User's Guide for Estimating
Methane and Nitrous Oxide
Emissions From Mobile
Combustion Using the State
Inventory Tool
January 2017
Prepared by:
ICF
Prepared for:
State Climate and Energy Program,
U.S. Environmental Protection Agency
This section of the User's Guide provides instruction on using the Mobile Combustion module
of the State Inventory Tool (SIT), and describes the methodology used for estimating
greenhouse gas (GHG) emissions from highway and non-highway vehicles at the state level.
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Module 3 -Mobile Combustion Module
January 2017
Table of Contents
1.1 Getting Started 2
1.2 Module Overview 4
1.2.1 Data Requirements 5
1.2.2 Tool Layout 6
1.3 Methodology 7
1.4 Uncertainty 18
1.5 Explanation of Mobile Combustion Module Updates 19
1.6 References 20
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
1.1
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Module 3 -Mobile Combustion Module
January 2017
1.1 Getting Started
The Mobile Combustion module was developed using Microsoft® Excel 2000. While the
module will operate with older versions of Excel, it functions best with Excel 2000 or later.
If you are using Excel 2007, instructions for opening the module will vary as outlined in the
Excel basics below. Some of the Excel basics are outlined in the sections below. Before you
use the Mobile Combustion module, make sure your computer meets the system
requirements. In order to install and run the Mobile Combustion module, you must have:
• IBM-PC compatible computer with the Windows 95 operating system or later;
• Microsoft® Excel 1997 or later, with calculation set to automatic and macros
enabled;
• Hard drive with at least 20MB free; and
• Monitor display setting of 800 x 600 or greater.
Microsoft Excel Settings
Excel 2003 and Earlier: For the SIT modules to function properly, Excel must be set to
automatic calculation. To check this setting, launch Microsoft Excel before opening the
Mobile Combustion module. Go to the Tools menu and select "Options..." Click on the
"Calculations" tab and make sure that the radio button next to "Automatic" is selected, and
then click on "OK" to close the window. The security settings (discussed next) can also be
adjusted at this time.
Excel 2007: For the SIT modules to function properly, Excel must be set to automatic
calculation. Go to the Formulas ribbon and select "Calculation Options." Make sure that the
box next to the "Automatic" option is checked from the pop-up menu.
Microsoft Excel Security
Excel 2003 and Earlier: Since the SIT employs macros, you must have Excel security set
to medium (recommended) or low (not recommended). To change this setting, launch
Microsoft Excel before opening the Mobile Combustion module. Once in Excel, go to the
Tools menu, click on the Macro sub-menu, and then select "Security" (see Figure 1). The
Security pop-up box will appear. Click on the "Security Level" tab and select medium.
When set to high, macros are automatically disabled; when set to medium, Excel will give
you the choice to enable macros; when set to low, macros are always enabled.
When Excel security is set to medium, users are asked upon opening the module whether to
enable macros. Macros must be enabled in order for the Mobile Combustion module to
work. Once they are enabled, the module will open to the control worksheet. A message
box will appear welcoming the user to the module. Clicking on the "x" in the upper-right-
hand corner of the message box will close it.
Excel 2007: If Excel's security settings are set at the default level a Security Warning
appears above the formula box in Excel when the Mobile Combustion module is initially
opened. The Security Warning lets the user know that some active content from the
spreadsheet has been disabled, meaning that Excel has prevented the macros in the
spreadsheet from functioning. Since SIT needs macros in order to function properly, the
user must click the "Options" button in the security message and then select, "Enable this
content" in the pop-up box. Enabling the macro content for the SIT in this way only enables
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module 1.2
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Module 3 -Mobile Combustion Module
January 2017
macros temporarily in Excel but does not change the macro security settings. Once macros
are enabled, a message box will appear welcoming the user to module. Click on the "x" in
the upper right-hand corner to close the message box.
If the Security Warning does not appear when the module is first opened, it may be
necessary to change the security settings for macros. To change the setting, first exit out
of the Mobile Combustion module and re-launch Microsoft Excel before opening the Mobile
Combustion module. Next, click on the Microsoft Excel icon in the top left of the screen.
Scroll to the bottom of the menu and select the "Excel Options" button to the right of the
main menu. When the Excel Options box appears, select "Trust Center" in left hand menu of
the box. Next, click the gray "Trust Center Settings" button. When the Trust Center
options box appears, click "Macro Settings" in the left hand menu and select "Disable all
macros with notification." Once the security level has been adjusted, open the Stationary
Combustion module and enable macros in the manner described in the preceding
paragraph.
Viewing and Printing Data and Results
The Mobile Combustion module contains some features to allow users to adjust the screen
view and the appearance of the worksheets when they are printed. Once a module has
been opened, you can adjust the zoom by going to the Module Options Menu, and either
typing in a zoom percentage or selecting one from the drop down menu. In addition, data
may not all appear on a single screen within each worksheet; if not, you may need to scroll
up or down to view additional information.
You may also adjust the print margins of the worksheets to ensure that desired portions of
the Mobile Combustion module are printed. To do so, go to the File menu, and then select
"Print Preview." Click on "Page Break Preview" and drag the blue lines to the desired
positions (see Figure 2). To print this view, go to the File menu, and click "Print." To return
to the normal view, go to the File menu, click "Print Preview," and then click "Normal View."
Figure 1. Changing Security Settings
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State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
1.3
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1.2 Module Overview
This User's Guide accompanies and explains the Mobile Combustion module of the SIT. The
SIT was developed in conjunction with EPA's Emissions Inventory Improvement Program
(EIIP). Prior to the development of the SIT, EPA developed the States Workbook for
estimating greenhouse gas emissions. In 1998, EPA revisited the States Workbook and
expanded it to follow the format of EIIP guidance documents for criteria air pollutants. The
result was a comprehensive, stepwise approach to estimating greenhouse gas emissions at
the state level. This detailed methodology was appreciated by states with the capacity to
devote considerable time and resources to the development of emission inventories. For
other states, the EIIP guidance was overwhelming and impractical for them to follow from
scratch. EPA recognized the resource constraints facing the states and developed the SIT.
The ten modules of the SIT corresponded to the EIIP chapters and attempted to automate
the steps states would need to take in developing their own emission estimates in a manner
that was consistent with prevailing national and state guidelines.
Since most state inventories developed today rely heavily on the tools, User's Guides have
been developed for each of the SIT modules. These User's Guides contain the most up-to-
date methodologies that are, for the most part, consistent with the Inventory of U.S.
Greenhouse Gas Emissions and Sinks. Volume VIII of the EIIP guidance is a historical
document that was last updated in August 2004, and while these documents can be a
valuable reference, they contain outdated emissions factors and in some cases outdated
methodologies. States can refer to Volume VIII of the EIIP guidance documents if they are
interested in obtaining additional information not found in the SIT or the companion User's
Guide.
