan 

Requirements for Nonattainment Areas”) and Subpart 4 (“Additional Provisions for Particulate Matter 

Nonattainment Areas”) of Part D, title 1. EPA had (incorrectly) required states to develop their SIPs 

based only on Subpart 1. Therefore, as of January 4, 2013, Subpart 4 also applies.

Under Subpart 4, nonattainment areas for particulate matter may carry the classification of either 

moderate or serious. Subpart 4 addresses the attainment dates and planning provisions for both 

moderate and serious PM nonattainment areas.

In the wake of the decision by the D.C. Circuit, EPA has promulgated a “Deadlines Rule” that identifies 

each of Utah’s three PM2.5 nonattainment areas as moderate. It specifies December 31, 2014 as the SIP 

submission deadline for these moderate PM2.5 nonattainment areas, and further specifies December 31, 

2015 as the attainment date for each area.

More specific requirements for the preparation, adoption, and submittal of implementation plans are 

specified in 40 CFR Part 51. Subpart Z of Part 51 had contained provisions for Implementation of PM2.5

National Ambient Air Quality Standards. However, one consequence of the January 4, 2013 Court ruling 

was to revoke Subpart Z. This leaves only the more general requirements of Part 51.
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2.2 PM2.5 SIP Guidance

Beyond what had been codified in Subpart Z of Part 51 concerning the Implementation of the PM2.5

NAAQS, EPA had provided additional clarification and guidance in its Clean Air Particulate 

Implementation Rule for the 1997, PM2.5 NAAQS (FR 72, 20586) and its subsequent Implementation 

Guidance for the 2006, 24-Hour Fine Particle NAAQS (March 2, 2012). This too was revoked by the D.C. 

Circuit Court’s decision. Until such time as a new implementation rule for PM2.5 is promulgated, the 

Deadlines Rule recommends the General Preamble, EPA’s longstanding general guidance that interprets 

the 1990 amendments to the CAA, as the applicable guidance for states to follow while preparing SIPs 

for PM2.5 nonattainment areas.

2.3 Summary of this SIP Proposal

This implementation plan was developed to meet the requirements specified in the law, rule, and 

appropriate guidance documents identified above. Discussed in the following chapters are: air 

monitoring, reasonably available control measures, modeled attainment demonstration, emission 

inventories, reasonable further progress toward attainment, transportation conformity, and 

contingency measures. Additional information is provided in the technical support document (TSD).
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Chapter 3 – Ambient Air Quality Data

3.1 Measuring Fine Particle Pollution in the Atmosphere

Utah has monitored PM2.5 in its airsheds since 2000 following the promulgation of the 1997, PM2.5

NAAQS which was set at 65 μg/m

3

for a 24-hour averaging period. PM2.5 monitoring sites were initially 

located based on concentrations of PM10, which historically were measured at sites located based on 

emissions of primary particles. PM2.5 concentrations, especially during Utah’s wintertime valley 

temperature inversions, tend to be distributed more homogenously within a specific airshed. 

Homogeneity of PM2.5 concentrations supports that one or two monitors are adequate to determine 

compliance with the NAAQS in specific airsheds. DAQ’s monitors are appropriately located to assess 

concentration, trends, and changes in PM2.5 concentrations. During Utah’s wintertime cold-pool 

episodes, every day sampling and real time monitoring are needed for modeling and public notification. 

3.2 Utah’s Air Monitoring Network

The Air Monitoring Center (AMC) maintains an ambient air monitoring network in Utah that collects 

both air quality and meteorological data. Figure 3.1 shows the location of sites along the Wasatch Front 

that collect PM2.5 data. Twelve sites collect PM2.5 data using the Federal Reference Method (FRM); PM2.5

is collected on filters over a 24 hour period and its mass is measured gravimetrically. Seven of those 

sites also measure PM2.5 concentrations continuously in real-time. Real-time PM2.5 data is useful both 

for pollution forecasting and to compare with 24-hour concentrations of PM2.5 collected on filters. Of 

the twelve sites that use the FRM to measure PM2.5, six sites collect PM2.5 data daily and six sites collect 

PM2.5 data on every third day. Three sites along the Wasatch Front collect speciated PM2.5. Particulate 

matter on the speciated PM2.5 filters is analyzed for organic and inorganic carbon and a list of 48 

elements. PM2.5 speciation data is particularly useful in helping to identify sources of particulate matter. 

The ambient air quality monitoring network along Utah’s Wasatch Front and in the Cache Valley meets 

EPA requirements for monitoring networks.
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Figure 3.1, Utah’s PM2.5 Air Monitoring Network

3.3 Annual PM2.5 – Mean Concentrations

The procedure for evaluating PM2.5 data with respect to the NAAQS is specified in Appendix N to 40 CFR 

Part 50. Generally speaking, the annual PM2.5 standard is met when a three-year average of annual 

mean values is less than or equal to 12.0 μg/m3. Each annual mean is itself an average of four quarterly 

averages.
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Table 3.1, below shows the running 3-year averages of annual mean values for each of Utah’s 

monitoring locations. The data in the table spans the years 2008 through 2012. These are the years 

surrounding 2010, the year for which the baseline modeling inventory was prepared. It can be seen 

from the data that there are no locations at which the annual NAAQS was violated. It should be noted 

that the conclusion would be no different if the most recent data from 2013 were considered. 

Table 3.1, PM2.5 Annual Mean Concentrations

3.4 Daily PM2.5 – Averages of 98th Percentiles and Design Values

The procedure for evaluating PM2.5 data with respect to the NAAQS is specified in Appendix N to 40 CFR 

Part 50. Generally speaking, the 24-hr. PM2.5 standard is met when a three-year average of 98th

percentile values is less than or equal to 35 μg/m

3

. Each year’s 98th percentile is the daily value below 

which 98% of all daily values fall.

Table 3.2, below shows the running 3-year averages of 98th percentile values for each of Utah’s 

monitoring locations. Again, the data in the table spans the years 2008 through 2012 which are the 

years surrounding 2010, the baseline modeling inventory. It can be seen from the data that there are 

many locations at which the 24-hr. NAAQS has been violated, and this SIP has been structured to 

specifically address the 24-hr. standard.

Location County 08 - 10 09 - 11 10 - 12

Logan (Combined POC 1 & 2) Cache 10.0 9.7 8.7

Brigham City Box Elder 8.3 8.2 7.7

Ogden 2 (POC 1) Weber 9.7 9.5 9.1

Harrisville Weber 8.6 8.3 7.6

Bountiful Davis 9.8 9.2 8.3

Rose Park (POC 1) Salt Lake 10.4 9.7 9.2

Magna Salt Lake 8.5 8.4 7.7

Hawthorn (POC 1) Salt Lake 10.4 9.7 8.8

Tooele Tooele 6.8 6.8 6.3

Lindon (POC 1) Utah 9.8 9.1 8.3

North Provo Utah 9.4 8.7 8.1

Spanish Fork Utah 8.8 8.5 7.7

3-Year Average of Annual Mean Concentrations
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Table 3.2, 24-hour PM2.5 Monitored Design Values

As mentioned in the forgoing paragraph, this SIP is structured to address the 24-hr. PM2.5 NAAQS. As 

such the modeled attainment test must consider monitored baseline design values from each of these 

locations. EPA’s modeling guidance1recommends this be calculated using three-year averages of the 

98th percentile values. To calculate the monitored baseline design value, EPA recommends an average 

of three such three-year averages that straddle the baseline inventory. 2010 is the year represented by 

the baseline inventory. Therefore, the three-year average of 98th percentile values collected from 2008-

2010 would be averaged together with the three-year averages for 2009-2011 and 2010-2012 to arrive 

at the site-specific monitored baseline design values. These values are also shown in Table 3.22.

3.5 Composition of Fine Particle Pollution – Speciated Monitoring Data

DAQ operates three PM2.5 speciation sites. The Hawthorne site in Salt Lake County is one of 54 

Speciation Trends Network (STN) sites operated nationwide on an every-third day sampling schedule. 

Sites at Bountiful/Viewmont in Davis County and Lindon in Utah County are State and Local Air 

Monitoring Stations (SLAMS) PM2.5 speciation sites that operate on an every-sixth-day sampling 

schedule. 

 

1

Guidance on the Use of Models and Other Analyses for Demonstrating Attainment of Air Quality Goals for ozone, 

PM2.5, and Regional Haze (EPA -454B-07-002, April 2007)

2

Recalculating the design values by replacing the 98

th percentiles from 2008 with the most recent 98th percentiles 

from 2013 has a mixed effect throughout the monitoring network, with some sites increasing and others 

decreasing. The design value for Logan, the controlling monitor, would increase by 1.1 μg/m3. This increase is not 

significant enough to change the conclusion drawn in Section 5.9.

Location County 08 - 10 09 - 11 10 - 12

Logan (Combined POC 1 & 2) Cache 42.6 42.4 37.2 40.7

Brigham City Box Elder 42.5 40.1 37.2 39.9

Ogden 2 (POC 1) Weber 37.0 41.1 37.4 38.5

Harrisville Weber 35.6 36.6 33.2 35.1

Bountiful Davis 37.7 40.3 34.4 37.5

Rose Park (POC 1) Salt Lake 40.9 40.7 35.4 39.0

Magna Salt Lake 32.8 34.5 30.3 32.5

Hawthorn (POC 1) Salt Lake 43.6 44.5 38.1 42.1

Tooele Tooele 25.9 27.1 24.4 25.8

Lindon (POC 1) Utah 40.5 40.9 32.4 37.9

North Provo Utah 36.4 35.1 28.6 33.4

Spanish Fork Utah 39.3 41.7 34.6 38.5

Site-Specific Baseline Design Values:

3-Year Average of 98th Percentiles Baseline Design Value
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Filters are prepared by the EPA contract laboratory and shipped to Utah for sampling. Samples are 

collected for particulate mass, elemental analysis, identification of major cations and anions, and 

concentrations of elemental and organic carbon as well as crustal material present in PM2.5. Carbon 

sampling and analysis changed in 2007 to match the Interagency Monitoring of Protected Visual 

Environments (IMPROVE) method using a modified IMPROVE sampler at all sites. 

The PM2.5 is collected on three types of filters: teflon, nylon, and quartz. Teflon filters are used to 

characterize the inorganic contents of PM2.5. Nylon filters are used to quantify the amount of 

ammonium nitrate, and quartz filters are used to quantify the organic and inorganic carbon content in 

the ambient PM2.5.

Data from the speciation network show the importance of volatile secondary particulates during the 

colder months. These particles are significantly lost in FRM PM2.5 sampling. 

During the winter periods between 2009 and 2011, DAQ conducted special winter speciation studies 

aimed at better characterization of PM2.5 during the high pollution episodes. These studies were 

accomplished by shifting the sampling of the Chemical Speciation Network monitors to 1-in-2 schedule 

during the months of January and February. Speciation monitoring during the winter high-pollution 

episodes produced similar results in PM2.5 composition each year. 

The results of the speciation studies lead to the conclusion that the exceedances of the PM2.5 NAAQS are 

a result of the increased portion of the secondary PM2.5 that was chemically formed in the air and not 

emitted directly into the troposphere.
Logan – Page 22

Figure 3.2 below shows the contribution of the identified compounds from the speciation sampler both 

during a winter atmospheric inversion period and during a clear winter period.

