Document ID: EPA-HQ-OAR-2014-0827-0364
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2015-07-13T04:00Z

Exhaust Emission Rates for Heavy-Duty On-road Vehicles in MOVES2014
                                 DRAFT REPORT

                                       
                                       
                                       
                                       
                USEPA Office of Transportation and Air Quality 
                      Assessment and Standards Division  
                                     2015

                                       
                                       
                                  Disclaimer

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 of the release of such reports is to facilitate the exchange of technical information and to inform the public of technical developments which may form the basis for a final EPA decision, position, or regulatory action.

    Table of Contents
1	Principles of Modeling Heavy-duty Emissions in MOVES	5
1.1	Heavy-duty Regulatory Classes	6
1.2	Emission Pollutants and Processes	7
1.3	Operating Modes	8
1.4	Vehicle Age	12
2	Heavy Duty Diesel Emissions	14
2.1	Running Exhaust Emissions	14
2.1.1	Nitrogen Oxides (NOx)	14
2.1.2	Particulate Matter (PM)	43
2.1.3	Hydrocarbons (HC) and Carbon Monoxide (CO)	58
2.1.4	Energy	64
2.2	Start Exhaust Emissions	70
2.2.1	HC, CO, and NOx	70
2.2.2	Particulate Matter	73
2.2.3	Adjusting Start Rates for Soak Time	73
2.2.4	Start Energy Rates	76
2.3	Extended Idling Exhaust Emissions	78
2.3.1	Data Sources	78
2.3.2	Analysis	79
2.3.3	Results	81
2.3.4	MOVES Extended Idle Emission Rates	81
2.3.5	Auxiliary Power Unit Exhaust	83
3	Heavy-Duty Gasoline Vehicles	85
3.1	Running Exhaust Emissions	85
3.1.1	HC, CO, and NOx	85
3.1.2	Particulate Matter	110
3.1.3	Energy Consumption	114
3.2	Start Emissions	118
3.2.1	Available Data	118
3.2.2	Estimation of Mean Rates	118
3.2.3	Estimation of Uncertainty	121
3.2.4	Projecting Rates beyond the Available Data	123
3.2.5	Start Energy Rates	129
4	Heavy Duty Compressed Natural Gas Transit Bus Emissions	131
4.1	Transit Bus Driving Cycles and Operating Mode Distributions	131
4.1.1	Heavy-Duty Transit Bus Driving Cycles	131
4.1.2	Transit Bus Operating Mode Distributions	133
4.2	Comparison of Simulated Rates and Real-World Measurements	134
4.2.1	Simulating Cycle Emission Aggregates from MOVES2010b Rates	134
4.2.2	Published Chassis Dynamometer Measurements	134
4.2.3	Plots of Simulated Aggregates and Published Measurements	136
4.3	Development of New Running Exhaust Emission Rates	140
4.3.1	Determining Model Year Groups	140
4.3.2	Scaling Model Years After 2007	141
4.3.3	Creating CNG Running Rates for Future Model Years	143
4.4	Start Exhaust Emission Rates for CNG Buses	144
4.5	Applications to Other Model Years and Age Groups	145
4.6	PM and HC Speciation for CNG Buses	145
4.7	Ammonia and Nitrous Oxide emissions	147
5	Heavy-Duty Crankcase Emissions	148
5.1	Background on Heavy-duty Diesel Crankcase Emissions	148
5.2	Modeling Crankcase Emissions in MOVES	149
5.3	Conventional Heavy-Duty Diesel	150
5.4	2007 + Heavy-Duty Diesel	151
5.5	Heavy-duty Gasoline and CNG Emissions	152
6	Nitrogen Oxide Composition	154
6.1	Heavy-duty Diesel	155
6.2	Heavy-duty Gasoline	155
6.3	Compressed Natural Gas	156
Appendix A	Calculation of Accessory Power Requirements	158
Appendix B	Tampering and Mal-maintenance	160
Appendix C	Extended Idle Data Summary	171
Appendix D	Developing PM emission rates for missing operating modes	176
Appendix E	Heavy-duty Diesel EC/PM Fraction Calculation	177
Appendix F	Heavy-duty Gasoline Start Emissions Analysis Figures	199
Appendix G	Heavy-duty CNG Bus Emissions Supplemental Figures	204
References	209

Principles of Modeling Heavy-duty Emissions in MOVES
This report describes the analysis conducted to generate emission rates and energy rates representing exhaust emissions and energy consumption for heavy-duty vehicles in MOVES2014.  Heavy-duty vehicles in MOVES are defined by any vehicle with a Gross Vehicle Weight Rating (GVWR) above 8,500 lbs. This report discusses the development of emission rate for total hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM).  From HC emissions, MOVES produces other measures of organic gases, including volatile organic compounds (VOCs), and total organic gases (TOG). From VOC emission rates and fuel property, MOVES estimates individual toxic compounds such as formaldehyde and benzene. The derivation of the aggregate measures of organic gases and individual toxic emissions are available in the Speciation41 and Toxics MOVES Reports. MOVES estimate the PM emission rates according to 18 subspecies as outlined in the Speciation Report41. This report covers the derivation of EC/PM fractions used to estimate elemental carbon (EC) emission rates and the remaining non-elemental carbon PM (nonEC) emission rates 
Energy consumption rates were developed based on measurements of carbon dioxide (CO2), CO and THC. We developed emission rates for heavy-duty vehicles powered by both diesel and gasoline fuels, as well as compressed natural gas (CNG) vehicles, although emissions from the heavy-duty sector predominantly come from diesel vehicles.  As a result, the majority of the data analyzed were from diesel vehicles.  
This report first introduces the principles used to model heavy-duty vehicles in MOVES. Then the emission rates for heavy-duty diesel, heavy-duty gasoline, and CNG transit buses are documented. Chapter 5 documents the crankcase emission rates used for each fuel type of heavy-duty vehicles. Chapter 6 documents the NO, NO2, and HONO ratios that are used to estimate NO, NO2, and HONO emissions from NOx emissions.
Emission rates for criteria pollutants (HC, CO, NOx, and PM) are stored in the "EmissionRateByAge" table in the MOVES database.  The emission rates in the EmissionRateByAge table are stored according to 
   1. MOVES regulatory class
   2. Fuel Type (Diesel, Gasoline, and CNG)
   3. Model year group 
   4. Vehicle age 
   5. Emission process (e.g. running exhaust, start exhaust, crankcase emissions)
   6. Vehicle operating mode  
Energy emission rates are stored in the "EmissionRate" table, which is similar to the "Emission RateByage" table, except emission rates are not differentiated by vehicle age. The MOVES framework and additional details regarding the "EmissionRateByAge" and "EmissionRate table are discussed in the report documenting the rates for light-duty vehicles8.
In the next sections, the following parameters used to classify heavy-duty emissions in MOVES are discussed in more detail: heavy-duty regulatory classes, vehicle age, emission processes, and vehicle operating modes. Although not discussed in detail, the model year groupings are designed to represent major changes in EPA emission standards.   

Heavy-duty Regulatory Classes
The MOVES heavy-duty regulatory groups are largely determined based on gross vehicle weight rating (GVWR) classifications. Each regulatory class groups vehicles together that have similar emission standards that may not be solely distinguished by GVWR. For example, Urban Bus engines are distinguished from other heavy heavy-duty vehicles (GVWR >33,000 lbs) because they have tighter EPA PM emission standards between 1994 and 2006 model years. Urban bus is a regulatory class that is also defined by its intended use, and not just the GVWR ("heavy heavy-duty diesel-powered passenger-carrying vehicles with a load capacity of fifteen or more passengers and intended primarily for intra-city operation"). 
Regulatory class 40 and 41 are also defined according to additional criteria than GVWR. LHD<=10K (RegClassID 40) are defined as trucks with GVWR between 8,500 and 10,000 lbs (Class 2b trucks), and are trucks with only two axles and four tires.  Class 2b trucks between 8,500 and 10,000 lbs with two axles and six tires are classified in regulatory class 41 (LHD <=14K), as well as all trucks between 10,000 and 14,000 lbs (Class 3 trucks). 
Unlike Urban Buses, the distinction between regClassID 40 and 41 in MOVES is not caused by differences in EPA exhaust emission standards. The reasons for the distinction between regulatory class 40 and 41 is due to (1) available activity information, and (2) the assignment of operating modes within MOVES source types. 
   (1) Available Activity Information. As discussed in the Population and Activity Report, the FHWA reports vehicle-miles traveled (VMT) of Class 2b trucks with two axles and four tires into light-duty vehicle categories, which correspond to MOVES sourceTypeID 31 (Passenger Trucks) and sourceTypeID 32 (Light Commercial Trucks). FHWA reports VMT from Class 2b trucks with two axles and six tires, as single-unit vehicles, which corresponds to a different set of MOVES source types: Refuse Trucks (51), Single Unit Short-haul (52), Single Unit Long-Haul (53), and Motor Homes (54).
   (2) Assignment of Operating Modes with MOVES source types. As discussed in the Population and Activity Report4, MOVES assigns operating modes within source types. For light-duty source types (including passenger trucks and light-commercial) running operating modes as assigned according to Vehicle Specific Power (VSP). For single-unit source types, operating modes are assigned according to Scaled Tractive Power (STP). As discussed in the operating mode subsection, the emission rates for regulatory class 40 use a different scaling factor when computing STP, such that the emission rates are consistent with VSP-based operating modes. The emission rates for regulatory class 41 are based on the standard STP scaling factor, to be consistent with the way MOVES assigns operating modes for heavy-duty source types. 
Regulatory class 40 is a new regulatory class introduced in MOVES2014. Previous versions of MOVES classified all light-heavy duty trucks with GVWR under 14,000 lbs as LHD2b3. The emission rates for LHD2b3 were compatible with VSP-based emission rates. As such, previous versions of MOVES were unable to model emission rates for LHD2b3 emission rates for single-unit trucks. With the addition of regulatory class 40, and the new definition of regulatory class 41, MOVES is able to model light-heavy duty trucks that are classified in both the light-duty and heavy-duty source types. 
The emission rates for all the heavy-duty sources types are discussed in this report. As discussed later in the report, the data used to derive the emission rates for regulatory class 40 and 41 trucks are often the same, but analyzed with separate scaling factors to derive separate emission rates for regulatory class 40, and regulatory class 41. Occasionally, the term LHD2b3 is used in this report, to refer to all light-heavy duty trucks with GVWR under 14,000 lbs.
Table 1-1 provides an overview of the regulatory class definitions in MOVES for Heavy-Duty vehicles. Table 1-1 also provide a distinction if the emission rates are developed to be consistent with VSP or STP-based operating modes. 

             Table 1-1. Regulatory Classes for Heavy-Duty Vehicles
Regulatory Class Description
regClassName
regClassID
Gross Vehicle Weight Rating (GVWR) [lb]
Source Types (SourceTypeID)
Operating Mode Basis[2]
Light-heavy duty < 10,000 lbs. (Class 2b Trucks with 2 Axles and 4 Tires.)
LHD<= 10 K
40
8,501  -  10,000
Passenger Trucks,(31) Light Commercial Trucks(32)
VSP
Light-heavy duty <= 14,000 lb. Class 2b (Trucks with 2 Axles and at least 6 Tires or Class 3 Trucks.)
LHD<=14k
41
 8,501  -  14,000
Buses (41, 43), and Single Unit Trucks (51,52,53,54) 
STP
Light-heavy duty 4-5
LHD45
42
14,001  -  19,500
Buses (41, 42, 43) and Single Unit Trucks (51,52,53,54) 
STP
Medium-heavy duty
MHD
46
19,501  -  33,000
Buses (41,42,43), Single Unit Trucks (51,52,53,54), and Combination Trucks (61,62) 
STP
Heavy-heavy duty
HHD
47
> 33,000
Buses (41,42,43), Single Unit Trucks (51,52,53,54), and Combination Trucks (61,62)
STP
Urban Bus 
Urban Bus[1]
48
> 33,000
Transit Bus (42)
STP
[1] see CFR § 86.091(2).
[2] MOVES assigns operating modes based on VSP or STP, depending on source type

Emission Pollutants and Processes
MOVES models vehicle emissions from fourteen different emission processes as listed in Table 1-2. This report covers the emission rates for the exhaust emission processes (running exhaust, start exhaust, extended idle exhaust, auxillary power exhaust, crankcase running exhaust, crankcase start exhaust, and crankcase extended idle exhaust) for HC, CO, NOx and PM. The `running' process occurs as the vehicle is operating on the road either under load or in idle mode.  This process is further delineated by 23 operating modes as discussed in the next subsection.  The `extended idle' process occurs during an extended period of idling operation such as when a vehicle is parked for the night and left idling.  Extended idle is generally a different mechanism (usually a higher RPM engine idle to power truck accessories for operator comfort) than the regular `curb' idle that a vehicle experiences while it is operating on the road.
Estimation of energy consumption rates for heavy-duty vehicles is also covered in this report. Energy consumption ( in units of kJ) is modeled from running exhaust, start exhaust, extended idle exhaust, and auxiliary power exhaust. Emissions of greenhouse gases other than CO2 are not covered. Estimation of the emissions of methane, nitrous oxide (N2O),  and ammonia (NH3) for gasoline and diesel heavy-duty vehicles are described in separate reports.[,]  The estimation of these emission rates from these pollutants for CNG transit bus vehicles are covered in this report. 
Evaporative and refueling emissions from heavy-duty vehicles are not covered in this report. Estimation of evaporative hydrocarbon emissions from heavy-duty gasoline vehicles is described in the evaporative report.  The model does not estimate evaporative emissions for diesel-powered vehicles, but does estimate fuel spillage emissions which are part of the fueling emissions documented in the evaporative report.7 
Brake and Tire wear emission rates from heavy-duty vehicles are discussed in the Brake and Tire Wear Report.10
         Table 1-2. Emission Processes for On-road Heavy-Duty Vehicles
processID	
processName	
Covered in this report?
1
Running Exhaust
Y
2
Start Exhaust
Y
9
Brakewear
N
10
Tirewear
N
11
Evap Permeation
N
12
Evap Fuel Vapor Venting
N
13
Evap Fuel Leaks
N
15
Crankcase Running Exhaust
Y
16
Crankcase Start Exhaust
Y
17
Crankcase Extended Idle Exhaust
Y
18
Refueling Displacement Vapor Loss
N
19
Refueling Spillage Loss
N
90
Extended Idle Exhaust
Y
91
Auxiliary Power Exhaust
Y

Operating Modes
Operating modes for heavy-duty vehicles running exhaust are defined in terms of power output (with the exception of the idle and braking modes). For light-duty vehicles, the parameter used is known as vehicle-specific power (VSP), which is calculated by normalizing the continuous power output for each vehicle to its own weight. Light-duty vehicles are tested on full chassis dynamometers, and emission standards are in units of grams per mile. Thus, the emission standards are largely independent of the weight (and other physical characteristics) of the vehicle and dependent on distance (or miles). More in depth discussion of VSP is contained in the light-duty emission rate report. 
 For heavy-duty vehicles, we have continued to relate emissions to power output, but in a different way. Rather than normalize the tractive power for each vehicle to its own weight, we scale the power by a fixed multiple designed to fit the resulting means into the existing operating mode framework. We refer to this parameter as "scaled-tractive power" (STP). Heavy-duty vehicles are regulated using engine dynamometers, and emissions standards are in units of grams per brake-horsepower-hour (g/bhp-hr).  With these work-based emission standards, emission rates relate strongly to power and are not independent of vehicle mass, so normalizing by mass is not appropriate.  Thus, for heavy-duty modal modeling, the tractive power is used in its natural form but simply scaled by a constant as described above to bring its numerical values into the same range as the VSP values used for light-duty vehicles.  

The equation for STP is located here, with units in scaled kW or skW.  :
                                       
                                            Equation 1-1

Where: Paxle is the power demands at the axle for the heavy-duty truck. As discussed later, Paxle can be estimated from an engine dynamometer or from an engine control unit (ECU) for on-road or chassis testing, by measuring the engine power and estimating the accessory loads and power-train efficiencies for the vehicle. 

For on-road tests, measuring power from the ECU is in general more accurate at than estimating power from road load coefficients. Unlike a generic road load equation where vehicle characteristics, such as aerodynamic drag and rolling resistance are assumed, the ECU measures engine speed and torque directly during the test. Also, wind speed and wind direction, which can have a significant effect on aerodynamic drag, are not typically measured on the on-road tests. Additionally, the road load equations may not reflect the actual vehicle test weight, and the tests may not have accurate grade information for the entire route tested. For on-road tests we generally use power calculated from the ECU measurements, because the vehicle and environmental characteristics determine the axle power (Section 2.1.1.2). 

In chassis dynamometer tests, the road load equation works well because it directly determines the axle power during the test.  For data collected on chassis dynamometer tests, with vehicles that do not have ECU measurements, we use road load equation to estimate power (Section 2.1.2.2.1). 
The values of fscale are located in Table 1-3. As mentioned previously, the operating modes for regulatory class 40 are VSP-based, because regulatory class 40 are modeled as passenger trucks and light commercial trucks, and MOVES assigns operating modes to these source types using VSP. Thus, for regulatory class 40, fscale  is equal to the mean source mass of light-commercial trucks4, to yield emission rates that are consistent with VSP-based operating modes.

In contrast, all other heavy-duty source types use a constant 17.1 power scaling factor, which is approximately the average running weight for all heavy-duty vehicles, and yields STP ranges that are within the same range as the definitions for VSP, as shown in Table 1-4. 

                    Table 1-3. Power scaling factor fscale
                         Regulatory Class (RegClassID)
                     Power scaling factor (metric tonnes)
                               LHD<=10K (40)
                                     2.06
          LHD<= 14K (41), LHD45 (42), MHD (46), HHD (47), Bus (48)
                                     17.1

In cases where the power is not measured at the engine, it can be estimated from instantaneous speed, vehicle mass, and road load coefficients, using the following equation:

                  STP=Avt+Bvt2+Cvt3+M∙vtat+g∙sinθfscale
                                                                   Equation 1-2
where
    A = the rolling resistance coefficient [kWsec/m],
    B = the rotational resistance coefficient [kWsec[2]/m[2]],
    C = the aerodynamic drag coefficient [kWsec[3]/m[3]],
    m = mass of individual test vehicle [metric ton],
    fscale = fixed mass factor (see Table 1-3),
    vt = instantaneous vehicle velocity at time t [m/s],
    at = instantaneous vehicle acceleration [m/s[2]]
    g is the acceleration due to gravity 9.8 ms2
    sinθ is the (fractional) road grade
The derivation of the load road parameters is discussed in the Population and Activity Report4. This is the equation used by MOVES to estimate the operating mode distribution from average speed and second-by-second driving cycles as discussed in the Population and Activity Report. However, this equation is also used in this report to estimate the STP-based emission rates from emission tests where a more direct measure of Paxle is not available. 

Table 1-4. Definition of the Operating Mode Attribute for Heavy-Duty Vehicles (opModeID)
Operating Mode
Operating Mode
Description
Scaled Tractive Power
(STPt, skW)
Vehicle Speed
(vt, mph)
Vehicle Acceleration
(a, mph/sec)
0
Deceleration/Braking

at  -2.0 OR
(at < -1.0 AND
at-1 <-1.0 AND
at-2 <-1.0)
1
Idle

-vt <  1.0

11
Coast
STPt< 0
0    vt <  25

12
Cruise/Acceleration
0    STPt< 3
0    vt <  25

13
Cruise/Acceleration
3    STPt< 6
0    vt <  25

14
Cruise/Acceleration
6    STPt< 9
0    vt <  25

15
Cruise/Acceleration
9    STPt< 12
0    vt <  25

16
Cruise/Acceleration
12  STPt
0    vt <  25

21
Coast
STPt< 0
25  vt <  50

22
Cruise/Acceleration
0    STPt< 3
25  vt <  50

23
Cruise/Acceleration
3    STPt< 6
25  vt <  50

24
Cruise/Acceleration
6    STPt< 9
25  vt <  50

25
Cruise/Acceleration
9    STPt< 12
25  vt <  50

27
Cruise/Acceleration
12  STPt< 18
25  vt <  50

28
Cruise/Acceleration
18  STPt< 24
25  vt <  50

29
Cruise/Acceleration
24  STPt< 30
25  vt <  50

30
Cruise/Acceleration
30  STPt
25  vt <  50

33
Cruise/Acceleration
STPt< 6
50  vt

35
Cruise/Acceleration
6    STPt< 12
50  vt

37
Cruise/Acceleration
12  STPt<18
50  vt

38
Cruise/Acceleration
18  STPt< 24
50  vt

39
Cruise/Acceleration
24  STPt< 30
50  vt

40
Cruise/Acceleration
30  STPt
50  vt

Start emission rates are also distinguished according to operating modes in MOVES. MOVES uses eight operating modes to classify starts according to different soak times, varying from a hot start (opMode 101) where the vehicle has been soaking for less than 6 minutes, to a cold start (opMode 108) where the vehicle has been soaking for more than 12 hours.

  Table 1-5. Operating modes for start emissions (as a function of soak time)
                                Operating Mode
Description
                                      101
Soak Time < 6 minutes
                                      102
6 minutes <= Soak Time < 30 minutes
                                      103
30 minutes <= Soak Time < 60 minutes
                                      104
60 minutes <= Soak Time < 90 minutes
                                      105
90 minutes <= Soak Time < 120 minutes
                                      106
120 minutes <= Soak Time < 360 minutes
                                      107
360 minutes <= Soak Time < 720 minutes
                                      108
720 minutes <= Soak Time

Extended idle exhaust and diesel APU exhaust are each modeled in MOVES with a single operating mode.
Vehicle Age
Emission rates for HC, CO, NOx and PM are differentiated by vehicle age. Currently, start and running emission rates for HC, CO, NOx and PM are stored in the "emissionratebyage" table by age group, meaning that different emission rates can be derived for different aged vehicles of the same model year, regulatory class, fuel type and operating mode.
MOVES uses six different age classes to model the age effects, as shown in Table 1-6. The effects of age on the emission rates are developed separately for gasoline and diesel vehicles. For diesel vehicles, we estimated the effects of tampering and mal-maintenance on emission rates as a function of age. We adopted this approach due to the lack of adequate data to directly estimate the deterioration for heavy-duty vehicles.  Based on surveys and studies, we developed estimates of frequencies and emission impacts of specific emission control component malfunctions, and then aggregated them to estimate the overall emissions effects for each pollutant.For gasoline vehicles, the age effects are estimated directly from the emissions data, or are adopted from light-duty deterioration as discussed in the text. 
                    Table 1-6. MOVES Age Group Definitions
ageGroupID
Lower bound (years)
Upper bound (years)
3
0
3
405
4
5
607
6
7
809
8
9
1014
10
14
1519
15
19
2099
20
~
Emission processes stored in the "EmissionRate" table do not distinguish emissions by age. Energy rates are stored in the "EmissionRate table." This table also includes HC, CO, NOx, PM , and ammonia (NH3) emissions from extended idle and auxiliary power units (APU), and nitrous oxide (N2O) from start and running emissions, tire and brake wear from running emissions. This report documents the HC, CO, NOx, and PM emissions from extended idle and APU usage, however the documentation of heavy-duty nitrous oxide and ammonia and tire and brake wear emission rates are documented in separate reports.

Heavy Duty Diesel Emissions
Running Exhaust Emissions
This section details our analysis of data to develop emission rates for heavy-duty diesel vehicles.  Four emission processes (running, extended idling, starts, and auxiliary power unit exhaust) are discussed.  Running Exhaust Emissions
MOVES running-exhaust emissions analysis requires accurate second-by-second measurements of emission rates and parameters that can be used to estimate the tractive power exerted by a vehicle. This sections describes how we analyzed continuous "second-by-second' heavy-duty diesel emissions data to develop emission rates applied within the predefined set of operating modes.  Stratification of the data sample and generation of the final MOVES emission factors were done according to the combination of regulatory class (shown in Table 1-1) and the model year group.  As mentioned, the emission rates were using scaled-tractive power (STP), rather than VSP.
Nitrogen Oxides (NOx)
For NOx rates, we stratified heavy-duty vehicles into the model year groups listed in Table 1-6  These groups were defined based on changes in NOx emissions standards and the outcome of the Heavy Duty Diesel Consent Decree, which required additional control of NOx emissions during highway driving for model years 1999 and later.  This measure is referred to as the "Not-to-Exceed" (NTE) limit.
  Table 2-1. Model year groups for NOx analysis based on emissions standards
Model year group
FTP standard (g/bhp-hr)
NTE limit (g/bhp-hr) 
Pre-1988
None
None
1988-1989
10.7
None
1990
6.0
None
1991-1997
5.0
None
1998
4.0
None
1999-2002
4.0
7.0 HHD; 5.0 other reg. classes
2003-2006
2.4
1.25 times the family emission level
2007-2009
1.2

2010+
0.2

Data Sources
In MOVES2010, we relied on two data sources for NOX emissions from HHD, MHD, and urban buses:
      ROVER.  This dataset includes measurements collected during on-road operation using the ROVER system, a portable emissions measurement system (PEMS) developed by the EPA.  The measurements were conducted by the U.S. Army Aberdeen Test Center on behalf of U.S. EPA:  This ongoing program started in October 2000.  Due to time constraints and data quality issues, we used only data collected from October 2003 through September 2007.  The data was compiled and reformatted for MOVES analysis by Sierra Research.  The process of analysis and rate development was performed by EPA.  The data we used represents approximately 1,400 hours of operation by 124 trucks and buses in model years 1999 through 2007.
      The vehicles were driven mainly over two routes:
             "Marathon" from Aberdeen, MD to Colorado and back along Interstate 70
             Loop around Aberdeen Proving Grounds in Maryland
      Consent Decree Testing.   These data were conducted by West Virginia University using the Mobile Emissions Measurement System (MEMS).[,]  This program was initiated as a result of the consent decree between the several heavy-duty engine manufacturers and the US government, requiring the manufacturers to test in-use trucks over the road.  Data was collected from 2001 through 2006.  The data we used represented approximately 1,100 hours of operation by 188 trucks in model years 1994 through 2003.  Trucks were heavily loaded and tested over numerous routes involving urban, suburban, and rural driving.  Several trucks were re-acquired and tested a second time after 2-3 years.  Data were collected at 5-Hz frequency, which we averaged around each second to convert the data to a 1.0-Hz basis.
However, since the release of MOVES2010, two additional sources of data have become available. One source comprises data collected during compliance evaluations for the 2004 and 2007 Heavy-Duty Diesel Motor Vehicle Engines Rule.  This dataset includes results for HHD, MHD and LHD vehicles.  The second source includes the results of a study of heavy-duty trucks in drayage service in and around the port of Houston (Houston Drayage).  Both programs are described in detail below.  
      Heavy-Duty Diesel In-Use testing (HDIU).  The in-use testing program for heavy-duty diesel vehicles was promulgated in June 2005 to monitor the emissions performance of the engines operated under a wide range of real world driving conditions, within the engine's useful life.  It requires each manufacturer of heavy-duty highway diesel engines to assess the in-use exhaust emissions from their engines using onboard, portable emissions measurement systems (PEMS) during typical operation while on the road.  The PEMS unit must meet the requirements of 40 CFR 1065 subpart J.  The in-use testing program began with a mandatory two-year pilot program for gaseous emissions in calendar years 2005 and 2006.  The fully enforceable program began in calendar year 2007 and is ongoing.  The vehicles selected for participation in the program are within the engine's useful life, and generally, five unique vehicles are selected for a given engine family.  The data available for use in MOVES2014 were collected during calendar years 2005 through 2010 and represent trucks manufactured in model years 2003 to 2009 (Table 2-2).  
      Houston Drayage Data.  In coordination with the Texas Commission on Environmental Quality (TCEQ), the Houston-Galveston Area Council (H-GAC), and the Port of Houston Authority (PHA), EPA conducted a study collecting emissions data from trucks in drayage service using portable emission measurement systems (PEMS) from December 2009 to March 2010.  The trucks studied were diesel-fueled, heavy-heavy-duty trucks used to transport containers, bulk and break-bulk goods to and from ports and intermodal rail yards to other locations.  These trucks conduct the majority of their travel on short-haul runs, repeatedly moving containers across fixed urban routes.  Note that only small fractions of trucks involved in drayage service are dedicated solely to this function, with most trucks spending large fractions of their time performing other types of short-haul service. No specific drive cycles were used and all PEMS testing was based on actual in-use loads and speeds.  
      
For MOVES2014, the HDIU and Houston Drayage data were analyzed to fulfill two objectives: 
      (1) to evaluate the rates in MOVES2010 and 
      (2) to be used as a new data source for updating the emission rates
         
Updating MOVES emission rates currently in use was considered when two conditions were met: (1) when MOVES2010 rates for a specific regulatory-class and model-year-group combination were not based on actual data (i.e., due to gaps in the coverage of ROVER and Consent-Decree testing data) and (2) when the comparisons between MOVES2010 and independent data show a clear indication of disagreement.   
From each data set, we used only tests we determined to be valid.  For ROVER dataset, due to time constraints, we eliminated all tests that indicated any reported problems, including GPS malfunctions, PEMS malfunctions, etc, whether or not they affected the actual emissions results.  For HDIU and Houston Drayage, the time-alignment was visually confirmed by comparing relevant time-series plots, such as exhaust mass-flow rate vs. CO2 concentration, and exhaust-mass flow rate vs. engine speed, as measured by the ECU.  Data was generally aligned within one second.  When an issue with the time-alignment was found, efforts were made to realign the data as much as possible.  As our own high-level check on the quality of PEMS and ECU output, we, then, eliminated any trip from ROVER, HDIU, and Houston Drayage where the Pearson correlation coefficient between CO2 (from PEMS) and engine power (from ECU) was less than 0.6.  In addition, data were excluded from the analysis when the vehicle speed was not available due to GPS and/or ECU malfunctions, when no exhaust flow was reported, and when a periodic zero correction was being performed on gas analyzers.   For the WVU MEMS data, WVU itself reported on test validity under the consent decree procedure and no additional detailed quality checks were performed by EPA.  Table 2-2 shows the total distribution of vehicles by model year group from the emissions test programs above, following evaluation of the validity of the data.

Table 2-2. Numbers of vehicles by model year group from the ROVER, WVU MEMS, HDIU, and Houston Drayage programs used for emission rate analysis
 

                               Regulatory Class
                                  Data Source
                                      MYG
                                      HHD
                                      MHD
                                      LHD
                                      BUS
                       ROVER and Consent Decree Testing
1991-1997
                                      19
                                       -
                                       -
                                       2

1998
                                      12
                                       -
                                       -
                                       -

1999-2002
                                      78
                                      30
                                       -
                                      25

2003-2006
                                      91
                                      32
                                       -
                                      19
                                     HDIU
2003-2006
                                      40
                                      25
                                      15
                                       -

2007-2009
                                      68
                                      71
                                      24
                                       -
                                Houston Drayage
1991-1997
                                       8
                                       -
                                       -
                                       -

1998
                                       1
                                       -
                                       -
                                       -

1999-2002
                                      10
                                       -
                                       -
                                       -

2003-2006
                                       8
                                       -
                                       -
                                       -

Calculate STP from 1-Hz data
With on-road testing, using vehicle speed and acceleration to estimate tractive power is not accurate given the effect of road grade and wind speed.  As a result, we needed to find an alternate approach. Therefore, we decided to use tractive power from engine data collected during operation.  We first identified the seconds in the data that the truck was either idling or braking based on acceleration and speed criteria shown in Table 1-4.  For all other operation, engine speed eng and torque eng from the ECU were used to determine engine power Peng, as shown in Equation 2-1.  Only torque values greater than zero were used so as to only include operation where the engine was performing work.
                                       
                                       
                                                                   Equation 2-1
We then determined the relationship between the power required at the wheels of the vehicle and the power required by the engine.  We first had to account for the losses due to accessory loads during operation.  These power loads are not subtracted in the engine torque values that are output from the engine control unit.  Heavy-duty trucks use accessories during operation.  Some accessories are engine-based and are required for operation.  These include the engine coolant pump, alternator, fuel pump, engine oil pump, and power steering.  Other accessories are required for vehicle operation, such as cooling fans to keep the powertrain cool and air compressors to improve braking.  The third type of accessories is discretionary, such as air conditioning, lights, and other electrical items used in the cab.  The calculation of the accessory load requirements is derived below.
We grouped the accessories into five categories:  cooling fan, air conditioning, engine accessories, alternator (to run electrical accessories), and air compressor.  We identified where the accessories were predominately used on a vehicle speed versus vehicle load map to properly allocate the loads.  For example, the cooling fan will be on at low vehicle speed where the forced vehicle cooling is low and at high vehicle loads where the engine requires additional cooling.  The air compressor is used mostly during braking operations; therefore it will have minimal load requirements at highway, or high, vehicle speeds.  Table 2-3 identifies the predominant accessory use within each of the vehicle speed and load areas.
At this point, we also translated the vehicle speed and engine load map into engine power levels.  The power levels were aggregated into low (green), medium (yellow) and high (red) as identified in Table 2-3.  Low power means the lowest third, medium is the middle third, and high is the highest third, of the engine's rated power.  For example, for an engine rated at 450 hp, the low power category would include operation between 0 and 150 hp, medium between 150 and 300 hp, and high between 300 and 450 hp.

Table 2-3. Accessory use as a function of speed and load ranges, coded by power level
                                       

We next estimated the power required when the accessory was "on" and percentage of time this occurred.  The majority of the load information and usage rates are based on information from "The Technology Roadmap for the 21st Century Truck."  
The total accessory load is equal to the power required to operate the accessory multiplied by the percent of time the accessory is in operation.  The total accessory load for a STP bin is equal to the sum of each accessory load.  The calculations are included in Appendix A.
The total accessory loads Ploss,acc listed below in Table 2-4 are subtracted from the engine power determined from Equation 2-1 to get net engine power available at the engine flywheel.  For LHD vehicles, we assumed negligible accessory losses.
                                          
          Table 2-4. Estimates of accessory load in kW by power range
                                 Engine power
                                      HDT
                                      MHD
                                   Urban Bus
                                      Low
                                      8.1
                                      6.6
                                     21.9
                                      Mid
                                      8.8
                                      7.0
                                     22.4
                                     High
                                     10.5
                                      7.8
                                     24.0
      
We then accounted for the driveline efficiency.  The driveline efficiency accounts for losses in the wheel bearings, differential, driveshaft, and transmission.  The efficiency values were determined through literature searches.  Driveline efficiency driveline varies with engine speed, vehicle speed, and vehicle power requirements.  Using sources available in the literature, we estimated an average value for driveline efficiency.[,][,][,][,][,][,][,][,]  Table 2-5 summarizes our findings. 
                                       
      Table 2-5. Driveline efficiencies found through literature research
                                       
Based on this research, we used a driveline efficiency of 90% for all HD regulatory classes.
                         Equation 2-2 shows the translation from engine power Peng to axle power Paxle.