The Mobile Combustion module calculates
methane (Cl-U) and nitrous oxide (N2O)
emissions from highway vehicles, aviation,
boats and vessels, locomotives, other non-
highway sources, and alternative fuel
vehicles. This module also includes optional
calculations of carbon dioxide (CO2) from these sources, which are also calculated in the CO2
from Fossil Fuel Combustion (CO2FFC) module. The Mobile Combustion module-based CO2
calculations provide detail by transportation mode not available in the CO2FFC module.
For highway vehicles, it calculates emissions based on vehicle miles traveled (VMT) for eight
types of control technologies: three-way catalyst, early three-way catalyst, oxidation
catalyst, non-catalyst, low-emission vehicle, advanced, moderate, and uncontrolled; and for
seven classes of vehicles, using the Federal Highway Administration (FHWA) vehicle
classifications. For other transportation types, emissions are based on fuel consumption in
gallons or British thermal units (BTU). While the module provides default data for most
inputs, if you have access to more comprehensive data sources, they should be used in
place of the default data (see Box 1 for suggestions of possible data sources). If using
outside data sources, or for a more thorough understanding of the tool, please refer to the
following discussion of data requirements and methodology.
Although there is virtually no ChU in either gasoline or diesel fuel, ChU is emitted as a
combustion product that is influenced by fuel composition, combustion conditions, and
control technologies. Depending on the control technologies used, ChU emissions may also
result from hydrocarbons passing unburned or partially burned through the engine, and
then be affected by any post-combustion control of hydrocarbon emissions, such as catalytic
Box 1: State Mobile Combustion
Data Sources
In-state sources, such as state highway agencies,
should be consulted first. Otherwise, default data
provided by the Mobile Combustion module may
be used.
State Greenhouse Gas Inventory Tool User's Guide
1.4
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Module 3 -Mobile Combustion Module
January 2017
converters. For highway vehicles, the emissions of unburned hydrocarbons, including ChU,
are generally lowest in uncontrolled engines when the air/fuel ratio is high or "lean," which
means that there is excess oxygen available relative to the quantity of hydrogen and carbon
present. However, such conditions favor the formation of nitrogen oxides, which are a
major air pollutant and key component in the formation of smog. In modern three-way
closed loop catalyst highway vehicles, the lowest emissions are achieved when hydrogen,
carbon, and oxygen are present in the ideal combination for complete combustion.
Conditions favoring high ChU emissions include aggressive driving, low speed operation, and
cold start operation. Poorly tuned highway vehicle engines may have a particularly high
output of ChU.
Emissions are also strongly influenced by the engine type and the fuel combusted. N2O
formation in internal combustion engines is not yet well understood, and data on these
emissions are scarce. It is believed that N2O emissions come from two distinct processes.
In the first process, during combustion in the cylinder, N2O is formed as nitrogen oxide
interacts with combustion intermediates such as NH and NCO. The N2O is then removed
very rapidly in the post-flame gas by the reaction between N2O and hydrogen. While a
significant amount of N2O may be formed in the flame, it can only survive if there is very
rapid quenching of the flame, which is not common. Thus, only small amounts of N2O are
produced as engine-out emissions.
The second INhO-forming process occurs during catalytic after-treatment of exhaust gases.
The output of N2O from the catalyst is highly temperature dependent. Prigent and De Soete
(1989) showed that as the catalyst warms up after a cold start, N2O levels increase greatly
(to 4.5 times the inlet value) at around 360°C. The emissions then decrease to the inlet
level as the catalyst reaches a temperature of 460°C. Above this temperature there is less
N2O exiting the catalyst than entering it. These results demonstrate that N2O is formed
primarily during cold starts of catalyst-equipped vehicles. This explains why N2O emissions
data for the Federal Test Procedure (which includes a cold-start phase) are much higher
than data for the U.S. Highway Fuel Economy Test (which does not include a cold start
phase).
Emissions of CH4 and N2O from non-highway mobile sources have received relatively little
study. Non-highway sources include jet aircraft, gasoline-fueled piston aircraft, agricultural
and construction equipment, railway locomotives, boats, and ships. Except for aircraft
(fueled by jet fuel or gasoline), all of these sources are typically equipped with diesel
engines.
In 2013, additional updates were made to the mobile combustion module to improve
disaggregation of CO2 estimates, and compliment the CO2 from Fossil Fuel Combustion
module. An explanation of these updates can be found in Section 1.5, "Explanation of Mobile
Combustion Module Updates."
1.2.1 Data Requirements
To calculate GHG emissions from mobile combustion, the data listed in Table 1 are required
inputs (again, note that defaults are available for most of these data).
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
1.5
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Module 3 -Mobile Combustion Module
January 2017
Table 1. Required Data Inputs for the Mobile Combustion Module
Module Worksheet
Input Data Required
4a Highway Vehicles -
Emission Factors and
VMT
CH4 and N2O emission factors (g/km traveled) for each type of control
technology
State total VMT, 1990-present, for all vehicle types
4b Highway Vehicles -
Allocating VMT by Model
Year
Annual vehicle mileage accumulation (miles) for each model year in use
Age distribution of vehicles (%) in the current year
4c Highway Vehicles -
Allocating Control
Technology by Model
Year
Percentage of vehicles with each control type, 1960-present
5 Aviation Factors and
Fuel Consumption
Energy contents (kg/million BTU) for kerosene jet fuel, naphtha jet fuel,
and aviation gasoline
N2O and CH4 emission factors (g/kg fuel) for each type of fuel
Aviation fuel consumption (million BTU), 1990-present
6 Marine Factors and
Fuel Consumption
Density factors (kg/gal) for residual fuel, distillate fuel, and motor
gasoline
N2O and CH4 emission factors (g/kg fuel) for each type of fuel
Marine fuel consumption (gallons), 1990-present
7 Locomotive Factors
and Fuel Consumption
Density factors (kg/gal or ton) for residual fuel, diesel fuel, and coal
N2O and CH4 emission factors (g/kg fuel) for each type of fuel
Locomotive fuel consumption (gal or tons), 1990-present
8 Other Non-Highway
Factors and Fuel
Consumption
Density factors (kg/gal) for diesel and gasoline
N2O and CH4 emission factors (g/kg fuel) for diesel and gasoline tractors,
construction equipment, snowmobiles, and other equipment
Fuel consumption (gal), 1990-present, for the above types of equipment
9 Alternative Fuel
Vehicles Factors and
VMT
CH4 and N2O emission factors (g/km traveled) for each type of alternative
fuel (methanol, ethanol, LPG, LNG, CNG)
State total VMT, 1990-present, for alternative fuel vehicles
1.2.2 Tool Layout
Since there are multiple sections to complete within the Mobile Combustion module, it is
important to have an understanding of the module's overall design. The layout of the
module and the purpose of its worksheets are presented in Figure 3.
