Air Toxic Emissions from Onroad
Vehicles in MOVES3
United States
Environmental Protection
^1 Agency
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Air Toxic Emissions from Onroad
This technical report does not necessarily represent final EPA decisions
or positions. It is intended to present technical analysis of issues using
data that are currently available. The purpose in the release of such
reports is to facilitate the exchange of technical information and to
inform the public of technical developments.
Vehicles in MOVES3
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
NOTICE
&EPA
United States
Environmental Protection
Agency
EPA-420-R-20-022
November 2020
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Table of Contents
Table of Contents 1
List of Acronyms 3
1 Introduction 5
2 Gasoline Exhaust 10
2.1 Volatile Organic Compounds 10
2.1.1 Vehicles Operating on Fuel Blends Containing 0-15 Percent Ethanol 10
2.1.2 Vehicles Operating on Fuel Blends Containing 70-100 Percent Ethanol 40
2.2 Polycyclic Aromatic Hydrocarbons (PAHs) 44
2.2.1 Vehicles Operating on Fuel Blends Containing 0-15 Percent Ethanol 44
2.2.2 Vehicles Operating on Fuel Blends Containing 70-100 percent Ethanol 48
2.3 Metals 49
2.4 Dioxins and Furans 52
2.4.1 Vehicles Operating on Fuel Blends Containing 0-15 Percent Ethanol 52
2.4.2 Vehicles Operating on Fuel Blends containing 70-100 percent Ethanol 53
3 Diesel Exhaust 55
3.1 Volatile Organic Compounds 55
3.1.1 Pre-2007 Diesel Engines 55
3.1.2 2007+ Diesel Engines 56
3.2 Polycyclic Aromatic Hydrocarbons 57
3.2.1 Pre-2007 Diesel Engines 58
3.2.2 2007+ Diesel Engines 59
3.3 Metals 60
3.4 Dioxins and Furans 61
4 Compressed Natural Gas (CNG) Exhaust 63
4.1 Volatile Organic Compounds 63
4.2 Polycyclic Aromatic Hydrocarbons 63
4.3 Metals 64
4.4 Dioxins and Furans 65
5 Evaporative and Refueling Emissions 66
5.1 Gasoline Vehicles 66
5.1.1 Vapor Venting, Fuel Leaks, and Refueling Emission Processes 66
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5.1.2 Permeation 68
5.2 Diesel Vehicles 70
6 Crankcase Emissions 71
6.1 Volatile Organic Compounds 71
6.2 Poly cyclic Aromatic Hydrocarbons 71
6.3 Metal and Dioxin Emissions 71
Appendix A. Development of Motor Vehicle Emission Factors for Chromium 73
Appendix B. Development of Motor Vehicle Emission Factors for Mercury 76
7 References 81
2
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List of Acronyms
ACES
Advanced Collaborative Emissions Study
APU
auxiliary power units
CARB
California Air Resource Board
CAS
Chemical Abstracts Service Registry number
CBD
Central Business District Driving Schedule
CH4
methane
CNG
compressed natural gas
CO
carbon monoxide
C02
carbon dioxide
CRC
Coordinating Research Council
DOE
U.S. Department of Energy
DRI
Desert Research Institute
DVPE
dry vapor pressure equivalent
EF
emission factor
EGR
exhaust-gas recirculation
ETBE
ethyl tertiary-butyl ether
EtOH
ethyl hydroxyl
EPA
U.S. Environmental Protection Agency
EO
gasoline containing 0 percent ethanol by volume
E10
gasoline containing 10 percent ethanol by volume
E15
gasoline containing 15 percent ethanol by volume
E20
gasoline containing 20 percent ethanol by volume
E70
gasoline containing 70 percent ethanol by volume
E85
gasoline containing 70-85 percent ethanol by volume
FTP
Federal Test Procedure
HAP
hazardous air pollutants
ICP-MS
inductively-coupled plasma mass spectrometry
KCVES
Kansas City Light-Duty Vehicle Emissions Study
LA92
Unified Driving Schedule
LIFEREG
accelerated failure time regression model
LRT
likelihood-ratio tests
MOBILE
EPA highway vehicle emission factor model (predecessor to MOVES)
MSAT2
Control of Hazardous Air Pollutants from Mobile Sources Rule
MTBE
methyl tertiary-butyl ether
NATA
National Air Toxics Assessment
NEI
National Emission Inventory
NERL
National Exposure Research Laboratory
NVFEL
EPA's National Vehicle Fuel Emissions Laboratory
NLEV
National Low Emission Vehicle
NMHC
non-methane hydrocarbons
NMIM
National Mobile Inventory Model
NMOG
non-methane organic gases
NOX
nitrogen oxide
NREL
National Renewable Energy Laboratory
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OC organic carbon
Oxy oxidation catalyst
PAHs polycyclic aromatic hydrocarbons
PFI port fuel injection
PM particulate matter
PUF-XAD polyurethane foam-macroreticular resins
RVP Reid Vapor Pressure
SAS Statistical Analysis System
SCR selective catalytic reduction
SPECIATE repository of volatile organic gas and PM speciation profiles of air
pollution sources
svoc semi-volatile organic compound
TAME tertiary amyl methyl ether
TBI throttle body injection
THC total hydrocarbon
TIGF teflon-impregnated glass filters
TOG total organic gases
T50 temperature at which 50 vol% of a fuel has been evaporated (°F)
T90 temperature at which 50 vol% of a fuel has been evaporated (°F)
VMT vehicle miles traveled
VOC volatile organic compound
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1 Introduction
The United States Environmental Protection Agency's Motor Vehicle Emission Simulator
(MOVES) is a set of modeling tools for estimating air pollution emissions produced by onroad
(highway) and nonroad mobile sources. MOVES estimates the emissions of greenhouse gases
(GHGs), criteria pollutants and selected air toxics. The MOVES model is currently the official
model for use for state implementation plan (SIP) submissions to EPA and for transportation
conformity analyses outside of California. The model is also the primary modeling tool for
estimating the impact of mobile source regulations on emission inventories, and thus, provides
important inputs to air quality models.
Through MOVES, users can estimate inventories for selected compounds identified as air toxics
in the National Emission Inventory (NEI) and National Air Toxics Assessment (NATA), and for
which adequate data are available to develop mobile source emissions estimates.
The toxics included in MOVES are classified into four categories:
1) Volatile Organic Compounds (VOC): EPA defines VOC as any compound of carbon,
excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or
carbonates, and ammonium carbonate, which participates in atmospheric photochemical
reactions, except those designated by EPA as having negligible photochemical
reactivity.1 For use in MOVES in defining emission rates and application of speciation
profiles, VOC is defined as total organic gas (TOG) minus methane, ethane, and acetone.
2) Polycyclic aromatic hydrocarbons (PAHs): This category is defined as hydrocarbons
containing fused aromatic rings. In MOVES, the PAHs are treated separately than VOC
toxics, because PAHs are semi-volatile organic compounds (SVOC) and may be
measured in the gaseous phase, particulate phase, or both, depending on properties of the
compound, particle characteristics and conditions in the exhaust stream or the
atmosphere. MOVES estimates the sixteen PAHs (Table 1-2) that are included in the
National Emissions Inventory (NEI), which does not include nitrated PAHs.
3) Dioxins and furans: This category includes polychlorinated organic compounds which are
persistent in the environment and considered bioaccumulative in aquatic and terrestrial
food chains.
4) Metals: This category includes metals or metal-containing compounds in elemental,
gaseous and particulate phases.
Specific compounds in each category are listed in Table 1-1 through Table 1-4. Note that each
compound is identified by its pollutantID in the MOVES database. With the exception of the
metal species in Table 1-4, each compound is also identified by its Chemical Abstracts Service
Registry number (CAS number).2 For most other compounds, the identifier for the National
Emissions Inventory (NEIPollutantCode in the pollutant table) is identical to the CAS number
(minus the dashes). In MOVES3, methyl-tertiary-butyl-ether (MTBE) has been removed from
the volatile organic compounds (Table 1-1), since it has been many years since this pollutant has
been used as a gasoline additive in any significant quantity.
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Table 1-1. Hydrocarbons and Volatile Organic Compounds Included in MOVES
Pollutant
pollutantID
CAS Number
Benzene
20
71-43-2
Ethanol
21
64-17-5
1,3-Butadiene
24
106-99-0
Formaldehyde
25
50-00-0
Acetaldehyde
26
75-07-0
Acrolein
27
107-02-8
2,2,4-Trimethylpentane
40
540-84-1
Ethyl Benzene
41
100-41-4
Hexane
42
110-54-3
Propionaldehyde
43
123-38-6
Styrene
44
100-42-5
Toluene
45
108-88-3
Xylene(s)1
46
1330-20-7
Note:
1 These species represent the sum of emissions from three isomers of xylene, i.e., ortho-,
meta-, and para-xylene. In the MOVES database the sum of the different isomers of
xylene is referred to simply as xylene.
Table 1-2. Polycyclic Aromatic Hydrocarbons Included in MOVES
Pollutant
pollutantID
CAS Number
(gaseous phase)
(particulate phase)
Acenaphthene
170
70
83-32-9
Acenaphthylene
171
71
208-96-8
Anthracene
172
72
120-12-7
Benz(a)anthracene
173
73
56-55-3
Benzo(a)pyrene
174
74
50-32-8
Bcn/o(/))fluoranthcnc
175
75
205-99-2
B c n / o (w. /?,/) pc ry 1 c n c
176
76
191-24-2
B e n/o (/i') fl no ra n t lie nc
111
77
207-08-9
Chrysene
178
78
218-01-9
Dibcn/o(fl, /?)anthraccne
168
68
53-70-3
Fluoranthene
169
69
206-44-0
Fluorene
181
81
86-73-7
Indeno( 1,2,3 ,c, d) pyrene
182
82
193-39-5
Naphthalene
185
23
91-20-3
Phenanthrene
183
83
85-01-8
Pyrene
184
84
129-00-0
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Table 1-3. Dioxins and Furans Included in MOVES
Pollutant
pollutantID
CAS Number
2,3,7,8-Tetrachlorodibenzo-p-Dioxin
142
1746-01-6
1,2,3,7,8-Pentachlorodibenzo-p-Dioxin
135
40321-76-4
1,2,3,4,7,8-Hexachlorodibenzo-p-Dioxin
134
39227-28-6
1,2,3,6,7,8-Hexachlorodibenzo-p-Dioxin
141
57653-85-7
1,2,3,7,8,9-Hexachlorodibenzo-p-Dioxin
130
19408-74-3
1,2,3,4,6,7,8-Heptachlorodibenzo-p-Dioxin
132
35822-46-9
Octachlorodibenzo-p-dioxin
131
3268-87-9
2,3,7,8-Tetrachlorodibenzofuran
136
51207-31-9
1,2,3,4,6,7,8-Heptachlorodibenzofuran
144
67562-39-4
1,2,3,4,7,8,9-Heptachlorodibenzofuran
137
55673-89-7
1,2,3,4,7,8-Hexachlorodibenzofuran
145
70648-26-9
1,2,3,6,7,8-Hexachlorodibenzofuran
140
57117-44-9
1,2,3,7,8,9-Hexachlorodibenzofuran
146
72918-21-9
1,2,3,7,8-Pentachlorodibenzofuran
139
57117-41-6
2,3,4,6,7,8-Hexachlorodibenzofuran
143
60851-34-5
2,3,4,7,8-Pentachlorodibenzofuran
138
57117-31-4
Octachlorodibenzofuran
133
39001-02-0
Table 1-4. Metals Included in MOVES
Pollutant
pollutantID
Mercury (elemental gaseous)
60
Mercury (divalent gaseous)
61
Mercury (particulate)
62
Arsenic compounds
63
Chromium (Cr6+)
65
Manganese compounds
66
Nickel compounds
67
The report is structured around the four MOVES toxic categories, discussed by fuel type and
emission processes. Toxics from exhaust emissions from both light-duty and heavy-duty vehicles
are discussed for gasoline (Section 2), diesel (Section 3) and compressed natural gas (Section 4).
For gasoline vehicles, MOVES includes the capability to estimate emissions for ethanol blends
containing more than 10 percent ethanol, including E15 and E85 (70-100 percent ethanol).
The toxic emissions from the evaporative and refueling processes are discussed in Section 5, and
from crankcase processes in Section 6. For exhaust, evaporative, refueling and crankcase
emissions, MOVES estimates emissions from vehicles representing relevant combinations of
technology and fuel; however, the availability and comprehensiveness of toxics data varies
widely. Consequently, the methods and approaches used to develop model inputs also varied as
necessary to incorporate the latest and best data into the model.
During MOVES runs, emissions of toxic compounds (except for metals and dioxins/furans), are
estimated as fractions of the emissions of VOC, or for toxic species in the particulate phase,
fractions of total organic carbon < 2.5 [j,m (OC2.5) MOVES estimates of VOC emissions are
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calculated from emissions of total hydrocarbon (THC) as discussed in the MOVES Speciation
Report.21 All toxic fractions are mass-based (as opposed to using molar-ratios).
For some compounds, the toxic emissions are estimated using fractions that vary with levels of
fuel properties, such as ethanol, aromatics or Reid Vapor Pressure (RVP). Fractions that vary
according to fuel properties are termed "complex" by MOVES. For other sets of compounds,
"simple" fractions are used, meaning that the fractions are constants and do not vary with fuel
properties. Note that the generalizations made here apply to evaporative as well as to exhaust
emissions. In addition, in some cases, available data were sufficient to model different fractions
for the two MOVES combustion processes, e.g., start and running exhaust emissions. In other
cases, available data were not adequate for this purpose, with the result that the same fraction is
used for both start and running emissions. Similarly, for evaporative emissions, separate fraction
were developed for "permeation" and "non-permeation" processes. Finally, fractions vary with
the levels of emission control (different ratios for vehicles before and after MY 2001), and for
pre-2001 MY vehicles, catalyst type and fuel delivery systems.
The approach differs for estimation of emissions of metals and dioxin/furans. These species are
estimated directly through application of emission rates that are assumed to be independent of
operating mode. Rates for metals and dioxins/furans are expressed on a distance-specific basis
(g/mile). Metals and dioxin emission rates are only produced from the 'running' exhaust
emission process with the g/mile rates. Due to a lack of data, MOVES does not estimate their
emissions explicitly from other exhaust emission processes such as start, extended idle, auxiliary
power unit usage, and crankcase processes. However, in some cases, the start emissions for these
pollutants are included in the driving cycle used to derive distance-based emission factors as
discussed in the report.
The inputs used to estimate emissions of toxics do not vary with the ambient temperature
simulated during a run. However, the inventories of toxic compounds estimated by the model
may vary because VOC and OC2.5, do vary by temperature, and as described above, emissions of
toxics compounds are estimated as fractions of VOC or OC2.5 emissions.
Toxics inputs for MOVES are often based on very limited data, particularly for diesel and CNG
engines and non-VOC pollutants. Thus, uncertainties in emission estimates may be substantial
for some vehicle type/emission process/pollutant combinations. In addition, for some advanced
technology vehicles, emission rates are quite low, increasing uncertainty about the toxic fraction.
Additional uncertainty is introduced when we apply toxic fractions measurements from the
available test programs to represent national fleet-average emissions. For VOC toxics and PAHs,
this includes multiplying the fractions derived from one set of test programs by VOC emission
rates from different test programs. The measurement values in this report are limited to four
significant figures, to so as not to overly convey precision in the data. However, the number of
significant figures should not be interpreted as the precision of the toxic emissions. Values that
were not reported or were below the detection limit are listed as not-detected (ND), but are
modeled as zero in MOVES. We include qualitative discussion of uncertainty, but we do not
have quantitative estimates of the uncertainty of the MOVES air toxic emission estimates.
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This report contains several updates made from MOVES2014b3 to MOVES3. These include
minor corrections to the database to be consistent with the documentation, updated text to
improve clarity of the report, and an updated speciation profile used to estimate diesel refueling
toxics. Two major content updates were made to the report
First, we have removed methyl-tertiary-butyl-ether (MTBE) from the list of toxics estimated by
MOVES. As discussed in the fuel supply report4, MOVES no longer adjusts emissions according
to the gasoline oxygenate additives methyl-tertiary-butyl-ether (MTBE), ethyl-tertiary-butyl-
ether (ETBE), or tertiary-amyl-methyl-ether (TAME). These oxygenates have been phased-out
of the gasoline market, and we do not have data on how emissions of MY 2001 and later vehicles
respond to them. For example, the EPAct fuel effects model discussed in Section 2.1.1.2 did not
consider MTBE. Instead, we model historic use of MTBE in the fuel supply with matching levels
of ethanol. Any equations that were functions of fuel oxygenates in MOVES2014 are now only
dependent on the ethanol content of the gasoline fuel.
Second, we updated the toxic fractions and rates from MOVES2014b for model year 2007 and
later diesel engines. The updated diesel exhaust emission values in Sections 3.1.2, 0, and 3.3
were peer-reviewed in September 2017. The peer-reviewed report, charge questions to the peer-
reviewers, peer-review comments, EPA responses and other associated peer-review materials are
located on EPA's science inventory webpage.5
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2 Gasoline Exhaust
The gasoline toxic emissions apply to gasoline vehicles operating on gasoline with ethanol levels
between 0-15 percent ethanol, as well as flex-fuel vehicles operating on high ethanol blends,
with over 70% ethanol (referred to generically as E85). The toxic fractions are developed from
light-duty gasoline emission rates and are applied to all gasoline vehicles, including motorcycles
and heavy-duty gasoline trucks.
For volatile organic compound toxic emissions (Section 2.1), the rates are derived from two
broad groups of gasoline and flex-fuel vehicles, incorporating differences in vehicle
technologies, emission-control technologies and emissions standards, as well as subsets of
available data and analytic methods. These two groups are defined as "model year 2000 and
earlier," and "model year 2001 and later." The "model year 2001 and later" group applies to
emissions starting with light-duty gasoline vehicles regulated under the National Low Emission
Vehicle (NLEV) program, which began with 2001 model year vehicles, followed by the Tier 2
light-duty vehicle emission standards6, which began with 2004 model year vehicles and the Tier
3 light-duty vehicle emission standards, which began with 2017 model year vehicles.7 In
addition to other technology changes due to EPA emission standards, gasoline direct injection
(GDI) vehicles have entered the market; understanding the impact of GDI technology on toxics
emissions is an area for future work.
For other toxic emissions from gasoline vehicles (PAHs, metals, and dioxins), we estimated
fleet-average toxic emission ratios, with no distinction for vehicle technology or model year, as
discussed in Sections 2.2, 2.3 and 2.4.
2.1 Volatile Organic Compounds
Within VOCs, there are separate subsections for vehicles operating on gasoline containing low
ethanol percentages (Section 2.1.1) and high-ethanol percentages (Section 0).
2.1.1 Vehicles Operating on Fuel Blends Containing 0-15 Percent
Ethanol
Within this sub-section, we further delineate the methods and data used for estimating toxic
VOCs from 2000 and earlier vehicles (Section 2.1.1.1) and 2001 and later model year vehicles
(Section 2.1.1.2).
2.1.1.1 2000 and Earlier Model Year Vehicles
Table 2-1 summarizes the methods used to estimate VOC toxic fractions. The complex model
equations are stored in the MOVES tables ComplexModelParameters. Ethanol and acrolein are
stored in the GeneralFuelRatioExpression table. The remaining toxic ratios based on SPECIATE
profiles are stored in the MinorHapRatio MOVES tables. The specific data and methods used for
each are described in further detail below.
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Table 2-1 Calculation Methods for Gasoline Model Year 2000-and-earlier VOC Air Toxics
Compound
Fraction Type
Basis for Estimation
Benzene
complex
Complex Model
1,3-Butadiene
complex
Complex Model
Acetaldehyde
complex
Complex Model
Formaldehyde
complex
Complex Model
2,2,4-Trimethylpentane
Simple
SPECIATE profile
Acrolein
Simple
SPECIATE profile
Ethylbenzene
Simple
SPECIATE profile
n-Hexane
Simple
SPECIATE profile
Propionaldehyde
Simple
SPECIATE profile
Styrene
Simple
SPECIATE profile
Xylene(s)
Simple
SPECIATE profile
Ethanol
Simple
4 test programs outlined in Section 2.1.1.3
2.1.1.1.1 Overview of the Complex Model
For the first four compounds listed in Table 2-1, "complex" toxic fractions of VOC were
estimated through application of equations developed for the Complex Model for Reformulated
Gasoline.8 The equations are based on about 1,800 observations collected on vehicles equipped
with three-way or three-way-plus-oxidation catalysts.51 The equations were developed by
stratifying the light-duty gasoline fleet into ten technology groups (described in Table 2-2) and
fitting statistical models to subsets of data for each group. The resulting sets of equations are
known collectively as the "unconsolidated Complex Model." The ten groups were assigned as
combinations of fuel system, catalyst type, air injection (yes/no), exhaust-gas recirculation
(EGR), and normal/high emitter status. The first nine groups were intended to represent the
"normal-emitting" vehicles. The tenth group represents the "high emitters," regardless of
technology.
The Complex Model was designed to model the "complex" behavior of selected emissions in
relation to changes in a set of selected fuel properties. The underlying dataset included
measurements collected on a sample of vehicles manufactured in model year (MY) 1990 or
earlier and reflecting "Tier 0" standards over a variety of gasoline formulations.
In fitting the Complex Model, the measurements for all fuel properties were "centered," meaning
that the mean of all measurements for the property was subtracted from each individual
measurement. This step aids in scaling the dataset so that each fuel property is centered on a
mean of 0.0. Thus, if ln7 is the natural logarithm of a specific compound, such as acetaldehyde,
the model is fit as shown in Equation 1 using terms for oxygenate (wt. percent), aromatics (vol.
percent) and RVP (psi) as examples.
" While more recent emissions data are available for Tier 1 and earlier vehicles, such as data from the Kansas City
Light-Duty Vehicle Emissions Study (KCVES) mentioned later, testing was not done on a matrix of fuels which
enable development of a fuel effects model.
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In Y Po ~l~ Poxy(j^oxy,i
X,
oxy
) + A
arom (-^arom,i
Xn
0 +
+ few(xRW,i ~ xRVp)
Equation 1
The mean values used for centering all individual fuel-property values are presented in Table
2-3. Even though the input fuels in MOVES3 assume zero percent MTBE and ETBE content, because the
Complex Model base fuel (see Section 2.1.1.1.2) has non-zero content of MTBE and ETBE, these
centering values and coefficients are used in the Complex Model calculations. Sets of coefficients (fi
values in Equation 1) for models by technology group are presented for acetaldehyde,
formaldehyde, benzene and 1,3-butadiene in Table 2-4 to Table 2-7. Dashes in table cells
indicate no coefficient was fit for that property. It should be noted that the sulfur effects terms in
the original Complex Model were not included when the model was adapted for inclusion in
MOVES; rather, the sulfur effects on toxic emissions are assumed to be proportional to the
effects of sulfur on total VOC, as estimated by MOVES.