Figure 3.2, Composite Wintertime PM2.5 Speciation Profiles

Ammonium

(17%)

Nitrate

(41%)

Organic Matter

(19%)

Elemental 

Carbon

(3%)

Sulfate

(6%)

Crustal:

(3%)

Missing Mass

(11%)

Mean Contributions to PM2.5 During the Inversion 

Episodes 

(HW, Winter 2010-2011)

Ammonium:

Nitrate:

OC (mass):

EC:

Sulfate:

Crustal:

Sodium:

Missing Mass:

Ammonium

(10%)

Nitrate

(31%)

Organic Mass

(32%)

EC

(8%)

Sulfate:

5%

Crustal:

4%

Sodium:

1%

Missing Mass:

8%

Mean Contributions to PM2.5 During the Non-Inversion 

Days 

(HW, Winter 2010-2011)

Ammonium:

Nitrate:

OC (mass):

EC:

Sulfate:

Crustal:

Sodium:

Missing Mass:
Logan – Page 23

3.6 PM2.5 Saturation Studies

Utah State University conducted a study of the homogeneity of PM10 in Cache Valley in 2002-2003 and a 

study of the homogeneity of PM2.5 in 2003-2004. In addition to the permanent DAQ air quality 

monitoring site in Logan, seventeen sites measuring PM2.5 concentrations were established in Cache 

Valley. Measurements of PM2.5 concentrations were made every six days from November 2003 –

February 2004. Several temperature inversions developed during the course of the study with PM2.5

concentrations in Logan ranging from 3-128 μg/m

3

. In general, the study found that PM2.5

concentrations were homogenous throughout the entirety of Cache Valley. On days with PM2.5

concentrations < 65 μg/m

3

, mean PM2.5 concentrations at 11 of the 17 sites had values within 20% of the 

mean PM2.5 concentration for the entire valley. PM2.5 concentrations were generally most homogenous 

throughout Cache Valley on days when PM2.5 concentrations were > 65 μg/m

3

. On high PM2.5 days (> 65 

μg/m

3

), mean PM2.5 concentrations at only two sites were statistically different from the mean PM2.5

concentration for all of Cache Valley. The study concluded that PM2.5 concentrations in Cache Valley 

were homogenous, within a 95% confidence interval, during the winter of 2003-2004.1 PM2.5 saturation 

studies have not been conducted in other regions of Utah.

3.7 PCAP Study

The Persistent Cold Air Pooling Study (PCAPS) is a National Science Foundation-funded project 

conducted by the University of Utah to investigate the processes leading to the formation, maintenance 

and destruction of persistent temperature inversions in Salt Lake Valley. The study ended in March of 

2014. Field work for the project was conducted in the winter of 2010-2011 and focused on the 

meteorological dynamics of temperature inversions in the Salt Lake Valley and in the Bingham Canyon 

pit mine in the southwest corner of Salt Lake Valley. In addition to identifying key meteorological 

processes involved in the dynamics of temperature inversions in Salt Lake Valley, the other primary 

objectives of PCAPS is to determine how persistent temperature inversions affect air pollution transport 

and diffusion in urban basins and to develop more accurate meteorological models describing the 

formation, persistence and dispersion of temperature inversions in Salt Lake Valley. 

Analyses of most data sets collected during the PCAPS are still underway. However, one study 

examining PM2.5 concentrations along an elevation gradient north of Salt Lake City (1300-1750 meters) 

showed that PM2.5 concentrations generally decreased with altitude and increased with time during a 

single temperature inversion event.2 Final results from PCAPS will help DAQ understand both how 

persistent temperature inversions affect PM2.5 concentrations along the Wasatch Front and will enhance 

DAQ’s ability to accurately forecast the formation and breakup of temperature inversion that lead to 

poor wintertime air quality.

 

1 Martin, R., and G.W. Koford, 2006: Valley-wide PM10 and PM2.5 Saturation (Homogeneity) Studies, found within: 

Cache Valley Air Quality Studies: A Summary of Research Conducted.

2

Silcox, G.D., K.E. Kelly, E.T. Crosman, C.D. Whiteman, and B.L. Allen, 2012: Wintertime PM2.5 concentrations in 

Utah’s Salt Lake Valley during persistent multi-day cold air pools. Atmospheric Environment, 46, 17-24.
Logan – Page 24

3.8 Ammonia (NH3) Studies

The Division of Air Quality deployed an ammonia monitor as a part of the special winter study for 2009. 

A URG 9000 instrument was used to record hourly values of ambient ammonia between the months of 

December and February. 

The resulting measurements showed that the ambient concentration of ammonia tended to be 

generally an order of magnitude higher than those of nitric acid: 12-17 ppbv and 1-2 ppbv, respectively. 

Unfortunately, the use of the instrument proved to be excessively labor intensive due to the high 

frequency of calibrations and corrections for drift. The data obtained during the winter of 2009, albeit 

valuable for rough estimation of the ambient ammonia concentrations, contained an abnormal amount 

of error for accurate mechanistic analysis.
Logan – Page 25

Chapter 4 – EMISSION INVENTORY DATA

4.1 Introduction

The emissions inventory is one means used by the state to assess the level of pollutants and precursors 

released into the air from various sources. The methods by which emissions inventories are collected 

and calculated are constantly improving in response to better analysis and more comprehensive rules. 

The inventories underlying this SIP were compiled using the best information available. 

The sources of emissions that were inventoried may be discussed as belonging to four general 

categories: industrial point sources, on-road mobile sources, off-road mobile sources., and area sources 

which represent a collection of smaller, more numerous point sources, residential activities such a 

home heating, and in some cases biogenic emissions.

This SIP is concerned with PM2.5, both primary in its origin and secondary, referring to its formation 

removed in time and space from the point of origin for certain precursor gasses. Hence, the pollutants 

of concern, at least for inventory development purposes, included PM2.5, SO2, NOx, VOC, and NH3.

On-road mobile sources are inventoried using EPA’s MOVES2010 model, in conjunction with information 

generated by travel demand models such as vehicle speeds and miles traveled. The inventory 

information is calculated in units of tons per day, adjusted for winter conditions. Emissions from the 

other three categories are calculated in terms of tons per year.

Prior to use in the air quality model, the emissions are pre-processed to account for the seasonality of 

Utah’s difficulty with secondary PM2.5 formation during winter months. These temporal adjustments 

also account for daily and weekly activity patterns that affect the generation of these emissions.

To acknowledge the episodic and seasonal nature of Utah’s elevated PM2.5 concentrations, inventory 

information presented herein is, unless otherwise noted, a reflection of the temporal adjustments made 

prior to air quality modeling. This makes more appropriate the use of these inventories for such 

purposes as correlation with measured PM2.5 concentrations, control strategy evaluation, establishing 

budgets for transportation conformity, and tracking rates of progress.

There are various time horizons that are significant to the development of this SIP. It is first necessary to 

look at past episodes of elevated PM2.5 concentrations in order to develop the air quality model. The 

episodes studied as part of the SIP occurred in 2007, 2008, 2009, and 2010. It is then necessary to look 

several years into the future when developing emission control strategies. The significant time horizon 

for this plan relates to the statutory attainment date, December 31, 2015. A projected inventory for 

2015 is prepared and compared with a baseline inventory that is contemporaneous with the monitored 

design values discussed in Section 3.4. This baseline is represented by the year 2010. Inventories must 

be prepared to evaluate all of these time horizons.
Logan – Page 26

4.2 The 2008 Emissions Inventory

The forgoing paragraph identified numerous points in time for which an understanding of emissions to 

the air is important to plan development. The basis for each of these assessments was the 2008 triannual inventory. This inventory represented, at the time it was selected for use, the most recent 

comprehensive inventory compiled by UDAQ. In addition to the large major point sources that are 

required to report emissions every year, the tri-annual inventories consider emissions from many more,

smaller point sources. These inventories are collected in accordance with state and federal rules that 

ensure proper methods and comprehensive quality assurance.

Thus, to develop other inventories for each of the years discussed above, the 2008 inventory was either 

back-cast and adjusted for certain episodic conditions, or forecast to represent more typical conditions.

4.3 Characterization of Utah’s Airsheds

As said at the outset, an emissions inventory provides a means to assess the level of pollutants and 

precursors released into the air from various sources. This in turn allows for an overall assessment of a 

particular airshed or even a comparison of one airshed to another.

The modeling analysis used to support this SIP considers a regional domain that encompasses three 

distinct airsheds belonging to three distinct PM2.5 nonattainment areas; The Cache Valley (the Logan 

UT/ID nonattainment area), the central Wasatch Front (Salt Lake City, UT nonattainment area), and the 

southern Wasatch Front (Provo, UT nonattainment area).

The inventories developed for each of these three areas illustrate many similarities but also a few 

notable differences. All three areas are more or less dominated by a combination of on-road mobile and 

area sources. However, emissions from large point sources are non-existent in the Cache Valley. These 

emissions are situated along the Wasatch Front, and primarily exhibited in the Salt Lake City 

nonattainment area. Conversely, most of the agricultural emissions are located in the Cache Valley.

The tables presented below provide a broad overview of the emissions in the respective areas. They are 

organized to show the relative contributions of emissions by source category (e.g. point / area / mobile). 
Logan – Page 27

Table 4.1 shows the 2010 Baseline emissions in each area of the modeling domain. 

Table 4.1, Emissions Summary for 2010 (SMOKE). Emissions are presented in tons per average winter day. 

Mobile source emissions summaries are from the AP-42 (road dust) and MOVES model output. PM2.5 for mobile 

sources includes tire and brake wear, sulfate, elemental and organic carbon, and road dust. VOC for mobile 

sources includes refueling spillage and displacement vapor loss emissions.

NA-Area Source Category PM2.5 NOX VOC NH3 SO2

2010 Logan, UT-ID

Sum of Emissions (tpd) Area Sources 0.54 1.63 4.16 4.31 0.26

Mobile Sources 0.67 6.48 4.99 0.12 0.04

NonRoad 0.13 1.15 2.28 0.00 0.02

Point Sources 0.00 0.02 0.63 0.00 0.00

Total 1.35 9.28 12.06 4.43 0.32

2010 Provo, UT

Sum of Emissions (tpd) Area Sources 1.86 5.56 12.77 6.53 0.28

Mobile Sources 2.20 25.39 15.63 0.44 0.16

NonRoad 0.31 4.40 1.71 0.00 0.09

Point Sources 0.26 0.93 0.67 0.29 0.03

Total 4.63 36.29 30.78 7.26 0.56

2010 Salt Lake City, UT

Sum of Emissions (tpd) Area Sources 5.87 17.71 51.53 17.96 0.88

Mobile Sources 8.59 99.63 62.51 1.86 0.63

NonRoad 1.27 23.04 9.50 0.01 0.66

Point Sources 3.89 20.14 6.48 0.64 10.64

Total 19.62 160.51 130.02 20.47 12.81

2010 Surrounding Areas

Sum of Emissions (tpd) Area Sources 1.78 3.08 13.95 34.29 1.13

Mobile Sources 2.31 28.89 11.03 0.33 0.15

NonRoad 0.57 7.73 10.66 0.00 0.14

Point Sources 3.39 129.34 2.92 0.75 43.43

Total 8.04 169.03 38.57 35.38 44.85

2010 Total
Logan – Page 28

Table 4.2 is specific to the Logan, UT-ID nonattainment area, and shows emissions for both the baseline 

year and the attainment year. These totals include projections concerning growth in population, vehicle 

miles traveled, and the economy. They also include the effects of emissions control strategies that are 

either already promulgated or were required as part of the SIP.

Table 4.2, Emissions Summaries for the Logan, UT-ID Nonattainment Area; Baseline and Attainment Year 

(SMOKE). Emissions are presented in tons per average winter day. Mobile source emissions summaries are from 

the AP-42 (road dust) and MOVES model output. PM2.5 for mobile sources includes tire and brake wear, sulfate, 

elemental and organic carbon, and road dust. VOC for mobile sources includes refueling spillage and 

displacement vapor loss emissions.

The 2010 Baseline and 2015 projected emissions estimates are calculated from the Sparse Matrix 

Operator Kernel Model (SMOKE). More detailed inventory information may be found in the Technical 

Support Document (TSD).

NA-Area Source Category PM2.5 NOX VOC NH3 SO2

2010 Logan, UT-ID

Sum of Emissions (tpd) Area Sources 0.54 1.63 4.16 4.31 0.26

Mobile Sources 0.67 6.48 4.99 0.12 0.04

NonRoad 0.13 1.15 2.28 0.00 0.02

Point Sources 0.00 0.02 0.63 0.00 0.00

Total 1.35 9.28 12.06 4.43 0.32

2015 Logan, UT-ID

Sum of Emissions (tpd) Area Sources 0.40 1.59 3.75 4.08 0.27

Mobile Sources 0.32 4.49 3.36 0.10 0.03

NonRoad 0.10 0.81 1.77 0.00 0.01

Point Sources 0.00 0.00 0.00 0.00 0.00

Total 0.82 6.89 8.88 4.19 0.31
Logan – Page 29

Chapter 5 – ATTAINMENT DEMONSTRATION

5.1 Introduction 

UDAQ conducted a technical analysis to support the development of Utah’s 24-hr PM2.5 State 

Implementation Plan (SIP). The analyses include preparation of emissions inventories and 

meteorological data, and the evaluation and application of regional photochemical model. An analysis 

using observational datasets will be shown to detail the chemical regimes of Utah’s Nonattainment 

areas. 

