Cache Valley Idaho PM2.5 Nonattainment 

Area State Implementation Plan

State of Idaho 

Department of Environmental Quality

December 2012
Printed on recycled paper, DEQ December 2012,

PID CVP, CA code 61215. Costs associated with this 

publication are available from the State of Idaho 

Department of Environmental Quality in accordance 

with Section 60-202, Idaho Code.
Cache Valley Idaho PM2.5 Nonattainment 

Area State Implementation Plan

December 2012

Prepared by

Idaho Department of Environmental Quality

Pocatello Regional Office

444 Hospital Way, #300

Pocatello, Idaho 83201
This page intentionally left blank for correct double-sided printing.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

iii

Table of Contents

1 Introduction.............................................................................................................................. 1

1.1 Background....................................................................................................................... 1

1.2 Nonattainment Area Description...................................................................................... 2

1.2.1 Nonattainment Area Location and Topography .......................................................... 2

1.2.2 Cache Valley Secondary Aerosol Precursors .............................................................. 5

1.2.3 Climatology and Meteorology..................................................................................... 6

2 Air Quality............................................................................................................................... 8

2.1 Monitoring Sites............................................................................................................... 8

2.1.1 Idaho Monitors............................................................................................................. 9

2.2 Air Quality Data ............................................................................................................. 10

2.2.1 Idaho Summary.......................................................................................................... 10

2.2.2 Utah Summary........................................................................................................... 12

2.3 Meteorological Data during High PM2.5 Events Summary ............................................ 13

2.4 Correlation between Utah and Idaho Monitors .............................................................. 17

2.5 Special Studies................................................................................................................ 19

2.5.1 PM2.5 Saturation Studies ............................................................................................ 19

2.5.2 Fine Particle Pollution Composition—Speciated Monitoring Data .......................... 19

2.6 Design Value Determination—24-Hour Standard ......................................................... 21

3 Emissions Inventory .............................................................................................................. 22

3.1 Seasonal Adjustment ...................................................................................................... 23

3.2 2008 Baseline Emissions Inventory ............................................................................... 23

3.2.1 On-Road Mobile Emissions Inventory ...................................................................... 23

3.2.2 Emissions Inventory Results Summary..................................................................... 24

3.2.3 Primary PM2.5 Emissions........................................................................................... 27

3.3 Attainment Year Inventory............................................................................................. 29

4 Attainment Demonstration..................................................................................................... 31

4.1 Photochemical Model Selection ..................................................................................... 31

4.2 Domain/Grid Resolution ................................................................................................ 32

4.3 Episode Selection ........................................................................................................... 33

4.4 Meteorological Inputs..................................................................................................... 33

4.5 Photochemical Model Performance Evaluation ............................................................. 34

4.6 Model Performance Summary........................................................................................ 35

4.7 Additional Model Sensitivity Tests of Nitrogen Oxides and Volatile Organic 

Compounds Chemistry................................................................................................ 36

4.8 Modeled Attainment Test............................................................................................... 36
Cache Valley Idaho PM2.5 Nonattainment Area SIP

iv

4.9 Unmonitored Areas ........................................................................................................ 37

4.10 Attainment Date.............................................................................................................. 38

5 Control Strategies .................................................................................................................. 38

5.1 Control Strategy Consideration ...................................................................................... 38

5.1.1 Sulfur Dioxide ........................................................................................................... 38

5.1.2 Nitrogen Oxides......................................................................................................... 38

5.1.3 Volatile Organic Compounds.................................................................................... 39

5.1.4 Ammonia ................................................................................................................... 39

5.1.5 Direct PM2.5 Emissions.............................................................................................. 39

5.2 Reasonably Available Control Measures ....................................................................... 39

5.2.1 Road Sanding............................................................................................................. 39

5.2.2 Residential Wood Combustion Ordinances............................................................... 40

5.2.3 Air Quality Index Program........................................................................................ 40

5.2.4 Woodstove Change Outs ........................................................................................... 40

5.3 Contingency Measures ................................................................................................... 41

5.3.1 Forecasting................................................................................................................. 42

5.3.2 Road Sanding............................................................................................................. 42

5.3.3 Certified Woodstoves ................................................................................................ 42

5.3.4 Revised Woodstove New Source Performance Standard.......................................... 43

5.3.5 Air Pollution Emergency Rule (Open Burning Ban)................................................. 43

5.3.6 Agricultural Sources.................................................................................................. 43

5.3.7 Idaho Permitting Program.......................................................................................... 43

5.3.8 Tier 2 Federal Motor Vehicle Emission Requirements............................................. 43

5.3.9 Diesel Emission Reduction Program—School Bus Retrofits.................................... 44

5.3.10 Transportation Control Measures .............................................................................. 44

5.3.11 Other Measures.......................................................................................................... 45

5.4 Reasonably Available Control Technology.................................................................... 45

5.5 Transportation Conformity............................................................................................. 45

5.5.1 Motor Vehicle Emissions Budget Requirements....................................................... 45

5.5.2 Motor Vehicle Emission Budget ............................................................................... 47

5.5.3 Adequacy Determination ........................................................................................... 47

6 Administrative Requirements................................................................................................ 48

6.1 Consultation and Public Notification Procedures........................................................... 52

6.2 Continued Air Monitoring and Verification of Attainment ........................................... 53

6.3 Permitting Program Role................................................................................................ 53

6.4 Review Commitment and Plan Update .......................................................................... 53

7 Conclusions............................................................................................................................ 54

8 References.............................................................................................................................. 55
Cache Valley Idaho PM2.5 Nonattainment Area SIP

v

Appendix A. Special Air Quality Studies

Appendix B. Emissions Inventory and Technical Support Document—Utah Department of 

Air Quality

Appendix C. Idaho Documentation

Appendix D. Modeling—Utah Department of Air Quality

Appendix E. Reasonably Available Control Methods

Appendix F. Public Involvement

List of Tables

Table 1. Average weather in Franklin County, Idaho..................................................................... 6

Table 2. Cache Valley air quality monitoring site locations........................................................... 9

Table 3. Specific Cache Valley air quality monitors and measurement frequency. ....................... 9

Table 4. Cache Valley emissions inventory, tons per day, for the 2008 base year and 2014 

attainment year for PM2.5, NOx, VOC, NH3, and SO2; emissions shown are for Utah 

and Idaho. ....................................................................................................................... 30

Table 5. Franklin County emissions summary. ............................................................................ 30

Table 6. Emissions reductions due to burn cessation ordinances. ................................................ 31

Table 7. Road sanding emission reductions.................................................................................. 40

Table 8. Emissions reductions due to the woodstove change outs. .............................................. 41

Table 9. Motor vehicle emission budget for the Idaho side of the Cache Valley nonattainment 

area. ................................................................................................................................ 47

Table 10. Crosswalk between the regulatory requirements and how the requirement is met 

within this State Implementation Plan............................................................................ 48

List of Figures

Figure 1. Location map showing the Cache Valley and the boundaries for Franklin County, 

Idaho, and Cache County, Utah........................................................................................ 3

Figure 2. Cache Valley nonattainment area showing the nonattainment area boundary in Idaho 

and Utah............................................................................................................................ 5

Figure 3. January 2004 temperature contour map with PM2.5 concentration levels (yellow line) 

and 1997 PM2.5 National Ambient Air Quality Standards (green line) (Martin 2006). ... 7

Figure 4. Average temperature profiles in Cache Valley during January 1–17, 2004 

(Martin 2006).................................................................................................................... 8

Figure 5. The 98th percentile of Franklin County 24-hour PM2.5 values. .................................... 11

Figure 6. Franklin County annual average PM2.5 values............................................................... 11

Figure 7. The 98th percentile of Cache County 24-hour PM2.5 values......................................... 12

Figure 8. Cache County annual average PM2.5 values.................................................................. 12
Cache Valley Idaho PM2.5 Nonattainment Area SIP

vi

Figure 9. Franklin County daily mean PM2.5 concentrations from January 1, 2008 to 

December 31, 2008......................................................................................................... 14

Figure 10. Cache County daily mean PM2.5 concentrations from January 1, 2008 to 

December 31, 2008......................................................................................................... 14

Figure 11. Franklin County daily mean PM2.5 concentrations from January 1, 2009 to 

December 31, 2009......................................................................................................... 15

Figure 12. Cache County daily mean PM2.5 concentrations from January 1, 2009 to 

December 31, 2009......................................................................................................... 15

Figure 13. Franklin County daily mean PM2.5 concentrations from January 1, 2010 to 

December 31, 2010......................................................................................................... 16

Figure 14. Cache County daily mean PM2.5 concentrations from January 1, 2010 to 

December 31, 2010......................................................................................................... 16

Figure 15. Correlation between the Franklin beta attenuation monitor and the Logan Filter 

Dynamic Measurement System monitor for winter 2011–2012. ................................... 17

Figure 16. Franklin versus Logan PM2.5 concentrations............................................................... 18

Figure 17. Composite wintertime PM2.5 speciation profile during an inversion period. .............. 20

Figure 18. Composite wintertime PM2.5 speciation profile during a clear period. ....................... 20

Figure 19. Franklin County running 24-hour PM2.5 design values. .............................................. 21

Figure 20. Cache County running 24-hour PM2.5 design values................................................... 22

Figure 21. Nitrogen oxide emission totals sorted by source type and county. ............................. 24

Figure 22. Volatile organic compound emission totals sorted by source type and county........... 25

Figure 23. Ammonia emission totals sorted by source type and county. ..................................... 25

Figure 24. Sulfur dioxide emission totals sorted by source type and county. .............................. 26

Figure 25. PM2.5 emission totals sorted by source type and county. ............................................ 26

Figure 26. PM2.5 emissions from all source types (area, point, and mobile) for the entire 

nonattainment area including Utah and Idaho emissions. .............................................. 27

Figure 27. PM2.5 emissions from all source types (area, point, and mobile) for the Utah side of 

the nonattainment area (Cache County). ........................................................................ 28

Figure 28. PM2.5 emissions from all source types (area, point, and mobile) for the Idaho side 

of the nonattainment area (Franklin County). ................................................................ 29

Figure 29. Cache Valley photochemical modeling domain.......................................................... 32

Figure 30. Twenty-four-hour PM2.5 time series (Logan). Observed PM2.5 (blue line), modeled 

with vertical advection activated (red line). ................................................................... 34

Figure 31. Composition of model-simulated average 24-hour PM2.5 concentrations averaged 

over days when a modeled day had 24-hour concentrations >25 micrograms per 

cubic meter at the Logan monitor................................................................................... 35

Figure 32. Model results for the Cache Valley nonattainment area, Logan monitor.................... 37
Cache Valley Idaho PM2.5 Nonattainment Area SIP

vii

Acronyms, Abbreviations, and Symbols

oF degrees Fahrenheit

μg/m3 micrograms per cubic meter

AQI Air Quality Index

AQS Air Quality System

asl above sea level

BAM beta attenuation monitor

CAA Clean Air Act

CCV closed crankcase ventilation

CFR Code of Federal Regulations

CMAQ community multiscale air quality model

CO carbon monoxide

CVNAA Cache Valley Nonattainment Area

DERP Diesel Emission Reduction Program

DOC diesel oxidation catalyst

DSL deep stable layers

EPA United States Environmental Protection Agency

FDMS Filter Dynamic Measurement System

FEM federal equivalent method

FR Federal Register

FRM federal reference method

IDAPA Idaho Administrative Procedures Act

IDEQ Idaho Department of Environmental Quality

IMPROVE Interagency Monitors of Protected Visual Environments

ITD Idaho Transportation Department

km kilometers

LRTP Long Range Transportation Plan
Cache Valley Idaho PM2.5 Nonattainment Area SIP

viii

MATS Model Attainment Test Software

MOVES motor vehicle emission simulator

MPO Metropolitan Planning Organization

msl mean sea level

MVEB motor vehicle emissions budget

NAA nonattainment area

NAAQS National Ambient Air Quality Standards

NH3 ammonia

NOx nitrogen oxides

PLSS Public Land Survey System

PM2.5 particulate matter under 2.5 microns in size

ppm parts per million

RACM reasonably available control methods

RACT reasonably available control technology

RFP reasonable further progress

RWC residential wood combustion

SIP State Implementation Plan

SO2 sulfur dioxide

SPM special purpose monitor

STN Speciation Trends Network

TCM transportation control measure

TEOM tapered element oscillating microbalance

TIP Transportation Improvement Program

tpd tons per day

TPY tons per year

UDAQ Utah Division of Air Quality 

VOC volatile organic compounds
Cache Valley Idaho PM2.5 Nonattainment Area SIP

ix

VSCC very sharp cut cyclone

WRF weather research and forecasting

WRF-ARW weather research and forecasting advanced research
Cache Valley Idaho PM2.5 Nonattainment Area SIP

x

This page intentionally left blank for correct double-sided printing.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

xi

Executive Summary

Air pollution in the intermountain west is becoming an increasing problem because of two key 

factors. First, increasing populations in these areas increase the number of pollution emission 

sources such as vehicles. Secondly, air sheds in the intermountain west region consist of high 

altitude valleys confined by mountains often resulting in climatic wintertime air stagnation and 

inversions that limit the ability of air pollution to disperse. These two components increase the 

likelihood of the occurrence of significant air pollution exposures to population centers if left 

unmitigated.