Table 2-2 Technology Groups Included in the Complex Model
Technology Group
Fuel System1
Catalyst2
Air Injection
Exhaust-gas Recirculation
1
PFI
3-Way
No
Yes
2
PFI
3-Way
No
No
3
TBI
3-Way
No
Yes
4
PFI
3-Way + Oxy
Yes
Yes
5
PFI
3-Way
Yes
Yes
6
TBI
3-Way
Yes
Yes
7
TBI
3-Way + Oxy
Yes
Yes
8
TBI
3-Way
No
No
9
carburetor
3-Way + Oxy
Yes
Yes
10 ("High Emitters")
ALL
ALL
ALL
ALL
Notes:
1 Fuel System: PFI = port fuel injection, TBI = throttle body injection.
2 Catalyst: "3-way" = three-way catalyst, "Oxy" = oxidation catalyst.
Table 2-3 Mean Fuel-Property Values Used for Centering Terms in the Complex Model
Property
Units
Mean
Value
Aromatics
Vol. %
28.26
Olefins
Vol. %
7.32
Methyl-tertiary-butyl-ether (MTBE)1
Wt.%
0.95
Ethyl-tertiary-butyl-ether (ETBE)1
Wt. %
0.023
Ethanol (EtOH)1
Wt. %
0.314
Tertiary-amyl-methyl-ether (TAME)1
Wt. %
0.016
Oxygenate2
Wt. %
1.77
RVP
Psi
8.61
E200
%
46.73
E300
%
85.90
Notes:
1 Species-specific values used in the aldehyde models.
2 Aggregate value used for the butadiene and benzene models. As calculated using the volumes of MTBE,
ETBE, EtOH, and TAME and additional parameters documented in Appendix B of the MOVES Fuel Effects
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Table 2-4 Complex Model Coefficients for Acetaldehyde, by Technology Group
Technology
Group
Fuel Property
Aromatics
Olefins
W
OS
H
2
W
OS
H
W
EtOH
TAME
RVP
E200
E300
1
-0.055
-
-0.036
0.316
0.249
-
-
-
-0.012
2
-0.055
-
-
0.316
0.249
-
-
-
-0.012
3
-0.055
-
-
0.316
0.249
-
-
-
-0.012
4
-0.055
-
-
0.316
0.249
-
0.242
-
-0.012
5
-0.055
-
-
0.316
0.249
-
-
-
-0.012
6
-0.055
-
-
0.316
0.249
-
-
-
-0.012
7
-0.055
-
-
0.316
0.249
-
-
-
-0.012
8
-0.055
-
-
0.316
0.249
-
-
-
-0.012
9
-0.055
-
-
0.316
0.249
-
-
-
-0.012
10
-0.055
-
-0.056
0.316
0.249
-
-
-
-0.012
Notes:
1 Even though the input fuels in MOVES3 assume 0 percent MTBE and ETBE content, because the base fuel
has non-zero content of MTBE and ETBE, these coefficients are used in the Complex Model calculations
(Table 2-3)
Table 2-5 Complex Model Coefficients for Formaldehyde, by Technology Group
Technology
Group
Fuel Property
Aromatics
Olefins
W
OS
H
S
ETBE
EtOH
TAME
RVP
E200
E300
1
-0.007
-
0.046
-
-
-
-
-
-0.010
2
-0.007
-
0.046
-
-
-
-
-
-0.010
3
-0.007
-
0.046
-
-
-
-
-
-0.010
4
-0.007
-
0.046
-
-
-
-
-
-0.010
5
-0.007
-
0.046
-
-
-
-
-
-0.010
6
-0.007
-
0.046
-
-
-
-
-
-0.010
7
-0.007
-
0.046
-
-
-
-
-
-0.010
8
-0.007
-
0.046
-
-
-
-
-
-0.010
9
-0.007
-
0.046
-
-
-
-
-
-0.010
10
-0.007
-0.031
0.046
-
-
-
-
-
-0.010
Notes:
1 Even though the input fuels in MOVES3 assume 0 percent MTBE content, because the base fuel has non-
zero content of MTBE, these coefficients are used in the Complex Model calculations (Table 2-3)
13
-------
Table 2-6 Complex Model Coefficients for Exhaust Benzene, by Technology Group
Fuel Property
Technology
Group
Aromatics
Olefins
Oxygenate
Fuel
Benzene
RVP
E200
E300
1
0.026
-
-
0.222
-
-0.0095
-
2
0.026
-
-
0.222
-
-
-
3
0.026
-
-
0.222
-
-0.0058
-
4
0.026
-
-
0.222
-
-
-
5
0.049
-
-
0.222
-
-
-
6
0.026
-
-
0.222
-
-
-
7
0.026
-
-
0.222
-
-
-
8
-
-
0.222
-
-
-
9
0.026
-
-
0.222
-
-
-
10
0.012
-
-0.096
0.222
-
-
0.011
Table 2-
7 Complex
Model Coefficients for 1,3-Butadiene, by Technology Group
Fuel Property
Technology
Group
Aromatics
Olefins
Oxygenate
E200
E300
1
-0.004
0.028
-
-0.0073
-0.017
2
-0.004
0.028
-
-0.0073
-0.017
3
-0.004
0.028
-
-0.0073
-0.006
4
-0.004
0.028
-
-0.0073
-0.017
5
-0.004
0.028
-
-0.0073
-0.017
6
-0.004
0.028
-
0.0058
-0.017
7
-0.004
0.028
-
-0.0073
-0.017
8
-0.004
0.028
-
-0.0073
-0.017
9
-0.004
0.028
-
-0.0073
-0.017
10
-0.004
0.044
-0.061
-0.0073
-0.008
2.1.1.1.2
Application of the Complex Model
In MOVES, the complex model equations are consolidated by weighting them together using
model-year specific weights based on the mix of technologies in the sales fleet for each model
year, as obtained from MOBILE6.2.54
For each compound, Equation 1 is used to estimate the effects of both "base" and "target" fuels.
We assume that vehicles were running on a specific fuel when the data underlying the base
emission rates were measured. We refer to these fuels as "base" fuels and use them as reference
points to estimate the effects of "target" fuels simulated during MOVES runs.22 The "target"
fuels are represented by specific sets of fuel properties and represent fuels "in-use" in the
geographic area(s) and season(s) being modeled in MOVES.
14
-------
Initially, an adjustment for the difference in emissions of the compound modeled on the target
fuel relative to the base fuel is calculated. If the model, as shown in Equation 2, is expressed,
using matrix notation as XPtarget and XPbase for estimates on the target and base fuels, then the
fractional difference in emissions is given by:
^ = ==4-10
The expression in Equation 2 is evaluated for target and base fuels for each of the ten technology
groups. A mean value of the adjustment is then calculated for each model year from 2000 back to
1970, as a weighted average of the fraction of sales in each group in each model year, for the
groups, as shown in Equation 3. The weights are shown in Table 2-8. The weights represent the
sales fractions and high emitter fractions for the ten vehicle technologies defined in Table 2-2
above.
Note that the use of varying weights in applying the Complex Model in MOVES differs from the
original application in which the weights were invariant. The application of Equation 3 to each of
the thirty ages listed in Table 2-8 gives a set of 30 adjustments; the one that is applied for each
model year depends on the calendar year simulated.
10 10
/adj ,mean ^ ' ^Group/adj,Group > ^ ' WGroup 1-0
Group=1 Group=1
Equation 3
The mean adjustments calculated in Equation 3 are then applied to estimate emissions of the
toxic on the target fuel (^relative,toxic), representing the effect on the emissions of the toxic due to
the changes in fuel properties between the target and base fuels. If the target and base fuels were
identical, the values of/adj ,mean would be 0.0.
-relative,toxic
^base,toxic(l /adj,mean) Equation 4
The calculations in Equation 1 to Equation 4 are also applied to VOC emissions, ending with the
generation of a value of irrelative,voc. The Complex Model coefficients for VOC are documented
in the rulemaking analysis.8 This value for VOC is then combined with that of each toxic to
calculate a fraction of VOC used to estimate the total mass of emissions for each toxic during a
model run. These fractions are denoted as ftomc and calculated as shown in Equation 5.
^relative,toxic
/toxic = p Equation 5
^relative,VOC
As a final step, the mass emissions of each toxic (/toxic) during a model run are estimated by
multiplying the mass of VOC emissions estimated by MOVES (/voc) by the values of /toxic.
hoxic /toxic^VOC Equation 6
15
-------
The equations and parameters presented are used to estimate the fuel impacts for both Tier 0 and
Tier 1 gasoline vehicles. This approach is based on the assumption that the proportional
responses of air toxic emissions to changes in fuel properties are similar for vehicles certified to
both sets of standards.
The Complex Model equations are applied to running, start and extended idle emissions for
gasoline-fueled vehicles for all 2000 and earlier model years for the first four pollutants listed in
Table 2-1 (acetaldehyde, formaldehyde, benzene and 1,3-butadiene). In addition, MOVES
applies the Complex Model based on light-duty gasoline vehicles to heavy-duty gasoline
vehicles. This step was taken because the very limited data specific to heavy-duty gasoline
vehicles used in MOBILE6.2 were considered not adequate to accurately capture the effects of
fuel properties on those vehicles.
16
-------
Table 2-8 Weights Applied to Complex Model Coefficients for Technology Groups, by Age (Vehicle Age 0
Represents Model Year 2000)b
Age
Technology Group
1
2
3
4
5
6
7
8
9
10
0
0.2360
0.2829
0.1806
0.1814
0.0290
0.0042
0.0556
0.0
0.0203
0.0100
1
0.2339
0.2803
0.1789
0.1797
0.0287
0.0042
0.0551
0.0
0.0201
0.0190
2
0.2315
0.2774
0.1771
0.1779
0.0284
0.0041
0.0546
0.0
0.0199
0.0290
3
0.2272
0.2723
0.1738
0.1746
0.0279
0.0041
0.0536
0.0
0.0196
0.0470
4
0.2229
0.2672
0.1706
0.1713
0.0274
0.0040
0.0525
0.0
0.0192
0.0650
5
0.2189
0.2623
0.1675
0.1682
0.0269
0.0039
0.0516
0.0
0.0188
0.0820
6
0.2148
0.2574
0.1644
0.1651
0.0264
0.0038
0.0506
0.0
0.0185
0.0990
7
0.2110
0.2529
0.1614
0.1621
0.0259
0.0038
0.0497
0.0
0.0182
0.1150
8
0.2072
0.2483
0.1585
0.1592
0.0254
0.0037
0.0488
0.0
0.0178
0.1310
9
0.2036
0.2440
0.1558
0.1565
0.0250
0.0036
0.0480
0.0
0.0175
0.1460
10
0.2000
0.2397
0.1530
0.1537
0.0246
0.0036
0.0471
0.0
0.0172
0.1610
11
0.1967
0.2357
0.1505
0.1512
0.0241
0.0035
0.0464
0.0
0.0169
0.1750
12
0.1934
0.2317
0.1479
0.1486
0.0237
0.0035
0.0456
0.0
0.0166
0.1890
13
0.1903
0.2280
0.1456
0.1462
0.0234
0.0034
0.0448
0.0
0.0164
0.2020
14
0.1872
0.2243
0.1432
0.1438
0.0230
0.0033
0.0441
0.0
0.0161
0.2150
15
0.1843
0.2209
0.1410
0.1416
0.0226
0.0033
0.0434
0.0
0.0159
0.2270
16
0.1814
0.2174
0.1388
0.1394
0.0223
0.0032
0.0428
0.0
0.0156
0.2390
17
0.1786
0.2140
0.1366
0.1372
0.0219
0.0032
0.0421
0.0
0.0154
0.2510
18
0.1760
0.2109
0.1346
0.1352
0.0216
0.0031
0.0415
0.0
0.0151
0.2620
19
0.1736
0.2080
0.1328
0.1334
0.0213
0.0031
0.0409
0.0
0.0149
0.2720
20
0.1712
0.2052
0.1310
0.1315
0.0210
0.0031
0.0403
0.0
0.0147
0.2820
21
0.1688
0.2023
0.1291
0.1297
0.0207
0.0030
0.0398
0.0
0.0145
0.2920
22
0.1664
0.1994
0.1273
0.1279
0.0204
0.0030
0.0392
0.0
0.0143
0.3020
23
0.1643
0.1969
0.1257
0.1262
0.0202
0.0029
0.0387
0.0
0.0141
0.3110
24
0.1624
0.1946
0.1242
0.1248
0.0199
0.0029
0.0383
0.0
0.0140
0.3190
25
0.1602
0.1920
0.1226
0.1231
0.0197
0.0029
0.0378
0.0
0.0138
0.3280
26
0.1602
0.1920
0.1226
0.1231
0.0197
0.0029
0.0378
0.0
0.0138
0.3280
27
0.1602
0.1920
0.1226
0.1231
0.0197
0.0029
0.0378
0.0
0.0138
0.3280
28
0.1602
0.1920
0.1226
0.1231
0.0197
0.0029
0.0378
0.0
0.0138
0.3280
29
0.1602
0.1920
0.1226
0.1231
0.0197
0.0029
0.0378
0.0
0.0138
0.3280
30
0.1602
0.1920
0.1226
0.1231
0.0197
0.0029
0.0378
0.0
0.0138
0.3280
2.1.1.1.3 Simple Fractions of VOC
MOVES uses a simpler approach to model emissions of 2,2,4-trimethylpentane, acrolein,
ethylbenzene, n-hexane, propionaldehyde, styrene, xylene(s) and ethanol. Table 2-9 lists toxic
fractions of VOC for these compounds for a range of gasoline-ethanol blends. With the
exception of ethanol, these fractions were developed for EO and E10 by Sierra Research using
speciation profiles estimated from EPA's SPECIATE 4.2 database.9
b Note that in the MOVES database, these weights are stored in the table FuelModelWtFactor.
17
-------
Emissions of ethanol in exhaust are estimated for gasoline blends containing ethanol at levels of
0 to 10 vol percent. For vehicles running on 10 percent ethanol, ethanol was estimated to
comprise 2.39 percent of exhaust VOC. This estimate is based on results measured on nine
vehicles in four test programs. 10'U'12'13 The fraction of ethanol in exhaust VOC for blends
containing 5.0 percent and 8.0 percent ethanol is estimated by interpolating linearly between the
fractions for 0.0 percent and 10.0 percent ethanol.
No data exist for MY 2000 and earlier vehicles running on El 5 or E20. Pre-2000 MY gasoline
vehicles do not have an EPA waiver to operate on ethanol fractions higher than 10 percent. 14'°
For acrolein and ethanol, we simply extended the E10 toxic fractions as shown in Table 2-9. For
pollutantlDs 40 - 46, we used toxics ratios for 2001 and later vehicles for E15 and E20, found in
Table 2-35.
Table 2-9 Toxic Fractions of VOC for Selected Air Toxics, Representing Gasoline and Ethanol Blends
Compound
pollutantID
Fuel Blend (by Ethanol Level)
0%
(E0)
10%
(E10)
15%
(E15)
20%
(E20)*
Ethanol
21
0
0.024
0.024
0.024
Acrolein
27
0.00063
0.00063
0.00063
0.00063
2,2,4-
T rimethy lpentane
40
0.018
0.018
0.022
0.0046
Ethyl Benzene
41
0.021
0.019
0.016
0.022
Hexane
42
0.016
0.016
0.011
0.025
Propionaldehyde
43
0.00086
0.00086
0.00060
0.00066
Styrene
44
0.0011
0.0010
0.0046
0.0041
Toluene
45
0.096
0.087
0.073
0.096
Xylene
46
0.078
0.070
0.069
0.093
*Note, MOVES versions after MOVES2014a do not estimate emissions for vehicles using E20 fuel, but
these fractions currently remain in the MOVES database.
In the MOVES database, these inputs are stored in the table "minorHAPratio." In the label, the
term "HAP" refers to "hazardous air pollutant." In MOVES, we refer to these pollutants stored in
this table as minor HAPs. A description of the table is provided in Table 2-10.
0 Due to the small volume of E15 fuel sales and the uncertainty of allocating the E15 across the country, MOVES3
assumes no marketshare of E15 in the default fuel supply. Users can specify marketshare of E15 for the individual
use cases, in which MOVES would use the E15 toxic fractions in Table 2-9. In MOVES, all model year gasoline
vehicles use the same market of gasoline fuels specified in the fuel supply table. Ideally, MOVES would not model
E15 usage from MY 2000 and earlier vehicles when users specify E15 marketshare for their runs. However, we have
not incorporated this additional complexity into the model due to the small contribution of MY 2000 vehicles to
current emission inventories from E15 fuel blends.
18
-------
Table 2-10 Description of the Database Table "minorHAPRatio"
Field
Description
RelevantValues
polProcessID
Identifies the pollutant (1st two
digits and Emissions Process (last
two digits).
Pollutants are identified in the table
above;
Relevant processes include:
"Running Exhaust" (processID =1)
"Start Exhaust" (processID = 2)
fuelTypelD
Identifies broad classes of fuels,
e.g., "gasoline." "diesel."
1 = "Gasoline"
2 = "Diesel"
5 = "Ethanol"
fuelSubTypelD
Identifies specific fuel classes
within the fuelTypelD
10 = "Conventional Gasoline"
11 = "Reformulated Gasoline"
12 = "Gasohol (E10)"
13 = "Gasohol (E8)"
14 = "Gasohol (E5)"
15 = "Gasohol (E15)"
18 = "Gasohol (E20)"*
51 = "Ethanol (E85)"
52 = "Ethanol (E70)"
modelY earGroupID
Identifies a set of model years
covered by a specific value of
atRatio.
1960-1970
1971-1977
1978-1995
1996-2003
2004-2060
atRatio
Fraction, or "ratio" of the toxic
relative to total VOC.
atRatioCV
"Coefficient of Variation of the
Mean" or "relative standard error"
of the atRatio.
dataSourcelD
Indicates source data and methods
used to estimate atRatio.
*Note MOVES versions after MOVES2014a do not estimate emissions for vehicles using E20 fuel.
2.1.1.2 2001 and later model year vehicles
For vehicles manufactured in model year 2001 and later and certified to NLEV or Tier 2
standards more recent data were available. As for the earlier model years, toxic emissions are
estimated as fractions of VOC, with toxic fractions for various compounds estimated using
differing datasets and methods. For some compounds and processes, models were developed to
estimate "complex" fractions (as a function of gasoline properties), whereas for others, "simple"
constant fractions were estimated. In some cases, different fractions could be estimated for the
start and running emission processes. For the compounds included in MOVES, data sources and
estimation methods are summarized in Table 2-11. The data used to estimate the toxic fractions
were obtained from the EPAct Program which is discussed in the following section. For benzene
and 1,3-butadiene there are additional adjustments based on the benzene and olefin content of the
fuel as discussed in Section 2.1.1.2.3.
19
-------
Table 2-11 Data Sources and Methods Used to Estimate Gasoline Model Year 2001-and later Toxic Fractions
forVOCs
Compound
Process
Fraction Type
Basis for Estimation
Acetaldehyde
Start
complex
application of EPAct models1
Running
complex
application of EPAct models
Formaldehyde
Start
complex
application of EPAct models
Running
complex
application of EPAct models
Acrolein
Start
complex
application of EPAct models
Running
simple
Data from EPAct Project (Phase 3)2
Ethanol
Start
complex
application of EPAct models
Running
complex
application of EPAct models
Benzene*
Start
complex
application of EPAct models
Running
simple
Data from EPAct Project (Phase 3)
1,3-Butadiene*
Start
complex
application of EPAct models
Running
simple
Data from EPAct Project (Phase 3)
2,2,4-Trimethylpentane
Both
simple
Speciation Profile (EPAct Phase l)3
Ethylbenzene
Both
simple
Speciation Profile (EPAct Phase 1)
N-Hexane
Both
simple
Speciation Profile (EPAct Phase 1)
Propionaldehyde
Both
simple
Speciation Profile (EPAct Phase 1)
Styrene
Both
simple
Speciation Profile (EPAct Phase 1)
Xylene(s)
Both
simple
Speciation Profile (EPAct Phase 1)
*Additional adjustments are made to the benzene and 1,3-butadiene emissions as discussed in Section 2.1.1.2.3.
2.1.1.2.1 Overview of the EPAct Program
To better understand the effect of gasoline fuel properties on exhaust emissions from Tier-2
certified vehicles, EPA entered a partnership with the Department of Energy (DOE) and the
Coordinating Research Council (CRC). The resulting research program was dubbed the
"EPAct/V2/E-89" program (or "EPAct" for short). The program was conducted in three phases.
Phases 1 and 2 were pilot efforts involving measurements on 19 light-duty cars and trucks using
three fuels, at two temperatures. These preliminary efforts laid the groundwork for design of a
full-scale research program, designated as Phase 3.
Initiated in March 2009, the Phase 3 program involved measurement of exhaust emissions from
fifteen high-sales-volume Tier-2 certified vehicles. The vehicles were selected to represent the
latest technologies in the market at the time the program was launched (2008). The vehicles were
to reflect a majority of sales for model year 2008. In addition, the vehicles were to conform
primarily to Tier-2 Bin-5 exhaust standards, and to reflect a variety of emission-control
technologies, as realized through the selection of a range of vehicle sizes and manufacturers. The
vehicle sample is summarized in Table 2-12.
20
-------
Make
Brand
Model
Engine Size
Tier 2 Bin
LEVII
Std
Odometer
GM
Chevrolet
Cobalt
2.2L 14
5
NA
4,841
GM
Chevrolet
Impala FFV
3.5L V6
5
L2
5,048
GM
Saturn
Outlook
3.6L V6
5
L2
5,212
GM
Chevrolet
Silverado FFV
5.3L V8
5
NA
5,347
Toyota
Toyota
Corolla
1.8LI4
5
U2
5,019
Toyota
Toyota
Camry
2.4L 14
5
U2
4,974
Toyota
Toyota
Sienna
3.5L V6
5
U2
4,997
Ford
Ford
Focus
2.0L 14
4
U2
5,150
Ford
Ford
Explorer
4.0L V6
4
NA
6,799
Ford
Ford
F150 FFV
5.4L V8
8
NA
5,523
Chrysler
Dodge
Caliber
2.4L 14
5
NA
4,959
Chrysler
Jeep
Liberty
3.7L V6
5
NA
4,785
Honda
Honda
Civic
1.8LI4
5
U2
4,765
Honda
Honda
Odyssey
3.5L V6
5
U2
4,850
Nissan
Nissan
Altima
2.5L 14
5
L2
5,211
The study used a total of twenty-seven test fuels spanning wide ranges of five fuel properties
(ethanol, aromatics, vapor pressure, and two distillation parameters: T50 and T90). The number
of test points and values of each property are shown in Table 2-13. The properties of the test
fuels were not assigned to represent in-use fuels, but rather to allow development of statistical
models that would enable estimation of relative differences in emissions across the ranges of fuel
properties expected in commercially available summer fuels in the U.S. (5111 to 95th percentiles
for each property).