5.2 Photochemical Modeling 

Photochemical models are relied upon by federal and state regulatory agencies to support their 

planning efforts. Used properly, models can assist policy makers in deciding which control programs are 

most effective in improving air quality, and meeting specific goals and objectives.

The air quality analyses were conducted with the Community Multiscale Air Quality (CMAQ) Model

version 4.7.1, with emissions and meteorology inputs generated using SMOKE and WRF, respectively. 

CMAQ was selected because it is the open source atmospheric chemistry model co-sponsored by EPA 

and the National Oceanic Atmospheric Administration (NOAA), thus approved by EPA for this plan.

5.3 Domain/Grid Resolution 

UDAQ selected a high resolution 4-km modeling domain to cover all of northern Utah including the 

portion of southern Idaho extending north of Franklin County and west to the Nevada border (Figure 

5.1). This 97 x 79 horizontal grid cell domain was selected to ensure that all of the major emissions 

sources that have the potential to impact the nonattainment areas were included. The vertical 

resolution in the air quality model consists of 17 layers extending up to 15 km, with higher resolution in 

the boundary layer.
Logan – Page 30

Figure 5.1: Northern Utah photochemical modeling domain.

5.4 Episode Selection 

According to EPA’s April 2007 “Guidance on the Use of Models and Other Analyses for Demonstrating 

Attainment of Air Quality Goals for Ozone, PM2.5, and Regional Haze” the selection of SIP episodes for 

modeling should consider the following 4 criteria:

1. Select episodes that represent a variety of meteorological conditions that lead to elevated 

PM2.5.

2. Select episodes during which observed concentrations are close to the baseline design value.

3. Select episodes that have extensive air quality data bases.

4. Select enough episodes such that the model attainment test is based on multiple days at each 

monitor violating NAAQS.
Logan – Page 31

In general, UDAQ wanted to select episodes with hourly PM2.5 concentrations that are reflective of 

conditions that lead to 24-hour NAAQS exceedances. From a synoptic meteorology point of view, each 

selected episode features a similar pattern. The typical pattern includes a deep trough over the eastern 

United States with a building and eastward moving ridge over the western United States. The episodes 

typically begin as the ridge begins to build eastward, near surface winds weaken, and rapid stabilization 

due to warm advection and subsidence dominate. As the ridge centers over Utah and subsidence peaks, 

the atmosphere becomes extremely stable and a subsidence inversion descends towards the surface. 

During this time, weak insolation, light winds, and cold temperatures promote the development of a 

persistent cold air pool. Not until the ridge moves eastward or breaks down from north to south is there 

enough mixing in the atmosphere to completely erode the persistent cold air pool. 

From the most recent 5-year period of 2007-2011, UDAQ developed a long list of candidate PM2.5

wintertime episodes. Three episodes were selected. An episode was selected from January 2007, an 

episode from February 2008, and an episode during the winter of 2009-2010 that features multi-event 

episodes of PM2.5 buildup and washout. Further detail of the episodes is below:

 Episode 1: January 11-20, 2007

A cold front passed through Utah during the early portion of the episode and brought very cold 

temperatures and several inches of fresh snow to the Wasatch Front. The trough was quickly followed 

by a ridge that built north into British Columbia and began expanding east into Utah. This ridge did not 

fully center itself over Utah, but the associated light winds, cold temperatures, fresh snow, and 

subsidence inversion produced very stagnant conditions along the Wasatch Front. High temperatures in 

Salt Lake City throughout the episode were in the high teens to mid-20’s Fahrenheit.

Figure 5.2 shows hourly PM2.5 concentrations from Utah’s 4 PM2.5 monitors for January 11-20, 2007. The 

first 6 to 8 days of this episode are suited for modeling. The episode becomes less suited after January 

18 because of the complexities in the meteorological conditions leading to temporary PM2.5 reductions. 

Figure 5.2: Hourly PM2.5 concentrations for January 11-20, 2007
Logan – Page 32

 Episode 2: February 14-18, 2008

The February 2008 episode features a cold front passage at the start of the episode that brought 

significant new snow to the Wasatch Front. A ridge began building eastward from the Pacific Coast and 

centered itself over Utah on Feb 20th. During this time a subsidence inversion lowered significantly 

from February 16 to February 19. Temperatures during this episode were mild with high temperatures 

at SLC in the upper 30’s and lower 40’s Fahrenheit. 

The 24-hour average PM2.5 exceedances observed during the proposed modeling period of February 14-

19, 2008 were not exceptionally high. What makes this episode a good candidate for modeling are the 

high hourly values and smooth concentration build-up. The first 24-hour exceedances occurred on 

February 16 and were followed by a rapid increase in PM2.5 through the first half of February 17 (Figure 

5.3). During the second half of February 17, a subtle meteorological feature produced a mid-morning 

partial mix-out of particulate matter and forced 24-hour averages to fall. After February 18, the 

atmosphere began to stabilize again and resulted in even higher PM2.5 concentrations during February 

20, 21, and 22. Modeling the 14th through the 19th of this episode should successfully capture these 

dynamics. The smooth gradual build-up of hourly PM2.5 is ideal for modeling. 

Figure 5.3: Hourly PM2.5 concentrations for February 14-19, 2008

 Episode 3: December 13, 2009 – January 18, 2010 

The third episode that was selected is more similar to a “season” than a single PM2.5 episode (Figure 

5.4). During the winter of 2009 and 2010, Utah was dominated by a semi-permanent ridge of high 

pressure that prevented strong storms from crossing Utah. This 35 day period was characterized by 4 to 

5 individual PM2.5 episodes each followed by a partial PM2.5 mix out when a weak weather system 

passed through the ridge. The long length of the episode and repetitive PM2.5 build-up and mix-out 

cycles makes it ideal for evaluating model strengths and weaknesses and PM2.5 control strategies.
Logan – Page 33

Figure 5.4: 24-hour average PM2.5 concentrations for December-January, 2009-10.

5.5 Meteorological Data 

Meteorological inputs were derived using the Weather Research and Forecasting (WRF), Advanced 

Research WRF (WRF-ARW) model version 3.2. WRF contains separate modules to compute different 

physical processes such as surface energy budgets and soil interactions, turbulence, cloud microphysics, 

and atmospheric radiation. Within WRF, the user has many options for selecting the different schemes 

for each type of physical process. There is also a WRF Preprocessing System (WPS) that generates the 

initial and boundary conditions used by WRF, based on topographic datasets, land use information, and 

larger-scale atmospheric and oceanic models.

Model performance of WRF was assessed against observations at sites maintained by the Utah Air 

Monitoring Center. A summary of the performance evaluation results for WRF are presented below:

 The biggest issue with meteorological performance is the existence of a warm bias in surface 

temperatures during high PM2.5 episodes. This warm bias is a common trait of WRF modeling 

during Utah wintertime inversions. 

 WRF does a good job of replicating the light wind speeds (< 5 mph) that occur during high PM2.5

episodes. 

 WRF is able to simulate the diurnal wind flows common during high PM2.5 episodes. WRF 

captures the overnight downslope and daytime upslope wind flow that occurs in Utah valley 

basins. 

 WRF has reasonable ability to replicate the vertical temperature structure of the boundary 

layer (i.e., the temperature inversion), although it is difficult for WRF to reproduce the inversion 

when the inversion is shallow and strong (i.e., an 8 degree temperature increase over 100 

vertical meters).
Logan – Page 34

5.6 Photochemical Model Performance Evaluation 

The model performance evaluation focused on the magnitude, spatial pattern, and temporal variation of 

modeled and measured concentrations. This exercise was intended to assess whether, and to what 

degree, confidence in the model is warranted (and to assess whether model improvements are 

necessary).

CMAQ model performance was assessed with observed air quality datasets at UDAQ-maintained air 

monitoring sites (Figure 5.5). Measurements of observed PM2.5 concentrations along with gaseous 

precursors of secondary particulate (e.g., NOx, ozone) and carbon monoxide are made throughout 

winter at most of the locations in Figure 5.5. PM2.5 speciation performance was assessed using the three 

Speciation Monitoring Network Sites (STN) located at the Hawthorne site in Salt Lake City, the Bountiful 

site in Davis County, and the Lindon site in Utah County.

Figure 5.5: UDAQ monitoring network.
Logan – Page 35

A spatial plot is provided for modeled 24-hr PM2.5 for 2010 January 03 in Figure 5.6. The spatial plot 

shows the model does a reasonable job reproducing the high PM2.5 values, and keeping those high 

values confined in the valley locations where emissions occur.

Figure 5.6: Spatial plot of CMAQ modeled 24-hr PM2.5 (μg/m3) for 2010 Jan. 03. 

Time series of 24-hr PM2.5 concentrations for the 13 Dec. 2009 – 15 Jan. 2010 modeling period are 

shown in Figs. 5.7 – 5.10 at the Hawthorne site in Salt Lake City (Fig. 5.7), the Ogden site in Weber 

County (Fig 5.8), the Lindon site in Utah County (Fig. 5.9), and the Logan site in Cache County (Fig. 5.10). 

For the most part, CMAQ replicates the buildup and washout of each individual episode. While CMAQ 

builds 24-hr PM2.5 concentrations during the 08 Jan. – 14 Jan. 2010 episode, it was not able to produce 

the > 60 μg/m3concentrations observed at the monitoring locations. 

It is often seen that CMAQ “washes” out the PM2.5 episode a day or two earlier than that seen in the 

observations. For example, on the day 21 Dec. 2009, the concentration of PM2.5 continues to build while 

CMAQ has already cleaned the valley basins of high PM2.5 concentrations. At these times, the observed 
Logan – Page 36

cold pool that holds the PM2.5 is often very shallow and winds just above this cold pool are southerly and 

strong before the approaching cold front. This situation is very difficult for a meteorological and 

photochemical model to reproduce. An example of this situation is shown in Fig. 5.11, where the lowest 

part of the Salt Lake Valley is still under a very shallow stable cold pool, yet higher elevations of the 

valley have already been cleared of the high PM2.5 concentrations. 

During the 24 – 30 Dec. 2009 episode, a weak meteorological disturbance brushes through the 

northernmost portion of Utah. It is noticeable in the observations at the Ogden monitor at 25 Dec. as 

PM2.5 concentrations drop on this day before resuming an increase through Dec. 30. The meteorological 

model and thus CMAQ correctly pick up this disturbance, but completely clears out the building PM2.5; 

and thus performance suffers at the most northern Utah monitors (e.g. Ogden, Logan). The monitors to 

the south (Hawthorne, Lindon) are not influence by this disturbance and building of PM2.5 is replicated 

by CMAQ. This highlights another challenge of modeling PM2.5 episodes in Utah. Often during cold pool 

events, weak disturbances will pass through Utah that will de-stabilize the valley inversion and cause a 

partial clear out of PM2.5. However, the PM2.5 is not completely cleared out, and after the disturbance 

exits, the valley inversion strengthens and the PM2.5 concentrations continue to build. Typically, CMAQ 

completely mixes out the valley inversion during these weak disturbances. 

Figure 5.7: 24-hr PM2.5 time series (Hawthorne). Observed 24-hr PM2.5 (blue trace) and CMAQ modeled 24-hr 

PM2.5 (red trace).

Hawthorne

0

10

20

30

40

50

60

70

80

8-Dec 13-Dec 18-Dec 23-Dec 28-Dec 2-Jan 7-Jan 12-Jan 17-Jan

2009-2010

24-hr PM2.5 (ug/m3)

Obs.

