DAQ-2025-000776

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Technical Support Document
On-road Mobile Sources
Ozone Episodic Inventory:
2017 May-August

June 2024
Utah Division of Air Quality
Inventory Section

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Abstract

This report discusses the on-road mobile source section of the Ozone SIP episodic inventory for the domain comprising all 29 counties within the state of Utah. The on-road mobile source episodic inventories were developed utilizing Environmental Protection Agency’s (EPA) emission software for on-road mobile sources: Motor Vehicle
Emissions Simulator (MOVES4). Inventories were created for an average episode Weekday and Weekend based on monthly 24 hour temperatures and relative humidity recorded 2017 May 1st – August 31st. Multiple local and state agencies provided key activity inputs for the 2017 episodic on-road inventory: Utah Department of Transportation (UDOT) and local Metropolitan Planning
Organizations (MPOs) provided key transportation inputs: Vehicle Miles of Travel (VMT), VMT seasonal adjustment factors, VMT travel mix factors (fractions of vehicles traveling on network roads), and network speed profiles. Utah Division of Air Quality (UDAQ) provided vehicle fleet profiles: age, fuel type, and vehicle counts. Where required, local county health departments provided vehicle inspection and maintenance (I/M) testing procedures and results covering applicable and required vehicles. EPA provided local fuel profiles and specifications.
Summary on-road emissions inventory tables for a representative summer weekday are located at the end of the TSD: 2017 May-August.

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3.e.ii) ON-ROAD MOBILE SOURCES OZONE EMISSIONS INVENTORIES

i. Table of Contents……………………………………………………………………......... 3

ii. Glossary of Acronyms…………………………………………………………………….. 4

iii. Overview………………………………………………………………………................. 5

iv. MOVES4 Modeling Procedure............................................................................................ 6

v. Review Methodology……………………………………………………………………… 11

vi. Speciation Runs……………………………………………………………………………. 11

vii. Appendix: On-road 2017 Baseline Ozone emission inventories....................................... 19

viii. References……………………………………………………..….................................. 19

LIST OF TABLES
Table 1. Utah I/M Programs……………………………………....………..................................................................10 Table 2. MOVES4 Regulatory Classification Mapping……………………………………………………………....12
Table 3. On-road Mobile Sources May 2017 Episodic Summertime Ozone emissions inventory representing: Summer Weekday Emissions
(Tons per Summer Weekday)………………………………………………………………………………………...13
Table 4. On-road Mobile Sources June 2017 Episodic Summertime Ozone emissions inventory representing: Summer Weekday Emissions
(Tons per Summer Weekday)………………………………………………………………………………………...13 Table 5. On-road Mobile Sources July 2017 Episodic Summertime Ozone emissions
inventory representing: Summer Weekday Emissions (Tons per Summer Weekday)………………………………………………………………………………………...14
Table 6. On-road Mobile Sources August 2017 Episodic Summertime Ozone emissions
inventory representing: Summer Weekday Emissions (Tons per Summer Weekday)…………………………………………………………………………………….…..14
Table 7. On-road Mobile Sources Summertime 2017 May Episodic Ozone emissions inventory representing: Summer Weekday Emissions (Tons per Summer Weekday) by County………………...……………………………………………………...……15
Table 8. On-road Mobile Sources Summertime 2017 June Episodic Ozone emissions inventory representing: Summer Weekday Emissions
(Tons per Summer Weekday) by County…………………...……………………………………...……………...….16
Table 9. On-road Mobile Sources Summertime 2017 July Episodic Ozone emissions inventory representing: Summer Weekday Emissions
(Tons per Summer Weekday) by County………………………………………...………………...………………....17 Table 10. On-road Mobile Sources Summertime 2017 August Episodic Ozone emissions
inventory representing: Summer Weekday Emissions (Tons per Summer Weekday) by County…………………...……………………………...…………...…………….18
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ii. Glossary of Acronyms:

Alternative Vehicle and Fuels & Technology (AVFT)

Average Annual Daily Traffic (AADT)

County Data Manager (CDM)

Environmental Protection Agency (EPA)

Gross Vehicle Weight Rating (GVWR)

Highway Performance Management System (HPMS)

Inspection/Maintenance (I/M)

Mountainland Association of Governments (MAG)

MOVES4 (Motor Vehicle Emission Simulator)

Nonattainment Area (NA)

On-Board Diagnostics (OBD)

Two Speed Idle (TSI)

Utah (UT)

Utah Department of Transportation (UDOT)

Utah Division of Air Quality (UDAQ)

Utah Division of Motor Vehicles (UDMV)

Vehicle Hours Traveled (VHT)

Vehicle Miles Traveled (VMT)

Wasatch Front Regional Council (WFRC)

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iii. Overview

The purpose of this document is to explain what emissions modeling assumptions were used to
develop the on-road mobile source Ozone SIP episodic inventories for 2017 May 1st – August
31st. The inventory covers all 29 counties within the state of Utah including the Northern
Wasatch Front, Utah (UT), Non-Attainment Area (NA).