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
1.6
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Module 3 -Mobile Combustion Module
January 2017
Figure 3. Flow of Information in the Mobile Combustion Module*
Control Worksheet
Mode-Specific Worksheets
1. Select Modes of Transport
4a. Highway Vehicles - Emission Factors and VMT Worksheet
/ | Enter emission factors and VMT for highway vehicles
2. Choose a State
/ 4b. Highway Vehicles - Allocating VMT by Model Year Worksheet
/ | Enter annual mileage accumulation and age distribution by rrodel year
3. Select Optional C02 Calculations /
4c. Highway Vehicles - Allocating Control Technology by Model Year Worksheet
I Enter percent of vehicles w ith each type of pollution control by year
4. -11. Proceed to Calculation Worksheets
5. Aviation Worksheet
I Enter energy contents, emission factors, and aviation fuel consumption
6. Marine Worksheet
I Enter density factors, emission factors, and marine fuel consumption
7. Locomotive Worksheet
I Enter density factors, emission factors, and locorrotive fuel consumption
12. View Summary Data
8. Other Non-Highway Worksheet
I Enter density factors, emission factors, and other non-highw ay fuel consumption
13. Export Data
9. Alternative Fuel Vehicles Worksheet
I Enter emission factors and VMT for alternative-fuel highway vehicles
10. Highway C02 Worksheet
I Review highway 0O2 calculations
11. Non-Highway C02 Worksheet
S. 1 Review non-highway 0O2calculations
* Summary Data
| Resented in both table and graphical formats in MMT0O2E
Uncertainty
Review information on uncertainty associated w ith the default data
* These worksheets are the primary worksheets used in the Mobile Combustion module; subsequent worksheets
are used to populate the default data and are provided for informational purposes only.
1.3 Methodology
This section provides a guide to using the Mobile Combustion module of the SIT to estimate
GHG emissions from the following types of vehicles (or transportation modes): highway
vehicles, airplanes, boats, trains, non-highway equipment (e.g. tractors and snowmobiles),
and alternative-fuel highway vehicles. The module estimates ChU, N2O, and CO2 emissions
from mobile sources using activity data, information on the combustion technologies used,
and information on the type of emission control technologies employed during and after
combustion. Operating conditions during combustion also have an impact on emissions,
and are reflected in the emission factor. The basic approach for estimating emissions is
presented in Equation 1, but variations on this equation will be discussed in subsequent
sections, following this general methodology discussion.
Equation 1. General Mobile Combustion Equation
Emissions = Z(EFabc x Activityabc)
Where,
EF = emissions factor (e.g., grams/kilometer traveled);
Activity = activity level measured in the units appropriate to the emission
factor (e.g., miles);
a = fuel type (e.g., diesel or gasoline);
b = vehicle type (e.g., passenger car, light duty truck, etc.); and
c = emission control type (if any)
The Mobile Combustion module automatically calculates emissions once you have entered
the required data on the control and transportation mode worksheets. The tool provides
default data for all parameters.
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
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Module 3 -Mobile Combustion Module
January 2017
There are six general steps involved in estimating emissions using the Mobile Combustion
module: (1) select relevant modes of transport; (2) select a state; (3) select an option to
conduct optional CO2 calculations; (4) complete highway vehicle worksheets; (5) complete
aviation worksheet; (6) complete marine worksheet; (7) complete locomotives worksheet;
(8) complete other non-highway worksheet; (9) complete alternative fuel vehicles
worksheet; (10) review highway CO2 emissions worksheet; (11) review off-road CO2
emissions worksheet; (12) review summary information; and (13) export data.
Step (1) Select Modes of Transport
In order for the emissions calculations to be successful, the user must choose the desired
transportation modes. Once these selections are made, information on other modes will
automatically drop out of the navigation scheme, saving time and streamlining the analysis.
Step (2) Choose a State
Next, select the state you are interested in evaluating. By selecting a state, the rest of the
tool will automatically reset to reflect the appropriate state default data and assumptions for
use in subsequent steps of the tool. Figure 4 shows the control worksheet with these two
steps completed.
Figure 4. Control Worksheet for the Mobile Combustion Module
E State Inventory Tool - CH4 and N20 Emissions from Mobile Combustion Module
:aj File Edit Module Options
State Inventory Tool - CH4 and N2O Emissions from Mobile Combustion Module
1. Select those modes of transport you wish to analyze.
Reset
W Boats & Vessels j
W Locomotives
W Other Non-Hiahwav Sources
|7 Alternative Fuel Vehicles
2. Choose a State | Colorado
This is very important - it selects the correct default variables for your,
3. Would you like to conduct optional C02 calculations?
The CO 3FFC module is responsible for the main CO 3 calculations from the mobile sector, but this module provic
Choose a state
C Yes C No
4.-11. Proceed with transportation mode-specific analysis...
You will be led through the following series of worksheets using navigational arrows located at the top of each worksheet:
4. Highway Vehicle Worksheets
4a. Highway Vehicles - Emission Factors and VMT Worksheet
4b. Highway Vehicles - Allocating VMT by Model Year Worksheet
4c. Highway Vehicles - Allocating Control Technology by Model Year Worksheet
8. Other Non-Highway Worksheet
10. Highway C02 Worksheet
11. Off-Road C02 Worksheet
Step (3) Decide on an option to conduct CO2 calculations
This module will estimate ChU and N2O emissions, and CO2 emission calculations are
optional. The CO2FFC module is responsible for the main CO2 calculations from the mobile
sector, but this module provides a mode-specific analysis through a different emission
estimation approach; the CO2FFC module calculations emissions using fuel consumption
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module 1.8
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Module 3 -Mobile Combustion Module
January 2017
data and this module calculates emissions using mode-specific activity data already used in
this module.
Selecting "Yes" will allow you to walk through the CO2 calculations worksheets later in the
module. Selecting "No" will allow you to skip steps 10 and 11.
Step (4) Complete the Sector Worksheets for Highway Vehicles
The gray arrow in on the control worksheet takes you to the first of the mode-specific
worksheets.
The calculation of ChU and N2O emissions from highway vehicles follows a complicated
methodology. The module breaks highway vehicles into the following categories: heavy-
duty diesel vehicles (HDDV), heavy-duty gasoline vehicles (HDGV), light-duty diesel trucks
(LDDT), light-duty diesel vehicles (LDDV), light-duty gasoline trucks (LDGT), light-duty
gasoline vehicles (LDGV), and motorcycles (MC). Emissions depend heavily on the type of
emissions control technology used in the vehicle; the type of control technology used
generally correlates with year of vehicle manufacture.
Due to the number of factors involved, the steps for estimating ChU and N2O emissions from
highway vehicles are spread out over three worksheets. The steps necessary to complete
these worksheets are as follows: (1) enter emission factors for each control technology and
vehicle class; (2) enter the vehicle miles traveled for each vehicle type, by year; (3)
distribute vehicle miles traveled by vehicle age and enter age distribution for vehicles on the
road, by year; and (4) enter percentage of vehicles with each control technology, by vehicle
type. To complete these worksheets, follow the steps as explained below. Keep in mind
that the tool provides default data for these parameters.