Table 2-13 Levels Assigned to Experimental Factors (Fuel parameters) for the Phase-3 EPAct Program
Factor
No. Levels
Levels
Low
Middle
High
Ethanol (vol.%)
4
0
10, 15
20
Aromatics (vol.%)
2
15
35
RVP (psi)
2
7
10
T50 (°F)
5
150
165, 190, 220
240
T90 (°F)
3
300
340
The LA92 test cycle was used, with emissions measured over three phases analogous to those in
the Federal Test Procedure (FTP), at an ambient temperature of 75°F. Note that throughout this
chapter, the terms "start," "cold start" and "Bag 1" will be treated as synonymous, and similarly,
the terms "running," "hot-running" and "Bag 2" will also be treated as synonymous.
The experimental design embodied in the fuel set is the product of an iterative process involving
balancing among research goals, fuel-blending feasibility and experimental design. As fuel
properties tend to be moderately to strongly correlated, and as the goal was to enable analysis of
fuel effects as though the properties were independent (uncorrelated), it was necessary to address
these issues in design and analysis. Accordingly, the fuel set was designed using a computer-
generated optimal design, as modified by additional requirements such as the total number of
fuels and specific properties for subsets of fuels. In addition, to generate the design, it was
21
-------
necessary to specify the fuel effects to be estimated by the resulting model. The fuel set was
designed to allow estimation of linear effects for the five properties shown in Table 2-13, plus
two-way interactions of ethanol and the other five properties, as shown in Equation 7, in which fi
represents a linear coefficient for each effect.
Y = p o + ftetOH + /?2Arom + £3RVP + /34T50 + (isT9Q +
PqTSO +/?11etOH Equation 7
/?7etOH x Arom + /?aetOH x RVP + /?9etOH x T50 + /?10etOH x T90
+ £
In the equation, the linear terms (e.g., /?ietOH, etc.) describe linear associations between
emissions (7) and the value of the fuel property. The quadratic terms are used to describe some
degree of curvature in the relationship between emissions and the fuel property. Note that a
minimum of three test levels for a property is needed to assess curvilinear relationships and that
the design included such effects only for ethanol and T50. Two-way interaction terms indicate
that the relationship between emissions and the first fuel property is dependent on the level of the
second fuel property. For example, if an etOHx Arom interaction is included in a model, it
implies that the effect of ethanol on the emission Y cannot be estimated without accounting for
the aromatics level, and vice versa. Note that inclusion of the 11 effects in the design does not
imply that all effects will be retained in all models following the fitting process. Properties for
each of the test fuels are shown in Table 2-14.
Emissions measured include carbon dioxide (CO2), carbon monoxide (CO), THC, methane
(CH4), oxides of nitrogen (NOx), and PM2.5. In addition, hydrocarbons were speciated for
subsets of vehicles and fuels, allowing calculation of derived parameters such as non-methane
organic gases (NMOG) and non-methane hydrocarbons (NMHC). Speciation also allowed
independent analyses of selected toxics including acetaldehyde, formaldehyde, acrolein,
benzene, 1,3-butadiene and ethanol.
Due to limitations in budget, the entire study design was not applied to speciated hydrocarbons,
including those discussed in this chapter. For the speciated compounds, the number of relevant
measurements varies by bag, compound and vehicle. For selected compounds, measurements for
Bag 1 were taken for all vehicles over the entire fuel set, thus encompassing the entire study as
designed, including replication. However, for the remaining compounds in Bag 1 and for all
compounds in Bags 2, measurements were taken for a smaller number of vehicles over a reduced
set of fuels, without replication. The combinations of fuels and vehicles included for each
compound analyzed are summarized in Table 2-15.
Throughout this chapter, the complete set of 27 fuels will be denoted as the "full design," as it
includes all the fuel parameter points for which the design was optimized. Similarly, the set of 11
fuels will be denoted as the "reduced design," as it covers a set of fuel parameter points narrower
than that for which the design was originally optimized. Note that Table 2-14 also identifies the
subset of fuels included in the reduced design.
Phase 3 data collection was completed in June 2010. Dataset construction and analysis was
conducted between January 2010 and November 2012. This process involved ongoing
22
-------
collaboration among EPA staff, Department of Energy (DOE) staff and contractors, and CRC
representatives. Following the completion of data collection, construction of the dataset
involved intensive evaluation and quality assurance. The analysis involved several iterations
between analysis and additional physical and chemical review of the data. Successive rounds of
statistical modeling were applied to the data to achieve several goals, including identification of
potential candidate models, identification and review of outlying observations, identification and
review of subsets of data from influential vehicles, and identification of models including subsets
of terms that best explain the results obtained. The EPAct exhaust research program and analysis
are extensively documented in the "EPAct Test Program Report"15 and "EPAct Analysis
Report".16
This document describes how the data and statistical models developed during the EPAct study
are applied to model toxics in the MOVES model.
Table 2-14 Measured Parameters for Fuels in the Phase-3 EPAct Program
Fuel1
etOH (vol.%)
Aromatics (vol.%)
RVP (psi)2
T50 (°F)
T90 (°F)
1
10.03
15.4
10.07
148.9
300.2
2
0
14.1
10.2
236.7
340.1
33
10.36
15.0
6.93
217.5
295.9
4
9.94
15.5
10.01
221.9
337.5
5
0
34.7
6.95
237.0
300.0
63
10.56
15.0
7.24
188.5
340.4
73
0
17.0
7.15
193.1
298.4
8
0
15.7
10.2
221.1
303.1
9
0
35.8
10.30
192.8
341.8
103
9.82
34.0
7.11
217.1
340.2
11
10.30
35.0
9.93
189.3
298.6
12
9.83
34.8
10.13
152.2
339.8
133
0
34.1
6.92
222.5
337.9
143
0
16.9
7.14
192.8
338.5
15
0
35.3
10.23
189.7
299.4
16
10.76
35.6
7.12
218.8
300.6
20
20.31
15.2
6.70
162.7
298.7
213
21.14
35.5
7.06
167.6
305.0
22
20.51
15.0
10.21
163.2
297.3
233
20.32
15.9
6.84
162.5
338.2
24
20.51
15.3
10.12
165.1
338.1
25
20.03
35.2
10.16
166.9
337.9
26
15.24
35.6
10.21
160.3
338.7
273
14.91
14.9
6.97
221.5
340.3
283
14.98
34.5
6.87
216.6
298.8
30
9.81
35.5
10.23
152.9
323.8
313
20.11
35.5
6.98
167.3
325.2
Notes:
1 Note that numbering of fuels is not entirely sequential throughout.
2 This parameter was measured as "DVPE," but for simplicity, will be referred to as "RVP" in this
document.
3 These fuels included in the "reduced design."
23
-------
Compound
Bag 1
Bag 2
No. vehicles
No. Fuels
replication
No. vehicles
No. Fuels
replication
Acetaldehyde
15
27
YES
5
11
NO
Formaldehyde
15
27
YES
5
11
NO
Acrolein
15
27
YES
5
11
NO
Ethanol
15
27
YES
5
11
NO
Benzene
15
11
NO
5
11
NO
1,3-Butadiene
15
11
NO
5
11
NO
Ethane
15
11
NO
5
11
NO
Standardizing Fuel Properties
In model fitting, as well as in applying the resulting sets of coefficients, it is necessary to first
"center" and "scale" the properties of fuels, also known as "standardization." This process
simply involves first "centering" the measured fuel properties by subtracting the sample mean
from the given value, and then "scaling" by then dividing the centered values by their respective
standard deviations, as shown in Equation 8. Note that the means and standard deviations are
calculated from the fuel set used for the program (see Table 2-14). The result is a "Z score,"
representing a "standard normal distribution" with a mean of 0.0 and a standard deviation of 1.0.
Zt =
Equation 8
For the linear effects in the model, standardization is performed using the values of each fuel
property, each in their respective scales (vol. percent, psi, °F.). Using aromatics as an example,
the standardization of the linear term is shown in Equation 9.
7 =
¦^arom
Equation 9
For second-order terms, however, the process is not performed on the values of the fuel
properties themselves. Rather, quadratic and interaction terms are constructed from the Z scores
for the linear terms, and the process is repeated. Using the quadratic term for ethanol as an
example (etOHxetOH), the standardized value, denoted by ZZetoHxetoH, is calculated as shown in
Equation 10, where mz^z^ and sare the mean and standard deviation of the quadratic
term constructed from the Z score for the linear effect.
ZZ,
¦^etOH^etOH — mZ,„,, ,Z,
etOHxetOH
etOHxetOH
SZ,
Equation 10
etOHxetOH
Standardized terms for interaction effects are constructed similarly. For example, Equation 11
shows the standardization of an interaction term between ethanol and aromatics.
24
-------
rjrj _ ^etOH^Arom mZetOHZArom
^^etOHxeArom Equation 11
"^etOH ^Arom
Means and standard deviations for relevant model terms are shown in Table 2-16. Note that the
means and standard deviations shown in the table are calculated from the fuel set itself as shown
in the table; in this calculation the properties are not weighted for numbers of replicates on each
fuel and emission combination. In this way, the process is simplified by using the same
standardization in fitting all models, as well as in subsequent applications of the models. Note
also that the reduced fuel set is standardized using a different set of parameters than the full fuel
set.
The process of standardization is illustrated for three test fuels in Table 2-17. Overall, the
process applied here is similar to the "correlation transformation" sometimes applied in multiple
regression. One difference in this case is that the standardization is applied only to the predictor
variables, whereas it is also possible to apply it to the response variable.17
Table 2-16 Means and Standard Deviations for Fuel Properties, Based on Fuel Matrices for the Full and
Reduced Designs
Model Term
Ethanol (%)
Aromatics (%)
RVP (psi)
T50 (°F)
T90 (°F)
etOH x etOH
T50x T50
etOH x Arom
etOH x RVP
etOH x T50
etOH x T90
Full Design1
Mean
Standard
deviation
10.31
7.88
25.63
10.02
8.52
1.61
190.61
28.58
320.53
19.48
0.96
0.80
0.96
0.74
-0.037
0.98
-0.10
1.00
-0.54
0.77
0.016
0.97
Reduced Design2
Mean
Standard
deviation
11.02
8.06
24.39
9.92
197.00
23.45
323.53
19.60
Notes:
1 Applies to models fit with data for 15 vehicles measured on 27 fuels.
2 Applies to models fit with data for 5 or 15 vehicles measured on 11 fuels. Note that these models have
no linear term for RVP and no 2nd order terms.
25
-------
Table 2-17 Examples of One-Stage and Two-Stage Standardization for Three Test Fuels (1,5 and 20)
Fuel
etOH
Arom
RVP
T50
T90
etOH
T50
etOH
etOH
etOH
etOH
(vol.%)
(vol.%)
(psi)
(°F)
(°F)
X
X
X
X
X
X
etOH
T50
Arom
RVP
T50
T90
Fuel Properties
1
10.03
15.4
10.07
148.9
300.2
5
0.00
34.7
6.95
237.0
300.0
20
20.31
15.2
6.70
162.7
298.7
Mean1
10.314
25.630
8.518
190.6
320.5
Std.
Dev.1
7.880
10.015
1.611
28.6
19.5
One-Stage Standardized Values (Z) (Equation 9)
Ze
za
zr
z5
z9
1
-0.036
-1.021
0.963
-1.460
-1.044
5
-1.309
0.906
-0.973
1.623
-1.054
20
1.269
-1.041
-1.128
-0.977
-1.121
Mean2
0.9630
0.9630
-0.0367
-0.0992
-0.5413
0.1633
Std.
Dev.2
0.8028
0.7398
0.9785
0.9996
0.7692
0.9728
Two-Stage Standardized Values (ZZ) (Equation 10, Equation 11)
ZZee
ZZ55
ZZea
ZZer
ZZe5
ZZe 9
1
-1.198
1.578
0.075
0.065
0.772
0.022
5
0.935
2.260
-1.174
1.373
-2.058
1.401
20
0.805
-0.012
-1.313
-1.332
-0.907
-1.478
Notes:
1 Mean and Standard Deviations of fuel properties for the entire fuel set. See Table 2-16.
2 Mean and Standard Deviations of 2nd order terms values for the entire fuel set, constructed from the one-stage Z
values.
Model Fitting
Throughout model fitting, the response variable was the natural logarithm transformation of the
emissions results (InF), and the predictor variables were the one- or two-stage standardized fuel
properties, as shown in Table 2-17. Thus, the model to be fit includes some subset of the 11
candidate terms shown in Equation 12.
InY = /?0 +
PiZe + /?2 Za + /?3 Zr + P4Z5 + PsZc, +
/?6ZZ55 + f]7ZZee + Equation 12
fi%ZZea + (i9ZZer + (]10ZZeS + /?nzze9 +
£
A model containing all potential candidate terms is referred to as a "full model," whereas a
model containing some subset of the candidate terms is referred to as a "reduced model." The
goal of model fitting is to identify a reduced model by removing terms from the full model that
do not contribute to fit.
26
-------
Where the available data were sufficient, "mixed models" were fit, in which the terms listed in
Table 2-16 were included as "fixed" terms. In addition, a "random intercept" was fit for each
vehicle, which represents the high degree of variability contributed to the dataset by the vehicles
measured. One way of understanding this distinction that the fuel properties are "fixed" because
the fuels studied span the entire range of properties under study, and because the goal of the
analysis is to estimate the effect of these parameters on the mean levels of emissions. On the
other hand, "vehicle" is treated as a "random" factor because the sample of vehicles measured is
but one of many samples that could have been measured. In the analysis, the emission levels of
the specific vehicles are not of interest per sc\ but rather the degree of variability contributed to
the analysis by the different vehicles. Analyses were performed using the MIXED procedure in
the Statistical Analysis System (SAS®), version 9.2.18
When data were not sufficient for the mixed-model approach, models were fit by "Tobit
regression." This technique was used when specific datasets were affected by low-end
"censoring." For some measurements, the sample ostensibly obtained from the vehicle exhaust
was lower than that attributable to background levels. In these cases, we assumed that a small but
detectable mass was not measured accurately due to limitations in the sampling technique. In the
Tobit model, the fitting method (maximum likelihood) is modified so as to compensate for the
absence of the censored measurements. As with the mixed models, individual intercepts were fit
for each vehicle; however, as the Tobit procedure does not distinguish "fixed" and "random"
factors, vehicles were entered into the model as fixed factors (i.e., "dummy" variables). The
Tobit models were fit using the LIFEREG procedure in SAS 9.2.19
Model fitting was conducted by backwards elimination, in which all terms in the full model were
included at the outset. In fitting successive models, terms not contributing to fit were removed
based on results of likelihood-ratio tests (LRT).20 Note that the LRT were used for model
selection because all models were fit using "maximum-likelihood" (rather than "least-squares")
methods.
Model fitting results for acetaldehyde, formaldehyde, acrolein and ethanol are shown in Table
2-18 through Table 2-21. Note that these four models represent "Bag 1" or "start" emissions on
the LA92 cycle, based on datasets incorporating the full design. Also note that in fitting these
models, an additional six terms beyond the original 11 design terms were included in the full
models. These terms included one quadratic term (T90xT90), three interaction terms for
aromatics, one interaction for RVP, and one interaction for the distillation parameters
(T50xT90). However, none of these additional terms were retained as significant, with the single
exception of the T50xT90 term.
In MOVES, emissions of toxics are estimated as fractions of volatile organic compounds in
exhaust (VOC). To allow estimation of VOC, it was necessary to develop models for non-
methane organic gases (NMOG). NMOG is equivalent to VOC, plus the mass of ethane and
acetone.d It is calculated in MOVES from non-methane hydrocarbons (NMHC) by correcting for
the mass of oxygenated compounds not fully measured by the flame ionization detector used to
determine NMHC.21 EPA and CARB regulations set NMOG emission standards for motor
vehicles, so NMOG is an important model output. The model representing start emissions for
d Note that acetone was treated as negligible for purposes of these calculations.
27
-------
NMOG, fit using the full design, is shown in Table 2-22. This model was fit using the same
methods as that for total hydrocarbons (THC), as described in the Fuel Effects Report.22
Table 2-18 Acetaldehyde (Bag 1): Coefficients and Tests of Effect for the Full and Reduced Models1
Effect
Intercept
Z,
Zp
zzei
zz«
zze(
zze,
ZZe.5
ZZep
zza,
ZZa5
ZZaP
ZZpp
7.7.59
ZZri
Vfih
Full Model
Estimate
Std.Err.
d.f.
/-value
Pr>f
-5.2324
0.08802
15
-59.4
0.000000
0.8250
0.01297
898
63.6
0.000000
0.03999
0.009279
898
4.31
0.000018
-0.03667
0.01297
898
-2.83
0.0048
0.09927
0.01826
898
5.44
0.000000
0.04235
0.01115
898
3.80
0.00016
-0.1716
0.01548
898
-11.09
0.000000
0.07115
0.01314
898
5.42
0.000000
0.03016
0.01304
898
2.31
0.021
0.02020
0.008769
898
2.30
0.021
-0.01614
0.01673
898
-0.965
0.33
-0.01486
0.01072
898
-1.39
0.17
0.01738
0.01618
898
1.07
0.28
0.004828
0.01729
898
0.28
0.78
0.008759
0.008852
898
0.99
0.32
0.01270
0.01503
898
0.84
0.40
0.02718
0.01132
898
2.49
0.013
-0.0206
0.009971
898
-2.07
0.039
0.1154
0.08743
Reduced Model
Estimate
Std.Err.
d.f.
t-
value
Pr>f
-5.2323
0.08785
15
-59.6
0.000000
0.8145
0.01020
898
79.9
0.000000
0.03484
0.008249
898
4.22
0.000027
-0.04170
0.008833
898
-4.72
0.000003
0.08670
0.01063
898
8.16
0.000000
0.03801
0.007764
898
4.90
0.000001
-0.1669
0.007849
898
-21.3
0.000000
0.06665
0.007993
898
8.34
0.000000
0.01840
0.007777
898
2.37
0.018
0.02194
0.007845
898
2.80
0.0053
0.03959
0.008256
898
4.80
0.000002
0.1149
0.08850
1 See 9.2.2 and 8.7.3 in the Project Report.1
28
-------
Table 2-19 Formaldehyde (Bag 1): Coefficients and Tests of Effect for Full and Reduced Models1
Effect
Intercept
Z5
zzei
ZZ55
zze<
ZZe,
ZZe5
zze9
ZZa,
ZZgi
ZZaff
ZZpp
ZZ59
ZZri
vph
Full Model
Estimate
Std.Err.
d.f.
f-value
Pr>f
-5.9771
0.1498
15
-39.9
0.000000
0.2279
0.01234
898
18.5
0.000000
0.03528
0.008841
898
3.99
0.000071
-0.05202
0.01234
898
-4.21
0.000028
0.1577
0.01738
898
9.07
0.000000
0.1357
0.01064
898
12.7
0.000000
-0.01498
0.01475
898
-1.02
0.31
0.05026
0.01251
898
4.02
0.000064
0.02017
0.01241
898
1.63
0.10
0.004100
0.008366
898
0.490
0.62
-0.03686
0.01594
898
-2.31
0.021
0.02181
0.01023
898
2.13
0.033
0.007384
0.01535
898
0.481
0.63
-0.006739
0.01645
898
-0.41
0.68
-0.01036
0.008437
898
-1.23
0.22
0.02104
0.01435
898
1.47
0.14
0.03974
0.01080
898
3.68
0.00025
-0.003140
0.009498
898
-0.331
0.74
0.3360
0.1395
Reduced Model
Estimate
Std.Err.
d.f.
t-
value
Pr>?
-5.9771
0.1498
15
-39.9
0.000000
0.2299
0.009640
898
23.8
0.000000
0.02822
0.007979
898
3.54
0.00043
-0.04718
0.008457
898
-5.58
0.000000
0.1672
0.01001
898
16.7
0.000000
0.1302
0.007360
898
17.7
0.000000
0.05262
0.008341
898
6.31
0.000000
0.01651
0.007340
898
2.25
0.025
-0.01627
0.008177
898
-1.99
0.047
0.02004
0.008838
898
2.27
0.024
0.03489
0.009322
898
3.74
0.00019
0.3358
0.1406
1 See 9.2.2 and Appendix L.3 in the Project Report.1
29
-------
Table 2-20 Acrolein (Bag 1): Coefficients and Tests of Effect for Full and Reduced Models
Effect
Intercept
Z,
zze<
zz„
zze(
zze,
ZZgj)
ZZeg
zza
ZZa5
ZZaP
ZZpp
72.59
ZZr.
Full Model
Estimate
Std.Err.
d.f.
t-
value
Pr>f
-7.9337
0.2571
0.02638
15
9.74
0.000000
0.1149
0.02128
15
5.40
0.000074
-0.05815
0.01799
15
-3.23
0.0056
0.1979
0.03123
15
6.34
0.000013
0.2465
0.02979
15
8.28
0.000000
-0.06009
0.01880
15
-3.20
0.0060
0.02735
0.01709
15
1.60
0.13
0.01716
0.01838
15
0.93
0.37
0.01253
0.01404
15
0.89
0.39
-0.09661
0.02096
15
-4.61
0.00034
0.04178
0.01618
15
2.58
0.021
0.02002
0.01562
15
1.28
0.22
0.01127
0.01822
15
0.62
0.55
-0.007484
0.01726
15
-0.43
0.67
0.0004162
0.01481
15
0.028
0.98
0.06274
0.01552
15
4.04
0.0011
0.0002551
0.01709
15
0.015
0.99
Reduced Model (FM8)
Estimate
Std.Err.
d.f.
t-
value
Pr>?