                                       
                                       
                                              Equation 2-2

Finally, we scaled the axle power by a multiplicative factor fscale to fit light-duty operating-mode ranges. The LHD<= 14K, MHD, HHD, and Bus classes were scaled by 17.1, which is approximately the average running weight for all heavy-duty vehicles, and the LHD<= 10K trucks were scaled by 2.06, which is equivalent to the fleet-average mass of light commercial trucks in MOVES as previously discussed in Section 1.4 to obtain emission rates for LHD<= 10K that are consistent with the VSP-based operating modes for passenger trucks and light-commercial trucks.                         shows the conversion of axle power to scaled tractive power using the method explained above.
                                       
                                       
                                            Equation 1-1
                                       
We then constructed operating mode bins defined by STP and vehicle speed according to the methodology outlined earlier in MOVES development and described in Table 1-4.  The implementation of STP in MOVES for heavy-duty emission rates is the same as that of VSP for light-duty emission rates.  We will refer to the units of STP as scaled kW or skW.  
Calculate emission rates
Means
Emissions in the data set were reported in grams per second.  First, we averaged all the 1-Hz NOx emissions by vehicle and operating mode.  Then the emission rates were again averaged by regulatory class and model year group.  Data sets were assumed to be representative and each vehicle received the same weighting.  However, we averaged rates by vehicles first because we did not believe the amount of driving done by each truck was necessarily representative.  Equation 2-3 summarizes how we calculated the mean emission rate for each stratification group (i.e. model year group, regulatory class, and operating mode bin).
                                       
                                       
                                                                   Equation 2-3
                                       
where 
      nj     = the number of 1-Hz data points for each vehicle j,
      nveh = the total number of vehicles, 
      rp,j,i = the emission rate of pollutant p for vehicle j at second i,
       = the mean emission rate (meanBaseRate) for pollutant p.  
For NOx, we calculated a mean emission rate, denoted as the "meanBaseRate" in the MOVES emissionRateByAge table, for each combination of regulatory class, model year group, and operating mode bin combination.
Statistics
Estimates of uncertainty were calculated for all the emission rates.  Because the data represent subsets of points "clustered" by vehicle, we calculated and combined two variance components, representing "within-vehicle" and "between-vehicle" variances. First, we calculated the overall within-vehicle variance.  

                                       
                                       
                                                                   Equation 2-4
where
      = the variance within each vehicle, and 
      ntot = the total number of data points for all the vehicles.  
Then we calculated the between-vehicle variance (by source bin, age group, and operating mode) using the mean emission rates for individual vehicles () as shown in                      Equation 2-5.

                                       
                                            Equation 2-5

Then, we estimated the total variance by combining the within-vehicle and between-vehicle variances to get the standard error  (Equation 2-6) and dividing the standard error by the mean emission rate to get the coefficient-of-variation of the mean (Equation 2-7).
                                       
                                       
                                           Equation 2-6
                                          
                                       
                                       
                                           Equation 2-7
                                       
Heavy-Duty Trucks (HHD, MHD, Bus, and LHD not equipped with Lean NOx Traps)
Since the data only covered model years 1994 through 2009, we needed to develop a method to forecast emissions for future model years and back-cast emissions for past model years. For future model years (2010-and-later), we decreased the emission rates for all operating mode bins by a ratio proportional to the decrease in the applicable emissions standards. Starting in MY2010, the NOx standard for all heavy-duty trucks is 0.2 g/bhp-hr. We projected that almost all of these trucks will be using SCR after-treatment technology, which we assume to have a 90 percent NOx reduction efficiency from levels for MY2006 levels (2.4 g/bhp-hr), and thus, we estimated the rates for model year 2010 and later by decreasing MY2003-2006 rates by 90 percent.
For model year groups 1988-1989 and 1990, we increased the 1991-1997 model year group emission rates by a factor proportional to the increase of the certification levels. The certification levels came from analysis conducted for MOBILE6. We applied the 1988-1989 emission rates to model years 1987 and earlier.
For MHD and HHD trucks, the maximum operating mode (opModeID = 40) represents a tractive power greater than 513 kW (STP= 30 skW x 17.1). This value exceeds the capacity of most HHD vehicles, and MHD vehicles and buses exert even lower levels. As a result, data are very limited in these modes.  
To estimate rates in the modes beyond the ranges of available data, we linearly extrapolated the rates from the highest operating mode in each speed range where significant data were collected for each model year group.  In most cases, this mode was mode 16 for the lowest speed range, 27 or 28 for the middle speed range, and 37 or 38 for the highest speed range.  For each of these operating modes, work-specific emissions factors (g/kW-hr) were calculated using the midpoint STP.  Then, these emissions factors were multiplied by the midpoint STP of the higher operating modes (e.g. modes 39 and 40 for speed>50mph) to input emission rates for the modes lacking data.  For the highest bins in each speed range, a "midpoint" STP of 33 skW (564.3 kW) was used.
For model year 1998, data existed for HHD trucks but not  buses.  In these cases, the ratio of emission rates between the Bus regulatory class and HHD regulatory class from the 1999-2002 model year group was used to calculate rates for the Buses by multiplying that ratio by the existing HHD emission rates for the corresponding model year group, as shown in Equation 2-8. 
Bus rates1998=HHD rates1998HHD rates1999-2002xBus rates1999-2002
                                                                   Equation 2-8

Pickup trucks equipped with Lean NOx Traps
To meet NOx emissions standards for the 2010 model year, the use of after-treatment will probably be needed.  For example, Cummins decided to use after-treatment starting in 2007 in engines designed to meet the 2010 standard and used in vehicles such as the Dodge Ram.  The technology adopted for this purpose was the "Lean NOx Trap" (LNT).  This technology allows for the storage of NOx during fuel-lean operation and conversion of stored NOx into N2 and H2O during brief periods of fuel-rich operation.  In addition, to meet particulate standards in MY 2007 and later, heavy-duty vehicles are equipped with diesel particulate filters (DPF).  At regular intervals, the DPF must be regenerated to remove and combust accumulated PM to relieve backpressure and ensure proper engine operation.  This step requires high exhaust temperatures.  However, these conditions adversely affect the LNT's NOx storage ability, resulting in elevated NOx emissions. 
In 2007, EPA acquired a truck equipped with LNT and DPF and performed local on-road measurements using portable instrumentation and chassis dynamometer tests.  We distinguished regimes of PM regeneration from normal operation based on operating characteristics, such as exhaust temperature, air-fuel ratio, and ECU signals.  During the testing conducted on-road with onboard emission measurement and on the chassis dynamometer, we observed a PM regeneration frequency of approximately 10 percent of the operating time. We will look for opportunities to update this assumption based on any additional information that becomes available.
Emissions from this vehicle were not directly used to calculate emission rates. Rather, adjustments were made from the 2003-2006 model year group to develop emission rates for this model year group and regulatory class. During PM regeneration, we assumed that the LNT did not reduce emissions from 2003-2006 levels. During all other times, we assumed that emissions were reduced by 90 percent from 2003-2006 levels. 
Because we assume that LNT-equipped trucks account for about 25 percent of the LHDDT market, we again weighted the rates for the two LHD regulatory classes for model years 2007 and later.  For MY 2007-09, we assume that the remaining 75 percent of LHD diesel trucks will not have after-treatment and will exhibit the 2007-2009 model year emission rates described earlier in this section.  Starting in MY2010, we assume that the remaining 75 percent of LHD diesel trucks are equipped with SCR, and exhibit 90 percent NOx reductions from 2006 levels, described in Section 2.1.1.3.3.  
Incorporation of Tier 3 Standards
 The Tier-3 standards will affect "medium-duty" (MD) diesel vehicles, i.e., vehicles in regulatory classes LHD<=10k and LHD<=14k (regClassID = 40, 41, respectively).  However, reductions in emission rates attributable to the introduction of Tier 3 standards are applied only to rates for NOx. 
For HC and CO emissions, the emission rates currently in MOVES imply levels on the FTP cycle substantially below the Tier 3 HC and CO standards.  For example, when MOVES rates are combined to estimate a simulated FTP estimate for NMHC, the result is a rate of approximately 0.05 grams per mile, while the simulated FTP estimate for CO is less than 1.0 gram/mile.  Consequently, we assumed that no additional reductions in HC and CO emissions would be realized through implementation of the Tier 3 standards on MD diesel vehicles.
By contrast, we estimate that the Tier 3 NOx standard will results in a reduction emissions from  diesel vehicles in Classes 2b and 3.  Data on current NOx emissions are limited, as there is little in-use data on MY 2010 and 2011 vehicles using selective catalytic reduction as a NOx control strategy, we used a proportional approach to estimate the reductions related to Tier 3, reducing NOX in proportion to the change in the emission standard.  Because emission standards tend to impact start and running emissions differently, we applied a greater portion of the reduction to running emissions and a smaller reduction to start emissions.  These reductions were phased-in over the same schedule as for gasoline vehicles, as detailed in Table 2-6.  
 
Table 2-6.  Phase-in Assumptions for Tier-3 Standards for medium-duty diesel vehicles.
                                  Model Year
                             Phase-in fraction (%)
                    Reduction in Running Emission Rate (%)
                     Reduction in Start Emission Rate (%)
                                     2017
                                       0
                                       0
                                       0
                                     2018
                                      38
                                      23
                                       9
                                     2019
                                      54
                                      33
                                      12
                                     2020
                                      69
                                      42
                                      16
                                     2021
                                      85
                                      52
                                      19
                                     2022
                                      100
                                     61.5
                                      23

In generating the reduced rates for running operation, the starting point was a subset of rates for MY2017, extracted from a previous database, and taken to represent the pre-Tier-3 baseline. 
Then ending point, representing full Tier-3 control, was model year 2022.  These rates were calculated by multiplying the rates for MY2017 by a fraction of 0.3855.  This fraction reflects application of the reduction fraction for running rates in MY2022 as shown in Table 2-6.    
Rates in MY 2018 and later were calculated as weighted averages of the values for MY2017 and MY2022, using the same fractions applied to gasoline vehicles, as shown in Table 3-16 (page 93) and Equation 3-2 (page 92). Note that these calculations were applied to running rates for the LHD<=10K regulatory class (based on VSP) and to those for the LHD<=14k regulatory class (based on STP).  Examples of rates for selected operating modes are shown in Figure 2-1.  Note that on the logarithmic scale used, the parallelism of the trends shows that the proportional reductions are identical for both regulatory classes.
As with light-duty vehicles, reductions in standards are assumed to be associated with an increase in the regulatory useful life. An increase in the useful life is interpreted as an improvement in durability, which is expressed through a delay in deterioration effects. To express this effect, rates estimated for the 0-3 yr ageGroup are replicated to the 4-5 year ageGroup, i.e., the onset of deterioration is delayed until the onset of the 6-7 year ageGroup.  This effect is realized partially for model years 2018-2020 and fully in 2021.

Figure 2-1.  NOx:  Emission rates for running-exhaust operation in selected operating modes vs. model year, for two light-heavy-duty regulatory classes (LOGARITHMIC SCALE).
                                       

Figure 2-2.  NOx:  :  Emission rates for running-exhaust operation in a single operating mode (27) vs. age, for two light-heavy-duty regulatory classes (LINEAR SCALE).
                                       
Summary
Table 2-6 summarizes the methods used to estimate emission rates for each regulatory - class/model-year-group combination. The emission rates based on the analysis of ROVER and Consent Decree testing data were used to populate the rates in MOVES2010.  For MOVES2014, we made a decision to update the emission rates, for MYG2007-2009 for HHD and MYG2003-2006 for LHD, based on the comparison of the emission rates in MOVES2010 to HDIU and Houston Drayage data, discussed in Section 2.1.1.5.  For all other combinations of regulatory classes and model year groups, the rates from MOVES2010 were retained in MOVES2014.

Table 2-7. Summary of methods for heavy-duty diesel NOx emission rate development for each regulatory class and model year group
                               Model year group
                                      HHD
                                      MHD
                                   Urban Bus
                             LHD34 and LHD<=14K
                                  LHD<=10K
                                   1960-1989
      HHD 1991-1997 rates proportioned to ratio of certification levels 
                               Same rates as HHD
   Bus 1991-1997 rates proportioned using ratio of HHD certification levels 
                               Same rates as HHD
    LHD <=10K 1991-1993 rates proportioned to LHD certification levels 
                                     1990
           HHD 1991-1997 rates proportioned to certification levels 
                               Same rates as HHD
Bus 1991-1997 rates proportioned using ratio of HHD certification levels from 1991-1997
                               Same rates as HHD
    LHD <=10K 1991-1993 rates proportioned to LHD certification levels 
                                   1991-1997
                              Data analysis[1,3]
                               Same rates as HHD
                               Data analysis[1]
                               Same rates as HHD
               Proportioned to 1998 FTP standards per Table 2-1
                                     1998
                              Data analysis[1,3]
                               Same rates as HHD
Bus 1999-2002 rates proportioned using ratio of  HHD 1998 rates to HHD 1999-2002 rates
                               Same rates as HHD
                            Same rates as 1999-2002
                                   1999-2002
                              Data analysis[1,3]
                               Data analysis[1]
                               Data analysis[1]
                              Same rates as MHD 
                     MHD engine data with 2.06 mass factor
                                   2003-2006
                              Data analysis[1,3]
                              Data analysis[1,3]
                               Data analysis[1]
                               Data analysis[2]
                    Data analysis with 2.06 mass factor[2]
                                   2007-2009
                               Data analysis[2]
           Proportioned to 2003-2006 FTP standards per Table 2-1[3]
       Bus 2003-2006 rates proportioned to   FTP standards per Table 2-1
            Proportioned to 2003-2006 FTP standards per Table 2-1[3]
             Data (LNT), and same rates as 2003-2006 (non-LNT)[3]
                                  2010 -2016
        HHD 2003-2006 rates proportioned to FTP standards per Table 2-1
        MHD 2003-2006 rates proportioned to FTP standards per Table 2-1
        Bus 2003-2006 rates proportioned to FTP standards per Table 2-1
          LHD34 2003-2006 proportioned to FTP standards per Table 2-1
       LHD<10K 2003-2006 proportioned to FTP standards per Table 2-1
                                   2017-2050
                             Same as HHD 2010-2016
                             Same as MHD 2010-2016
                             Same as Bus 2010-2016
                       Proportioned to Tier 3 standards
                       Proportioned to Tier 3 standards
      1Analysis based on ROVER and Consent Decree testing data; 2 Analysis based on HDIU data; 3 Confirmed by HDIU and Houston Drayage data

An important point to note is that we did not project increases in NOx emissions with age for vehicles not equipped with NOx after-treatment technology (largely 2009 model year and earlier).  This is because of a few reasons:
     The WVU MEMS data did not show an increase in NOx emissions with odometer (and consequently, age) during or following the regulatory useful life.  Since the trucks in this program were collected from in-use fleets, we do not believe that these trucks were necessarily biased toward cleaner engines.
     Manufacturers often certify zero or low deterioration factors.
We estimated tampering and mal-maintenance effects on NOx emissions to be small compared to other pollutants  -  around a 10 percent increase in NOx over the useful life of the engine.  Our tampering and mal-maintenance estimation methods are discussed below and detailed in Appendix 
Tampering and Mal-maintenance
Table 2-7 shows the estimated aggregate NOx emissions increases due to T&M.  It also shows the values that we actually used for MOVES emission rates.  As previously mentioned, we assumed that in engines not equipped with aftertreatment, NOx does not increase due to T&M or deterioration.
Table 2-8. Fleet-average NOx emissions increases from zero-mile levels over the useful life due to tampering and mal-maintenance
Model years
NOx increase from T&M analysis [%]
NOx increase in MOVES [%]
1994-1997
10
0
1999-2002
14
0
2003-2006
9
0
2007-2009
11
0
2010-2012 SCR
77
77
2010-2012 LNT
64
64
2013+
58
58

As described in Appendix B, these emissions increases are combined with information in Table B-2 to estimate the emissions increase for each age group prior to the end of the useful life for each regulatory class.  With the introduction of aftertreatment systems to meet regulatory requirements for MY 2010 and later, EPA expects tampering and mal-maintenance to substantially increase emissions over time compared to the zero-mile level.  Though 77 percent may appear to be a large increase in fleet-average emissions over time, it should be noted that the 2010 model year standard (0.2 g/bhp-hr) is about 83 percent lower than the 2009 model year effective standard (1.2 g/bhp-hr).  This still yields a substantial reduction of about 71 percent from 2009 zero-mile levels to 2010 fully deteriorated levels.  As more data becomes available for future model years, we hope to update these tampering and mal-maintenance and overall aging effects.  

Defeat Device and Low-NOx Rebuilds
The default emission rates in MOVES for model years 1991 through 1998 are intended to include the effects of defeat devices as well as the benefits of heavy-duty low-NOx rebuilds (commonly called reflash) that occurred as the result of the heavy-duty diesel consent decree.  Reflashes reduce NOx emissions on these engines by reconfiguring certain engine calibrations, such as fuel injection timing.  The MOVES database also includes a set of alternate emission rates for model years 1991 through 1998 assuming a hypothetical fully reflashed fleet.  
Since defeat devices were in effect mostly during highway or steady cruising operation, we assumed that NOx emissions were elevated for only the top two speed ranges in the running exhaust operating modes (>25mph).  To modify the relevant emission rates to represent reflash programs, we first calculated the ratios from the emission rates in modes 27 and 37 to that for opMode 16, for model year 1999 (the first model year with not-to-exceed emission limits).  We then multiplied the MY 1999 ratios by the  emission rates in mode 16 for model years 1991 through 1998,  to get estimated "reflashed" emission rates for operating modes 27 and 37.  This step is described in Equation 2-9 and Equation 2-11. To estimated "reflashed" rates in the remaining operating modes, we multiplied the reflashed rates by ratios of the remaining operating modes to mode 27 for MY1991-98, as shown in Equation 2-10 and Equation 2-12.

                          Operating modes (OM) 21-30
                                       
                                       
  Equation 2-9

Equation 2-10
                                       

                                                                               
                          Operating modes (OM) 31-40
                                       
                                       

Equation 2-11
                                       
                                       

Equation 2-12
                                                                               

The default emission rates were also slightly adjusted for age for the consent decree model years.  An EPA assessment shows that about 20 percent of all vehicles eligible for reflash had been reflashed by the end of 2008.  We assumed that vehicles were receiving the reflashes after the heavy-duty diesel consent decree (post 1999/2000 calendar year) steadily, such that in 2008, about 20 percent had been reflashed.  We approximated a linear increase in reflash rate from age zero.
Sample results
The charts in this sub-section show examples of the emission rates that resulted from the analysis of the data described in Section 2.1.1.1.  Not all rates are shown; the intention is to illustrate the most common trends and hole-filling results.  
Figure 2-1 and Figure 2-2 show that NOx emission rates increase with STP for HHD trucks.  Figure 2-3 adds the MHD and bus regulatory classes, with the error bars removed for clarity.  As expected, the emissions increase with power, with the lowest emissions occurring in the idling/coasting/braking bins.  
Figure 2-3. Trends in NOx Emissions by operating mode from HHD trucks for model year 2002. Error bars represent the 95% confidence interval of the mean.
                                       
                                       
Figure 2-4. Trends in NOx Emissions by operating mode from HHD trucks for model year 2007. Error bars represent the 95% confidence interval of the mean.
                                       

The highest operating modes in each speed range will rarely be attained due to the power limitations of heavy-duty vehicles, but are included in the figures (and in MOVES) for completeness.  Nearly all of the activity occurs in modes 0, 1, 11-16, 21-28, and 33-38, with activity for buses and MHD vehicles usually occurring over an even smaller range.  In some model year groups, the MHD and HHD classes use the same rates, based on lack of significant differences between those two classes' emission rates.
Figure 2-5. Trends in NOx emissions by operating mode from LHD<=14K, LHD45, MHD, HHD, and bus regulatory classes for model year 2002. LHD<=14K, LHD45, and MHD have the same NOx zero-mile NOx emission rates. 
                                       

The effects of model year, representing a rough surrogate for technology or standards, can be seen in Figure 2-4, which shows decreasing NOx rates by model year group for a sample operating mode (#24) for HHD trucks.  Other regulatory classes show similar trends.  The rates in this chart were derived with a combination of data analysis (model years 1991 through 2009) and hole filling.  The trends in the data are expected, since the model year groups were formed on the basis of NOx standards.  Increasingly stringent emissions standards have caused NOx emissions to decrease significantly.
                                       
Figure 2-6. Trends in NOx by model year for HHD trucks in operating mode 24. Error bars represent the 95% confidence interval of the mean.
                                       
                                       

Age effects were only implemented for after-treatment-equipped trucks (mostly model year 2010 and later) based on an analysis of tampering and mal-maintenance effects. Due to faster mileage accumulation, the heavy-heavy duty trucks reach their maximum emission at the youngest ages, as shown in Figure 2-5. Relative Standard Errors (based on coefficients-of-variation for means) from previous model year groups were used to estimate uncertainties for MY 2010.

Figure 2-7. Modeled NOx trends by age for model year 2010 for operating mode 24 for MHD, HHD, and Urban Bus regulatory classes for model year 2002. Error bars represent the 95% confidence interval of the mean.
                                       
                                       
Figure 2-6 and Figure 2-7 shows the mean emission rates for LHD<= 10K trucks for model years 2003-2006 and 2007-2009, respectively. The estimated uncertainties are greater than for the other heavy-duty regulatory classes, since there were fewer vehicles in our test data.  As described previously, model years 2007-2009 vehicles includes vehicles with LNTs (with NOx increases during PM regeneration) and vehicles without any aftertreatment.  

Figure 2-8. Mean NOx rates by operating mode for model years 2003-2006 LHD<=10K (RegClass 40) trucks age 0-3. Error bars represent the 95% confidence interval of the mean.
                                       
                                       
Figure 2-9. Mean NOx rates by operating mode for model years 2007-2009 LHD<=10K trucks age 0-3. Error bars represent the 95% confidence interval of the mean.
                                       
                                       
                                       
Evaluation of NOx Emission Rates in MOVES2010
This section presents the results from the efforts to verify the NOx emission rates in MOVES2010 by comparing the rates in the database to the emissions data from the Heavy Duty In-Use and Houston Drayage data programs.  The HDIU data includes results for HHD, MHD, and LHD trucks, whereas the Houston Drayage data only includes HHD trucks.  
As discussed in Section Data Sources, HDIU and Houston Drayage data have become available after the MOVES2010 release and have served two purposes  -  to evaluate the rates in MOVES2010 and to be used as a new data source for updating existing emission rates.  The emission rates for a regulatory class and model year group combination were considered for an update if:
   1) MOVES2010 rates were not based on actual data, and 
   2) the comparison to independent data shows a clear indication of disagreement.

Heavy-Heavy Duty Trucks
Figure 2-8 through Figure 2-10 show that MOVES2010 rates for pre-2003 model years are generally in good agreement with the Houston Drayage data and within the range of uncertainty of means calculated from these data.  The error bars represent the 95% confidence intervals of the mean.  MOVES rate is lower in the high speed operating modes (33 and above) compared to 1998 model year trucks (Figure 2-9).  However, only a single truck is represented in the Houston Drayage data. As expected, the drayage fleet typically did not reach the high-speed/high-power operating modes (operating modes 28-30 and 38-40) during normal operation.

Figure 2-10. Comparison of Means: MOVES emission rates vs. Houston Drayage Data (n=8) for model years 1991-1997 HHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       
                                       
Figure 2-11. Comparison of Means: MOVES emission rates vs. Houston Drayage Data (n=1) for model year 1998 HHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

Figure 2-12.  Comparison of Means: MOVES emission rates vs. Houston Drayage Data (n=10) for model year 1999-2002 HHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

In Figure 2-11 and Figure 2-12, MOVES rates for model years 2003-2006 are compared to results from the Houston Drayage and HDIU datasets, respectively. Although MOVES' rates for middle and high speed operating modes are lower, it is within the 95% confidence intervals of the mean of Houston Drayage data in Figure 2-11. When compared to HDIU data in Figure 2-12, MOVES is generally within the variability of the data except for the low speed operating modes.  Although both comparisons showed that MOVES rates are slightly lower, since the rates in MOVES2010 for model years 2003-2006 were also based on the analysis of the testing data (ROVER and Consent Degree Testing), no change was made to the rates in MOVES2014.
Figure 2-13.  Comparison of Means: MOVES emission rates vs. Houston Drayage Data (n=8) for model year 2003-2006 HHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

Figure 2-14. Comparison of Means: MOVES rates vs. HDIU (n=40) for model years 2003-2006 HHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

In the MOVES2010 database, rates for model years 2007-2009 were forecasted from those for MYG 2003-2006 based on the ratio of emissions standards for these two model-year groups, as described in Section 2.1.1.3.3. This approach was adopted in view of the fact that neither of the two datasets used at the time (ROVER and Consent-Decree) included data for trucks in this model-year group. However, the availability of the HDIU dataset makes it possible to compare the projected rates to a set of relevant measurements. Figure 2-13 shows that the MOVES rates are lower than corresponding means from the HDIU data and are generally outside the uncertainty of these means across operating modes. Because the rates for this model year group met the two conditions described above in Section 2.1.1.5, this subset of rates was updated in MOVES2014 on the basis of HDIU data.

Figure 2-15. Comparison of Means: MOVES rates vs. HDIU (n=68) for model years 2007-2009 HHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

Medium-Heavy Duty Trucks
Figure 2-14. and Figure 2-15 show that MOVES rates for MHD trucks compare well with the HDIU data for both model years groups 2003-2006 and 2007-2009.  The data is generally scarce in high-power operation modes, and thus, no 95% confidence interval was calculated.  The comparisons validated the MOVES2010 rates for MHD trucks, and no change was made in MOVES2014.

Figure 2-16. Comparison of Means: MOVES rates vs. HDIU (n=25) for model years 2003-2006 MHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

Figure 2-17. Comparison of Means: MOVES rates vs. HDIU (n=71) for model years 2007-2009 MHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

Light-Heavy Duty Trucks
In MOVES2010, the LHD rates were not based on actual measurements  -  they were scaled from MHD rates and forecast based on standards, for model years 2003-2006 and 2007-2009, respectively, as described in Sections 2.1.1.3.3 and 2.1.1.3.4.  The comparison to HDIU data for model years 2003-2006 (Figure 2-16) shows that existing MOVES rates are generally higher than the HDIU results.  Thus, the LHD rates for model years 2003-2006 were updated based on HDIU data in MOVES2014. In contrast, MOVES compares well with the HDIU data for model years 2007-2009 (Equation 2-18), and thus, MOVES2010 rates for this model-year group were retained in MOVES2014.

Figure 2-18. Comparison of Means: MOVES rates vs. HDIU (n=15) for model years 2003-2006 LHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       
                                       

Figure 2-19. Comparison of Means: MOVES rates vs. HDIU (n=24) for model years 2007-2009 LHD trucks. Error bars represent the 95% confidence interval of the mean.
                                       

Particulate Matter (PM)
In this section, particulate matter emissions refers to particles emitted from heavy-duty engines which have a mean diameter less than 2.5 microns, known as PM2.5.  Conventional diesel particulate matter are primarily carbonaceous, measured by elemental carbon (EC) and organic carbon (OC). Particles also contain a complex mixture of metals, elements, and other ions, including sulfate. The total PM2.5 emission rates are typically filter-based, which measure the mass of all the chemical components in the particle-phase. As described above for NOx, the heavy-duty diesel PM emission rates in MOVES are a function of: (1) source bin, (2) operating mode, and (3) age group.   
We classified the data into the following model year groups for purposes of emission rate development.  These groups are generally based on the introduction of emissions standards for heavy-duty diesel engines.  They also serve as a surrogate for continually advancing emission control technology on heavy-duty engines.   Table 2-8 shows the model year group range and the applicable brake-specific emissions standards. 

Table 2-9. Model year groups used for analysis based on the PM emissions standard
                            Model Year Group Range
                            PM Standard [g/bhp-hr]
                                   1960-1987
                          No transient cycle standard
                                   1988-1990
                                     0.60
                                   1991-1993
                                     0.25
                                   1994-1997
                                     0.10
                                   1998-2006
                                     0.10
                                     2007+
                                     0.01

Data Sources
All of the data used to develop the MOVES PM2.5 emission rates was generated in the CRC E-55/59 research program.  The following description by Dr. Ying Hsu and Maureen Mullen of E. H. Pechan, in the "Compilation of Diesel Emissions Speciation Data  -  Final Report" provides a good summary of the program.  It is reproduced in the following paragraphs immediately below:  
 
The objective of the CRC E55/59 test program was to improve the understanding of the California heavy-duty vehicle emissions inventory by obtaining emissions from a representative vehicle fleet, and to include unregulated emissions measured for a subset of the tested fleet.  The sponsors of this project include CARB, EPA, Engine Manufacturers Association, DOE/NREL, and SCAQMD.  The project consisted of four segments, designated as Phases 1, 1.5, 2, and 3.  Seventy-five vehicles were recruited in total for the program, and recruitment covered the model year range of 1974 through 2004. The number and types of vehicles tested in each phase are as follows:

:: Phase 1: 	25 heavy heavy-duty (HHD) diesel trucks 
:: Phase 1.5: 	13 HHD diesel trucks
      :: Phase 2: 	10 HHD diesel trucks, 7 medium heavy-duty (MHD) diesel trucks,				  2 MHD gasoline trucks
      :: Phase 3: 		  9 MHD diesel, 8 HHD diesel, and 2 MHD gasoline
The vehicles tested in this study were procured in the Los Angeles area, based on model years specified by the sponsors and by engine types determined from a survey. WVU measured regulated emissions data from these vehicles and gathered emissions samples. Emission samples from a subset of the vehicles were analyzed by Desert Research Institute for chemical species detail. The California Trucking Association assisted in the selection of vehicles to be included in this study. Speciation data were obtained from a total of nine different vehicles.   Emissions were measured using WVU's Transportable Heavy-Duty Vehicle Emissions Testing Laboratory. The laboratory employed a chassis dynamometer, with flywheels and eddy-current power absorbers, a full-scale dilution tunnel, heated probes and sample lines and research grade gas analyzers. PM was measured gravimetrically. Additional sampling ports on the dilution tunnel supplied dilute exhaust for capturing unregulated species and PM size fractions. Background data for gaseous emissions were gathered for each vehicle test and separate tests were performed to capture background samples of PM and unregulated species.  In addition, a sample of the vehicles received Tapered Element Oscillating Microbalance (TEOM) measurement of real time particulate emissions.

The HHDDTs were tested under unladen, 56,000 lb, and 30,000 lb truck load weights. The driving cycles used for the HHDDT testing included:
      :: AC50/80;
      :: UDDS;
      :: Five modes of an HHDDT test schedule proposed by CARB: Idle, Creep, Transient, Cruise, and HHDDT_S (a high speed cruise mode of shortened duration)
      :: The U.S. EPA transient test
The proposed CARB HHDDT test cycle is based on California truck activity data, and was developed to improve the accuracy of emissions inventories. It should be noted that the transient portion of this proposed CARB test schedule is similar but not the same as the EPA certification transient test.

The tables below provide a greater detail of the data used in the analysis.  Vehicles counts are provided by number of vehicles, number of tests, model year group and regulatory class (46 = MHD, 47=HHD) in Table 2-9.  

 Table 2-10. Vehicle and Test Counts by Regulatory Class and Model Year Group
Regulatory Class
Model Year Group
Number of tests
Number of vehicles
MHD

1960 - 1987
82
7

1988 - 1990
39
5

1991 - 1993
22
2

1994 - 1997
39
4

1998 - 2006
43
5

2007 +
0
0
HHD
1960 - 1987
31
6

1988 - 1990
7
2

1991 - 1993
14
2

1994 - 1997
22
5

1998 - 2006
171
18

2007 +
0
0

Counts of tests are provided by test cycle in Table 2-10.
                 Table 2-11. Vehicle Test Counts by Test Cycle
Test Cycle 
                                Number of tests
CARB-T
                                      71
CARB-R
                                      66
CARB-I
                                      42
UDDS_W
                                      65
AC5080
                                      42
CARB-C
                                      24
CARBCL
                                      34
MHDTCS
                                      63
MHDTLO
                                      23
MHDTHI
                                      24
MHDTCR
                                      29

Analysis
Calculate STP in 1-hz data
Within source bins, data was further sub-classified on the basis of operating mode. For motor vehicles, 23 operating modes are defined in terms of scaled tractive power (STP), vehicle speed and vehicle acceleration.  These modes are defined above in Table 1-4.
The first step in assigning operating mode is to calculate scaled tractive power (STP) for each emissions measurement.  At a given time t, the instantaneous STPt represents the vehicle's tractive power scaled by a constant factor. STP is calculated as a third-order polynomial in speed, with additional terms describing acceleration and road-grade effects. The coefficients for this expression, often called road load coefficients, factor in the tire rolling resistance, aerodynamic drag, and friction losses in the drivetrain.  We calculated STP using Equation 2-13 (which is the same as Equation 1-2 with grade = 0):
                                       
                                       
                                       
                                           Equation 2-13
                                       
where
    A = the rolling resistance coefficient [kWsec/m],
    B = the rotational resistance coefficient [kWsec[2]/m[2]],
    C = the aerodynamic drag coefficient [kWsec[3]/m[3]],
    m = mass of individual test vehicle [metric ton],
    fscale = fixed mass factor (see Table 1-3),
    vt = instantaneous vehicle velocity at time t [m/s],
    at = instantaneous vehicle acceleration [m/s[2]]
                                       
The values of coefficients A, B, and C are the road load coefficients pertaining to the heavy-duty vehicles as determined through previous analyses for EPA's Physical Emission Rate Estimator (PERE). This method of calculating STP calculates tractive power using the same equation used to calculate vehicle-specific power (VSP) in the development of emission rates for light-duty vehicles except that the scaling factor is used in the denominator, instead of the actual test weights of individual vehicles.   
Note that this approach differs from that the NOX emission rates analysis described in Section 2.1.1.2, since the particulate data was collected on a chassis dynamometer from vehicles lacking electronic control units (ECU). We have not formally compared the results of the two methods of calculating STP. However, on average, we did find the operating-mode distributions to be similar between the two calculation methods for a given vehicle type.  For example, we found that the maximum STP in each speed range was approximately the same.
Compute Normalized TEOM Readings
The TEOM readings were obtained for a subset of tests in the E-55/59 test program. Only 29 vehicles had a full complement of 1-hz TEOM measurements. However, the continuous particulate values were modeled for the remaining vehicles by West Virginia University, and results were provided to EPA. In the end, a total of 56 vehicles (out of a total of 75) and 470 tests were used in the analysis out of a possible 75 vehicles. Vehicles and tests were excluded if the total TEOM PM2.5 reading was negative or zero, or if corresponding full-cycle filter masses were not available. Table 2-11 provides vehicle and test counts by vehicle class and model year.  The HDDV6 and HDDV7 groups were combined in the table because there were only seven HDDV6 vehicles in the study.