A major component of air pollution in the intermountain west that may cause significant human 

health issues is the level of particulate matter within the affected air. More specifically, it is the 

size of the particulate matter that is directly linked to their potential for causing health problems. 

Fine particulate matter with a diameter less than or equal to 2.5 micrometers (1/30th the width of 

a human hair) is referred to as particulate matter 2.5 (PM2.5). These small particles pose the 

greatest risk to human health because they can lodge deep into the lungs, and some particles may 

get into the bloodstream, affecting heart function. Because of this relationship, PM2.5 exposure is 

linked to a variety of health problems including increased respiratory stress (irritation of airways, 

coughing, or difficulty breathing); decreased lung function; aggravated asthma; development of 

chronic bronchitis; irregular heartbeat; nonfatal heart attacks; and premature death in people with 

heart or lung disease.

In the intermountain west, the major direct (primary) sources of PM2.5 are vehicle emissions, 

wood combustion, and ambient dust created from road maintenance and vehicular use. 

Secondary sources contribute to chemical reactions of gases in the atmosphere, which include 

sulfur dioxide, nitrogen oxides, volatile organic compounds, and ammonia. In addition to vehicle 

emissions, secondary emission sources also include agricultural emissions, commercial solvent

use, nonroad mobile sources (planes, trains, construction equipment, all-terrain vehicles, and 

small engines), and commercial cooking emissions.

The Environmental Protection Agency (EPA) promulgated the current National Ambient Air 

Quality Standards (NAAQS) for PM2.5 in 2006 to protect human health. These standards require 

that concentrations of PM2.5 in the air not exceed 35 micrograms per cubic meter (μg/m3) on a 

daily basis and 15 μg/m3on an annual basis. Within 12 months of the 2006 promulgation, states 

were required to submit a statewide finding that defined which areas of a state attained the 

standard, which areas did not attain the standard, and which areas were unclassifiable. Based on 

monitoring data, the Cache Valley, spanning Utah and Idaho, did not meet the 35 μg/m3standard 

and was designated a nonattainment area for the 24-hour PM2.5 NAAQS in 2011. The major 

emission sources contributing to the nonattainment status designation in the Cache Valley 

include the following:

 Mobile dust emissions

 Vehicle emissions

 Woodstove emissions

The Clean Air Act (CAA) further requires states to submit an air quality improvement plan,

known as a State Implementation Plan (SIP), to EPA for concurrence when an area has been 

designated nonattainment. The SIP must demonstrate that sufficient measures have been put into 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

xii

place to return the area to attainment and to maintain that attainment into the future. Since the 

Logan, UT-ID (Cache Valley) nonattainment area spans two states and two EPA regions, both 

Utah and Idaho are required to develop a SIP. Utah, EPA Region 8 (Denver), and Idaho, EPA 

Region 10 (Seattle), have cooperated throughout this SIP development process. In addition, there 

has been extensive public involvement in the selection of reasonable control strategies to bring 

the Cache Valley into attainment.

This document contains the necessary evidence, analysis, and Idaho control strategies (in 

conjunction with the Utah SIP) to demonstrate that the area will attain the NAAQS by 

January 1, 2015. Key elements of the Idaho control strategies and contingency measures include

the following:

 Reduce the amount of wintertime road sanding material.

 Implement residential woodstove combustion control ordinances by the cities and 

Franklin County to control burning during air quality alerts.

 Institute the Idaho Department of Environmental Quality’s (IDEQ’s) Air Quality Index 

program for the Idaho side of the Cache Valley as an education and information tool for 

the public.

 Provide incentives to replace outdated woodstoves with energy and emission efficient 

EPA-certified woodstoves.

 Continued application of Idaho’s industrial air permitting program.

 Continued application of IDEQ’s diesel emission reduction program.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

1

1 Introduction

The Idaho Department of Environmental Quality (IDEQ) is required to submit a particulate 

matter 2.5 (PM2.5) State Implementation Plan (SIP) for the Idaho side of the Cache Valley 

nonattainment area (CVNAA) to the United States Environmental Protection Agency (EPA). The 

purpose of the SIP is to show that the area will attain the 24-hour standard for airborne 

particulate matter less than or equal to 2.5 micrometers in aerodynamic diameter (PM2.5) by the 

attainment date of January 1, 2015. This document includes all of the necessary components to 

demonstrate timely attainment within the Cache Valley airshed.

1.1 Background

In September 2006, EPA revised the National Ambient Air Quality Standards (NAAQS) for 

PM2.5. While the annual standard remained unchanged at 15 micrograms per cubic meter 

(μg/m3), the 24‐hour standard was lowered from 65 μg/m3to 35 μg/m3. Fine particles consist of 

a complex mixture of extremely small particles and liquid droplets. Exposure to fine particles has 

been linked to a variety of health effects and is known to cause or contribute to respiratory

disease, asthma attacks, and heart conditions. An area in violation of the PM2.5 standard (based 

on the most recent 3 years of federal reference method [FRM] monitoring data) is designated as a 

nonattainment area (NAA). 

PM2.5, or fine particulate matter, is referred to as primary if it is directly emitted into the air as a 

solid or liquid particle and its chemical form is stable. PM2.5 that is formed by chemical reactions 

of gases (termed precursors) in the atmosphere is referred to as secondary PM2.5. These reactions 

form condensable matter that either forms new particles or condense onto other particles in the 

air.

This SIP addresses the PM2.5 NAA, designated by EPA as the Logan, UT–ID NAA, and referred 

to here as Cache Valley or CVNAA (74 FR 58688). Straddling the border between Utah and 

Idaho, this NAA presents unique challenges with respect to topographical features and

jurisdictional authority issues—an NAA that spans two states (Utah–Idaho) and two EPA regions 

(Region 8–Region 10).

Cache Valley experiences air stagnation events in the wintertime. During these periods, the 

stable layer above the ground is much deeper than a typical nocturnal inversion. Cold air is 

trapped in the basins, and the air mass stabilizes as high pressure aloft overtakes the region. 

Under such circumstances, a prolonged strong inversion layer (or layers) limits vertical mixing, 

trapping local pollutants in a thin layer against the valley floor. During episodes such as this, 

emissions increase above typical winter days because more home heating occurs due to the cold 

temperatures. The low sun angle, short length of the days during winter months, and strong 

likelihood of snow cover to reflect the solar radiation are all factors that limit daytime surface 

heating and aggravate the situation. As a result, some inversions may not break for many days. 

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

for PM2.5. In other parts of the year PM2.5 concentrations are generally low, and even when 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

2

averaged with the high peaks occurring during the winter, are well within the annual health 

standard for PM2.5.

1.2 Nonattainment Area Description

The following subsections offer a brief glimpse of the CVNAA to orient the reader to the area. 

Descriptions are given for the area’s climatology, topography, and meteorology. The legal 

descriptions provided for the CVNAA demonstrate the complexity of the airshed spanning two 

states and the need to cooperatively address the PM2.5 air quality issues. 

1.2.1 Nonattainment Area Location and Topography

The Cache Valley PM2.5 NAA lies within Cache County, Utah, (northern Utah) and Franklin 

County, Idaho (southeastern Idaho) (Figure 1). The CVNAA encompasses a bowl-shaped, 

topographically isolated valley measuring approximately 37.3 miles north to south and 

12.4 miles east to west. The Wellsville Mountains (with altitudes up to 9,900 feet above mean 

sea level [MSL]) lie to the west and on the east lie the Bear River Range (with altitudes up to 

8,300 feet MSL); both are northern branches of the Wasatch Range. These mountain ranges are 

approximately 3,000 to 5,000 feet above the Cache Valley floor. The Wellsville Mountains, Bear 

River Range, and northern Wasatch Range converge in southern Cache County to form a 

topographical barrier between Cache Valley and other adjacent counties. As with the southern 

area of Cache Valley, the mountain ranges of the northern area of Cache Valley, bordering the 

eastern and western portions of Franklin County, meteorologically and topographically, isolate 

Franklin County from other counties. The inversions that produce the high concentrations of 

PM2.5 in the CVNAA are only confined to areas below the elevated, mountainous terrain areas of 

both Cache and Franklin Counties.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

3

Figure 1. Location map showing the Cache Valley and the boundaries for Franklin County, Idaho,

and Cache County, Utah.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

4

1.2.1.1 Franklin County, Idaho, Legal Description

The Idaho portion of the CVNAA includes those areas of Franklin County bounded as follows 

(Figure 2): 

Begin in the bottom left corner (southwest) of the nonattainment area boundary, 

southwest corner of the Public Land Survey System (PLSS)-Boise Meridian, Township 

16 South, Range 37 East, Section 25. The boundary then proceeds north to the northwest 

corner of Township 15 South, Range 37 East, Section 25; then the boundary proceeds 

west to the southeast corner of Township 15 South, Range 38 East, Section 19; then north 

to the Franklin County boundary at the northwest corner of Township 13 South, Range 

38 East, Section 20. From this point the boundary proceeds east 3.5 sections along the 

northern border of the county boundary where it then turns south 2 sections, and then 

proceeds east 5 more sections, and then north 2 sections more. At this point, the boundary 

leaves the county boundary and proceeds east at the southeast corner of Township 13 

South, Range 39 East, Section 14; then the boundary heads north 2 sections to northwest 

corner of Township 13 South, Range 39 East, Section 12; then the boundary proceeds 

east 2 sections to the northeast corner of Township 13 South, Range 40 East, Section 7. 

The boundary then proceeds south 2 sections to the northwest corner of Township 13 

South, Range 40 East, Section 20; the boundary then proceeds east 6 sections to the 

northeast corner of Township 13 South, Range 41 East, Section 19. The boundary then 

proceeds south 20 sections to the southeast corner of Township 16 South, Range 41 East, 

Section 30. Finally, the boundary is completed as it proceeds west 20 sections along the 

southern Idaho state boundary to the southwest corner of the Township 16 South, Range 

37 East, Section 25.

1.2.1.2 Cache County, Utah, Legal Description

The Utah portion of the CVNAA includes the following townships, or portions thereof located in 

Cache County (Figure 2), which forms the eastern boundary of the NAA, and then proceeds west 

to include all areas over to the western boundary of Cache County:

Township 15 North Range 1 East

Township 14 North Range 1 East

Township 13 North Range 1 East

Township 12 North Range 1 East

Township 11 North Range 1 East

Township 10 North Range 1 East

Township 9 North Range 1 East (portion located in Cache County)
Cache Valley Idaho PM2.5 Nonattainment Area SIP

5

Figure 2. Cache Valley nonattainment area showing the nonattainment area boundary in Idaho and 

Utah.

1.2.2 Cache Valley Secondary Aerosol Precursors

The majority of ambient PM2.5 collected during a typical cold‐air pool episode of elevated 

concentration is secondary particulate matter, born of precursor emissions. The main precursor 

gases associated with fine particulate matter are discussed in EPA’s “Clean Air Particulate 

Implementation Rule” (72 FR 20586). In accordance with the rule, this SIP specifically 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

6

addresses emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds 

(VOC), and ammonia (NH3). 

1.2.3 Climatology and Meteorology

The weather in Franklin County can be described as a mild northern climate. Summer 

temperatures average in the high sixties, with days that can exceed 100 degrees Fahrenheit (°F). 

These hot spells are usually short in duration, or the afternoons are punctuated by clouds and a 

brief rain shower. Winter temperatures average in the low twenties. Table 1 illustrates these 

temperature changes.

Table 1. Average weather in Franklin County, Idaho.

Month Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

Average 

temp. (oF)

21.3 26.4 36.6 45.0 53.5 61.9 69.4 68.2 58.6 46.9 33.6 23.3

High temp.

(oF)

30.3 36.6 47.7 57.9 67.5 78.0 87.1 86.1 76.1 62.5 44.6 32.8

Low temp 

(oF)

12.2 16.2 25.5 32.1 39.5 45.8 51.6 50.3 41.1 31.3 22.6 13.8

Precipitation 

(inches)

1.4 1.3 1.5 1.4 2.1 1.2 0.9 1.0 1.3 1.6 1.2 1.3

Note: degrees Fahrenheit (°F).

The mountains surrounding the Cache Valley rise to 8,356 feet above sea level (asl) to the west 

and 9,900 feet asl to the east. The isolated valley floor ranges from 4,500 to 5,200 feet asl. The 

mountains trap pollutants in the valley when dispersion conditions are poor. 

Excluding wind‐blown dust events, wildland fires, and holiday-related fireworks, elevated PM2.5 

in southern Idaho and Utah occurs when stagnant cold-air pools develop during the winter 

season. The weather conditions that lead to the formation of cold-air pools in the Cache Valley 

are synoptic scale (> 600 miles) 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 wintertime cold-air pool episode, dispersion is poor 

due to the very stable air mass, and concentrations of primary and secondary PM2.5 elevate

because the pollutants are trapped in the cold-air pool. Episodes may last from a few days to tens 

of days until meteorological conditions change to once again allow for good mixing.