-7.9338
0.2476
0.02738
15
9.04
0.000000
0.1122
0.02184
15
5.14
0.00012
-0.0645
0.01364
15
-4.73
0.00027
0.1881
0.03554
15
5.29
0.000091
0.2488
0.03125
15
7.96
0.000000
-0.08306
0.01392
15
-5.97
0.000026
-0.1185
0.02415
15
-4.91
0.00019
0.04618
0.01120
15
4.12
0.00091
0.05985
0.01271
15
4.71
0.00028
T2 1
yph
0.3633
0.03206
0.3629
0.3213
1 See 9.2.2 and 8.7.4 in the Project Report16
2 Not fit by the Tobit model, manually recalculated from intercepts for individual vehicles.
30
-------
Table 2-21 Ethanol (Bag 1): Coefficients and Tests of Effect for Full and Reduced Models
Effect
Intercept
Z,
ZZel
zz55
ZZel
ZZe 5
ZZe 9
ZZa
ZZa5
ZZa9
ZZ99
ZZ59
ZZa,
ZZ19
n2 1
°vfih
07
Full Model
Estimate
Std.Err.
d.f.
t-
value
Pr>f
15
1.4759
0.07240
15
20.38
<0.00001
-0.0067
0.04327
15
-0.16
0.88
-0.05004
0.04316
15
-1.16
0.26
0.1050
0.03806
15
2.76
0.015
-0.1261
0.03701
15
-3.47
0.0034
-0.4787
0.06014
15
-7.96
<0.00001
0.1261
0.05018
15
2.51
0.024
-0.005952
0.03881
15
-0.15
0.88
0.02820
0.05277
15
0.54
0.60
0.0008509
0.06491
15
0.0090
0.99
0.03237
0.05103
15
0.64
0.53
0.03318
0.03212
15
1.04
0.32
-0.01143
0.03461
15
-0.33
0.74
-0.5112
0.04523
15
-1.13
0.28
0.05311
0.04341
15
1.22
0.24
0.04136
0.02855
15
1.45
0.17
-0.008676
0.04644
15
-0.20
0.85
0.5697
Reduced Model
Estimate
Std.Err.
d.f.
t-
value
Pr>f
-4.9081
1.4643
0.07115
15
20.56
<0.00001
-0.05990
0.02940
15
-2.06
0.057
0.07188
0.02964
15
2.37
0.032
-0.09990
0.03574
15
-2.78
0.014
-0.4967
0.05229
15
-9.51
<0.00001
0.1121
0.03826
15
2.90
0.011
0.1283
0.05739
1 See 9.2.2 in the Project Report.16
2 Not fit by the Tobit model, manually recalculated from intercepts for individual vehicles.
31
-------
Table 2-22 NMOG (Bag 1): Coefficients and Tests of Effect for Full and Reduced Models
Effect
Intercept
Z,
Zp
zze<
zz«
zze(
zze,
ZZe5
ZZep
Full Model
Estimate
Std.Err.
d.f.
t-
value
Pr> t
-0.9520
0.09077
15
-10.49
<0.0001
0.07981
0.01326
941
6.02
<0.0001
0.08789
0.00929
941
9.46
<0.0001
-0.04595
0.01053
941
-4.36
<0.0001
0.1344
0.01329
941
10.12
<0.0001
0.01593
0.00925
941
1.72
0.0855
0.04594
0.01760
941
2.61
0.00918
0.07680
0.01336
941
5.75
<0.0001
0.01635
0.00906
941
1.80
0.0714
-
-
-
-
-
0.04754
0.01893
941
2.51
0.0122
0.01961
0.00902
941
2.17
0.0300
Reduced Model
Estimate
Std.Err.
d.f.
lvalue
Pr> t
-0.9521
0.09089
15
-10.48
<0.0001
0.08019
0.01330
941
6.027
<0.0001
0.08782
0.00932
941
9.424
<0.0001
-0.04224
0.01046
941
-4.037
<0.0001
0.1345
0.01333
941
10.09
<0.0001
0.04432
0.01764
941
2.513
0.012
0.07579
0.01340
941
5.656
<0.0001
0.01693
0.00909
941
1.862
0.063
0.04653
0.01898
941
2.452
0.014
2
°veh
0.1224
0.07538
0.1224
0.07538
1 See 9.1.2 in the Project Report1'
Model Development under the Reduced Design
As previously discussed, the "reduced design" involved the measurement of 11 fuels on 5 or 15
test vehicles, whereas the "full design" involved measurement of 27 fuels on 15 vehicles.
As shown in Table 2-15, measurements of two compounds in Bag 1, and all compounds in Bag
2, were performed under the reduced design. Supplementary analyses suggested that the reduced
design was not adequate to support model fitting as described in Section 0 above. These results
suggested that in these cases, full models retaining all four linear terms would perform as well or
better than corresponding reduced models, many of which would retain only single terms. Thus,
this sub-section presents results for full models under the reduced design.
Models representing start (Bag 1 on LA92) emissions are presented for benzene, 1,3-butadiene,
non-methane organic gases (NMOG) and ethane in Table 2-23 through Table 2-26. These
models were fit using subsets of data incorporating 15 vehicles measured over 11 fuels.
Similarly, models representing hot-running (Bag 2 on LA92) emissions are presented for
acetaldehyde, formaldehyde, ethanol, NMOG and ethane in Table 2-27 through Table 2-31.
These models were fit using subsets of data incorporating five vehicles measured over 11 fuels.
The development of these models is described in greater detail in sub-section 9.2.1 of the EPAct
analysis report.16
32
-------
Table 2-23 Benzene (Bag 1): Coefficients and Tests of Effect for the Full Model
Effect
Intercept
Ze
2a
25
2g
2
°veh
Full Model
Estimate
Std.Err.
d.f.
/-value
Pr>f
-4.1019
0.1392
15
-29.48
<0.0001
-0.004685
0.03704
161
-0.126
0.90
0.4056
0.03389
161
11.97
<0.0001
0.04142
0.03789
161
1.09
0.28
0.01133
0.03255
161
0.35
0.73
0.2741
0.1873
1 See 9.2.2 and Appendix 0.3 to the Project Report.16
Table 2-24 1,3-Butadiene (Bag 1): Coefficients and Tests of Effect for the Full Model
Effect
Intercept
Ze
2a
25
Z9
2
°veh
Full Model
Estimate
Std.Err.
d.f.
/-value
Pr>f
-5.8371
0.1235
15
-47.28
1.06xl0"17
-0.01729
0.03071
160
-0.56
0.57
0.02673
0.02730
160
0.98
0.33
0.01247
0.03031
160
4.11
0.000062
0.10036
0.02657
160
3.78
0.00022
0.2192
0.1089
:See 9.2.2 in the Project Report.16
Table 2-25 NMOG (Bag 1): Coefficients and Tests of Effect for the Full Models
Effect
Intercept
Ze
2a
25
Z9
2
°veh
Full Model
Estimate
Std.Err.
d.f.
/-value
Pr>f
-0.8943
0.08668
15
-10.32
0.000000033
0.1040
0.01921
362
5.411
0.00000011
0.09435
0.01697
362
5.559
0.000000053
0.1527
0.01890
362
8.079
0.000000000
0.02127
0.01648
362
1.290
0.198
0.1091
0.08907
:See 9.2.2 in the Project Report.1
33
-------
Table 2-26 Ethane (Bag 1): Coefficients and Tests of Effect for the Full Models
Effect
Intercept
Ze
Za
z5
z9
2
°veh
Full Model
Estimate
Std.Err.
d.f.
/-value
Pr>f
-4.308
0.09833
15.0
-43.81
2.84xl0"17
0.1204
0.02075
160
5.805
3.37xl0"8
-0.1728
0.01844
160
-9.373
6.51xl0"17
0.2169
0.02047
160
10.59
3.30xl0"20
0.09531
0.01795
160
5.311
3.60xl0"7
0.1407
0.04970
1 See 9.2.2 in the Project Report.16
Table 2-27 Acetaldehyde (Bag 2): Coefficients and Tests of Effect for the Full Models
Effect
Intercept
Ze
Za
z5
z9
2
°veh
<*1
Full Model
Estimate
Std.Err.
d.f.
f-value
Pr>f
-9.4189
0.1177
5
-80.1
0.000000
0.1520
0.06080
58
2.50
0.0152
0.07991
0.05279
58
1.51
0.136
-0.02997
0.05957
58
-0.503
0.617
-0.07836
0.05153
58
-1.52
0.134
0.05654
0.3814
1 See 9.2.2 and Appendix K.3 to the Project Report.16
Table 2-28 Formaldehyde (Bag 2): Coefficients and Tests of Effect for the Full Model
Effect
Intercept
Ze
Za
z5
Zg
2
°veh
Full Model
Estimate
Std.Err.
d.f.
lvalue
Pr>f
-8.6574
0.1372
5.01
-63.10
<0.00001
0.08456
0.05937
58.04
1.424
0.16
0.01575
0.05154
58.05
0.306
0.76
0.01863
0.05815
58.03
0.320
0.75
-0.08138
0.05031
58.16
-1.62
0.11
0.08205
0.3762
1 See 9.2.2 and Appendix L.4 to the Project Report.1
34
-------
Table 2-29 Ethanol (Bag 2): Coefficients and Tests of Effect for the Full Model
Effect
Intercept1
Z,
T2 1
vph
Full Model
Estimate
Std.Err.
d.f.
f-value
Pr>f
-9.3072
0.6333
5
-15.45
0.000021
0.9233
0.2824
5
3.27
0.022
-0.3772
0.28499
5
-1.32
0.24
-.01910
0.2091
5
-0.091
0.93
-0.3017
0.2416
5
-1.25
0.27
0.3707
1.0889
1 See 9.2.2 and Appendix N.4 to the Project Report.1
Table 2-30 NMOG (Bag 2): Coefficients and Tests of Effect for the Full Model
Effect
Intercept1
Z,
T2 1
vsh
Full Model
Estimate
Std.Err.
d.f.
f-value
Pr>f
-4.777
0.4784
5
-9.99
0.00017
0.01778
0.03574
124
0.497
0.62
0.03320
0.03117
124
1.07
0.29
0.04258
0.03494
124
1.22
0.23
0.09051
0.03038
124
2.98
0.0035
1.1405
0.1026
See 9.2.2 in the Project Report.
Table 2-31 Ethane (Bag 2): Coefficients and Tests of Effect for the Full Model
Effect
Intercept1
Z,
Z9
U2,1
vfih
Full Model
Estimate
Std.Err.
d.f.
f-value
Pr>f
-7.724
0.7325
5
-10.54
0.00013
0.07345
0.05873
57
1.251
0.22
-0.1260
0.05151
57
-2.447
0.018
0.1815
0.05727
57
3.168
0.0025
0.1322
0.04994
57
2.647
0.010
2.6712
0.1476
1 See 9.2.2 and Appendix Q.4 to the Project Report.1
2.1.1.2.2 Application of EPAct Statistical Models in MO VES
We estimate the emissions of VOC toxic compounds as a fraction of emissions for VOC, on the
same fuel. To model the behavior of the fraction with respect to changes in fuel properties, it was
necessary to develop models for NMOG and ethane, as well as the toxics, because VOC is
estimated as NMOG minus ethane.®
e In MOVES, VOC is typically calculated as NMOG - ethane - acetone, but for this purpose, acetone was
considered negligible, and was not subtracted.
35
-------
The models generated using EPAct results allow estimation of emissions effects related to the
five fuel properties included in the study design: ethanol content (vol. percent), aromatics content
(vol percent), RVP (psi), T50 (°F) and T90 (°F), as well as selected interaction terms among
these five parameters.
The statistical models generated from the EPAct data follow the general structure shown in
Equation 13 below, which uses the model for acetaldehyde as an example (see Table 2-18). Note
that the subsets of the potential terms vary by emission and process, depending on the results of
model fitting, as described in the previous two sub-sections.
Emissions (g/mi) = ex^
(Po + Pe^e + Pa^a + Pr^r + Ps^s + P^9 +N
= exp PeeZZee + PsSZZSS + .
VeaZZea + ftrZZer + 0.5(4h + s|) / ""j""1
/—5.23 + 0.814Ze + 0.0348Zo - 0.0417Zr + 0.0867Z5 + 0.0380Z, -
= exp f 0.1669ZZee + 0.0667ZZ55 +
\0.0184ZZea + 0.0219ZZer + 0.5(0.1149 + 0.08850)
Where the data were sufficient, two sets of exhaust fuel effect coefficients were employed for
each pollutant; one set representing cold start emissions and a second set representing hot-
running emissions. In some cases, fuel effects estimated for these two processes differed
substantially, as the effects of fuel properties on start emissions are dominated by changes in
combustion and catalyst warm-up, while the impact of gasoline properties on running emissions
is dictated by catalyst efficiency when fully operational. Thus, using convenient matrix notation,
the expressions XPtoxic, Xoinmog and XGethane represent models for a selected toxic compound,
NMOG and ethane, respectively, calculated by applying Equation 13 to each compound for a
specified fuel. The toxic emissions as a fraction of VOC emissions (/toxic) are given by
Toxic Fraction = /toxic = —r- Equation 14
j gAaNMQG — eXt>ethane
For all compounds, the calculation shown in Equation 14 is recorded in the MOVES
GeneralFuelRatioExpression table. In calculating toxic fractions, we elected to use models for
NMOG and ethane fit using study designs and datasets similar to those for the toxic compounds.
In other words, if the toxic model was fit with the reduced design, we combined it with the
NMOG and ethane models also fit with the reduced design. We followed this approach to
prevent the calculation and propagation of artifacts in the estimated fractions resulting from
differing levels of information and complexity in the numerator and denominator in Equation 14.
In this context, we considered it important to apply "information parity" to the toxic model in the
numerator and the NMOG model in the denominator, as the vast majority of VOC mass is
represented by NMOG, with ethane comprising only a small fraction.
Note that for three compounds in Bag 2, levels of "left censoring," were high enough that
modeling was not considered feasible. Again, "censoring" occurs when background levels of the
compounds under study were as high as or higher than levels ostensibly measurable in vehicle
36
-------
exhaust. Estimation of "simple" toxic fractions for these compounds is covered in the following
sub-section.
Estimating Simple Fractions of VOC for Running Emissions
As noted in Table 2-15, the bag 2 data were not sufficient to fit models for running emissions for
three compounds: acrolein, benzene and 1,3-butadiene. The bag 1 data for these pollutants was
sufficient to estimate start emission adjustments as discussed in the previous subsections.
Therefore, running emissions were represented as "simple" (constant) fractions of VOC, with
values derived from the available data, as shown in Table 2-32.
Table 2-32 Simple Fractions of VOC for Running Emissions for 2001 and Later Model Year Gasoline
Vehicles
Compound
Simple Fraction
Acrolein
0.00077
Benzene*
0.047
1,3-butadiene
0.0
*Benzene fractions are further adjusted according to the benzene content of the fuel as discussed in Section
2.1.1.2.3
These values were derived as "ratios of means" (ROM), in which the toxic and VOC values were
averaged first by vehicle and then across vehicles, as described below. The ROM approach is
generally preferred as it provides an unbiased estimator of the true fraction as the sample size
increases.
23
For benzene, results were available for four vehicles, differing widely in their benzene and VOC
levels, and also in numbers of available measurements, as shown in Table 2-33. The averaging
was performed in two steps so that the vehicle(s) with the greatest numbers of measurements
would not dominate the overall mean. In the first step, the benzene and VOC values were
averaged for each vehicle. In the second step, the four vehicle means were averaged to give an
overall mean. Finally, the overall mean for benzene was divided by that for VOC to give a
simple ratio estimator for benzene as a fraction of VOC.
Table 2-33 Benzene (Running): Derivation of a Ratio-of-Means Estimator for Benzene as a Fraction of VOC1
Vehicle
n
Benzene (mg)
VOC (mg)
Ratio of means (ROM)2
Corolla
2
0.054
2.269
F150
10
2.224
28.427
Impala
3
0.108
10.670
Silverado
4
0.294
16.216
All vehicles
4
0.670
14.396
0.0465
1 Benzene fractions are adjusted according to the benzene content of the fuel as discussed in Section 2.1.1.2.3
2 This value is a simple average of the means for all four vehicles, as listed above.
The VOC fraction for acrolein was derived similarly (Table 2-34). For this compound results
were available for five vehicles. Values for acrolein are considerably lower than for benzene, so
results are expressed in jag, rather than mg. The resulting fraction is two orders of magnitude
lower than that for benzene.
37
-------
Table 2-34 Acrolein (Bag 2): Derivation of a Ratio-of-Means Estimator for Acrolein as a Fraction of VOC
Vehicle
n
Acrolein (jig)
VOC (Jig)
Ratio of means
(ROM)
Civic
3
5.42
3,038.9
Corolla
5
2.89
2,929.6
F150
5
8.36
24,321
Impala
6
8.02
10,408
Silverado
10
19.66
17,192
All vehicles
5
8.87
11,578
0.00077
1 This value is a simple average of the means for all five vehicles, as listed above.
For 1,3-butadiene in hot-running operation, measurements were extremely low; in fact, we
considered the dataset so heavily affected by "left-censoring" that we did not consider it
adequate for either model fitting or development of ratio estimators. Accordingly, for modeling
purposes, we have adopted an assumption that this compound is not emitted during hot-running
operation, i.e., the ROM estimator is 0.0.
2.1.1.2.3 Additional Fuel Adjustments for Benzene and 1,3-Butadiene
For two compounds, benzene and 1,3-butadiene, additional refinements were applied to
supplement the study design of the EPAct fuel set. These adjustments are applied to both start
and running emissions.
For benzene, the issue is that the fuel matrix in the EPAct test program included aromatics
generally, but not benzene specifically. As we considered it inadequate to model benzene in
exhaust without explicitly accounting for benzene levels in fuel, we developed a "post-EPAct
model" refinement using data external to the EPAct program. In this case, the source was a
program conducted in support of the 2007 MSAT2 rule. This program performed measurements
on nine Tier-2 certified vehicles on fuels with benzene levels ranging from 0.6 to 1.1 percent by
weight.24,25 With benzene represented as a fraction of VOC (as in Equation 14) denoted as
./benzene, a value modified to account for benzene levels in different fuels (/^benzene) is calculated as
shown in Equation 15 where Xbenzene is the benzene level for the fuel modeled (weight percent),
A is the mean benzene level in the EPAct exhaust program fuel set (0.66 weight percent), and B
is an empirical coefficient, taking a value of 0.24.
/benzene [(-^benzene B ' /benzene] /benzene Equation 15
Similarly, given the importance of olefins to estimation of emissions for 1,3-butadiene, and that
the EPAct exhaust program study design did not incorporate olefins as a factor, we considered it
appropriate to develop a post-EPAct model adjustment explicitly accounting for olefin level.
This adjustment was derived by varying olefin levels in the Complex Model and fitting a
polynomial trend to the results.26 Starting with an unadjusted toxic fraction for 1,3-butadiene
(/buta), the modified fraction f buta is calculated using Equation 16, in which x0iefm is the olefin
level, and^4, B, C and D are coefficients, taking values of 0.000008, 0.0002, 0.0069 and
0.008823, respectively.
38
-------
Equation 16 is applied to the estimated 1,3-butadiene fraction for start emissions estimated from
the EPAct equations in Table 2-24. MOVES does not apply similar fuel adjustments to the 1,3-
butadiene running exhaust emissions because they are estimated to be zero (Table 2-32).
2.1.1.2.4 Additional Air Toxics Estimated from EPAct Speciation Profiles
As summarized in Table 2-11, and analogous to what was done for 2000-and-earlier vehicles, we
used a simpler approach for the seven hazardous air toxics listed in Table 2-35.
For fuel blends with 0 percent, 10 percent and 15 percent ethanol, composite speciation profiles
developed from the results of EPAct (Phase 1) were used to develop toxic fractions of VOC for
the hazardous air toxics listed in Table 2-35.f These profiles were based on averaging results of
tests from 3 vehicles.27'28 Toxic fractions for E10 are used for all gasolines containing ethanol
levels of 5 vol. percent or greater. For fuel blends containing 20 percent ethanol, fractions were
developed using a composite speciation profile from the EPAct (Phase 3) program. The fractions
are also presented in Table 2-35. The values shown in Table 2-35 are stored in the database table
minorHAPRatio (see Table 2-10).
Table 2-35 Toxic Fractions of VOC for
Pollutant (pollutantID)1
2,2,4-Trimethylpentane (40)
Ethyl Benzene (41)
Hexane (42)
Propionaldehyde (43)
Styrene (44)
Toluene (45)
Xylene(s) (46)
1 For fuels containing 0-20 percent ethanol, fractions for ethanol, benzene, acetaldehyde, formaldehyde, 1,3-
butadiene, and acrolein were estimated using methods described in the previous subsections.
2 Values also applied for fuels containing 5 percent and 8 percent ethanol, (E5 and E8)
3MOVES versions after MOVES2014a do not estimate emissions for vehicles using E20 fuel, but these fractions
currently remain in the MOVES database.
Selected Compounds, Representing Model Years 2001 and Later
Fuel Blends (Gasoline and Ethanol)
0% (E0)
10% (E10)2
15% (El5)
20% (E20)3
0.03188
0.01227
0.02198
0.004625
0.01683
0.01660
0.01568
0.022199
0.002790
0.02911
0.0110
0.02497
0.00122
0.00054
0.0005984
0.0006607
0.00085
0.00083
0.004588
0.004096
0.07542
0.07440
0.0727
0.09646
0.06127
0.06047
0.06902
0.09302
f Phase 1 testing was done using fuels more representative of in-use fuels, in contrast to the orthogonal matrix used
for EPAct Phase 3.
-------
2.1.2 Vehicles Operating on Fuel Blends Containing 70-100 Percent
Ethanol
Flexible-fueled vehicles (FFVs) may operate on gasoline, or on "E85" fuel, which is a mix of
gasoline with high levels of ethanol (typically 70-85%). Within this sub-section, we further
delineate the methods and data used for estimating hazardous air pollutants in vehicles from
model years 2000 and earlier (Section 2.1.2.1), 2001 and later model year vehicles (Section
2.1.1.2), and data that applies to all model year vehicles (Section 2.1.2.3). In this section, we
distinguish "major HAPs" (benzene; ethanol; 1,3-butadiene, formaldehyde, acetaldehyde and
acrolein) which have toxic ratios that can be a function of fuel properties. Other toxic VOCs
("minor HAPs": 2,2,4-trimethylpentane; ethyl benzene; hexane; propionaldehyde; styrene,
toluene, and xylene(s)) use toxic ratios that vary by fuel subtype, but not as a function of fuel
properties.
2.1.2.1 2000 and Earlier Model Year Vehicles
For major HAP emissions for vehicles in model years 2000 and earlier operating on fuel blends
containing 70-100 percent ethanol are estimated as fractions of VOC. There are few pre-2000
FFVs, and little data on their emissions using E85 fuel. Thus, the toxic fractions were derived
from data from four newer flexible-fuel vehicles running on E85 gasoline, collected during the
EPAct program (Phase 3) as displayed in Table 2-36. Since no measurements were obtained on
an E70 blend (more typically used in winter) or blends above E85, the same toxic-to-VOC
fractions are used for all ethanol-gasoline blends containing 70-100 percent ethanol. These ratios
are applied to older technology (2000 and earlier vehicles), even though data were collected from
Tier 2 vehicles. The 2000 and earlier HAP emission rates are stored in the database table
"ATRatioNonGas" (see Table 2-37).