    Table 2-12. Vehicle and Test Counts by Heavy-Duty Class and Model Year
Model Year
                                    HDDV6/7
                                     HDDV8

                                 No. Vehicles
                                   No. Tests
                                 No. Vehicles
                                   No. Tests
1969
                                       -
                                       -
                                       1
                                       6
1974
                                       1
                                      10
                                       -
                                       -
1975
                                       -
                                       -
                                       2
                                      10
1978
                                       -
                                       -
                                       1
                                       5
1982
                                       1
                                       5
                                       -
                                       -
1983
                                       1
                                      10
                                       1
                                       6
1985
                                       1
                                      28
                                       1
                                      10
1986
                                       1
                                       3
                                       1
                                       4
1989
                                       2
                                      11
                                       1
                                       4
1990
                                       1
                                      12
                                       1
                                       3
1992
                                       1
                                      11
                                       1
                                      11
1993
                                       1
                                      11
                                       1
                                       3
1994
                                       1
                                       9
                                       3
                                      15
1995
                                       2
                                      24
                                       3
                                      13
1998
                                       2
                                      20
                                       3
                                      28
1999
                                       -
                                       -
                                       3
                                      43
2000
                                       2
                                      18
                                       5
                                      44
2001
                                       1
                                       5
                                       2
                                      21
2004
                                       -
                                       -
                                       4
                                      29
2005
                                       -
                                       -
                                       1
                                       6

Since the development of MOVES emission rates is cycle independent, all available cycles / tests which met the above requirements were utilized. As a result, 488,881 seconds of TEOM data were used. The process required that each individual second by second TEOM rate be normalized to its corresponding full-cycle filter mass, available for each combination of vehicle and test.  This step was necessary because individual TEOM measurements are highly uncertain and vary widely in terms of magnitude (extreme positive and negative absolute readings can occur). The equation below shows the normalization process for a particular one second TEOM measurement.

                                       
                                       
                                                                  Equation 2-14
  Where
      i = an individual 1-Hz measurement (g/sec),
      j = an individual test on an individual vehicle,
      PMTEOM,j,i = an individual TEOM measurement on vehicle j at second i,
      PMfilter,j  = the Total PM2.5 filter mass on  j,
      PMnormalized,i,j = an estimated continuous emission result (PM2.5) emission result on vehicle j at second i.
Kinsey et al. (2006)  demonstrated that time-integrated TEOM measurements compare well with gravimetric filter measurements of diesel-generated particulate matter.
Compute Average Normalized TEOM measures by MOVES Bin
After normalization, the data were classified by regulatory class, model-year group and the 23 operating modes. Mean average results, sample sizes and standard deviation statistics for PM2.5 emission values were computed in terms of g/hour for each mode. In cases where the vehicle and TEOM samples were sufficient for a given mode, these mean values were adopted as the MOVES emission rates for total PM2.5. In cases of insufficient data for particular modes, a regression technique was utilized to impute missing values.    
Hole filling and Forecasting
Missing operating modes
Detailed in Appendix D, a log-linear regression was performed on the existing PM data against STP to fill in emission rates for missing operating mode bins. Similar to the NOx rates, emission rates were extrapolated for the highest STP operating modes.
Other Regulatory Classes
The TEOM data was only available in quantity for MHD and HHD classes. There were no data available for the LHD or bus classes. The Urban Bus (regulatory class 48) emission rates were proportioned to HHD rates according to differences in the PM standards.  
Because the certification standards in terms of brake horsepower-hour (bhp-hr) are the same for all of the heavy-duty engines, the emission rate of LHD<=14K and LHD45 is assumed to be equivalent to the MHD emission rate. 
The emission rates of LHD<= 10K (regulatory class 40) need to be compatible with VSP-based operating modes as discussed in Section 1.2. In Draft MOVES2009, heavy-duty emission rates were VSP-based.28 The PM emission rates for LHD<=10K in MOVES2014 are equivalent to the PM emission rates for LHD2b3 from MOVES2009. The LHD2b3 emission rates in MOVES2009 were derived by applying a factor to the VSP-based MHD PM emission factors derived from the E55/59 TEOM data. A factor of 0.46 was obtained from the MOBILE6.2 heavy-duty conversion factors, which accounts for the lower power requirements per mile (bhp-hr/mile) of light-heavy duty trucks versus MHD trucks. The equation used to derive the PM emission rates for regulatory class 40 is shown below:
      LHD<=10K emission rate=0.46 xMHD VSP_basedemission rate
                                                                  Equation 2-15
Where the MHD VSP-based emission rate is obtained from MOVES2009.
Urban Bus (Regulatory class48) emission rates are assumed to be either the same as the HHD emission rates, or for some selected model year groups, to be a ratio of the EPA certification standards. Table 2-12 displays the model years for which the Urban Bus regulatory class has different PM emission standards from other heavy-duty compression-ignition engines. For the these model years (1991-2006), the urban bus PM emission standards are equal to the HHD emission rates multiplied by the ratio in emission standards. In addition, the urban bus emissions have different emission deterioration effects as discussed in Appendix B.6.
Table 2-13. Urban Bus PM Standards in Comparison to Heavy-duty Highway Compression Engines.
 
                Heavy-duty Highway Compression-Ignition Engines
                                  Urban Buses
                              Ratio in standards
                                 1991-1993[a]
                                     0.25
                                      0.1
                                      0.4
                                   1994-1995
                                      0.1
                                     0.07
                                      0.7
                                   1996-2006
                                      0.1
                                     0.05
                                      0.5
[a]The 0.1 g/bhp-hr US EPA Urban Bus standard began with model year 1993. In California, the  0.1 g/bhp-hr Urban Bus standard began in 1991. MOVES assumes all Urban Buses met the stricter CA standard beginning in 1991. 

Model year 2007 and later trucks (with diesel particulate filters)
EPA heavy-duty diesel emission regulations were made considerably more stringent for total PM2.5 emissions starting in model year 2007. Ignoring phase-ins and banking and trading issues, the basic emission standard fell from 0.1 g/bhp-hr to 0.01 g/bhp-hr. This increase by a factor of ten in the level of regulatory stringency required the use of particulate trap systems on heavy-duty diesels. As a result, we expect the emission performance of diesel vehicles has changed dramatically.
Unfortunately, no continuous TEOM data were available for analysis on the 2007 and later model-year vehicles.  However, heavy and medium heavy-duty diesel PM2.5 data are available from the EPA engine certification program on model years 2003 through 2007.  These data provide a snapshot of new engine emission performance before and after the introduction of particulate trap technology in 2007.  The existence of these data makes it possible to determine the relative improvement in PM emissions from model years 2003 through 2006 to model year 2007.  This same relative improvement can then be applied to the existing, TEOM based, 1998-2006 model year PM emission factors to estimate in-use factors for 2007 and later vehicles.    
An analysis of the available certification data is shown in Table 2-13 below.  It suggests that the actual ratio of improvement due to the particulate trap is reduction of a factor of 27.7.  This factor is considerably higher than the relative change in the certification standards, i.e., a factor of 10.  The reason for the change is that the new trap equipped vehicles certify at emission levels which are much lower than the standard and thus create a much larger `margin of safety' than previous technologies could achieve.
As an additional check on the effectiveness of the trap technology EPA conducted some limited in-house testing of a Dodge Ram truck, and carefully reviewed the test results from the CRC Advanced Collaborative Emission Study (ACES) phase-one program, designed to characterize emissions from diesel engines meeting 2007 standards.  The limited results from these studies demonstrate that the effectiveness of working particulate traps is very high.  The interested reader can review the ACES report.

Table 2-14. The average certification results for model years 2003-2007.  Average ratio from MYs 2003-2006 to MY 2007 is 27.7
Certification Model Year
Mean
(g/bhp-hr)
St. Dev.
n
2003
0.08369
0.01385
91
2004
0.08783
0.01301
59
2005
0.08543
0.01440
60
2006
0.08530
0.01374
60
2007
0.00308
0.00228
21

Tampering and Mal-maintenance
The MOVES model contains assumptions for the frequency and emissions effect of tampering and mal-maintenance on heavy-duty diesel trucks and buses. The assumption of tampering and mal-maintenance (T&M) of heavy-duty diesel vehicles is a departure from the MOBILE6.2 model which assumed such vehicles operated from build to final scrappage at a design emission level which was lower than the prevailing EPA emission standards. Both long term anecdotal data sources and more comprehensive studies now suggest that the assumption of no natural deterioration and/or no deliberate tampering of emission control components in the heavy-duty diesel fleet was likely an unrealistic assumption, particularly with the transition to emission aftertreatment devices with the 2007/2010 standards  
The primary data set was collected during a limited calendar year period, yet MOVES requires data from a complete range of model year/age combinations. As a result, the T&M factors shown below in Table 2-14 were used to forecast or back-cast the basic PM emission rates to predict model year group and age group combinations not covered by the primary data set.  For example, for the 1981 through 1983 model year group, the primary dataset contained data which was in either the 15 to 19 or the 20+ age groups. However, for completeness, MOVES must have emission rates for these model years for ageGroups 0-3, 4-5, 6-7, etc. As a result, unless we assume that the higher emission rates which are were measured on the older model year vehicles have always prevailed  -  even when they were young, a modeling approach such as T&M must be employed. Likewise, more recent model years could only be tested at younger ages. The T&M methodology used in the MOVES analysis allows for the filling of age  -  model year group combinations for which no data is available.
One criticism of the T&M approach is that it may double count the effect of T&M on the fleet because the primary emission measurements, and base emission rates, were made on in-use vehicles that may have had some maintenance issues during the testing period. This issue would be most acute for the 2007 and later model year vehicles where all of the deterioration is subject to projection. However, for this model year group of vehicles, the base emission rates start at low levels, and represent vehicles that are virtually free from T&M.
We followed the same tampering and mal-maintenance methodology and analysis for PM as we did for NOx, as described in Appendix B.8. The overall MOVES tampering and mal-maintenance effects on PM emissions over the fleet's useful life are shown in Table 2-14. The value of 89 percent for 2010-2012 model years reflects the projected effect of heavy-duty on-board diagnostic deterrence/early repair of Tampering and Mal-maintenance effects. It is an eleven percent improvement from model years which do not have OBD (i.e., 2007-2009). The 67% value for 2013+ is driven by the assumed full-implementation of the OBD in 2013 and later trucks, which assumes a 33% decrease in tampering and mal-maintenance emission effects. 

Table 2-15. Estimated increases in PM emissions attributed to Tampering and mal-maintenance over the useful life of Heavy-Duty Vehicles
                               Model Year Group
                     Percent increase in PM due to T&M
                                   Pre-1998
                                      85
                                  1998 - 2002
                                      74
                                 2003  -  2006
                                      48
                                 2007  -  2009
                                      100
                                 2010  -  2012
                                      89
                                     2013+
                                      67

Computation of Elemental Carbon and Non-Elemental Carbon Emission Factors
Particulate matter from conventional diesel engines is dominantly composed of elemental carbon emissions. Elemental carbon emissions are often uses synonymously with soot and black carbon emissions. Black carbon is important because of its negative-health effects and to its environmental impacts as a climate forcer.  Elemental carbon from vehicle exhaust is routinely measured with filter-based measurements using thermal optical methods.  Continuous surrogate measures of elemental carbon can also be made with available photoacoustic instruments. 
MOVES models EC emissions explicitly at the operating mode level, because of the availability of EC emission measurements at the operating mode level, and its importance in quantifying the composition of PM emissions. 
MOVES models Total PM2.5 emissions by vehicle operating mode using elemental carbon (EC) and non-elemental particulate matter carbon (NonECPM), as shown in Equation 2-16. 

                                       
                                                                  Equation 2-16
NonECPM is a species used to represent the fraction of PM that is not elemental carbon, computed using Equation 2-17. 

                                       
                                                                  Equation 2-17

The EC fractions used in MOVES for pre-2007 model year trucks (i.e. before diesel particulate filters (DPFs) were standard) are shown in Figure 2-18.  These vary according to regulatory class and MOVES operating mode.  They typically range from 25 percent at low loads (low STP) to over 90 percent at highly loaded modes.  All of the EC fractions were developed in a separate analysis and are documented in Appendix E.  The primary dataset used in the analysis came from Kweon et al. (2004) where particulate composition and mass rate data were collected on a Cummins N14 series test engine over the CARB eight-mode engine test cycle. The EPA PERE model and a Monte Carlo approach were used to simulate and translate the primary PM emission results into MOVES parameters (i.e., operating modes).  

Figure 2-20. Elemental Carbon fraction by operating mode for pre-DPF-equipped trucks

For 2007 and later model year DPF-equipped diesel engines, we used the elemental carbon fraction of 9.98% measured in Phase 1 of the Advanced Collaborative Emissions Study (ACES) Report.  Diesel particulate filters preferentially reduce elemental carbon emissions, resulting in the low percentage of elemental carbon emissions. The average EC/PM fraction is based on the 16-hour cycle which composes several different operating cycles. Because the fraction is based upon a range of driving conditions, we applied the constant 9.98% EC/PM fraction across all operating modes for the 2007+ diesel emissions rates.
The nonECPM fraction of emissions contains organic carbon (OC), sulfate, and other trace elements and ions. MOVES uses the fuel sulfur content to adjust the sulfate emission contribution to NonECPM as discussed in the MOVES2014 Fuel Adjustment Report. MOVES uses speciation profiles to estimate the composition of organic carbon, ions, and elements in NonECPM as discussed in the MOVES2014 TOG and PM Speciation Report.
Sample results
Figure 2-19 and Figure 2-20 show the trend of increasing PM rates  with STP.  As with the NOx plots, the highest operating modes in each speed range will rarely be attained due to the power limitations of heavy-duty vehicles, but are included in the figures for completeness.  At high speeds (greater than 50 mph; operating modes  30), the overall PM rates are lower than the other speed ranges.  For pre-2007 model years the PM rates are dominated by EC.  With the introduction of DPFs in model year 2007, we model the large reductions in overall PM rates and the smaller relative EC contribution to PM emissions. 
Figure 2-21. Particulate Matter rates by operating mode representing Heavy heavy-duty vehicles (model year 2002 at age 0-3 years)
                                       

Figure 2-22. Particulate Matter rates by operating mode for Heavy heavy-duty vehicles (model year 2007 at age 0-3 years)
                                       
Figure 2-21 shows an example of how tampering and mal-maintenance estimates increase PM with age.  The EC/PM proportion does not change by age, but the overall rate increases and levels off after the end of useful life.  This figure shows the age effect for MHD.  The rate at which emissions increase toward their maximum depends on regulatory class.

Figure 2-23. Particulate Matter rates by age group for Medium heavy-duty vehicles (model year 2002, operating mode 24)
                                       
Figure 2-22.  shows the effect of model year on emission rates.  Emissions generally decrease with new PM standards.  The EC fraction stays constant until model year 2007, when it is reduced to less than ~10% due the implementation of diesel particle filters. The overall PM level is substantially lower starting in model year 2007.  The emission rates shown here for earlier model years are an extrapolation of the T&M analysis since young-age engines from early model years could not be tested in the E-55 program.

Figure 2-24. Particulate Matter rates for Heavy heavy-duty vehicles by model year group (age 0-3 years, operating mode 24)
                                       
                                       
Hydrocarbons (HC) and Carbon Monoxide (CO)
Diesel engines account for a substantial portion of the mobile source HC or CO emission inventories.  Recent regulations on non-methane hydrocarbons (NMHC) (sometimes in conjunction with NOx) combined with the common use of diesel oxidation catalysts will yield reductions in both HC and CO emissions from heavy-duty diesel engines.  As a result, data collection efforts do not focus on HC or CO from heavy-duty engines.  In this report, hydrocarbons are sometimes referred to as total hydrocarbons (THC).
We used certification levels combined with emissions standards to develop appropriate model year groups.  Since standards did not change frequently in the past for either HC or CO, we created fewer model year groups than we did from NOx and PM.  The HC/CO model year groups are:
     1960-1989
     1990-2006
     2007+
Data Sources
The heavy-duty diesel HC and CO emission rate development followed a methodology that resembles the light-duty methodology, where emission rates were calculated from 1-hz data produced from chassis dynamometer testing.  Data sources were all heavy-duty chassis test programs:
   1. CRC E-55/59[32]:  Mentioned earlier, this program represents the largest volume of heavy-duty emissions data collected from chassis dynamometer tests.  All tests were used, not just those using the TEOM.  Overall, 75 trucks were tested on a variety of drive cycles.  Model years ranged from 1969 to 2005, with testing conducted by West Virginia University from 2001 to 2005.    
   2. Northern Front Range Air Quality Study (NFRAQS):  This study was performed by the Colorado Institute for Fuels and High-Altitude Engine Research in 1997.  Twenty-one HD diesel vehicles from model years 1981 to 1995 selected to be representative of the in-use fleet in the Northern Front Range of Colorado were tested over three different transient drive cycles.
   3. New York Department of Environmental Conservation (NYSDEC):  NYSDEC sponsored this study to investigate the nature and extent of heavy-duty diesel vehicle emissions in the New York Metropolitan Area.  West Virginia University tested 25 heavy-heavy and 12 medium-heavy duty diesel trucks under transient and steady-state drive cycles.
   4. West Virginia University:  Additional historical data collected on chassis dynamometers by WVU is available in the EPA Mobile Source Observation Database. 
The on-road data used for the NOx analysis was not used since HC and CO were not collected in the MEMS program, and the ROVER program used the less accurate non-dispersive infrared (NDIR) technology instead of flame-ionization detection (FID) to measure HC.  To keep HC and CO data sources consistent, we used chassis test programs exclusively for the analysis of these two pollutants.  Time-series alignment was performed using a method similar to that used for light-duty chassis test data.  The numbers of vehicles in the data sets are shown in Table 2-15.
     
Table 2-16. Numbers of vehicles by model year group, regulatory class, and age group
Model year group
Regulatory class
Age group

                                                                            0-3
                                                                            4-5
                                                                            6-7
                                                                            8-9
                                                                          10-14
                                                                          15-19
                                                                            20+
1960-2002
HHD
                                                                             58
                                                                             19
                                                                             16
                                                                              9
                                                                             16
                                                                              6
                                                                              7

MHD
                                                                              9
                                                                              6
                                                                              5
                                                                              4
                                                                             12
                                                                             15
                                                                              6

Bus
                                                                             26
                                                                               
                                                                               
                                                                              1
                                                                              3
                                                                               
                                                                               

LHD45
                                                                              2
                                                                               
                                                                               
                                                                              1
                                                                               
                                                                               
                                                                               

LHD2b3
                                                                              6
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
2003-2006
HHD
                                                                              6
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
                                                                               
Analysis
As for PM, STP was calculated using an equation similar to the light-duty VSP equation, but normalized with average regulatory class weight instead of test weight, as described by Equation 2-18.
                                       
                                       
                                                                  Equation 2-18
The track road-load coefficients A, B, and C pertaining to heavy-duty vehicles[33] were estimated through previous analyses for EPA's Physical Emission Rate Estimator (PERE). [21]
Using a method similar to that used in the NOx analysis, we averaged emissions by vehicle and operating mode.  We then averaged across all vehicles by model year group, age group, and operating mode.  Estimates of uncertainty for each mean rate were calculated using the same equations and methods used in development of the NOx rates.  Instead of using our results to directly populating all the emission rates, we directly populated only the age group that was most prevalent in each regulatory class and model year group combination.  These age groups are shown in Table 2-16.
  
Table 2-17. Age groups used directly in MOVES emission rate inputs for each regulatory class and model year group present in the data
Regulatory class
Model year group
Age group
HHD
1960-2002
0-3
HHD
2003-2006
0-3
MHD
1960-2002
15-19
BUS
1960-2002
0-3
LHD41
1960-2002
0-3
We then applied tampering and mal-maintenance effects through that age point, either lowering emissions for younger ages or raising them for older ages, using the methodology described in Appenidx B.9.  We applied the same  tampering and mal-maintenance effects for CO as HC , which are shown in Table 2-17.
Table 2-18. Tampering and mal-maintenance effects for HC and CO over the useful life of trucks
                                  Model years
                      Increase in HC and CO Emissions (%)
                                   Pre-2003
                                      300
                                2003  -  2006 
                                      150
                                 2007  -  2009
                                      150
                                 2010 - 2012 
                                      29
                                     2013+
                                      22

We multiplied these increases by the T&M adjustment factors in Table B-2 in Appendix B.6 to get the emissions by age group.
With the increased use of diesel oxidation catalysts (DOCs) in conjunction with DPFs, we assume an 80 percent reduction in zero-mile emission rates for both HC and CO starting with model year 2007.
Sample results
The charts in this sub-section show examples of the emission rates that derived from the analysis described above.  Not all rates are shown; the intent is to illustrate the most common trends and hole-filling results.  For simplicity, the light-heavy duty regulatory classes are not shown, but since the medium-heavy data were used for much of the light-heavy duty emission rate development, the light-heavy duty rates follow similar trends.  Uncertainties were calculated as for NOx.
In Figure 2-23.  and Figure 2-24, we see that HC and CO mean emission rates increase with STP, though there is much higher uncertainty than for the NOx rates.  This pattern could be due to the smaller data set or may truly reflect a less direct correlation between HC, CO and STP.  In these figures, the data for HHD and bus classes were combined to generate one set of rates for HHD and buses.

Figure 2-25.  THC emission rates [g/hr] by operating mode for model year 2002 and age group 0-3. Error bars represent the 95% confidence interval of the mean.
                                       
Figure 2-26. CO emission rates [g/hr] by operating mode for model year 2002 and age group 0-3. Error bars represent the 95% confidence interval of the mean.
Figure 2-25 and Figure 2-26 show HC and CO emission rates by age group.  Due to our projections of T&M effects, there are large increases as a function of age.  Additional data collection would be valuable to determine if real-world deterioration effects are consistent with those in the model, especially in model years where diesel oxidation catalysts are most prevalent (2007 and later).
                                       
Figure 2-27. THC emission rates [g/hr] by age group for model year 2002 and operating mode 24. Error bars represent the 95% confidence interval of the mean.
                                       
Figure 2-28. CO emission rates [g/hr] by age group for model year 2002 and operating mode 24. Error bars represent the 95% confidence interval of the mean.
                                       
Figure 2-27 and Figure 2-28 show sample HC and CO emission rates by model year group.  The two earlier model year groups are relatively similar.  The rates in the model year group reflect the use of diesel oxidation catalysts.  Due to the sparseness of the data and the fact that HC and CO emission do not correlate as well with STP (or power) as NOx and PM do, uncertainties are much greater.  Rates from HHD regulatory class were used for buses.  All regulatory classes have the same rates for model years 2003 and later.

Figure 2-29. THC emission rates by model year group for operating mode 24 and age group 0-3. Error bars represent the 95% confidence interval of the mean.
                                       
Figure 2-30. CO emission rates by model year group for operating mode 24 and age group 0-3. Error bars represent the 95% confidence interval of the mean.
                                       
Energy

LHD<=10k Energy Rates for Model Years 1960-2013

. The energy rates for LHD<=10k for pre-2007 diesel energy rates are unchanged from the LHD2b3 regulatory class from MOVES2010a. In MOVES2010a, the energy rates for this regulatory class, along with the light-duty regulatory classes, were consolidated across weight classes and engine technologies, as discussed in the energy updates report.5
LHD<=10k Energy Rates for Model Years 2014-2050
Lower energy consumption rates for LHD<=10k vehicles are expected due to the Phase 1 Medium and Heavy Duty Greenhouse Gas Rule, as discussed in more detail in Section 2.1.4.4. The CO2 emission reductions for diesel 2b-3 trucks in Table 2-19 were applied equally to the 2013 model year energy consumption rates in each running operating mode bins to derive 2014 and later energy consumption rates. Figure 2-29 displays the average energy consumption (across all running operating modes) for model years 1970 through 2030. The rates are constant between 1960 to 1983, and from 2018 to 2050.
Figure 2-31. Average Energy Consumption Rates for LHD<=10K diesel vehicles across all running operating modes
                                       

LHD<=14k,  LHD45, MHD, Urban Bus, and HHD Energy Rates for Model Years 1960-2013
The data used to develop NOx rates was also used to develop running-exhaust energy rates for most of the heavy-duty source types.  The energy rates were based on the same data, STP structure and calculation steps as in the NOx analysis; however, unlike NOx, we did not classify the energy rates by model year or by age, because neither variable had a significant impact on energy rates or CO - 2.
As for previous versions of MOVES, CO2 emissions were used as the basis for calculating energy rates. To calculate energy rates [kJ/hour] from CO2 emissions, we used a heating value (HV) of 138,451 kJ/gallon and CO2 fuel-specific emission factor (fCO2) of 10,084 g/gallon for diesel fuel, using Equation 2-19.  

                                       
                                       
                                 Equation 2-19
This analysis updates the running-exhaust energy rates estimated for MOVES2004 for diesel LHD<=14k, LHD45, MHD, urban bus, and HHD regulatory classes.[28]  The energy rates for these heavy-duty diesel vehicle classes are shown in Figure 2-30. 
. 
Figure 2-32. Diesel running exhaust energy rates for LHD<=14K, LHD45 , MHD, HHD, and Urban Buses for 1960-2013 model years. Error bars represent the 95% confidence interval of the mean.
                                       
Compared to other emissions, the uncertainties in the energy rates are smaller in part because there is no classification by age, model year, or regulatory class.  Thus, the number of vehicles used to determine each rate is larger, providing for a greater certainty of the mean energy rate.

LHD<=14k,  LHD45, MHD, Urban Bus, and HHD Energy Rates for Model Years 2014-2050

The energy rates are revised for 2014 and later model years, to reflect the impact of the 2014 Medium and Heavy Duty Greenhouse Gas Rule.44 The medium and heavy duty greenhouse gas program begins with 2014 model year and increases in stringency through 2018.  The standards continue indefinitely after 2018.  The program breaks the diverse truck sector into 3 distinct categories, including
   * Line haul tractors (largest heavy-duty tractors used to pull trailers, combination trucks in MOVES) 
   * Heavy-duty pickups and vans (3/4 and 1 ton trucks and vans) 
   * Vocational trucks (buses, refuse trucks, motorhomes, single-unit trucks) 
The program set separate standards for engines and vehicles and ensures improvements in both.  It also sets separate standards for fuel consumption, CO2, N2O, CH4 and HFCs.  
In MOVES, the improved fuel consumption from the HD GHG Rule is implemented in two ways. First, the running emission rates for total energy are reduced. Second, the truck weights and road load coefficients are updated to reflect the lower vehicle weights, lower resistance tires, and improved aerodynamics of the vehicle chassis. The discussion of the vehicle weights and road load coefficients is included in the Population and Activity Report.4  
The revised running emission rates for total energy are drawn from the HDGHG rulemaking modeling.  The estimated reductions for heavy-duty diesel vehicles, including all rates are for include new running, start and extended idle rates, are shown in Table 2-18 .  These rates are for the 2014 and later model years, and reflect the improvements expected from improved energy efficiency in the powertrain. The reductions from the baseline were applied to the appropriate regulatory classes and model years in the MOVES emissionrate table.  
Table 2-19 Estimated Reductions in Diesel and Gasoline Engine CO2 -  Emission Rates from the HD GHG Program Phase 1
GVWR Class
FUEL
MODEL YEARS
CO2 Reduction From Baseline
HHD (8a-8b)
Diesel
2014-2016
3%

2017+
6%
LHD(4-5) and
MHD (6-7) 
Diesel
2014-2016
5%

2017+
9%

Gasoline
2016+
5%

Unlike the HHD standards, the HD pickup truck/van standards are evaluated in terms of grams of CO2 per mile or gallons of fuel per 100 miles. Table 2-21 describes the estimated expected changes in CO2 emissions due to improved engine and vehicle technologies. Since nearly all HD pickup trucks and vans will be certified on a chassis dynamometer, the CO2 reductions for these vehicles are not represented as engine and road load reduction components, but total vehicle CO2 reductions. MOVES2014 models the HD pickup truck/van standards by lowering the energy rates stored in the emissionrate table. No change is made to the road-load coefficients or weights of passenger or light-duty truck source types. The energy consumption rates for LHD<=10 and LHD<=14K were lowered by the percentages shown in Table 2-21 for the corresponding model years. 
      
Table 2-20 Estimated Total Vehicle CO2 Reductions for HD Diesel and Gasoline Pickup Trucks and Vans
GVWR CLASS
FUEL
MODEL YEARS
CO2 REDUCTION FROM BASELINE
LHD 2b-3
Gasoline
2014
1.5%

2015
2%

2016
4%

2017
6%

2018+
10%

Diesel
2014
2.3%

2015
3%

2016
6%

2017
9%

2018+
15%
      
Figure 2-31 displays the average energy consumption rates for the heavy-duty diesel source types that are modeled using Scaled Tractive Power (STP) with a fixed mass factor of 17.1. The energy rates for all these source types are equivalent for model years 1960-2013. The reduction in the average energy consumption rates is displayed in Figure 2-31, with separate reductions for the class 2b and 3 trucks (LHD<=14k), class 4-7 trucks (LHD45, MHD), and class 8 trucks (HHD). The  urban bus regulatory is by definition a heavy heavy-duty vehicle, and is treated the same as the other heavy-heavy duty vehicles (HHD). For LHD<=14k the energy rates are constant 2018 going forward, for the other categories (LHD45, MHD, Urban Bus, HHD) the energy rates  are constant going forward starting in model year 2017. 
Figure 2-33. Average Energy Consumption Rates for LHD<=14k (41), LHD45 (42), MHD (46), Urban Bus (48), and HHD (47) diesel vehicles across all running operating modes.

Start Exhaust Emissions
The `start' process occurs when the vehicle is started and is operating in some mode in which the engine is not fully warmed up.  For modeling purposes, we define start emissions as the increase in emissions due to an engine start.  That is, we use the difference in emissions between a test cycle with a cold start and the same test cycle with a hot start.  There are also eight intermediate stages which are differentiated by soak time length (time duration between engine key off and engine key on),  between a cold start (> 720 minutes of soak time) and a hot start FTP (< 6 minutes of soak time).  More details, on how start emission rates are calculated as a function of soak time, can be found later in this section and in the MOVES light-duty emission rate counterpart document8.   The impact of ambient temperature on cold starts is discussed in the Emission Adjustments MOVES report.
HC, CO, and NOx
For light-duty diesel vehicles, start emissions are estimated by subtracting FTP bag 3 emissions from FTP bag 1 emissions.  Bag 3 and Bag 1 are the same dynamometer cycle, except that Bag 1 starts with a cold start, and Bag 3 starts with a hot start.  A similar approach was performed for LHD vehicles tested on the FTP and ST01 cycles, which also have separate bags containing cold and hot start emissions over identical drive cycles.  Data from 21 LHD diesel vehicles, ranging from model years 1988 to 2000, were analyzed.  No classifications were made for model year or age due to the limited number of vehicles. The results of this analysis for HC, CO, and NOx are shown in Table 2-20.

Table 2-21. The average start emissions increases for light-heavy duty diesel vehicles (g) for regulatory class 40, 41, and 42. No differentiation by model year or age.
                                      HC
                                      CO
                                      NOx
                                     0.13
                                     1.38
                                     1.68

For HHD and MHD trucks, data were unavailable.  To provide at least a minimal amount of information, we measured emissions from a 2007 Cummins ISB on an engine dynamometer at the EPA National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan.  Among other idle tests, we performed a cold start idle test at 1,100 RPM lasting four hours, long enough for the engine to warm up.  Essentially, the "drive cycle" we used to compare cold start and warm emissions was the idle cycle, analogous to the FTP and ST01 cycles used for LHD vehicles.  Emissions and temperature stabilized about 25 minutes into the test.  The emission rates through time are shown in Figure 2-32.  The biggest drop in emission rate through the test is with CO, whereas there is a slight increase in NOx (cold start NOx is lower than hot start NOx), and an insignificant change in HC.

Figure 2-34. Trends in the stabilization of idle emissions from a diesel engine following a cold start. Data were collected from a 2007 Cummins ISB measured on an engine dynamometer
                                       
                                       
We calculated the area under each trend for the first 25 minutes and divided by 25 minutes to get the average emission rate during the cold start idle portion.  Then, we averaged the data for the remaining portion of the test, or the warm idle portion.  The difference between cold start and warm start is in Table 2-21.  The NOx increment is negative since cold start emissions are lower than warm start emissions.

  Table 2-22. Cold-start emissions increases in grams on the 2007 Cummins ISB
                                      HC
                                      CO
                                      NOx
                                      0.0
                                     16.0
                                     -2.3
                                       
We also considered data from University of Tennessee, which tested 24 trucks with PEMS at different load levels during idling.  Each truck was tested with a cold start going into low-RPM idle with air-conditioning on.  We integrated the emissions over the warm-up period to get the total cold start idling emissions.  We calculated the hot-start idling emissions by multiplying the reported warm idling rate by the stabilization time.  We used the stabilization period from our engine dynamometer tests (25 minutes).  Then we subtracted the cold-idle emissions from the warm idle emissions to estimate the cold start increment.  We found that several trucks produced lower NOx emissions during cold start (similar to our own work), and several trucks produces higher NOx emissions during cold start.  Due to these conflicting results, and the recognition that many factors affect NOx emission during start (e.g. air-fuel ratio, injection timing, etc), we set the cold-start increment to zero.  Table 2-22 shows our final MOVES inputs for HHD and MHD diesel start emissions increases from our 2007 MY in-house testing. Due to the limited data, the emission rate is constant for all model years and ages. 

Table 2-23. MOVES inputs for HHD and MHD diesel start emissions (grams/start) for regulatory class 46, 47, and 48. No differentiation by model year or age.
                                      HC
                                      CO
                                      NOx
                                      0.0
                                     16.0
                                      0.0
                                       
As discussed in the Emission Adjustments Report45, MOVES2014 applies an additive adjustment to HC cold-start emissions to the diesel start emissions for ambient temperatures below 72F. No adjustments are applied to CO or NOx. Therefore, MOVES2014 produces start emissions from heavy-duty diesel vehicles for HC and CO at ambient temperatures below 72 F.
Incorporation of Tier-3 Standards for Light-Heavy-Duty Diesel
The Tier-3 exhaust emission standards affect medium-duty diesel vehicles in the LHD<=10k and LHD<=14k (regClassID = 40, 41, respectively).  Reductions are applied to rates for NOx only starting in MY2018 and culminating in MY2021.  No reductions are applied to HC and CO rates. 
For NOx, reductions for start emissions are applied as previously described for running emissions in 2.1.1.3.5 (page 23).   Examples of rates during the phase-in period are shown in Figure 2-35.  Note that start rates are identical for the two regulatory classes.