Model
Logan – Page 37

Figure 5.8: 24-hr PM2.5 time series (Ogden). Observed 24-hr PM2.5 (blue trace) and CMAQ modeled 24-hr PM2.5

(red trace). 

Figure 5.9: 24-hr PM2.5 time series (Lindon). Observed 24-hr PM2.5 (blue trace) and CMAQ modeled 24-hr PM2.5

(red trace).

Ogden

0

10

20

30

40

50

60

8-Dec 13-Dec 18-Dec 23-Dec 28-Dec 2-Jan 7-Jan 12-Jan 17-Jan

2009-2010

24-hr PM2.5 (ug/m3)

Obs.

Model

Lindon

0

10

20

30

40

50

60

70

8-Dec 13-Dec 18-Dec 23-Dec 28-Dec 2-Jan 7-Jan 12-Jan 17-Jan

2009-2010

24-hr PM2.5 (ug/m3)

Obs.

Model
Logan – Page 38

Figure 5.10: 24-hr PM2.5 time series (Logan). Observed 24-hr PM2.5 (blue trace) and CMAQ modeled 24-hr PM2.5

(red trace).

Figure 5.11: An example of the Salt Lake Valley at the end of a high PM2.5 episode. The lowest elevations of the 

Salt Lake Valley are still experiencing an inversion and elevated PM2.5 concentrations while the PM2.5 has been 

‘cleared out’ throughout the rest of the valley. These ‘end of episode’ clear out periods are difficult to replicate 

in the photochemical model.
Logan – Page 39

Generally, the performance of CMAQ to replicate the buildup and clear out of PM2.5 is good. However, it 

is important to verify that CMAQ is replicating the components of PM2.5 concentrations. PM2.5 simulated 

and observed speciation is shown at the 3 STN sites in Figures 5.12 – 5.14. The observed speciation is 

constructed using days in which the STN filter 24-hr PM2.5 concentration was > 35 μg/m3. For the 2009-

2010 modeling period, the observed speciation pie charts were created using 8 filter days at Hawthorne, 

6 days at Lindon, and 4 days at Bountiful. The speciation of this small dataset appears similar to a 

comparison of a larger dataset of STN filter speciated data from 2005-2010 for high wintertime PM2.5

days (see Figure 3.2 for one of these at Hawthorne).

The simulated speciation is constructed using modeling days that produced 24-hr PM2.5 concentrations > 

35 μg/m3. Using this criterion, the simulated speciation pie chart is created from 18 modeling days for 

Hawthorne, 14 days at Lindon, and 14 days at Bountiful. 

At all 3 STN sites, the percentage of simulated nitrate is greater than 40%, while the simulated 

ammonium percentage is at ~15%. This indicates that the model is able to replicate the secondarily 

formed particulates that typically make up the majority of the measured PM2.5 on the STN filters during 

wintertime pollution events. 

The percentage of model simulated organic carbon is ~13% at all STN sites, which is in agreement with 

the observed speciation of organic carbon at Hawthorne and slightly overestimated (by ~3%) at Lindon 

and Bountiful.

There is no STN site in the Logan nonattainment area, and very little speciation information available in 

the Cache Valley. Figure 5.15 shows the model simulated speciation at Logan. Ammonium (17%) and 

nitrate (56%) make up a higher percentage of the simulated PM2.5 at Logan when compared to sites 

along the Wasatch Front.

Figure 5.12: The composition of observed and model simulated average 24-hr PM2.5 speciation averaged over 

days when an observed and modeled day had 24-hr concentrations > 35 μg/m3at the Hawthorne STN site.
Logan – Page 40

Figure 5.13: The composition of observed and model simulated average 24-hr PM2.5 speciation averaged over 

days when an observed and modeled day had 24-hr concentrations > 35 μg/m3at the Bountiful STN site.

Figure 5.14: The composition of observed and model simulated average 24-hr PM2.5 speciation averaged over 

days when an observed and modeled day had 24-hr concentrations > 35 μg/m3at the Lindon STN site.
Logan – Page 41

Figure 5.15: The composition of model simulated average 24-hr PM2.5 speciation averaged over days when a 

modeled day had 24-hr concentrations > 35 μg/m3at the Logan monitoring site. No observed speciation data is 

available for Logan. 

5.7 Summary of Model Performance 

Model performance for 24-hr PM2.5 is good and generally acceptable and can be characterized as 

follows:

 Good replication of the episodic buildup and clear out of PM2.5. Often the model will clear out 

the simulated PM2.5 a day too early at the end of an episode. This clear out time period is 

difficult to model (i.e., Figure 5.11).

 Good agreement in the magnitude of PM2.5, as the model can consistently produce the high 

concentrations of PM2.5 that coincide with observed high concentrations.

 Spatial patterns of modeled 24-hr PM2.5, show for the most part, that the PM2.5 is being confined 

in the valley basins, consistent to what is observed.

 Speciation and composition of the modeled PM2.5 matches the observed speciation quite well. 

Modeled and observed nitrate are between 40% and 50% of the PM2.5. Ammonium is between 

15% and 20% for both modeled and observed PM2.5, while modeled and observed organic 

carbon falls between 10% to 13% of the total PM2.5.
Logan – Page 42

Several observations should be noted on the implications of these model performance findings on the 

attainment modeling presented in the following section. First, it has been demonstrated that model 

performance overall is acceptable and, thus, the model can be used for air quality planning purposes. 

Second, consistent with EPA guidance, the model is used in a relative sense to project future year 

values. EPA suggests that this approach “should reduce some of the uncertainty attendant with using 

absolute model predictions alone.” Furthermore, the attainment modeling is supplemented by 

additional information to provide a weight of evidence determination.

5.8 Modeled Attainment Test 

UDAQ employed Model Attainment Test Software (MATS) for the modeled attainment test at grid cells 

near monitors. MATS is designed to interpolate the species fractions of the PM mass from the Speciation 

Trends Network (STN) monitors to the FRM monitors. The model also calculates the relative response 

factor (RRF) for grid cells near each monitor and uses these to calculate a future year design value for 

these cells. 

MATS results for future year modeling is presented in Figure 5.16. The future year design values are 

presented with and without SIP controls for 2015 (the attainment year). For comparison purposes, the 

monitored design value is also presented for the base year, 2010.

Figure 5.16, Model Results for the Logan, UT-ID Nonattainment Area

Table 5.1 presents the same information in tabular form, and also includes any additional monitoring 

locations in the nonattainment area.
Logan – Page 43

Table 5.1, Modeled Concentrations (μg/m3) for the Salt Lake City, UT Nonattainment Area

The "Control Basket" inventory that is presented in Table 5.1 consists of a combination of SIP reductions 

on point sources and new rules to be implemented that will affect smaller commercial and industrial 

businesses. All of these changes are detailed in Chapter 6 - Control Measures. Summary tables of the 

emission inventories that result from the Control Basket reductions are available in the TSD: Section 3 

Baseline and Control Strategies.

5.9 Air Quality as of the Attainment Date 

The attainment date for this moderate PM2.5 nonattainment area is December 31, 2015. The plan 

provisions for moderate areas call, in Section 189(a)(1)(B), for either a demonstration that the plan will 

provide for attainment by the applicable attainment date or a demonstration that attainment by such 

date is impracticable. 

As shown in the modeled attainment test, the emissions reductions achievable in 2015 allow for a 

demonstration that the Logan, UT-ID nonattainment area can attain the 24-hour PM2.5 NAAQS by the 

attainment date. 

As discussed in Section 6.6, the emissions modeled in the “control basket” scenario reflect all RACM and 

RACT measures achievable in practice by the statutory implementation date (December 14, 2014). 

2010

Observed Business-As-Usual Control Basket

Logan 41 37 34

Franklin 39 34 32

2015
Logan – Page 44

Chapter 6 – CONTROL MEASURES

6.1 Introduction

Attaining the 2006, 24-hour NAAQS for PM2.5 will require emission controls from directly emitted PM2.5

as well as PM2.5 precursors (SO2, NOx and VOC). It will involve emission sources from each of the four 

sectors identified in the discussion on emission inventories (stationary point sources, area sources, onroad mobile sources and off-road mobile sources). Furthermore, it will entail control measures of three 

basic types: existing measures, measures imposed through this SIP, and additional measures requiring 

additional development before they are ready for implementation.

This chapter summarizes the overall control strategy for the plan. Additional detail concerning 

individual emission control measures, including the emissions reductions to be expected, is contained in 

the Technical Support Document.

6.2 Utah Stakeholder Workgroup Efforts

In response to increasing interest in Utah’s air quality problems and the need for greater participation in 

reducing air emissions, the Utah Division of Air Quality (DAQ) created a significant and meaningful role 

for public participation in the PM2.5 SIP development process. The public involvement process was 

driven by a need for transparency and inclusivity of public health and business interests impacted by air 

quality issues. 

DAQ’s measures of success for the public involvement process were: 

 Buy-in from public, stakeholders, and elected officials,

 SIP recommendations that are championed and implemented, and

 Close working relationship with partner organizations to deliver a unified message.

Measures of success for participants were:

 Having a say in plans that impacted their communities,

 Access to information and time to understand issues and provide input,

 Access to DAQ staff and the SIP development process,

 Meaningful participation in the process, and

 Transparency in the process. 
Logan – Page 45

Public participation centered on creating workgroups with members from each county within the PM2.5

nonattainment area—Box Elder, Cache, Davis, Salt Lake, Tooele, Utah, and Weber. More than 100 

people from agriculture, academia, environmental groups, state and local elected officials, industry, and 

the public volunteered to participate. Their participation ensured that the SIP development process 

would have grassroots-level input about strategies and their impacts on a countywide level.

Workgroup members were engaged in four rounds of meetings created to provide and gather 

information. After providing a baseline level of knowledge during Meeting One, draft emissions 

reductions were discussed during Meetings Two and Three, each followed by a survey to capture new 

ideas and feedback. Responses from the survey, and other feedback received during the process, were 

used to refine emissions inventories, in some cases significantly, refine mitigation strategies, provide 

new strategies, and provide ideas for implementation. Meeting Four was an opportunity for workgroup 

members to introduce the SIP package to the public and talk about the development process before one 

of several public comment hearings held in the nonattainment counties. 

The public participation process was not without challenges. One of the most difficult was providing 

information that could get a diverse group of stakeholders to understand very complex and technical air 

quality and emissions reductions issues. Despite the challenges, the process was successful and 

contributed to a well-rounded and well-vetted SIP package. 

6.3 Identification of Measures

In considering the suite of control measures that could be implemented as part of this plan several 

important principles were applied to expedite the analysis.

Filter data shows that secondary particulate is the portion of mass most responsible for exceedances of 

the standard on episode days, and specifically shows that ammonium nitrate is the single largest 

component of that material. In addition, it shows that organic carbon represents the bulk of primary 

PM2.5.

Priority was given to those source categories or pollutants responsible for relatively larger percentages 

of the emissions leading to exceedances of the PM2.5 NAAQS. The emissions inventory compiled to 

represent base-year conditions was useful in identifying the contributors to these emissions, particularly 

in their relation to the formation of ammonium nitrate. 

At the same time, the air quality modeling shed light on the sensitivity of the airshed in its response to 

changes in different pollutants. VOC was immediately identified as a significant contributor to elevated 

PM2.5 concentrations, and proved to be more limiting in the overall atmospheric chemistry than NOx. 

This pointed the search for viable control strategies toward VOC emissions, and somewhat away from 

NOx. It also became apparent that directly emitted PM2.5, while a relatively small portion of the overall 

filter mass, is independent of the non-linear chemical transformation to particulate matter. Therefore, 

any reduction in PM2.5 emissions will directly improve future PM2.5 concentrations, and like VOC, made 
Logan – Page 46

these emissions an attractive target for potential control measures. . Subsequent modeling revealed 

that, as time progressed and the relative concentrations of NOx and VOC changed, controlling for NOx

would yield more benefit in terms of controlling PM2.5. Ammonia is also prominent in chemical reactions 

that produce secondary PM2.5, but it occurs in such abundance that PM2.5 concentrations are sensitive 

only to unachievable reductions in ammonia.