Table 2-36 E70/E85 Major HAP VOC Fraction for 2000 and Earlier Model Year Vehicles
Pollutant (pollutantID)
Toxic Fraction
Benzene (20)
0.0170
Ethanol (21)
0.3724
1,3-butadiene (24)
0.0011
Formaldehyde (25)
0.0291
Acetaldehyde (26)
0.1644
Acrolein (27)
0.0010
40
-------
Table 2-37 Description of the Database Table "ATRatioNonGas," as Applied to Light-Duty Vehicles
Field
Description
RelevantValues
polProcessID
Identifies the pollutant (1st
two digits and Emissions
Process (last two digits).
Pollutants are identified in the table above;
Relevant processes include:
"Running Exhaust" (processID = 1)
"Start Exhaust" (processID = 2)
"Extended Idle Exhaust" (processID = 90)
"Auxiliary Power Exhaust" (processID = 91)
sourceTypelD
Identifies types of vehicles,
classified by function
Motorcycle (11)
Passenger Car (21)
Passenger Truck (31)
Light Commercial Truck (32)
fuelSubTypelD
Identifies specific fuel
classes within the
fuelTypelD
51 = "Ethanol (E85)"
52 = "Ethanol (E70)"
modelY earGroupID
Identifies a set of model
years covered by a specific
value of atRatio.
In this table, the first and last model year of the group
are concatenated, such as "19601970", or "20302030".
atRatio
Fraction, or "ratio" of the
toxic relative to total VOC.
atRatioCV
"Coefficient of Variation of
the Mean" or "relative
standard error" of the
atRatio.
dataSourcelD
Indicates source data and
methods used to estimate
atRAtio.
2.1.2.2 2001 and Later Model Year Vehicles
For major HAPs in 2001 and later model year vehicles using E-85 fuels, we conducted a more
comprehensive analysis than for the older model year vehicles. Instead of deriving toxic fractions
of VOC, we developed adjustment factors that were compatible with the EPAct toxic ratios
derived for gasoline 2001 and later model year vehicles discussed in the Section 2.1.1.2. The
toxic adjustment factors were developed based on the analysis of EPAct (Phase 3) program,
National Renewable Energy Laboratory (NREL) E4029, Coordinating Research Council (CRC)
E-80 30, and the PM Speciation Program.31 All programs measured emissions from LA92 test
cycle on both E10 and E85, except CRC E-80 which tested E6 and E85. Only the vehicles tested
on both E10 (E6) and E85 were included in the analysis. Numbers of vehicles in each program
are summarized in Table 2-38.
41
-------
Table 2-38 Numbers of Vehicles Included in the Analysis of Major HAPs
Test Program
Number of Vehicles
EPAct (phase 3)
4
NRELE40
9
CRC E-80
7
PM Speciation
2
Consistent emission trends were observed across datasets; thus, the datasets were pooled to
examine the effect of E85 on emissions compared to E10. First, the test of significance of
differences between E10 and E85 was performed using Student's paired Mests. Next, when
statistically significant differences in emissions between E10 and E85 were evident, the
adjustment factors were calculated using Equation 17. The adjustment factor was set to one when
the differences in emissions were not statistically different (i.e., acrolein).
ToxicsE85
VOCpc. s
£85 adjustment factor = ~—— Equation 17
i OXlCSg-^Q
vocEW
The resulting adjustment factors are shown in Table 2-39. As expected, ethanol and the
aldehydes (formaldehyde, acetaldehyde) have higher toxic ratios than the ElO-fueled vehicles.
Table 2-39 E70/E85 Adjustment Factors for Major HAPs for 2001 and Later Model Year Vehicles
Pollutant (pollutantID)
Adjustment Factor for E70/E85
Benzene (20)
0.6672
Ethanol (21)
7.587
1,3-butadiene (24)
0.2167
Formaldehyde (25)
1.572
Acetaldehyde (26)
7.126
Acrolein (27)
1
The toxic fractions for the pollutants in Table 2-39 are calculated using Equation 18.
E85 Toxic Fraction = $'toxic x £"85 adjustment factor
( e Atoxic \ Equation 18
= — -r-r, x £85 adjustment factor
yg-^'^NMOG — g-^'"ethane J
The ft0XiC uses the same equations and coefficients as were derived for MY 2001+ gasoline
vehicles discussed in Section 2.1.1.2 (including the adjustments for benzene and 1,3-butadiene).
The difference between ft'0XjC used for E85 vehicles and the ft0Xic used for gasoline vehicles is
that ft0XiC uses a combination of fuel properties from E85 and E10 fuels as shown in Table 2-40.
As explained in the MOVES Fuel Effects Report22, MOVES uses the E10 fuel properties for
ethanol content, aromatics, T50 and T90 from E10 fuels (stored in the ElOFuelProperties table),
because these fuel effects are obtained from the EPAct program, and the fuel equations are not
intended to be used for the E85-specific levels of ethanol content, aromatics, T50 and T90, which
are outside the bounds of the fuel properties included in the sample design. In addition, the E85
adjustment factors are intended to account for the differences between E85 and E10 emissions,
42
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not the fuel effects from the EPAct study. Olefin content is also used from the E10 fuel
properties table, because the olefin content from E85 fuel is significantly lower than typical
gasoline fuels, and the 1,3-butadiene adjustments were developed from the Complex Model on
gasoline fuels, not E85 fuels (Section 2.1.1.2.3). MOVES accounts for the differences in 1,3-
butadiene for E85 fuels using the E85 adjustment factor (Table 2-39).
For RVP, benzene and sulfur levels, we use the E85-specific values because these fuel properties
are within the range of gasoline fuels (RVP) or were not accounted for in the EPAct fuel design
(benzene and sulfur), and we believe it is appropriate to apply the E85 specific-fuel properties.
Table 2-40 Source of Fuel Properties (E85 or E10) used to Estimate Toxic Fractions for MY 2001 and Later
E85 Vehicles
Ethanol
Volume
RVP
Sulfur
Level
Benzene
Content
Aromatic
Content
Olefin
Content
T50
T90
E10 (10%)
E85
E85
E85
E10
E10
E10
E10
Equation 18 and the accompanying E85 adjustment factors are stored in the MOVES
GeneralFuelRatioExpression table to estimate emissions for the six air toxics pollutants that are
a function of fuel properties ("major HAPs"). Because the E85 toxic fractions are calculated
using the fuel properties of RVP, sulfur and benzene content from E85 fuels, the resulting ratios
between toxic emission rates from E85 and E10 fueled vehicles in MOVES are slightly different
than the adjustment factors shown in Table 2-39. In addition, the VOC emissions from E85-
fueled and ElO-fueled vehicles (to which the toxic fractions apply) are slightly different due to
the lower sulfur level of E85 fuel as discussed in the MOVES3 Fuel Effects Report.22
2.1.2.3 Air Toxics Fractions that Apply to All Model Year Vehicles
Fractions for the remaining "minor HAPs" air toxic compounds modeled in MOVES were
developed from the four flexible-fuel vehicles tested during the EPAct program (Phase 3)
running on fuels containing 70-100 percent ethanol. The E85 toxics are consistent with the
speciation profile developed from the same test data.21. As stated earlier, the vehicles were tested
on a single E85 gasoline fuel. These ratios are applied to older technology (2000 and earlier
vehicles) as well as the modern technology vehicles in the test program; thus, while there are few
pre-2000 FFVs, there is more uncertainty in emission estimates for older technology vehicles
running on high ethanol blends than for newer vehicles. As expected, the toxic fractions for the
E85 vehicles shown in Table 2-41 are lower than ElO-fueled vehicles for both pre-2001 MY
(Table 2-9) and MY 2001 and later vehicles (Table 2-35), with the exception of
propionaldehyde. The toxic fractions for the pollutants shown in Table 2-41 are stored in the
minorHAPRatio table (see Table 2-10).
43
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Table 2-41 Toxic Fractions of VOC for Vehicles Running on E70/E85 for All Model Year Vehicles
Pollutant (pollutantID)
Toxic Fraction of VOC
2,2,4-Trimethylpentane (40)
0.0078
Ethyl Benzene (41)
0.0055
Hexane (42)
0.0045
Propionaldehyde (43)
0.0025
Styrene (44)
0.0003
Toluene (45)
0.0177
Xylene(s) (46)
0.0185
2.2 Poly cyclic Aromatic Hydrocarbons (PAHs)
Emissions of PAHs are estimated using fractions similar to that used for VOCs as described in
the previous section. However, for PAHs, the process is complicated by the fact that exhaust and
crankcase emissions of these compounds are emitted in both the gaseous and particulate phases.
Accordingly, emissions in the gaseous phase are estimated as fractions of total VOC, and
emissions in the particulate phase as fractions of organic carbon < 2.5 [j,m (OC2.5) We discuss
the derivation of PAH fractions for vehicles operating on gasoline containing low ethanol
percentages (Section 2.2.1) and high-ethanol percentages (Section 2.2.2).
2.2.1 Vehicles Operating on Fuel Blends Containing 0-15 Percent
Ethanol
The PAH emission fractions for gasoline vehicles are estimated from a set of 99 vehicles
selected for chemical speciation that were measured in the Kansas City Light-duty Vehicle
Emissions Study (KCVES).32 Each vehicle was measured on the LA92 driving cycle that
includes both start and running operation. For each vehicle, emissions of THC and particulate
matter 2.5 microns in diameter or less (PM2.5) were measured. Fleet-average fractions of
PAH/THC and PAH/PM2.5 were calculated with each sample weighted by total emissions,g
vehicle-miles traveled (VMT), and an equal weight between summer and winter. We used a
VOC/THC fraction of 0.86 developed from the total organic-gas speciation profile developed
from the Kansas City program (8750a) to estimate PAH/VOC fractions. Because the PAH
measurements from the LA92 cycle include both start and running emissions, we use the same
VOC fractions for both start and running PAH emissions. We adjusted the PAH/PM2.5 fraction
by the fraction of OC measured in the start (42.6 percent) and running emission processes (55.7
percent) to produce PAH/OC2.5 emission fractions. Because OC/PM fractions differ for start and
running, we have separate PAH/OC toxic fractions for start and running.
The partitioning of PAH emissions between gaseous and particulate phases is assigned on the
basis of average temperature and dilution conditions at the time of measurement, i.e., in the
sample train and constant-volume sampler. Thus, the partitioning reflected in the emission
fractions does not reflect cooling and dilution occurring in the "real world" after the exhaust
leaves the tailpipe. The sampling conditions set forth in EPA regulations for particulate and
8 Each sample contained emissions from one to five vehicles.
44
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hydrocarbon measurement differ for light-duty and heavy-duty vehicles, which affects the phase
partitioning of PAH emissions obtained from both engine types. In preparing inputs for MOVES,
we developed one set of phase allocation factors for gasoline sources and another for diesel
sources in order to streamline data processing, and to be consistent with the measurement
conditions reflected in the PAH measurements.
The allocations of PAHs into gaseous and particulate phases for gasoline vehicles was based on
measurement samples analyzed by Desert Research Institute (DRI) on a subset of vehicles in the
KCVES that were measured with dilution air at both low and high dilution temperatures.33 One
of the purposes of this follow-up study was to examine the impact of sampling conditions on
PAH emission measurements. DRI measured PAH species with Teflon-impregnated glass filters
(TIGF) and backup glass cartridges with Amberlite XAD-4 adsorbent resins over the LA92
cycle. Relative concentrations of individual PAH were measured on the TIGF and the XAD with
sampling line and dilution temperatures of 20°C and 47°C for four composite samples, with each
composite sample containing one to three vehicles. Table 2-42 reports the TIGF/XAD phase
allocation factors measured at 47°C (which was the measurement temperature for the Kansas
City Light-duty Vehicle Emissions Study), for the composite sample referred to as the 'medium-
emitters.' This class contained a 1989 Camry and 1992 Voyager. In MOVES, we used the PAH
phase-partitioning of this sample to estimate the relative gas and particle portioning of all
gasoline-source emissions. Clearly, this sample may not adequately represent phase-partitioning
of PAH emissions from the current in-use fleet; however, it was deemed the most representative
of the breadth of gasoline vehicles sampled in the KCVES. Note that the PAH species
partitioning was heavily dependent on molar mass (molecular weight); compounds with lighter
molar masses (e.g., naphthalene) were measured almost entirely in the gaseous phase, whereas
compounds with heavier molar masses were measured almost entirely in the particulate phase
(e.g., dibenzo(a,h)anthracene).
45
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Table 2-42 Gasoline PAH Phase Allocation Factors
PAH species
Molar Mass
(g/mol)
Phase Fraction
Gaseous
Particulate
Naphthalene
128
0.9996
0.0004
Acenaphthylene
152
0.9985
0.0015
Acenapthene
154
1.0000
0.0000
Fluorene
166
1.0000
0.0000
Anthracene
178
0.9915
0.0085
Phenanthrene
178
0.9953
0.0047
Fluoranthene
202
0.9822
0.0178
Pyrene
202
0.9831
0.0169
Benz(a)anthracene
228
0.6721
0.3279
Chrysene
228
0.7307
0.2693
Benzo(a)pyrene
252
0.0426
0.9574
Benzo(b)fluoranthene
252
0.5546
0.4454
Benzo(k)fluoranthene
252
0.5546
0.4454
Benzo(g,h,i)perylene
276
0.0000
1.0000
Indeno( 1,2,3 -cd)pyrene
276
0.0000
1.0000
Dibenzo(a,h)anthracene
278
0.0000
1.0000
The PAH/VOC and PAH/OC emission fractions used in MOVES are calculated by multiplying
the PAH/VOC, and PAH/OC fractions calculated from KCVES by the gas/particle partitioning
factors in Table 2-42. The calculation is displayed with Equation 19 and Equation 20 for each
PAH, i= 1:16.
PAHj
VOC
PAHt
OC
(Table 2-43) =
PAHj
VOC
(KCVES) x Gaseous Fractiorii (Table 2-42)
(Table 2-43)
PAHt
~OC
¦(KCVES) x Particulate Fractiorii (Table 2-42)
Equation 19
Equation 20
Within MOVES, the PAH fractions in Table 2-43 are applied to all gasoline fuels with ethanol
content less than 20 percent. In the MOVES database, these fractions are stored in two tables.
Fractions for the gaseous and particulate phases are stored in the tables pahGasRatio and
pahParticleRatio, respectively. The two tables have the same structure, which is presented in
Table 2-43.
46
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Table 2-43 Toxic Fractions for PAH Compounds, in Gaseous and Particulate Phases for Gasoline Vehicles
Fueled with Ethanol Content < 20 percent
Species
Gaseous
Phase
(PAH/VOC)
Particulate Phase
(PAH/OC2.5)
Start
Running
Naphthalene
2.07 xlO"3
1.68xl0"4
1.29 xlO"4
Acenaphthylene
1.81 xlO"4
5.01xl0"5
3.83 xlO"5
Acenaphthene
3.99xl0"5
0.0
0.0
Fluorene
8.08xl0"5
0.0
0.0
Anthracene
3.35xl0"5
5.19xl0"5
3.97 xlO"5
Phenanthrene
2.14xl0"4
1.81xl0"4
1.39xl0"4
Fluoranthene
5.60xl0"5
1.83xl0"4
1.40 xlO"4
Pyrene
6.40 xlO"5
1.98xl0"4
1.52xl0"4
Benz(a)anthracene
5.40xl0"6
4.76xl0"4
3.64 xlO"4
Chrysene
6.05 xlO"6
4.02xl0"4
3.08 xlO"4
Benzo(a)pyrene
2.94xl0"7
1.19xl0"3
9.13 xlO"4
Benzo(b)fluoranthene
4.01 xlO"6
5.81xl0"4
4.45 xlO"4
Benzo(k)fluoranthene
4.01 xlO"6
5.81xl0"4
4.45 xlO"4
Benzo(g,h,i)perylene
0.0
3.23xl0"3
2.47 xlO"3
Indeno( 1,2,3 ,c,d)pyrene
0.0
1.21X10-3
9.28xl0"4
Dibenzo(a,h)anthracene
0.0
2.79xl0"5
2.13 xlO"5
Note: The zero values are estimated because of the zero-phase fractions from Table 2-42
47
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Table 2-44 Description of the Database Tables pahGasRatio and pahParticleRatio
Field
Description
Relevant Values
polProcessID
Identifies the pollutant (1st two
digits and Emissions Process
(last two digits).
Pollutants are identified in the table above;
Relevant polprocesses include:
18501 = "Naphthalene gas, running exhaust"
18502 = "Naphthalene gas, start exhaust"
fuelTypelD
Identifies broad classes of fuels,
e.g., "gasoline." "diesel."
1 = "Gasoline"
2 = "Diesel"
3 = "CNG"
5 = "Ethanol"
modelY earGroupID
Identifies a set of model years
covered by a specific value of
atRatio.
1960-1970
1971-1977
1978-1995
1996-2006
2007-2060
atRatio
Average PAH/VOC emission
ratio for a combination of
process, fuel type, sourceType
and modelYearGroup.
meanBaseRateCV
"Coefficient of Variation of the
Mean" or "relative standard
error" of the meanBaseRate.
dataSourcelD
Indicates source data and
methods used to estimate
atRAtio.
2.2.2 Vehicles Operating on Fuel Blends Containing 70-100percent
Ethanol
As noted above, flexible-fueled vehicles (FFVs) may operate on gasoline, or on "E85" fuel,
which is a mix of gasoline with high ethanol levels (typically 70-85%). Hays et al. (2013)34
reported speciated filter-collected semi-volatile organic compound (SVOC) measurements from
three Tier 2 compliant vehicles tested using E0, E10 and E85 fuels. Reductions in total PAH
between E0 and E85 in total measured filter-collected PAHs ranged between 22 percent and 93
percent depending on the temperature and phase of the LA92 cycle. They found that E85
significantly reduced the lighter PAHs, including naphthalene, fluorene, anthracene,
phenanthrene, fluoranthene, pyrene, benzo(a)anthracene and chrysene. However, no significant
effect was observed for the heavier PAHs, including benzo(a)pyrene, benzo(£)fluoranthene,
benzo(g/zz')perylene, and indeno(l,2,3-cJ)pyrene.
Because Hays et al. (2013) reported only the filter-collected PAH emissions, and the results were
conducted on a limited number of vehicles, we used the results to adjust the fleet-average PAH
ratios derived from KCVES tested on E0 fuel. We reduced the VOC phase PAH ratios by 74
percent, assuming that (1) the annual average ethanol content of high ethanol fuels is 74 percent,
and (2) the PAH in the gaseous phase are reduced proportionally to the gasoline content
48
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reductions. The 74 percent reduction is within the range of reductions observed by Hays et al.
(20 1 3)34 for total PAHs. Because Hays et al. (20 1 3)34 observed no significant decrease of the
heavier PAHs for which MOVES assumes exist primarily in the particle-phase (Table 2-42), we
assume the E85 particle PAH/OC fractions are the same as the E0-E20 fractions derived from
KCVES. The resulting fractions are presented in Table 2-45.
Table 2-45 Toxic Fractions for PAH species for Vehicles Running on High-Ethanol Blends
PAH species
Gaseous
Phase
(PAH/VOC)
Particulate Phase (PAH/OC2.5)
Start
Running
Naphthalene
5.38xl0"4
1.68X10"4
1.29 xlO"4
Acenaphthylene
4.71 xlO"5
5.01X10"5
3.83 xlO"5
Acenaphthene
1.04xl0-5
0.0
0.0
Fluorene
2.10X10"5
0.0
0.0
Anthracene
8.70 xlO"6
5.19xl0"5
3.97 xlO"5
Phenanthrene
5.57xl0"5
1.81xl0"4
1.39xl0"4
Fluoranthene
1.45 xlO"5
1.83xl0"4
1.40 xlO"4
Pyrene
1.66 xlO"5
1.98xl0"4
1.52xl0"4
Benz(a)anthracene
1.41 xlO"6
4.76xl0"4
3.64 xlO"4
Chrysene
1.57xl0"6
4.02xl0"4
3.08 xlO"4
Benzo(a)pyrene
7.65 xlO"8
1.19xl0"3
9.13 xlO"4
B e 11 /o (/>) fl no ra 111 lie 11c
1.04 xlO"6
5.81X10"4
4.45 xlO"4
Bcn/o(/i')fluoranthcnc
1.04 xlO"6
5.81X10"4
4.45 xlO"4
Bcnzofe/-// )pcry lcnc
0.0
3.23xl0"3
2.47 xlO"3
Indeno( 1.2.3.«/)pvrcnc
0.0
1.21 xlO"3
9.28xl0"4
Dibcnzo(a/?)anthraccnc
0.0
2.79xl0"5
2.13 xlO"5
by Process
Note: The zero values are estimated because of the zero-phase fractions from Table 2-42
As discussed in the MOVES Fuel Effects report22, the VOC and PM2.5 emission rates (g/mile or
g/start) calculated using MOVES for vehicles fueled on E10 and E85 are quite similar, except for
VOC emissions for pre-2001 MY vehicles. As such, the difference in the gas-phase PAH
emission rates between E10 and E85 fueled-vehicles for the MY 2001 and later are driven by the
differences in the toxic fractions shown in Table 2-45 (74% lower). Because the particle-phase
PAH toxic ratios are the same between E85 and E10 vehicles, the particle-phase PAH emission
rates for these vehicles from MOVES are roughly equivalent.
2.3 Metals
Emissions of metals in vehicle exhaust result from trace-level contamination of fuel and engine
oil, as well as attrition from engine, exhaust system, and emission-control components. MOVES
models two groups of metal emissions, 1) metals that are used for air quality modeling, and 2)
metals that are included due to their known toxicity. The metals that are included for air quality
modeling, which include metals such as iron, aluminum and calcium are discussed in the
MOVES3 Speciation report.21 Emissions of these metals are estimated as fractions of PM2.5
emission rates.
49
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This report covers seven metal species included due to their known toxicity, including five
metals and three forms of mercury, as listed in Table 1-4. The toxic metal emissions are
estimated using distance-specific emission rates (g/mile). Manganese is the only metal that is
required for both air quality and toxicity purposes and is estimated using the g/mile approach. In
the database, these rates are stored in the metalEmissionRate table, described in Table 2-47. Note
that while the table contains a field for "fuel type," the emission rates listed in the table do not
vary among fuel types.
Emission rates for magnesium and nickel were developed from the 99 vehicles sampled for
chemical composition in the KCVES. The mean rates are calculated as weighted averages of
metal measured on Bag 2 of the LA92, using weights designed to represent the onroad vehicle
fleet.35 The use of Bag 2 emissions in the averaging helps ensure that the emission rates for these
metals are consistent with the PM2.5 emission profile for running emissions discussed in the
MOVES3 Speciation Report.21 These approaches were adopted because, while PM2.5 emissions
are much lower during hot-stabilized running conditions, PM2.5 emissions are more enriched in
metals during hot-stabilized running conditions than during start emissions. We compared the
g/mi emission rates from Bag 2 to the average of the entire LA92; the difference in the Bag 2
emission rates from the average of the LA92 is 38 percent and -16 percent for manganese and
nickel. Thus, in using Bag 2 emission rates for metal emission rates, the approach is both
consistent with the PM2.5 speciation running emission profile and provides a likely upper limit (in
the case of manganese) when compared to the cycle average.