Figure 2-35.  NOx: Start emission rates in selected operating modes vs. model year for two regulatory classes (LOGARITHMIC SCALE).
                                       
                                       
Particulate Matter
Data for particulate start emissions from heavy-duty vehicles are rare.  Typically, heavy-duty vehicle emission measurements are performed on fully warmed up vehicles.  These procedures bypass the engine crank and early operating periods when the vehicle is not fully warmed up.   
Data from engine dynamometer testing performed on one heavy-heavy-duty engine, using the FTP cycle with particulate mass collected on filters.  The engine was manufactured in MY2004. The cycle was repeated six times, under both hot and cold start conditions (two tests for cold start and four replicate tests for hot start).  The average difference in PM2.5 emissions (filter measurement - FTP cycle) was 0.10985 grams.  The data are shown here:
      Cold start FTP average	 =  	1.9314 g PM2.5
      Warm start FTP average	 =	1.8215 g PM2.5
      Cold start  -  warm start	 =  	 0.1099 g PM2.5
We applied this value to 1960 through 2006 model year vehicles.  A corresponding value of 0.01099 g was used for 2007 and later model year vehicles (90 percent reduction due to DPFs).  We plan to update this value when more data becomes available. The value is the same for all heavy-duty diesel regulatory class vehicles.
Adjusting Start Rates for Soak Time
The discussion to this point has concerned the development of rates for cold-start emissions. In addition, it was necessary to derive rates for additional operating modes that account for varying (shorter) soak times.  As with light-duty vehicles, we accomplished this step by applying soak fractions. As no data are available for heavy-duty vehicles, we applied the same fractions used for light-duty emissions. Table 2-23 describes the different start-related operating modes in MOVES as a function of soak time.  The value at 720 min (12 hours) represents cold start.  These modes are not related to the operating modes defined in Table 1-4 which are for running exhaust emissions.

 Table 2-24. Operating modes for start emissions (as a function of soak time)
                                Operating Mode
Description
                                      101
Soak Time < 6 minutes
                                      102
6 minutes <= Soak Time < 30 minutes
                                      103
30 minutes <= Soak Time < 60 minutes
                                      104
60 minutes <= Soak Time < 90 minutes
                                      105
90 minutes <= Soak Time < 120 minutes
                                      106
120 minutes <= Soak Time < 360 minutes
                                      107
360 minutes <= Soak Time < 720 minutes
                                      108
720 minutes <= Soak Time

The soak fractions we used for HC, CO, and NOx are illustrated in Figure 2-33 below. Due to limited data, we applied the same soak fractions that we applied to 1996+ MY light-duty gasoline vehicle as documented in the light-duty emission rate report8. For light-heavy duty vehicles (regulatory classes 40, 41, and 42), the soak distributions apply to the cold starts for HC, CO and NOx. For heavy-heavy duty vehicles (regulatory classes 46, 47, and 48)  only the CO soak fractions in Figure 2-33 is applied to the cold-start emissions, because the base cold start HC and NOx emission rates for heavy-heavy duty emission rates are zero. 

Figure 2-36. Soak Fractions Applied to Cold-Start Emissions (opModeID = 108) to Estimate Emissions for shorter Soak Periods (operating modes 101-107). This Figure is reproduced from Figure 43 in the Light-duty emissions Report8
                                       
The start emission rates used for heavy-duty vehicles, derived from applying the soak fractions are displayed in Table 2-24 for HC, CO, and NOx.
Table 2-25. Heavy-duty diesel HC, CO, and NOx Start emissions (g/start) by operating mode for all model year and all ages in MOVES.
                                       
                                      HC
                                      CO
                                      NOx
opModeID
LHD[1]
Other HD[2]
LHD
Other HD
LHD
Other HD
101
0.0052
0
0.055
0.64
0.275
0
102
0.0273
0
0.276
3.2
0.760
0
103
0.0572
0
0.607
7.04
1.350
0
104
0.0780
0
0.869
10.08
1.481
0
105
0.0832
0
1.007
11.68
1.481
0
106
0.0949
0
1.090
12.64
1.468
0
107
0.1183
0
1.256
14.56
1.376
0
108
0.1300
0
1.380
16
1.298
0
[1]LHD refers to regClassIDs 40, 41, and 42
[2] Other HD refers to the Medium-heavy duty, heavy-heavy duty, and Urban Bus Regulatory classes (46, 47, and 48)

The PM start rates by operating mode are given in Table 2-25 below. They are estimated assuming a linear decrease in emissions between a full cold start (>720 minutes) and zero emissions at a short soak time (< 6 minutes). 
Table 2-26.  Particulate Matter Start Emission Rates by Operating Mode (soak fraction) for all HD vehicles (regClass ID 40 through 48)
                                Operating Mode
                            PM2.5 (grams per start)
                                 1960-2006 MY
                            PM2.5 (grams per start)
                                   2007+ MY
                                      101
                                    0.0000
                                    0.00000
                                      102
                                    0.0009
                                    0.00009
                                      103
                                    0.0046
                                    0.00046
                                      104
                                    0.0092
                                    0.00092
                                      105
                                    0.0138
                                    0.00138
                                      106
                                    0.0183
                                    0.00183
                                      107
                                    0.0549
                                    0.00549
                                      108
                                    0.1099
                                    0.01099

Adjusting Start Rates for Ambient Temperature
The emission adjustments report discusses the impact of ambient temperature on cold start emission rates (opModeID 108)45. The ambient temperature effects in MOVES model the ambient temperature has on cooling the engine and aftertreatment system on vehicle emissions. The temperature effect is greatest for a vehicle that has been soaking for a long period of time, such that the vehicle is the same temperature of the ambient conditions. Accordingly, the impact of ambient temperature should be less for vehicles that are still warm from driving. 
However, for HC the temperature effects applied in MOVES are modeled as additive adjustments. Accordingly, the additive temperature adjustments need to be reduced for the hot and warm starts. Due to lack of data, we applied soak fractions, to obtain cold start temperature adjustments for opModeID 101 through 107. The additive cold start adjustment for HC emission factors are displayed in Table X, along with the soak fractions applied. The soak fractions are taken from the non-catalyst soak fractions derived in a CARB report and reproduced in a Mobile 6 report. We used the non-catalytic converter soak fractions to adjust the diesel start temperature adjustments for HC temperature starts. These additive HC starts are applied to all diesel sources in MOVES, including light-duty diesel (regulatory class 20 and 30).
As stated in the emissions adjustments report, there are currently no diesel temperature effects in MOVES for PM, CO, and NOx. 
        Table 2-27. HC Diesel Start Temperature Adjustment by opModeID.
opModeID
Start Temp Adjustment
Soak fraction
                                      101
                            -0.0153x(Temp  -  75)
                                     0.38
                                      102
                            -0.0152x(Temp  -  75)
                                     0.37
                                      103
                            -0.0180x(Temp  -  75)
                                     0.44
                                      104
                            -0.0201x(Temp  -  75)
                                     0.50
                                      105
                            -0.0211x(Temp  -  75)
                                     0.52
                                      106
                            -0.0254x(Temp  -  75)
                                     0.62
                                      107
                            -0.0349x(Temp  -  75)
                                     0.86
                                      108
                            -0.0406x(Temp  -  75)
                                     1.00
Start Energy Rates
The MOVES start energy rates for the heavy-duty diesel regulatory classes are shown in Figure 2-37. The energy start rates were developed for MOVES200428, and updated in MOVES2010 as documented in the updates report5. As shown, there is more granularity in the pre-2000 emission rates. The spike in fuel economy at 1984-1985 reflects variability in the data used to derive starts, which was consistent with the `data-driven' approach used to derive the energy rates in MOVES2004. The only updates to the energy rates post-2000 is the impact of the Phase 1 Heavy-duty GHG standards, which begin phase-in in 2014 and have the same reductions as the running energy rates as presented in Table 2-19.

                                       
                                       

Figure 2-37. Heayv-duty energy cold start energy rates (opMode 108) by model year and regulatory class. 
                                       

The start energy rates are adjusted in MOVES for increased fuel consumption required to start a vehicle at cold ambient temperatures. The temperature effects are documented in the 2004 Energy Report28. Additionally, the energy consumption is reduced for starts that occur when the vehicles is soaking for a short period of time. The soak fractions used to reduced by the energy consumption emission rates at cold start are provided in Table X. These fractions are used for all model years and regulatory classes of diesel vehicles.

Table 2-28. Fraction of energy consumed at start of varying soak lengths compared to the energy consumed at a full cold start (operating mode 108).
                                Operating Mode
                                  Description
             Fraction of energy consumption compared to cold start
                                      101
Soak Time < 6 minutes
                                     0.013
                                      102
6 minutes <= Soak Time < 30 minutes
                                    0.0773
                                      103
30 minutes <= Soak Time < 60 minutes
                                    0.1903
                                      104
60 minutes <= Soak Time < 90 minutes
                                    0.3118
                                      105
90 minutes <= Soak Time < 120 minutes
                                    0.4078
                                      106
120 minutes <= Soak Time < 360 minutes
                                    0.5786
                                      107
360 minutes <= Soak Time < 720 minutes
                                    0.8751
                                      108
720 minutes <= Soak Time
                                       1
                                       
Table 2-28 displays the relative contribution of total energy consumption estimated from a National MOVES calendar year 2011, using MOVES2014. As shown, the estimated energy consumed due to starts, is minor in comparison to the energy use of running activity. One of the reasons that energy rates for heavy-duty starts has not been updated, is the relatively small contribution the starts have on the energy inventory.

Table 2-29. Relative contribution of total energy consumption from each pollutant process by regulatory class for heavy-duty diesel vehicles in calendar year 2011.
processID
processName
                                      40
                                      41
                                      42
                                      46
                                      47
                                      48
                                                                              1
Running Exhaust
                                     97.4%
                                     99.2%
                                     99.3%
                                     98.1%
                                     95.1%
                                     99.7%
                                                                              2
Start Exhaust
                                     2.6%
                                     0.8%
                                     0.7%
                                     0.6%
                                     0.1%
                                     0.3%
                                                                             90
Extended Idle Exhaust
                                       
                                       
                                       
                                     1.3%
                                     4.7%
                                       
                                                                             91
Auxiliary Power Exhaust
                                       
                                       
                                       
                                     0.01%
                                     0.04%
                                       

Extended Idling Exhaust Emissions
In the MOVES model, extended idling is "discretionary" idle operation characterized by idle periods more than an hour in duration, typically overnight, including higher engine speed settings and extensive use of accessories by the vehicle operator. Extended idling most often occurs during long layovers between trips by long-haul trucking operators where the truck is used as a residence, and is sometimes referred to as "hotelling." The use of accessories such as air conditioning systems or heating systems will affect emissions emitted by the engine during idling. Extended idling by vehicles will also allow cool-down of the vehicle's catalytic converter system or other exhaust emission after-treatments, when these controls are present. Extended idle is treated as a separate emission process in MOVES.  
Extended idling does not include vehicle idle operation which occurs during normal road operation, such as the idle operation which a vehicle experiences while waiting at a traffic signal or during a relatively short stop, such as idle operation during a delivery. Although frequent stops and idling can contribute to overall emissions, these modes are already included in the normal vehicle hours of operation. Extended idling is characterized by idling periods that last hours, rather than minutes.
In the MOVES model, diesel long-haul combination trucks are the only sourceType assumed to have any significant extended idling activity. As a result, an estimate for the extended idling emission rate has not been made for any of the other source use types modeled in MOVES. 
Data Sources
The data used in the analysis of extended idling emission rates includes idle emission results from several test programs conducted by a variety of researchers at different times.  Not all of the studies included all the pollutants of interest.  The references contain more detailed descriptions of the data and how the data was obtained.
Testing was conducted on twelve heavy-duty diesel trucks and twelve transit buses in Colorado (McCormick).  Ten of the trucks were Class 8 heavy-duty axle semi-tractors, one was a Class 7 truck, and one of the vehicles was a school bus.  The model year ranged from 1990 through 1998.  A typical Denver area wintertime diesel fuel (NFRAQS) was used in all tests.  Idle measurements were collected during a 20 minute time period.  All testing was done at 1,609 meters above sea level (high altitude).
Testing was conducted by EPA on five trucks in May 2002 (Lim).  The model years ranged from 1985 through 2001. The vehicles were put through a battery of tests including a variety of discretionary and non-discretionary idling conditions.
Testing was conducted on 42 diesel trucks in parallel with roadside smoke opacity testing in California (Lambert). All tests were conducted by the California Air Resources Board (CARB) at a rest area near Tulare, California in April 2002.  Data collected during this study were included in the data provided by IdleAire Technologies (below) that was used in the analysis.
A total of 63 trucks (nine in Tennessee, 12 in New York and 42 in California) were tested over a battery of idle test conditions including with and without air conditioning (Irick).  Not all trucks were tested under all conditions.  Only results from the testing in Tennessee and New York are described in the IdleAire report.  The Tulare, California, data are described in the Clean Air Study cited above.  All analytical equipment for all testing at all locations was operated by Clean Air Technologies.
Fourteen trucks were tested as part of a large Coordinating Research Council (CRC) study of heavy duty diesel trucks with idling times either 900 or 1,800 seconds long (Gautam).
The National Cooperative Highway Research Program (NCHRP) obtained the idling portion of continuous sampling during transient testing was used to determine idling emission rates on two trucks.
A total of 33 heavy-duty diesel trucks were tested in an internal study by the City of New York (Tang).  The model years ranged from 1984 through 1999.   One hundred seconds of idling were added at the end of the WVU five-mile transient test driving cycle.
A Class 8 Freightliner Century with a 1999 engine was tested using EPA's on-road emissions testing trailer based in Research Triangle Park, North Carolina (Broderick).  Both short (10 minute) and longer (five hour) measurements were made during idling.  Some testing was also done on three older trucks.
Five heavy-duty trucks were tested for particulate and NOx emissions under a variety of conditions at Oak Ridge Laboratories (Story).  These are the same trucks used in the EPA study (Lim).
The University of Tennessee tested 24 1992 through 2006 model year heavy duty diesel trucks using a variety of idling conditions including variations of engine idle speed and load (air conditioning)[46].
Analysis
EPA estimated mean emission rates during extended idling operation for particulate matter (PM), oxides of nitrogen (NOx), hydrocarbons (HC), and carbon monoxide (CO).  This analysis used all of the data sources referenced above.  The MOVES2010b update reflects new data available since the initial development of extended idle emissions for the MOVES model.  The additions include the testing at Research Triangle Park (Broderick), the University of Tennessee study (Calcagno), and the completed E-55/59 study conducted by WVU and CRC.  In addition, the data was separated by truck and bus and by idle speed and accessory usage to develop an emission rate more representative of extended idle rates.
The important conclusion from the 2003 analysis was that factors affecting engine load, such as accessory use, and engine idle speed are the important parameters in estimating the emission rates of extended idling.  The impacts of most other factors, such as engine size, altitude, model year within MOVES groups, and test cycle are negligible.  This makes the behavior of truck operators very important in estimating the emission rates to assign to periods of extended idling. 
The use of accessories (air conditioners, heaters, televisions, etc.) provides recreation and comfort to the operator and increases load on the engine.  There is also a tendency to increase idle speed during long idle periods for engine durability.  The emission rates estimated for the extended idle pollutant process assume both accessory use and engine idle speeds set higher than used for "curb" (non-discretionary) idling.  
The studies focused on three types of idle conditions.  The first is considered a curb idle, with low engine speed (<1,000 rpm) and no air conditioning.  The second is representative of an extended idle condition with higher engine speed (>1,000 rpm) and no air conditioning.  The third represents an extended idle condition with higher engine speed (>1,000 rpm) and air conditioning.
The idle emission rates for heavy duty diesel trucks prior to the 1990 model year are based on the analysis of the 18 trucks from 1975-1990 model years used in the CRC E-55/59 study and one 1985 truck from the Lim study.  The only data available represents a curb idle condition.  No data was available to develop the elevated NOx emission rates characteristic of higher engine speed and accessory loading, therefore, the percent increase developed from the 1991-2006 trucks was used.
Extended idle emission rates for 1991-2006 model year heavy duty diesel trucks are based on several studies and 184 tests detailed in Appendix C.  The increase in NOx emissions due to higher idle speed and air conditioning was estimated based on three studies that included 26 tests.  The average emissions from these trucks using the high idle engine speed and with accessory loading was used for the emission rates for extended idling. 
The expected effects of the 2007 heavy duty diesel vehicle emission standards on extended idling emission rates are taken from the EPA guidance analysis (EPA 2003).  The 2007 heavy duty diesel emission standards are expected to result in the widespread use of PM filters and exhaust gas recirculation (EGR) and 2010 standards will result in after-treatment technologies.  However, since there is no requirement to address extended idling emissions in the emission certification procedure, EPA expects that there will be little effect on HC, CO, and NOx emissions after hours of idling due to cool-down effects on EGR and most aftertreatment systems.  However, we do not expect DPFs to lose much effectiveness during extended idling.  As a result, we project that idle NOx emissions will be reduced 12 percent and HC and CO emissions will be reduced 9 percent from the extended idle emission rates used for 1988-2006 model year trucks.  The reduction estimates are based on a ratio of the 2007 standard to the previous standard and assuming that the emission control of the new standard will only last for the first hour of an eight hour idle.  For PM, we assume an extended idling emission rate equal to the curb idling rate (operating mode 1 from the running exhaust analysis). Detailed equations are included in the appendix.  
Results
Table 2-27 shows the resulting NOx, HC, and CO emission rates estimated for heavy-duty diesel trucks from the data analysis.  Extended idling measurements have large variability due to low engine loads, which is reflected in the variation of the mean statistic.
   Table 2-30. Mean Extended idle emission rates from data analysis (g/hour)
Model years
NOx
HC
CO
PM
Pre-1990
112
108
84
8.4
1990-2006
227
56
91
4.0
2007 and later
201
53
91
0.2
MOVES Extended Idle Emission Rates
Table 2-28 shows the emission rates used in MOVES for extended idle for diesel MHD67 and HHD trucks. These are the only regulatory classes in MOVES within diesel combination trucks, which are the only types of trucks with extended idle vehicle activity in MOVES. The emission rates for regulatory class 47 (HHD) are equal to the mean extended emission rates from Table 2-27 for HC, CO, and NOx. Due to limited data we used the calculated the MHD67 (regClassID 46) extended idle emission rates as (1/2) of the extended idle emission rates of the HHD emission rates for HC, CO and NOx. There are no age effects modeled for extended idle emissions in MOVES.
Table 2-31. Extended idle emission rates in MOVES by pollutant and regulatory class (g/hour)
 
                                      HC
                                      CO
                                      NOx
 
MHD67
HHD
MHD67
HHD
MHD67
HHD
1960-1990
54
108
42
84
56
112
1991-2006
28
56
45.5
91
113.5
227
2007+
26.5
53
45.5
91
100.5
201

Table 2-29 shows the extended idle PM emission rates in MOVES. MOVES stores PM emission rates according to EC and NonECPM, but the total PM, and EC/PM fraction are reported in Table 2-29 as well. The PM emission rates in MOVES are similar in magnitude to the PM emission rates measured to the mean rates reported in Table 2-27. 
Table 2-32. Particulate Matter Emission rates for Extended Idle Emission Rates
                                       
                            Regulatory Class MHD67
                                       
                                       
                                      EC
                                    NonECPM
                                      PM
                                     EC/PM
                                  1960 - 1993
                                     1.77
                                     2.44
                                     4.21
                                     42.1%
                                  1994 - 1997
                                     3.07
                                     4.21
                                     7.28
                                     42.1%
                                  1998 - 2002
                                     2.91
                                     4.00
                                     6.91
                                     42.1%
                                  2003 - 2006
                                     2.63
                                     3.60
                                     6.23
                                     42.1%
                                     2007+
                                     0.032
                                     0.288
                                     0.32
                                     9.98%
                                       
                             Regulatory Class HHD
                                       
                                       
                                       
                                      EC
                                    NonECPM
                                      PM
                                     EC/PM
                                  1960 - 1993
                                     1.08
                                     3.13
                                     4.21
                                     25.7%
                                  1994 - 1997
                                     1.66
                                     4.78
                                     6.44
                                     25.7%
                                  1998 - 2002
                                     1.58
                                     4.57
                                     6.16
                                     25.7%
                                  2003 - 2006
                                     1.43
                                     4.13
                                     5.56
                                     25.7%
                                     2007+
                                     0.03
                                     0.31
                                     0.35
                                     9.98%

The extended idle energy emission rates were originally developed in MOVES200428, and are displayed in Figure 2-38. The extended idle energy consumption rates are the same for both regulatory class MHD67 and HHD diesel vehicles. As shown in Table 2-29, extended idle is estimated to contribute 1.3% and 4.7% of the energy consumption from regulatory class MHD67 and HHD8 diesel vehicles in the United States in calendar year 2011. 

Figure 2-38. Extended idle energy emission rates for regulatory class HHD8 and MHD67 diesel trucks.

Auxiliary Power Unit Exhaust
      
In MOVES2014, we added a new emission process for auxiliary power unit (APU) exhaust.  APU usage only applies to the vehicles with extended idling activity, which are the heavy-duty regulatory classes (MHD and HHD) within the combination truck source types. The MOVES default activity assumes APU's are used for 30% hotelling activity for model year 2010 and later trucks, with extended idling occurring for the remaining 70% of hotelling activity. Users can update hotelling activity among extended idling, APU usage, and engine off activity as discussed in the MOVES2014 User Guide
The APUs in MOVES are assumed to be Tier 4-compliant, small (<8 kW) nonroad compression-ignition engines. We use the THC, CO, NOx, and PM2.5 emission rates from the NONROAD2008 model for this category of nonroad engine to develop the APU emissions rates, as was done in the 2014 Medium and Heavy Duty Greenhouse Gas Rule44. The PM2.5 emissions were divided into EC (25%) and 75% (nonEC) using fractions similar to the EC/PM split for conventional extended idling exhaust from HHD trucks (Table 2-29). The APU emission rates are displayed in Table 2-30. The APU energy usage (per hour) is 22% of the MOVES extended idle emission rate for 2002 and later trucks, demonstrating the potential energy savings from using an auxiliary power unit.
                       Table 2-33  -  APU emission rates
Pollutant
Emission Rate
Units
THC
                                     6.72
g/hr
CO
                                      36
g/hr
NOx
                                     26.88
g/hr
EC
                                     0.45
g/hr
NonEC
                                     1.35
g/hr
EC/PM2.5
                                      25%
%
Total Energy
                                   27171.336
KJ/hr

      

Heavy-Duty Gasoline Vehicles
        	Running Exhaust Emissions 
HC, CO, and NOx
Data and Analysis for 1960-2007 Model Year Trucks
As gasoline-fueled vehicles are a small percentage of the heavy-duty vehicle fleet, the amount of data available for analysis was small. We relied on four medium-heavy duty gasoline trucks from the CRC E-55 program and historical data from EPA's Mobile Source Observation Database (MSOD), which has results from chassis tests performed by EPA, contractors and outside parties. The heavy-duty gasoline data in the MSOD is mostly from pickup trucks which fall mainly in the LHD2b3 regulatory class. Table 3-1 shows the number of vehicles in cumulative data sets. In the real world, most heavy-duty gasoline vehicles fall in either the LHD2b3 or LHD45 class, with a smaller percentage in the MHD class. There are very few, if any, HHD gasoline trucks remaining in use. 

Table 3-1. Distribution of vehicles in the data sets by model-year group, regulatory class and age group
Model year group
Regulatory class
                                   Age group

                                      0-5
                                      6-9
1960-1989
MHD
                                       
                                       2

LHD2b3
                                       
                                      10
1990-1997
MHD
                                       
                                       1

LHD2b3
                                      33
                                      19
1998-2002
MHD
                                       1
                                       

LHD2b3
                                       1
                                       

Similar to the HD diesel PM, HC, and CO analysis, the chassis vehicle speed and acceleration, coupled with the average weight for each regulatory class, were used to calculate STP (Equation 1-2).  To supplement the meager data available, we examined certification data as a guide to developing model year groups for analysis. Figure 3-1 shows averages of certification results by model year.  
Figure 3-1. Brake-specific certification emission rates by model year for heavy-duty gasoline engines
Based on these certification results, we decided to classify the data into the coarse model year groups listed below.  
   * 1960-1989
   * 1990-1997
   * 1998-2007
Unlike the analysis for HD diesel vehicles, we used the age effects present in the data itself. We did not incorporate external tampering and mal-maintenance assumptions into the HD gasoline rates. Due to sparseness of data we used only the two age groups listed in Table 3-1. We also did not classify by regulatory class since there was not sufficient data to estimate emission rates by separate regulatory classes.  The derivation of the model year 2008 and later emission rates are discussed in Sections 3.1.1.3 and 3.1.1.6.
Emission Rates for Regulatory Class LHD <=10K
The emission rates are initially analyzed by binning the emission rates using the STP with a fixed mass factor of 2.06, to bring the emission rates into VSP-equivalent space, used for modeling emissions for regulatory class 40 (LHD<=10K).  Figure 3-2 shows all three pollutants vs. operating mode for the LHD<=10K. In general, emissions follow the expected trend with STP, though the trend is most pronounced for NOx. As expected, NOx emissions for light-heavy-duty gasoline vehicles are much lower than for light-heavy-duty diesel vehicles.
Figure 3-2. Emission Rates by operating mode for MY groups 1960-1989, 1990-1997, and 1998-2007  at age 0-3 years for Regulatory Class LHD <= 10K

Figure 3-3 shows the emissions trends by age group.  Since we did not use the tampering and mal-maintenance methodology as we did for diesels, the age trends reflect our coarse binning with age.  For each pollutant, only two distinct rates exist  -  one for ages 0-5 and another for age 6 and older. 

Figure 3-3. Emission rates by operating mode and age group for MY 1998-2007 vehicles in Regulatory Class LHD <=10K
                                       
Table 3-2 displays the multiplicative age effects by operating mode for Regulatory Class LHD<=10K vehicles. The relative age effects are derived from the sample of vehicle tests summarized in Table 3-1. The multiplicative age effects are used to estimate the aged emission rates (ages 6+) years from the base emission rates (ages 0-5) for HC, CO, and NOx. These multiplicative age effects apply to all model year groups between 1960-2007.  

Table 3-2. Relative age effect on emission rates between age 6+ and age 0-5 for LHD<=10K gasoline vehicles in model years 1960-2007.
OpModeID
                                      HC
                                      CO
                                      NOx
                                                                              0
                                     2.85
                                     1.45
                                     1.67
                                                                              1
                                     2.43
                                     1.79
                                     1.85
                                                                             11
                                     3.12
                                     1.66
                                     1.88
                                                                             12
                                     2.85
                                     2.05
                                     1.69
                                                                             13
                                     3.55
                                     2.68
                                     1.48
                                                                             14
                                     3.43
                                     2.84
                                     1.46
                                                                             15
                                     3.37
                                     3.03
                                     1.26
                                                                             16
                                     3.76
                                     3.88
                                     1.06
                                                                             21
                                     2.78
                                     1.67
                                     1.42
                                                                             22
                                     2.64
                                     1.64
                                     1.36
                                                                             23
                                     2.96
                                     1.67
                                     1.32
                                                                             24
                                     2.83
                                     1.62
                                     1.21
                                                                             25
                                     3.23
                                     2.79
                                     1.43
                                                                             27
                                     3.21
                                     3.20
                                     1.21
                                                                             28
                                     3.20
                                     4.04
                                     1.11
                                                                             29
                                     3.00
                                     3.90
                                     1.05
                                                                             30
                                     2.55
                                     2.56
                                     1.05
                                                                             33
                                     1.95
                                     2.00
                                     1.77
                                                                             35
                                     2.67
                                     2.20
                                     1.59
                                                                             37
                                     2.80
                                     2.24
                                     1.42
                                                                             38
                                     2.46
                                     2.06
                                     1.34
                                                                             39
                                     2.46
                                     2.30
                                     1.27
                                                                             40
                                     2.47
                                     2.59
                                     1.17
                                       
Emission Rates for RegClass 40 for 2008 through 2017 model years 
In MOVES2014, we introduced a new regulatory class (40) that classifies LHD2b trucks that are classified as passenger or light-commercial trucks. Regulatory class 41 also contains LHD2b trucks, but only vehicles that are classified as single-unit trucks. The distinction was made in MOVES2014 because passenger and light-commercial trucks assign operating modes using VSP, and MOVES assigns STP-based operating modes to single-unit trucks. In previous versions of MOVES (2010b and earlier), regulatory class 41 was used to model all Class 2b and 3 trucks. 
Most of the analysis conducted in this section was conducted assuming that there would be a single regulatory class to represent Class 2b and 3 trucks (LHD2b3). We thus used the term LHD2b3 trucks to refer to trucks in both regulatory class 40 and 41. However, we only used the data in this section to update the emission rates for regulatory class 40. Emission rates for regulatory class 41 for 2008+ vehicles are discussed in the following section. 
Comparison of LHD2b3 emission rates in MOVES2010 with relevant emission standards
Gasoline vehicles in MOVES regulatory class LHD2b3 (RegClassID 40 and 41) are a mixture of engine certified HD vehicles, chassis certified HD vehicles, and medium duty passenger vehicles (MDPVs).  Each group has a separate set of regulations governing their emissions.  These emission standards are summarized below (Table 3-3). 

                     Table 3-3. Useful Life FTP Standards
                                                                               
                                     MDPV
                                (Tier 2 Bin 5) 
                            8.5k  -  10k (Class 2B)
                                    10k-14k
                                   (Class 3)
                                    Engine
                                   Certified
 Units
                                    g/mile
                                    g/mile
                                    g/mile
                                   g/bhp-hr
Fully Phased in MY
                                     2009
                                     2009
                                     2009
                                     2010
HC
                                   0.09 NMOG
                                   0.195NMHC
                                  0.230 NMHC
                                   0.14 NMHC
CO
                                      4.2
                                      7.3
                                      8.1
                                     14.4
NOx
                                     0.07
                                      0.2
                                      0.4
                                      0.2

The relative proportions of the vehicles within MOVES LHD2b3 regulatory class vary each year depending on demand. Consequently, we estimated proportions based on recent year data and engineering judgment. MOBILE6 documentation from 2003 indicates that MDPVs are approximately 16% of the gasoline 8,500 to 10,000 truck class.  In MOVES2014, we project that MDPVs are 15% of total MOVES LHD2b3 regulatory class  in MYs 2008 and later.  The MOBILE6 document also states that more than 95% of class 2B trucks are chassis certified.60  Extrapolating, we estimate that 5% of all vehicles in the LHD2b3 regulatory class are engine certified.  Based on analysis from the recent medium and heavy duty greenhouse gas rulemaking, we assume that sales of 2B class trucks vehicles were triple that of 3 class trucks. This is roughly consistent with recent model year sales totals.  Combining these assumptions, we get the sales fractions shown below (Table 3-4). 
               Table 3-4. Population Percentage of LHD2b3 Trucks
 
% of Reg Class 
MDPV
                                                                            15%
Class 2B
                                                                            60%
Class 3
                                                                            20%
Engine Certified
                                                                             5%

To generate an aggregate FTP standard for LHD2b3 regulatory class, we weighted the individual certification standards shown in Table 3-3 using the proportions shown in Table 3-4.  While the model produces estimates of on-road emissions rather than certification emissions, the weighted certification standard is a useful benchmark for the modeled rates (Table 3-5).
            Table 3-5. Aggregate Useful Life FTP for LHD2b3 Trucks
 
g/mile
NMOG
                                                                           0.18
CO
                                                                           7.49
NOX
                                                                           0.22

As a benchmark, we compared the calculated aggregate FTP standard to an FTP calculated using the emission rates in the MOVES2010a database.  The Physical Emission Rate Estimator (PERE),33 modified to produce Scaled Tractive Power (STP) distributions, was used to generate the operating mode mix of a LHD2b3 regulatory class  vehicle on the Federal Test Procedure drive cycle.  For the STP modification, we changed the vehicle weight in PERE to match sourceTypeID 32 (Light Commercial Truck) in MOVES (2.06 Tons).  We incorporated emission rates from the MOVES DB for the age 0-3 group, and added in a cold start (operating mode 108) and a hot start (operating mode 102) from the MOVES database. The modified version of PERE produced the operating mode distribution shown in Table 3-6.
Table 3-6. Operating Mode Bin Distribution for a Light-Commercial Truck on the Federal Test Procedure (FTP)
                                                                       OpModeID
                                                                              N
                                                                              %
                                                                       OpModeID
                                                                              N
                                                                              %
                                                                              0
                                                                            160
                                                                            12%
                                                                             25
                                                                             41
                                                                             3%
                                                                              1
                                                                            258
                                                                            19%
                                                                             27
                                                                             49
                                                                             4%
                                                                             11
                                                                             94
                                                                             7%
                                                                             28
                                                                             17
                                                                             1%
                                                                             12
                                                                             68
                                                                             5%
                                                                             29
                                                                             13
                                                                             1%
                                                                             13
                                                                             70
                                                                             5%
                                                                             30
                                                                             15
                                                                             1%
                                                                             14
                                                                             36
                                                                             3%
                                                                             33
                                                                             13
                                                                             1%
                                                                             15
                                                                             48
                                                                             3%
                                                                             35
                                                                             12
                                                                             1%
                                                                             16
                                                                            141
                                                                            10%
                                                                             37
                                                                             13
                                                                             1%
                                                                             21
                                                                             68
                                                                             5%
                                                                             38
                                                                             17
                                                                             1%
                                                                             22
                                                                             44
                                                                             3%
                                                                             39
                                                                             15
                                                                             1%
                                                                             23
                                                                             97
                                                                             7%
                                                                             40
                                                                              6
                                                                             0%
                                                                             24
                                                                             77
                                                                             6%

                                                                               
                                                                               
                                                                               
Total
                                                                           1372
                                                                           100%

Using this operating mode distribution, we constructed a simulated FTP out of four components (bag 1/3 running, cold start, hot start, and bag 2 running).  We constructed bag 1 (cold start + bag 1 running) and bag 3 (hot start + bag 3 running)  and weighted the resulting components together according to the FTP formula, and compared the 2008 and later rates in MOVES to the aggregate standard calculated above (Table 3-7).  MOVES 2010a estimates at age 0-3 are two to ten times larger than the standard, which indicates that the average vehicle HD gas vehicle in MOVES2010a is significantly out of compliance with the relevant standard in this timeframe.

Table 3-7. Comparison between MOVES DB FTP and Aggregate FTP for LHD2b3 Trucks
 
                                   MOVES2010
                        FTP for LHD2b3 Trucks (g/mile)
                               LHD2b3 Aggregate
                             FTP Standard (g/mile)
                                Ratio  -  MOVES
                             to Aggregate Standard
                                       
NMOG
                                                                           0.36
                                                                           0.18
                                                                           1.93
CO
                                                                          14.54
                                                                           7.49
                                                                           1.94
NOx
                                                                           2.04
                                                                           0.22
                                                                           9.28

Validation against In-Use Verification Program Data
We reviewed In Use Verification Program (IUVP) data for MYs 2004-2008 vehicles (estimated test weights of 7,500 pounds to 10,000 pounds) to determine the appropriateness of the MOVES2010 emission rates.  We evaluated whether vehicles during these MYS were achieving the standard, or if alternate methods were being used for compliance. While the IUVP data is not fully representative of the in-use fleet, it provides a reasonable snap-shot.  Without weighting for sales, and accounting for the standards applicable to each vehicle, we calculate average ratios of test value to standard of 0.42 (NMOG) and 0.23 (NOx) (Table 3-8 & Figure 3-4).   These ratios indicate that vehicles typically comply with the standard, with a significant amount of headroom. 
      