A study of deep stable layers (DSL) in western air basins (Wolyn and McKee 1989) revealed that 

DSL can cause the stagnation of cold air in basins. In other words, only light winds occur at the 

surface, even if moderately strong winds aloft are present, and restriction of the growth of 

daytime convective boundary layers occurs. IDEQ analyzed DSL in the Treasure Valley in 

southwestern Idaho and found high correlation between DSL and particulate levels in the area. 

Salt Lake City was found to have a high frequency of DSL occurrence, averaging about 12 days 

per year in the period from 1959–1983 (Wolyn and McKee 1989). The Cache Valley is most 

likely under the same stagnation conditions as the Salt Lake City area during most of these 

periods. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

7

Figure 3, which is from a Utah State University inversion study (Martin 2006), provides an 

excellent example of correlation between the PM2.5 concentration levels and the evolution of the 

stable layer over the Cache Valley. In Figure 3, blue represents cold air and red indicates warmer 

air. The solid yellow line represents the ambient PM2.5 concentration as measured at the Logan 

monitoring site. The dotted green line represents the 1997 PM2.5 NAAQS. From January 9 

through January 17, 2004, the cold-air pool strengthened and deepened each day, eventually 

reaching a depth of about 5,500 feet asl on January 15 when the PM2.5 concentrations peaked. 

The PM2.5 concentration levels rose steadily as trapped pollutants accumulated from each day to 

the next.

Figure 3. January 2004 temperature contour map with PM2.5 concentration levels (yellow line) and 

1997 PM2.5 National Ambient Air Quality Standards (green line) (Martin 2006).

Under this type of stagnation condition, the pollutants may quickly build, especially in areas like 

the Cache Valley where airflow is greatly restricted by terrain. Figure 4, also taken from the Utah 

State University inversion study (Martin 2006), provides an example of inverted temperature 

profiles in the Cache Valley during the January 2004 extended stagnation episode. During the 

period from January 1 to January 17, 2004, as shown in the figure, a strong inversion about 

1,500 feet thick persistently occupied the area. The record high PM2.5 concentration of 

132.7 μg/m3 was observed at Logan on January 15, 2004. The right-slanted temperature profiles 

indicate strong temperature inversion from the ground to 6,300 feet asl during the night (the

green dotted line represents the adiabatic lapse rate, typical of profiles that occur when 

temperature inversion is not present). The strong, deep, stable layer persisted through the entire 

period, even in the afternoon hours (noon and 3 p.m.) when the base of the inversion rose to an 

average 5,500 feet asl trapping pollutants below this elevation. The average 24-hour PM2.5

concentration observed at a Franklin monitor, placed for the study, during this same period was 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

8

39.0 μg/m3, with the highest 24-hour concentration of 82.6 μg/m3occurring on January 17, 2005. 

Thus, it appears that the low afternoon mixing height during stagnation episodes (at 

approximately 5,500 feet asl) is the controlling factor in accumulating pollutants from day to

day.

Figure 4. Average temperature profiles in Cache Valley during January 1–17, 2004 (Martin 2006).

2 Air Quality

The basis for determining the air quality of any area is accurate and adequate monitoring data. 

Data collected from an area’s monitoring network are used to establish air quality trends, to 

determine if and when air quality standards are exceeded, and to aid in developing appropriate 

air quality control strategies when standards are exceeded. Likewise, because local meteorology 

plays an important role in the area’s air quality, high-quality meteorological data are extremely 

important in conducting modeling studies and interpreting the results. 

2.1 Monitoring Sites 

PM2.5 ambient air quality monitoring in the Cache Valley has been conducted since 2005 on the 

Idaho side of the CVNAA and 2000 on the Utah side of the CVNAA. The monitoring is 

conducted to characterize problems and support air quality improvement planning and analysis. 

Analysis of the Cache Valley shows that topographical features and wintertime meteorology 

limit the transport of pollutants into or out of the area. Pollutants emitted within the Cache 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

9

Valley (Idaho and Utah) remain trapped. The Cache Valley experiences inversions that build 

from day to day when strong high-pressure systems are present in the region. Table 2 details the 

air monitoring locations across the Cache Valley.

Table 2. Cache Valley air quality monitoring site locations.

State Monitor Address EPA-AIRS Parameters Monitored

Idaho Franklin East 4800 South 

Road

160410001 PM2.5, AQI

Utah Logan–L4 125 W. Center 490050004 PM2.5, PM10, O3, NO2, SO2, AQI

Notes: United States Environmental Protection Agency (EPA); aerometric information retrieval system 

(AIRS); particulate matter (PM); Air Quality Index (AQI); ozone (O3); nitrogen dioxide (NO2); sulfur 

dioxide (SO2)

The state and local air monitoring stations air quality data are collected from federal reference 

method (FRM) or federal equivalent method (FEM) monitors that are sited and operated in 

accordance with 40 CFR Part 58. These data are stored in the EPA Air Quality System (AQS).

Procedures for using the data to determine whether a violation has occurred are codified in 

40 CFR 50, Appendix N. Data collected at both monitoring sites are used for Air Quality Index 

(AQI) forecasting. Table 3 details the air quality monitors used in the Cache Valley and the 

measurement frequency. 

Table 3. Specific Cache Valley air quality monitors and measurement frequency.

State Monitor Pollutant 

Monitored

Dates in 

Operation

Monitoring 

Frequency Instrument

Idaho Franklin PM2.5–FRM 2005–present Every sixth day 

(1/6)

R&P Model 2025 Sequential 

with VSCC

Idaho Franklin PM2.5–SPM 2010–present Continuous Met One beta gauge (BAM)

Utah Logan PM2.5–FRM 2000–present Daily Manual gravimetric

Utah Logan PM2.5–FEM 2004–present Continuous Instrumental TEOM FDMS

Notes: particulate matter (PM); federal reference method (FRM); very sharp cut cyclone (VSCC); special purpose 

monitor (SPM); beta attenuation monitor (BAM); federal equivalent method (FEM); tapered element oscillating 

microbalance (TEOM); Filter Dynamic Measurement System (FDMS).

2.1.1 Idaho Monitors

The following are brief descriptions of the PM2.5 monitors used by IDEQ in the CVNAA. The 

Partisol Plus 2025 Sequential Ambient Particulate Sampler is an FRM, while the beta attenuation 

monitor (BAM) is listed as a special purpose monitor (SPM). 

2.1.1.1 Partisol Plus 2025 Sampler

The Partisol Plus 2025 Sequential Ambient Particulate Sampler is an FRM sampler for PM2.5. 

The unit measures PM2.5 on 47-millimeter filter cassettes contained in removable magazine

cartridges. The Partisol Plus 2025 is a performance-based stand-alone unit that meets EPA’s

guidelines for manual air samplers. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

10

2.1.1.2 Beta Attenuation Monitor-1020

The BAM 1020 automatically measures and records airborne particulate concentrations levels 

(μg/m3) using the principle of beta ray attenuation. The BAM 1020 (properly equipped) can be 

an FEM, and data collected by the BAM 1020 are suitable for NAAQS compliance monitoring. 

The BAM 1020 is a continuous monitor, providing hourly-averaged data, which makes it useful 

for air quality forecasting, air quality index reporting, and NAAQS compliance determinations. 

2.2 Air Quality Data

PM2.5 standards are based on averaging air quality measurements both annually and on a 24-hour 

basis. The annual standard is designed to provide an appropriate level of protection from longterm exposures to PM2.5. The annual standard for PM2.5 is met whenever the 3-year average of 

the annual mean PM2.5 concentrations for designated monitoring sites in an area is less than or 

equal to 15 μg/m3. The 24-hour standard is designed to provide an appropriate level of protection 

from short-term exposures to PM2.5. The 24-hour standard for PM2.5 is met whenever the 3-year 

average of the annual 98th percentile of values at designated monitoring sites in an area is less 

than or equal to 35 μg/m3. Sampling may not occur every day, so the number of days with 

measured values above the standard must be adjusted to account for days that were not sampled. 

The 98th percentile is the daily value out of a year of PM2.5 monitoring data below which 98% of 

all daily values fall. IDEQ submits all air quality data to EPA, through the AQS. 

The analysis of the PM2.5 data for the monitoring sites across the valley shows violations of the 

24-hour PM2.5 NAAQS on both the Utah and the Idaho sides of the CVNAA. Both the Utah and 

Idaho sides of the CVNAA attain the annual PM2.5 standard. 

2.2.1 Idaho Summary

Figure 5 details the 98th percentile monitoring data for the Franklin County air quality monitor.

The 2010 data should not be considered representative of the area; due to upgrades to the 

Franklin sewage lagoons, the area was without power for a considerable portion of the year. 

During 2010, none of the quarters for data collection met EPA criteria for data completeness.

However, for the 24-hour standard, years with less than complete data are considered valid if the 

resulting 98th percentile for that year is greater than the standard.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

11

Figure 5. The 98th percentile of Franklin County 24-hour PM2.5 values.

Figure 6 shows the annual average PM2.5 monitoring data for the Franklin County air quality 

monitor. From 2004 through 2011, Franklin County has met the annual NAAQS.

Figure 6. Franklin County annual average PM2.5 values.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

12

2.2.2 Utah Summary

Figure 7 details the 98th percentile monitoring data for the Cache County (Logan) air quality 

monitor, and Figure 8 presents the annual air quality data. From 2005 to 2011, the annual 

standard has been attained.

Figure 7. The 98th percentile of Cache County 24-hour PM2.5 values.

Figure 8. Cache County annual average PM2.5 values.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

13

2.3 Meteorological Data during High PM2.5 Events Summary

Elevated 24-hour PM2.5 concentrations in the Cache Valley have been observed during the 

wintertime, typically from November through February, throughout the airshed. Analysis of the 

PM2.5 air quality data suggests local meteorological conditions often played a significant role 

during these episodes by providing adverse dispersion conditions or favoring the formation of 

secondary aerosols. During these periods, the stable layer above the ground is much deeper than 

a typical nocturnal inversion. Cold air is trapped in the basins, and the air mass stabilizes as high 

pressure aloft overtakes the region. Under such circumstances, a prolonged strong inversion layer 

(or layers) limits vertical mixing, trapping local pollutants in a thin layer against the valley floor. 

The low sun angle, short length of the days during winter months, and strong likelihood of snow 

cover to reflect the solar radiation are all factors that limit daytime surface heating and aggravate 

the situation. As a result, some inversions may not break for many days. For additional 

information pertaining to the meteorological conditions, see Section 1.2.3 Climatology and 

Meteorology.

Figure 9 through Figure 14 illustrate the seasonal nature of the air quality issues in the Cache 

Valley. These figures also show that, with very few exceptions, the concentrations measured in 

Franklin County are lower than those measured in Cache County. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

14

Figure 9. Franklin County daily mean PM2.5 concentrations from January 1, 2008 to 

December 31, 2008.

Figure 10. Cache County daily mean PM2.5 concentrations from January 1, 2008 to 

December 31, 2008.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

15

Figure 11. Franklin County daily mean PM2.5 concentrations from January 1, 2009 to 

December 31, 2009.

Figure 12. Cache County daily mean PM2.5 concentrations from January 1, 2009 to 

December 31, 2009.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

16

Figure 13. Franklin County daily mean PM2.5 concentrations from January 1, 2010 to 

December 31, 2010.

Figure 14. Cache County daily mean PM2.5 concentrations from January 1, 2010 to 

December 31, 2010.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

17

2.4 Correlation between Utah and Idaho Monitors

Figure 15 shows the correlation between the Logan, Utah, and the Franklin, Idaho, monitors. 

These monitors are used to forecast the AQI for both sides of the Cache Valley. The correlation 

coefficient, R

2

, of 0.9002 shows good correlation between the two continuous monitors during 

the winter months.

The data in Figure 16 show that both of the real-time monitors over-predict the actual PM2.5 

concentrations in the Cache Valley. This over-prediction is more significant during warm 

weather (summer months) than during the cold weather (winter months).

Figure 15. Correlation between the Franklin beta attenuation monitor and the Logan Filter 

Dynamic Measurement System monitor for winter 2011–2012.

y = 0.9767x - 0.5798

R2 = 0.9002

0

5

10

15

20

25

0 5 10 15 20 25

FDMS

BAM

Frk BAM vs Logan FMDS Winter 2011-2012
Cache Valley Idaho PM2.5 Nonattainment Area SIP

18

Figure 16. Franklin versus Logan PM2.5 concentrations.

0

5

10

15

20

25

30

35

40

45

50

Micrograms per cubic meter

Date

Franklin vs Logan PM 2.5 Particulate Matter

Franklin BAM

Logan FMDS

Franklin FEM
Cache Valley Idaho PM2.5 Nonattainment Area SIP

19

2.5 Special Studies

To understand the contributions of various types of emissions sources and secondary aerosol 

formation to the total PM2.5 concentrations in the Cache Valley, the following special studies 

have been conducted:

 PM2.5 saturation studies–Utah State University

 Speciated monitoring data—Utah Division of Air Quality (UDAQ)

2.5.1 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 (Appendix A). In addition to 

the permanent UDAQ air quality monitoring site in Logan, 17 sites measuring PM2.5 

concentrations were established in Cache Valley. Measurements of PM2.5 concentrations were 

made every 6 days from November 2003 to February 2004. Several temperature inversions 

developed during the course of the study with PM2.5 concentrations in Logan ranging from 

3 μg/m3to 128 μg/m3. In general, the study found that PM2.5 concentrations were homogenous 

throughout the Cache Valley. 