Step (4a) Highway Vehicles - Emission Factors and VMT Worksheet
1. Enter emission factors for each control technology and vehicle class, for both ChU
and N2O on the Highway 4a worksheet.
a. Default emission factors for each gas, control technology, and vehicle class
are used to populate the tables and are from U.S. EPA (2016), as shown in
Figure 5.
b. To use your state-specific emission factors, either click the "Clear Data"
button and enter your emission factors in the yellow cells, or overwrite the
default emission factors in the yellow cells. To restore all default emission
factors, click the "Restore Default Data" button.
2. Enter the vehicle miles traveled for each vehicle type, by year, from 1990 to the
present year. These default data are from FHWA (2016).
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
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Module 3 -Mobile Combustion Module January 2017
Figure 5. Example of the Highway 4a Worksheet
~ State Inventory Tool CH4 and N20 Emissions from Mobile Combustion Module
Ejle Edit Module Options
4a. Highway Vehicles - Emission Factors and VMT
Click here for
pc-ssibie
Continue
CK.and emissions from highway vehides are calculated using four steps: 1) calculate the vehicte miles
tra v etei for each v ehitie type; 2} con vert the vehicle mfles tra veled data for use with existing emission Actors; 3)
distribute vehicle miles traveled by vehicle age, arid 4} determine emissions control systems for each vehicle type.
This 'worksheet provdes input ce#s for vetocie miles traveled (VMT) by vehicle type, and emission factors that are
! to calculate CR. and N:G emissions from highway vehicles. For further information, refer to the MobSe
Combu-stbr. chapter of the User's Guide
Enter emission factors
I. Verifg Ihe Emission Factors (hat are used to calculate CH« and NtO emis'.N 'is from Highvag Vehicles. 1 Click tor Code Help |
MjQ Emission Factors (g/mi traveled)
LDGV
LDGT
HUG*
LDDr
U LDDT
UDDY
MC
Three-way Catalyst (T2)
0.004
0.007
0.013
Three-way Catalyst (T1)
0.043
0.087
0.175
Early 3-way Catalyst (TO)
0.065
0.106
0.213
Oxidation Catalyst
0.050
0.064
0.132
Non-Catalyst
0.020
0.022
0.047
0.007
Low Emission Vehicle
0.015
0.016
o.MA
Advanced
* ftm
0.001
0.005
Moderate
fx 0001
0.001
0.005
Uncontrolled
0.020
0.022
0.050
// 0.001
0.002
0.005
0.009
Restore/clear defaults
Source: Default values from EPA, 2010. In1^
CtJj Emission Factors (g/mi traveled)
fy of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008.
Control Technologi
LDGV
LDGT
r LDDV
LDDT
HDDV
MC
Three-way Catalyst (T2)
0.017
0.016
aoa#
Three-way Catalyst (T1)
0.027
0.045
Early 3-way Catalyst (TO)
0.070
0.078
Oxidation Catalyst
0.135
0.152
0236
Non-Catalyst
0.170
0.191
0.418
0.067
Low Emission Vehicle
0.010
0.015
0.030
Advanced
0.000
0.001
0.005
Moderate
0.000
0.001
0.005
Uncontrolled
0.178
0.202
0.460
0.001
0.001
0.005
0.090
Restore Default Cst=
Source: Default values from EPA, 2010. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2008.
2. Enter state-specific data on vehicle miles traveled (VMT) b| vehicle tjpe.
Enter custom data in the tahfe heiots>, or use the provided default data '
Restore Default Data
1990
1991
1992
1993
1994
1995
1997
1998
1999
2000
2001
2002
2003
2004
HDDV
1,664
1,685
1,866
2,049
2,206
2,359 4
2.615
2,725
2,803
2,861
2,898
2,944
2,905
3,143
HDGV
386
407
425
429
435
441
447
451
465
470
456
417
432
434
469
LDDT
202
224
267
300
311
326
341
367
379
402
417
423
430
437
459
LDDV
172
157
167
171
167
161
156
158
153
149
145
133
134
132
140
LDGT
7,039
8,026
9,380
10,277
10,562
11,056
11,484
12,118
12,552
13,196
13,578
14,060
14,302
14,538
15,254
LDGV
17,604
17,133
18,578
19,355
19,855
20,572
21,147
21,908
22,952
23,562
24,158
24,877
25,157
24,789
26,271
MC
110
112
125
132
136
142
145
149
154
159
158
147
146
143
156
Total
27.178
27.744
30.808
32.714
33.671
35.057
36.190
37.765
39.379
40.741
41.771
42.955
43.545
43.379
45.891
'Default data for this table is not complete for at/years and vehicle tt/pesbt/state. AM values skmift/ unavailable data
VaAses are derived from tables VM-tand of FederalMffbts/affAe^ninistratiort's 'Mibva# Statistics' 'series fhttp »rt>w fh&a. dot.govtffohimfohimstat.html Please see these reports for specific notes on state-
reported data
Step (4b) Highway Vehicles - Allocating VMT by Model Year Worksheet
1. Distribute vehicle miles traveled by vehicle age on the Highway 4b worksheet. In
order to account for changes over time in the control technologies used by vehicles,
estimates of VMT by vehicle type must be distributed across vehicle model years. To
make this apportionment, it is necessary to incorporate the following distributions:
(1) vehicle age distribution, and (2) annual age-specific vehicle mileage
accumulation. Vehicle age distribution simply refers to the age distribution of the
vehicle fleet. This distribution may vary by state due to climate and road
maintenance practices (e.g., whether roads are salted, which causes faster
deterioration of cars), cultural reasons (e.g., higher demand for older "cruisers" in
Los Angeles), and/or economic reasons.
a. First, choose the year of the inventory you are performing in the yellow box
at the top of the sheet using the arrow buttons, as shown in Figure 6. Default
data (U.S. EPA 2016) for the current year's age distribution is automatically
selected as you change the inventory year using the arrow buttons; you may
overwrite it if you wish or clear it by clicking "Clear Age Distribution Entries";
to restore the default data, click "Restore Default Data."
State Greenhouse Gas Inventory TooI User's Guide for the Mobile Combustion Module 1.10
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Module 3 -Mobile Combustion Module
January 2017
Next, enter the mileage accumulation for each vehicle age class/model year in
the year of the inventory in Table I. This table refers to the relative distance
vehicles are driven annually, by vehicle type. The vehicle ages are displayed
as numbers in ascending order from the inventory year. That is, if the
inventory year is 2005, cars built in 2005 are year "0" vehicles, cars built in
2004 are year "1" vehicles, and so forth.
Enter the percent age distribution for vehicles in the inventory year in Table
II. This age distribution represents the percent of vehicles on the road in the
inventory year, based on the year the vehicle was manufactured. This table
is similar to Table I in that if the inventory year is 2005, cars built in 2005 are
year "0" vehicles, cars built in 2004 are year "1" vehicles, and so forth.