      Table 3-8. Average Compliance Margin and Headroom for LHD2b3 Trucks
 
                                    Average
                                    Average
 
                       Ratio Certification FTP/ Standard
                                   Headroom
NMOG
                                                                           0.42
                                                                           0.58
NOx
                                                                           0.23
                                                                           0.77

         Figure 3-4. Distribution of IUVP FTP Tests for LHD2b3 Trucks
      
The emission rates in MOVES include all vehicles, and consequently represent a broader sample than the IUVP data.  As a result, we expect that the onroad vehicles would have higher emission rates than vehicles in the IUVP program.  However, the emission rates represented by MOVES2010 are higher than those that would be expected from vehicles compliant with the standards in place in MY 2008 and later.
Emission Rates
Given that (a) the MOVES2010 LHD2b3 emission rates are significantly above the calculated aggregate standard, and (b) the IUVP data shows that most light-heavy 2b trucks achieve the standard, we calculated new MOVES2014 HC/CO/NOx emission rates for Regulatory Class ID 40  vehicles in 2008 and later MYs.  
In conducting this analysis, we lacked any modal data on regulatory class 40  vehicles. As such, we conducted the analysis using a method that we have used repeatedly on the light duty side, which is ratioing the modal emission profile by the difference in standards.34 By MY 2008, the medium duty vehicles are nearing the emission levels of Tier 2 Bin 8 vehicles.  Consequently, we relied on the analysis of in-use Tier 2 Bin 8 vehicles conducted for the light duty vehicle emission rates.34 Because we are basing the emission rates from light-duty emission rates (which are also VSP-based), the emission rate update is limited to regulatory class 40 vehicles.
We  scaled the modal data from Tier 2 Bin 8 vehicles by the ratio of FTP standards so that the rates would be consistent with the higher emission rates of regulatory class 40 vehicles.  
     Table 3-9. Aggregate LHD2b3 Standard Ratios against Bin 8 Modal Rates
 
Aggregate LHD2b3 FTP Standard
Bin 8 FTP Standard
Aggregate/Bin 8
NMOG
0.18
0.1
1.8
CO
7.49
3.4
2.2
NOx
0.22
0.14
1.6
 We converted this ratio into a "split" ratio, where the running rates increased twice as much as the start rates, but the same overall emissions were simulated on the FTP. This split ratio is consistent with typical emission reduction trends, where running emissions are reduced about twice as much as start emissions34. The "split" ratios for running and start, which were applied to the light-duty Tier 2 Bin 8 vehicle emission rates are shown in Table 3-10.
Table 3-10. Ratio Applied to Light-Duty Tier 2 Bin 8 emission rates to estimate Regulatory Class 40 emission rates for 2008-2017 MY.
 
                                      HC
                                      CO
                                      NOx
Running
                                     2.73
                                     2.73
                                     1.95
Start
                                     1.37
                                     1.37
                                     1.00
We also adopted the light-duty deterioration effects and applied them to the 2009 and later regulatory class emission rates. The light-duty emission rates have age effects that change with each of the 6 age groups in MOVES, as shown in Table 3-11. 
Table 3-11. Multiplicative Age Effect Used for Running Emissions for RegClass 40 2008+ model years.
ageGroupID
                                      HC
                                      CO
                                      NOx
                                                                              3
                                       1
                                       1
                                       1
                                                                            405
                                     1.95
                                     2.31
                                     1.73
                                                                            607
                                     2.80
                                     3.08
                                     2.21
                                                                            809
                                     3.71
                                     3.62
                                     2.76
                                                                           1014
                                     4.94
                                     4.63
                                     3.20
                                                                           1519
                                     5.97
                                     5.62
                                     3.63
                                                                           2099
                                     7.20
                                     6.81
                                     4.11
                                       
After applying the above mentioned steps (scaling the emission factors by ratio of FTP standards, and applying light-duty deterioration trends), we restricted the scaled data so that the individual emission rates by operating mode were never scaled to be higher than MY 2006 regulatory class 40 rates. This essentially capped the emission rates, such that none of the operating mode, or age - specific emission rates for 2009 and later model year vehicles are higher than the 2007 and earlier model year emission rates.
This final step capped emission rates in the highest operating modes. For HC, emission rates in operating modes 28-30 and 38-40 were capped for some or all age groups by the pre-2007 emission rates. For CO, emission rates in 12 of the 23 running operating modes (1, 16, 23-24, 27-30, 35-40) were capped by the pre-2007 rates. None of the NOx emission rates were impacted by this step. Figure 3-5 shows the regclass 40 model year 2008-2017 emission rates for CO, HC, and NOx. Emission rates that exhibit the start-step deterioration trend are the emission rates that were capped with the pre-2007 emission rates. Even with the capped emission rates, the regulatory 40 emission rates are higher than the regulatory 30 emission rates with a few exceptions. The few exceptions are some of the age-dependent HC and or CO emission rates in operating modes 1, 30, 38, 39, and 40. However, the majority of emission rates are significantly higher in regulatory class 40 than regulatory class 30, and when used in MOVES, the simulated FTP emission rates are significantly higher for regulatory class 40 vehicles. 
Figure 3-5. Age Effects for CO, HC, and NOx emission rates for RegClass 40 vehicles in Running Operating Modes for MY 2008-2017.
After calculating new regulatory class 40 emission rates, we used the emission rates to simulate an FTP cycle, as shown in Table 3-12.  We compared these emission rates to the the calculated aggregate standard. The calculated headroom for NOx is less than that shown in the IUVP data, and the calculated headroom for NMOG is greater than that shown in the IUVP data (Table 3-8). For NOx, this difference is more significant. However, as stated above, the IUVP data is not fully representative of in-use vehicles. By contrast, the Bin 8 rates are based on extensive I/M testing, and are considered more representative of the entire fleet. 

              Table 3-12. Ratio of Final rates against standards
 
            Simulated regulatory class class 40 2008+ FTP (g/mile)
                            Aggregate 2010+ LHD2b3
                             FTP Standard (g/mile)
                                  Achieved /
                                  Aggregate 
                                      FTP
NMOG
                                     0.06
                                     0.18
                                      33%
CO
                                     3.08
                                     7.49
                                      41%
NOx
                                     0.18
                                     0.22
                                      84%

In terms of the phase-in, we assumed that the regulatory class 40 rates phase in at a rate of 50% in MY2008 and considered fully phased in MY2009. The MY2008  running emission rates are interpolated values between the 2007 and 2009 emission rates by operating mode and age group. 

Running Emission Rates for RegClass 40 Vehicles for 2018 and later 
The Tier 3 program will affect not only light-duty vehicles (below 8,500 pounds GVWR), but also chassis-certified vehicles between 8,500 and 14,000 pounds GVWR.  This class of vehicles is referred to "light-heavy-duty" or "medium-duty" vehicles. 
This regulatory class comprises several classes of vehicles, including Class 2b and Class 3 trucks, medium-duty passenger vehicles (MDPV) and engine-certified trucks.  However, the latter two groups of vehicles are not regulated under the medium-duty standards described here. However, for completeness, however, they are reflected in the emission rates. 
During the phase-in period, we assumed that Class 2b and 3 vehicles would be certified to four standard levels.  Composite FTP values for these standard levels are shown in Table 3-13. Phase-in fractions for each standard level are also shown in Table 3-14.  The phase-in fractions were applied to the FTP values to calculate weighted average FTP values for these two truck classes for each model year during the phase-in, as shown in Table 3-15.
In addition to 2b and 3 vehicles, "medium-duty" vehicles also include MDPV and engine-certified vehicles.  Composite FTP values were estimated for these classes as well.   The levels for MDPV were assumed to be equivalent to Bin 8 vehicles in 2017 and to light-duty vehicles in 2022 (30 mg/mi).  Interim values were calculated for each model year during the phase-in by assuming a linear decrease over each year between the initial and final values.   The FTP values for the engine-certified vehicles were assumed to be unaffected by the new standards and to therefore remain constant throughout.  The projected averaged FTP values for these two vehicle classes are also shown in Table 3-15.
Finally, weighted average values for all four vehicle classes were calculated as shown in Equation 3-1.  Note that the weights assigned to each vehicle class are equivalent to those previously shown in Table 3-4 (page 82). Values of the weighted means by model year are shown in Table 3-15.

                                                                   Equation 3-1
Table 3-13.  Composite FTP NMOG+NOx Standards for Class 2b and 3 Vehicles (mg/mi).
Vehicle Class
                                      LEV
                                    ULEV34
                                    ULEV25
                                    SULEV17
2b
                                      395
                                      340
                                      250
                                      170
3
                                      630
                                      570
                                      400
                                      230

Table 3-14.  Phase-in fractions by standard level for Class 2b and 3 Vehicles.
Model Year
LEV
ULEV34
ULEV25
SULEV17
2017
0.10
0.50
0.40
0.0
2018
0.0
0.40
0.50
0.10
2019
0.0
0.30
0.40
0.30
2020
0.0
0.20
0.30
0.50
2021
0.0
0.10
0.20
0.70
2022
0.0
0.0
0.10
0.90

Table 3-15.  Projected FTP composite values for four vehicle classes (mg/mi), plus weighted means, by model year during the Tier-3 phase-in.
Model Year
                                 Vehicle Class
                                       
                                 Weighted Mean

                                                                             2b
                                                                              3
                                                                           MDPV
                               Engine-Certified
                                       
                                       
2017
                                                                               
                                                                               
                                                                               
                                       
                                       
                                      400
2018
                                                                            278
                                                                            451
                                                                            102
                                      408
                                       
                                      293
2019
                                                                            253
                                                                            400
                                                                             84
                                      408
                                       
                                      265
2020
                                                                            228
                                                                            349
                                                                             66
                                      408
                                       
                                      237
2021
                                                                            203
                                                                            298
                                                                             48
                                      408
                                       
                                      209
2022
                                                                            178
                                                                            247
                                                                             30
                                      408
                                       
                                      181

If we take the initial value before onset of the phase-in (400 mg/mi) and the final value when the phase-in is complete (181 mg/mi), and treat these two values as references, we can calculate the phase-in fractions that correspond to the weighted means in each intervening model year from 2018 to 2021 inclusive, as shown in Equation 3-2. Resulting phase-in fractions so calculated are shown in Table 3-16.

                                                                   Equation 3-2

Table 3-16.  Phase-in fractions applied to rates in model years 2018 and later to represent partial and full Tier-3 control.
Model Year
                                      fT3
                                   1 − fT3
2017
                                     0.00
                                     1.00
2018
                                     0.49
                                     0.51
2019
                                     0.62
                                     0.38
2020
                                     0.75
                                     0.25
2021
                                     0.87
                                     0.13
2022[1]
                                     1.00
                                     0.00
[1]Also applicable to model years 2022 and later.

To calculate modal emission rates in MY2018 and later, we applied the fractions shown in Table 3-16 above to sets of modal rates representing MY 2017 and MY2022.
The rates for MY2017 were extracting from a previous version of the MOVES database used in analyses supporting the Tier-3 Rulemaking, and represented existing rates prior to the adoption of Tier-3 standards. The rates for MY2022 were estimated as equivalent to light-duty rates, assuming a fleet composition of 10% Bin 8 and 90% Bin 5 standards. These rates were designed to represent full Tier-3 control. 
Thus, starting with these subsets of rates for MY2017 and MY2022, the calculation shown in Equation 3-2 was performed for all rates across all operating modes and ageGroups. 
Resulting rates for HC, CO and NOx are shown in <F to <F, respectively.
Figure 3-6.  THC: Running-exhaust emission rates for vehicles in the LHD<=10k regulatory class (regClassID=40), during the Tier-3 phase-in.
                                       

Figure 3-7.  CO: Running-exhaust emission rates for vehicles in the LHD<=10k regulatory class (regClassID=40), during the Tier-3 phase-in.
                                       

Figure 3-8.  NOx: Running-exhaust emission rates for vehicles in the LHD<=10k regulatory class (regClassID=40), during the Tier-3 phase-in.
                                       

Figure 3-9 displays the average emission rates (across all operating modes) for CO, HC, and NOx across 1980 to 2007 model years for LHD<=10k vehicles. Although not shown, the emission rates within the model years 1960-1980 are the same, as well as the emission rates within model years 2030-2050. Figure 3-9 summarizes the decreasing trend in emissions from the analysis documented in this chapter.
Figure 3-9. Average emission rate (across all operating modes) for regulatory class 40 trucks for CO, HC, and NOx. The1960-2007 emission rates only differ according to two broad age groups (0-5) and (6+). For 2008 and later emission rates, the emissions differ according to the age groups shown in the legend.

Running Emission Rates for Regulatory Class LHD <14 K, LHD45, and MHD, and HHD for 1960-2007 model years
The emission rates are equivalent across all the heavy-duty gasoline running emission rates for these regulatory classes (41, 42, 46, and 47). The same emissions data is used to derive these regulatory class emission rates as was used to derive the regulatory class 40 emission rates. As discussed earlier, the emissions data comes from a mix of LHD2b/3 and MHD vehicles outlined in Table xx. 
The only difference in the analysis with regulatory class 40 emission rates is that these emission   rates were analyzed using STP operating modes with a fixed mass factor of 17.1. The same model year groups are used to classify the emission rates: 1960-1989, 1990-1997, and 1998-2007. Also, the same relative increase in emission rates for the age effect as derived for LHD <= 10K is used. Sample emission rates for HC, CO, and NOx for the 1994 MY Group are presented in Figure X for these source types. 

Figure 3-10. Emission Rates by STP operating mode for MY 1994 at age 0-3 years for Regulatory Class LHD < 14K, LHD45, MHD, and HHD
                                       

Figure 3-11 and Table 3-17  display the multiplicative age effects by operating mode for LHD<14K, LHD45, MHD, and HHD gasoline vehicles. Once again, the age effects were derived from the same data as the LHD<=10K vehicles. The age effects are slightly different for these vehicles, because the operating modes are defined with the STP scaling factor of 17.1. For operating modes that do not depend on the scaling factor (opModeID 0, 1, 11, and 21) the age effects are the same as the LHD<10K age effects. Also, because the vehicles tested were LHD2b/3 and MHD vehicles, no data was binned in the high STP power modes (that typically only a HHD truck would reach). As such, the higher operating modes use the same values as the closest bin with data (opModeID 13-16, 24-30, and 35-40).
Figure 3-11. Emission rates by operating mode and age group for MY 1998-2007 vehicles in Regulatory Class LHD <=14K, LHD45, MHD, and HHD gasoline vehicles.

Table 3-17 Relative age effect on emission rates between age 6+ and age 0-5 for LHD<14K, LHD45, MHD, and HHD gasoline vehicles in all model years 1960-2050.
OpModeID
                                      HC
                                      CO
                                      NOx
                                                                              0
                                     2.85
                                     1.45
                                     1.67
                                                                              1
                                     2.43
                                     1.79
                                     1.85
                                                                             11
                                     3.12
                                     1.66
                                     1.88
                                                                             12
                                     3.36
                                     3.12
                                     1.13
                                                                             13
                                     3.53
                                     3.16
                                     1.11
                                                                             14
                                     3.53
                                     3.16
                                     1.11
                                                                             15
                                     3.53
                                     3.16
                                     1.11
                                                                             16
                                     3.53
                                     3.16
                                     1.11
                                                                             21
                                     2.78
                                     1.67
                                     1.42
                                                                             22
                                     3.08
                                     2.59
                                     1.23
                                                                             23
                                     2.97
                                     3.31
                                     1.05
                                                                             24
                                     1.80
                                     1.54
                                     1.03
                                                                             25
                                     1.80
                                     1.54
                                     1.03
                                                                             27
                                     1.80
                                     1.54
                                     1.03
                                                                             28
                                     1.80
                                     1.54
                                     1.03
                                                                             29
                                     1.80
                                     1.54
                                     1.03
                                                                             30
                                     1.80
                                     1.54
                                     1.03
                                                                             33
                                     2.45
                                     2.41
                                     1.33
                                                                             35
                                     2.16
                                     2.41
                                     1.19
                                                                             37
                                     2.16
                                     2.41
                                     1.19
                                                                             38
                                     2.16
                                     2.41
                                     1.19
                                                                             39
                                     2.16
                                     2.41
                                     1.19
                                                                             40
                                     2.16
                                     2.41
                                     1.19
                                       
Running Emission Rates for Regulatory Class LHD <14 K, LHD45, and MHD, and HHD for 2008 and later model years
Of the on-road heavy duty vehicles GVW class 4 and above, about 15% are gasoline, as opposed to 85% diesel. The gasoline percentage decreases as the GVW class increases. Consequently, there is relatively little data on these vehicles, and we did not update the 2008 and later model year emission rates from MOVES2010 The 2008 and later  model years are modeled with a 70% reduction in the running rates starting in MY 2008, which is consistent with the emission standard reduction with the "Heavy-duty 2007 Rule".   The 2008 and later model year emission rates have two age groups (0-5, and 6+) and the same relative multiplicative age effects as the pre-2007 emission rates, as shown in Figure 3-14. The analysis of regulatory class 40 emission rates for 2008 and later model years is based on light-duty truck VSP-based emission rates. We did not have load-based data on class 2b and 3 trucks to derive STP-based emission rates specific for regulatory class 41 trucks. As such, we estimate regulatory class 41 trucks for 2008 -2017, using the relatively simple 70% reduction from the 1998-2007 baseline
Running Emission Rates for Regulatory Class LHD<14K for 2018 and later model years
As discussed earlier, regulatory class 41 includes Class 2b and 3 trucks, as such the Tier 3 Vehicle Emission standards apply to 2b trucks. Rates for vehicles in this regulatory class were developed in the same way as those for the LHD<=10k regulatory class, as described in 3.1.1.4 (page 89). 
However, for these two classes, the rates for running operation differ in that those for regClass 40 are based on vehicle-specific power (as are rates for light-duty vehicles), whereas those for regulatory class 41 are based on "scaled-tractive power" (STP), as are rates for heavy-duty vehicles in regClasses 42, 46 and 47.
For these two sets of rates, the absolute values of the running rates differ but the relative reductions representing Tier-3 control in each model year are applied in the same proportions. These patterns are shown in Figure 3-12 and Figure 3-13, which show rates for regClasses 40 and 41 in selected operating modes for running emissions. Note that the results are shown on logarithmic scales, and that the parallelism in the trends indicates that the proportional reductions are identical for both the VSP-based (regClass 40) and the STP-based (regClass 41) rates.  Note also that start rates for the two regulatory classes are identical, as they are not defined in terms of either VSP or STP.

Figure 3-12.  THC emission rates vs. model year for regulatory classes 40 and 41, showing selected operating modes for the running-exhaust process (Note the logarithmic scale).
                                       

Figure 3-13.   NOx emission rates vs. model year for regulatory classes 40 and 41, showing selected operating modes for the running exhaust process (Note the logarithmic scale).
                                       

Figure 3-14. Average emission rate (across all operating modes) for regulatory class 41, 42, 46, 47, and 48 for CO, HC, and NOx. Emission rates for 1960-1989, and 2022  -  2050 are constant.

                                       
Particulate Matter
Unfortunately, the PM2.5 emission data from heavy-duty gasoline trucks are too sparse to develop the detailed emission rates for which the MOVES model is designed. As a result, only a very limited analysis could be done. EPA will likely revisit and update these emission rates when sufficient additional data on PM2.5 emissions from heavy-duty gasoline vehicles become available.
In MOVES2010 and MOVES2014, the heavy-duty gas PM2.5 emission rates are calculated by multiplying the light-duty gasoline truck PM2.5 emission rates by a factor of 1.40, as explained below. Since the MOVES light-duty gasoline PM2.5 emission rates comprise a complete set of factors - classified by particulate sub-type (EC and nonECPM), operating mode, model year and regulatory class, the heavy-duty PM2.5 emission factors are  also a complete set. No change to the PM emission rates are made, because the HD 2007 Rule PM standards are not assumed to be technology-forcing standards for spark-ignition medium and heavy-duty gasoline vehicles..
Data Sources
This analysis is based on the PM2.5 emission test results from the four gasoline trucks tested in the CRC E55-E59 test program. The specific data used were collected on the UDDS test cycle.  Each of the four vehicles in the sample received two UDDS tests, conducted at different test weights. Other emission tests using different cycles were also available on the same vehicles, but were not used in the calculation. The use of the UDDS data enabled the analysis to have a consistent driving cycle.  The trucks and tests are described in Table 3-18.

   Table 3-18. Summary of data used in HD gasoline PM emission rate analysis
Vehicle
MY
Age
Test cycle
GVWR [lb]
PM2.5 mg/mi
1
2001
3
UDDS
12,975
1.81

2001
3
UDDS
19,463
3.61
2
1983
21
UDDS
9,850
43.3

1983
21
UDDS
14,775
54.3
3
1993
12
UDDS
13,000
67.1

1993
12
UDDS
19,500
108.3
4
1987
18
UDDS
10,600
96.7

1987
18
UDDS
15,900
21.5

The table shows only four vehicles, two of which are quite old and certified to fairly lenient standards.  A third truck is also fairly old at 12 years and certified to an intermediate standard.  The fourth is a relatively new truck at age three and certified to a more stringent standard.  No trucks in the sample are certified to the Tier2 or equivalent standards.  
Examination of the heavy-duty data shows two distinct levels: vehicle #1 (MY 2001) and the other three vehicles. Because of its lower age (3 years old) and newer model year status, this vehicle has substantially lower PM emission levels than the others, and was separated in the analysis. The emissions of the other three vehicles were averaged together to produce these mean results:

Mean for Vehicles 2 through 4:	65.22 mg/mi			Older Group
Mean for Vehicle 1:			  2.71 mg/mi			Newer Group
Emission Rates for Regulatory Class LHD <=10K
To compare these rates with rates from light-duty gasoline vehicles, we simulated UDDS cycle emission rates based on MOVES light-duty gas PM2.5 emission rates (with normal deterioration assumptions) for light-duty gasoline trucks (regulatory class 30).  The UDDS cycle represents standardized operation for the heavy-duty vehicles.  
To make the comparisons appropriate, the simulated light-duty UDDS results were matched to the results from the four heavy-duty gas trucks in the sample.  This comparison meant that the emission rates from the following MOVES model year groups and age groups for light-duty trucks were used:

   * MY group 1983-1984, age 20+
   * MY group 1986-1987, age 15-19
   * MY group 1991-1993, age 10-14
   * MY group 2001, age 0-3	

The simulated PM2.5 UDDS emission factors for the older light-duty gas truck group using MOVES2010b are 38.84 mg/mi 2.5(Ignoring sulfate emissions which are on the order of 110[-][4] mg/mile for low sulfur fuels), This value leads to the computation of the ratio:.
The simulated PM2.5 UDDS emission rates for the newer light-duty gas truck group are 4.687 mg/mi using MOVES2010b (Ignoring sulfate emissions(which are in the order of 110[-][5] mg/mile for low sulfur fuels), 
This value leads to the computation of the ratio:.
The newer model year group produces a ratio which is less than one and implies that large trucks produce less PM2.5 emissions than smaller trucks. This result is intuitively inconsistent, and is the likely result of a very small sample and a large natural variability in emission results.
All four data points were retained and averaged together by giving the older model year group a 75 percent weighting and the newer model year group (MY 2001) a 25 percent weighting. This is consistent with the underlying data sample. It produces a final ratio of:
                                       
                                       
                         = 1.6790.75 + 0.5780.25 = 1.40

We then multiplied this final ratio of 1.40 by the light-duty gasoline truck PM rates to calculate the input emission rates for heavy-duty gasoline PM rates. This approach works for regulatory class 40 (LHD <= 40) because the emission rates for both regulatory class 30 and 40 are normalized to vehicle mass (or VSP-based emission rates). 
As documented in the light-duty report (cite), the PM emission rates for light-duty vehicles were revised in MOVES2014. This analysis used the light-duty truck PM emission rates from MOVES2010b PM emission rates to derive the 1.4 ratio, and the subsequent heavy-duty gasoline PM emission rates. Hence, a comparison of PM emission rates in MOVES2014 between light-duty, and LHD < 10K, will yield a different ratio than the 1.4 derived for MOVES2010b.
Emission Rates for Regulatory Class LHD <14 K, LHD45, MHD, and HHD
For the larger heavy-duty gasoline emission rates, the emission rates are STP-based with a fixed mass factor of 17.1. Unlike for the gaseous emission rates, we do not have sec/sec emission rates associated with power output that would enable us to calculate a 17.1 metric ton STP-based PM emission rates directly. 
We used an indirect approach to derive STP-based PM emission rates from the emission rates derived for the LHD <= 10K regulatory class. We assume that the relationship of HC between STP and VSP based emission rates is a reasonable surrogate to map PM emission rates to STP-based emission rates. To do so, we first calculated the emission rate ratio for HC emissions for each operating mode between regulatory class 41 and 40. We then multiplied this ratio to the PM emission rates in regulatory class 40 to obtain STP-based PM emission rates in regulatory class 41, 42, 46 and 47. The regulatory class 40 PM emission rates, STP/VSP HC ratios, and the calculated STP-based PM2.5 emission rates are displayed in Table 3-19.
Table 3-19. A demonstration of how STP-based PM emission rates were derived from VSP-based rates using the ratio of HC VSP to STP emission rates as a surrogate, using model year 2001 as an example.
                                   opModeID
                              RegClass 40 (g/hr)
                              HC STP to VSP Ratio
                        RegClass 41, 42, 46, 47 (g/hr)
                                       0
                                     0.59
                                     1.000
                                     0.59
                                       1
                                     0.54
                                     1.000
                                     0.54
                                      11
                                     0.60
                                     1.000
                                     0.60
                                      12
                                     0.79
                                     2.263
                                     1.78
                                      13
                                     1.38
                                     3.677
                                     5.08
                                      14
                                     2.62
                                     5.095
                                     13.37
                                      15
                                     5.55
                                     5.443
                                     30.22
                                      16
                                     64.52
                                     5.427
                                    350.13
                                      21
                                     8.38
                                     1.000
                                     8.38
                                      22
                                     2.92
                                     1.154
                                     3.37
                                      23
                                     2.08
                                     2.173
                                     4.52
                                      24
                                     2.92
                                     2.825
                                     8.24
                                      25
                                     10.94
                                     4.842
                                     52.95
                                      27
                                     20.50
                                     7.906
                                    162.10
                                      28
                                    126.42
                                     8.796
                                   1,112.05
                                      29
                                    523.16
                                     6.471
                                   3,385.32
                                      30
                                   2,366.75
                                     7.102
                                   16,809.50
                                      33
                                     26.59
                                     2.121
                                     56.40
                                      35
                                     10.76
                                     4.780
                                     51.42
                                      37
                                     13.29
                                     4.010
                                     53.28
                                      38
                                     43.61
                                     8.979
                                    391.56
                                      39
                                     75.73
                                     9.522
                                    721.06
                                      40
                                     74.96
                                     5.300
                                    397.26

Energy Consumption
LHD<=10k Energy Rates for Model Years 1960-2013
The energy rates for LHD<=10k for pre-2007 gasoline energy rates are unchanged from the LHD2b3 regulatory class from MOVES2010a. In MOVES2010a, the energy rates for this regulatory class, along with the light-duty regulatory classes, were consolidated across weight classes and engine technologies, as discussed in the energy updates report.5 

LHD<=10k Energy Rates for Model Years 2014-2050
Lower energy consumption rates for LHD<=10k vehicles are expected due to the Phase 1 Medium and Heavy Duty Greenhouse Gas Rule, as discussed in more detail in Section 2.1.4.4. The CO2 emission reductions for gasoline 2b trucks in Table 2-19 were applied equally to the 2013 model year energy consumption rates in each running operating mode bins to derive 2014 and later energy consumption rates. Figure 2-29 displays the average energy consumption (across all running operating modes) for model years 1970 through 2030. The rates are constant between 1960 to 1973, and from 2018 to 2050.
                                       
Figure 3-15. Average Energy Consumption Rates for LHD<=10K gasoline vehicles across all running operating modes

          

LHD<=14k,  LHD45, MHD, and HHD Energy Rates for Model Years 1960-2013
The data used to develop heavy-duty running exhaust gasoline rates were the same as those used for HC, CO, and NOx. However, new energy rates were only developed for LHD<14K, LHD45, MHD, HHD, and bus classes. Similar to the diesel running exhaust energy rates, classifications were not made based on model year group, age, or regulatory class. To calculate energy rates (kJ/hour) from CO2 emissions, we used a heating value (HV) of 122,893 kJ/gallon and CO2 fuel-specific emission factor (fCO2) of 8,788 g/gallon for gasoline (see Equation 2-19).  STP was calculated using Equation 1-2. Figure 3-16 summarizes the gasoline running exhaust energy rates stored in MOVES for the STP-based regulatory classes (LHD= <14K, MHD, and HHD). 
Figure 3-16. Gasoline running exhaust energy rates for LHD <14K (1960-2013),, LHD45 (1960-2015),  MHD (1960-2015), and HHD (1960-2015)

A linear extrapolation to determine rates at the highest operating modes in each speed range was performed analogously to diesel energy and NOx rates (see Section 2.1.1.3.3).

         .1..1 LHD<=14k,  LHD45, MHD, Urban Bus, and HHD Energy Rates for Model Years 2014-2050

 Updates to the rates displayed in Figure 3-16 were made to the heavy-duty gasoline energy rates for model years 2014+ based on the 2014 Medium and Heavy-duty Greenhouse Gas Rule44 as discussed in Section 2.1.4.4. Figure 3-17 displays the average energy consumption rates for the heavy-duty gasoline source types that are modeled using Scaled Tractive Power (STP) with a fixed mass factor of 17.1. The energy rates for all these source types are equivalent for model years 1960-2013. The reduction in the average energy consumption rates is displayed in Figure 3-17,  with separate reductions for the class 2b and 3 trucks (LHD<=14k), class 4-7 trucks (LHD45, MHD), and class 8 trucks (HHD). For LHD<=14k the energy rates are constant 2018 going forward, for the other categories (LHD45, MHD, HHD) the energy rates  are constant going forward starting in model year 2017. 
 
Figure 3-17. Average Energy Consumption Rates for LHD<=14k (41), LHD45 (42), MHD (46) and HHD (47) gasoline vehicles across all running operating modes.
                                       

Start Emissions
Available Data
To develop start emission rates for heavy-duty gasoline-fueled vehicles, we extracted data available in the USEPA Mobile-Source Observation Database (MSOD).  These data represent aggregate test results for heavy-duty spark-ignition (gasoline powered) engines measured on the Federal Test Procedure (FTP) cycle. The GVWR for all trucks was between 8,500 and 14,000 lb, placing all trucks in the LHD2b3 regulatory class.
Table 3-20 shows the model-year by age classification for the data. The model year groups in the table were assigned based on the progression in NOx standards between MY 1990 and 2004.  Standards for CO and HC are stable over this period, until MY 2004, when a combined NMHC+ NOx standard was introduced. However, no measurements for trucks were available for MY2004 or later.
Start emissions are not dependent on power, and the emission rates do not need to be calculated differently to account for different scaling factors used to calculate STP-based operating modes, as was done for running exhaust rates. As discussed later, start emission rates are modeled differently among regulatory classes to account for differences in the emission standards/and or the data supported different start emission rates. No differences in start emissions are modeled between regulatory class 40 and 41 vehicles, because no differentiation by STP mass scaling factor are needed.
Table 3-20. Model-year Group by AgeGroup Structure for the Sample of Heavy-Duty Gasoline Engines
Model-year Group
Standards (g/hp-hr)
Age Group (Years)
Total

CO
HC
NOx
0-3
4-5
6-7
8-9
10-14

1960-1989

19
22
41
1990
14.4
1.1
6.0

1
29

30
1991-1997
14.4
1.1
5.0
73
59
32
4

168
1998-2004
14.4
1.1
4.0
8

8
Total

81
59
33
52
22
247
Estimation of Mean Rates
As with light-duty vehicles, we estimated the "cold-start" as the mass from the cold-start phase of the FTP (bag 1) less the "hot-start" phase (Bag 3). As a preliminary exploration of the data, we averaged by model year group and age group and produced the graphs shown in Appendix F

Heavy-duty Gasoline Start Emissions Analysis FiguresSample sizes are small overall and very small in some cases (e.g. 1990, age 6-7) and the behavior of the averages is somewhat erratic. In contrast to light-duty vehicle emissions, strong model-year effects are not apparent. This may not be surprising for CO or HC, given the uniformity of standards throughout. This result is more surprising for NOx but model year trends are no more evident for NOx than for the other two. Broadly speaking, it appears that an age trend may be evident.
If we assume that the underlying population distributions are approximately log-normal, we can visualize the data in ways that illustrate underlying relationships. As a first step, we calculated geometric mean emissions, for purposes of comparison to the arithmetic means calculated by simply averaging the data. Based on the assumption of log-normality, the geometric mean (xg) was calculated in terms of the logarithmic mean (xl) as

                                       
                                 Equation 3-3

This measure is not appropriate for use as an emission rate, but is useful in that it represents the "center" of the skewed parent distribution. As such, it is less strongly influenced by unusually high or outlying measurements than the arithmetic means in Appendix F.
In general, the small differences between geometric means and arithmetic means suggest that the distributions represented by the data do not show strong skew in most cases.  Assuming that emissions distributions should be strongly skewed suggests that these data are not representative of "real-world" emissions for these vehicles. This conclusion appears to be reinforced by the values in Figure F-3 which represent the "logarithmic standard deviation" calculated by model-year and age groups.  This measure (sl), is the standard deviation of natural logarithm of emissions (xl). The values of sl are highly variable, and generally less than 0.8, showing that the degree of skew in the data is also highly variable as well as generally low for emissions data; e.g., corresponding values for light-duty running emissions are generally 1.0 or greater. Overall, review of the geometric means confirms the impression of age trends in the CO and HC results, and the general lack of an age trend in the NOx results.
Given the conclusion that the data as such are probably unrepresentative, assuming the log-normal parent distributions allows us to re-estimate the arithmetic mean after assuming reasonable values for sl. For this calculation we assumed values of 0.9 for CO and HC and 1.2 for NOx. These values approximate the maxima seen in these data and are broadly comparable to rates observed for light-duty vehicles.
The re-estimated arithmetic means are calculated from the geometric means, by adding a term that represents the influence of the "dirtier" or "higher-emitting" vehicles, or the "upper tail of the distribution," as shown in Figure F-4.