Hexavalent chromium was estimated using data collected at U.S. EPA's National Vehicle
Emissions Laboratory and analyzed at the Wisconsin State Laboratory of Hygiene at the
University of Wisconsin-Madison. These data were collected on a single vehicle, a 2008
Chevrolet Impala flexible-fuel vehicle. At the time of the analysis, they were the only available
data with direct measurement of hexavalent chromium from a highway vehicle. Development of
a gasoline vehicle emission rate from these data is detailed in Appendix A.
Emission factors for arsenic were developed from data reported for tunnel tests.36 These data
were collected in two Milwaukee tunnels in 2000/2001, using inductively-coupled plasma mass
spectrometry (ICP-MS). The emission rates are fleet-average, however the fleet had between
1.5% and 9.4% percentage of heavy-duty trucks. We use the same fleet-average emission rate for
both gasoline and diesel vehicles.11
Emission factors for mercury were obtained from a 2005 test program at EPA's National
Exposure Research Laboratory (NERL). In this program mercury samples in raw exhaust were
collected from 14 light-duty gasoline vehicles and two heavy-duty diesel vehicles.
Documentation describing development of these emission factors can be found in Appendix B.
h Schauer et a. (2006)36 used a chemical mass balance (CMB) model to apportion metal emissions to diesel exhaust,
combined gasoline tailpipe and tire wear, brake wear, and road dust sources. However, arsenic was not measured in
significant quantities to conduct the CMD source apportionment. We used the total tunnel emission rates to
represent arsenic exhaust emission rates in MOVES for both gasoline and heavy-duty vehicles, however, some of
the arsenic may be coming from non-tailpipe or road dust sources.
50
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Table 2-46 Metal Emission Rates for Gasoline Motor Vehicles
Pollutant
Emission Rate (g/mi)
Chromium, hexavalent (6+)
1.20xl0"8
Manganese
1.33 xlO"6
Nickel
1.50xl0"6
Mercury, Elemental (Gaseous Phase)
l.lOxlO"7
Mercury, Reactive (Gaseous Phase)
9.90xl0"9
Mercury, Particulate Phase
4.00xl0"10
Arsenic
2.30xl0"6
Fleet-average metal emission rates were derived for vehicles running on gasoline and gasoline-
ethanol blends. Since metal emissions can result from trace level contamination of fuel and
engine oil, as well as wear on engine and exhaust aftertreatment components, the metal emission
rates for E85-fueled vehicles were assumed to be the same as those used for gasoline vehicles
(see Table 2-46).
Table 2-47 Description of the Database Table metalEmissionRate
Field
Description
RelevantValues
polProcessID
Identifies the pollutant (1st two
digits and Emissions Process
(last two digits).
Pollutants are identified in the table above;
Relevant processes include:
1 = "Running Exhaust"
fuelTypelD
Identifies broad classes of fuels,
e.g., "gasoline." "diesel."
1 = "Gasoline"
2 = "Diesel"
5 = "Ethanol"
sourceTypelD
Identifies vehicle types,
classified by function
Motorcycles (11)
Passenger Cars (21)
Passenger Trucks (31)
Light Commercial Trucks (32)
modelY earGroupID
Identifies a set of model years
covered by a specific value of
atRatio.
1960-1970
1971-1977
1978-1995
1996-2006
2007-2060
Units
Identifies units in which the
meanBaseRate is expressed.
grams/mile
meanBaseRate
Average emission rate for a
combination of process, fuel
type, sourceType and
modelYearGroup.
meanBaseRateCV
"Coefficient of Variation of the
Mean" or "relative standard
error" of the meanBaseRate.
dataSourcelD
Indicates source data and
methods used to estimate
atRAtio.
51
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2.4
Dioxins and Furans
The MOVES model estimates mass and distance-based emission rates for 17 dioxin and furan
congeners (gram/mile). We discuss the derivation of dioxin and furan emission rates for vehicles
operating on gasoline containing low ethanol percentages (Section 2.4.1) and high-ethanol
percentages (Section 2.4.2).
2.4.1 Vehicles Operating on Fuel Blends Containing 0-15 Percent
Ethanol
The emission rates for dioxins and furans were obtained from the tunnel study used in EPA's
dioxin assessment.37'38 The emission rates from the tunnel study did not vary among fuel types
and we applied theses rates to all gasoline vehicles in MOVES. In the absence of additional data,
the fractions for more recently-manufactured vehicles were assumed to be the same as those for
vehicles employing older technologies. Of course, this extrapolation from one set of technologies
to another involves some degree of uncertainty. The rates are stored in the dioxinEmissionRate
table, which is described in Table 2-49.
Table 2-48 Dioxin Emission Rates for Motor Vehicles Running on Gasoline Fuel Blends with 0-20 Percent
Ethanol
Pollutant
mg/mi
2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD)
8.27xlO"10
1,2,3,7,8-Pentachlorodibenzo-p-Dioxin
3.70xl0"10
1,2,3,4,7,8-Hexachlorodibenzo-p-Dioxin
3.87xlO"10
1,2,3,6,7,8-Hexachlorodibenzo-p-Dioxin
7.92xlO"10
1,2,3,7,8,9-Hexachlorodibenzo-p-Dioxin
4.93 xlO"10
1,2,3,4,6,7,8-Heptachlorodibenzo-p-Dioxin
5.95 xlO"9
Octachlorodibenzo -p-dioxin
4.70 xlO"8
2,3,7,8-Tetrachlorodibenzofuran
2.76 xlO"9
1,2,3,7,8-Pentachlorodibenzofuran
1.32xl0"9
2,3,4,7,8-Pentachlorodibenzofuran
9.68xlO"10
1,2,3,4,7,8-Hexachlorodibenzofuran
1.09 xlO"9
1,2,3,6,7,8-Hexachlorodibenzofuran
1.16 xlO"9
1,2,3,7,8,9-Hexachlorodibenzofuran
3.17xlO"10
2,3,4,6,7,8-Hexachlorodibenzofuran
1.36xl0"9
1,2,3,4,6,7,8-Heptachlorodibenzofuran
1.21 xlO"8
1,2,3,4,7,8,9-Heptachlorodibenzofuran
3.87xlO"10
Octachlorodibenzofuran
1.37xl0"8
52
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Table 2-49 Description of the Database Table DioxinEmissionRate
Field
Description
RelevantValues
polProcessID
Identifies the pollutant (1st
two digits and Emissions
Process (last two digits).
Pollutants are identified in the table above;
Relevant processes include:
1 = "Running Exhaust"
fuelTypelD
Identifies broad classes of
fuels, e.g., "gasoline."
"diesel."
1 = "Gasoline"
2 = "Diesel"
5 = "Ethanol"
modelY earGroupID
Identifies a set of model
years covered by a specific
value of atRatio.
1960-2050
1960-2006
2007-2009
2010-2060
Units
Identifies units in which the
meanBaseRate is expressed.
grams/mile
meanBaseRate
Average emission rate for a
combination of process, fuel
type, sourceType and
modelYearGroup.
meanBaseRateCV
"Coefficient of Variation of
the Mean" or "relative
standard error" of the
meanBaseRate.
dataSourcelD
Indicates source data and
methods used to estimate
atRAtio.
2.4.2 Vehicles Operating on Fuel Blends containing 70-100percent
Ethanol
No emissions data exist for dioxin and furan emissions from vehicles running on E85 or E70.
Thus, dioxin emission factors for E85 and E70 were estimated by multiplying fractions for
vehicles running on EO fuels (Table 2-48) by the fraction of gasoline in the fuel, assuming no
emission of dioxins or furans resulting from the combustion of ethanol. Resulting ratios are
given in Table 2-50.
53
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Table 2-50 Emission Factors for Dioxins and Furans, for Vehicles Operating on High-Ethanol Blends
Congener
Emission rate
(mg/mile)
2,3,7,8-Tetrachlorodibenzo-p-dioxin
2.15xlO"10
1,2,3,7,8-Pentachlorodibenzo-p-Dioxin
9.61xl0"n
1,2,3,4,7,8-Hexachlorodibenzo-p-Dioxin
l.OlxlO"10
1,2,3,6,7,8-Hexachlorodibenzo-p-Dioxin
2.06xl0"10
1,2,3,7,8,9-Hexachlorodibenzo-p-Dioxin
1.28xlO"10
1,2,3,4,6,7,8-Heptachlorodibenzo-p-Dioxin
1.55xl0"9
Octachlorodibenzo -p-dioxin
1.22xl0"8
2,3,7,8-Tetrachlorodibenzofuran
7.19xlO"10
1,2,3,7,8-Pentachlorodibenzofuran
3.43xlO"10
2,3,4,7,8-Pentachlorodibenzofuran
2.52xlO"10
1,2,3,4,7,8-Hexachlorodibenzofuran
2.84xlO"10
1,2,3,6,7,8-Hexachlorodibenzofuran
3.02X10"10
1,2,3,7,8,9-Hexachlorodibenzofuran
8.24xl0"n
2,3,4,6,7,8-Hexachlorodibenzofuran
3.52xlO"10
1,2,3,4,6,7,8-Heptachlorodibenzofuran
3.16xl0"9
1,2,3,4,7,8,9-Heptachlorodibenzofuran
l.OlxlO"10
Octachlorodibenzofuran
3.57xl0"9
54
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3 Diesel Exhaust
Toxic fractions, dioxin and metal emission rates were developed for exhaust emissions from
heavy-duty diesel vehicles and applied to all diesel vehicle categories. The development of
inputs for diesel vehicles are defined as "pre-2007", "model year 2007 through 2009", and "2010
and later" based on technology and emissions standards for heavy-duty vehicles. These
distinctions are made because emission controls on 2007 through 2009 and 2010 and later
engines differ and have a substantial effect on composition of emissions. The pre-2007 diesel
toxic fractions for VOCs and PAHs are applied to auxiliary power unit exhaust for all model year
vehicles until 2024, because auxiliary power units are not subject to the same stringency of
control as highway engines. There are no separate emission ratios or factors for diesel engines
running on biodiesel fuels or synthetic diesel fuels, due to limited data. Biodiesel vehicles use the
same toxic ratios and factors as regular diesel. Due to a lack of applicable data, the toxic
emission data are based on heavy-duty testing but are applied to light-duty diesel with the same
model year distinctions (pre-2007, 2007 to 2009, and 2010 and later).
3.1 Volatile Organic Compounds
The composition of VOC emissions for heavy-duty diesel engines lacking the advanced control
technologies applied in more recently-manufactured vehicles differs substantially from earlier
technologies. Thus, we developed one set of toxic fractions for pre-2007 diesel engines and
another set for engines manufactured between 2007 to 2009, and 2010 and later. For each model
year group, the toxic fractions were developed from test cycles that included both running and
start exhaust emissions and the same toxic fractions are applied to both emission processes in
MOVES.
3.1.1 Pre-2007 Diesel Engines
To estimate toxic fractions of VOC for vehicles in the pre-2007 model-year group, EPA relied on
a database compiled for the Coordinating Research Council and the National Renewable Energy
Laboratory (NREL) (CRC E-75).39 This database was developed from a literature survey and
compiled data collected in 13 different studies. The studies included were conducted in various
countries and included heavy-duty and light-duty engines, a variety of diesel and biodiesel fuels,
and a number of different operating modes and cycles.
For 2,2,4-trimethylpentane, hexane, propionaldehyde, and toluene, toxic fractions of VOC were
developed by Sierra Research. Their analysis of CRC E-75 data is described in detail in the
technical report.45'39 Data from tests using non-conventional diesel fuel (Fischer-Tropsch, bio-
diesel, ethanol-diesel blends, emulsified fuel, European blends, and other obvious research fuels)
were excluded, as were data from light-duty engines. A single set of toxic fractions were
developed from the measurements on different test cycles, with no differentiation between cycles
with start emissions and running emissions only.39 The fractions are provided in Table 3-1. Toxic
fractions for other compounds in Table 3-1 were developed by EPA from the E-75 database. We
relied on data collected in the United States from heavy-duty diesel engines running on
conventional diesel fuels, collected on test-cycles representative of real-world operation. Some
55
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studies reported results on a distance-specific basis (g/mi) whereas others reported results on a
brake-specific basis (g/hp-hr). For both subsets of data, we calculated mean emissions for each
toxic and for VOC, and then calculated mean fractions for each reporting basis. We then
calculated an overall mean fraction using the respective sample sizes to weight the two fractions.
Table 3-1 Toxic Fractions of VOC for Pre-2007 Diesel Engines
Pollutant
Toxic fraction
1,3-Butadiene
0.00292
2,2,4-Trimethylpentane
0.00180
Acetaldehyde
0.03555
Acrolein
0.00662
Benzene
0.00783
Ethanol
0
Ethyl Benzene
0.00266
Formaldehyde
0.07823
n-Hexane
0.00197
Propionaldehyde
0.00468
Styrene
0.00131
Toluene
0.00433
Xylenes
0.00378
Since extended idle emissions associated with auxiliary power units (APUs) are not subject to
2007 standards, toxic to VOC ratios for pre-2007 diesel engines were used for the APU VOC
toxic emission rates for all model years until 2024.40' However, we anticipate that APU
standards promulgated as part of the Phase 2 greenhouse gas regulation for medium and heavy-
duty engines41 will result in use of diesel particulate filters in 2024; thus we are using 2007-2009
diesel toxic emissions data for those units.
3.1.2 2007+ Diesel Engines
For heavy-duty diesel engines manufactured in 2007 and later, advanced emission controls
change the composition of VOCs. For these engines, we relied on speciated emissions data from
the Advanced Collaborative Emissions Study (ACES), directed by the Health Effects Institute
and Coordinating Research Council, with participation from a range of government and private-
sector sponsors.42'43 ACES was conducted in two phases, with the first focusing on engines
complying with 2009 standards and the second focusing on engines meeting 2010 standards.
Engines tested in ACES that met the 2007 and 2010 standards had different emission control
systems which had significant impact on composition of emissions. Whereas 2007-compliant
engines added diesel particulate filters, 2010-compliant engines also had urea-based selective
catalytic reduction (SCR) catalysts and ammonia oxidation catalysts. In ACES Phase 1, detailed
emissions measurements were performed on four engines, while in ACES Phase 2 measurements
were performed on three engines. In both test programs, vehicles were operated on low-sulfur
diesel fuel over several test cycles, with new engine and aftertreatment systems. We made use of
data from the 16-hour transient cycle which is composed of FTP and CARB 5-Mode cycles,
developed specifically to gain sufficient mass of toxics emitted at low concentrations, and to
capture diesel particulate filter regeneration events. The ACES measurements for the selected
VOC emissions were background-corrected using background dilution air.42 Toxic fractions of
56
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VOC calculated from the ACES data are provided in Table 3-2. Because VOC emissions are so
low in the advanced technology diesels with new engine and aftertreatment systems, there is
considerable measurement uncertainty for gaseous air toxics. Also, while VOC measurements
included several alcohol species, including ethanol, these measurements were likely due to
sample contamination and were not included in the speciation profiles used to develop toxic
fractions, (See discussion in Appendix D of the Speciation Report21) and the ethanol toxic
fraction is set to zero (Table 3-2).
Table 3-2 Toxic Fractions of VOC for 2007 and Later Diesel Vehicles
Toxic Fraction
Pollutant
2007-2009
2010 and later
1,3-Butadiene
0.0008
0.0000
2,2,4-Trimethylpentane
0.0078
0.0045
Acetaldehyde
0.0693
0.0417
Acrolein
0.0100
0.0036
Benzene
0.0129
0.0000
Ethanol
0
0
Ethyl Benzene
0.0063
0.0112
Formaldehyde
0.2174
0.0266
N-Hexane
0.0054
0.0009
Propionaldehyde
0.0031
0.0029
Styrene
0.0000
0.0000
Toluene
0.0300
0.0183
Xylene(s)
0.0380
0.0848
3.2 Polycyclic Aromatic Hydrocarbons
PAH emissions from diesel vehicles can be formed by combustion as well as post-combustion in
the engine and aftertreatment systems.47 We have developed separate PAH emission rates for
pre-2007 diesel, 2007-2009 diesel, and 2010+ diesel to represent the different combustion and
aftertreatment strategies as discussed in the following subsections.
As with gasoline emissions, PAH mass emissions from diesel engines were apportioned into
gaseous and particulate phases, using a single set of allocation factors for all temperature
conditions. The partitioning factors for diesel PAHs were developed using estimates from EPA's
SPECIATEdatabase44 and information on compounds' physical and chemical properties. 45 The
allocations from SPECIATE were based on exhaust measured from two medium-duty diesel
trucks tested in 1996 with low mileage.46 The phase-partitioning factors are shown in Table 3-3.
Compared to the partitioning for gasoline (Table 2-42), the fraction of PAH in the particulate
phase is higher for diesel emissions, which is consistent with the higher concentrations of
particles in diesel exhaust. It should be noted that the data used represent gas-particle phase
partitioning in the sampled diluted exhaust, which is not fully representative of partitioning in the
atmosphere.
Emissions of PAH in the gaseous and particulate phases were estimated as fractions of total
VOC and OC2.5, respectively. We used the phase-partitioning factors in Table 3-3 for both pre-
2007 and 2007+ diesel engines. We note that we introduce additional uncertainty when we apply
57
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the phase-partitioning derived from two pre-2007 technology vehicles to the 2007+ diesel
engines
Table 3-3 Phase-Partition Fractions for Emissions of Polycyclic Aromatic Hydrocarbons from Diesel Engines
PAH species
Molar Mass
(g/mol)
Phase Fraction
Gaseous
Particulate
Naphthalene
128
1.0
0.0
Acenaphthylene
152
1.0
0.0
Acenapthene
154
1.0
0.0
Fluorene
166
0.785
0.215
Anthracene
178
0.534
0.466
Phenanthrene
178
0.665
0.335
Fluoranthene
202
0.484
0.516
Pyrene
202
0.448
0.552
Benz(a)anthracene
228
0.277
0.723
Chrysene
228
0.177
0.823
Benzo(a)pyrene
252
0.0
1.0
B c n zo (/>) fl 110 ra 111 lie ne
252
0.0
1.0
B c 11 /o (A') fl no ra 111 lie 11c
252
0.0
1.0
Bcnzo(w/?/)pcrvlcnc
276
0.227
0.773
Indeno( 1,2.3-«/)pvrcnc
276
0.0
1.0
Dibenzo( a/?)anthracene
278
0.0
1.0
3.2.1 Pre-2007 Diesel Engines
PAH fractions for pre-2007 diesel engines were calculated using results from the E-75 database.
A single set of PAH/VOC fractions were derived for the E-75 database that represent both start
and running exhaust. For the particulate phase, a single fraction was first calculated with respect
to total PM2.5, and then converted to a fraction of total OC2.5 using estimates of OC as a fraction
of total PM2.5. Note that the OC/PM fractions differed by emissions process, thus for MOVES
we obtained separate PAH/OC2.5 fractions for start, running and extended-idle emissions.
In estimating fractions, we relied on data collected in the United States on heavy-duty diesel
engines running on conventional diesel fuels, measured on test-cycles representative of real-
world operation. It should be noted that for some compounds, substantially more data were
available than for others; thus, the level of confidence in emission rates varies among individual
compounds. For instance, while data from 66 tests were available for acenaphthene, data from
only two tests were available for dibenz(c//?)anthracene. Table 3-4 shows fractions for PAH
emissions relative to OC and VOC, by emissions process.
58
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Table 3-4 Toxic Fractions for PAH Species, by Phase and Process, for Pre-2007 Diesel Vehicles
PAH
Gaseous
Phase
(PAH/VOC)
Particulate Phase (PAH/OC2.5)
Start/Idle
Running
Extended Idle
Naphthalene
9.05 xlO"3
0.0
0.0
0.0
Acenaphthylene
5.01 xlO"4
0.0
0.0
0.0
Acenaphthene
2.98xl0"4
0.0
0.0
0.0
Fluorene
4.85 xlO"4
2.80xl0"4
8.49xl0"4
2.54xl0"4
Anthracene
2.35xl0"4
1.63 xlO"4
4.94xl0"4
1.48xl0"4
Phenanthrene
7.08X10"4
6.44 xlO"4
1.96 xlO"3
5.86xl0"4
Fluoranthene
3.55xl0"4
6.24 xlO"4
1.90 xlO"3
5.68xl0"4
Pyrene
4.27 xlO"4
9.02 xlO"4
2.74 xlO"3
8.21X10"4
Benzo(a)anthracene
4.36xl0"5
3.23 xlO"4
9.81 xlO"4
2.94xl0"4
Chrysene
1.70 xlO"5
2.04 xlO"4
6.20 xlO"4
1.86X10"4
Benzo(a)pyrene
0.0
1.21 xlO"4
3.69 xlO"4
1.10 xlO"4
B e 11 /o (/>) fl 110 ra 111 lie 11c
0.0
3.60 xlO"5
1.10 xlO"4
3.28xl0"5
Bcn/o(/i')fluoranthcnc
0.0
5.08X10"6
1.50xl0"5
4.62xl0"6
Benzofe/?/ )pcrv lcnc
8.3xl0"7
5.78xl0"6
1.80 xlO"5
5.26xl0"6
Indeno( 1.2.3-«/)pvrcnc
0.0
9.24 xlO"6
2.81 xlO"5
8.41xl0"6
D i b c 11 /(fl/?) a 111 h rac c 11c
0.0
4.85 xlO"6
1.50xl0"5
4.41xl0"6
Note: The zero values are estimated because of the zero-phase fractions from Table 3-3
The PAH Toxic fractions in Table 3-4 are applied to exhaust emission for 2006 and earlier model
year diesel vehicles in MOVES. The extended idle toxic fractions are applied to auxiliary power
unit (APUs) exhaust for all model year vehicles in MOVES prior to 2024, because the APUs are
not subject to the same control as exhaust from the highway engines. However, as previously
discussed, we are using 2007-2009 diesel toxic emissions data for 2024 and later units.
3.2.2 2007+ Diesel Engines
Advanced emission controls used in 2007 and later model year diesel including diesel vehicles
particulate filters, diesel oxidation catalysts, and selective catalytic reduction (SCR) catalysts and
ammonia oxidation catalysts can reduce or facilitate the formation of individual PAHs. PAHs are
destroyed through oxidation by diesel oxidation catalysts, catalyzed-diesel particulate filters and
NO2 present in the aftertreatment that is produced by the diesel particulate filter but controlled by
the SCR47'48 Modern aftertreatment systems can also facilitate the formation of individual PAH
emissions. For example, Liu et al. 201547 measured an increase in nitro-PAHs emissions in some
tests configurations of a nonroad diesel engine with an oxidation catalyst + SCR aftertreatment
system compared to a baseline case with no diesel aftertreatment system1.