On days with PM2.5 concentrations < 65 μg/m3, 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/m3. On these high PM2.5 days (> 65 μg/m3), 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 2003–2004.

2.5.2 Fine Particle Pollution Composition—Speciated Monitoring Data

UDAQ 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 station PM2.5 speciation sites that operate on an every‐sixth‐day sampling 

schedule. 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.

Data from the STN show the importance of volatile secondary particulates during the colder

months. 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. While none of the speciation sites were in the Cache Valley, data from these sites 

were used by UDAQ in their overall model validation process. Figure 17 and Figure 18 show the 

contribution of the identified compounds from the speciation sampler during a winter 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

20

atmospheric inversion period (Figure 17) and during a clear winter period (Figure 18) at the 

Hawthorne (HW) site.

Figure 17. Composite wintertime PM2.5 speciation profile during an inversion period.

Figure 18. Composite wintertime PM2.5 speciation profile during a clear period.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

21

2.6 Design Value Determination—24-Hour Standard

Design values are the metrics that are compared to the NAAQS to determine compliance. For the 

24-hour standard, the design value is the 3-year average of annual 98th percentile, 24-hour 

average values. The 24-hour PM2.5 NAAQS is met when the design value is less than or equal to 

35 μg/m3. Years with less than complete data, like 2010, are considered valid if the resulting 

98th percentile for that year is greater than the standard. The 3-year average, 24-hour PM2.5 

design values for the Franklin County monitor and Cache County monitor are shown in Figure 

19 and Figure 20, respectively. 

Figure 19. Franklin County running 24-hour PM2.5 design values.

0

10

20

30

40

50

60

2004-2006 2005-2007 2006-2008 2007-2009 2008-2010 2009-2011

24-hr Design Value

(micrograms per cubic meter) 

Years

Franklin County
Cache Valley Idaho PM2.5 Nonattainment Area SIP

22

Figure 20. Cache County running 24-hour PM2.5 design values.

EPA recommends an average of three such 3-year averages that straddle the baseline inventory

be used to calculate the monitored baseline value. The year 2008 is represented by the baseline 

inventory. Therefore, the 3-year average of 98th percentile values collected from 2006–2008 

would be averaged together with the 3-year averages from 2007–2009 and 2008–2010 to arrive 

at the site-specific monitored baseline design value.

For this SIP, the baseline design value concentration for the Utah side of the CVNAA is 

39.5 μg/m3and is 34.7 μg/m3for the Idaho side of the CVNAA. The SIP demonstrations will be 

based on the Utah design value because it is the highest in the NAA. 

3 Emissions Inventory

A detailed emissions inventory using the best information available was prepared for the Cache 

Valley airshed to assess direct PM2.5 emissions as well as emissions of precursors to secondary 

PM2.5 formation. The inventory addresses industrial (or point) sources, on-road mobile sources

(cars, trucks, and buses), nonroad mobile sources (planes, trains, boats, off-road vehicles, 

construction equipment, agricultural equipment, generators, lawn care equipment, and other 

assorted equipment), and area sources (sources of emissions not captured in the previous 

categories). Emissions inventory information pertinent to Franklin County is summarized in this 

section. Additional details concerning the technical analysis, including links to UDAQ 

documents, for this SIP can be found in Appendix B.

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

three distinct airsheds belonging to three distinct PM2.5 NAAs; CVNAA, central Wasatch Front 

(Salt Lake City, Utah, NAA), and the southern Wasatch Front (Provo, Utah, NAA).

0

10

20

30

40

50

60

70

2004-2006 2005-2007 2006-2008 2007-2009 2008-2010 2009-2011

24-hour Design Value

(micrograms per cubic meter)

Years

Cache County
Cache Valley Idaho PM2.5 Nonattainment Area SIP

23

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 nonexistent in the 

Cache Valley. These emissions sources are situated along the Wasatch Front, and primarily 

influence the Salt Lake City NAA. Conversely, most of the agricultural emissions are located in 

Cache Valley.

Various time horizons are significant to developing the emissions inventories for this SIP. The 

first is the emissions inventory base year. This year is selected to represent the time(s) when 

exceedances were measured and will serve as the basis for modeling and control strategy 

evaluation. The episodes studied as part of this SIP occurred in 2007, 2008, 2009, and 2010. 

Another important horizon is the attainment date.

3.1 Seasonal Adjustment

Prior to use in the air quality model, the emissions are preprocessed to account for seasonality

because all attainment modeling reflects the winter stagnation episodes when secondary PM2.5 

formation dominates. 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 here, unless 

otherwise noted, reflects the temporal adjustments made prior to air quality modeling. These 

adjustments make more appropriate use of the inventories for such purposes as correlating

measured PM2.5 concentrations, evaluating control strategies, establishing budgets for 

transportation conformity, and tracking rates of progress. 

3.2 2008 Baseline Emissions Inventory 

The basis for this SIP was the 2008 triannual National Emissions Inventory (NEI). This 

inventory represented, at the time it was selected for use, the most recent comprehensive 

inventory compiled by both Idaho and Utah. In addition to the large major point sources that are 

required to report emissions every year, the triannual inventories consider emissions from many 

more, smaller point sources. These inventories were 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 in section 3, the 2008 inventory was either back‐

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

3.2.1 On-Road Mobile Emissions Inventory

Idaho’s 2008 NEI included on-road mobile emissions estimated using EPA’s MOBILE6.2 and 

paved road dust emissions using an estimation method recommended by the AP-42 Air Pollutant 

Emission Factors (EPA 1996). Since the completion of that inventory, EPA released the Motor 

Vehicle Emission Simulator (MOVES) model and required that the model be used for SIPs and 

conformity analyses by March 2012. As a result, IDEQ developed new on-road emissions 

estimates for NOx, VOCs, and exhaust, brake wear, and tire wear direct particulate emissions, 

using the MOVES2010a model for Franklin County and the other 10 Idaho counties within or 

partly within the UDAQ’s photochemical modeling domain. This effort was conducted 

independently of the UDAQ MOVES modeling effort, using detailed traffic information from 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

24

the Idaho Transportation Department (ITD) automatic traffic recorders, and detailed Idaho 

weather conditions for each Idaho county. Nevertheless, the on-road emission estimates for 

Idaho counties were in close agreement with those UDAQ developed for Utah counties, when 

adjusted for population. The MOVES modeling is described in Appendix C.

In addition to the revised vehicle emissions, EPA released an improved estimation procedure for 

paved road dust emissions in January 2011. This procedure provides the capability of more 

explicitly modeling wintertime episodic road dust emissions that reflect more realistic road dust 

levels following winter storms when sand is applied and the dust suppression effects of 

precipitation (EPA 2011). Since these enhancements are critical to obtaining realistic road dust 

estimates during winter episodes, consistent with UDAQ emission estimation methods, IDEQ 

developed new paved road dust estimates for Franklin County and the other Idaho counties in the 

photochemical modeling domain, using the January 2011 EPA methodology. Paved road dust 

emissions calculations are described fully in Appendix C.

3.2.2 Emissions Inventory Results Summary

Figure 21 through Figure 25 illustrate the emissions contributions from source categories 

representing the majority of emissions of primary PM2.5 and precursor gases. The same scale was 

used for the precursor gases to provide perspective on their relative contributions. Because 

primary PM2.5 concentrations do not depend on atmospheric chemistry, the emissions rate scale 

differs to better show detail. This information was used to determine which pollutants and source 

categories should be the focus of control efforts. For this SIP, Idaho considered both the absolute 

and relative amount of pollutants contributed by Idaho sources. See Appendix C for details 

regarding Figure 24.

Figure 21. Nitrogen oxide emission totals sorted by source type and county.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

25

Figure 22. Volatile organic compound emission totals sorted by source type and county.

Figure 23. Ammonia emission totals sorted by source type and county.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

26

Figure 24. Sulfur dioxide emission totals sorted by source type and county.

Figure 25. PM2.5 emission totals sorted by source type and county.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

27

3.2.3 Primary PM2.5 Emissions

Figure 26 represents the relative PM2.5 emissions contributions for the entire CVNAA; the 

emissions presented here are for all source types emitting primary PM2.5 and include both Cache 

County, Utah, and Franklin County, Idaho. The three top contributors to PM2.5 across the

CVNAA were mobile dust (38%) mainly from road sanding, mobile emissions (24%) from 

tailpipe emissions, and residential wood combustion (18%).

Figure 26. PM2.5 emissions from all source types (area, point, and mobile) for the entire 

nonattainment area including Utah and Idaho emissions.

On the Utah side of the CVNAA (Figure 27), the same source categories were the top PM2.5 

contributors—mobile emissions (34%), residential wood combustion (RWC) (21%), and mobile 

dust (20%). Figure 28 depicts the same three top source categories but at much different 

percentages. In rural Idaho, mobile dust from road sanding accounts for 70% of all directly 

emitted PM2.5, while residential wood combustion accounts for 14%, and mobile emissions 

account for only 6%.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

28

Figure 27. PM2.5 emissions from all source types (area, point, and mobile) for the Utah side of the 

nonattainment area (Cache County). 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

29

Figure 28. PM2.5 emissions from all source types (area, point, and mobile) for the Idaho side of the 

nonattainment area (Franklin County).

3.3 Attainment Year Inventory 

Table 4 lists total daily winter emissions (for both Utah and Idaho) for the 2008 base year as well 

as the 2014 attainment year. The attainment year totals include projections concerning growth in 

population, vehicle miles traveled, and the economy. The totals also include the effects of

emissions control strategies that are either already promulgated or were required as part of the

Utah SIP. More detailed inventory information are found in Appendix B. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

30

Table 4. Cache Valley emissions inventory, tons per day, for the 2008 base year and 2014 

attainment year for PM2.5, NOx, VOC, NH3, and SO2; emissions shown are for Utah and Idaho.

Notes: particulate matter 2.5 (PM2.5); nitrogen oxides (NOx); volatile organic compounds (VOC); ammonia (NH3); 

sulfur dioxide (SO2); tons per day (tpd).

Emissions reductions due to woodstove change-outs and changes in road sanding practices 

reduce the 2014 Cache Valley emissions further as shown in blue in Table 5. Franklin County 

PM2.5 emissions are reduced 68% and VOC emissions are reduced 1.5%. Emissions of primary

PM2.5 will be reduced 71% from the 2008 base year through the 2014 attainment year. This 

moves Franklin county emissions from 21% of the entire CVNAA primary PM2.5 inventory in 

2008 to 7% of the inventory in 2014.

Table 5. Franklin County emissions summary.

Franklin County Emissions Summary (tons per episode day)

Pollutant PM2.5 NOX VOC NH3 SO2*

2008 baseline emissions** 0.21 1.54 1.97 6.25 0.08

2014 Utah model without 

Idaho control measures** 0.19 1.15 2.16 5.54 0.08

2014 with Idaho control 

measures 0.06 1.15 2.10 5.54 0.08

Notes: particulate matter 2.5 (PM2.5); nitrogen oxides (NOx); volatile organic compounds (VOC); ammonia (NH3); 

sulfur dioxide (SO2)

*Corrected values—see Appendix C

**From Utah’s Technical Support Document for the PM2.5 Attainment SIPs

The residential woodstove ordinances shut off additional emissions sources when the AQI 

reaches, or is forecasted to reach, 75. The estimated maximum reductions are as shown in Table 

6. However, these emissions reductions, while having a proven track record in Idaho, are more 

difficult to quantify specifically. For this reason, IDEQ did not include reductions due to the 

woodstove ordinances in Table 5. Documentation for these estimated reductions are found in 

Appendix C.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

31

Table 6. Emissions reductions due to burn cessation ordinances.

Notes: particulate matter 2.5 (PM2.5); nitrogen oxides (NOx); volatile organic compounds (VOC); ammonia 

(NH3); sulfur dioxide (SO2); United States Environmental Protection Agency.

4 Attainment Demonstration

UDAQ led the efforts with respect to developing the technical components for the Cache Valley 

SIP attainment demonstration because they were dealing with two additional NAAs, Salt Lake 

City, Utah, and Provo, Utah, located along the Wasatch Front, and because 90% of the Cache 

Valley population resides in Utah. The Wasatch Front can generally be described as the 

population centers at the foot of the Wasatch Range from Brigham City to Santaquin. The 

attainment demonstration is summarized in this section, with excerpts from UDAQ technical 

support document included for continuity. Details concerning the SIP technical analysis, 

including links to UDAQ documents, are found in Appendix D. All modeling was performed by 

the UDAQ staff, with technical guidance from modeling experts around the country. A technical 

review group, including EPA Regions 8 and 10 and IDEQ technical staff, provided updates as 

the work progressed and provided peer review throughout the process.