Multiple agencies constructed the episodic inventory for on-road mobile sources at the county
level for the whole state of Utah.

Wasatch Front Regional Council (WFRC) Metropolitan Planning Organization (MPO) provided
emission estimates for the Northern Wasatch Front UT, NA covering Davis, Salt Lake, Tooele,
and Weber counties, including portions of those counties outside the NA. In addition, WFRC
provided emission estimates for Box Elder County, also outside the NA.

Mountainland Association of Governments (MAG) MPO provided modeling for Utah County
outside the NA.

Utah Division of Air Quality (UDAQ) and Utah Department of Transportation (UDOT) provided
modeling for rural counties outside the NA: Beaver, Cache, Carbon, Daggett, Emery, Garfield,
Grand, Iron, Juab, Kane, Millard, Morgan, Piute, Rich, San Juan, Sanpete, Sevier, Summit,
Wasatch, Washington, and Wayne.

Emission estimates are confined to the Environmental Protection Agency (EPA) approved Motor
Vehicle Emissions Simulator (MOVES4 4.0.1-movesdb20240104). This model produces daily
emissions estimates for on-road vehicles for a specific weekday or weekend for a given month.
MOVES4 modeling of vehicle activity inputs include: VMT (by month, weekday, and weekend),
vehicle type factors, vehicle population, network speeds, vehicle age profiles, I/M profiles, fuel
profiles and specifications, and meteorological conditions.

The MOVES4 model is run with the local activity data and is matched up with the appropriate
emission factors. The emissions factors within the model are determined by EPA using vehicle
specific test data matching existing Federal Emissions Standards. On-road emissions estimates
are broken into specific categories covering: starts, exhaust (idle and running), evaporative and
hot soak conditions.

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iv. MOVES4 Modeling Procedure
The discussion below identifies the procedures followed to model the episodic inventories.
1. MOVES4

The EPA MOVES4 model was used to produce on-road emissions estimates for an
average weekday and weekend in May, June, July, and August.

2. MOVES4 Daily Pollutants

Primary emission estimates included within the analysis:
● Ammonia (NH3)
● Carbon Monoxide (CO)
● Oxides of Nitrogen (NOx)
● PM2.5 Exhaust (PM25_Ex)
● Volatile Organic Compounds (VOC)

3. MOVE4 Local Model Inputs

(a) County Data Manager Development
MOVES4 organizes data inputs into databases called County Data Manager (CDM)
tables. CDMs were developed for 29 counties for the year 2017: average weekday and
weekend.
(1) Transportation Inputs: Average Speed Distribution, VMT, VMT factors, VMT
mix, and Road Distribution: UDOT and MPOs (MAG & WFRC)

WFRC obtained 2017 VMT estimates from the HPMS report published by
UDOT. Monthly factors for weekdays and weekends for May, June, July, and
August were applied to create the desired VMT estimates for each month and
day to be modeled. Vehicle type percentages based on counts from UDOT for
light duty and heavy duty vehicles, were expanded to thirteen vehicle types using
default proportions in the MOVES4 model. These vehicle percentages were then
used to disaggregate the total daily VMT by vehicle type. Local data for transit
buses and school buses were used in place of default values.

Travel demand models were used to define the VMT distribution by road type
and vehicle type, as well as detailed speed profiles. The WFRC model was used
for Salt Lake and Davis Counties. The Utah State Travel Model (USTM) was
used for Weber, Tooele, and Box Elder Counties because the WFRC model does
not cover the entirety of these counties.

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WFRC developed the TDM2MOVES_mysql application for the purpose of
extracting needed inputs for the MOVES4 model from the travel demand model.
MOVES4 input files for road type distribution, speed profile, and VMT by
vehicle type were generated using this application. The VMT by vehicle type
was prorated to match the total VMT for each month derived from the HPMS
report.