6.4 Existing Control Measures

Since about 1970 there have been regulations at both state and federal levels to mitigate air 

contaminants. It follows that the estimates of emissions used in modeled attainment demonstration for 

this Plan take into account the effectiveness of existing control measures. These measures affect not 

only the levels of current emissions, but some continue to affect emissions trends as well. 

An example of the former would be the effectiveness of an add-on control device at a stationary point 

source. It is presently effective in controlling emissions, and will continue to be that effective five years 

from now. 

An example of the latter would be a federal rule that affects the manufacture of engines. The engines 

already sold into the airshed are effective in reducing emissions, but the number of these engines 

replacing older, higher emitting engines is increasing. Therefore, a rule such as this also affects the 

trend of emissions for that source category in a positive way.

The effectiveness of any control measure that was in place, and enforceable, at the time this Plan was 

written has been accounted for in the tabulation of baseline emissions and projected emissions.

The following paragraphs discuss some of the more important control strategies that are already in 

place for the four basic sectors of the emissions inventory.

Stationary Point Sources:

Utah’s permitting rules require a review of new and modified major stationary sources in nonattainment 

areas, as is required by Section 173 of the Clean Air Act. Beyond that however, even minor sources and 

minor modifications to major sources planning to locate anywhere in the state are required to undergo 

a new source review analysis and receive an approval order to construct. Part of this review is an 

analysis to ensure the application of Best Available Control Technology (BACT). This requirement is 

ongoing and ensures that Utah’s industry is well controlled.

Any of the source-specific emission controls or operating practices that has been required as a result of 

the forgoing has been reflected in the baseline emissions calculated for the large stationary sources, and 

therefore evaluated in the modeled attainment demonstration.
Logan – Page 47

Area sources:

Stage 1 vapor control was introduced in Salt Lake and Davis Counties as part of the 1981 ozone SIP. This 

is a method of collecting VOC vapors, as underground gasoline storage tanks are filled at gas stations, 

and returning those vapors to a facility where they are collected and recycled. Since that time it has 

been extended to include the entire state.

Energy Efficiency 

EPA recognizes the benefits of including energy efficiency programs in SIP’s as a low cost means of 

reducing emissions. Two established energy efficiency programs that result in direct emission reductions 

within the Wasatch Front are already in place. 

Questar Gas ThermWise Rebate Programs

Questar started the ThermWise Rebate Programs on January 1, 2007 as a way to promote the use of 

energy-efficient appliances and practices among its customers. The ThermWise Programs offer rebates 

to help offset the initial cost of energy-efficient appliances and weatherization. There are also rebates 

available for energy efficient new construction. The cost of rebates is built into the Questar gas rate. The 

rebates are vetted by the Utah Public Service Commission's strict "cost-effectiveness" tests. To pass 

these tests, Questar must prove that the energy cost savings produced by the ThermWise Programs 

exceeds the cost of the rebates. There is no scheduled end to the ThermWise Programs. According to 

the Questar program information, the program will remain in place as long as rebates remain costeffective.

UDAQ calculates area source emissions for natural gas by multiplying emission factors against actual and 

projected yearly gas usage data submitted by Questar. In this way, actual realized program reductions 

are expressed in the past year (baseline) emission inventory. Future investment in energy efficiency is 

not captured in our projected future gas usage. Continuance of this program will result in future gas 

emissions that are lower than projected. 

Weatherization Assistance Program 

The Weatherization Assistance Program helps low-income individuals and families reduce energy costs. 

Individuals, families, the elderly and the disabled who are making no more than 200 percent of the 

current federal poverty income level are eligible for help. However, priority is given to the elderly and 

disabled, households with high-energy consumption, emergency situations and homes with preschoolage children.

The Utah Division of Housing and Community Development administer the program statewide through 

eight government and nonprofit agencies. Benefits are provided in the form of noncash grants to eligible 

households to make energy-efficiency improvements to those homes.

The energy efficiency realized from this program is also imbedded within the gas usage data UDAQ 

receives from Questar.
Logan – Page 48

On-road mobile sources:

The federal motor vehicle control program has been one of the most significant control strategies 

affecting emissions that lead to PM2.5. Since 1968, the program has required newer vehicles to meet 

ever more stringent emission standards for CO, NOx, and VOC. Tier 1 standards were established in the 

early 1990s and were fully implemented by 1997. The Tier 1 emission standards can be found in Table 

6.1. The EPA created a voluntary clean car program on January 7, 1998 (63 FR January 7, 1998), which 

was called the National Low Emission Vehicle (NLEV) program. This program asked auto manufacturers 

to commit to meet tailpipe standards for light duty vehicles that were more stringent than Tier 1 

standards. 

EPA Tier 1 Emission Standards for Passenger Cars and Light-Duty Trucks, FTP 75, g/mi

Category

100,000 miles/10 years1

THC NMHC CO

NOx

2 NOx

PM3diesel gasoline

Passenger cars - 0.31 4.2 1.25 0.6 0.1

LLDT, LVW <3,750 lbs 0.8 0.31 4.2 1.25 0.6 0.1

LLDT, LVW >3,750 lbs 0.8 0.4 5.5 0.97 0.97 0.1

HLDT, ALVW <5,750 lbs 0.8 0.46 6.4 0.98 0.98 0.1

HLDT, ALVW > 5,750 lbs 0.8 0.56 7.3 1.53 1.53 0.12

1 - Useful life 120,000 miles/11 years for all HLDT standards and for THC standards for LDT

2 - More relaxed NOx limits for diesels applicable to vehicles through 2003 model year

3 - PM standards applicable to diesel vehicles only

Abbreviations:

LVW - loaded vehicle weight (curb weight + 300 lbs)

ALVW - adjusted LVW (the numerical average of the curb weight and the GVWR)

LLDT - light light-duty truck (below 6,000 lbs GVWR)

HLDT - heavy light-duty truck (above 6,000 lbs GVWR)

Table 6.1, Tier 1 Emission Standards
Logan – Page 49

Shortly thereafter, EPA promulgated the Tier 2 program. This program went into effect on April 10, 

2000 (65 FR 6698 February 10, 2000) and was phased in between 2004 and 2008. Tier 2 introduced 

more stringent numerical emission limits compared to the previous program (Tier 1). Tier 2 set a single 

set of standards for all light duty vehicles. The Tier 2 emission standards are structured into 8 

permanent and 3 temporary certification levels of different stringency, called “certification bins”, and an 

average fleet standard for NOx emissions. Vehicle manufacturers have a choice to certify particular 

vehicles to any of the available bins. The program also required refiners to reduce gasoline sulfur levels 

nationwide, which was fully implemented in 2007. The sulfur levels need to be reduced so that Tier 2 

vehicles could run correctly and maintain their effectiveness. The EPA estimated that the Tier 2 program 

will reduce oxides of nitrogen emissions by at least 2,220,000 tons per year nationwide in 20201. Tier 2 

has also contributed in reducing VOC and direct PM emissions from light duty vehicles. Tier 2 standards 

are summarized in Table 6.2 below. 

Tier 2 Emission Standards, FTP 75, g/mi

Bin#

Full Useful Life 

NMOG* CO NOx† PM HCHO

Temporary Bins

11 MDPVc0.28 7.3 0.9 0.12 0.032

10a,b,d 0.156 (0.230) 4.2 (6.4) 0.6 0.08 0.018 (0.027)

9

a,b,e 0.090 (0.180) 4.2 0.3 0.06 0.018

Permanent Bins

8

b

0.125 (0.156) 4.2 0.2 0.02 0.018

7 0.09 4.2 0.15 0.02 0.018

6 0.09 4.2 0.1 0.01 0.018

5 0.09 4.2 0.07 0.01 0.018

4 0.07 2.1 0.04 0.01 0.011

3 0.055 2.1 0.03 0.01 0.011

2 0.01 2.1 0.02 0.01 0.004

1 0 0 0 0 0

* for diesel fueled vehicle, NMOG (non-methane organic gases) means NMHC (non-methane hydrocarbons)

† average manufacturer fleet NOx standard is 0.07 g/mi for Tier 2 vehicles

 

1

65 FR 6698 February 10, 2000 
Logan – Page 50

a - Bin deleted at end of 2006 model year (2008 for HLDTs)

b - The higher temporary NMOG, CO and HCHO values apply only to HLDTs and MDPVs and expire after 2008

c - An additional temporary bin restricted to MDPVs, expires after model year 2008

d - Optional temporary NMOG standard of 0.280 g/mi (full useful life) applies for qualifying LDT4s and MDPVs only

e - Optional temporary NMOG standard of 0.130 g/mi (full useful life) applies for qualifying LDT2s only

Abbreviations:

LDT2 – light duty trucks 2 (0-6,000 lbs. GVWR, 3,751-5,750 lbs. LVW)

LDT4 – light duty trucks 4 (6,001-8,500 lbs. GVWR, 5,751 lbs. and greater ALVW)

MDPV – medium duty passenger vehicle

HLDT - heavy light duty truck (above 6,000 lbs GVWR)

Table 6.2, Tier 2 Emission Standards

In addition to the benefits from Tier 2 in the current emissions inventories, the emission projections for 

2015 in this SIP continue to reflect significant improvements in both VOC and NOx as older vehicles are 

replaced with Tier 2 vehicles. This trend may be seen in the inventory projections for on-road mobile 

sources despite the growth in vehicles and vehicle miles traveled that are factored into the same 

projections.

Additional on-road mobile source emissions improvement stemmed from federal regulations for heavyduty diesel vehicles. The Highway Diesel Rule, which aimed at reducing pollution from heavy-duty diesel 

highway vehicles, was finalized in January 2001. Under the rule, beginning in 2007 (with a phase-in 

through 2010) heavy-duty diesel highway vehicle emissions were required to be reduced by as much 90 

percent with a goal of complete fleet replacement by 2030. In order to enable the updated emissionreduction technologies necessitated by the rule, beginning in 2006 (with a phase-in through 2009) 

refiners were required to begin producing cleaner-burning ultra-low sulfur diesel fuel. Specifically, the 

rule required a 97 percent reduction in sulfur content from 500 parts per million (ppm) to 15 ppm. The 

overall nationwide effect of the rule is estimated to be equivalent to removing the pollution from over 

90 percent of trucks and buses when the fleet turnover is completed in 2030.
Logan – Page 51

Off-road mobile sources:

Several significant regulatory programs enacted at the federal level will affect emissions from non-road 

mobile emission sources. This category of emitters includes airplanes, locomotives, hand-held engines, 

and larger portable engines such as generators and construction equipment. The effectiveness of these 

controls has been incorporated into the “NONROAD” model UDAQ uses to compile the inventory 

information for this source category. Thus, the controls have already been factored into the projection 

inventories used in the modeled attainment demonstration. 

EPA rules for non-road equipment and vehicles are grouped into various "tiers" in a manner similar to 

the tiers established for on-road motor vehicles. To date, non-road rules have been promulgated for 

Tiers 0 through IV, where the oldest equipment group is designated "Tier 0" and the newest equipment, 

some of which has yet to be manufactured, falls into "Tier IV." Of note are the following:

Locomotives 

Locomotive engine regulation began with Tier 0 standards promulgated in 1998, which apply to model 

year 2001 engines. 

In addition, because of the very long lifetimes of these engines, often up to forty years, Tier 0 standards 

include remanufacturing standards, which apply to locomotive engines of model years 1973 through 

2001. 

Subsequent tier standards for line-haul locomotives apply as follows:

Tier Applicable Model Years

Tier I 2002 - 2004

Tier II 2005 - 2011

Tier III 2012 - 2014

Tier IV 2015 - newer

Yard or "switch" locomotives are regulated under different standards than line-haul. 

Lastly, EPA has promulgated remanufacturing standards for Tier I and 2 locomotive engines to date.

Large Engines

Large non-road engines are usually diesel-powered but include some gasoline-powered equipment. 

Large land-based diesel equipment (> 37 kw or 50 hp) used in agricultural, construction and industrial 

applications are regulated under Tier I rules, which apply to model years 1996 through 2000. 

Subsequent Tier II through IV rules apply to newer model-year equipment. 
Logan – Page 52

Some large non-road engines are gasoline-powered (spark-ignition). These include equipment such as 

forklifts, some airport ground support equipment, recreational equipment such as ATVs, motorcycles 

and snowmobiles. These are regulated under various tiers in a manner similar to diesel equipment.