4.1 Photochemical Model Selection

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

planning efforts. Models assist policymakers in deciding which control programs are most 

effective in improving air quality and meeting specific goals and objectives. The air quality 

analyses for this SIP were conducted with the Community Multiscale Air Quality (CMAQ)

model version 4.7.1, with emissions and meteorology inputs generated using the SMOKE

(Sparse Matrix Operator Kernel Emissions) processor and Weather Research and Forecasting

(WRF) model, respectively. CMAQ was selected because it is the open source atmospheric 

chemistry model co‐sponsored by EPA and the National Oceanic and Atmospheric 

Administration.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

32

4.2 Domain/Grid Resolution

UDAQ selected a high-resolution 4‐kilometer (km) modeling domain to cover all of northern 

Utah and portions of Idaho, Wyoming, and Nevada (Figure 29). This 97 x 79 horizontal grid cell 

domain was selected to ensure that all of the 23 major emissions sources that have the potential 

to impact three PM2.5 NAAs, largely located in Utah, were included. The vertical resolution in 

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

boundary layer. The UDAQ modeling domain includes 11 Idaho counties or portions of counties 

to ensure that all Idaho emissions that could possibly contribute to the Cache Valley and other 

Utah NAAs would be included.

Figure 29. Cache Valley photochemical modeling domain.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

33

4.3 Episode Selection

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

Cache Valley, there are important differences related to topography. The Cache Valley is a 

closed basin with no significant outlets. The Cache Valley topographical features lead to faster 

forming, more intense, and more persistent cold-air pools relative to the Wasatch Front. The 

episodes chosen for the modeling were selected so that observed elevated PM2.5 concentrations 

occur simultaneously along the Wasatch Front and in Cache Valley. 

Each of the selected episodes features a similar pattern that 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 builds eastward and near surface winds weaken; rapid 

stabilization occurs due to warm advection and subsidence dominates. As the ridge centers over 

Utah and southeast Idaho 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 temperature promote 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. While each episode has its unique 

characteristics, the commanding similarity between each episode is stability and stagnation that 

traps locally produced emissions and allows secondary PM2.5 formation and concentration 

buildup.

Episodes selected for the model evaluation and attainment demonstration, described more fully 

in the UDAQ technical support document in Appendix D, are listed below. Episode 4 is the most 

complete modeling period, including multiple stagnation periods with high PM2.5 concentrations,

and was therefore used by UDAQ for the final attainment demonstration.

 Episode 1: January 11–20, 2007

 Episode 2: February 14–19, 2008

 Episode 3: January 13–23, 2009

 Episode 4: December 8, 2009–January 22, 2010

4.4 Meteorological Inputs

Meteorological inputs were derived using the WRF, Advanced Research WRF (ARW) model 

version 3.2. Model performance of WRF was assessed using actual observations at sites 

maintained by the Utah Air Monitoring Center. 

The most significant issue with meteorological performance is the existence of a warm bias in 

surface temperatures. WRF does a good job replicating the light wind speeds (< 5 miles per 

hour) and is able to simulate the diurnal wind flows common to the NAAs. Although, WRF has 

reasonable ability to replicate the vertical temperature structure of the boundary layer 

(temperature inversion), it is difficult for WRF to reproduce the inversion when the inversion is 

shallow and strong.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

34

4.5 Photochemical Model Performance Evaluation

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

variation of modeled and measured concentrations. This evaluation was intended to assess 

whether, and to what degree, confidence in the model is warranted and to assess whether model 

improvements were necessary. CMAQ model performance was compared to observed air quality 

data. PM2.5 speciation performance was assessed using the three STNs located along the Wasatch 

Front (Hawthorne, Bountiful, and Lindon).

Figure 30 shows the time series of the modeled versus measured Logan 24-hour PM2.5 

concentrations for the December 13, 2009–January 15, 2010, modeling period (Episode 4).

Figure 30. Twenty-four-hour PM2.5 time series (Logan). Observed PM2.5 (blue line), modeled with 

vertical advection activated (red line).

The model does a reasonably good job of capturing the multiday increases in PM2.5

concentrations, although not always at the same magnitude as the measurements. The model 

performance is not a critical problem as long as the speciation characteristics are captured 

reasonably well, since evaluating the effect of control measures on future PM2.5 levels is 

accomplished on a relative basis so that the influence of model inaccuracies is minimized. In 

their performance evaluation, UDAQ found that the model achieved a mean fractional bias of -

16% and a mean fractional error of 26% for the Logan monitor in Cache Valley, both within the 

performance goals generally accepted for SIP modeling (Boylan and Russell 2006).

There is no regularly operated speciation measurement site in the Logan CVNAA, and while 

there is very little speciation information available in Cache Valley for the simulation period, 

past studies have shown that ammonium nitrate contributes 60%–80% of the PM2.5 during 

inversion episodes (Martin 2006). Figure 31 shows the simulated speciation at the Logan monitor 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

35

site. Ammonium (20%) and nitrate (60%), which together comprise ammonium nitrate 

secondary aerosol, make up a higher percentage of the simulated PM2.5 at Logan when compared 

to sites along the Wasatch Front. In addition to the ammonium nitrate secondary aerosol, organic 

and elemental carbon from sources such as RWC and diesel emissions contribute 11% of the 

modeled PM2.5. Finally, geologic and trace metal species from road dust, fugitive dust, and 

combustion sources comprise less than 10% of the PM2.5, in close agreement with measurements. 

Figure 31. Composition of model-simulated average 24-hour PM2.5 concentrations averaged over 

days when a modeled day had 24-hour concentrations >25 micrograms per cubic meter at the 

Logan monitor.

4.6 Model Performance Summary

Model performance for 24‐hour PM2.5 for the entire domain, Wasatch Front and Cache Valley, is 

good and generally meets model performance goals accepted by EPA for SIP modeling. The 

model performance was summarized by UDAQ as follows: 

 Good replication exists of the episodic build up 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.

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

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

 Spatial patterns of modeled 24‐hour PM2.5 show, for the most part, that the PM2.5 is being

confined in the valley basins, which is consistent with actual observations. 

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

well. Modeled and observed nitrates are between 40% and 50% of the PM2.5. Ammonium 

is between 15% and 20% for both modeled and observed PM2.5. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

36

Consistent with EPA guidance, the model has been used in a relative sense to project future year 

values. 

4.7 Additional Model Sensitivity Tests of Nitrogen Oxides and Volatile 

Organic Compounds Chemistry

CMAQ sensitivity simulations were conducted by UDAQ to test the changes in PM2.5 secondary 

nitrate concentrations resulting from changes in the emissions of NOx and VOCs. The sensitivity 

simulations were performed on the 2008 inventory and the 2019 inventory that had incorporated 

emission reduction control strategies.

At Logan, where the inventory is smaller than that of the Wasatch Front airshed, reductions in 

both NOx and VOCs lead to the benefit of reducing particulate nitrate. This reduction is the 

expected behavior for more rural areas such as Cache Valley, contrary to the more populated 

areas of the Wasatch Front where a NOx decrease can actually cause nitrate aerosol to increase, a 

result found by UDAQ in sensitivity modeling of the Wasatch Front.

4.8 Modeled Attainment Test

UDAQ used the Model Attainment Test Software (MATS) for the modeled attainment test at 

grid cells near monitors. MATS was designed to perform two basic analyses of future year 

modeling.

1. Interpolate the species fractions of the particulate matter mass from the STN monitors to 

the FRM monitors. The model also calculates the relative response factor for grid cells 

near each monitor and uses these to calculate a future year design value for these cells.

2. Perform an unmonitored area analysis on grid cells in areas of the domain that are far 

from monitors. This analysis is done by adjusting the modeled values in grid cells with 

the observed values from monitors in the domain. The adjustment is based on an inverse 

distance weighting so that monitored data nearest to a grid cell exerts the most influence 

in the adjustment. The capability to perform an analysis of an unmonitored area for daily 

average PM2.5 is not currently implemented in MATS.

MATS results for future year modeling at the Logan monitor site are presented in Figure 32. The 

future year design value is presented for 2014, the attainment year, along with the MATS future 

year design values for modeling simulation that include control strategies. For comparison 

purposes, the monitored design value is also presented for the base year, 2008.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

37

Figure 32. Model results for the Cache Valley nonattainment area, Logan monitor.

4.9 Unmonitored Areas

While many areas within the CVNAA do not have permanent air quality monitors, Idaho does 

not believe any of those areas will have higher concentrations than the two existing monitor sites 

in Logan and Franklin. The bases for this conclusion are threefold:

1. Monitoring data—Monitoring data are provided in section 2 of this document. The 

highest values occur almost exclusively at the Logan monitor site, and there is a clear 

gradient decreasing from the Logan area toward the northern end of the valley.

2. Special study—Utah State University’s study of the Cache Valley included a network of 

monitors located throughout the valley (Martin 2006). Data from those monitors 

indicated that highest concentrations are expected in Logan, and again the gradient 

decreases from south to north on the highest days. When concentration levels drop 

somewhat, there are more areas with concentrations similar to those in Logan, but none 

expected to be significantly greater.

3. Understanding of model behavior—Because there are no large stationary sources, 

emissions inputs in the model will be based largely on the density of the population and 

location of roads. The majority of both population and roads are located in Logan and 

that is where the largest modeled concentrations, particularly in cases of stagnation, are 

expected to be found. Since only 10% of the Cache Valley population resides in Franklin 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

38

County, Idaho, any concentration hotspot that is in an unmonitored area is very unlikely 

to occur in Idaho.

4.10 Attainment Date

As shown in the modeled attainment test, the emissions reductions achievable in 2014 allow for a 

demonstration that the CVNAA can attain the 24-hour PM2.5 NAAQS. Therefore, this SIP

identifies an attainment date of January 1, 2015. This timeframe will allow for the consideration 

of monitoring data and inventory data collected during calendar year 2014 in making an 

assessment of whether the area has attained the standard in accordance with CAA Section 172 

(a)(2)(C).

5 Control Strategies

The overall strategy for improving air quality throughout the CVNAA consists of many different 

components across the multistate NAA. Collectively, these components will be responsible for 

reducing PM2.5 emissions in the CVNAA and allow Utah and Idaho to demonstrate attainment 

with the NAAQS by January 1, 2015. Both sides of the CVNAA (Utah and Idaho) dealt 

separately with various control measures, due to both jurisdictional authority and differences in 

the emissions inventory. Details concerning the control measures used on the Utah side of the 

Cache Valley can be found in the PM2.5 SIP and technical support document (Appendix B)

developed by UDAQ.

5.1 Control Strategy Consideration

In accordance with 40 CFR 51.1002, this SIP must address emissions of PM2.5 precursors (SO2, 

NOx, VOC, and NH3) in addition to direct emissions of PM2.5.

5.1.1 Sulfur Dioxide

Idaho has addressed SO2 as a PM2.5 precursor. SO2 emissions make up a very small portion of the 

overall inventory. Ammonium nitrate formation is the predominant process that leads to high 

PM2.5 concentrations in the Cache Valley during winter inversions. For these reasons, Idaho did 

not consider NAA specific controls for SO2.

5.1.2 Nitrogen Oxides

Emissions of NOx mainly due to combustion for heating and mobile sources, contribute to the 

PM2.5 problem in the Cache Valley through the formation of ammonium nitrate secondary 

aerosol. Additional controls for home heating of natural gas or distillate oil was deemed 

prohibitively expensive for very little reduction in overall emissions. Idaho's relative contribution 

to emissions from mobile sources is 10%. An inspection and maintenance program would be 

expected to reduce NOx emissions by 4.6% based on UDAQ MOVES modeling, with an 

estimated cost of $20,000 per ton (see Appendix C). Idaho determined this cost was not 

reasonable in light of federal vehicle regulations that are expected to provide ongoing emissions 

reductions.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

39

5.1.3 Volatile Organic Compounds

Utah's modeling team determined that VOCs do play a role in secondary PM2.5 formation in the 

Cache Valley. However, VOC emissions are a small portion of the Franklin County inventory 

and, therefore, were not considered reasonable to control. Some of the Utah VOC controls have 

an airshed-wide effect because many Franklin County residents obtain goods and services in 

Utah. IDEQ MOVES modeling results predict VOC emissions reductions from on-road mobile 

sources of 37%, from 0.61 to 0.39 tons per day, by January 1, 2015 (see Section 5.5.2).

5.1.4 Ammonia

Most of the secondary particulate matter collected during cold‐air pool conditions is ammonium 

nitrate. Studies performed at Utah State University have shown NH3 to be in abundance in the 

Cache Valley and that the limiting reagent in the formation of ammonium nitrate is nitric acid 

(HNO3). Sensitivity runs with the model indicate that significant reductions in the NH3

inventories have little to no effect on predicted PM2.5 concentrations. Therefore, NH3 reductions 

are not beneficial in reducing PM2.5 concentrations, and NH3 will not be considered as a PM2.5 

attainment plan precursor.

5.1.5 Direct PM2.5 Emissions

Idaho focused primarily on direct PM2.5 emissions for control efforts and, in particular, focused 

on the two sources (mobile source road dust and woodstoves) that make up 84% of those 

emissions. EPA guidance document, Implementation Guidance for the 2006 24-Hour Fine 

Particle (PM2.5) National Ambient Air Quality Standards (NAAQS) (Implementation Guidance) 

(EPA 2012), recommends that states place emphasis on reducing direct PM2.5 emissions because 

published literature has indicated there are higher estimated health benefits per ton of reduction 

when compared with emissions of precursor gases.