                                       
                                 Equation 3-4
For purposes of rate development using these data, we concluded that a model-year group effect was not evident and re-averaged all data by age group alone. Results of the coarser averaging are presented in Figure 3-18 with the arithmetic mean (directly calculated and re-estimated) and geometric means shown separately. 
We then addressed the question of the projection of age trends. As a general principle, we did not allow emissions to decline with age. We implemented this assumption by stabilizing emissions at the maximum level reached between the 6-7 and 10-14 age groups.

Figure 3-18. Cold-start FTP Emissions for Heavy-Duty Gasoline Trucks, averaged by Age Group only (g = geometric mean, a= arithmetic mean recalculated from xl and sl)
Estimation of Uncertainty
We calculated standard errors for each mean in a manner consistent with the re-calculation of the arithmetic means. Because the (arithmetic) means were recalculated with assumed values of sl, it was necessary to re-estimate corresponding standard deviations for the parent distribution s, as shown in Equation 3-5.

                                       
                                 Equation 3-5
After recalculating the standard deviations, the calculation of corresponding standard errors was simple. Because each vehicle is represented by only one data point, there was no within-vehicle variability to consider, and the standard error could be calculated as . We divided the standard errors by their respective means to obtain CV-of-the-mean or "relative standard error." Means, standard deviations and uncertainties are presented in Table 3-21 and in Figure 3-19. Note that these results represent only "cold-start" rates (opModeID 108).

Table 3-21. Cold-Start Emission Rates (g) for Heavy-Duty Gasoline Trucks, by Age Group (italicized values replicated from previous age Groups)
Age Group
n
Pollutant

CO
THC
NOx

Means

   0-3
81
101.2
6.39
4.23
   4-5
59
133.0
7.40
5.18
   6-7
33
155.9
11.21
6.12
   8-9
52
190.3
11.21
7.08
   10-14
22
189.1
11.21
7.08

Standard Deviations

   0-3

108.1
6.82
8.55
   4-5

142.0
7.90

   6-7

166.5
11.98
12.39
   8-9

203.2
11.98
14.32
   10-14

202.0
11.98
14.32

Standard Errors

   0-3

12.01
0.758
0.951
   4-5

18.49
1.03
1.18
   6-7

28.98
2.08
2.16
   8-9

28.18
2.08
1.99
   10-14

43.06
2.08
1.99

Figure 3-19. Cold-start Emission Rates for Heavy-Duty Gasoline Trucks, with 95% Confidence Intervals
Projecting Rates beyond the Available Data
The steps described so far involved reduction and analysis of the available emissions data. In the next step, we describe approaches used to impute rates for model years not represented in these data. For purposes of analysis we delineated four model year groups: 1960-2004, 2005-2007, 2008-2017 and 2018 and later. We describe the derivation of rates in each group below.
Regulatory class LHD2b3(RegClassID 40 and 41)
For CO the approach was simple. We applied the values in Table 3-21 to all model-year groups. The rationale for this approach is that the CO standards do not change over the full range of model years considered.
For HC and NOx we imputed values for the 2005-07 and 2008-2017 model-year groups by multiplying the values in Table 3-21 by ratios expressed in terms of the applicable standards. Starting in 2005, a combined HC+NOx standard was introduced. It was necessary for modeling purposes to partition the standard into HC and NOx components. We assumed that the proportions of NMHC and NOx would be similar to those in the 2008 standards, which separate NMHC and NOx while reducing both.
We calculated the HC value by multiplying the 1960-2004 value by the fraction fHC, where 

                                       
                                 Equation 3-6

This ratio represents the component of the 2005 combined standard attributed to NMHC.
We calculated the corresponding value for NOx as

                                       
                                 Equation 3-7
For these rates we neglected the THC/NMHC conversions, to which we gave attention for light-duty.
For the 2008-2017 model years, the approach to projecting rates was modified so as to adopt two refinements developed for light-duty rates.  First, start emission rates from LHD2b3 gasoline vehicles were estimated by applying the "start split-ratio" shown in Table 3-10 to a set of rates representing light-duty vehicles in Tier-2/Bin 8. Accordingly, start emission rates adopted the same age effects as the light-duty start emission rates. The multiplicative age effects for start emission rates for 2008-2017 vehicles are shown in Table 3-22.
Incorporating Tier-3 Standards:  Model years 2018 and later.
Emission rates for the start-exhaust process were developed employing the techniques described for running-exhaust emissions, as described above in 3.1.1.4 (page 89).  Start rates for HC, CO and NOx during the Tier-3 phase-in (2018-2022) are shown below in Figure 3-19 to Figure 3-22. Note that start rates are identical for both the LHD<=10k and LHD<=14k regulatory classes (regClassID = 40, 41, respectively). 

Figure 3-20.  THC: Emission rates for the start-exhaust process, for the LHD<=10k (40) and the LHD<=14k (41) regulatory classes, by operating mode and age group, during the Tier-3 phase-in.
                                       

Figure 3-21.  CO: Emission rates for the start-exhaust process, for the LHD<=10k (40) and the LHD<=14k (41) regulatory classes, by operating mode and age group, during the Tier-3 phase-in.
                                       

  Figure 3-22. NOx:  Emission rates for the start-exhaust process, for the LHD<=10k (40) and the LHD<=14k (41) regulatory classes, by operating mode and age group, during the Tier-3 phase-in.
                                       

Table 3-22. Multiplicative Age Effect Used for Start Emissions for RegClass 40 and 41 vehicles for 2008-2017 model years. Adopted from the deterioration effects for RegClass 30 vehicles from the Light-Duty Report. 
ageGroupID
                                      HC
                                      CO
                                      NOx
                                                                              3
                                       1
                                       1
                                       1
                                                                            405
                                     1.65
                                     1.93
                                     1.73
                                                                            607
                                     2.20
                                     2.36
                                     2.21
                                                                            809
                                     2.68
                                     2.54
                                     2.76
                                                                           1014
                                     3.30
                                     3.00
                                     3.20
                                                                           1519
                                     3.66
                                     3.35
                                     3.63
                                                                           2099
                                     4.42
                                     4.06
                                     4.11

Regulatory classes LHD45, MHD, and HHD
For LHD45 and MHD, we estimated values relative to the LHD2b3 start emission rates estimated in MOVES2010.
For CO and HC, we estimated values for the heavier vehicles by multiplying them by ratios of standards for the heavier class to those for the lighter class.
The value for CO based on 1990-2004 model year vehicles is 

                                       
           Equation 3-8
and the corresponding value for HC based on 1990-2004 model year vehicles is 1.73.

                                       
           Equation 3-9

The ratios derived in Equation 3-8 and Equation 3-9 (2.58 and 1.73)  are applied to estimate the start emission rates for all three  model year groups for the LHD45, MHD, and HHD gasoline vehicles (Table 3-23). For NOx, all MOVES2014 start emissions for medium and heavy-duty vehicles are equal to for the MOVES2010 LHD2b3 start emission rates, because the same standards apply to both classes throughout. The approaches for all three regulatory classes in all three model years are shown in Table 3-23.
Table 3-23. Methods used to Calculate and Start Emission Rates for Heavy-Duty Spark-Ignition Engines
Regulatory Class
Model-year Group
Method

CO
THC
NOx
LHD2b3 (LHD<= 10K and LHD < 14K)
1960-2004
Values from
Table 3-21
Values from
Table 3-21
Values from
Table 3-21

2005-2007
Values from
Table 3-21
Reduce in
proportion
to standards from 1960-2004
Reduce in proportion
to standards from 1960-2004

2008 - 2017  
Values from
Table 3-21
Section 3.2.4.1
Section 3.2.4.1

2018 +
Section 3.2.4.2
Section 3.2.4.2
Section 3.2.4.2 
LHD45, MHD, HHD
1960-2004
Increase in proportion
to standards from LHD2b3
Increase
in proportion
to standards from LHD2b3
Same values as
LHD2b3

2005-2007
Increase in proportion
to standards from LHD2b3
Increase in  proportion
to standards from LHD2b3
Same values as
LHD2b3

2008 +
Increase in  proportion
to standards from MOVES2010b LHD2b3
Increase in proportion
to standards from MOVES2010b LHD2b3
Same values as
MOVES2010b LHD2b3

As for heavy-duty diesel and light-duty vehicles we applied the curve in Figure 2-33 to adjust the start emission rates for varying soak times.  The rates described in this section were for cold starts (soak time > 720 minutes).
Particulate Matter
Data on PM start emissions from heavy-duty gasoline vehicles were unavailable.  As a result, we used the multiplication factor from the running exhaust emissions analysis of 1.40 to scale up start emission rates for light-duty trucks (regClassID 30) for model years 1960-2017. For 2018 and later model years, the start PM emissions for heavy-duty gasoline are estimated to be the same as the rates in 2017. As such, the start PM emission rates for heavy-duty gasoline vehicles exhibit the same relative effects of soak time, and deterioration as the light-duty PM start emission rates. 

Start Energy Rates
The heavy-duty gasoline start energy rates were originally derived in MOVES2004, and updated in MOVES2010 as described in the corresponding reports28[,]5. Post-2000, the only changes to the start energy rates, is the projected impact of the Phase 1 Heavy-duty GHG standards, which begin phase-in in 2014 and have the same reductions as the running energy rates as presented in Table 2-19. 

Figure 3-23. Heayv-duty gasoline cold start energy rates (opMode 108) by model year and regulatory class.

The start energy rates are reduced for shorter soak times using the same factors for diesel vehicles, as presented in Table 2-28. Table 3-24 displays the relative contribution of running and start operation to total energy consumption from the heavy-duty gasoline regulatory classes from a National MOVES run for calendar year 2011. As for diesel vehicles, starts are estimated to be a relatively small contributor to the total energy demand of vehicle operation. Due to the small contribution to the total energy inventory, the start emissions have not been prioritized to be updated with more recent data. 
                                       
Table 3-24. Relative contribution of total energy consumption from each pollutant process by regulatory class for heavy-duty gasoline vehicles in calendar year 2011.
processID
processName
                                      40
                                      41
                                      42
                                      46
                                      47
                                                                              1
Running Exhaust
                                     96.3%
                                     98.9%
                                     99.0%
                                     98.1%
                                     98.1%
                                                                              2
Start Exhaust
                                     3.7%
                                     1.1%
                                     1.0%
                                     1.9%
                                     1.9%

Heavy Duty Compressed Natural Gas Transit Bus Emissions
While natural gas lacks the ubiquitous fueling infrastructure of gasoline, compressed natural gas (CNG) has grown as a transportation fuel for public transit, government, and corporate fleets.  Such fleets typically utilize centralized, privately-owned refueling stations. Within this segment, some of the most rapid growth in CNG vehicles over the last 15 years has occurred among city transit bus fleets, as seen in Figure 4-1.
Figure 4-1. US natural gas bus population by year and fuel type from 1996-2011 (APTA) 

MOVES2010b and earlier versions can model emissions from CNG bus fleets. However, in absence of better data, MOVES2010b used the emission rates originally developed for medium heavy-duty gasoline trucks (regulatory class 46).  These rates were used for hydrocarbon (HC), nitrogen oxides (NOx), carbon monoxide (CO), and particulate matter (PM) emission rates. Medium HD gasoline trucks are reasonable proxies in terms of vehicle weight and engine size, but as this report shows, there are substantial differences in the MOVES2010b emissions rates and real-world measurements of CNG transit buses.  This section updates the CNG bus emission rates in MOVES based on measurements from CNG buses and future projections.
Transit Bus Driving Cycles and Operating Mode Distributions
Heavy-Duty Transit Bus Driving Cycles
To evaluate whether the existing MOVES2010b rates for gasoline vehicles were appropriate surrogates for buses powered with CNG, we generated test cycle simulations using MOVES and compared the simulated results against chassis dynamometer measurements from published test programs.  This process involved using MOVES to determine the distribution of operating modes for each drive cycle, and then multiplying the time spent in each mode by the corresponding emission rates in the EmissionRateByAge table.  As in a transient emissions test, the sum of the emissions at each second over the duration of the test yields the total mass of emissions over the test cycle.  Dividing the total by distance yields the emission rate over the test.  These test programs included only running emissions and were based on a variety of heavy-duty and transit bus driving cycles.  We configured MOVES to simulate the drive cycles by importing each drive cycle into MOVES using the Link Driving Schedules template in the Project Data Manager tool.  As these were dynamometer measurements, we set the grade to "0" over the duration of each cycle. We imported two driving cycles: 1) the Central Business District (CBD), and 2) Washington Metropolitan Area Transit Authority (WMATA).
The CBD cycle is defined as a driving pattern with constant acceleration from rest to 20 mph, a short cruise period at 20 mph, constant deceleration back to rest, and then repeated for 600 seconds (see Figure 4-2). The WMATA cycle was developed using GPS data from city buses in Washington, DC, and has higher speeds and greater periods of acceleration than the CBD cycle (see Figure 4-3).70
Figure 4-2. Driving schedule trace of the Central Business District (CBD) cycle (DieselNet)

Figure 4-3 Driving schedule trace of the Washington Metropolitan Area Transit Authority (WMATA) cycle Melendez et al. 2005)
                                       
                                       
Transit Bus Operating Mode Distributions
The MOVES project level importer was used to input the second-by-second drive cycle.  A single link was created, with the test cycle entered as a drive trace. Running MOVES generated the operating mode distribution, which is created by allocating the time spent in each operating mode according to the cycle speed and acceleration, as shown in Figure 4-4 and Figure 4-5. The derivation of scaled tractive power (STP) and operating mode attribution for heavy-duty vehicles are discussed earlier in this report, in Section 1.4. 
Since STP is dependent on mass (among other factors), the average vehicle inertial test mass for each cycle was inserted into the MOVES2010b sourceUseType table in place of the default transit bus mass to ensure a more accurate simulation. Using the measured vehicle masses across all the test programs reviewed, the CBD cycle had an average test mass of 14.957 metric tons and the WMATA cycle had an average mass of 16.308 metric tons, compared to the default of 16.556 metric tons. We used the road load coefficients from MOVES2010b for transit buses, and any changes in the coefficients (A, B, and C) with the tested buses were assumed to be negligible.
           Figure 4-4. Operating mode distribution for the CBD cycle
         Figure 4-5.  Operating mode distribution for the WMATA cycle
Comparison of Simulated Rates and Real-World Measurements
Simulating Cycle Emission Aggregates from MOVES2010b Rates 
   Having determined the total amount time spent in each operating mode over the course of each drive cycle, using the emission rates in the MOVES database (DB), we were able to simulate emissions over each cycle. Using this method, the simulated cycle emission aggregates were calculated as a function of the following parameters:
   * fuel type,
   * driving cycle,
   * age group,
   * regulatory class,
   * model year, and
   * pollutant and process.
We simulated a distance-specific emission factor (EFsim, g/mile) for each pollutant for each cycle based on the operating mode distributions, existing MOVES emission rates, and the distance of the drive cycle, using the equation below:
                                                                            			
                                                   		      Equation 4-1
where
	tOM,cycle = cycle's total time spend in operating mode OM,
	dcycle = distance of the cycle,
	rp,OM = time-specific emission rate of pollutant p in operating mode OM.
                                                                               
We compared the published test measurements to simulations using the MOVES2010b CNG transit bus rates from Equation 28. We also specified the age group and model year to match individual vehicles in the testing programs from the literature on CNG transit buses.
Published Chassis Dynamometer Measurements 
These programs were conducted at several research locations around the country on different heavy-duty chassis dynamometer equipment. In our analysis, we collected 35 unique dynamometer measurements -- which consisted of running emissions rates in mass per unit distance for each of the pollutants and total energy below:
   1. total hydrocarbons (THC),
   2. methane (CH4),
   3. carbon monoxide (CO),
   4. oxides of nitrogen (NOx),
   5. particulate matter (EC + non-EC), and
   6. total energy consumption. 
Note that methane emissions are not estimated using emission rates, as are the other pollutants listed above. Rather, methane is estimated in relation to THC, using ratios stored in the  "methaneTHCratio" table. The ratios are categorized by fuel type, pollutant process, source type, model-year group, and age group. We then multiplied the THC rate by the corresponding ratio from the "methanethcratio" table to calculate the CH4 rate. 
All criteria emission rates are dependent on vehicle age, and thus are stored in the emissionRateByAge table and, and total energy consumption is age independent, and therefore stored in the "emissionRate" table. Some of the published studies did not report total energy consumption directly, so it was necessary to compute energy from a stoichiometric equation based on the carbon content in the emitted pollutants or from reported values of miles per gallon equivalent of diesel fuel. In the former case, we used 0.8037 as the carbon fraction coefficient for nonmethane hydrocarbons (NMHC) when the bus was equipped with an oxidation catalyst and 0.835 without due to high ethene levels, using speciation profiles from Ayala et al. (2003) discussed later in this section. All other conversion factors to energy were taken from Melendez et al. (2005).70
On a similar note, MOVES does not report particulate matter (PM) as a single rate; it reports one rate for PM from elemental carbon (EC) of 2.5 microns or less, and another rate for non-elemental carbon of 2.5 microns or less. These separate rates for PM (EC) and PM (NonEC) from the emissionRateByAge table are added together for a total PM rate used for comparison to the measurements.
The number of unique measurements is approximately equal to the number of vehicles tested, although not exactly. Some vehicles were tested more than once because a variable in the experiment changed, such as the after-treatment technology.  All of the vehicles were in service with a transit agency at the time of testing. In addition, these measurements were typically reported as cycle averages based on multiple runs with the same vehicle and configuration over a specific driving cycle. Many of the testing programs also included diesel transit buses, but these vehicles were excluded from this analysis. Table 4-1 shows a summary of the number of unique CNG bus measurements by driving cycle for each study. Navistar published a similar study of CNG and diesel buses in 2008, and this analysis shares many of the same sources.
Table 4-1. Summary of external emissions testing programs by driving cycle and number of unique measurements
                                 Paper/Article
                              Lead Research Unit
                               Driving Cycle(s)
                         Number of Unique Measurements
Melendez 200570
National Renewable Energy Laboratory (NREL)
                                     WMATA
                                       7
Ayala 2002
California Air Resources Board (CARB)
                                      CBD
                                       2
Ayala 200371
CARB

                                      CBD
                                       6
Lanni 2003
New York Department of Environmental Conservation
                                      CBD
                                       3
McCormick 1999
Colorado School of Mines

                                      CBD
                                       3
LaTavec 2002
ARCO (a BP Company)

                                      CBD
                                       2
McKain 2000
WVU

                                      CBD
                                       3
Clark 1997
WVU

                                      CBD
                                      10
TOTAL

                                      35

As seen above, the CBD driving cycle was applied in each study except for one. Since it (a) had the largest sample size and (b) appeared to be representative of the data from other cycles, we focused our analysis on the CBD cycle results. 
We approximated the vehicle's age by subtracting the year the study was conducted from the model year of the vehicle. Most vehicles tested were less than three years old (ageGroupID "3"), whereas 9 vehicles fell into the four to five year-old age group (ageGroupID "405"). In the CBD cycle, 5 out of 28 vehicles were in ageGroupID "405", and their performance was generally similar to the 0-3 age vehicle results.  Consequently, we combined the vehicles from age group 405 with the vehicles from group 3. Vehicle model years ranged from MY 2001 to MY 2004 for the WMATA cycle and from MY 1994 to MY 2001 for the CBD cycle.
Plots of Simulated Aggregates and Published Measurements
Below are graphs of the CBD measurements by model year for each pollutant compared to simulated MOVES2010b CNG (MHD gasoline) rates. 

Figure 4-6. NOx emission comparisons of CNG transit bus dynamometer measurements and MOVES2010b simulated aggregates on the CBD cycle. 

                                       
Figure 4-7. CO emission comparisons of CNG transit bus dynamometer measurements and MOVES2010b simulated aggregates on the CBD cycle.

                                       
Figure 4-8. PM emission comparisons of CNG transit bus dynamometer measurements and MOVES2010b simulated aggregates on the CBD cycle.
 
                                       

Figure 4-9. THC emission comparisons of CNG transit bus dynamometer measurements and MOVES2010b simulated aggregates on the CBD cycle.

                                       
Figure 4-10. CH4 emission comparisons of CNG transit bus dynamometer measurements and MOVES2010b simulated aggregates on the CBD cycle.
Figure 4-11. Total energy consumption comparisons of CNG transit bus dynamometer measurements and MOVES2010b simulated aggregates on the CBD cycle.
                                       
In Figure 4-6, the MOVES2010b CNG rates slightly under-predict the bus NOx measurements. As shown in Figure 4-7, MOVES2010b predictions for CO emissions are similar to the CNG measurements, particularly after 1999. Figure 4-8 shows that the MOVES2010b CNG predictions are lower for PM. As seen in Figure 4-9, MOVES2010b CNG predictions for THC emissions are lower than the measurements by an order of magnitude.  As seen in Figure 4-10, this underestimate of THC is largely attributable to a significant underestimate of CNG related CH4 in MOVES2010b. These relatively high CH4 emissions from CNG buses compared to gasoline or diesel buses are likely from the exhaust of uncombusted natural gas, but further study is warranted. Figure 4-11 shows that MOVES2010b under-predicts the total energy consumption seen in the literature. We address these discrepancies by using the published measurements to develop new CNG exhaust emission rates MOVES2014 rates across all the pollutants and total energy discussed above.
These comparisons show that updating the MOVES2010b with these additional data from CNG buses have significant impact on the emissions inventories from CNG buses. As shown in this analysis, the existing CNG rates based on MHD gasoline trucks are not adequate surrogates.  As discussed in the next section, we developed new rates based on cycle averages from the dynamometer measurements. The remainder of this report is devoted to a discussion on the development of new time-based emission rates (g/hr) for CNG buses.
Development of New Running Exhaust Emission Rates
Determining Model Year Groups
Ideally, new MOVES emission rates are developed through analysis of second by second data of vehicles of the appropriate regulatory class, model year, and age.  Unfortunately, such modal data is not readily available in this case. However, we substantially improved the CNG bus emission rates in MOVES2014 relative to MOVES2010b by raising or lowering the MY emission rates wholesale (as opposed to individual adjustments by operating mode).
Fundamentally, the first necessary step is assigning a set of appropriate model year groups for the data.  Using too few model year groups may miss important differences in the emission rates, while using too many model year groups can give false prominence to outliers and introduce artificial "jumps" in the emission rates. We chose to group the model year groups according to similar emission rates in the criteria pollutants (THC, CO, NOx and PM).
We separated CNG buses - equipped with oxidation catalysts and those not equipped, to determine if this was a reasonable distinction, and to see if these vehicles' criteria emission rates varied by model year and by age.  For some model years, there are both after-treatment equipped and non-equipped vehicles.  In these years, there was not a visible difference in the criteria emission levels between the vehicles in the testing programs with after-treatment (AT) equipment and those with no after-treatment (see the figures in Section Heavy-duty CNG Bus Emissions Supplemental Figures in the appendix).  Given the small sample size, the lack of clear trends among the individual vehicle models, and our lack of data on the relative distribution of after-treatment equipped vehicles versus unequipped vehicles in each of these model years, we chose to group all the CBD measurements from the literature into one model year group, spanning from MY 1994 to MY 2001. No data on CNG buses equipped with three-way catalysts (TWC) was readily available at the time of this analysis; we will look to incorporate data from buses that have TWCs and spark ignited, stoichiometric-burn engine technology as it becomes available. 
Of the surveyed data, only one study had any vehicles newer than MY 2001. This paper, a joint study between NREL and WMATA, had a small sample of vehicles from MY 2004.  These vehicles have a visibly different emissions profile than the other vehicles.70 While these buses were only tested on the WMATA driving cycle, they were all equipped with oxidation catalysts and had substantially lower emissions from the 1994-2001 buses, particularly for PM emissions. As a result, a second model year group runs from MY 2002 to MY 2006 based on a group of MY 2004 WMATA buses.  This MY group ends before MY 2007 when a new series of stringent emission standards went into effect. We did, however, apply a sales-weighted adjustment factor to the unusually low CO rate for these John Deere CNG buses according to certification data, as described below.
Scaling Model Years After 2007	
Without published data on in-use vehicles past MY 2004, we use emission certification levels as a proxies to estimate emission rate changes since then. Certification levels are reported in grams per brake horsepower-hour and are not directly used in formulating MOVES emission rates because they do not include real-world effects such as vehicle mileage or deterioration.[,]   These effects were present in the testing programs, so we created scaling factors that we could apply to the measured data from the testing programs to estimate rates after MY 2004. 
Natural gas transit bus emission certification data by model year is publicly available on the EPA's Office of Transportation and Air Quality website. Analysis of these data showed that from MY 2002 to MY 2012 there have been changes in certification levels for all the pollutants considered in this report. In particular, NOx and PM levels have dropped dramatically over the past decade.  This effect is largely attributable to increasingly strict emission standards, which have affected both diesel and CNG buses. Table 4-2 below indicates the number of CNG transit bus models certified for each model year.
Table 4-2. A summary of the number of certified CNG transit buses by model year (USEPA OTAQ).
                                       
                                  Model Year
                           Number of Vehicle Models
                                     2002
                                       4
                                     2003
                                       4
                                     2004
                                       4
                                     2005
                                       6
                                     2006
                                       4
                                     2007
                                       3
                                     2008
                                       1
                                     2009
                                       1
                                     2010
                                       2
                                     2011
                                       2
                                     2012
                                       2
                                     TOTAL
                                      33

To improve the accuracy of the scaling factor we weighted the emission levels with projected US sales figures for the certified CNG buses. These figures are confidential business information and cannot be shared publicly but have been incorporated as ratios to calculate the MY group 2007-2012 emission rates. The aggregated certification levels with these annual sales weighted averages for MY group 2002-2006 and MY group 2007-2012 are shown in Table 4-3 below. 
Table 4-3.  Model year group 2002-2006 and 2007-2012 certification levels for CNG buses used for scaling of measured emission rate data
                                       
                               Model Year Group
                                     NOx 
                                      CO
                                      PM
                                    NMHC[1]
Certification
(g/bhp-hr) 
                                   2002-2006
                                     1.208
                                     1.355
                                    0.0078
                                     0.147
Certification
(g/bhp-hr)
                                   2007-2012
                                    0.2902
                                     3.032
                                    0.0033
                                     0.057
                                       
      1. Certification data has measurements of organic material non-methane hydrocarbon equivalent (OMNMHCE). For this analysis they were treated as NMHC values.
Methane levels are not reported in the certification data, so we estimate CH4 rates for MY group 2007-2012 through an analysis of the CH4 to THC ratio by model year from the dynamometer measurements from the WMATA study.  The CH4/THC ratio for every model year fell within one standard deviation of the average ratio across all model years. The CH4/THC ratios are calculated from averaged CH4 and THC measurements on the respective CBD and WMATA cycles, as displayed in Table 4-4. We left the CH4/THC ratio constant from MY group 2002-2006 to MY group 2007-2012 and estimated the new CH4 rate (given in Table 4-5) off that previous ratio. 
               Table 4-4 Summary of CH4/THC ratios for MOVES2014
Model Year
Age Group
CH4/THC Ratio
                                   1994-2001
                                      0-3
                                     0.917
                                   2002-2006
                                      0-3
                                     0.950
                                   2007-2012
                                      0-3
                                     0.950
We scaled the newer model year rates rp based off the measurements in the MY group 2002-2006 in proportion to the ratio of certification levels CLp from MY group 2007-2012 to MY group 2002-2006. In this case, 

rp,MY2007-2012=rp,MY2002-2006∙CLp,MY2007-2012CLp,MY2002-2006 .			Equation 4-2
As mentioned before, the measured CO rate for MY group 2002-2006 was not used. We adjusted the original rate by the ratio between the sales-weighted average for the MY 2004 certification level of all models and the certification level for that particular MY 2004 John Deere bus with the anomalous CO rate.
The estimated CO rate for MY group 2007-2012 is notably greater than the previous MY group, but this change was reflected in our certification level proxies, and has been observed in more recent testing with three-way catalyst, stoichiometric CNG buses. 
Note that there was limited data on older vehicles in the literature, so the ratios that were developed using vehicles in the 0-3 age group have been applied to all other age groups. Therefore, we are assuming that CNG buses exhibit deterioration rates in control equipment proportional to medium heavy-duty gasoline trucks.  
Since there is no certification data on carbon dioxide (CO2) or other greenhouse gases, until 2011, we maintained the same total energy consumption rate from MY group 2002-2006 to MY 2007-2012. 
Creating CNG Running Rates for Future Model Years 
Table 4-5 shows CNG transit bus emissions on each drive cycle calculated using MOVES2010b rates for each MY group.  These calculations are shown using a single model year within the group. The table also shows the emission rates estimated from our meta-analysis of the literature. The ratios between these rates were applied to the 1997, 2004 and 2009 MOVES2010b CNG bus rates in order to calculate the MOVES2014 rates. 

Table 4-5 Summary of MOVES2010b distance-dependent emission rates for CNG transit buses and the ratios to be applied to the MOVES2010b STP-based rates to compute the MOVES2014 rates. 

                         MOVES2010b CNG Rates (g/mile)
                                      MY
                                   Age Group
                                     Cycle
                                     NOx 
                                      CO
                                   PM_NonEC 
                                     PM_EC
                             TOTAL ENERGY (BTU/mi)
                                     THC 
                                      CH4
                                     1997
                                      0-3
                                      CBD
                                     9.63
                                     62.4
                                    0.0024
                                    0.0002
                                     31137
                                     1.84
                                     0.049
                                 2004 and 2009
                                      0-3
                                     WMATA
                                     5.45
                                     18.9
                                    0.0035
                                    0.0003
                                     35489
                                     1.43
                                     0.032

        MOVES2014 CNG Rates (g/mile - measured/estimated from analysis)
                                      MY
                                   Age Group
                                     Cycle
                                     NOx 
                                      CO
                                   PM_NonEC 
                                     PM_EC
                             TOTAL ENERGY (BTU/mi)
                                     THC 
                                      CH4
                                   1994-2001
                                      0-3
                                      CBD
                                     20.8
                                     9.97
                                     0.037
                                    0.0038
                                     42782
                                     13.2
                                     12.1
                                   2002-2006
                                      0-3
                                     WMATA
                                     9.08
                                    2.17[1]
                                    0.0039
                                    0.0005
                                     40900
                                     11.2
                                     10.6
                                2007 and later
                                      0-3
                                     WMATA
                                     2.18
                                    5.93[2]
                                    0.0016
                                    0.0002
                                     40900
                                     4.33
                                     4.12

                Ratios Applied to the STP-Based MOVES2014 Rates
                                      MY
                                   Age Group
                                 Cycle ratioed
                                     NOx 
                                      CO
                                   PM_NonEC 
                                     PM_EC
                                 TOTAL ENERGY
                                     THC 
                                      CH4
                                   1994-2001
                                      all
                                      CBD
                                     2.16
                                     0.16
                                     15.5
                                     21.6
                                     1.37
                                     7.17
                                      250
                                   2002-2006
                                      all
                                     WMATA
                                     1.67
                                     0.11
                                     1.09
                                     1.87
                                     1.15
                                     7.79
                                      330
                                2007 and later
                                      all
                                     WMATA
                                     0.40
                                     0.31
                                     0.46
                                     0.78
                                     1.15
                                     3.02
                                      128
      1. This CO rate was uncharacteristically low (0.14 g/mi), determined to be an outlier, and has been adjusted using sales-weighted certification data, as described in more detail in the text above.
      2. Note that the increase in the CO rate from MY group 2002-2006 to MY 2007 and later seems to be an outcome of transitioning from lean-burn CNG engines to stoichiometric-burn engines. This upward CO trend is supported by certification data as well as testing results from some recent studies comparing these two technologies.
         