Small Engines

Small engines are generally gasoline-powered (spark-ignition). Equipment includes handheld and larger 

non-handheld types. Handheld equipment includes lawn and garden power tools such as shrub

trimmers, saws and dust blowers. Non-handheld equipment includes equipment such as lawnmowers 

and lawn tractors. From an emissions standpoint, smaller engine size is offset by the large number of 

pieces of equipment in use by households and commercial establishments. This equipment is regulated 

under a tiered structure as well.

Emissions Benefit

Each major revision of the non-road tier standards results in a large reduction in carbon monoxide, 

hydrocarbons, nitrogen oxides and particulate matter. 

For example, the Non-road Diesel Tier II and III Rule, which regulates model-year 2001 through 2008 

diesel equipment (> 37 kw or 50 hp) is estimated by EPA, in its Regulatory Announcement for this rule 

dated August 1998, to decrease NOx emissions by a million tons per year by 2010, the equivalent of 

taking 35 million passenger cars off the road.

EPA further estimates, in its Regulatory Announcement dated May 2004, that the Tier IV non-road diesel 

rule is expected to decrease exhaust emissions per piece of equipment by over 90 percent compared to 

older equipment. 

Low-Sulfur Diesel

Non-road diesel equipment is required to operate on diesel fuel with a sulfur content of no greater than 

500 ppm beginning June 1, 2007. 

Beginning June 1, 2010, non-road diesel equipment must operate on "ultra-low" sulfur diesel with a 

sulfur content of no more than 15 ppm.

Locomotives and certain marine engines must operate on ultra-low sulfur diesel by June 1, 2012.

6.5 SIP Controls

Beyond the benefits attributable to the controls already in place, there are new controls identified by 

this SIP that provide additional benefit toward reaching attainment. A summary of the plan strategy is 

presented here for each of the emission source sectors. 

Overall, within the Logan, UT-ID nonattainment area, the strategy to reduce emissions results in 2.66 

tons per day of combined PM2.5, SO2, NOx and VOC in 2015.
Logan – Page 53

6.6 Reasonably Available Control Measures (RACM/RACT)

Section 172 of the CAA requires that each attainment plan “provide for the implementation of all 

reasonably available control measures (RACM) as expeditiously as practicable (including such reductions 

in emissions from existing sources in the area as may be obtained through the adoption, at a minimum, 

of reasonably available control technology (RACT)), and shall provide for attainment of the NAAQS.” 

Now that the Courts have determined that Subpart 4 applies to PM2.5 nonattainment areas, it is also 

instructive to consider paragraph 189(a)(1)(C), which requires that “provisions to assure that reasonably 

available control measures ... shall be implemented no later than ... 4 years after designation in the case 

of an area classified as moderate after the date of the enactment of the Clean Air Act Amendments of 

1990.” All three of Utah’s nonattainment areas for PM2.5 were designated so on December 14, 2009. 

Hence, December 14, 2013 was the date by which all RACM was to have been implemented.

EPA interprets RACM as referring to measures of any type that may be applicable to a wide range of 

sources (mobile, area, or stationary), whereas RACT refers to measures applicable to stationary sources. 

Thus, RACT is a type of RACM specifically designed for stationary sources. For Both RACT and RACM 

Potential control measures must be shown to be both technologically and economically feasible. 

Pollutants to be addressed by States in establishing RACT and RACM limits in their PM2.5 attainment 

plans will include primary PM2.5 as well as precursors to PM2.5. For the control strategy in this plan, 

those pollutants include SO2, NOx and VOC.

In general, the combined approach to RACT and RACM includes the following steps: 1) identification of 

potential measures that are reasonable, 2) modeling to test the control strategy, and 3) selection of 

RACT and RACM.

This basic process was applied to each of the four basic sectors of the emissions inventory:

Stationary Point sources:

Reasonably Available Control Technology – As stated above, RACT refers to measures applicable to 

stationary sources. Thus, RACT is a type of RACM specifically designed for stationary sources.

Section 172 does not include any specific applicability thresholds to identify the size of sources that 

States and EPA must consider in the RACT and RACM analysis. In developing the emissions inventories 

underlying the SIP, the criteria of 40 CFR 51 for air emissions reporting requirements was used to 

establish a 100 ton per year threshold for identifying a sub-group of stationary point sources that would 

be evaluated individually. The cut-off was applied to either a sources reported emissions for 2008 or for 

its potential to emit in a given year. The rest of the point sources were assumed to represent a portion 

of the overall area source inventory.
Logan – Page 54

Sources meeting the criteria described above were individually evaluated to determine whether their 

operations would be consistent with RACT.

For the Logan, UT-ID nonattainment area, there are no point sources with the potential to emit 100 tons 

per year of PM2.5 or any PM2.5 plan precursor. 

Additional information regarding the RACT analysis in the nonattainment area may be found in the 

Technical Support Document.

New Source Review / Banked Emission Reduction Credits – Under Utah’s new source review rules in 

R307-403-8, banking of emission reduction credits (ERCs) is permitted to the fullest extent allowed by 

applicable Federal Law as identified in 40 CFR 51, Appendix S, among other documents. Under Appendix 

S, Section IV.C.5, a permitting authority may allow banked ERCs to be used under the preconstruction 

review program (R307-403) as long as the banked ERCs are identified and accounted for in the SIP 

control strategy. In the past, Utah has accounted for existing banked ERCs in SIP control strategies, 

ensuring that a pool of ERCs was available for new or modified sources in nonattainment areas. For the 

PM2.5 SIP, however, it was not possible to include banked ERCs in the attainment demonstration. The 

PM2.5 SIP adopted by the Air Quality Board on December 5, 2012 did not include banked PM2.5 or PM2.5

precursor ERCs in the attainment demonstration1, and therefore under R307-403-8 any ERCs that were 

banked prior to December 5, 2012 may not be used as PM2.5 major source or major modification

emission offsets for PM2.5 nonattainment areas. Any ERCs generated after December 5, 2012 for PM2.5

or PM2.5 precursors would have been accounted for in this PM2.5 attainment demonstration and are 

eligible to be used as emission offsets for PM2.5 or PM2.5 precursors. DAQ has established a new registry 

for PM2.5 ERCs generated after December 5, 2012 to ensure that qualifying ERCs are tracked.

Area sources:

The area source RACM analysis consisted of a thorough review of the entire area source inventory for 

anthropocentrically derived direct PM2.5 and precursors constituents. There was no emission threshold 

level established in the review process; instead, the analysis centered on whether reasonable control 

measures are available for a given source category. The following table identifies these categories as 

well as the pollutant(s) likely to be controlled, and provides some remarks as to whether a control 

strategy was ultimately pursued. In considering what source categories might be considered, Utah 

made use of EPA recommendations included in Control Techniques Guideline Documents (CTG’s), as 

well as control strategies from other states. DAQ evaluated each strategy for technical feasibility as part 

of the RACM analysis. The screening column in the table identifies whether or not a strategy was 

retained for rulemaking or screened out for impracticability. 

 

1

Note that, because no part of Cache County had ever before been designated as a nonattainment area for any 

pollutant, there were no ERCs in the registry to even be considered in the modeled demonstration belonging to 

the SIP revision adopted by the Utah Air Quality Board on December 5, 2012. Furthermore, no ERCs were created 

in the Logan, UT-ID nonattainment area between December 5, 2012 and the effective date of this plan revision 

(prepared to also address the requirements of Subpart 4). Hence, no banked emission credits were included in this 

demonstration either.
Logan – Page 55

Table 6.3 Area Source Strategy Screening

Strategy Constituent(s) Screening 

Status Remarks

1. Repeal current surface coating rule, R307-

340. Replace this rule with individual rules 

for each category. New rules include PM2.5

nonattainment areas. New rules update 

applicability and control limits to most current 

CTG. Current rule includes, paper, fabric 

and vinyl, metal furniture, large appliance, 

magnet wire, flat wood, miscellaneous metal 

parts and graphic arts.

VOC Retained R307-340 previously applied to Davis and 

Salt Lake counties. R307-340 was 

withdrawn and re-enacted as separate rules 

for each existing category. The new rules 

were expanded to nonattainment areas and 

updated to the most current RACT based 

limit(s). 

2. New separate surface coating rules for 

following sources:

a. Aerospace

b. High performance

c. Architectural

d. Marine

e. Sheet, strip & coil

f. Traffic markings

g. Plastic parts

VOC See Remarks 

Column 

Aerospace – retained 

High performance – not retained, regulated 

under Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA)

Architectural – initially nor retained, further 

research indicated that adopting the Ozone 

Transport Commission model rule is 

feasible. 

Marine – not retained, only 1.2 tpy

Sheet, strip & coil – retained 

Traffic markings – not retained, regulated 

under FIFRA

Plastic parts - retained 

3. Agricultural practices using Natural 

Resources Conservation Service (NRSC) 

practice standards 

VOC, PM2.5, 

ammonia

Not Retained The NRCS has already enrolled most 

farmers in the erodible regions in their 

program thereby negating the need for 

rulemaking

4. Consumer products rule regulating VOC 

content

VOC Retained

5. Adhesives and sealant rule VOC Retained

6. Expand current solvent degreasing rule 

R307-335 to PM2.5 nonattainment areas and 

add a new section on industrial solvent 

cleaning

VOC Retained

7. Automobile refinishing rule VOC Retained

8. Expand wood furniture manufacturing rule to 

PM2.5 nonattainment areas. Update to most 

current CTG.

VOC Retained

9. Lower the no burn cut point for residential 

use of solid fuel burning devices. Require 

new sale of EPA certified stoves/fireplaces. 

Prohibit the sale/resale of noncertified stoves 

in nonattainment areas. 

VOC, PM2.5, 

NOx, SOx, 

ammonia

Retained

10. Ban new sales of stick type outdoor wood 

boilers in nonattainment areas.

VOC, PM2.5, 

NOx, SOx, 

ammonia

Retained

11. Industrial bakery rule VOC Initially 

Retained

Screened out after analysis of public 

comment, cost benefit analysis does not 

support rulemaking, high cost-low VOC 

reduction

12. Restaurant charbroiler emission control: 

- Chain-driven

-Underfire

VOC, PM2.5 Chain-driven 

Retained

No reasonable control measures available 

at this time for underfire charbroiling
Logan – Page 56

Strategy Constituent(s) Screening 

Status Remarks

Underfire-Not 

Retained

13. Appliance pilot light phase out VOC, PM2.5, 

NOx, SOx, 

ammonia

Retained

14. Expand current fugitive dust rule, R307-309 

to PM2.5 nonattainment areas. Require 

BMP’s for dust plans.

PM2.5 Retained

15. Amend fugitive dust rule to include cattle 

feed lot

PM2.5 Not Retained Sizeable feed lots are not located in 

nonattainment areas

16. Ultra-low NOx burners in commercial, 

industrial, and institutional boilers

NOx Tentatively 

Retained for 

Future 

Consideration 

Developing technology not readily available 

at this time

17. Ultra-low NOx burners in water heaters NOx Tentatively 

Retained for 

Future 

Consideration 

High cost and availability concerns

18. Manure management VOC, 

ammonia

Not Retained NRCS best management practices already 

encourages manure management. Limited 

viable options during winter months and 

treatment options are costly with low control 

efficiency that would not yield significant 

ammonia reduction in an ammonia rich 

inventory 

19. Ban testing of back-up generators on redalert daysVOC, PM2.5, 

NOx, SOx

Initially 

Retained

Screened out after review of public 

comment, rule implementation was more 

complicated than anticipated, generators 

cannot be easily re-programmed 

20. Prohibit use of cutback asphalt VOC Not Retained Cities and highway administration personnel 

need stockpile for winter time road repair. 

Very small inventory.