The following sections discuss control measures developed specifically for the Idaho side of the 

CVNAA as well as measures already in place that play a part in reducing PM2.5 emissions.

5.2 Reasonably Available Control Measures 

The following subsections detail the reasonably available control measures (RACM), see 

Appendix E.

5.2.1 Road Sanding

Within the Idaho side of the CVNAA, 70.5% of the directly emitted PM2.5 is due to mobile dust, 

which is primarily from reentrained dust on paved roads. Franklin County Road and Bridge and 

ITD have entered into road sanding agreements as part of the SIP. The Franklin Road and Bridge 

agreement reduces the amount of sand used on paved roads by applying brine, when conditions 

are appropriate, and by using a salt/sand mixture where antiskid treatment is required. ITD has 

moved to applying a straight solution of sodium chloride, thereby eliminating the amount of 

sanding material. Franklin County Road and Bridge has used a 10-to-1 ratio of sand to salt in 

past years; however, for this SIP they have agreed to use a 4-to-1 sand-to-salt ratio mix when 

antiskid treatment is required. In addition, brine will be applied when temperatures are above 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

40

22 oF, a measure which further reduces the amount of sand required by approximately 50%.

Table 7 shows the expected episode daily emissions reductions. The road sanding agreements are

found in Appendix E.

Table 7. Road sanding emission reductions.

Scenario

Weekday Emissions

Uncontrolled

Scenario (tpd)

Controlled Weekday 

Emissions (tpd)

Emission 

Reductions (tpd)

Assumed control 

scenario —

4-to-1 sand-to-salt 

mixture for antiskid 

application; with brine

—

2008 base year

0.45 NA NA

2014

0.47

0.37

0.10

2019 0.52 0.41 0.11

Notes: tons per day (tpd); not applicable (NA) 

5.2.2 Residential Wood Combustion Ordinances

RWC ordinances have been adopted within Franklin County and all six Idaho cities that lie 

within the Idaho side of the Cache Valley (Franklin, Preston, Weston, Dayton, Clifton, and 

Oxford). Key elements in the current RWC ordinances include issuing a mandatory burn ban 

when PM2.5 is at, or is forecasted to reach 75 on the AQI. (This corresponds directly to a PM2.5 

concentration of 25.4 μg/m3and lines up directly with the RWC ordinances that are applicable 

within Cache County, Utah). All of the cities and the unincorporated Franklin County have 

existing ordinances prohibiting both open burning and the use of a RWC device when an air 

quality alert is issued, as noted above. The ordinances also prohibit installing non EPA-certified 

devices. Appendix E contains copies of all of the RWC ordinances. 

5.2.3 Air Quality Index Program

IDEQ operates an AQI program to support the public information and regulatory components of 

the PM2.5 SIP. Through this program, IDEQ provides information on the measured and 

forecasted ambient air pollution levels for PM2.5 in Franklin County, Idaho. UDAQ also operates 

a similar program on the Utah side of the CVNAA.

Information on open burning bans and indoor wood burning bans is provided via several formats. 

These formats may include, but are not limited to, IDEQ’s website, recorded messages available 

24-hours per day, and e-mail to people who wish to be on a daily forecast list or an alert list. 

5.2.4 Woodstove Change Outs

IDEQ has operated two woodstove change-out programs on the Idaho side of the CVNAA (2006 

and 2011) changing out a total of 152 uncertified RWC devices. In addition, during the 

intervening years, two uncertified stoves were replaced by certified stoves in accordance with 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

41

Idaho’s Alternative Energy Device tax deduction, which allows Idaho citizens to deduct all, or 

most, of the cost to acquire and install a certified woodstove.

Table 8 lists the emissions reductions due to these woodstove change outs. Supporting 

documentation is found in Appendix C In addition to reductions in particulate matter, the 

woodstove change-out program has also led to the reduction in air toxics, such as formaldehyde, 

acrolein, and benzo(a)pyrene, which are generated as byproducts of combustion. 

Table 8. Emissions reductions due to the woodstove change outs.

Notes: woodstove (WS); carbon monoxide (CO); sulfur dioxide (SO2); nitrogen oxides (NOx); volatile organic 

compounds (VOC); particulate matter (PM2.5, 10); primary (PRI). 

5.3 Contingency Measures

CAA Section 172(c)(9) requires that any NAA implementation plan must contain contingency 

measures to be undertaken if the area fails to make reasonable further progress (RFP), or to attain 

the NAAQS by the applicable attainment date (CVNAA, January 1, 2015). These required 

contingency measures are required to take effect without further action by the state or EPA. The 

CAA does not specify the number of contingency measures to be adopted or the magnitude of 

the emission reductions to be achieved. However, the preamble of the 2007 PM2.5

Implementation Rule (72 FR 20586) states:

One basis EPA recommends for determining the level of reductions associated with contingency measures 

is the amount of actual PM2.5 emissions reductions required by the control strategy for the SIP to attain the 

standards. The contingency measures are to be implemented in the event that the area does not meet RFP, 

or attain the standards by the attainment date, and should represent a portion of the actual emissions 

reductions necessary to bring about attainment in area. Therefore, the emissions reductions anticipated by 

the contingency measures should be equal to approximately 1 years’ worth of emissions reductions 

necessary to achieve RFP for the area. (72 FR 20586, page 20643)

The EPA (2012) Implementation Guidance clarifies that this concept does not hinge on whether 

a given area is required to develop an RFP plan. Rather,

The basic concept is that an area's set of contingency measures should provide for an amount of emission 

reductions that would achieve "one year's worth" of air quality improvement proportional to the overall 

amount of air quality improvement to be achieved by the area's attainment plan; or alternatively, an amount 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

42

of emissions reductions (for all pollutants subject to the plan) that would achieve one year's worth of 

emission reductions proportional to the overall amount of emission reductions needed to show attainment.

Following the example provided in the Implementation Guidance and using data from the Logan 

monitor because it consistently measures the highest concentrations in the CVNAA, yields:

The CVNAA was designated in December 2009 with a 2006–2008 design value of 

36 g/m3. To demonstrate attainment, the CVNAA must reduce its air quality 

concentration from 36 g/m3in 2008 to 35 g/m3in 2014, equal to a rate of change of 

0.2 g/year. Utah's control measures are expected to reach a design value of 34 g/m3by 

the attainment date. 

The only Idaho emissions reductions included in the UDAQ attainment demonstration are those 

due to federal vehicle standards that are imbedded in the MOVES model. Idaho's controls, with 

reductions as shown in Table 5, provide additional emission reductions that are not relied on by 

UDAQ for attainment and are not included in their demonstration. Further, UDAQ has included 

3 contingency measures in their SIP; lowering the trigger for woodstove burn bans, offsets for 

new stationary sources and transportation control measures. The RACM for Franklin County 

has, therefore, met the contingency measure obligation as stated in the preamble to the 

Implementation Rule:

The key is that the statute requires that contingency measures provide for additional emission reductions 

that are not relied on for RFP or attainment and that are not included in the demonstration.

Idaho recognizes, however, that the real world does not always behave according to models. If

Cache Valley has a violation in the future, the event will be evaluated, and the filters will be 

chemically analyzed to target further controls. This step will allow the root cause of the violation 

to be determined so that the appropriate additional measures can be implemented. With this in 

mind, Idaho can and will make a number of adjustments to ensure air quality continues to 

improve in the CVNAA.

5.3.1 Forecasting

Forecasting when burn bans are called can be adjusted based on experience gained year to year. 

This experience allows IDEQ forecasters to use meteorological information related to the 

expected strength and duration of a developing air stagnation combined with knowledge of the 

rate of particulate matter buildup in the airshed to determine when to call a burn ban.

5.3.2 Road Sanding

If data indicate a significant amount of crustal matter is contributing to elevated values in 

Franklin County, IDEQ will work with Franklin County and ITD to further adjust sanding rates 

or road sweeping.

5.3.3 Certified Woodstoves

If experience indicates that solely banning the use of uncertified woodstoves is not sufficient to 

ensure attainment and maintenance of the NAAQS, IDEQ will work with the local governments 

to add a trigger for burn cessation to include certified woodstoves. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

43

5.3.4 Revised Woodstove New Source Performance Standard

EPA is expected to revise the “Standards of Performance for New Residential Wood Heaters”

(40 CFR 60 Subpart AAA) in the near future.

5.3.5 Air Pollution Emergency Rule (Open Burning Ban) 

In addition to the open burning ban that is enacted with the RWC ordinance (AQI 75), additional 

mandatory burn bans can be implemented by IDEQ at the stage one and caution level. The stage 

one levels for PM2.5 are set at 50 μg/m3for the 24-hour average and 80 μg/m3for the 1-hour 

average as defined in the “Rules for the Control of Air Pollution in Idaho” (IDAPA 

58.01.01.550-562).

5.3.6 Agricultural Sources

Agricultural operations occasionally contribute to the ambient PM2.5 levels in many rural areas 

and in some urban areas. Typically, all agricultural operations are generically classified as soil 

preparation, soil maintenance, and crop harvesting operations. Reasonable available control 

measures for agricultural sources include using best management practices and land conservation 

practices under the Food Security Act of 1985, which was reauthorized in 1996, 2002, 2008, and 

2012. Appendix C contains the reauthorized 2012 farm bill as it pertains to conservation.

In addition, Idaho’s crop residue burning program controls impacts from this activity so that 

NAAQS are attained and maintained. While this activity does not generally occur in winter 

months, the rules regarding when this activity can be allowed (burning cannot occur if 

concentrations are forecasted to reach 75% of the NAAQS or when dispersion characteristics are 

unfavorable) will allow this activity to occur in the CVNAA without causing or contributing to a 

violation, or interfering with maintenance, of the NAAQS. 

5.3.7 Idaho Permitting Program 

The industrial air permitting rules are found in IDAPA 58.01.01.200-500. The permitting 

program requires permits for constructing and operating new or modified major stationary 

sources within the CVNAA. New and modifying sources must demonstrate that they will not 

cause or interfere with maintenance of a NAAQS. Modeling must be in compliance with 40 CFR 

51, Appendix W, “Guideline on Air Quality Models.” The Tier II operating permit program 

allows IDEQ to develop permits for existing sources that must be controlled to attain or maintain 

compliance with the NAAQS.

5.3.8 Tier 2 Federal Motor Vehicle Emission Requirements

The federal motor vehicle emission program went into effect on April 10, 2000 (65 FR 6698) 

and was phased in between 2004 and 2008. Tier 2 introduced more stringent numerical emission 

limits compared to the previous program (Tier 1). 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 nitrogen oxide emissions by at least 

2,220,000 tons per year nationwide in 2020. Tier 2 has also contributed in reducing VOC and 

direct particulate matter emissions from light-duty vehicles.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

44

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

projections for this SIP from 2014 through 2019 (and beyond) continue to reflect significant 

reductions 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 

heavy-duty diesel vehicles. EPA’s Clean Air 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% with a goal of complete fleet 

replacement by 2030. To enable the updated emission reduction 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% 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% of trucks and buses 

when the fleet turnover is completed in 2030. All federal vehicle emission reduction programs 

are incorporated into the MOVES model used to develop on-road emission inventories.

5.3.9 Diesel Emission Reduction Program—School Bus Retrofits

IDEQ’s diesel emission reduction program (DERP) has been working to reduce emissions from 

school bus fleets. DERP has chosen to employ closed crankcase ventilation (CCV) units and 

diesel oxidation catalysts (DOC) to school buses located in Franklin County and the Idaho 

portion of the CVNAA. The CVV units are diesel emission reduction technologies that target 

and filter the combustion gases that escape past the piston rings in legacy engines. DOCs are 

technologies that target and break down the exhaust gases as they pass through the exhaust 

system towards the tailpipe. 

To date, DERP has retrofitted 8 school buses at the Westside School District in Dayton, Idaho,

with DOCs. The lifetime emission reductions assumed from these technologies are estimated at 

PM2.5—520 pounds, hydrocarbons—2,300 pounds, and carbon monoxide—9,780 pounds. 

Emission reductions are estimated using the diesel emissions quantifier, which uses the MOVES 

model. Through DERP, the Preston, Idaho, school district plans to retrofit 11 school buses with 

CCV and DOC technologies; the lifetime emission reductions are estimated to be PM2.5—

860 pounds, hydrocarbons—2,100 pounds, and carbon monoxide—11,480 pounds. Efforts will 

continue with Preston to install the emission reduction technologies. 

In addition to school buses, DERP is actively recruiting additional diesel engines in sectors 

beyond the school bus industry with legacy engines that meet the qualifications of emission 

reduction technologies within Franklin County and the Idaho portion of the CVNAA.

5.3.10 Transportation Control Measures

There are no required transportation control measures (TCMs) for the Idaho side of the CVNAA. 