Finally, populate similar tables for the entire time series by clicking the "Use
Default Data for All Years" button at the top of the page. This wiil populate
the historical time series based on default data from U.S. EPA (2016). This
step creates an emissions estimate for each year from 1990 to the current
inventory year.
Figure 6. Example of the Highway 4b Worksheet
D State Inventory Tool - CH4 and N20 Emissions from Mobile Combustion Module
: File Edit Module Options
Type a question for I
4b. Highway Vehicles - Allocating VMT by Model Year
Populate data for other years
2010
Clear Mileage Accumulation Entries
C.
Step (4c) Highway Vehicles - Allocating Control Technology by Model
Year Worksheet
1. In the Highway 4c worksheet, you will enter percentage of vehicles with each control
technology, by vehicle type.
a. Enter the distribution of emissions control equipment type by vehicle model
year for motorcycles and diesel vehicles in Table I, as shown in Figure 7. The
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module 1.11
-------
Module 3 -Mobile Combustion Module
January 2017
three types of control technology for motorcycles and diesel vehicles are
Advanced (A), Moderate (M), and Uncontrolled (U). Default data from U.S.
EPA (2016) are automatically entered in the yellow cells, but you may
overwrite or delete them if you wish, using the "Restore Default Data" buttons
above the Table I.
b. In Table II of this worksheet, enter the distribution of emissions control
equipment type by vehicle model year for gasoline vehicles (LDGV, LDGT, and
HDGV), as shown in Figure 7. The types of control technologies used are (in
order of most recent employment): three-way catalyst (T2), low-emission
vehicle (L), three-way catalyst (Tl), early three-way catalyst (TO), oxidation
catalyst (O), non-catalyst (N), and uncontrolled (U). Defaults are
automatically entered in the yellow cells, but you may overwrite or delete
them if you wish, using the buttons above the table.
Figure 7. Example of the Highway 4c Worksheet
C State Inventory Tool - CH4 and N20 Emissions from Mobile Combustion Module
File Edit Module Options
4c. Highway Vehicles - Allocating Control Technology by Model Year
CHt and N;0 emissions from highway vehiclesare calculated using foursteps: 1) calculate the vehicle miles traveled for each
vehicle type; 2) convert the vehicle miles traveled data for use with existing emission factors; 3) distribute vehicle miles traveled by
possible data
Enter emissions technology by
model year for motorcycles
and diesel vehicles
Enter emissions
technology by model year
for gasoline vehicles
For vehicle types In Table each model year vehicle must have exactly one (1) control technology code.
| Click for Technology I finitions |
& Motorcycles Table II. Motor Gasoline Vehicles (within each vehicle category, rows must total to 100%)
LDD(V,T) HDDV
Step (5) through Step (8) Complete the Non-Highway Worksheets
Although mobile sources other than road vehicles account for a significant fraction of total
mobile ChU and N2O emissions, they have received relatively little study compared to
passenger cars and heavy-duty trucks. Major sources of pollutant emissions among non-
highway vehicles include jet aircraft, gasoline-fueled piston aircraft, agricultural and
construction equipment, railway locomotives, boats, and ships. Although each
transportation mode has its own worksheet in the module, the method used for estimating
emissions for these non-highway sources is almost identical, and will be described
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
1.12
-------
Module 3 -Mobile Combustion Module January 2017
collectively. The steps below are illustrated in Figure 8 (the Marine worksheet is used as an
example; the other worksheets are very similar).
1. Enter energy contents (for aviation, in kg/million Btu) or density factors (for modes
other than aviation, in kg/gallon of fuel or ton coal). Select the defaults by clicking
the "Restore Default Data" button.1
2. Enter ChU and N2O emission factors for each fuel type in g gas/kg fuel.2
3. Enter fuel consumption data from 1990 to present for each type of fuel in million Btu
(aviation), gallons of liquid fuel (all modes except aviation), or tons of coal
(locomotives).3
4. On the "Other non-highway" worksheet, you must complete the above steps three
times: for farm equipment, for construction equipment, and for other non-highway
equipment, such as snowmobiles.
Figure 8. Example of Data Required for Non-Highway Mobile Sources
iSj File Edib Module Options Type a question for h|
6. Marine Factors and Fuel Consumption
CHt andN20
data on fuel c
emission fact
Combustion
steps: (1) obtain
jata with existing
:he Mobile
Click here for
possible data
Enter energy content/
density factors
Continue
-TEV
1. verily the tactors that are usea to calculate LH* ana n2
Default
s trom boats.
Restore Default Data
_! -: :
Densitv Factors (Kq/gal)
Residual Fuel
Distillate Fuel
Motor Gasoline
3.575
3.192
_ b. 1
Enter emission factors
7 .
a
source. Del
es from 1996 Revised IPCC guidelines
Enter fuel consumption
i
ore Default Data
~ear Data
N?0 Emission Factors (a/kg fuel)
Residual Fuel
Distillate Fuel
Motor Gasoline
CHj Emission Factors (a/ka fuel)
Residual Fuel
Distillate Fuel
Motor Gasoline
Source: Default values from 1996 Revised IPCC guidelines.
2. Verify the activity data (fuel consumption, in gallons) used to calculate CHi and N;Q emissions from boats*
Vehicle/Fuel Type
1990
1991
1992
1993
#^^*1994
1995
1996
1997
1998
Residual Fuel Oil**
Distillate Fuel Oil**
Gasoline
5,750,000
7,318,000
5,647,000
4,757,000
Efi» 42,000
15,596
4,855,000
5,986,000
5,250,000
5,416,000
5,497,000 6,0.
* Default data for this table is not complete for all years for every state. Null values signify unavailable data.
** Default data provided in this table includes international bunker fuels. Inventory estimates for boats should NOT include international bunker fuels, as emissions from these fuels are not inc
Please subtract bunker fuels from this fuel consumption estimate, to calculate the amount of fuel consumed by domestic boats.
Source: Default gasoline values from FHWA, 2010, Highway Statistics. Distillate and residual values derived from EPA, 2011. US Inventory of Greenhouse Gas Emissions and Sinks: 1990-20G
Step (9) Complete the Sector Worksheet for Alternative Fuel Vehicles
1 Default data are from EIA (2015a) (aviation, locomotives, other non-highway); U.S. EPA (2016)
(marine).
2 Default data are from U.S. EPA (2016) (alternative fuels, jet fuel); IPCC/UNEP/OECD/IEA (1997) (all
other fuels).
3 Default data are from EIA (2016) (aviation); FHWA (2016) (marine); U.S. EPA (2016) (marine,
other non-highway); EIA (2015b) (locomotives)
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module 1.13
-------
Module 3 -Mobile Combustion Module January 2017
The methodology for alternative fuel vehicles is a simplified version of the methodology
used for highway vehicles; an emission factor is multiplied by the VMT of each type of
vehicle, based on the fuel used. The alternative fuels for which you can calculate emissions
are methanol, ethanol, compressed natural gas (CNG), liquefied natural gas (LNG), and
liquefied petroleum gas (LPG). The steps below are illustrated in Figure 9.