21. Control limits on aggregate processing 

operations and asphalt manufacturing

PM2.5, NOx, 

SOx

Retained

22. R307-307 Road Salt and Sanding PM Retained Expand current rule to nonattainment areas

EPA published CTGs and Alternative Control Techniques documents (ACTs) for VOCs for a host of 

emission sources. The CTGs are used to presumptively define VOC RACT. The VOC ACTs describe 

available control techniques and their cost effectiveness, but do not define presumptive RACT levels as 

the CTGs do. Therefore, CTG’s are given highest priority in rule development. 

Where a CTG does not exist for an emission source or where a CTG is so dated that it no longer 

represents current industry practice, UDAQ considered rules from other states as reference sources. 

Additional reference sources include the Ozone Transport Commission (OTC) and the Northeast States 

for Coordinated Air Use Management.

As noted above, many CTGs were previously adopted into Utah’s air quality rules to address ozone 

nonattainment in Salt Lake and Davis Counties. In conducting this evaluation, consideration was given 

to whether an expansion of applicability for an existing CTG into additional counties would provide a 

benefit for PM2.5, and whether a strengthening of existing CTG requirements in Salt Lake and Davis 
Logan – Page 57

Counties would result in an incremental benefit that was economically feasible. Furthermore, EPA has 

updated some of its existing CTGs and added some new ones to the list.

As part of this SIP, Utah has identified relevant source categories covered by CTGs, and promulgated

rules based on the CTGs for reducing emissions from these categories. These rules apply to the 

following source categories: 

 Control of Volatile Organic Emissions from Surface Coating of Cans, Coils, Paper, Fabrics, 

Automobiles, and Light-Duty Trucks 

 Control of Volatile Organic Emissions from Solvent Metal Cleaning 

 Control of Volatile Organic Emissions from Surface Coating of Insulation of Magnet Wire 

 Control of Volatile Organic Emissions from Graphic Arts

 Control of Volatile Organic Compound Emissions from Wood Furniture Manufacturing 

Operations 

 Control Techniques Guidelines for Industrial Cleaning Solvents

 Control Techniques Guidelines for Flat Wood Paneling Coatings 

 Control Techniques Guidelines for Paper, Film, and Foil Coatings 

 Control Techniques Guidelines for Large Appliance Coatings 

 Control Techniques Guidelines for Metal Furniture Coatings 

 Control Techniques Guidelines for Miscellaneous Metal and Plastic Parts Coatings 

 Control of Volatile Organic Emissions from Coating Operations at Aerospace Manufacturing and 

Rework Operations 

While most VOC sources are addressed by CTGs, the remaining emission sources must be evaluated by 

engineering analysis, including an evaluation of rulings by other states including model rules developed 

by the Ozone Transport Commission. These include VOCs from autobody refinishing, restaurant 

charbroiling, and phasing out appliance pilot lights. 

CTGs for PM2.5 emissions sources do not exist. RACT for PM2.5 has been established through information 

from varied EPA and other state SIP sources. A useful source of data is the AP 42 Compilation of Air 

Pollutant Emission Factors, first published by the US Public Health Service in 1968. In 1972, it was 

revised and issued as the second edition by the EPA. The emission factor/control information was 

applied to fugitive dust and mining strategies. 
Logan – Page 58

Table 6.4 shows the effectiveness of the area source SIP control strategy for the Logan, UT-ID

nonattainment area by indicating the quantities of emissions eliminated from the inventory in 2015. 

Most of these rules became effective January 1, 2014.

Table 6.4, Emissions Reductions from Area Source SIP Controls

NOX PM2.5 SOX VOC

Area Source Rules

R307-302, Solid fuel burning 64 533 11 666

R307-303, Commercial cooking 25 7

R307-309, Fugitive dust 58

R307-312, Aggregate processing operations 1

R307-335, Degreasing 379

R307-342, Adhesives & sealants 148

R307-343, Wood manufacturing 64

R307-344, Paper, film & foil coating 12

R307-345, Fabric & vinyl coating 686

R307-346, Metal furniture coating

R307-347, Large appliance coating

R307-348, Magnet wire coating

R307-349, Flat wood panel coating 36

R307-350 Miscellaneous metal parts coating 26

 machinery 7

 other transportation 15

 Special 1

R307-351, Graphic arts 298

R307-352, Metal containers

R307-353, Plastic coating 261

R307-354, Auto body refinishing 137

R307-355, Aerospace coatings 25

R307-356, Appliance pilot light 51 0 0 3

R307-357, Consumer products 255

R307-361, Architectural coatings 563

Grand Totals 122 679 12 3,665

Logan, UT-ID Nonattainment Area

2015 lbs/day reduced
Logan – Page 59

On-road mobile sources:

A motor vehicle emission inspection and maintenance (I/M) program is a necessary control strategy for 

Cache County to attain the PM2.5 NAAQS based on the modeling conducted by UDAQ. This analysis can 

be found in the TSD. 

Therefore, pursuant to Utah Code Annotated 41-6a-1642(1), Cache County officials successfully 

implemented an I/M program on January 1, 2014. Cache County’s I/M program is comprised of a 

decentralized, test and repair network and requires a biennial test for all vehicles 1969 and newer. The 

program exempts vehicles less than six years old from an emission inspection. The details of the 

program can be found in Section X Part F of the Utah SIP. 

The emissions reductions associated with an I/M program for the year 2015 are 0.214 tons per day for 

NOx and 0.212 tons per day for VOC.

Off-road mobile sources:

Beyond the existing controls reflected in the projection-year inventories and the air quality modeling 

there are no emission controls that would apply to this source category.
Logan – Page 60

Chapter 7 – TRANSPORTATION CONFORMITY

7.1 Introduction

The federal Clean Air Act (CAA) requires that transportation plans and programs within the Logan, UT-ID 

PM2.5 nonattainment area conform to the air quality plans in the region prior to being approved by the 

Cache Metropolitan Planning Organization (CMPO). Demonstration of transportation conformity is a 

condition to receive federal funding for transportation activities that are consistent with air quality goals 

established in the Utah State Implementation Plan (SIP). Transportation conformity requirements are 

intended to ensure that transportation activities do not interfere with air quality progress. Conformity 

applies to on-road mobile source emissions from regional transportation plans (RTPs), transportation 

improvement programs (TIPs), and projects funded or approved by the Federal Highway Administration 

(FHWA) or the Federal Transit Administration (FTA) in areas that do not meet or previously have not met 

the National Ambient Air Quality Standards (NAAQS) for ozone, carbon monoxide, particulate matter 

less than 10 micrometers in diameter (PM10), particulate matter 2.5 micrometers in diameter or less 

(PM2.5), or nitrogen dioxide. 

The Safe, Accountable, Flexible, Efficient Transportation Equity Act – A Legacy for Users (SAFTEA-LU) and 

section 176(c)(2)(A) of the CAA require that all regionally significant highway and transit projects in air 

quality nonattainment areas be derived from a “conforming” transportation plan. Section 176(c) of the 

CAA requires that transportation plans, programs, and projects conform to applicable air quality plans 

before being approved by an MPO. Conformity to an implementation plan means that proposed 

activities must not (1) cause or contribute to any new violation of any standard in any area, (2) increase 

the frequency or severity of any existing violation of any standard in any area, or (3) delay timely 

attainment of any standard or any required interim emission reductions or other milestones in any area. 

The plans and programs produced by the transportation planning process of the CMPO are required to 

conform to the on-road mobile source emissions budgets established in the SIP, or absent an approved 

or adequate budget, required to meet the interim conformity test. Approval of conformity is 

determined by the FHWA and FTA. 

7.2 Consultation

The Interagency Consultation Team (ICT) is an air quality workgroup in Utah that makes technical and 

policy recommendations regarding transportation conformity issues related to the SIP development and 

transportation planning process. Section XII of the Utah SIP established the ICT workgroup and defines 

the roles and responsibilities of the participating agencies. Members of the ICT workgroup collaborated 

on a regular basis during the development of the PM2.5 SIP. They also meet on a regular basis regarding 

transportation conformity and air quality issues. The ICT workgroup is comprised of management and 

technical staff members from the affected agencies associated directly with transportation conformity.
Logan – Page 61

ICT Workgroup Agencies

 Utah Division of Air Quality (UDAQ)

 Metropolitan Planning Organizations MPOs

 CMPO

 Wasatch Front Regional Council

 Mountainland Association of Governments

 Utah Department of Transportation (UDOT)

 Utah Local Public Transit Agencies

 Federal Highway Administration (FHWA)

 Federal Transit Administration (FTA)

 U.S. Environmental Protection Agency (EPA)

During the SIP development process the CMPO coordinated with the ICT workgroup and developed 

PM2.5 SIP motor vehicle emissions inventories using the latest planning assumptions and tools for traffic 

analysis and the EPA-approved Motor Vehicle Emission Simulator (MOVES2010) emissions model. Local 

MOVES2010 modeling data inputs were cooperatively developed by the CMPO and the ICT workgroup 

using EPA-recommended methods where applicable.

7.3 Regional Emission Analysis

The regional emissions analysis is the primary component of transportation conformity and is 

administered by the lead transportation agency located in the EPA designated air quality nonattainment 

area. On December 2009, EPA designated the only multistate nonattainment area in the State of Utah 

by declaring portions of Cache County, Utah and Franklin County, Idaho (Cache Valley) as a PM2.5

nonattainment area. The Deadlines Rule (signed April 25, 2014) later classified this as a moderate PM2.5

nonattainment area. The responsible transportation planning organization for the Utah portion of the 

multistate nonattainment area is the CMPO while the Idaho portion is covered by the Idaho Department 

of Transportation. 

As a condition to receive federal transportation funding, transportation plans, programs, and projects 

are required to meet the criteria and procedures for demonstrating and assuring conformity to the 

applicable implementation plan developed pursuant to Section 110 and Part D of the CAA. The criteria, 

specified in 40 CFR 93.109, differ based on the action under review and the status of the 
Logan – Page 62

implementation plan. The satisfaction of criteria and procedures, for implementation plans submitted 

under Section 189(a)(1)(B)(i) of the CAA, which demonstrate attainment of the applicable NAAQS by the 

applicable attainment date, are addressed generally in paragraph 93.109(b) of the conformity rule. For 

such control strategy implementation plan revisions, the conformity test consists of either an interim 

emissions test or a motor vehicle emissions budgets test. 

Motor vehicle emissions budgets are defined in 40 CFR 93.101 as "that portion of the total allowable 

emissions defined in the submitted or approved control strategy implementation plan revision or 

maintenance plan for a certain date for the purpose of meeting reasonable further progress milestones 

or demonstrating attainment or maintenance of the NAAQS, for any criteria pollutant or its precursors, 

allocated to highway and transit vehicle use and emissions." Transportation plans, programs, and 

projects are required to meet those emission budgets through strategies that increase the efficiency of 

the transportation system and reduce motor vehicle use. 

The interim conformity test requirements apply until either EPA has declared the motor vehicle 

emissions budgets adequate for transportation conformity purposes or until EPA approves the budget in 

the Federal Register. 

7.4 Transportation Conformity PM2.5 Components

The transportation conformity requirements found in 40 CFR 93.102 require that the PM2.5 SIP include 

motor vehicle emissions budgets for direct PM2.5 (elemental carbon, organic carbon, SO4, brake and tire 

wear) and emissions of nitrogen oxide (NOx), a gaseous PM2.5 precursor.

Because UDAQ has identified volatile organic compounds (VOCs) as a PM2.5 precursor that significantly 

impact PM2.5 concentrations, the SIP will also require a motor vehicle emissions budget for VOC. 

The EPA conformity rule presumes that PM2.5 re-entrained road dust does not need to be included in the 

interim conformity test or have an established motor vehicle emissions budget unless either the state or 

EPA decides that re-entrained road dust emissions are a significant contributor to the PM2.5 

nonattainment problem. The UDAQ conducted a re-entrained road dust study that concluded that PM2.5 

re-entrained road dust emissions are negligible in the Utah portion of the Cache Valley PM2.5

nonattainment area. EPA Region 8 reviewed the study and concurred with the UDAQ’s findings. 