The CAA requires that TCMs are included as contingency measures in SIPs, addressing ozone 

and carbon monoxide. TCMs include a wide variety of measures used to reduce motor vehicle 

emissions primarily by reducing the total amount of vehicle miles traveled in an area. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

45

5.3.10.1 Commuter Bus Service 

The Preston/Logan Commuter Bus Service is operated jointly by the Pocatello Regional Transit 

(Idaho) and the Cache Valley Transit District (Utah). This bus service operates Monday through 

Friday, 6:00 a.m. to 6:30 p.m. There is an estimated 1,700 commuters daily who travel from the 

Idaho to the Utah sides of the Cache Valley. This bus service has been in operation since 2006.

5.3.10.2 Park-n-Ride Lots

Park-n-ride lots serve multiple travel needs, providing an appropriate parking area to leave a car 

and make connections to public transit services, intercity bus services, or carpool and vanpool 

partners. In addition, these lots serve as feeder locations for people in rural areas not served by 

public transit, who could be transported by family or friends to meet available bus services or 

human service agency-provided transportation. The need for alternative mobility choices helps to

mitigate the EPA NAA issue for the Logan-Preston corridor. Currently, there are two park-n-ride 

lots in Franklin County, one near Weston and the other near Franklin. 

5.3.11 Other Measures

Due to the continual changes in the mixture of the PM2.5 sources and evolving technologies to 

understand and control PM2.5 emissions and precursor gases, other measures may become viable 

in the future. IDEQ will continue to evaluate the need for additional measures and will consider 

future additions to the previously listed control measures if it becomes necessary. 

5.4 Reasonably Available Control Technology

CAA Section 172 (c)(1) requires SIPs for NAAs to implement RACM, including reasonably 

available control technology (RACT), for existing major stationary sources. EPA defines RACT 

as the lowest emissions limitations that a particular source is capable of meeting by the 

application of control technology that is reasonably available considering technological and 

economic feasibility. RACT is an emissions limit rather than a control technology and is

determined on a case-by-case basis. On the Idaho side of the CVNAA, there are no major 

stationary sources; therefore RACT has not been implemented. 

5.5 Transportation Conformity

The CAA requires that federal actions conform and are consistent with the approved SIP. 

Conformity addresses pollutant emissions through the process of reviewing plans, projects, and 

programs that are funded and/or approved by the federal government prior to implementation. 

The conformity process ensures that state and local entities plan and discuss programs that 

conform to the SIP. 

5.5.1 Motor Vehicle Emissions Budget Requirements

The PM2.5 SIP must identify not-to-be-exceeded limits on PM2.5, NOx, and VOC emissions from 

on-road mobile sources. The budgets outlined in this section apply specifically to the Idaho side 

of the CVNAA. Additional budgets exist for the Utah side of the CVNAA.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

46

CAA § 176 requires any activity that is federally supported or permitted to conform to approved 

air quality SIPs. To help guide the transportation process, CAA § 108 (e) compelled the EPA 

Administrator and the Secretary of Transportation to develop a “continuous transportation-air 

quality planning” process and guidance on developing and implementing transportation and 

other measures necessary to demonstrate and maintain attainment of NAAQS. This effort led to 

the conformity rules found in 40 CFR 93.100-129. 40 CFR 93.102 (b)(2)(iii) of the regulation 

identifies NOx and VOC as the two PM2.5 precursor pollutants that must also have an motor 

vehicle emission budget (MVEB) if deemed significant. SO2 is an insignificant contributor to the 

secondary aerosol formation in the CVNAA and is not included. Although NH3 contributes to 

secondary aerosol formation, the region is ammonia rich, so the very small mobile source NH3

emissions are also not considered in MVEBs.

The MVEB is developed following the transportation conformity rule under 40 CFR Section 

93.118 (as adopted by IDAPA 58.01.01.563-574). The intent of the conformity rules is to 

synchronize the air quality planning process with transportation plans developed by metropolitan 

planning organizations (MPOs) and other transportation organizations to ensure air quality 

standards are met. Simply put, transportation plans must conform to air quality plans and show 

that transportation projects using federal funds or deemed to be regionally significant in air 

quality nonattainment and maintenance areas do not contribute to a degradation of air quality.

On the Idaho side of the CVNAA, the area is both rural and small enough in population that it 

does not warrant the formation of an MPO. The Federal-Aid Highway Act of 1962 required the 

formation of an MPO for any urbanized area with a population greater than 50,000. Federal 

funding for transportation projects and programs are channeled through this planning process. 

On the Idaho side of the CVNAA, ITD is responsible for developing the long-range 

transportation plan (LRTP) that incorporates all the new transportation projects anticipated 

within the 20-year planning horizon. ITD is also responsible for developing the transportation 

improvement program (TIP) that incorporates all the transportation projects that have identified 

funding sources and are scheduled to be built within 3–5 years. The Utah side of the CVNAA is 

covered by the Cache Valley MPO.

To reconcile long-range transportation plans and TIPs with air quality implementation plans, the 

conformity rules require these plans be consistent with the MVEB, which is part of the air 

quality SIP. The CVNAA is unique in that the airshed covers two states and EPA regions

(Utah—Region 8 and Idaho—Region 10). Following EPA guidance to show adequacy of the 

MVEBs, both Utah and Idaho combined their respective MVEB (transportation emissions) along 

with both area and point source emissions as part of the attainment modeling demonstration

(EPA 2012). The modeling demonstration used wintertime episodes from 2007, 2008, 2009, 

2010 and included the future years 2014 and 2019. Following the modeling demonstration, each 

state will then use separate MVEBs as established in each state’s SIP as allowed in 40 CFR 

93.124(c). 

When establishing a MVEB, the conformity rule, 40 CFR 93.102(b)(2)(iv)and(v), requires the 

state to make a finding on whether NOx, SO2, VOC, or reentrained road dust from transportation 

are significantly contributing to PM2.5 nonattainment. On the Utah side of the CVNAA, they 

have determined that reentrained road dust is not an issue. However on the Idaho side of the 

CVNAA, it has been determined that reentrained road dust is an issue because of road sanding 

practices. SO2 from Idaho is a very small contributor to the nonattainment issue. As discussed in 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

47

section 5.1.1 and depicted in Figure 24, SO2 from transportation on the Idaho side of the 

CVNAA is not significantly contributing to nonattainment. Therefore, Idaho is making the 

determination to not include SO2 emissions in the MVEB. Idaho will include NOx, VOC, and 

reentrained road dust in the MVEB.

The Utah side of the CVNAA will continue to use the Cache Valley MPO for future conformity 

determinations. Since the Idaho side of the CVNAA does not have an established MPO, the 

entire Franklin County will be considered a rural donut area for conformity purposes. Rural 

donut areas are geographic areas outside a metropolitan planning area boundary but inside the 

boundary of a nonattainment or maintenance area that contains any part of a metropolitan area as 

described in 40 CFR 93.101.

5.5.2 Motor Vehicle Emission Budget

The MVEB is comprised of on-road mobile sources including fugitive dust from paved and 

unpaved roads and vehicle emissions (exhaust, tire, and brake wear). EPA’s MOVES model was 

used to develop vehicle emissions estimates for the MVEB. The MVEB becomes applicable 

when the EPA determines that the budget is adequate for transportation conformity purposes. In 

accordance with the conformity rule, the emissions budget acts as a ceiling on emissions in the 

year for which it is defined or until a SIP revision modifies the budget. 

The MVEB is developed as part of the SIP to place a ceiling or cap on emissions from 

transportation projects. The conformity process compares projected emissions from the TIPs and 

LRTPs with the budgeted emissions set out in the SIP MVEB. The emissions budgets included 

as part of this SIP are shown in Table 9. The conformity rule will require the emission 

projections from future TIPs and LRTPs be less than or equal to the budget levels. The 

conformity process ensures that transportation projects will not cause or contribute to NAAQS 

violations.

Table 9. Motor vehicle emission budget for the Idaho side of the Cache Valley nonattainment area.

Year County NOx (ton/day) VOC (ton/day)

Total PM2.5

(ton/day)

2008 Franklin 0.879 0.612 0.496

2014 Franklin 0.501 0.386 0.429

2019 Franklin 0.360 0.263 0.429

Notes: nitrogen oxides (NOx); volatile organic compounds (VOC); particulate matter 2.5 (PM2.5)

5.5.3 Adequacy Determination

Before the MVEB can be used for conformity purposes, it must demonstrate adequacy. For EPA 

to determine the MVEB is adequate, the conformity rule requires that MVEB emissions must be 

considered with all other emissions sources and be consistent with the applicable SIP. Modeling 

must demonstrate that all emission sources combined (point, area, and mobile sources) will not 

cause or contribute to a violation of the PM2.5 NAAQS. As discussed above, a modeling 

demonstration was performed by UDAQ that included point, area, and mobile sources from both 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

48

Idaho and Utah, showing attainment and maintenance of the NAAQS by 2014. This information 

is available in Appendix B.

6 Administrative Requirements

Table 10 provides a crosswalk between the regulatory requirements in 40 CFR 51 this SIP must 

address and how Idaho has met the requirements.

Table 10. Crosswalk between the regulatory requirements and how the requirement is met within 

this State Implementation Plan.

Regulatory Requirement (paraphrased) How Idaho Met Requirement

§ 51.102 Public hearings. States must provide notice, 

provide the opportunity to submit written comments, and 

allow the public the opportunity to request a public hearing.

Public participation in the development of 

this plan is discussed in section 6.2.

IDEQ will provide a 30-day public comment 

period with a public hearing. Complete 

documentation of the public comment 

process will be included with the submittal 

of this plan to EPA. 

§ 51.103 Submission of plans, preliminary review of plans. Idaho will submit plan in accordance to 

letter from Region 10 dated April 26, 2011.

§ 51.110 Attainment and maintenance of national 

standards. Each plan providing for the attainment of a 

primary or secondary standard must specify the projected 

attainment date.

Idaho’s 2006 PM2.5 Infrastructure SIP was 

submitted to EPA June 25, 2010, and 

updated August 8, 2011. 

The attainment date is January 1, 2015 

§ 51.111 Description of control measures.

Each plan must set forth an enforceable control strategy.

The control strategy for Franklin County is 

discussed in section 5.

In addition, the State of Utah has submitted 

a plan to EPA Region 8 that contains 

enforceable control measures for Cache 

County.

§ 51.112 Demonstration of adequacy. Each plan must 

demonstrate that the measures, rules, and regulations 

contained in it are adequate to provide for the timely 

attainment and maintenance of the national standard that it 

implements.

The adequacy of control measures for 

Franklin County is discussed in sections 4 

and 5.

In addition, the State of Utah has submitted 

a plan to EPA Region 8 demonstrating the 

adequacy of control measures for Cache 

County.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

49

§ 51.114 Emissions data and projections. 

Each plan must contain a detailed inventory of emissions 

from point and area sources and a summary of emission 

levels projected to result from application of the new control 

strategy.

The emissions inventory is discussed in 

section 3 and the emissions projections are 

discussed in section 4.

§ 51.115 Air quality data and projections. Each plan must 

contain a summary of data showing existing air quality and 

a summary of air quality concentrations expected to result 

from application of the control strategy.

Existing air quality data is discussed in 

section 2 and expected air quality 

concentrations are discussed in section 4.

§ 51.116 Data availability. The State must retain all detailed 

data and calculations used in the preparation of each plan 

or each plan revision, and make them available for public 

inspection and submit them to the Administrator at his 

request.

IDEQ maintains documents and data in a 

central record management system. SIP 

related documents are retained for 35 

years after the date of redesignation.

§ 51.213 Transportation control measures.

(a) The plan must contain procedures for obtaining and 

maintaining data on actual emissions reductions achieved 

as a result of implementing transportation control 

measures.

TCM does not apply in Franklin County, 

see section 5.3.10.

§ 51.230 Requirements for all plans. Each plan must show 

that the State has legal authority to carry out the plan, 

including authority to

(a) Adopt emission standards and limitations.

(b) Enforce applicable laws, regulations, and standards, 

and seek injunctive relief.

(c) Abate pollutant emissions on an emergency basis.

(d) Prevent construction, modification, or operation of a 

facility which results or may result in emissions of any air 

pollutant at any location which will prevent the attainment or 

maintenance of a national standard.

(e) Obtain information necessary to determine whether air 

pollution sources are in compliance with applicable laws.

(f) Require owners or operators of stationary sources to 

install, maintain, and use emission monitoring devices and 

to make periodic reports to the State on the nature and 

amounts of emissions from such stationary sources.

Idaho’s 2006 PM2.5 Infrastructure SIP was 

submitted to EPA June 25, 2010, and 

updated August 8, 2011.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

50

§ 51.231 Identification of legal authority.

The provisions of law or regulation which the State 

determines provide the authorities required under this 

section must be specifically identified, and copies of such 

laws or regulations be submitted with the plan. These must 

be legal authorities available to the State at the time of 

submission of the plan.

Idaho’s 2006 PM2.5 Infrastructure SIP was 

submitted to EPA June 25, 2010, and 

updated August 8, 2011. 

Local ordinances and the road sanding

agreements are included in Appendix E.

§ 51.232 Assignment of legal authority to local agencies.

The State may authorize a local agency to carry out a plan, 

or portion thereof, if the local agency has the legal authority 

necessary to implement the plan or portion of it.