1. Enter ChU and N2O emission factors for light-duty vehicles, heavy-duty vehicles, and
buses for each relevant fuel type. The default data are from U.S. EPA (2016) and
are populated by selecting the "Restore Default Data" buttons. If you would like to
use different data, you may overwrite the yellow cells, or use the "Clear Data" button
and enter your state-specific data.
2. Enter VMT for each vehicle by fuel type from 1990 to present.
3. Check the box to correct for alternative fuel vehicle VMT included in highway vehicle
VMT. Default data for highway VMT are assumed to include alternative fuel vehicle
miles traveled, therefore this box is checked in its default state and AFV VMT is
automatically subtracted from highway VMT. Uncheck this box if the highway VMT
data you entered do not include alternative fuel vehicles.
Figure 9. Alternative Fuel Vehicles Worksheet Data Entry
State Inventory Tool - CH4 and N20 Emissions from Mobile Combustion Module
;aj File Edit Module Options
Type a question for help
9. Alternative Fuel Vehicle Factors and VMT
possible data
Enter emission
factors
W£ L
Scroll down sheet for
highway VMT offset
Enter VMT data
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
1.14
-------
Module 3 -Mobile Combustion Module
January 2017
Step (10) Review the CO2 Emissions Calculation Worksheet for Highway
Vehicles
The gray arrows in the upper left of your screen will take you through Steps 10 and 11 if
you chose to conduct optional CO2 calculations in Step 3. The methodology to calculate CO2
emissions from highway vehicles requires a conversion from the measured activity (vehicle
miles traveled) to fuel consumption because CO2 emission factors are based on gallons of
fuel consumed instead of miles driven. Because vehicle miles traveled have already been
entered in Step 4, this step only requires the review of established data. Figure 10 shows
the automatic CO2 emissions calculations for highway vehicles.
1. Review the total vehicle miles traveled by highway vehicle type for each calendar
year. These total vehicle miles traveled values are automatically summed for each
calendar year based on the values entered in Step 4 of this module.
2. Review the total fuel consumption by highway vehicle type for each calendar year.
The fuel consumption is calculated based on the total vehicle miles traveled and
average vehicle fuel efficiency by vehicle class and model year.
3. Review the total emissions calculations for each highway vehicle type. Fuel
consumption is converted to MMBTU consumption using unit conversion factors and
then gasoline consumption is adjusted to account for ethanol blending in gasoline.
CO2 emissions are calculated using unit conversion and default CO2 emission factors.
Figure 10. Example of the Highway CO2 Worksheet in the Mobile Combustion
Module
File Edit Module Options
Type a question for help
10. Highway C02 Calculations
E State Inventory Tool CH4 and N20 Emissions from Mobile Combustion Module
Step (11) Review the CO2 Emissions Calculation Worksheet for Non-Highway
Vehicles
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module 1.15
-------
Module 3 -Mobile Combustion Module January 2017
Step 11 conducts similar calculations as those done in Step 10, but for non-highway
vehicles, including planes, boats, locomotives, and other off-road vehicles. This step
requires users to review established data and automatic calculations in the sheet, Figure 11
shows the automatic CO2 emissions calculations for highway vehicles. Note that calculations
for each separate class of non-highway vehicles (planes, boats, locomotives, and other) are
separately listed on the page. Scroll down through each section when conducting the
following steps.
1. Review the total fuel consumption by non-highway vehicle type for each calendar
year.
2. Review the total emissions calculations for each non-highway vehicle type. Fuel
consumption was converted to carbon content consumed using unit conversion
factors. CO2 emissions in metric tonnes were calculated using unit conversion and
default CO2 emission factors.
3. Review the total emissions calculations at the bottom of the page, which sums up the
emissions of each non-highway fuel type calculated in previous steps.
Figure 11 shows the automatic CO2 emissions calculations for off-road vehicles.
Figure 11. Example of the Off-road CO2 Worksheet in the Mobile Combustion
Module
ClofntouOTon MeSul* • Invmtory Too!
11. Non-highway C02 Calculations
wi»ii ftqn ofl-nwd whid»»—ci
)«nd rueiys* iiot o'm« n
.UuteV
* CmrtMten chapter •<#»!>»•«¦* flkrf*
Aviation
1891
iro
1993
1W
im
im
199/
1990
1999
2
UtTuU ItWBMTO"
330S2.SH)
» 154513
59 mi.569
*8985 1B3
43 2$8939
4S OR." 76*
41703 068
weei oes
a«4E66l
44.JJ6.7S7
4 2W2
HtliM
1.490 *ar
971.991
1 BW.257
11M26*
1 401281
l.B19 37t
mzu
213V
Anton Suir.c
848 4ST
7S5 854
865 i?4
K4 5<8
J4?5«
6?4 IM
634 673
719 741
735 9M
sueoi
7M
1W0
1991
1992
1933
1994
1995
1996
1997
1998
1999
¥UK«Wllf-
1.8tS»7.»7
5 MM 'ii *15
1 TD1.3*7.M»
3 0*3.!®* 33#
1 Ut 9U 331
i.rat.jir.os
i.m ?D3Tta
1.TU.WUCM
1.874 !»l
I *30 MS 486
1 MT3«I
6i.ao359
».*ei,s?2
«S.2S2«4
74,338.099
68 6" 1.9*1
83J01.7H
13.287 46®
1.36S.108
Airitfen S*»otre
34.90* ira
22.435.w7
si
n.Sw.sM
29.720344
asizai?
24 942W7
29 TOO 847
M 147 109
40J40«2
32-778
•or-i lljf'*
'-'Typ-
1M0
1991
1»3
1994
HM
19M
19(7
1998
ItH
>
Mt tiM »c«rs»«n*"
i.l«4,25J,l«4 52
eise.ofM*
7.671,397.210
6.772.327.213
«.2f'*9?.22<
6,9597 IS 603
t,4TSJ?5.0»8
7.(4 J 111.5*2
tw.w
Ht 1 Ml N»sMM"
23*404317
10B.SB.7W22
294 3CV 709
272112,994
asitrj m
tii rjv sai
4 »r.'384
AvWton flunk*
\77 w r?n
tis.Biiaeo
lUSHSt
95.184 6??
97 »?*««
95 047M7
wmiiu
109 SM M0
118*40 11?
149 77S Mfl
1?0 189
f»el7yp«
1W0
1991
1992
1993
1904
1995
19«
1997
1»8
1999
2
J* 1 **{ Kfiunt
M Furi N»pMto
A.atcnOMCHre
2341121
108138
58W2
2172218
WW
53,93?