1 Nitro-PAHs are not currently modeled in MOVES
59
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For these engines, we relied on speciated emissions data from the ACES studies42'43 The PAH
emissions measured in the ACES study were uncorrected for background concentrations 42 The
16-hour drive cycle used in the ACES studies comprises multiple driving modes and is used to
represent both start and running exhaust in MOVES. Toxic fractions applicable to these engines
are shown in Table 3-5, in which the fractions are differentiated by phase (gas or particulate) but
not by emissions process (start and running). We used the same phase fractions presented in
Table 3-3. For the particulate phase, a single fraction is provided for all processes (similar to
VOC) because the OC/PM fraction in MOVES for 2007+ diesel is a single fraction for both start
and running emission processes.21 The 2007 and later engines have lower gaseous PAH fractions
than the pre-2007 engines with the exception of naphthalene, and phenanthrene, and most of the
particulate phase PAHs. The 2010 and later engines emissions technologies facilitate further
reductions in PAHs and have significantly lower fractions of all gaseous and particle-phase PAH
emission rates than the 2007-2009 emission rates, with the exception of benzo(a)anthracene.
Table 3-5 Toxic Fractions for Polycyclic Aromatic Compounds, by Phase, for 2007 and Later Diesel Vehicles
2007-2009
2010 and later
PAH
Gaseous Phase
(PAH/VOC)
Particulate Phase
(PAH/OC25)
Gaseous
Phase
(PAH/VOC)
Particulate Phase
(PAH/OC25)
Naphthalene
1.63 xlO"2
0.0
5.84xl0"4
1.35xl0"5
Acenaphthylene
8.53 xlO"5
0.0
1.49 xlO"5
1.29 xlO"6
Acenaphthene
5.26xl0"5
0.0
1.56xl0"5
0
Fluorene
1.96 xlO"4
2.41 xlO"4
3.35xl0"5
0
Anthracene
3.04 xlO"5
1.19xl0"4
6.47 xlO"6
3.19xl0"6
Phenanthrene
8.51 xlO"4
1.92 xlO"3
9.62 xlO"5
2.61 xlO"5
Fluoranthene
4.57xl0"5
2.18X10"4
6.41 xlO"6
6.684xl0"6
Pyrene
3.79 xlO"5
2.09xl0"4
4.72 xlO"6
4.67 xlO"6
Benzo(a)anthracene
3.00 xlO"7
3.58xl0"6
6.92xl0"7
1.942xl0"5
Chrysene
5.00xl0"7
1.12 xlO"5
2.51 xlO"7
5.32xl0"6
Benzo(a)pyrene
0.0
1.48 xlO"5
0.0
0.0
Benzo(b)fluoranthene
0.0
6.27 xlO"6
0.0
0.0
Benzo(k)fluoranthene
0.0
6.27 xlO"6
0.0
0.0
Benzo(ghi)perylene
2.00 xlO"7
8.96xl0"7
0.0
0.0
Indeno( 1,2,3 -cd)pyrene
0.0
2.24 xlO"6
0.0
0.0
Dibenz(a,h)anthracene
0.0
4.48xl0"6
0.0
0.0
Note: The zero values are estimated because of the zero-phase fractions from Table 3-3
3.3 Metals
Emission rates for selected metals representing pre-2007 heavy-duty diesel engines were based
on data from the CRC E-75 program, with the exception of rates for hexavalent chromium,
mercury and arsenic. The hexavalent chromium emission rate was obtained by multiplying the
diesel vehicle emission rate by the ratio of hexavalent chromium to total chromium estimated
60
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from gasoline exhaust (0.29%). The total chromium estimates for diesel vehicles came from the
CRC E-75. More details are provided in Appendix A. The pre-2007 diesel emission rate for
arsenic is a fleet-average value that is also used for gasoline vehicles, obtained from a fleet-
average tunnel study (see Table 2-46). It does not vary with emission control technology. The
mercury emission rate for pre-2007 diesels is calculated from emission tests conducted on two
heavy-duty diesel vehicles, as documented in Appendix B. Table 3-6 provides metal emission
factors for all diesel vehicles.
Table 3-6 Emission Rates for Selected Metals for Diesel Vehicles
Pollutant
Emission Rate for
Emission Rate for
Emission Rate for
1960-2006 (g/mi)
2007-2009 (g/mi)
2010 and later (g/mi)
Chromium VI
2.00xl0"8
5.93xl0"9
2.16xl0"9
Manganese
8.00 xlO"6
6.82xl0"7
2.00xl0"7
Nickel
1.40xl0"5
6.92xl0"7
2.63xl0~7
Mercury, Elemental Gaseous
6.20 xlO"9
6.20 xlO"9
6.20xl0"9
Phase
Mercury, Reactive Gaseous
3.20xl0"9
3.20 xlO"9
3.20xl0-9
Phase
Mercury, Particulate Phase
1.60 xlO"9
1.60 xlO"9
1.60xl09
Arsenic
2.30xl0"6
2.30xl0"6
2.30xl0-6
Emissions rates for manganese and nickel representing diesel engines manufactured in 2007-
2009 were developed from the ACES Phase 1 program42, and 2010 and later were developed
from the ACES Phase 2 program.43 The ACES reported g/hp-hr rates from the 16-hour cycle
were used, and converted to g/mile using the equation on page 31 of the ACES Phase 1 final
report,42 and the measured brake-specific fuel consumption and an assumed heavy-duty fuel
economy of 6 miles per gallon. The ACES metal emission rates were uncorrected for
background concentrations.42 The emission rate for arsenic is identical to the emission rate used
for gasoline vehicles and pre-2007 diesels (Table 2-46). The emission rates for mercury are the
same as those derived for pre-2007 diesel engines, as discussed in Appendix B. The hexavalent
chromium emission rates for pre-2007, 2007 to 2009, and 2010 and later diesel engines were
obtained by multiplying the gasoline vehicle emission rate by the ratio of total chromium from
diesel and gasoline engines. The total chromium estimates came from the previously cited
KCVES and ACES test programs, respectively. More details are provided in Appendix A.
3.4 Dioxins and Furans
To represent emissions of dioxins and furans from pre-2007 heavy-duty diesel engines,
emissions rates for 17 congeners were calculated from the results of an EPA diesel dioxin/furan
study of legacy engines.48 In this study, dioxin emissions from three heavy-duty engines
manufactured prior to 1994 were measured. These engines included a 1985 GM 6.2 L, a 1987
Detroit Diesel 6V92 and 1993 Cummins L10. The emission factors in mg/mi are shown in Table
3-7. Since these engines are older than most of the pre-2007 fleet, dioxin emissions for pre-2007
engines may be overestimated.
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Table 3-7 Emission Rates for Dioxin/Furan Congeners for Diesel Vehicles (mg/mi)
Congener
1970-2006
2007 - 2009
2010 and later
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)
2.23 x 10"10
ND
ND
1,2,3,7,8-Pentachlorodibenzo-p-dioxin
ND
ND
ND
1,2,3,4,7,8-Hexachlorodibenzo-p-dioxin
ND
ND
ND
1.2.3.6.7.8-Hcxachlorodibcnzo-p-dioxin
1.03 x 10"10
ND
ND
1,2,3,7,8,9-Hexachlorodibenzo-p-dioxin
4.78 x 10"10
4.11 x 10"11
ND
1.2.3.4.6.7.8-Hcptachlorodibcnzo-p-dioxin
4.18 x 10"9
2.58xlO"10
1.05 xlO"9
Octachlorodibenzo -p-dioxin
1.61 x 10"8
9.30xl0"10
6.98xl0"9
2,3,7,8-Tetrachlorodibenzofuran
6.50 x 10"9
ND
5.09xl0"n
1,2,3,7,8-Pentachlorodibenzofuran
1.39 x 10"9
ND
1.07xl0"10
2,3,4,7,8-Pentachlorodibenzofuran
2.23 x 10"9
6.30xl0"n
3.24xlO"10
1,2,3,4,7,8-Hexachlorodibenzofuran
8.02 x 10"10
ND
2.20xl0"10
1,2,3,6,7,8-Hexachlorodibenzofuran
4.24 x 10"10
ND
2.43xlO"10
1,2,3,7,8,9-Hexachlorodibenzofuran
ND
ND
ND
2,3,4,6,7,8-Hexachlorodibenzofuran
3.03 x 10"10
ND
1.80xl0"10
1,2,3,4,6,7,8-Heptachlorodibenzofuran
2.16 x 10"9
3.00xl0"10
9.94xlO"10
1,2,3,4,7,8,9-Heptachlorodibenzofuran
ND
ND
5.81xl0"n
Octachlorodibenzofuran
1.85 x 10"9
7.06xl0"10
1.74xl0"9
Note: ND = non-detected, fractions set to 0.
The data used to calculate the emission rates for engines manufactured between 2007 and 2009
were obtained from the EPA diesel dioxin study of 2007 and later engines.49 The results
represent measurements during transient tests conducted on a MY2008 Cummins ISB engine
over 48 replicates on the FTP cycle in a 1:23 cold:hot start ratio, combined with several
emission-control technologies. To represent emissions from engines manufactured between
2007-2009, the results for the diesel oxidation-catalyst plus catalyzed diesel particulate filter
were used. For engines manufactured in 2010 and later, the results for the diesel oxidation
catalyst plus catalyzed diesel particulate-filter coupled with flow-through copper zeolite selective
catalytic reduction and urea and ammonia slip catalyst were used. The 2007-2009 and 2010 and
later emission rates are presented in Table 3-7.
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4 Compressed Natural Gas (CNG) Exhaust
MOVES3 estimates emissions of toxics from heavy-duty vehicles fueled by compressed natural
gas. This section describes the development of toxic emission inputs for this class of vehicles.
4.1 Volatile Organic Compounds
We used speciated hydrocarbon measurements from work sponsored by the California Air
Resources Board.50 These measurements were taken on a 2000 MY Detroit Diesel Series 50G
engine with and without an oxidation catalyst, measured on the Central Business District (CBD)
driving cycle. As discussed in the MOVES3 Speciation report21, we used the uncontrolled results
to represent speciation from pre-2002 CNG heavy-duty vehicles, and the results with oxidation-
catalyst to represent 2002-and-later model year vehicles. The use of the CBD cycle is also
consistent with the results used for criteria-pollutant emissions.
The toxic fractions of VOC derived from this set of measurements are displayed in Table 4-1.
The total VOC emission rates with oxidation catalyst are reduced by 70 percent from pre-2002
levels. As shown in the table, formaldehyde emissions are preferentially reduced by the
oxidation catalyst. Formaldehyde contributes over 50 percent of the VOC emissions for the
uncontrolled CNG bus, but only 16.2 percent of the VOC emissions for the CNG bus equipped
with an oxidation catalyst. The MOVES toxics not measured in this study are assumed to be
negligible and are modeled as 0. The toxic fractions for VOC were applied to both start and
running exhaust emissions in MOVES.
Table 4-1 Toxic Fractions of VOC for CNG Heavy-Duty Vehicles
No control
(pre-2002)
With oxidation
catalyst (2002+)
1,3 Butadiene
0.000234
ND
Benzene
0.00135
0.00253
Toluene
0.000691
0.00786
Ethylbenzene
0.0000841
0.00131
Xylenes
0.000823
0.00634
Formaldehyde
0.517
0.162
Acetaldehyde
0.0305
0.138
Acrolein
0.00235
ND
Propionaldehyde
0.0153
ND
Note: ND = non detect, fractions set to 0.
4.2 Poly cyclic Aromatic Hydrocarbons
The PAH toxic fractions for compressed natural gas are derived from tests on a model year 2000
DDC Series 50G engine on a New Flyer CNG transit bus tested by the California Air Resources
Board (CARB).51 This engine had no catalyst, but the emission fractions are used to represent
both catalyst and non-catalyst engines. Emissions were measured in two stages (the bus was re-
63
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tested after 3 months of service in the Los Angeles County Metropolitan Transit Authority). The
PAH emissions were measured in the semi-volatile phase using PUF-XAD and measured in the
particulate phase on Teflon-coated glass-fiber filters. VOC emissions are derived from the
NMHC and speciated hydrocarbon emissions. The OC emissions rates were provided to EPA by
CARB. We estimated the volatile PAH emissions by calculating PAH/VOC fractions from the
PUF-XAD measurements, and particle-phase PAH/OC fractions using the filter-based
measurements for both stages of the study. For use in MOVES, we averaged the ratios estimated
from both stages of the testing. The average ratios are displayed in Table 4-2. The PAH fractions
were applied to both start and running exhaust emissions in MOVES.
Table 4-2 PAH Fractions of Volatile Organic Carbon (Volatile PAHs), and of Organic Carbon (Particle-
Gaseous
Particulate
Phase
Phase
Compound
(PAH/VOC)
fraction
(PAH/OC)
fraction
Naphthalene
9.55xl0"6
2.11X10"5
Acenaphthylene
4.23 xlO"6
ND
Acenaphthene
1.24xl0"6
1.89xl0"5
Fluorene
2.99xl0"6
3.30xl0"5
Anthracene
1.16xl0"6
1.64xl0"6
Phenanthrene
8.36xl0"6
2.04 xlO"5
Fluoranthene
1.94xl0"6
2.87xl0"5
Pyrene
3.74xl0"6
5.35xl0"5
Benz(a)anthracene
1.68xl0"7
9.39xl0"6
Chrysene/triphenylene
2.44xl0"7
1.91X10-5
Benzo(a)pyrene
ND
ND
Bcn/o(/))fluoranthcnc
ND
ND
Be nzo(A') fl no ra nthc 11c
ND
ND
Indeno( 1,2,3 -«/)pvrcnc
ND
ND
Bcnzo(w/?/)pcrvlcnc
ND
5.50xl0"6
D ibc 11/(0/? )a nthraccnc
ND
ND
Note: ND = non detect, fractions set to 0.
4.3 Metals
We used the nickel emission rates reported from an uncontrolled 2000 MY DDC Series 50G
engine.52 We used the uncontrolled engine to be consistent with the PM2.5 speciation profile.
The hexavalent chromium emission rate was obtained by multiplying the total chromium from
the DDC Series 50G CNG engine by the ratio of hexavalent chromium to total chromium from
gasoline emissions (0.29%). More details are provided in Appendix A.
Results for the other metals predicted by MOVES were not available in the published literature.
We used the same emission rates as for gasoline vehicles, because CNG heavy-duty vehicles are
64
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largely spark ignition technology, with modern CNG vehicles having 3-way catalysts like light-
duty gasoline vehicles. The rates are presented in Table 4-3.
Table 4-3 Metal Emission Rates and Sources used for CNG Vehicles
Pollutant
Emission Rate (g/mi)
Source
Chromium 6+
2.1xlO"10
University of Wisconsin
(Appendix A) and Okamoto
et al. (2006)
Manganese
1.33xl0"6
Same as gasoline
Nickel
l.OOxlO"8
Okamoto et al. (2006)
Elemental Gas Phase Hg
l.lOxlO"7
Same as gasoline
Reactive Gas Phase Hg
9.90xl0"9
Same as gasoline
Particulate Hg
4.00xl0"10
Same as gasoline
Arsenic
2.30xl0"6
Same as gasoline
4.4 Dioxins and Furans
No published dioxin and furan emission rates for CNG vehicles were available. We are using the
dioxin emission rates for gasoline reported in Table 2-48, because they both utilize spark ignition
engines.
65
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5 Evaporative and Refueling Emissions
Emissions of toxics emitted through evaporation of unburned fuel are estimated as fractions of
total evaporative VOC. MOVES estimates toxic emission ratios for each evaporative process
from gasoline vehicles (including gasoline-ethanol blends) and for refueling emissions from
diesel vehicles. Currently, MOVES does not estimate evaporative emissions (e.g., refueling
natural gas leaks) from CNG vehicles as discussed in the evaporative emission report.53 This
section documents the source of the toxic ratios used for evaporative emissions from gasoline
and diesel vehicles.
5.1 Gasoline Vehicles
The derivation of the toxic fractions for vapor venting, fuel leaks and refueling emission
processes are documented in Section 5.1.1 and for permeation in Section 5.1.2.
5.1.1 Vapor Venting, Fuel Leaks, and Refueling Emission Processes
MOVES estimates evaporative emissions from gasoline vehicles using toxic fractions that
pertain to evaporative emission processes. The toxic fractions for some compounds are estimated
as complex fractions based on fuel properties such as oxygenate content and vapor pressure. For
other compounds, simple fractions are estimated. For the compounds modeled, fraction types and
data sources are summarized in Table 5-1.
Expressions used to generate complex fractions were adapted from those used in MOBILE6.2.54
These equations were adapted to compensate for a lack of data from newer vehicles collected in
the context of appropriate experimental designs. However, as the conceptual basis for modeling
evaporative emissions differs between MOBILE6 and MOVES, the equations are applied to the
emission processes considered most closely analogous. Thus, equations for hot soak in
MOBILE6.2 are used for vapor venting and refueling vapor loss, and equations for running loss
are used for fuel leaks and refueling spillage loss. The equations are applied for fuels containing
up to 20 percent ethanol and are presented in Table 5-2. We do not include naphthalene
emissions from evaporative processes in MOVES since it is inconsistently measured in
detectable quantities in evaporative emission testing. MOVES has fields for evaporative
naphthalene, but all values in the model are zero.
Simple fractions for other air toxics in evaporative non-permeation emissions were obtained
from profiles developed for EPA by Environ Corporation, using data from the Auto/Oil program
conducted in the early 1990's.55 The fractions for these compounds are the same for all pollutant
processes (except permeation) and are presented in Table 5-3.
The ratios for 10 percent ethanol are used for all fuels with greater than or equal to 5 percent
ethanol and less than 12 percent.
For vehicles operating on fuels containing 15 percent ethanol (El 5), no data describing
evaporative emissions are available. For the vapor-venting and spillage emission processes,
66
-------
emission rates calculated from E15 and E10 fuel speciation data from the EPAct Program were
used to adjust the E10 evaporative emissions speciation.15 Resulting toxic fractions are provided
in Table 5-3.
For vehicles containing 20 percent ethanol, toxic fractions were developed for fuel speciation
profiles created from data collected in the EPAct program. Average fractions by weight were
calculated as a composite of data from the seven E20 blends included in the fuel matrix.
Resulting fractions are shown in Table 5-3. Note, MOVES versions after MOVES2014a do not
estimate emissions for vehicles using E20 fuel, but these fractions currently remain in the
MOVES database.
For vehicles operating on fuels containing high levels of ethanol, ranging from 70 to 100 percent,
the toxic fractions were developed using results of two-day diurnal tests on four 2007 model year
flex-fuel vehicles from CRC E-80 program.30 Following typical speciation procedures, the
fraction of each compound in a test was first calculated by dividing its emission rates for each
compound by the sum of all rates for that test. The percentages for each compound were then
averaged across all tests to form the composite profile. The resulting fractions are presented in
Table 5-3.
Table 5-1 Data Sources and Estimation Methods Used in Estimation of Toxic Fractions for Evaporative
VOCs
Compound
Process
Fraction
Type
Basis for
Estimation
MOVES Table
Benzene
Vapor
venting/refueling
(vapor)
complex
Adapted from
MOBILE6.2
GeneralFuelRatioExpression for
E0 to E20;
atRatioNonGas for E70-E100
Fuel leaks/spillage
complex
Adapted from
MOBILE6.2
GeneralFuelRatioExpression for
E0 to E20;
atRatioNonGas for E70-E100
2,2,4-
trimethylpentane
All (except
permeation)
simple
Speciation
profile
minorHAPratio
Ethylbenzene
All (except
permeation)
simple
Speciation
profile
minorHAPratio
N-Hexane
All (except
permeation)
simple
Speciation
profile
minorHAPratio
Toluene
All (except
permeation)
simple
Speciation
profile
minorHAPratio
Xylene
All (except
permeation)
simple
Speciation
profile
minorHAPratio
Ethanol
All (except
permeation)
simple
Speciation
profile
GeneralFuelRatioExpression for
E0 to E20;
atRatioNonGas for E70-E100
1 For E70 through E100 fuels, the toxic ratios for benzene and ethanol are simple fractions stored in the
atRatioNonGas table
67
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Table 5-2 Complex Fractions of VOC for Evaporative Emissions of Benzene Applied to Vehicles Running on
Gasoline (EO to E20)
Pollutant
Process
Equation for Toxic Fraction
Benzene
Vapor venting/Refueling (vapor)
(-0.03420*OXY - 0.080274*RVP + 1.4448)*BNZ/100
Fuel Leaks/Spillage
(-0.03420*OXY - 0.080274*RVP + 1.4448)*BNZ/100
Table 5-3 Toxic Fractions for Evaporative VOC Emissions, for Vapor-venting and Refueling-Spillage
Processes
Pollutant
Ethanol Level
0.0%
(EO)
10%
(E10)
15%
(El 5)
20%
(E20)3
70-
100%
(E85)
Ethanol1
0.000
0.119
0.194
0.223
0.610
2,2,4-
T rimethy lpentane
0.020
0.034
0.053
0.043
0.008
Ethyl Benzene
0.025
0.017
0.017
0.016
0.001
N-Hexane
0.022
0.025
0.007
0.019
0.013
Toluene
0.096
0.143
0.141
0.087
0.016
Xylene
0.080
0.064
0.057
0.071
0.007
Benzene
Table 5-2
0.0066
Notes:
1 Ethanol toxic fraction is estimated 0.0119>
-------
suggests that the fraction of benzene from permeation is about 1.77 times higher than the ratio
associated with evaporation.59 Thus the diurnal emissions algorithm was multiplied by 1.77.
/benzene, permeation
(—0.0285 x OXY(wt%) - 0.080274 x RVP + 1.3758) x benzene
= 1.77 x
= 1.77 x
Where:
100
(-0.0285 x (ETOHVolume x 0.3653) - 0.080274 x RVP + 1.3758) x benzene
Equation
21
100
Oxy (wt%) = oxygenate fuel content, weight percentage (%)
RVP = reid vapor pressure (psi)
Benzene = benzene fuel content, volume percentage (%)
ETOHVolume = ethanol fuel content, volume percentage (%)
VolToWtPercent = 0.3653 = Parameter to convert ETOHVolume to Oxy (wt%). See Fuel
Effects22 report for documentation.
In MOVES, the permeation values are stored in the same location as the toxic values for other
evaporative processes. Ethanol and Benzene are stored in the GeneralFuelRatioExpression Table
for E0 through E20 fuels, and the atRatioNonGas Table for E70-E100 fuels. The other toxics
(2,2,4-Trimethylpentane, Ethylbenzene, Hexane, Toluene and Xylene) are stored in the
minorHAPratio table.