7.5 Interim PM2.5 Conformity Test

The EPA interim conformity test, for the purposes of this plan revision, will require that NOx, VOC, and 

direct PM2.5 (elemental carbon, organic carbon, SO4, brake and tire wear) emissions from RTPs, TIPs, and 

projects funded or approved by the FHWA or the FTA not exceed 2008 levels.
Logan – Page 63

Interim emissions budget tests performed by the CMPO must include the whole multistate PM2.5

nonattainment area of Cache Valley, including emissions estimates from Franklin County, Idaho. 

The Interim conformity test requirements apply until EPA has declared the motor vehicle emissions 

budgets adequate for transportation conformity purposes or until EPA approves the budget in the 

Federal Register. 

7.6 Transportation Conformity PM2.5 Budgets

Cache County, Utah and Franklin County, Idaho have requested separate motor vehicle emissions 

budgets for their respective areas; therefore, the budgets listed below only apply to the Cache MPO. 

In this SIP, the State is establishing transportation conformity motor vehicle emission budgets (MVEB) in 

the nonattainment portions of Cache County, Utah for 2015. Separate budgets are established for NOx, 

VOC, and PM2.5 (elemental carbon, organic carbon, SO4, brake and tire wear). 

The Transportation Conformity PM2.5 budgets emissions estimates for the mobile sources are calculated 

from the EPA approved Motor Vehicle Emission Simulator Model (EPA MOVES 2010a).

Cache MPO Transportation Conformity Budgets

Direct PM2.5 (tpd) NOx (tpd) VOC (tpd)

2015 0.32 4.49 3.23

Table 7.1, Emissions Budgets for Transportation Conformity Purposes (EPA MOVES 2010a). Note: PM2.5 budget 

only includes tire and brake wear, sulfate, elemental and organic carbon and does not include road dust. VOC 

emissions do not include refueling spillage and displacement vapor loss. Budgets are rounded to the nearest 

hundredth ton.

Per section 93.124 of the conformity regulations, for transportation conformity analyses using these 

budgets in analysis years beyond 2015, a trading mechanism is established to allow future increases in 

on-road direct PM2.5 emissions to be offset by future decreases in plan precursor emissions from onroad mobile sources at appropriate ratios established by the air quality model. Future increases in onroad direct PM2.5 emissions may be offset with future decreases in NOx emissions from on-road mobile 

sources at a NOx to PM2.5 ratio of 13.66 to 1 and/or future decreases in VOC emissions from on-road 

mobile sources at a VOC to PM2.5 ratio of 22.84 to 1. This trading mechanism will only be used if needed 

for conformity analyses for years after 2015. To ensure that the trading mechanism does not impact the 

ability to meet the NOx or VOC budgets, the NOx emission reductions available to supplement the direct 

PM2.5 budget shall only be those remaining after the 2015 NOx budget has been met, and the VOC 

emissions reductions available to supplement the direct PM2.5 budget shall only be those remaining after 

the 2015 VOC budget has been met. Clear documentation of the calculations used in the trading should 

be included in the conformity analysis.
Logan – Page 64

Chapter 8 – REASONABLE FURTHER PROGRESS

8.1 Introduction 

Clean Air Act Section 172(c)(2) requires that plans for nonattainment areas “shall require reasonable 

further progress (RFP).” The definition of RFP is given in Section 171 of the CAA. It means “such annual 

incremental reductions in emissions of the relevant air pollutant as are required by this part or may 

reasonably be required by the Administrator for the purpose of ensuring attainment of the applicable 

national ambient air quality standard by the applicable date.” 

In general terms, the goal of these RFP requirements is for areas to achieve generally linear progress 

toward attainment, as opposed to deferring implementation of all measures, where possible, until the 

end.

The pollutants to be addressed in the RFP plan are those pollutants that are identified for purposes of 

control measures in the attainment plan: PM2.5, SO2, NOx, and VOC. 

8.2 Moderate Area Planning Requirements 

Within the context of the moderate area planning requirements given in Subparts 1 and 4 of the CAA, 

RFP must be considered in light of the attainment date as well as the date by which all RACT and RACM 

must be implemented. The attainment date for all three of Utah’s moderate PM2.5 nonattainment areas 

was established in EPA’s Deadlines Rule. That date is December 31, 2015. The deadline for 

implementation of all RACT and RACM is described in paragraph 189(a)(1)(C) as four years from the date 

these areas were designated nonattainment. That date for implementation of RACM was thus 

December 14, 2013.

There are other moderate area planning requirements in Subpart 4 that relate to the showing of RFP. 

Paragraph 189(a)(1)(B) requires “either (i) a demonstration (including air quality modeling) that the plan 

will provide for attainment by the applicable attainment date; or (ii) a demonstration that attainment by 

such date is impracticable.”

This plan demonstrates the former; that with the implementation of all reasonably available controls, 

the area will attain the 2006, 24-hour standard for PM2.5 by December 31, 2015.

For plan revisions showing attainment, paragraph 189(c) requires the inclusion of “quantitative 

milestones which are to be achieved every three years until the area is redesignated attainment and 

which demonstrate reasonable further progress ... toward attainment by the applicable date.”
Logan – Page 65

8.3 RFP for the Logan, UT-ID Nonattainment Area 

The attainment demonstration for the Logan, UT-ID PM2.5 nonattainment area shows that the 2006, 24-

hr NAAQS can be achieved by the attainment date of December 31, 2015. Essentially, the attainment 

demonstration in the SIP may also be considered to demonstrate that the area is achieving RFP

Past Guidance on RFP, for showing generally linear progress towards attainment by the applicable 

attainment date, has described a straight line with a downward trend, ending at the attainment date 

and representing, there, a level of emissions that is consistent with attainment of the applicable NAAQS.

In this plan, the “reductions in emissions of the relevant air pollutant as are required by this part” have 

been determined through the application of all RACM and RACT measures. The emissions reductions 

associated with these control measures were factored into an inventory for 2015 that was assessed 

using air quality modeling. The air quality modeling demonstrated that these reductions in emissions 

would be sufficient to demonstrate attainment of the applicable standard by the applicable attainment 

date.

It is also necessary to define a period of time over which the RFP determination will be made.

The starting point for evaluating RFP should be the baseline year used in the modeling analysis. This is a 

year (2010) selected to coincide with the period used to establish the monitored design value for the 

modeling analysis; a period in which the area is violating the applicable NAAQS.

Thus, the magnitude of emissions reductions should be evaluated over a period spanning from 2010 

through 2015.

Quantitatively, the following assessment of emissions and incremental emissions reductions in Table 8.1 

will show that RFP is met using the criteria discussed above:
Logan – Page 66

Table 8.1, Reasonable Further Progress in the Logan, UT-ID nonattainment area

In addition to the emissions totals, the table also includes the 2010 baseline design value for the 

controlling monitor in the nonattainment area (Logan) and the predicted PM2.5 concentration in 2015. 

These concentrations are presented as another metric to establish progress toward meeting the 24-hour 

standard. 

Control Measures 

The inventory for 2015 “with growth and controls” reflects the implementation of all the reasonably 

available control measures and reasonably available control technologies identified in this plan, as well 

as all pre-existing control measures. As such, this inventory takes into account all controls that “may 

reasonably be required by the Administrator.”

For a complete discussion of RACM & RACT, and the control measures factored into the modeled 

demonstration for 2015, see Chapter 6 of the Plan.

Reasonable Further Progress

Logan, UT-ID PM2.5 Nonattainment Area

*Emissions / Year 2010 2015 Difference RFP

Annualized 

Difference

 PM2.5 1.3 0.8 0.5 0.1

 NOx 9.3 6.9 2.4 0.5

 SO2 0.3 0.3 0.0 0.0

 VOC 12.1 8.9 3.2 0.6

 Plan precursors 21.7 16.1 5.6 1.1

 Total 23.0 16.9 6.1 1.2

**Concentration (ug/m3) 41 34 7.1 1.4

* Emissions are presented in tons per average winter day

**Value for 2010 is Baseline design value for the Logan monitor

projected with growth and 

controls
Logan – Page 67

8.4 Milestones for the Logan, UT-ID Nonattainment Area 

For plan revisions showing attainment, the Act requires quantitative milestones, to be achieved every 

three years, which demonstrate reasonable further progress toward attainment by the applicable date.

Under section 189(c), the State is required to submit a SIP revision if it fails to submit the quantitative 

milestone demonstration or if EPA determines that the milestone was not met.

These milestones are addressed in EPA’s General Preamble (see Section 2.2 of this plan), which says that 

under the milestone requirement, the States must demonstrate to EPA that the SIP measures are being 

implemented and the milestones have been met.

The preamble notes that section 189(c) does not articulate the starting point for counting the 3-year 

period, and offers that it is reasonable to begin counting from the due date for the applicable plan 

revision containing the control measures that will give rise to the emission reductions.

Thus, the first quantitative milestone date is December 31, 2017. 

The emission levels at the milestone must demonstrate reasonable further progress toward attainment 

by the applicable date. As noted in the introduction to this section, RFP is defined so as to consider the 

reductions in emissions required to ensure attainment of the NAAQS by the attainment date or which

may reasonably be required by the Administrator. Since the applicable attainment date (December 31, 

2015) precedes the milestone date, the quantification of the emissions reductions to be achieved must 

be taken to mean the level of emissions in 2015 used to demonstrate attainment.

From the date of the milestone, the State shall have 90 days to submit to the Administrator “a 

demonstration that all measures in the plan approved under this section have been implemented and 

that the milestone has been met.”

UDAQ herein commits to prepare and submit a milestone report no later than 90 days from the 

milestone.
Logan – Page 68

Chapter 9 – CONTINGENCY MEASURES

9.1 Background 

Consistent with section 172(c)(9) of the Act, the State must submit in each attainment plan specific 

contingency measures to be undertaken if the area fails to make reasonable further progress, or fails to 

attain the PM2.5 NAAQS by its attainment date. The contingency measures must take effect without 

significant further action by the State or EPA.

Nothing in the statute precludes a State from implementing such measures before they are triggered, 

but the credit for a contingency measure may not be used in either the attainment or reasonable further 

progress demonstrations.

The SIP should contain trigger mechanisms for the contingency measures, specify a schedule for 

implementation, and indicate that the measures will be implemented without further action by the 

State or by EPA.

The CAA does not include the specific level of emission reductions that must be adopted to meet the 

contingency measures requirement under section 172(c)(9). Nevertheless, in the preamble to the Clean 

Air Fine Particulate Rule (see 72 FR 20643) EPA recommends that the “emissions reductions anticipated 

by the contingency measures should be equal to approximately 1 year’s worth of emissions reductions 

necessary to achieve RFP for the area.” 

9.2 Contingency Measures and Implementation Schedules for the Nonattainment Area 

The following measures have been set aside for contingency purposes:

Woodburning Control –As part of the control strategy for the SIP, rule R307-302 has been amended to 

change the no-burn call from 35 μg/m3to 25 μg/m

3

. Credit for this change is included in the modeled 

attainment demonstration as well as the RFP demonstration. However, R307-302 also includes a 

mechanism to further revise the no-burn call to only 15 μg/m

3

should a contingency situation arise. The 

benefit of this rule is to prevent a buildup of particulate matter due to woodsmoke during periods of 

poor atmospheric mixing which typically precede exceedances of the 24-hour PM2.5 NAAQS. This rule 

has been adopted, and can take effect immediately if so required.

This contingency measure will be triggered by an EPA determination that: 1) the area has, based on the 

state’s milestone report under 189(c), failed to make RFP; or 2) has failed to attain the NAAQS by the 

applicable attainment date. 
Logan – Page 69

9.3 Conclusions 

Control measures developed to meet increasingly stringent ozone and fine PM2.5 standards in Utah’s 

urbanized areas have likewise become increasingly stringent, and still it is a challenge to attain the 2006,

PM2.5 NAAQS. This leaves little room for additional reductions that can be set aside as contingency

measures.

In the Cache Valley, there are no major stationary point sources. Area sources and on-road mobile 

sources contribute the emissions that result in elevated PM2.5 concentrations. For the most part, further 

emission controls in these categories extend beyond the authorities of UDAQ. The most meaningful 

reductions in future emissions of VOC, an important PM2.5 precursor, will likely result from national 

programs that apply additional restrictions of VOC in consumer products, and from what will likely result 

from Tier III of the federal motor vehicle control program.