2U9.420
t»5?3
47.JS0
7 479 669
188*
3 C'l ISO
114.113
44 44(1
2.0*3.IT*
138 511
4>.ll>
31HIU
J? AM
45.147
2937 <20
2255 |
4J.7I J
i
97.9J0
-
Tout
2.517.715
2,875,454
3.01*391
164C471
W3IL413
3.024-498
X222.1Q3
2 909.059
2,834.528
3J02AJ3
3.160J
fuel lyue
1990
1891
1*97
1993
19M
im
1199
1197
1195
1139
I
Sneuai Fsjfi Of
Q«titi« >u«iar-
finofai
5 750 800
7 318. OK
5 847.006
4.757000
42.000
I45SQ
*855000
5.986 000
5.23000
6418000
5.497.000
6.051 COO
AMU
State Greenhouse Gas Inventory TooI User's Guide for the Mobile Combustion Module
1.16
-------
Module 3 -Mobile Combustion Module
January 2017
Step (12) Review Summary Information
The information from each sector worksheet is collected on the summary worksheets.
Step (12a) Review CHU and N2O Summary Information
The Steps 4-9 above provide estimates of total CbUand N?.0 emissions from mobile
combustion. This summary worksheet displays results in MTCCbE, Gg ChU, and Gg
N2O. Figure 12 shows the summary worksheet that sums the ChU and N2O emissions
from ali sectors in the Mobile Combustion module. In addition, the results are
displayed in graphical format at the right of the summary worksheet.
Figure 12. Example of the Emissions Summary Worksheet in the Mobile
Combustion Module
E3 Stale Inventory Tool CH4 and N20 Emissions from Mobile Combustion Module
• File Edit Module Options
SB®
¦ question for help » . S X
12a. Mobile Source Emissions Summary, CH4 and N20
Fuel Type/Vehicle Type
1990
1991
1992
199S
1994
1995
1996
1997
1998
1999
2000
2002
2003
2004
Sciolirvc Highway
905,053
957,136
1,089,933
944,126
Passenger Cars
571.275
564.228
619,287
651.354
665.675
676.281
674.635
676.318
682.981
674.351
653.806
624JH2
585,239 533.363
516.307
Light-Duly Trucks
314,450
371.375
447.102
502.024
523,536
548,967
566.555
592.591
599.642
585.298
575.617
55*185
480,076
429.139
398,166
Heavy-Duty Vehicles
18.514
20.703
22.622
23.659
24,794
25.857
27.492
29.449
31.816
31.796
30.272
&589
28.698
28.841
28.720
Motorcycles
813
830
921
978
1.007
1,050
1,021
996
989
1,037
1.005
H918
894
867
932
Diesel Highway
4.511
4,574
5,083
5,567
5,979
6,384
6,679
7,067
7.353
7.575
7,726
U 7.800
7,922
7,838
8,484
Passenger Cars
99
89
94
95
92
88
85
85
82
70
74
Light-Duly Trucks
159
175
208
232
240
251
262
282
291
3
Click to review CO2
336
352
Heavy-Dirty Vehicles
Non-Highway
4,253
109.650
4.310
114.844
4.782
122,226
5.240
120,824
5.647
112,522
6,045
108,210
6.332
106,307
6.699
100,347
6.980
107.113
7.1
102.5
emissions summary
7,432
11.759
8.057
148,547
Boats
607
469
395
409
497
436
449
456
5!
561
532
Locomotives
8,311
10.275
8.381
9.601
11.262
12.429
14.037
6.667
7.278
5.459
5,276
4.276
3,859
5,235
4.552
Farm Equipment
5.985
7.231
10.549
9.095
8.334
8.274
11.288
11.057
9.475
6.843
7.344
5.915
6.105
6.103
6.663
Construction Equipment
49.914
50.899
54.035
54.172
48,300
45,890
38.359
42.317
47.024
44,518
80.354
56.364
59,379
57,878
63.948
Aircraft
26,558
28,099
31516
38.031
33,798
31,690
33,086
30.796
29.238
33,774
32.580
34,010
30,725
24,448
52.061
Other*
18.405
17,731
17.276
9.531
10.419
9.431
9.101
9.060
13.641
11.447
6.104
17,809
17.848
17.534
20.791
Alternative Fuel Vehicles
3.305
3,164
3,023
3,826
3,709
3,780
4,193
4.801
S.049
4,846
5,525
6,774
6,989
6,319
5,944
Light Duly Vehicles
815
815
822
875
829
976
1,167
1512
1.603
1.630
1.879
2.025
2.152
1.949
1.810
Heavy Duty Vehicles
2.440
2,281
2.114
2.813
2.726
2,640
2.844
3.104
3.255
2.999
3.432
4.488
4,582
4.160
3.712
Buses
50
67
88
137
154
165
181
185
191
217
215
261
255
210
421
Total
1.022,518
1.079,718
1,220,267
1,308,233
1.337,221
1.370.529
1.386,882
1,411.570
1,434.943
1,407,4-
44
1,406,131
1,343,703
1,228,307 1.118,125
1,107,101
* "Other" includes snowmobiles, small gasoline powered utility equipment, heavy-duty gasoline powered utility equipment, and heavy-duty diesel powered utility equipment.
Total CH4 and N2O Emissions from Mobile Sources (MTCE)
Fuel Type/Vehicle Type
1990
1991
1992
1993
1994
199S
1996
1997
1998
1999
2000
2001
2002
2004
kisolirve Highway
Passenger Cars
Light-Duly Trucks
Heavy-Dirty Vehicles
Motorcycles
246,033 261,037 297,255 321,277 331,367 341,497 346,283 354.S69 358,753 352.495 343,827 3S0,056 298,611 270,603 257,489
155.602 153,880 168.897 177.642 181.548 184.440 183,991 184.450 186.267 183,914 178,311 170.294 159.611 145.463 140.811
85.759 101.284 121.937 136.916 142,783 149.718 154.515 161.616 163.539 159.627 156.986 151.987 130,930 117.038 108,591
5,049 5.646 6.170 6.453 6.762 7.052 7.498 8.032 8,677 8,672 8.256 7.524 7,827 7.866 7.833
222 226 251 267 275 286 279 272 270 283 274 250 244 236 254
Step (12b) Review CO2 Summary Information
If you conducted optional CO2 calculations in Steps 10-11 above, this summary
worksheet collects the CO2 emission results. The results are displayed in MTCO2E by
mobile source and fuel type from all sectors in the Mobile Combustion module. In
addition, the results are displayed in graphical format at the bottom of the summary
worksheet.
Step (13) Export Data
The final step is to export the summary
data. Exporting data allows the
estimates from each module to be
combined later by the Synthesis
Module to produce a comprehensive
greenhouse gas inventory for the state.
Note: the resulting export file should not be
modified. The export file contains a summary
worksheet that allows users to view the results, as well as
a separate data worksheet with an unformatted version of
the results. The second worksheet, the data worksheet,
contains the information that is exported to the Synthesis
Tool. Users may not modify that worksheet.