Affected governments in Franklin County 

have the authority to implement the local 

ordinances included in this plan.

§ 51.280 Resources. Each plan must include a description 

of the resources available to the State and local agencies 

at the date of submission of the plan and of any additional 

resources needed to carry out the plan.

Idaho’s 2006 PM2.5 Infrastructure SIP was 

submitted to EPA June 25, 2010, and 

updated August 8, 2011. 

No additional resources are necessary to 

implement this plan.

§ 51.281 Copies of rules and regulations. Emission 

limitations and other measures necessary for attainment 

and maintenance of any national standard must be adopted 

as rules and submitted with the plan. 

Local ordinances are included in 

Appendix E.

PM2.5 Specific Requirements (paraphrased) How Idaho Met Requirement

§ 51.1002 Submittal of State implementation plan.

(a) For any area designated by EPA as nonattainment, the 

State must submit a State implementation plan satisfying 

the requirements of section 172 of the Act to EPA no later 

than 3 years from the date of designation.

(b) The State must submit a plan consistent with the 

requirements of section 110(a)(2) of the Act unless the 

State already has fulfilled this obligation for the purposes of 

implementing the PM2.5 NAAQS.

(c) Pollutants contributing to fine particle concentrations. 

The State implementation plan must identify and evaluate 

sources of PM2.5 direct emissions and PM2.5 precursors. 

After January 1, 2011, States must establish such limits 

taking into consideration the condensable fraction of direct 

PM2.5 emissions. 

(1) The State must address sulfur dioxide as a PM2.5

attainment plan precursor and evaluate sources of SO2

emissions in the State for control measures.

(2) The State must address NOX as a PM2.5 attainment plan 

precursor and evaluate sources of NOX emissions in the 

This plan meets this requirement.

Idaho’s 2006 PM2.5 Infrastructure SIP was 

submitted to EPA June 25, 2010, and 

updated August 8, 2011.

In addition to the requirements addressed 

by Idaho’s Infrastructure SIP, this plan 

specifically identifies and evaluates

sources of direct PM2.5 emissions and 

PM2.5 precursors in sections 3, 4, and 5.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

51

State for control measures, unless the State and EPA 

provide an appropriate technical demonstration for a 

specific area showing that NOX emissions from sources in 

the State do not significantly contribute to PM2.5

concentrations in the nonattainment area.

(3) The State is not required to address VOC as a 

PM2.5attainment plan precursor and evaluate sources of 

VOC emissions in the State for control measures, unless 

the State provides an appropriate technical demonstration 

for a specific area showing that VOC emissions from 

sources in the State significantly contribute to PM2.5 

concentrations in the nonattainment area.

(4) The State is not required to address ammonia as a 

PM2.5 attainment plan precursor and evaluate sources of 

ammonia emissions from sources in the State for control 

measures.

§ 51.1004 Attainment dates. Consistent with section 

172(a)(2)(A) of the Act, the attainment date for an area 

designated nonattainment for the PM2.5 NAAQS will be the 

date by which attainment can be achieved as expeditiously 

as practicable, but no more than five years from the date of

designation. 

The attainment date is January 1, 2015. 

§ 51.1007 Attainment demonstration and modeling 

requirements.

(a) For any area designated as nonattainment for the PM2.5

NAAQS, the State must submit an attainment 

demonstration showing that the area will attain the annual 

and 24-hour standards as expeditiously as practicable. The 

attainment demonstration and supporting air quality 

modeling should be consistent with EPA's PM2.5 modeling 

guidance.

(b) The State implementation plan must provide for 

implementation of all control measures needed for 

attainment as expeditiously as practicable.

The attainment demonstration can be 

found in section 4 and the control 

measures are listed in section 5.

§ 51.1008 Emission inventory requirements for the PM2.5

NAAQS.

(a) For purposes of meeting the emission inventory 

requirements of section 172(c)(3) of the Act for 

nonattainment areas, the State shall submit to EPA 

Statewide emission inventories for direct PM2.5 emissions 

and emissions of PM2.5 precursors. 

(b) For inventories required for submission under paragraph 

(a) of this section, a baseline emission inventory is required 

for the attainment.

The emissions inventory is discussed in 

section 3.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

52

§ 51.1009 Reasonable further progress (RFP) 

requirements. If the State submits to EPA an attainment 

demonstration and State implementation plan for an area

which demonstrates that it will attain the PM NAAQS within 

five years of the date of designation, the State is not 

required to submit a separate RFP plan. 

RFP does not apply because this plan 

demonstrates attainment within 5 years of 

designation.

§ 51.1010 Requirements for reasonably available control 

technology (RACT) and reasonably available control 

measures (RACM). The State shall submit with the 

attainment demonstration a SIP revision demonstrating that 

it has adopted all reasonably available control measures 

necessary to demonstrate attainment as expeditiously as 

practicable. The SIP revision shall contain the list of the 

potential measures considered by the State, and 

information and analysis sufficient to support the State's 

judgment that it has adopted all RACM, including RACT. 

The State must consider the cumulative impact of 

implementing the available measures. Potential measures 

that are reasonably available considering technical and 

economic feasibility must be adopted as RACM if, 

considered collectively, they would advance the attainment 

date by one year or more.

RACT and RACM are discussed in section 

5.

§ 51.1012 Requirement for contingency measures. 

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.

Franklin County’s contingency measure 

obligation is addressed in section 5.

6.1 Consultation and Public Notification Procedures

CAA Section 110(a)(2)(M) requires that SIPs provide for public consultation and participation 

by affected local political subdivisions. The public participation effort by IDEQ and UDAQ on 

developing the CVNAA SIP has been extensive. Work commenced on this project in December 

2009. While developing the SIP’s technical portions (dispersion modeling, emissions inventory, 

and attainment and maintenance demonstrations), regular meetings were held with UDAQ, 

IDEQ, EPA Regions 8 and 10, MPO, and ITD. These meetings provided a cooperative 

atmosphere where the various PM2.5 and jurisdictional issues could be addressed. Agreement was 

made as each critical component was established, including developing the emissions inventory

and supporting document, resolving modeling issues, and evaluating control measures.

In addition to the technical committee listed above, IDEQ has worked and consulted with the 

cities of Preston, Franklin, Weston, Dayton, Clifton, and Oxford as well as Franklin County, and

ITD on issues related to air quality issue within the CVNAA, modification to existing 

ordinances, and a RWC ordinance. The tight working relationship between all parties and mutual 

interests in air quality in and around the Cache Valley has provided for a cooperative partnership 

in addressing the complex airshed issues. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

53

IDEQ also established a Cache Valley Airshed Advisory Group (see Appendix F). The group’s 

purpose is to serve as stakeholders for the community at large, provide IDEQ input and feedback 

during the SIP development phase, and help IDEQ identify and establish effective control 

measures for the Idaho side of the CVNAA. 

6.2 Continued Air Monitoring and Verification of Attainment

IDEQ is responsible for monitoring PM2.5 levels on the Idaho side of the CVNAA. IDEQ 

commits to complying with the continued air monitoring requirement of CAA Title III, Section 

319. The PM2.5 site is operated in compliance with EPA monitoring guidelines set forth in 40 

CFR 58, “Ambient Air Quality Surveillance,” and 40 CFR 58, Appendices A–D. 

On an annual basis, IDEQ will analyze the 3 most recent consecutive years of ambient PM2.5 

monitored data to verify continued attainment of the NAAQS for PM2.5 in accordance with 40 

CFR 50. In keeping with the requirements of CAA Title III, Section 319 (as defined in 40 CFR 

58.26), IDEQ will continue to submit to EPA by July 1 of each year an annual report on PM2.5 

data collected during the previous calendar year. These data, along with the data contained in the 

annual reports for the previous 2 years, will provide all the information needed to determine 

whether the Cache Valley attains the PM2.5 NAAQS. 

6.3 Permitting Program Role

IDAPA 58.01.01, “Rules for the Control of Air Pollution in Idaho,” contains various permitting 

rules. The stationary source air permitting rules are found in IDAPA 58.01.01.200–500. The 

permitting program requires permits for constructing and operating new, or modifying existing, 

stationary sources within the NAA. Section 204 applies specifically to major sources in NAAs.

Additionally, there are statewide SIP-approved rules that apply to the SIP NAA such as those 

dealing with fugitive dust (IDAPA 58.01.01.650–651) and open burning (IDAPA 58.01.01.600–

624).

6.4 Review Commitment and Plan Update

IDEQ commits to provide a revision to this plan if required in accordance with CAA Section 

110(a)(2)(H). The Environmental Protection and Health Act, Idaho Code § 39-105, and the Rules 

for the Control of Air Pollution in Idaho, IDAPA 58.01.01, promulgated thereunder, provide the 

authority to the state to revise SIPs and to satisfy CAA requirements. The monitoring data will 

be analyzed to verify continued attainment with the NAAQS, and the plan will be reviewed if 

significant an upward trend in design values occurs. Finally, if any of the underlying EPA 

assumptions are modified, such as the motor vehicle emissions or a large increase in industrial or 

fugitive dust emissions, the SIP will be reviewed to determine if any revision is necessary. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP

54

7 Conclusions

This SIP demonstrates that the CVNAA (Logan, Utah—Franklin, Idaho) will achieve attainment 

with the 24-hour PM2.5 NAAQS by January 1, 2015. The states of Utah and Idaho have worked 

cooperatively with each other, with EPA, and with citizens to develop control strategies in 

keeping with the inventories on both sides of the CVNAA.

The State of Idaho will continue to monitor PM2.5 concentrations in Franklin County. If

exceedances occur, IDEQ will determine the cause(s) and adjust the appropriate control 

measures to ensure prompt corrective action is taken. 

This CVNAA SIP fulfills the requirements of the CAA as they pertain to State Implementation 

Plans. IDEQ requests that EPA approve this attainment plan in accordance with CAA 

Section 110.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

55

8 References

Boylan, J.W. and A.G. Russell. 2006. “PM and Light Extinction Model Performance Metrics, 

Goals, and Criteria for Three Dimensional Air Quality Models.” Atmospheric 

Environment 40: 4946-4959.

CFR (Code of Federal Regulations). As of 2012. “Standards of Performance for New 

Residential Wood Heaters.” 40 CFR 60, subpart AAA.

CFR (Code of Federal Regulations). As of 2012. “Ambient Air Quality Surveillance.” 40 CFR 

Part 58.

CFR (Code of Federal Regulations). As of 2012. “Determining Conformity of Federal Actions to 

State or Federal Implementation Plans.” 40 CFR 93.

CFR (Code of Federal Regulations). As of 2012. “Interpretation of the National Ambient Air 

Quality Standards for PM2.5.” 40 CFR 50, Appendix N.

CFR (Code of Federal Regulations). As of 2012. “National Primary and Secondary Ambient Air

Quality Standards.” 40 CFR 50.

CFR (Code of Federal Regulations). As of 2012. “Requirement for Preparation, Adoption, and 

Submittal of Implementation Plans.” 40 CFR 51.

EPA (United States Environmental Protection Agency) 2012. “Implementation Guidance for the 

2006 24-Hour Fine Particle (PM2.5) National Ambient Air Quality Standards 

(NAAQS).” March 2, 2012 Memorandum to Regional Air Directors.

EPA (United States Environmental Protection Agency). 1996 update. Compilation of Air 

Pollutant Emission Factors. 5th ed. AP 42. 

EPA (United States Environmental Protection Agency). 2011 update. Compilation of Air 

Pollutant Emission Factors. 5th ed. AP 42.

EPA (United States Environmental Protection Agency). 2012. Guidance for Transportation 

Conformity Implementation in Multi-Jurisdictional Nonattainment and Maintenance 

Areas. EPA-420-B-12-046.

FR (Federal Register). 2000. “Control of Air Pollution From New Motor Vehicles: Tier 2 Motor 

Vehicle Emissions Standards and Gasoline Sulfur Control Requirements.” 65 FR 6698.

FR (Federal Register). 2001. “Control of Air Pollution From New Motor Vehicles: Heavy-Duty 

Engine and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements.” 

66 FR 5002.

FR (Federal Register). 2007. “Clean Air Fine Particle Implementation Rule.” 72 FR 20586.

FR (Federal Register). 2009.“Air Quality Designations for the 2006 24-Hour Fine Particle 

(PM2.5) National Ambient Air Quality Standards, Final Rule.” 74 FR 58688–58781.
Cache Valley Idaho PM2.5 Nonattainment Area SIP

56

Idaho Code. 2012. “Idaho Environmental Protection and Health Act.” Idaho Code 39-101 

through 39-130.

IDAPA. 2012. “Rules for the Control of Air Pollution in Idaho.” Idaho Administrative Code. 

IDAPA 58.01.01.

Martin, Randy. 2006. Cache Valley Air Quality Studies; a Summary of Research Conducted 

(through 2006). Logan, UT: Department of Civil & Environmental Engineering, Utah 

State University.

US Congress. 1970. Clean Air Act. 42 USC § 7401 et seq.

Wolyn, P. G. and T. B. McKee. 1989. “Deep Stable Layers in the Intermountain Western United 

States.” Monthly Weather Review 117: 461–472.