UDOT used the travel demand models across the state to estimate 2017 weekday
and weekend monthly VMT. These travel demand models produce spring/fall
weekday VMT, therefore UDOT utilized monthly/weekend factors to convert
spring/fall weekday VMT to May, June, July, and August weekday and weekend
VMT. UDOT also utilized 2017 VMT estimates from HPMS to ensure 2017
conditions align with previously reported VMT. Vehicle type percentages based
on counts from UDOT for light duty and heavy duty vehicles, were expanded to
thirteen vehicle types using default proportions in the MOVES4 model. These
vehicle percentages were then used to disaggregate the total daily VMT by
vehicle type.

(2) 2017 Age Distribution and Source Type Population

Age and source type populations are constructed for 31 model years for all
vehicle types. 2018 Utah DMV data contains registrations with an expiration of
January 1, 2018 or greater as of February 15, 2018. 2018 model years are added
to 2017 model years. This is done because there are not that many 2018 model
years and car manufacturers have model years available for sale before the actual
year has occurred, some car manufacturers sell model years early for customers as
a selling point. UDAQ includes 2018 model year vehicles to account for their
vehicle starts emissions, even though they do not ‘fit’ exactly within the model
year inputs available for MOVES4. After the initial first year, individual model
years are represented by their respective model year until the 31st year. The last
year, 1987, is compiled by combining model years 1987-1969.

DMV data is compiled by the following vehicle type: passenger cars, light duty
trucks, and heavy duty trucks. Registered vehicles are categorized by usage:
farm, motorhome, and truck standard: sorted by 14 GVWR (Gross Vehicle Weight
Rating) categories. Farm trucks and truck standard data sets are combined
together by weight categories. Motorhomes include vehicles that weigh >=
14,000 GVWR. DMV passenger cars and light duty truck data sets are combined
initially via HPMS classifications, with MOVES4 default fractions being utilized
to determine the percentage of passenger cars and light duty trucks.
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The state vehicle DMV data is matched with MOVES4 mapping of vehicles using
MOVES4 Regulatory Classifications to Highway Performance Monitoring
System to MOVES4 source types (see Table 2).

Age and Population vehicle profile adjustments were made to account for heavy
duty trucks operating out of state. Adjusted vehicles include: Source Type 53
Single Unit Long Haul Trucks and Source Type 62 Combination Long Haul
Trucks. National Default Age distributions were used for these vehicles. Vehicle
populations are based on using a population/VMT ratio equation. The equation
used is the following: UDMV Population/MOVES4 default VMT * Travel
Demand Model VMT. This ratio is used to calculate new vehicle population for
source types 53 and 62, accounting for out of state trucks. MOVES4 default age
profiles are used for source types 53 and 62. To be conservative, WFRC utilized
DMV registration data for heavy duty truck population profiles.

Past methodologies included using DMV counts only for passenger cars and light
duty trucks. MOVES4 default fractions were used to determine the fraction of
passenger cars and light duty trucks. Passenger cars and light duty trucks utilized
the same age profile. To account for heavy duty vehicle counts, default MOVES4
vehicle profiles were used. The heavy duty truck default profiles were adjusted
by DMV data by passenger car and light duty truck data. MOVES4 default age
distributions were used for heavy trucks.

(3) AVFT (Alternative Vehicle and Fuels & Technology: Electric, Diesel and
Gasoline Vehicle Fractions)

2017 AVFT profiles were created using the following data and methods. 2018
Utah DMV data includes registration of vehicles by fuel type. The data available
includes fleet data for the year and is not available by specific model year. The
data used for the AVFT profile covers passenger cars and light duty trucks up to
12,000 GVWR. Default AVFT profiles were used for heavy duty vehicles as
these vehicles mainly consist of out of state trucks.

The annual DMV data was adjusted in multiple ways: MOVES4 default
passenger car and light duty truck fractions were utilized to adjust the percentage
of passenger cars and light duty trucks and their associated fuel fractions.
MOVES4 runs were constructed with DMV age and population inputs along with
the EPA default AVFT profile. The modeling results provided output to construct
an annual default AVFT profile for passenger cars and light duty trucks. The
default AVFT profile was adjusted to match the annual DMV registration fuel
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type fractions. MPO counties have specific AVFT profiles and rural counties
were combined to create a single AVFT profile. Rural counties were combined to
reduce computational time as they have similar fleet characteristics.

Past methodologies include using DMV data for passenger cars and light duty
trucks. MOVE3 default passenger car and light duty truck fractions were utilized
to adjust the percentage of passenger cars and light duty trucks and their
associated fuel fractions. Annual DMV data was applied as a model year with
multiple annual DMV datasets being used.