Adding/removing rows, moving data, or making other
modifications jeopardize the ability of the Synthesis
Module to accurately analyze the data.
State Greenhouse Gas Inventory Tool User's Guide for the Mobile Combustion Module
1.17
-------
Module 3 -Mobile Combustion Module
January 2017
To access the "Export Data" button, return to the control worksheet and scroll down to the
bottom (13). Click on the "Export Data" button and a message box will open that reminds
the user to make sure all sections of the module have been completed. If you make any
changes to the Mobile Combustion module later, you will then need to re-export the results.
Clicking "OK" prompts you to save the file. The file is already named, so you only need to
choose a convenient place to save the file. After the file is saved, a message box will
appear indicating that the data were successfully exported.
While completing the modules, you are encouraged to save each completed module; doing
so will enable you to easily make changes without re-running it entirely.
Following data export, the module may be reset and run for an additional state.
Alternatively, you may run the remaining modules of the State Inventory Tool to obtain a
comprehensive profile of emissions for your state.
1.4 Uncertainty
In the upper right-hand corner of the summary worksheet is a button: "Review discussion of
uncertainty associated with these results." By clicking on this button, you are taken to a
worksheet that discusses the uncertainty surrounding the activity data and emission factors,
and how the uncertainty estimates for this source category affect the uncertainty of the
emission estimates for your state.
The uncertainty for the optional CO2 calculations bears special consideration because these
calculations are supplemental to those already contained in the CO2FFC module. The Mobile
module provides an additional level of detail by estimating CO2 emissions by transportation
mode and vehicle type. The CO2FFC module calculates CO2 emissions based on total fuel
consumption across all modes, while the Mobile module calculates CO2 emissions based on
activity data (such as vehicle miles traveled). It is anticipated that the CO2FFC module
provides a more accurate estimate of total CO2 emissions in the transportation sector due to
less uncertainty in the estimates of total fuel consumption than in the detailed activity data.
However, fuel consumption is not otherwise available on the detailed level needed for
analysis by mode and vehicle type.
With highway vehicles, the CO2 calculations rely on the same disaggregation of total vehicle
miles traveled by vehicle type and model year that is used for the non-CC>2 calculations. The
module then uses average fuel economy by vehicle type and model year to estimate fuel
consumption. Error in the vehicle split, age distribution, or fuel efficiency factors will affect
the estimates. The estimates may also differ from the CO2FFC module because there may
be differences between the state where fuel is sold and the state where that fuel is
consumed. For example, if a state has lower fuel taxes than its neighbors, interstate
travelers may purchase fuel in a low-tax state and consume that fuel in a state with higher
fuel taxes, causing a disconnect between reported fuel consumption and VMT.
As a result of these issues, the uncertainty surrounding the CO2 emissions estimates from
gasoline and diesel is particularly high. Caution should be used when interpreting these
results.
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1.5 Explanation of Mobile Combustion Module Updates
In the upper right-hand corner of the summary worksheet is a button: "Review discussion of
uncertainty associated with these results."
The bottom-up CO2 calculations in the Mobile Combustion module provide estimates of CO2
emissions from the transportation sector disaggregated by mode and vehicle type. Because
the bottom-up calculations require more assumptions than the top-down calculations in the
C02FFC module, the overall totals in the C02FFC module are assumed to be more accurate,
and the new calculations are intended as a complement to the C02FFC module. The
following methodologies were used:
Highway vehicles
1. Utilize the data on annual vehicle miles traveled for each vehicle type and model
year as determined in step 4 of the module;
2. Estimate gallons of fuel consumed for each vehicle type and model year with default
fuel efficiency data;
3. Adjust gasoline fuel consumption based on the reported amount of ethanol
consumed annually by the transportation sector in each state; and
4. Multiply fuel consumption by the appropriate energy content and carbon coefficient
to estimate CO2 emissions.
Non-highway vehicles
1. Utilize consumption data for each mode and fuel type from steps 5 through 8 of the
module (aviation, boats & vessels, locomotives, and other non-highway vehicles);
and
2. Multiply fuel consumption by the appropriate energy content and carbon coefficient
to estimate CO2 emissions.
The methods for non-highway vehicles are essentially the same those in the C02FFC
module, because they rely on a simple multiplication of fuel consumption times the CO2
emission factor. The only major source of uncertainty is with the data sources used for
disaggregating fuel consumption by type.
By contrast, the CO2 calculations for highway vehicles require estimating fuel consumption
based on vehicle miles traveled by vehicle type—which is itself the product of estimates—
because fuel consumption is not otherwise available on the detailed level needed for
analysis by mode and vehicle type.
With highway vehicles, the CO2 calculations rely on the same disaggregation of total vehicle
miles traveled by vehicle type and model year that is used for the non- CO2 calculations.
The module then uses average fuel economy by vehicle type and model year to estimate
fuel consumption. Error in the vehicle split, age distribution, or fuel efficiency factors will
affect the estimates. The estimates may also differ from the C02FFC module because there
may be differences between the state where fuel is sold and the state where that fuel is
consumed. For example, if a state has lower fuel taxes than its neighbors, interstate
travelers may purchase fuel in a low-tax state and consume that fuel in a state with higher
fuel taxes, causing a disconnect between reported fuel consumption and VMT. As a result of
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these issues, the uncertainty surrounding the CO2 emissions estimates from gasoline and
diesel is particularly high.
1.6 References
EIA. 2016. State Energy Data 2014 Consumption. Energy Information Administration, U.S.
Department of Energy. Internet address: http://www.eia.aov/state/seds.
EIA. 2015a. Annual Energy Review 2014. Energy Information Administration, U.S.
Department of Energy, Washington, DC, DOE/EIA-0384(2010).
EIA. 2015b. Fuel Oil and Kerosene Sales 2014. Energy Information Administration, U.S.
Department of Energy. Internet address: http://www.eia.QQv/petroleum/fueloilkerosene
IPCC/UNEP/OECD/IEA. 1997. Rev/sec/1996 IPCC Guidelines for National Greenhouse Gas
Inventories. Paris: Intergovernmental Panel on Climate Change, United Nations
Environment Programme, Organization for Economic Co-Operation and Development,
International Energy Agency.
Prigent, Michel and Gerard De Soete. 1989. "Nitrous oxide N2O in engines exhaust gases—a
first appraisal of catalyst impact." SAE Paper 890492. Society of Automotive Engineers.
FHWA 2016. Highway Statistics 2014. Federal Highway Administration, U.S. Department of
Transportation. Tables VM-1 and VM-2. Internet address:
http://www.fhwa.d0t.g0v///p0licv/0hpi/hss/index.htm.
U.S. EPA. 2016. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 - 2014.
Office of Atmospheric Programs, U.S. Environmental Protection Agency. EPA 430-R-16-
004. Internet address:
http://www.epa.aov/climatechanQe/ahaemissions/usinventorvreport.html
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