The model year basis for scaling was selected based on temporal similarity. For instance, our choice to use MY 1997 for MY group 1994-2001 was due to it being a median year in the group.  For MY group 2002-2006, we selected MY 2004 because that was the year all the vehicles in that group were manufactured. As for MY group 2007-2012, MY 2009 was also chosen simply for being one of the two model years near the median for the group. 
For 2014 and later model year, the CNG energy consumption rates are reduced by the same reduction as diesel Urban Bus vehicles, in response to the 2014 Medium and Heavy Duty Greenhouse Gas Rule as documented in Table 2-18.
Start Exhaust Emission Rates for CNG Buses
In the absence of any measured start exhaust emissions from CNG transit buses, their start rates are copies of heavy-duty diesel start rates, for all pollutants including energy rates. We believe this is an environmentally conservative approach, rather than assuming zero CNG start emissions. MOVES still estimates that the majority of emissions from CNG buses are from running emissions, which are based on CNG test programs. We readily acknowledge that the diesel start rates may not accurately represent CNG start rates. This assumption will be revisited for future releases of MOVES as new data on CNG start rates becomes available.
Applications to Other Model Years and Age Groups
We applied the ratios in Table 4-5 to all ages of CNG bus emission running rates in MOVES2010b.  In this way, the deterioration assumptions for criteria pollutants in the MOVES2010b running rates are preserved in the MOVES2014 CNG bus rates.  For completeness, CNG buses prior to MY 1994 use the same rates as MY group 1994-2001. Rates for buses built after MY 2012 maintain the same rate as MY group 2007-2012. As new certification data arrives and more testing programs are run, these rates will be revisited in future MOVES releases.
PM and HC Speciation for CNG Buses
MOVES estimate methane and nonmethane hydrocarbons (NMHC) through the use of CH4 /THC ratios, as shown in Table 4-4. The MOVES2014 CH4/THC ratios are constant across all age groups. We set the start CH4/THC ratios equal to the running ratios for all model years and ages. 
MOVES calculates emissions of total organic gases (TOG), nonmethane organic gases (NMOG) and volatile organic carbons (VOC) using information regarding the hydrocarbon speciation of emissions. Studies have shown that the speciation of hydrocarbon can be drastically different between uncontrolled CNG buses and CNG buses with oxidation catalysts. For example, formaldehyde emissions can be quite large from uncontrolled CNG buses72[,] 74[,][,], but are significantly reduced with oxidation catalysts71. Large formaldehyde emissions have a large impact on the NMOG and VOC emissions estimated from THC emissions from CNG buses because THC-FID measurements have a small response to formaldehyde concentrations41,.
We used hydrocarbon speciation measurements from the Ayala et al. (2003) using measurements from the 2000 MY Transit Bus, with a Detroit Diesel Series 50G engine with and without an oxidation catalyst collected on the CBD cycle. We used the speciated measurements made on the single transit bus to isolate the impact of the oxidation catalyst. We used the CBD test cycle to be consistent with our analysis of the criteria emission rates. The NMOG and VOC conversion factors are located in Table 4-6. The NMOG values are calculated following EPA's regulation requirements using Equation 9 from the MOVES2014 Speciation Report41. 
The VOC emissions are calculated from subtracting the ethane from the NMOG values. MOVES definition of VOC emissions from mobile-sources is NMOG minus ethane and acetone . The emissions of hazardous air pollutants, including formaldehyde and acetaldehyde, are also estimated from this study as documented in the MOVES2014 Toxics Emissions Report. 
Table 4-6 NMOG and VOC Conversion values for CNG transit emissions with no control and with oxidation catalyst from Ayala et al. (2003)71 
Measured values (mg/mile)
                                  No Control
                              Oxidation Catalyst
THC
                                                                           8660
                                                                           6150
Methane
                                                                           7670
                                                                           5900
Ethane
                                                                            217
                                                                           72.2
Acetone
                                                                           4.67
                                                                           5.51
Formaldehyde
                                                                            860
                                                                           38.4
Acetaldehyde
                                                                           50.7
                                                                           32.6
Calculated values (mg/mile)
 
 
NMHC
                                                                            990
                                                                            250
NMOG
                                                                         1881.0
                                                                          309.0
VOC 
                                                                         1664.0
                                                                          236.8
Ratios
 
 
NMOG/NMHC
                                                                           1.90
                                                                           1.24
VOC/NMHC
                                                                           1.68
                                                                           0.95
                                       
In MOVES2014, we applied the uncontrolled NMOG and VOC factors to the pre-2002 model year vehicles. This analysis demonstrated that majority of the 2001 and earlier model year CNG transit buses were not equipped with exhaust aftertreament. The study conducted on MY 2004 buses70, suggested that 2002-2006 model year vehicles are equipped with oxidation catalysts. Therefore we apply the oxidization catalyst profile to CNG emissions for the 2002 to 2006 MY group. At the time of the analysis, we did not have information on 2007 and later CNG buses, and also applied the oxidation catalyst from the lean-burn engine results to 2007 and later groups. 
The composition of PM2.5 emissions are estimated from CARB's measurementson the 2000 MY Detroit Diesel Series 50G with and without the oxidation catalyst. The EC/PM2.5 fractions are reported in Table 4-7 and are used to estimate the base PM components in MOVES: elemental carbon (EC) and non-elemental carbon (nonECPM) rates. By using the single bus, we again isolate the impact of the control, without confounding differences in different engine technologies. Similar for the HC speciation, we apply the uncontrolled EC/PM fraction to the pre-2002 MY CNG buses, and the oxidation catalyst equipped EC/PM profile for the 2002 and later buses.
Table 4-7 MOVES2014 EC/PM Fraction for CNG transit bus emissions by model year groups
                                   Pre-2002
                                     2003+
                                     9.25%
                                    11.12%
The CARB measurements are also used to estimate the individual PM2.5 composition, including organic carbon, elements, and sulfate as discussed in the TOG and PM2.5 speciation report. stoichiometric-burn spark ignition CNG engines with three-way catalysts have been introduced in 2007 and later buses. Future work should be done to improve the emission rates and speciation profiles used in MOVES to represent emissions from recent technology CNG buses.
Ammonia and Nitrous Oxide emissions 
No data were available on ammonia emissions rates. As such, we used the ammonia emissions for heavy-duty gasoline vehicles, which are documented in a separate report6.
We did not update the nitrous oxide emission rates for CNG in MOVES2014. They remain unchanged from MOVES2009 and later versions as documented in a separate MOVES report5

Heavy-Duty Crankcase Emissions
Crankcase emissions, also referred to as crankcase blowby, are combustion gases that pass the piston rings into the crankcase, and are subsequently vented to the atmosphere. Crankcase blowby includes oil-enriched air from the turbocharger shaft, air compressors, and valve stems that enters the crankcase. The crankcase blowby contains combustion generated pollutants, as well as oil droplets from the engine components and engine crankcase. 
Background on Heavy-duty Diesel Crankcase Emissions
Federal regulations permit 2006 and earlier heavy-duty diesel-fueled engines equipped with "turbochargers, pumps, blowers, or superchargers" to vent crankcase emissions to the atmosphere. Crankcase emissions from pre-2007 diesel engines were typically vented to the atmosphere, using an open unfiltered crankcase system, referred to as a `road draft tube'.88 Researchers have found that crankcase emissions vented to the atmosphere can be the dominant source of diesel particulate matter concentrations measured within the vehicle cabin   .
Beginning with 2007 model year heavy-duty diesel vehicles, federal regulations no longer permit crankcase emissions to be vented to the atmosphere, unless they are included in the certification exhaust measurements. Most manufacturers have adopted open crankcase filtration systems.88 These systems vent the exhaust gases to the atmosphere after the gases have passed a coalescing filter which removes oil and a substantial fraction of the particles in the crankcase blowby.88 In the ACES Phase 1 program, four MY2007 diesel engines from major diesel engine manufactures (Caterpillar, Cummins, Detroit Diesel, and Volvo) all employed filtered crankcase ventilation systems. 
A summary of published estimates of diesel crankcase emissions as percentages of the total emissions (exhaust + crankcase) are provided in Table 5-1. For the conventional diesel technologies, hydrocarbon and particulate matter emissions have the largest contributions from crankcase emissions. There is a substantial decrease in PM emissions beginning with the 2007 model year diesel engines. The 2007 diesel technology reduces the tailpipe emissions more than the crankcase emissions, resulting in an increase in the relative crankcase contribution for HC, CO, and PM emissions. NOx emissions for the 2007 and later are reported as a negative number. In reality, the crankcase emission contribution cannot be negative, and the negative number is attributed to sampling variability from the tests with and without the crankcase emissions.

Table 5-1 Literature review on the contribution of crankcase emissions to diesel exhaust.
Study
                                  Model Year
                                     Type
# Engines/ Vehicles
                                      HC
                                      CO
                                      NOx
                                      PM
Hare and Baines, 197797
                                   1966, 1973
                                 Conv. Diesel
                                       2
                                   0.2%-3.9%
                                   0.01-0.4%
                                  0.01%-0.1%
                                   0.9%-2.8%
Zielinska et al. 200890, Ireson et al. 201191
                                  2000, 2003
                                 Conv. Diesel
                                       2
                                       
                                       
                                       
                                 13.5% - 41.4%
Clark et al. 200696, Clark et al. 2006
                                     2006
                                 Conv. Diesel
                                       1
                                     3.6%
                                     1.3%
                                     0.1%
                                     5.9%
Khalek et al. 2009
                                     2007
                                 DPF-equipped
                                       4
                                     95.6%
                                     27.2%
                                     -0.2%
                                     38.2%
Modeling Crankcase Emissions in MOVES
MOVES2014 calculates THC, CO, NOx, and PM2.5 using a gaseous and a particulate crankcase emission calculator. Within the calculator, crankcase emissions are calculated as a fraction of tailpipe exhaust emissions, including start, running, and extended-idle. As discussed in the background, the 2007 heavy-duty diesel emission regulations impacted the technologies used to control exhaust and crankcase emissions. The regulations also expanded the types of emissions data included in certification tests, by including crankcase emissions in the regulatory standards, which previously included only tailpipe emissions. Because heavy-duty diesel engine manufacturers are using open-filtration crankcase systems, the crankcase emissions are included in the emission certification results. In MOVES2014, the base exhaust rates for 2007 and later diesel engines are based on certification levels.
In response to the changes in certification testing, we changed the data and the methodology with which crankcase emissions are modeled in MOVES. For 2007 and later diesel engines, the crankcase emissions are included in the base exhaust emission rates. A new crankcase calculator in MOVES2014 divides the base exhaust emission rates into components representing the contributions from exhaust and crankcase emissions. The exhaust emission ratio is equal to 1.0 for all pre-2007 diesel engines, and less than 1.0 for all 2007 and later diesel engines, to account for the inclusion of crankcase emissions in the base rates. Unfortunately, due to budget and time constraints, only the PM2.5 species are incorporated using the new crankcase calculator in MOVES2014. An overview of the crankcase calculator is provided in the MOVES2014 Speciation Report.41 
MOVES2014 continues to use the same calculator as MOVES2010 for the gaseous crankcase pollutants, THC, CO, and NOx. The gaseous crankcase calculator chains the crankcase emission rates to the base exhaust emissions, but it does not allow the ability to reduce the exhaust emission contribution, which is desired for the 2007+ diesel technologies. The 2007+ diesel subsection discusses how MOVES2014  handles THC, CO, and NOx to avoid double-counting crankcase emissions. We anticipate that future versions of MOVES will include the updated crankcase calculator for all crankcase emission pollutants, including THC, CO, and NOx.
Conventional Heavy-Duty Diesel 
Table 5-2 includes the crankcase/tail-pipe emission ratios used for conventional diesel exhaust. For HC, CO, and NOx, we selected the values reported on the MY2006 diesel engine reported by Clark et al. 2006. These values compare well with the previous HC, CO, NOx values reported much earlier by Hare and Baines (1977),  which represent much older diesel technology. The similarity of the crankcase emission ratios across several decades of diesel engines, suggests that for conventional diesel engines, crankcase emissions can be well represented as a fraction of the exhaust emissions. 
For PM2.5 emissions, we selected a crankcase/tail-pipe ratio of 20%. Zielinska et al. 200890 and Ireson et al. 201191 reported crankcase contributions to total PM2.5 emissions as high as 40%. Jääskeläinen (2012)88 reported that crankcase can contribute as much as 20% of the total emissions from a review of six diesel crankcase studies. Similarly, an industry report estimated that crankcase emissions contributed 20% of total particulate emissions from 1994-2006 diesel engines.  
Table 5-2 MOVES2014 Conventional Diesel Crankcase/Tail-pipe Ratios for HC, CO, NOx and PM2.5
Pollutant
Crankcase/Tailpipe ratio
Crankcase/(Crankcase + Tailpipe) ratio
HC
0.037
0.036
CO
0.013
0.013
NOx
0.001
0.001
PM2.5
0.200
0.167

As outlined in the MOVES 2014 TOG and PM Speciation Report, MOVES does not apply the crankcase/tailpipe emission ratio in Table 5-4 to the total exhaust PM2.5 emissions. MOVES applies the crankcase/tailpipe emission ratios to PM2.5 subspecies: elemental carbon PM2.5, sulfate PM2.5, aerosol water PM2.5, and the remaining PM (nonECnonSO4PM). This allows MOVES to account for important differences in the PM speciation between tailpipe and crankcase emissions. 
The pre-2007 diesel ratios are derived such that the crankcase PM2.5/exhaust PM2.5 ratio is 20%, and the crankcase emissions EC/PM fraction reflects measurements from in-use crankcase emissions. Zielinska et al. 200890 reported that the EC/PM fraction of crankcase emissions from two conventional diesel buses is 1.57%. Tailpipe exhaust from conventional diesel engines is dominated by elemental carbon emissions from combustion of the diesel fuel, while crankcase emissions are dominated by organic carbon emissions largely contributed from the lubricating oil. 90[,]91. The crankcase emission factors shown in Table 5-3 are derived such that the crankcase PM2.5 emissions are 20% of the PM2.5 exhaust measurements, and have an EC/PM split of 1.57%. 

The PM10 emission rates are subsequently estimated from the PM2.5 exhaust and crankcase emission rates using PM10/PM2.5 emission ratios as documented in the MOVES2014 TOG and PM Speciation Report.

Table 5-3.  MOVES2014 Exhaust and Crankcase Emission Factors for pre-2007 Diesel by Pollutant, Process, and Model Year Group for PM2.5 species.
                                   Pollutant
                                    Process
                                     Start
                                    Running
                                 Extended Idle
                                      EC
                                    Exhaust
                                       1
                                       1
                                       1
                                 nonECnonSO4PM
                                       
                                       1
                                       1
                                       1
                                      SO4
                                       
                                       1
                                       1
                                       1
                                      H2O
                                       
                                       1
                                       1
                                       1
                                      EC
                                  Crank-case
                                     0.009
                                     0.004
                                     0.012
                                 nonECnonSO4PM
                                       
                                     0.295
                                     0.954
                                     0.268
                                      SO4
                                       
                                     0.295
                                     0.954
                                     0.268
                                      H2O
                                       
                                     0.295
                                     0.954
                                     0.268
2007 + Heavy-Duty Diesel 
The 2007+ heavy-duty diesel THC, CO, and NOx crankcase emissions are included in the exhaust emissions. However, with the current gaseous crankcaseemission calculator, the crankcase contribution of THC, CO, and NOx to the base exhaust emission rates cannot be properly accounted. For MOVES2014, the crankcase to tailpipe emission ratios for THC, CO, and NOx are set to 0 as shown in Table 5-4, and MOVES2014 produces no crankcase emissions for each of the pollutants. Table 5-4 also lists the crankcase to tailpipe emission ratios based on ACES Phase 1 tests. Based on the ACES Phase 1 program, the MOVES2014 estimate of no crankcase emissions is reasonable for NOx, but not for THC and CO emissions. MOVES2014 does not report crankcase emissions for THC and CO because they are included in the exhaust emission rates for 2007 and later model years from heavy-duty diesel vehiclesl. Users can use the ratios listed in Table 5-4 to post-process the exhaust emission rates if the crankcase contributions to THC and CO emissions are desired. 
Table 5-4 MOVES2014 2007 and Later Diesel Crankcase/Tailpipe ratio for HC, CO, and NOx.
                                   Pollutant
                      MOVES2014 Crankcase/Tailpipe ratio
                    ACES Phase 1 Crankcase/Tail-pipe ratio
             ACES Phase 1 Crankcase/(Crankcase + Tail-pipe)l ratio
                                      HC
                                       0
                                     21.95
                                     95.6%
                                      CO
                                       0
                                     0.37
                                     27.2%
                                      NOx
                                       0
                                     0.00
                                     0.0%
                                       
For PM2.5 emissions, we used data from the ACES Phase 1 test program to inform the crankcase and exhaust ratios for the updated PM2.5 crankcase emissions calculator. The crankcase emissions measured in the ACES Phase 1 test program contributed 38% of the total PM2.5 emissions on the hot-FTP driving cycle. Emission results reported from industry, have reported that the crankcase emissions can contribute to over 50% of the particulate matter emissions from 2007 and later diesel technologies98. 
For PM2.5 emissions, MOVES applies crankcase ratios to each of the intermediate PM2.5 species (EC, nonECnonSO4PM, SO4, and H2O). For 2007+ heavy-duty diesel engines, the same crankcase ratio is applied to each of the intermediate species. The MOVES PM2.5 speciation profile developed from the ACES Phase 1 study combined the crankcase and tailpipe emissions. As such, MOVES2014 uses the same speciation profile for both crankcase and tailpipe emissions. The resulting exhaust and crankcase emission ratios for 2007 and later heavy-duty diesel are provided in Table 5-5. As shown, the exhaust crankcase emission factor is less than one for 2007+ diesel vehicles, to account for the contribution of crankcase emissions in the base exhaust emission rates.
Table 5-5 MOVES2014 Exhaust and Crankcase Emission Factors for 2007 + Heavy-duty Diesel by Pollutant, Process, and Model Year Group for PM2.5 species.
                                   Pollutant
                                    Process
                                 All processes
                                      EC
                                    Exhaust
                                     0.62
                                 nonECnonSO4PM
                                       
                                     0.62
                                      SO4
                                       
                                     0.62
                                      H2O
                                       
                                     0.62
                                      EC
                                  Crank-case
                                     0.38
                                 nonECnonSO4PM
                                       
                                     0.38
                                      SO4
                                       
                                     0.38
                                      H2O
                                       
                                     0.38
Heavy-duty Gasoline and CNG Emissions
The data on heavy-duty gasoline and CNG crankcase emissions are limited. All 1969 and later otto-cycle (spark ignition) heavy-duty engines are required to control crankcase emissions. All gasoline engines are assumed to use positive crankcase ventilation (PCV) systems, which route the crankcase gases into the intake manifold. For heavy-duty gasoline engines we use the same values of crankcase emission ratios as light-duty gasoline, which are documented in the MOVES2014 light-duty emission rates report.8 We assume 4% of PCV systems fail, resulting in the small crankcase to exhaust emission ratios shown in Table 5-6 for 1969 and later gasoline engines. Due to limited information, we used the gasoline heavy-duty crankcase emission factors for heavy-duty CNG engines because they have low blow-by particle emissions.
Table 5-6 Crankcase to Tailpipe Exhaust Emission Ratio for Heavy-duty Gasoline and CNG Vehicles for HC, CO, NOx and PM2.5
                                   Pollutant
                                   pre-1969)
                                1969 and later
                                      HC
                                     0.33
                                     0.013
                                      CO
                                     0.013
                                    0.00052
                                      NOx
                                     0.001
                                    0.00004
                               PM (all species)
                                     0.20
                                     0.008

The crankcase and exhaust ratios used by the crankcase calculator for PM2.5 emissions from heavy-duty gasoline and compressed natural gas vehicles are provided in Table 5-7. No information is available to estimate separate speciation between exhaust and crankcase, so the factors are the same between the PM subspecies. 

Table 5-7 MOVES2014 Exhaust and Crankcase Emission Factors by Pollutant, Process, Model Year Group, and Fuel Type, and Source Type for PM2.5 Species
                                       
                                       
                          1960-1968 Gasoline Vehicles
                            1969-2050 Gasoline/ CNG
                                   Pollutant
                                    Process
                                 All processes
                                 All processes
                                      EC
                                    Exhaust
                                       1
                                       1
                                 nonECnonSO4PM
                                       
                                       1
                                       1
                                      SO4
                                       
                                       1
                                       1
                                      H2O
                                       
                                       1
                                       1
                                      EC
                                   Crankcase
                                      0.2
                                     0.008
                                 nonECnonSO4PM
                                       
                                      0.2
                                     0.008
                                      SO4
                                       
                                      0.2
                                     0.008
                                      H2O
                                       
                                      0.2
                                     0.008

Nitrogen Oxide Composition

Nitrogen oxides (NOx) are defined as NO + NO2.[,] NOx is considered a subset of reactive nitrogen species (NOy) with an nitrogen oxidation state of +2 or greater which contain other nitrogen containing species (NOz), thus NOy = NOx + NOz.99 NOz compounds are formed in the atmosphere as oxidation products of NOx100.
Chemiluminescent analyzers used for exhaust NOx measurements, directly measure NO, as NO is oxidized by ozone to form NO2  and produces florescence light. Chemiluminescent analyzers measure NOx (NO + NO2) by using a catalyst that reduces the NO2  to NO in the sample air stream before measurement. NO2  is calculated as the difference between NOx and NO measurements. The NOx converter within chemiluminescent analyzers can also reduce other reactive nitrogen species (NOz), including HONO to NO. If the concentrations of NOz interfering species in the sample stream are significant relative to NO2  concentrations, than they can bias the NO2  measurements high. 
MOVES produces estimates of NO and NO2 by applying an NO/NOx or NO2/NOx fraction to the NOx emission rates. The NO/NO2  and NO2/NOx fractions are stored in a MOVES table called nono2ratio. The nono2ratio enables the nitrogen oxide composition to vary according to source type, fuel type, model year, and pollutant process. For the heavy-duty vehicle source types, the NOx fractions only vary according to fuel type, model year, and emission process. The NOx fractions in MOVES were developed from a literature review reported by Sierra Research to the EPA, from emission test programs conducted in the laboratory with constant volume sampling dilution tunnels.6 
MOVES also produces estimates of one important NOz species, nitrous acid (HONO), from the NOx values. HONO emissions are estimated as a fraction (0.8%) of NOx emissions from all vehicle types in MOVES, based on HONO and NOx measurements made at road tunnel in Europe. In MOVES, we assume HONO contributes to the NOx values, because either (1) the  chemiluminescent analyzers are biased slightly high by HONO in the exhaust stream, or (2) HONO is formed almost immediately upon dilution into the roadway environment from NO2  emissions. To avoid overcounting reactive nitrogen formation, we include HONO in the sum of NOx in MOVES. HONO emissions are also estimated using the non2ratio MOVES table. For each source type, fuel type, and emission process, the NO, NO2, and HONO values in the non2ratio sum to unity.
MOVES users should be aware that the definition of NOx in MOVES (NO+NO2+HONO) is different than the actual NOx definition of NOx (NO + NO2).This is because we are correcting the exhaust NOx emission in MOVES for potential interference with HONO measurements. MOVES users should consider which measure they would like to use depending on their use-case. For example, for comparing NOx results with a vehicle emission test program, MOVES may want to simply use NOx (pollutantID 3), whereas a MOVES users developing air quality inputs of NO, NO2, and HONO, should estimate NOx as the sum of NO + NO2  (pollutantIDs 32 and 33), rather than using the direct NOx output in MOVES (polluantID 3).  
Future work is needed to (1) update the NOx and HONO fractions in MOVES based on more recent measurements, (2) reconcile the definition of NOx in MOVES, while also correctly accounting for the emissions of NOz species that  may impact NOx measurements and (3) reconcile measurement differences that may occur between NOy species measured at the tailpipe, with NOy species measured on road side measurements.
Heavy-duty Diesel
The conventional diesel (1960-2006 model year) NOx fractions were estimated as the average reported fraction from three studies of heavy-duty vehicles not equipped with diesel particulate filters. 6 The 2010+ NO2  fractions are based on the average of three diesel programs of diesel vehicles measured with diesel particulate filters. The 2007-2009 values are an average of the 1960-2006 and 2010-2050 values, which assumes that the NOx fractions change incrementally, as trucks equipped with catalyzed diesel particulate filters were phased-into the fleet. The NOx fractions are the same across all diesel source types (including light-duty) and across all emission processes (running, start, extended idle), except for auxiliary power units, which use the conventional NOx fractions (1960-2006) for all model years because it is assumed that they are not fitted with diesel particulate filters. The NO2  fractions originally developed from the Sierra report6, were reduced by 0.008, to account for the HONO emissions.  
       Table 6-1. NOx and HONO fractions for Heavy-Duty Diesel Vehicles
                                  Model Year
                                      NO
                                      NO2
                                     HONO
                                  1960-2006* 
                                                                          0.935
                                                                          0.057
                                                                          0.008
                                   2007-2009
                                                                          0.764
                                                                          0.228
                                                                          0.008
                                   2010-2050
                                                                          0.594
                                                                          0.398
                                                                          0.008
* All Model Year of Auxiliary Power Units (APUs) use the 1960-2006 NOx and HONO fractions.
 Heavy-duty Gasoline
The NOx fractions for heavy-duty gasoline are based on the MOVES values used for light-duty gasoline measurements. Separate values are used for running and start emission processes. As stated in the Sierra Report,6 the values are shifted to later model year groups to be consistent with emission standards and emission control technologies. These values are shown in Table 6-2for both light-duty and heavy-duty gasoline vehicles. The NO2 fractions originally developed from the Sierra report6, were reduced by 0.008, to account for the HONO emissions.  
Table 6-2. NOx and HONO Fractions for Light-duty (sourceTypeID 21, 31, 32) and Heavy-duty Gasoline Vehicles (sourceTypeID 41, 42, 43, 51, 52, 53, 54, 61, and 62)
                     Light-Duty Gasoline Model Year Groups
                     Heavy-Duty Gasoline Model Year Groups
                                    Running
                                     Start

                                      NO
                                      NO2
                                     HONO
                                      NO
                                      NO2
                                     HONO
                                   1960-1980
                                   1960-1987
                                                                          0.975
                                                                          0.017
                                                                          0.008
                                                                          0.975
                                                                          0.017
                                                                          0.008
                                   1981-1990
                                   1988-2004
                                                                          0.932
                                                                           0.06
                                                                          0.008
                                                                          0.932
                                                                          0.031
                                                                          0.008
                                   1991-1995
                                   2005-2007
                                                                          0.954
                                                                          0.038
                                                                          0.008
                                                                          0.987
                                                                          0.005
                                                                          0.008
                                   1996-2050
                                   2008-2050
                                                                          0.836
                                                                          0.156
                                                                          0.008
                                                                          0.951
                                                                          0.041
                                                                          0.008

Compressed Natural Gas 
We used the average of three NO2/NOx fraction reported on three CNG transit buses with DDC Series 50 G engines by Lanni et al. (2003)74, along with the 0.008 HONO fraction assumed for other source types, to estimate the NOx fractions of NO, NO2, and the HONO fraction. These assumptions yield the NOx and HONO fractions in Table 6-3, which are used for all model year CNG transit buses. 
              Table 6-3 NOx and HONO fractions CNG transit buses
                                  Model Year
                                      NO
                                      NO2
                                     HONO
                                   1960-2050
                                                                          0.865
                                                                          0.127
                                                                          0.008
                                       

Calculation of Accessory Power Requirements 

              Table A-1. Accessory load estimates for HHD trucks
                                       
                                       
              Table A-2. Accessory load estimates for MHD trucks
                                       
                                       
                 Table A-3. Accessory load estimates for buses
                                       
                                       
 Tampering and Mal-maintenance
Tampering and mal-maintenance (T&M) effects represent the fleet-wide average increase in emissions over the useful life of the engines.  In laboratory testing, properly maintained engines often yield very small rates of emissions deterioration through time.  However, we assume that in real-world use, tampering and mal-maintenance yield higher rates of emissions deterioration over time.  As a result, we feel it is important to model the amount of deterioration we expect from this tampering and mal-maintenance.  We estimated these fleet-wide emissions effects by multiplying the frequencies of engine component failures by the emissions impacts related to those failures for each pollutant.  Details of this analysis appear later in this section. 
Modeling Tampering and Mal-maintenance
As T&M affects emissions through age, we developed a simple function of emission deterioration with age.  We applied the zero-age rates through the emissions warranty period (5 years/100,000 miles), then increased the rates linearly up to the useful life.  Then we assumed that all the rates level off beyond the useful life age. Figure B-1 shows this relationship.

    Figure B-1. Qualitative Depiction of the implementation of age effects.
Final emission rate due to T&M 
Zero-mile emission rate 
End of warranty period
 
End of useful life 
Age 
Emission rate 
Final emission rate due to T&M 
Zero-mile emission rate 
End of warranty period
 
End of useful life 
Age 
Emission rate 
\s

The useful life refers to the length of time that engines are required to meet emissions standards.  We incorporated this age relationship by averaging emissions rates across the ages in each age group.  Mileage was converted to age with VIUS (Vehicle Inventory and Use Survey) data, which contains data on how quickly trucks of different regulatory classes accumulate mileage.  Table B-1 shows the emissions warranty period and approximate useful life requirement period for each of the regulatory classes.

     Table B-1. Warranty and useful life requirements by regulatory class
Regulatory class
                          Warranty age (Requirement:
                           100,000 miles or 5 years)
                      Useful life mileage/age requirement
                                Useful life age
HHD
                                       1
                                  435,000/10
                                       4
MHD
                                       2
                                  185,000/10
                                       5
LHD45
                                       4
                                  110,000/10
                                       4
LHD2b3
                                       4
                                  110,000/10
                                       4
BUS
                                       2
                                  435,000/10
                                      10

While both age mileage metrics are given for these periods, whichever comes first determines the applicability of the warranty.  As a result, since MOVES deals with age and not mileage, we need to convert all the mileage values to age equivalents, as the mileage limit is usually reached before the age limit.  The data show that on average, heavy-heavy-duty trucks accumulate mileage much more quickly than other regulatory classes.  Therefore, any deterioration in heavy-heavy-duty truck emissions will presumably happen at younger ages than for other regulatory classes.  Buses, on average, do not accumulate mileage quickly.  Therefore, their useful life period is governed by the age requirement, not the mileage requirement.
Since MOVES deals with age groups and not individual ages, the increase in emissions by age must be calculated by age group.  We assumed that there is an even age distribution within each age group (e.g. ages 0, 1, 2, and 3 are equally represented in the 0-3 age group).  This is important since, for example, HHD trucks reach useful life at four years, which means they will increase emissions through the 0-3 age group.  As a result, the 0-3 age group emission rate will be higher than the zero-mile emission rate for HHD trucks.  Table B-2 shows the multiplicative T&M adjustment factor by age.  We determined this factor using the mileage-age data from Table B-1 and the emissions-age relationship that we described in Figure B-1.  We multiplied this factor by the emissions increase of each pollutant over the useful life of the engine, which we determined from the analysis in this section.

  Table B-2. T&M multiplicative adjustment factor by age (fTM,age group).
Age Group
                                      LHD
                                      MHD
                                      HHD
                                      Bus
0-3
                                       0
                                     0.083
                                     0.25
                                    0.03125
4-5
                                       1
                                     0.833
                                       1
                                    0.3125
6-7
                                       1
                                       1
                                       1
                                    0.5625
8-9
                                       1
                                       1
                                       1
                                    0.8125
10-14
                                       1
                                       1
                                       1
                                       1
15-19
                                       1
                                       1
                                       1
                                       1
20+
                                       1
                                       1
                                       1
                                       1
In this table, a value of 0 indicates no deterioration, or zero-mile emissions level (ZML), and a value of 1 indicates a fully deteriorated engine, or maximum emissions level, at or beyond useful life (UL).  The calculation of emission rate by age group is described in the equation below.  TMpol represents the estimated emissions rate increase through the useful life for a given pollutant.
                                       
                                       
                                       
                                 Equation B-1
                                       
 Data Sources
EPA used the following information to develop the tamper and mal-maintenance occurrence rates used to develop emission rates used in MOVES:
      * California's ARB EMFAC2007 Modeling Change Technical Memo (2006).  The basic EMFAC occurrence rates for tampering and mal-maintenance were developed from the Radian and EFEE reports and internal CARB engineering judgment.
      * Radian Study (1988).  The report estimated the malfunction rates based on survey and observation.  The data may be questionable for current heavy-duty trucks due to advancements such as electronic controls, injection systems, and exhaust aftertreatment.
      * EFEE report (1998) on PM emission deterioration rates for in-use vehicles.  Their work included heavy-duty diesel vehicle chassis dynamometer testing at Southwest Research Institute.
      * EMFAC2000 (2000) Tampering and Mal-maintenance Rates
      * EMA's comments on ARB's Tampering, Malfunction, and Mal-maintenance Assumptions for EMFAC 2007
      * University of California  - Riverside (UCR) "Incidence of Malfunctions and Tampering in Heavy-Duty Vehicles"
      * Air Improvement Resources, Inc.'s Comments on Heavy-Duty Tampering and Mal-maintenance Symposium
      * EPA internal engineering judgment  
T &M Categories
EPA generally adopted the categories developed by CARB, with a few exceptions.  The high fuel pressure category was removed.  We added a category for misfueling to represent the use of nonroad diesel, not ULSD onroad diesel.  We combined the injector categories into a single group.  We reorganized the EGR categories into "Stuck Open" and "Disabled/Low Flow."  We included the PM regeneration system, including the igniter, injector, and combustion air system in the PM filter leak category.  
EPA will group the LHDD, MHDD, HHDD, and Diesel bus groups together, except for 2010 and beyond.  We assumed that the LHDD group will primarily use Lean NOx Traps (LNT) for the NOx control in 2010 and beyond.  On the other hand, we also assumed that Selective Catalyst Reduction (SCR) systems will be the primary NOx aftertreatment system for HHDD.  Therefore, the occurrence rates and emission impacts will vary in 2010 and beyond depending on the regulatory class of the vehicles.
T&M Model Year Groups
   EPA developed the model year groups based on regulation and technology changes.  
      * Pre-1994 represents non-electronic fuel control.  
      * 1998-2002 represents the time period with consent decree issues.  
      * 2003 represents early use of EGR.  
      * 2007 and 2010 contain significant PM and NOx regulation changes.  
      * EPA issued a rule to require OBD for heavy duty trucks, beginning in MY 2010 with complete phase-in by MY 2013.  
T &M Occurrence Rates and Differences from EMFAC2007
EPA adopted the CARB EMFAC2007 occurrence rates, except as noted below.
Clogged Air Filter:  EPA reduced the frequency rate from EMFAC's 15 percent to 8 percent.  EPA reduced this value based on the UCR results, the Radian study, and EMA's comments that air filters are a maintenance item.  Many trucks contain indicators to notify the driver of dirty air filters and the drivers have incentive to replace the filters for other performance reasons.  
Other Air Problems:  EPA reduced the frequency rate from EMFAC's 8 percent to 6 percent based on the UCR results.
Electronics Failed:  EPA will continue to use the 3 percent frequency rate for all model years beyond 2010.  CARB increased the rate to 30 percent in 2010 due to system complexity.  EPA does not agree with CARB's assertion that the complexity of electronic systems will increase enough to justify a ten-fold increase in malfunction occurrence rates.  We believe that the hardware will evolve through 2010, rather than be replaced with completely new systems that would justify a higher rate of failure.  EPA asserts that many of the 2010 changes will occur with the aftertreatment systems which are accounted for separately.  
EGR Stuck Open:  EPA believes the failure frequency of this item is rare and therefore set the level at 0.2 percent.  This failure will lead to drivability issues that will be noticeable to the driver and serve as an incentive to repair.
EGR Disabled/Low Flow:  EPA believes the EMFAC 20 percent EGR failure rate is too high and reduced the rate to 10 percent.  All but one major engine manufacturer had EGR previous to the 2007 model year and all have it after 2007.  Therefore, EMFAC's frequency rate increase in 2010 due to the increase truck population using EGR does not seem valid.  However, the Illinois EPA stated that "EGR flow insufficient" is the top OBD issue found in their LDV I/M program so it cannot be ignored.  
NOX Aftertreatment malfunction:  EPA developed a NOx aftertreatment malfunction rate that is dependent on the type of system used.  We assumed that HHDD will use primarily SCR systems and LHDD will primarily use LNT systems.  We estimated the failure rates of the various components within each system to develop a composite malfunction rate.
The individual failure rates were developed considering the experience in agriculture and stationary industries of NOx aftertreatment systems and similar component applications.  Details are included in the chart below.  We assumed that tank heaters had a 5 percent failure rate, but were only required in one third of the country and one fifth of the year.  The injector failure rate is lower than fuel injectors, even though they have similar technology, because there is only one required in each system and it is operating in less severe environment of pressure and temperature.  We believe the compressed air delivery system is very mature based on a similar use in air brakes.  We also believe that manufacturers will initiate engine power de-rate as incentive to keep the urea supply sufficient.  