(4) Fuel

MOVES4 default fuel parameters were used for all fuel types, including 20.68
ppm gasoline sulfur levels in 2017. The local gasoline sulfur level reflects the
Federal Rule, that small volume refineries were not required to comply with
Federal Tier 3 gasoline (10 ppm sulfur), until January 1, 2020.

Past methodologies utilized gasoline sulfur levels inputs directly from EPA.
MOVES4 did not include Utah specific local gasoline specifications that had
higher sulfur content as allowed by Federal Rule. MOVES4 Fuel Wizard tool
was utilized, in conjunction with EPA inputs, to construct local Utah gasoline
profiles with higher sulfur content.

(5) Hour VMT Fraction

MOVES4 default Hour VMT Fraction values were used.
Past methodologies utilized MOVES4 default Hour VMT Fractions.

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(6) I/M Coverage: Cache, Davis, Salt Lake, Utah, and Weber Counties
UDAQ constructed I/M programs in consultation with the local county health
departments in Cache, Davis, Salt Lake, Utah, and Weber Counties. In 2017,
MOVES4 does not provide I/M emissions credit for vehicles older than 1987, as
the model only provides emission estimates for 31 model years.

Vehicles older than 1995 undergo a Two Speed Idle (TSI) test and vehicles newer
than 1996 undergo On-Board Diagnostic Testing (OBD). Heavy Duty Trucks did
not have OBD capability until 2008. Davis, Salt Lake, Utah and Weber Counties
I/M programs exempt the first two model years, biennially test the third through
sixth model years, and perform an annual test on the remaining vehicles. The
Cache County I/M program started in 2014 and exempt the first six model years
and perform a biennial test on vehicles beginning in the seventh model year.
Below is a summary covering I/M programs in 2017.

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(7) Zone Month Hour (Meteorological Data)

The UDAQ Technical Analysis Section provided meteorological conditions from
the MesoWest archives. MesoWest (mesowest.utah.edu) is a database of current
and archived meteorological data from weather stations in the United States
maintained by the University of Utah.

2017 May 1st – August 31st
Meteorological data was identified by locating the largest population center for
each county. Then the nearest weather station was acquired from the MesoWest
data archives. Since ozone events along the Wasatch Front occur sporadically
throughout the summertime, the following representative months were used: May,
June, July and August.

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v. Review Methodology

Multiple quality assurance and quality control methodologies are utilized to ensure that
the correct inputs are utilized to create the on-road mobile inventory. Checks are
instituted along several steps of creating the inventory. The type of checks being used
extend from text file comparisons, built in Excel checks, MySQL scripts comparing
inputs to main input databases, comparing default MOVES4 inputs and output emissions,
and comparing past emissions inventories. Specific error checking results are stored
within workbooks and/or shared with submitting agencies to ensure file completeness.

vi. Speciation Runs

On-road mobile VOC speciation runs for Salt Lake County were created to assist the
modeling section in creating ozone speciation profiles. The total emissions created from
these profile runs are no different than the one utilized in airshed modeling. The main
difference is that the output being used in the speciation profile is quantified by model
year.

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vii. Appendix: On-road 2017 Baseline Ozone emissions inventories

Input files will be furnished upon request.

viii. References

The following documents were used as references in creating the on-road mobile source Ozone
SIP emissions inventories:

1. U.S. Environmental Protection Agency, Office of Transportation and Air Quality, "MOVES4
Technical Guidance: Using MOVES to Prepare Emission Inventories for State Implementation
Plans and Transportation Conformity", EPA-420-B-23-011 August 2023,
https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P101862T.pdf

2. I/M Programs

a. Davis County Health Department, Environmental Health Services Division, Davis County
Testing Center, 20 North 600 West, Kaysville, UT 84037, 801-546-8860.

b. Salt Lake County Health Department, Environmental Health, Air Pollution Control, I/M Tech
Center, 788 East Woodoak Lane (5380 South), Murray, UT 84107-6369, 385-468-4837.

c. Utah County Health Department, Utah County Environment Health, Bureau of Air Quality,
I/M Tech Center, 3255 North Main Street, Spanish Fork, UT, 84660, 801-851-7600.

d. Weber-Morgan Health Department, Environmental Health, 477 23rd Street, 2nd floor, Ogden,
UT 84401, 801-399-7160.

e. Bear River Health Department, 655 East 1300 North. Logan, UT 84341, 801-792-6500

3. MESOWEST Utah, (meteorological data archive), University of Utah, Department of
Atmospheric Sciences, http://mesowest.utah.edu/

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