Table 5-4 Toxic Fractions Representing Permeation Emissions as Components of Total VOC Emissions, by
Pollutant
Ethanol Level
0.0% (E0)
10% (E10)
15% (El5)
20% (E20)2
70-100% (E85)
Ethanol
0.000
0.202
0.2694
0.3296
0. 61041
2,2,4-Trimethylpentane
0.036
0.024
0.0172
0.0107
0. 00831
Ethylbenzene
0.003
0.001
0.0017
0.0019
0. 00121
Hexane
0.050
0.065
0.0472
0.0308
0. 01281
Toluene
0.110
0.101
0.0666
0.0354
0. 01611
Xylene(s)
0.016
0.011
0.0127
0.0140
0. 00731
Benzene
Equation 21
0. 00661
Note:
1 Identical to fractions for the vapor-venting process, based on CRC E-80 program (Table 5-3).
2 MOVES versions after MOVES2014a do not estimate emissions for vehicles using E20 fuel, but these
fractions currently remain in the MOVES database.
For ethanol levels of 70-100 percent, no permeation data were available. Thus, the toxic fraction
for non-permeation evaporative emissions was also applied to permeation.
69
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5.2 Diesel Vehicles
For diesel-fueled vehicles, evaporative emissions are estimated for the refueling-spillage process
only. In MOVES3, we updated the diesel spillage air toxic fractions to be based on the liquid
diesel fuel (Profile 95120 Liquid Diesel - California composite) stored in the SPECIATE
database.44 This profile is also used to speciate the other VOC emissions from diesel refueling
spillage.21 The fractions are shown in Table 5-5 and are stored in the minorHAPratio table,
except for benzene which is stored in the atRatioNonGas table.
Table 5-5 Toxic Fractions for the Fuel-S
Pollutant
Toxic fraction
2,2,4-Trimethylpentane
0
Ethyl Benzene
0.00103
N-Hexane
0
Toluene
0.00235
Xylene
0.00706
Benzene
0
Naphthalene gas
0.00048
tillage Process for Diesel Fuel
70
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6 Crankcase Emissions
Crankcase emissions are modeled as a ratio of the exhaust emissions. Discussion of the ratios
used to estimate THC, CO, NOx, and PM crankcase emissions can be found in the light-duty60
and heavy-duty61 emission rate reports. MOVES calculates gaseous crankcase toxics as a
fraction of the exhaust toxics described in the sections above. Particulate toxics are handled
differently. MOVES does not model crankcase dioxins, furans, or many metals. The details on
crankcase emissions are discussed in the following sections.
6.1 Volatile Organic Compounds
Table 1-1 lists the VOC toxics modeled in MOVES which are also modeled from crankcase
emission processes. MOVES models the crankcase emissions of these toxics by multiplying the
exhaust emissions of these species by the non-methane hydrocarbon (NMHC) crankcase
emission fraction listed in the light-duty and heavy-duty emissions reports. For example, the
NMHC crankcase/exhaust fraction for light-duty gasoline (1969 and later model year) is 0.013.
Thus, crankcase emissions for 1,3-butadiene are calculated as 1.3 percent of the exhaust
emissions of 1,3-butadiene. Similar calculations are applied to all VOC toxic emissions. The
crankcase emission ratios are stored in the MOVES table CrankcaseEmissionRatio, which
differentiates the factors according to pollutant, process, model year range, source type and fuel
type.
6.2 Poly cyclic Aromatic Hydrocarbons
Crankcase gaseous PAHs are modeled in a similar fashion as the crankcase VOC toxic
emissions. The PAH crankcase emissions are modeled as a fraction of the tailpipe exhaust
gaseous PAH emissions, with factors stored in the CrankcaseEmissionRatio table. The PAH
crankcase emission factors are the same as the NMHC crankcase emission factors (e.g. 0.013 for
1969 and later gasoline vehicles, and 0.39 for 2010 and later heavy-duty diesel vehicles).
Because the OC/PM speciation can be substantially different between crankcase emissions and
exhaust emissions, we use a different approach for these calculations. To estimate crankcase
particulate PAH emissions, MOVES applies the same PAH/OC fractions developed for exhaust
emissions to the crankcase OC emissions. The PAH/OC ratios are stored in the pahParticleRatio
table for the crankcase emission processes (15, 16, and 17). For example, because conventional
diesel crankcase emissions have a higher OC/PM composition than the tailpipe exhaust
emissions, MOVES models elevated particulate PAH emissions in crankcase PM2.5 emissions
compared to tailpipe PAH emissions. Research on conventional diesel vehicles validates that PM
emissions from the crankcase are more enriched with PAHs than emissions from the exhaust.62
6.3 Metal and Dioxin Emissions
MOVES models crankcase metal emissions for the metal species included in the PM2.5 exhaust
speciation profiles, such as iron and aluminum, which are also applied to crankcase emissions.
Details on speciation of crankcase emissions are included in the speciation report.21 MOVES
71
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does not produce crankcase emission rates for metals that are not included in the speciation
profiles such as arsenic, mercury and other metals listed in Table 1-4. Similarly, MOVES does
not estimate dioxin and furan emissions from crankcase emissions, assuming that the emissions
from crankcase are negligible compared to exhaust emissions.
72
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Appendix A. Development of Motor Vehicle Emission Factors for
Chromium
In 2010, the EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL) collected
particulate matter (PM) and volatile organic compound (VOC) exhaust samples, as well as CO,
NOx, CO2, and CH4 samples from a 2008 3.5L V6 Chevrolet Impala flex fuel light-duty gasoline
vehicle. This testing also included direct Cr(VI) measurements.
The Impala had a beginning odometer reading of 38,934 miles and was tested using E10
gasoline. The vehicle test procedure used four sample bags and the LA92 "unified"
dynamometer driving schedule.63 The bags in this study represent the following conditions:
Bag 1 - concentrated cold start compared to FTP (Federal Test Procedure); short distance, low
speeds.
Bag 2 - hot and running; longer distance and higher speeds than FTP (represents realistic real
world driving).
Bag 3 - hot start; short distance, low speeds.
Bag 4 - hot and running; long distance.
PM was collected on four (labeled A-D) pre-cleaned and prepared filter media per bag. The PM
filter samples labeled D were sent to the Wisconsin State Laboratory of Hygiene at the
University of Wisconsin-Madison for chromium metal speciation. Total and hexavalent
chromium was measured in extracts of filter-collected PM sent from NVFEL. Detection limits
were in the <0.2 ng/filter range. A comparison of 47mm filter collection substrates was
performed using Polyvinyl Chloride (PVC) and bicarbonate-impregnated Mixed Cellulose Ester
(MCE) filters. Total chromium was analyzed by SF-ICPMS (Sector Field Inductively Coupled
Plasma Mass Spectrometry) and Cr(VI)was analyzed by Inductively Coupled (IC)-post-column
derivation. The Cr(VI) results obtained using PVC collection substrates were below the detection
limit, with the exception of the tunnel blanks, and thus not listed in this memo. The extractable
total chromium levels in the filters and bicarbonate were at such a level that swamp any signal
from the PM, making the ICPMS data useless. However, the Cr(VI) data from the MCE filters
analyzed by IC could be used to develop new emission rates as described below.
Spike and blank studies were performed. Spike studies had a recovery between 93-104 percent,
indicating the matrix did not interfere with the chromium results. The Cr(VI) MCE filter results
were blank corrected by subtracting the mean background value of 0.298 ng/filter (standard
deviation±0.098 ng/filter; 95 percent confidence interval±0.157). The 95 percent confidence
interval was calculated from student's ^-distribution as a function of the probability and degrees
of freedom and multiplied by the standard deviation over the square root of the number of
blanks.
Cr(VI) speciation results and emission rates are reported in Table A-l along with the
corresponding distance driven per sample. The emission rates were calculated by dividing the
blank-corrected Cr(VI) MCE mass/filter by the distance driven per sample and multiplying by a
factor representing the CVS (constant volume sampler) volume over the individual filter sample
73
-------
volume (NVFEL filter sample D was used for each bag). This factor was used because all
exhaust was not passed through the collection filter during the test.
blankcorrected Cr(VI)MCE mass/filter CVS volume
Emission Rate = x
distance Sample volume
The overall emission rate in Table A-l is a composite average of the total Cr(VI) measured
divided by the total distance of the test and then multiplied by the sum of CVS volumes/sum of
filter sample volumes.
Table A-l Cr(VI) Emission Rates from an Onroad Gasoline Engine
Sample/bag Cr(VI)
Mean IC
Blank± Std
Deviation
Blank-
corrected
Cr(VI)
CVS
Volume
(scf at
Sample
Volume
(scf at
Distance
Emission
Rate
number
(ng/filter)
(ng/filter)
(ng/filter)
68°F)
68°F)
(miles)
(g/mile)
1
0.792
0.298±0.098
0.49
1666.87
7.675
1.194
8.9xlO"8
2
0.493
0.298±0.098
0.20
6280.73
28.815
8.612
5.1xl0"9
3
0.488
0.298±0.098
0.19
1682.74
7.711
1.186
3.5xl0"8
4
0.508
0.298±0.098
0.21
6281.82
28.894
8.620
5.3xl0-9
Overall
1.1
15912.2
73.10
19.61
1.2xl08
Direct Cr(VI) emission factors were not measured from a diesel engine. To develop on-road
diesel emission factors, the total chromium from diesel engines was multiplied by the ratio of
Cr(VI) to total chromium from onroad gasoline emissions (0.29%). The Cr(VI) onroad emission
rates are shown in Table A-l. The total chromium emission factor for gasoline comes from the
Kansas City Particulate Matter Characterization Study (4.07xl0"6 g/mi).32 The KCVES program
sampled 99 vehicles for chemical composition from which a total chromium emission factor of
4.07xl0"6 grams/mile was developed.35 This average grams/mile rate was calculated by
averaging the metal measured in Bag 2 of the LA92 driving schedule test with a weighted-
average computed using vehicle miles traveled (VMT).
Diesel Cr(VI) emission factors are calculated for diesel engines based on total chromium from
test programs conducted on diesel engines before39 and after implementation of EPA's 200742'
and 201043 heavy-duty highway rule which reduced PM emissions from heavy-duty diesel
vehicles, as outlined in the following equations
Cr(VI) Pre-2007 On-road Diesel Emission Factor
Gasoline Cv(\o 1.2x10 ^ ^• n
EF = Total Cr EFPre2007 diesel x —— = 6.8xl0"6 — x = 6.8xl0"6 — x 0.29%
Total CrEF ne mi 407 10_6l mi
mi
= 2.0xl0~8 9
mi
74
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Cr(VI) 2007 to 2009 On-roadDiesel Emission Factor
Gasoline Cr(VI)EF , g a g
EF = Total CrEF2007-2009dieselx v = 2.01xl(r6— x 0.29% = 5.9xl(T9
1 OtCLL LT fcrgasoline Tttl
Cr(VI) 2010 and Later On-road Diesel Emission Factor
Gasoline Cr(VI)EF _ g a g
EF = Total Cr EF2010+diesel X V = 7.3xl0"7 X 0.29% = 2.2xl0~9
Total Cv EFgasonne mi till
A Cr(VI) emission factor for vehicles using compressed natural gas is calculated by multiplying
the overall Cr(VI) emission factor from Table A-l by the ratio of total chromium from CNG
transit buses64 verses gasoline light-duty vehicle engines (from KCVES study).
Cr(VI) Compressed Natural Gas (CNG) Emission Factor
Gasoline Cr(VI)EF „ g g
EF = Total Cr EFCNG x —— = 7.0xl0"8 — x 0.29% = 2. lxlO"10
Total CrEFgasoline mi mi
A summary of the results for Cr(VI) emission factors is presented in Table A-2. While these
results are based on measured Cr(VI), the results are limited by the following:
• Emissions from only one vehicle were measured, so the data do not provide information
regarding variability among vehicles.
• No Cr(VI) measurements have been made for diesel and CNG vehicles or engines.
Table A-2 Summary: Cr(VI) Emission Factors
Onroad gasoline (MY2008)
Onroad diesel (pre-2007)
Onroad diesel (2007-2009 and
later)
Onroad diesel (2010 and later)
CNG heavy-duty vehicles
Emission Factor Units
1.2x10
grams/mile
2.0xl0"8
grams/mile
5.9xl0"9
grams/mile
2.2xl0"9
grams/mile
2.1xlO"10
grams/mile
75
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Appendix B. Development of Motor Vehicle Emission Factors for
Mercury
Calculation of Mercury Emission Factors from Vehicle Tests
In 2005, the USEPA National Exposure Research Laboratory (NERL) collected mercury (Hg)
samples in the raw exhaust from 14 light-duty gasoline vehicles and two heavy-duty diesel
vehicles. The work plan for this project includes details of the methods used that are not
reproduced here including quality assurance and quality control for Hg collection and analysis.
This information can be obtained from EPA upon request. Briefly, mercury and regulated
pollutant data were collected during two sets of three consecutive LA92 drive cycles for each
vehicle. The morning set of LA92 cycles began with one 'cold start' and the afternoon set of
three LA92 cycles began with a 'hot start'. The intake air was filtered through charcoal to greatly
reduce background mercury concentrations entering the vehicle intake. Separate sample lines
were used for gaseous and particulate mercury species. Samples analyzed for mercury were
drawn from raw exhaust at a constant flow rate and fixed dilution. Carbon dioxide measurements
were also taken in the exhaust stream where mercury samples were collected.
Mercury samples were collected in the raw exhaust since previous data suggested that mercury
levels might be sufficiently low to challenge mercury detection limits. This sampling method
imposed a challenge in calculating emission factors since it assumes that the exhaust flow rate
from the vehicle is constant. Calculation of exhaust flow and its application to the development
of mercury emission rates is described below.
Evaporative losses of mercury from motor vehicles and loss of mercury during refueling were
not measured. The emission of mercury through evaporative processes is expected to be
negligible compared with that expected from exhaust emissions.
A description of the vehicles tested for which data were used in developing emission rates is
provided in Table B-l. The data collected from these vehicles in diluted exhaust in the constant
volume sampler (CVS) included THC, carbon dioxide (CO2), nitrogen oxides (NOx), methane
(CH4), and carbon monoxide (CO). In raw, undiluted exhaust, data collected included elemental
and total gas-phase mercury, particulate mercury and CO2. Gas-phase mercury was also
measured in the intake air. Total air flow was measured for all sampling systems and corrected to
standard temperature and pressure conditions. The data streams had different reporting
frequencies, all due to the nature of the instrumentation. The dilute measurement of the standard
emission gases (THC, CO2, NOx, CH4, and CO), CVS flows, and vehicle speed were reported at
1 Hertz. The gas-phase mercury samples were analyzed at 2.5-minute intervals and particle-
phase mercury samples were collected cumulatively for the duration of three consecutive LA92
cycles. Gas-phase elemental mercury in the engine intake air was measured at five-minute
intervals.
76
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Table B-l Vehicles Tested for Mercury Emissions
Model Year
Make
Model
Fuel Type
Odometer
(mi)
Cylinders
Displacement
(L)
2005
MERCURY
GRAND MARQUIS LS
Gasoline
9,953
8
4.6
2005
FORD
MUSTANG
CONVERTIBLE
Gasoline
5,424
6
4.0
2003
SATURN
L 200
Gasoline
29,667
4
2.2
2002
HONDA
ACCORD EX
Gasoline
51,824
4
2.3
2001
HONDA
ACCORD EX
Gasoline
88,611
4
2.3
2001
CHRYSLER
PT CRUISER
Gasoline
54,010
4
2.4
2000
CHEVROLET
SUBURBAN
Gasoline
39,787
8
6.0
2000
JEEP
CHEROKEE SPORT
Gasoline
48,468
6
4.0
1999
FORD
F250 XLT
Diesel
113,897
8
7.3
1999
FORD
F250 XLT SD
Diesel
109,429
8
7.3
1998
HONDA
CIVIC DX
Gasoline
204,983
4
1.6
1994
CHEVROLET
SILVERADO
Gasoline
129,521
8
5.7
1992
CHEVROLET
S10 BLAZER
Gasoline
162,249
6
4.3
1991
HONDA
ACCORD EX
Gasoline
143,289
4
2.2
1987
CHRYSLER
FIFTH AVENUE
Gasoline
72,573
8
5.2
1984
FORD
F150 PICKUP
Gasoline
36,727
8
5.8
Exhaust flow was integrated at the same reporting frequency as the mercury exhaust values for a
particular test and then used to calculate total, elemental, and reactive gas-phase mercury mass
emissions. The intake air mercury values were typically collected at half the frequency of the
mercury exhaust values and used to correct exhaust measured values that are reported at higher
frequencies. The particulate matter measurements were filter-based, test-level measurements and
were corrected in that manner.
Calculation of Emission Rates
Emission rates were calculated separately for elemental gas-phase mercury, reactive gas-phase
mercury and particulate mercury. Elemental gas-phase mercury in the exhaust was corrected for
the intake air concentration of elemental mercury. To estimate the gas-phase mercury
concentration in dilute exhaust from the measured mercury in raw exhaust, the dilution factor
was applied. For light-duty gasoline vehicles, the dilution factor equation found in 40 CFR
90.426 (d) was used:
Dilution factor = 13.4 / ([C02%] + ([THC, ppm] + [CO, ppm])* 0.0001)
Exhaust flow = (CVS flow / dilution factor)
Exhaust flow calculation was initiated when the analytical equipment indicated that the dilute
exhaust CO2 concentration was greater than the background CO2 concentration.
To calculate exhaust flow for the diesel vehicles, the dilution factor was calculated by simply
dividing CO2 in the raw exhaust by CO2 in the CVS. This method was used because diesel
engines operate across a very wide range of fuel to air mixtures and the CFR method described
above was not appropriate.
77
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Determination of Reactive Gas Mercury Mass in Exhaust
Reactive gas-phase mercury (RGM) was calculated by subtracting elemental gas-phase mercury
measurements from total gas-phase mercury measurements. RGM values were typically small
and therefore influenced by the variability in the elemental mercury measurements. Negative
RGM values for a given measurement period were observed. Values for which there was not a
positive RGM measurement were treated as non-detects and were nulled in the aggregation of
RGM values for the test. The measurement uncertainty for gas-phase elemental mercury was
estimated from quantitative recovery of injections of known amounts of mercury into the
sampling system. The uncertainty in measuring elemental mercury was applied to the total gas-
phase and elemental gas-phase measurements to determine when the RGM value was above the
measurement uncertainty. Values within the measurement uncertainty were not included in the
emission factor calculation.
Calculating Weighted Emission Test Results
Highway vehicles were tested on the LA92 cycle; a more aggressive chassis-dynamometer test
similar in concept to the Federal Test Procedure's (FTP) UDDS or LA4. Like the FTP, the LA92
includes a cold start, a hot start, and a hot stabilized phase using identical drive schedules for the
starts. We considered it appropriate to calculate a weighted emission factor (representing cold
start and hot start driving) for each vehicle in the same manner as the FTP, using the equation
below for each test (a test consisting of all six LA92 cycles performed on each vehicle).
We summed the gas-phase mercury mass emissions for the first phase (300 seconds) of the
morning test and last phase (1,135 seconds) of the individual LA92 drive schedules for all the
tests (e.g., 'hot stabilized emissions'), divided by the total distance covered in these phases and
multiplied by 0.43. We also summed the sum of the mass gas-phase mercury emissions of the
first phase of the afternoon test and last phase (1,135 seconds) of all the tests, divided by the total
distance covered in these phases and multiplied by 0.57. The two terms were summed to
calculate a test level emission rate for each of the gasoline powered vehicles.
The equation used to calculate test-level emission rates is as follows:
Where:
Eug = mean aggregate emission rate (g/mi),
C = mercury mass collected in the first 300 seconds of the first morning test ('cold start', g),
Cm = distance covered in the cold start phase (mi),
R = mercury mass collected in the last 1,135 seconds of all six cycles of the LA92 ('hot
stabilized', g),
Rm = cumulative distance covered in all six cycles of the LA92 ('hot stabilized', mi),
H = mercury mass collected in the first 300 seconds of the first afternoon test ('hot start', g),
Hm = distance covered by the hot start (mi).
78
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It should be noted that the 'hot start' in the afternoon typically occurred after the vehicle had
been off for at least 1 hour, making this start closer to a 'cold start' than 'hot start'. Since the true
cold start emissions were slightly higher than hot start emissions, it is expected that this approach
would bias the emission factors high by a small amount, relative to the value expected for a cycle
composite.
Particulate mercury emissions could not be apportioned into modes of operation in similar
manner because filters were collected across all three LA92 cycles and could not be parsed into
the three phases. A test-level composite emission rate was calculated by multiplying the morning
particulate mercury emission rate by 0.43 and the afternoon particulate mercury emission rate by
0.57 and adding the two values together.
The average of emission factors across vehicles was calculated for each form of mercury and is
reported in Table B-2. A simple average was used since the data did not suggest that mercury
concentrations varied by vehicle age, mileage, displacement or other factors.
Mercury emission factors for on-road diesel engines were obtained from the first 715 seconds of
the morning and afternoon tests on the Ford F250 XLT SD; data from the second diesel vehicle
could not be used. The first 715 seconds is approximately half of the first of the three LA92
drive cycles that made up a single test. The truncation of the test was due to sample flow
problems in the mercury sampling manifold due to particulate matter restricting flow across the
particulate matter filters. Graphical analysis of exhaust flow indicated that they appeared
nominal during the first LA92 cycle. We decided that only using measurements collected before
715 seconds in both tests provided the most reliable data.
Nonroad grams per gallon emission factors in Table B-2 were calculated from the onroad factors
using a fuel economy estimate of 17 miles per gallon for the gasoline vehicle and 19 for the
diesel vehicle.
79
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Table B-2 Mercury Emission Factors from Mobile Sources
Source Category
Pollutant
Pollutant
ID
Emission
Rate
Units
Gasoline motor
vehicles
Elemental gas-
phase
200
1.1E-07
grams/mile
Reactive gas-phase
201
9.9E-09
grams/mile
Particulate phase
202
4.0E-10
grams/mile
Diesel motor vehicles
Elemental gas-
phase
200
6.2E-09
grams/mile
Reactive gas-phase
201
3.2E-09
grams/mile
Particulate phase
202
1.6E-09
grams/mile
Gasoline nonroad
engines
Elemental gas-
phase
200
1.8E-06
grams/gallon
Reactive gas-phase
201
1.7E-07
grams/gallon
Particulate phase
202
6.9E-09
grams/gallon
Diesel nonroad engines
Elemental gas-
phase
200
1.2E-07
grams/gallon
Reactive gas-phase
201
6.2E-08
grams/gallon
Particulate mercury
202
3.2E-08
grams/gallon
80
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obtained from page 338, Table 6)
85
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