                  Table B-3. NOx Aftertreatment Failure Rates
                                       

NOx aftertreatment sensor:  EPA believes the 53 percent occurrence rate in EMFAC2007 is too high and will use 10 percent.  CARB assumed a mix of SCR, which uses one sensor per vehicle, and NOx adsorbers, which use two sensors per vehicle.  They justified the failure rate based on the increased number of sensors in the field beginning in 2010.  
   We developed the occurrence rate based on the following assumptions:
   * Population:  HHDD: vast majority of heavy-duty applications will use SCR technology with a maximum of one NOx sensor.  NOx sensors are not required for SCR  -  manufacturers can use models or run open loop.   Several engine manufacturers representing 30 percent of the market plan to delay the use of NOx aftertreatment devices through the use of improved engine-out emissions and emission credits.  
   * Durability expectations:  SwRI completed 6000 hours of ESC cycling with NOx sensor.  Internal testing supports longer life durability.  Discussions with OEMs in 2007 indicate longer life expected by 2010.
   * Forward looking assumptions:  Manufacturers have a strong incentive to improve the reliability and durability of the sensors because of the high cost associated with frequent replacements.
PM Filter Leak:  EPA will use 5 percent PM filter leak and system failure rate.  CARB used 14 percent failure rate.  They discounted high failure rates currently seen in the field.
PM Filter Disable:  EPA agrees with CARB's 2 percent tamper rate of the PM filter.  The filter causes a fuel economy penalty so the drivers have an incentive to remove it.
Oxidation Catalyst Malfunction/Remove:  EPA believes most manufacturers will install oxidation catalysts initially in the 2007 model year and agrees with CARB's assessment of 5 percent failure rate.  This rate consists of an approximate 2 percent tampering rate and 3 percent malfunction rate.  The catalysts are more robust than PM filters, but have the potential to experience degradation when exposed to high temperatures.
Misfuel:  EPA estimated that operators will use the wrong type of fuel, such as agricultural diesel fuel with higher sulfur levels, approximately 0.1 percent of the time.
   
Tampering & Mal-maintenance Occurrence Rate Summary

NOx Emission Effects
EPA developed the emission effect from each tampering and mal-maintenance incident from CARB's EMFAC, Radian's dynamometer testing with and without the malfunction present, EFEE results, and internal testing experience.
EPA estimated that the lean NOx traps (LNT) in LHDD are 80 percent efficient and the selective catalyst reduction (SCR) systems in HHDD are 90 percent efficient at reducing NOx.
EPA developed the NOx emission factors of the NOx sensors based on SCR systems' ability to run in open-loop mode and still achieve NOx reductions.  The Manufacturers of Emission Controls Association (MECA) has stated that 75-90 percent NOX reduction with open loop control and >95 percent reduction with closed loop control.  Visteon reports 60-80 percent NOX reduction with open loop control.  
The failure of the NOx aftertreatment system had a different impact on the NOx emissions depending on the type of aftertreatment.  The HHDD vehicles with SCR systems would experience a 1000 percent increase in NOx during a complete failure, therefore we estimated a 500 percent increase as a midpoint between normal operation and a complete failure.  The LHDD vehicles with LNT systems would experience a 500 percent increase in NOx during a complete failure.  We estimated a 300 percent increase as a value between a complete failure and normal system operation.    
The values with 0 percent effect in shaded cells represent areas which have no occurrence rate.

    
PM Emission Effects
EPA developed the PM emission effects from each tampering and mal-maintenance incident from CARB's EMFAC, Radian's dynamometer testing with and without the malfunction present, EFEE results, and internal testing experience.
EPA estimates that the PM filter has 95 percent effectiveness.  Many of the tampering and mal-maintenance items that impact PM also have a fuel efficiency and drivability impact.  Therefore, operators will have an incentive to fix these issues.
EPA estimated that excessive oil consumption will have the same level of impact on PM as engine mechanical failure.  The failure of the oxidation catalyst is expected to cause a PM increase of 30 percent; however, this value is reduced by 95 percent due to the PM filter effectiveness.  We also considered a DOC failure will cause a secondary failure of PM filter regeneration.  We accounted for this PM increase within the PM filter disabled and leak categories.
The values with 0 percent effect in shaded cells represent areas which have no occurrence rate.

Tamper & Malmaintenance

PM Emission Effect

 
                                   1994-1997
                                   1998-2002
                                   2003-2006
                                   2007-2009
                                     2010
Federal Emission Standard
                                      0.1
                                      0.1
                                      0.1
                                     0.01
                                     0.01
 
 
 
                                       
                                       
                                       
Timing Advanced
                                     -10%
                                     -10%
                                     -10%
                                      0%
                                      0%
Timing Retarded 
                                      25%
                                      25%
                                      25%
                                      1%
                                      1%
Injector Problem
                                     100%
                                     100%
                                     100%
                                      5%
                                      5%
Puff Limiter Mis-set
                                      20%
                                      0%
                                      0%
                                      0%
                                      0%
 Puff Limiter Dsabled
                                      50%
                                      0%
                                      0%
                                      0%
                                      0%
Max Fuel High
                                      20%
                                      0%
                                      0%
                                      0%
                                      0%
Clogged Air Filter 
                                      50%
                                      50%
                                      30%
                                      2%
                                      2%
Wrong/Worn Turbo
                                      50%
                                      50%
                                      50%
                                      3%
                                      3%
Intercooler Clogged
                                      50%
                                      50%
                                      30%
                                      2%
                                      2%
Other Air Problem
                                      40%
                                      40%
                                      30%
                                      2%
                                      2%
Engine Mechanical Failure
                                     500%
                                     500%
                                     500%
                                      25%
                                      25%
Excessive Oil Consumption
                                     500%
                                     500%
                                     500%
                                      25%
                                      25%
Electronics Failed 
                                      60%
                                      60%
                                      60%
                                      3%
                                      3%
Electronics Tampered
                                      50%
                                      50%
                                      50%
                                      3%
                                      3%
EGR Stuck Open
                                      0%
                                      0%
                                     100%
                                      5%
                                      5%
EGR Disabled/Low Flow
                                      0%
                                      0%
                                     -30%
                                     -30%
                                     -30%
Nox Aftertreatment Sensor
                                      0%
                                      0%
                                      0%
                                      0%
                                      0%
Replacement Nox Aftertreatment Sensor
                                      0%
                                      0%
                                      0%
                                      0%
                                      0%
Nox Aftertreatment Malfunction
                                      0%
                                      0%
                                      0%
                                      0%
                                      0%
PM Filter Leak
                                      0%
                                      0%
                                      0%
                                     935%
                                     935%
PM Filter Disabled 
                                      0%
                                      0%
                                      0%
                                     2670%
                                     2670%
Oxidation Catalyst Malfunction/Remove
                                      0%
                                      0%
                                      0%
                                      0%
                                      0%
Mis-fuel - EPA
                                      30%
                                      30%
                                      30%
                                     100%
                                     100%
                                       
   
HC Emission Effects
EPA estimated oxidation catalysts are 80 percent effective at reducing hydrocarbons.  All manufacturers will utilize oxidation catalysts in 2007, but only a negligible number were installed prior to the PM regulation reduction in 2007.
We reduced CARB's HC emission effect for timing advanced because earlier timing should reduce HC, not increase them.  The effect of injector problems was reduced to 1000 percent based on internal experience.  We increased the HC emission effect of high fuel pressure to 10 percent because the higher pressure will lead to extra fuel in early model years and therefore increased HC.  Lastly, we used the HC emission effect of advanced timing for the electronics tampering since this was the most significant type of tampering that occurred.
The values with 0 percent effect in shaded cells represent areas which have no occurrence rate. 

                                       
                                       

A separate tampering analysis was not performed for CO; rather,  the HC effects were assumed to apply for CO.
Combining all of the emissions effects and failure frequencies discussed in this section, we summarized the aggregate emissions impacts over the useful life of the fleet due to in the main body of the document in Table 2-7 (NOx), Table 2-14 (PM), and Table 2-17 (HC and CO).

HD OBD impacts
With the finalization of the heavy-duty onboard diagnostics (HD OBD) rule, we made adjustments to our draft 2010 and later model year to reflect the rule's implementation.
Specifically, we reduced our emissions increases for all pollutants due to tampering and mal-maintenance by 33 percent.  As data are not yet available for heavy-duty trucks equipped with OBD, this number is probably a conservative estimate.  Still, PM and NOx reductions from 2010 and later model year vehicles will be substantial compared to prior model years regardless of the additional incremental benefit from OBD.  We assumed, since the rule phases in OBD implementation, that 33 percent of all engines will have OBD in 2010, 2011, and 2012 model years, and 100 percent will have OBD by 2013 model year and later. Equation B-2 describes the calculation of TMpol, the increase in emission rate through useful life, where fOBD represents the fraction of the fleet equipped with OBD (0 percent for model years 2009 and earlier, 33 percent for model years 2010-2012, and 100 percent for model years 2013 and later).  The result from this equation can be plugged into Equation B-1 to determine the emission rate for any age group.

                                       
                                       
                                                                   Equation B-2
These OBD impacts apply to any truck in Class 4 and above. Any lighter trucks are assumed to follow light-duty OBD impacts and will be fully phased in starting in model year 2010. As data for current and future model years become available, we may consider refining these estimates and methodology.
Extended Idle Data Summary

2007 Extended Idle Emissions calculation:
* Assumed 8 hour idle period where the emissions controls, such as EGR, oxidation catalyst, and NOx aftertreatment, are still active for the first hour.
* HC emissions standards:
      o Pre-2007: 0.50 g/bhp-hr
      o 2007:  0.14 g/bhp-hr
* NOx emissions standards:
      o Pre-2010: 5.0 g/bhp-hr
      o 2010:  0.2 g/bhp-hr

Idle HC Rate Reduction = 1 - [(1/8 * 0.14 g/bhp-hr + 7/8 * 0.5 g/bhp-hr) / 0.5 g/bhp-hr] = 9%
Idle NOx Rate Reduction = 1 - [(1/8 * 0.2 g/bhp-hr + 7/8 * 5.0 g/bhp-hr) / 5.0 g/bhp-hr] = 12%

Developing PM emission rates for missing operating modes 
In cases where an estimated rate could not be directly calculated from data, we imputed the missing value using a log-linear least-squares regression procedure.  Regulatory class, model year group and speed class (0 - 25 mph, 25-50 mph and 50+ mph ) were represented by dummy variables in the regression.  The natural logarithm of emissions was regressed versus scaled tractive power (STP) to represent the operating mode bins.  The regression assumed a constant slope versus STP for each regulatory class.  Logarithmic transformation factors (mean square error of the regression squared / 2) were used to transform the regression results from a log based form to a linear form.  Due to the huge number of individual second-by-second data points, all of the regression relationships were statistically significant at a high level (99% confident level).  The table below shows the regression statistics, and the equation shows the form of the resulting regression equation.
Table D-1. Regression Coefficients for PM Emission Factor Model
Model-year group
Speed Class (mph)
Type
Medium Heavy-Duty
Heavy Heavy-Duty
1960-87
1-25
Intercept (β0)
-5.419
-5.143

25-50

-4.942
-4.564

50+

-4.765
-4.678
1988-90
1-25

-5.366
-5.847

25-50

-4.929
-5.287

50+

-4.785
-5.480
1991-93
1-25

-5.936
-5.494

25-50

-5.504
-5.269

50+

-5.574
-5.133
1994-97
1-25

-5.927
-6.242

25-50

-5.708
-5.923

50+

-5.933
-6.368
1998-2006
1-25

-6.608
-6.067

25-50

-6.369
-5.754

50+

-6.305
-6.154

STP
Slope  (β1)
0.02821
0.0968

Transformation Coefficient (0.5σ[2])

0.5864

0.84035

Where :
β0 = an intercept term for a speed class within a model year group, as shown in the table above,
β1 =  a slope term for STP, and
σ2 = the mean-square error or residual error for the model fit,
STP = the midpoint value for each operating mode (kW/metric ton, see Table 1-4).

Heavy-duty Diesel EC/PM Fraction Calculation
Introduction
This memo describes the development and application of a "rough cut" emission model for estimating elemental and organic carbonaceous material (EC and OM) emission rates (or EC/OM ratios) from MOVES.  The memo describes the following steps involved in predicting EC/OM ratios.  The memo also briefly describes comparisons with independent emission data collected using the  "Mobile Emission Laboratory," Operated by the University of California Riverside.
The subsequent sections of the memo describe the following topics:
      * the extension of Physical Emission Rate Simulator (PERE)  to estimate heavy-duty fleet-average emission factors for any specified driving cycle;
      * the acquisition of data used in estimating EC/OC rates as a function of engine operating mode and the fitting of simple empirical models to them;
      * the application of PERE to estimate EC and OC emission rates for different test cycles; and,
      * the comparison of PERE-based EC and OC emission rates to those measured by independent researchers in HD trucks.
 PERE for Heavy-duty Vehicles (PERE-HD) and Its Extensions
The Physical Emission Rate Estimator (PERE) is a model employed by EPA in early development of MOVES.33  In particular, the MOVES team employed it in development of MOVES2004 to impute greenhouse gas emission rates for combinations of SourceBin and Operating Mode for which data was unavailable or of insufficient quality.
The underlying theory behind PERE and its comparison with measured fuel consumption data is described by Nam and Giannelli (2005).33 Briefly, PERE estimates fuel consumption and emission rates on the basis of fundamental physical and mathematical relationships describing the road load that a vehicle meets when driving a particular speed trace.  Accessory loads are handled by addition of an accessory power term.  In the heavy-duty version of PERE (hereafter, "PERE-HD"), accessory loads were described by a single value. 
For the current project, PERE was modified to incorporate several "extensions" that allowed it to estimate fleet-average emission rates, simulate a variety of accessory load conditions, and predict EC rates for any given driving cycle.
PERE-HD Fleet-wide Average Emission Rate Estimator
PERE-HD requires a number of user-specified inputs, including:
      * vehicle-level descriptors (model year, running weight, track road-load coefficients (A,B,C), transmission type, class [MDT/HDT/bus]);
      * engine parameters (fuel type, displacement); and
      * driving cycle (expressed through a speed trace).

The specification of these inputs allows PERE to model the engine operation, fuel consumption, and GHG emissions for a HDV on a specified driving cycle.
However, the baseline PERE-HD provides output for only one combination of these parameters at once.  To estimate fleet-wide average a large number of PERE-HD runs would be required.  Furthermore, the specification of only fleet-wide average coefficients is likely to substantially underestimate variability in fuel consumption and emissions.  Emissions data from a large number of laboratory and field studies suggest that a very large fraction of total emissions from all vehicles derives from a small fraction of the study fleet.  Therefore, it is desirable to develop an approach that comes closer to spanning the range of likely combinations of inputs than using a small selection of "average" or "typical" values.
For the current application, PERE-HD (built within Microsoft Excel) was expanded to allow for a representative sample of [running weight] x [engine displacement] x [model year] combinations.  A third-party add-on package to Excel, @Risk 4.5 (Palisade Corporation, 2004), allows users to supplement deterministic inputs within spreadsheet models with selected continuous probability distributions, sample input values from each input distribution, and re-run the spreadsheet model with sets of selected inputs over a specified number of iterations.  This type of procedure is commonly referred to as "Monte Carlo" simulation.
Monte Carlo Simulation in PERE-HD
To illustrate how @Risk performs this process, we illustrate the application of a simple model, employing both deterministic calculations and stochastic Monte Carlo simulation:
                                          
This equation defines the body mass index for humans, a simple surrogate indicating overweight and underweight conditions.  According to the Centers for Disease Control and Prevention (CDC), the average U.S. woman weighed 164.3 lb (74.5 kg) in 2002 and was 5'4" (1.6 m) tall.  This result  corresponds to a BMI of 28, suggesting that the average U.S. woman is overweight.  While this is useful information from a public health perspective, it does not provide any indication as to which individuals are likely to experience the adverse effects of being overweight and obese.  However, if we were to assume (arbitrarily) that the range of weight and height within the U.S. population was +/-50% of the mean, distributed uniformly, and perform a Monte Carlo simulation (5,000 iterations) using @Risk, we would predict a probability distribution of BMI in the population as follows:

In contrast, here is the BMI distribution in the entire U.S. population, according to the CDC's National Health and Nutrition Examination Survey (NHANES):

These graphs illustrate how Monte Carlo simulation can be used to provide meaningful information about the variability in a population.  Although the model example is very simple, it illustrates the point that a model with "typical" inputs provides much less information than Monte Carlo simulation does with variable inputs.
For emission modeling purposes using PERE-HD, several key inputs were modeled as probability distributions.
Model Year
Model year is an important factor in PERE, as the frictional losses in the model, expressed as "friction mean effective pressure" (FMEP), vary by model year, improving with later model years.  As such, model year was simulated as a probability distribution, based on data from the Census Bureau's 1997 Vehicle Inventory and Use Survey (VIUS), which reports "vehicle miles traveled" (VMT) by model year. Accordingly these data were normalized to total VMT to develop a probability distribution.  Model year distributions in 1997 were normalized to the current calendar year (2008).  For instance, the fraction of 1996 vehicles reported in the 1997 VIUS is treated as the fraction of 2002 vehicles in the 2003 calendar year.  Although a 2002 VIUS is available, previous analyses (unpublished) have shown the "relative" model year distribution of trucks to have changed little between 1997 and 2002, though this assumption is one limitation of this analysis.
The model year distribution for PERE-HD was represented as a discrete probability distribution, as shown below:

Vehicle Weight and Engine Displacement
Vehicle running weights and engine displacements were modeled as a two-way probability distribution with engine displacement depending on running weight.  These data were derived from VIUS micro data obtained from the Census Bureau.  A two-way table was constructed to estimate VMT classified by combinations of [weight class] x [displacement class].  Analyses were restricted to diesel-powered trucks only.
As a first step, @Risk selects a running weight from a probability distribution representing the fraction of truck VMT occurring at a given running weight:

Because VIUS reports classes defined as ranges in running weight, any value of weight within each VIUS-specified class was considered equally likely and modeled as a uniform probability distribution within the class.  For the upper and lower bounds of the distribution the minimum and maximum running weights were assumed to be 7,000 and 240,000 lb, respectively.
After @Risk selects a running weight, it selects an engine displacement based on a discrete distribution assigned to every weight class in VIUS, represented below:

Again, because VIUS describes ranges of values for displacement, all values within each range were given uniform weight and assigned a uniform distribution.  For the extreme classes, the minimum and maximum engine displacements were assumed to be 100 in[3] and 915 in[3], respectively.

This procedure reflects the range in running weights present among HDV in operation, and constrains the combinations of weight and displacement to plausible pairs of values based on surveyed truck operator responses.  These steps allow for plausible variability in weight-engine pairings, which translates into differences in engine parameters influencing EC and OC emissions.
	For use in PERE-HD, all units were converted to SI units (kg and L).
Accessory Load
The original PERE-HD treats accessory load as a fixed value, which may be varied by the user.  It is set at 0.75, and used in calculating fuel rate and total power demand at each second of driving.
Following the development of PERE-HD, a more detailed set of accessory load estimates was developed based on several accessories' power demand while in use and the fraction of time each accessory is in use (see Table 2-4).  High, medium, and low accessory use categories were estimated for three vehicle classes:  HDT, MDT, and buses.  For the current version of the model, only the HDT accessory load estimates were employed, though a sensitivity analysis indicated that mean EC/OM ratios were most sensitive to accessory load during idle and creep driving cycles.  In the "base case," a mean ratio of 0.54 was predicted, while in the sensitivity case, a mean ratio of 0.50 was predicted.  This issue may be revisited at some point, although the limited sensitivity of total results limits the importance of the accessory terms within the current exercise.
Within @Risk, the variable in PERE-HD, Pacc for accessory use was substituted with a variable representing the distribution (in time) of accessory loads as estimated as the sum of a number of discrete probability distributions.  
Depending on the assumption of high, medium or low use, the power demand for these accessories is distributed in time as follows:
                                       
Driving Cycle
For purposes of this exercise, the four phases of the California Air Resources Board's Heavy Heavy-Duty Diesel Truck (HHDDT) chassis dynamometer testing cycle were used to reflect variability in vehicle operations for PERE-HD.
Other Factors
Some elements of variability were not examined as part of this study.  Hybrid-electric transmissions and fuel cell power plants were excluded from the analysis, due to their low prevalence within the current truck fleet.
One important source of variability that was not examined in this analysis is the variation in resistive forces among vehicles with identical running weights.  This exclusion is important, given the potential role for aerodynamic improvements, low rolling resistance tires, and other technologies in saving fuel for long-distance trucking firms and drivers.  Such considerations could be incorporated into PERE-HD in the future as a means of estimating the emission benefits of fuel-saving technologies.  

Prediction of Elemental Carbon and Organic Mass based on PERE-HD
Definition of Elemental and Organic Carbon and Organic Mass
In motor vehicle exhaust, the terms "EC," "elemental carbon," and "black carbon" refer to the fraction of total carbonaceous mass within a particle sample that consists of light-absorbing carbon.  Alternatively, they refer to the portion of carbonaceous mass that has a graphitic crystalline structure.  Further, one can define EC as the portion of carbonaceous mass that has been altered by pyrolysis, that is, the chemical transformation that occurs in high temperature in the absence of oxygen.
EC forms in diesel engines as a result of the stratified combustion process within a cylinder.  Fuel injectors spray aerosolized fuel into the cylinder during the compression stroke.  The high-pressure and high temperature during the cylinder cause spontaneous ignition of the fuel vaporizing from the injected droplets.  Because temperature can rise more quickly than oxygen can diffuse to the fuel at the center of each droplets, pyrolysis can occur as hydrogen and other atoms are removed from the carbonaceous fuel, resulting in extensive C-C bond interlinking.  As a result, pyrolyzed carbon is produced in a crystalline form similar to graphite.
"Organic carbon" or "organic mass" (OC or OM) is used to denote the portion of carbonaceous material in exhaust that is not graphitic.  Chemical analysis of this non-graphitic carbon mass indicates that it is composed of an extensive mixture of different organic molecules, including C15 to C44 alkanes, polycyclic aromatic hydrocarbons, lubricating oil constituents (hopanes, steranes, and carpanes), and a sizeable fraction of uncharacterized material.  This component of exhaust can derive from numerous processes inside the engine involving both fuel and oil.  Because of the complex chemical mixture that comprises this mass, its measurement is highly dependent on sampling conditions.  The wide range of organics that compose it undergo evaporation and condensation at different temperatures, and the phase-partitioning behavior of each molecule is dependent on other factors, such as the sorption of vapor-phase organics to available surface area in a dilution tunnel or background aerosol.

EPA Carbon Analysis Techniques in Ambient Air
The definitions of EC and OM are critical, as different groups use different techniques for quantifying their concentrations within a given medium.  For purposes of this document, it is assumed that EC, OC, and OM are operationally defined quantities, meaning that they are defined by the measurement technique used to quantify their concentrations on a filter or in air.
The different types of commonly used approaches for carbon include:
      * Thermal/optical techniques, where the evaporation and oxidation of carbon are used in conjunction with a laser to measure optical properties of a particle sample.  The major methods used for this type of analysis include:
            o Thermal/optical reflectance (TOR).  EPA is adopting this technique for the PM2.5 speciation monitoring network nationwide.  It is also employed by the IMPROVE program (Interagency Monitoring of Protected Visual Environments) in national parks.  This technique heats a punch from a quartz fiber filter according to a certain schedule.  A Helium gas atmosphere is first employed within the oven, and the evolved carbon is measured with a FID as temperatures are increased in steps up to 580°C.  All carbon evolved in this way is assumed to be volatilized organic material.  Next, 2% oxygen gas is added to the atmosphere, and temperatures are stepped up a number of times to a maximum of 840°C.  All carbon evolved after the introduction of oxygen is assumed to be elemental carbon.  The reflection of light from a laser by the filter is employed to account for the pyrolysis of organic carbon that occurs during the warm-up process.
            o Thermal/optical transmission (TOT). The National Institute of Occupational Safety and Health (NIOSH) uses this technique for measuring EC concentrations in occupational environments.  It is based on similar principles to TOR, but employs a different heating schedule and transmission of light as opposed to reflectance.
      * Radiation absorption techniques
            o Aethalometer(R)  -  This instrument reports "black carbon" (BC) concentrations based the extent of light absorption by a "filter tape," that allows for a time series of BC concentrations to be estimated.  It has a time resolution of several minutes.
            o Photoacoustic Spectrometer (PAS)  -  This instrument irradiates an air sample with a laser.  The resulting heat that occurs from the absorption of the laser light by light-absorbing carbon in the air sample produces a pressure wave that is measured by the device.  The signal from this pressure wave is proportional to the light-absorbing carbon content in exhaust.
      * Thermogravimetric techniques, where the "volatile organic fraction" (VOF) is separated by heat from the non-volatile refractory component of a particle sample.
      * Chemical extraction, where solvents are used to separate the soluble and insoluble components of exhaust.
A number of additional techniques are also described in the published literature, but the above techniques have been most commonly applied in emissions and routine ambient PM measurement.
Among the available techniques, it has been a point of controversy among academics as to which  method provides the "correct" carbon signal.  Rather than addressing these arguments in detail, this analysis adopts the technique employed by the EPA ambient speciation monitoring network, TOR.  Needless to say, different researchers employ different sampling, measurement and analysis techniques.  Desert Research Institute (DRI) employed TOR in analyzing the Kansas City gasoline PM emission study samples , while other prominent academics employ TOT, notably the University of California Riverside College of Engineering Center for Environmental Research and Technology (CE-CERT) and the University of Wisconsin-Madison (UWM) State Hygiene Laboratory.  As research results from these groups is employed throughout this analysis, an inter-comparison of the methods of TOT/TOR is necessary to "recalibrate" various datasets with respect to each other.
EPA defines measurement techniques for dynamometer-based sampling and analysis of particulate matter, in addition to techniques for sampling and analyzing particles in ambient air.  Inventories estimated for EC and OM can be considered to reflect both broad categories of measurement techniques, depending on context.
The user community for MOVES is predominantly concerned with emissions that occur into ambient air.  EPA regulations for demonstration of attainment of state implementation plans (SIPs) are based on monitored ambient particulate matter using Federal Reference Methods (FRM) for ambient air.  FRM monitors for particle speciation in ambient air undergo analysis for EC and OC according to a defined standard operating procedure.  That standard operating procedure defines thermal/optical reflectance (TOR) as the desired method for analysis of ambient carbon PM.  
TOR  -  TOR Calibration Curve
In the course of the Gasoline/Diesel PM Split Study funded by the Department of Energy (DOE), researchers from DRI analyzed filter samples using both TOR and TOT methods[cite].  These data were obtained and analyzed in the SPSS 9.0 statistical package.
Briefly, the DOE study included emissions characterizations of 57 light-duty gasoline vehicles (LDGV) and 34 HD diesel vehicles (HDDV).  The vehicles were operated on a number of different test cycles including cold-start and warm-start cycles.  The data set employed in this study was generated by DRI and obtained from the DOE study web site. Both EC and OC were analyzed using the same approach.  All data from all vehicles were compiled.
First, EC and OC measured by TOR (denoted EC-TOR and OC-TOR) were regressed on EC-TOT and OC-TOT.  Studentized residuals from these regressions were noted, and those with Studentized residuals >3 were excluded from further analysis.
Second, each test in the reduced data set was assigned a random number (RAND) on the range [0,1].  Those cases with RAND >= 0.95 were set aside as a cross-validation data set, and excluded from additional regression analyses.
Third, those cases with RAND < 0.95 were regressed again, this time using an inverse uncertainty weighting procedure for each data point.  When DRI analyzes a filter sample, it reports an analytical uncertainty associated with the primary estimate of EC and OC.  Accordingly, the quality of each datum depends on the level of analytical uncertainty reported.  The inverse of the DRI-reported uncertainty (1/) associated with the TOR-based measurement was used to weight each point in the weighted regression.
It should be noted that for each regression, the intercept term was set to zero.  Models including intercepts did not have intercept terms that reached statistical significance.  As such, R[2] values are not considered valid.
      
      Coefficients from the weighted regression for EC and OC are reported below:
Slope
Beta
Std. Error
t-value
Sig.
EC-TOR
1.047
0.011
91.331
<0.0001
OC-TOR
1.014
0.007
153.923
<0.0001
      
To evaluate the quality of predictions resulting from these statistically-based adjustment factors, they were used to predict EC-TOR and OC-TOR values for the subset of data with RAND >= 0.95.  Scatter plots of the statistical fits are illustrated below (note logarithmic scaling).

	When measured values are regressed against predicted values, the following statistical estimates of fit are obtained:
Prediction
Slope
Std. Error
Intercept
Std. Error
EC
1.080
0.009
3.737
3.173
OC
1.092
0.069
-4.417
16.188
As shown, the prediction vs. observed comparison yields a slope near unity for both EC-TOR and OC-TOR, with nonsignificant intercepts.  On this basis, the "calibration" factors for converting EC-TOT and OC-TOT into their respective TOR-based metrics appear reasonable.
It remains an unverified assumption that the "calibration" factors derived from the emissions data derived from DRI as part of the DOE Gasoline / Diesel PM Split Study are general enough to apply to EC-TOT measurements obtained by other research groups.
EC and OC Emission Rates
 Selection of Engine Parameters for Predictive Modeling
PERE-HD produces estimates of engine operating conditions and fuel consumption for a given driving cycle.  Prediction of EC and OM emissions requires information on the composition of particulate matter as a function of some factor that may be related back to MOVES' activity basis, the time spent in a particular operating mode (opModeID).

It should be noted that continuous ("second-by-second, or  "real time") measurement of EC and OM is an exceptionally complicated endeavor.  While measurement techniques for EC have been developed that produce apparently good correlation with traditional filter-based methods,  
While numerous publications report the EC and OM (or OC) exhaust emission rates across an entire driving cycle, it is not clear which parameter of a particular driving cycle, such as average speed (or power), might be applicable to the extrapolation of the observed rates to other vehicles or driving conditions.  As a result, identifying one or more engine parameters that explain the observed variation in driving cycle-based emission rates for EC and OM is desirable.  Such  parameter(s) will assist in estimating emission associated with short-term variations in driving.
One good candidate for establishing an engine-based emission model is mean effective pressure (MEP).  MEP is defined as:
                                       
                                       
                                       
Here, P is the power (in kW or hp), nR is the number of crank revolutions per power stroke per cylinder (2 for four-stroke engines, 1 for two-strokes), Vd is the engine displacement, and N is the engine speed.  In other words, MEP is the engine torque normalized by volume.
MEP can be broken into various components.  "Indicated MEP" or IMEP refers to the sum of BMEP (brake MEP) and FMEP (friction MEP).  Heywood (1988) writes that maximum BMEP is an indicator of good engine design and "essentially constant over a wide range of engine sizes.[cite]"  Nam and Giannelli (2004) note that it can be related to fuel MEP multiplied by the indicated or thermal efficiency of an engine, and have developed trend lines in FMEP by model year.  As such, since maximum BMEP is comparable across well-designed engines and FMEP can be well-predicted by Nam and Giannelli's trends within PERE, IMEP should be an appropriate metric for building an engine emission model that can be applied across vehicles with different loads and engine displacements.
 Emission Data
Kweon et al. (2004) measured particle composition and mass emission rates from a single-cylinder research engine based on an in-line 2.333 liter turbo-charged direct-injection six cylinder Cummins N14-series engine, with a quiescent, shallow dish piston chamber and a quiescent combustion chamber.  Emission data were obtained from all eight modes of the CARB 8-mode engine test cycle:

Mode 1
Mode 2
Mode 3
Mode 4
Mode 5
Mode 6
Mode 7
Mode 8
Speed
1800
1800
1800
1200
1200
1200
1200
700
Load%
100
75
50
25
100
75
50
10 (idle)
Equiv. Ratio (φ)
0.69
0.50
0.34
0.21
0.82
0.69
0.41
0.09
IMEP (MPa)
1.083
0.922
0.671
0.524
1.491
1.225
0.878
0.150
The study reports exhaust mass composition, including PM2.5, EC, and organic mass (OM, estimated as 1.2 x OC) measured with TOT (denoted here as EC-TOT and OC-TOT).  In the main study, the authors report that EC and OC are highly sensitive to the equivalence ratio.  However, IMEP is highly correlated with the measured equivalence ratio (R[2] = 0.96).  As such, it is reasonable to report the data as a function of IMEP, expecting it to have approximately equal explanatory power as has the equivalence ratio variable.  The figure below plots the emission data from Kweon et al. (2002) as a function of IMEP.

As shown in the figure, the EC-TOT work-specific emission rate is relatively insensitive to IMEP except between IMEP of approximately 0.85 and 1.1, where it undergoes a rapid increase.  Overall, the EC-TOR/IMEP curve is S-shaped, similar to a logistic curve or growth curve.  OC-TOT work-specific emissions are highest at low IMEP (i.e. idle) and are monotonically lower with higher IMEP.  Total work-specific PM2.5 is not monotonic, but appears to be described by a single global minimum around IMEP ~ 0.9 and two local maxima around IMEP of 0.2 and 1.2, respectively.
The oppositely signed slopes of the emission-IMEP curves for EC-TOT and OC-TOT suggest that there are different underlying physical processes.  It is not the intent of this document to explicitly describe the particle-formation mechanisms in a diesel engine.  However, the use of two separate functions to predict EC-TOT and OC-TOT separately is warranted.  This implies that the EC/OC ratio will vary by engine operating mode.  The following figure depicts the EC/OC ratio as a function of IMEP.

 Estimation of IMEP-based Emissions of EC and OC
To produce a relationship that generalizes the implied relationship between EC-TOT and OC-TOT work-specific emissions and IMEP in the data presented by Kweon et al. (2004), it is necessary to specify some functional form of a relationship between the two.
A priori, on the basis of visual inspection of the data, a flexible logistic-type curve was fit to the data by a least-squares minimization procedure using the Microsoft Excel "Solver" tool, which employs the GRG2 optimization approach.
The functional form of the logistic-type curves fit to both the EC-TOT and OC-TOT data from Kweon et al. (2004) is as follows:
                                       
A least-squared error approach was implemented within Microsoft Excel to derive the coefficients for the logistic curves for EC-TOT and OC-TOT.  The solutions to the fits are as follows:
                                       Y
                                       A
                                       B
                                       C
                                    EC-TOT
                                2.12 x 10[-5]
                                     -9.79
                                 4.67x 10[-5]
                                    OC-TOT
                                     0.155
                                    -2.275
                                    -0.859
Graphically, in comparison to observed values of EC-TOT and OC-TOT, the fitted curves result in predictions reasonably close to the observed values.  Furthermore, when compared to the observed PM2.5 values, the sum of predicted EC-TOT and OC-TOT values predict the lack of monotonicity and patterns of maxima and minimum seen in the PM2.5 data.
However, as a result of the values predicted by these sigmoid-type curves at high and low IMEP values, extreme patterns in the EC-TOT/OC-TOT ratios predicted occur.  These extreme values are artifacts that result solely from the behavior of simplistic logistic curves at the bounds of IMEP in the observed data sets.  As a result, for predictive purposes, the maximum and minimum observed EC-TOT and OC-TOT values observed in the data set were set as the artificial limits of predicted EC-TOT and OC-TOT, respectively.  While this approach is arbitrary, it does ensure that extreme predictions resulting from the selection of the logistic functional form do not occur.
The following graph (log-scale) depicts the behavior of the TOT-based EC/OC ratio as a function of IMEP.  As demonstrated on the graph, without the max/min constraints on predicted EC-TOT and OC-TOT, the predicted ratio assumes values with a much broader range than found in the data.

The approach of constraining predictions to the maximum and minimum values observed in the measured data set is not grounded in any theoretical basis, but is a "brute force" approach.  Future revisions to this analysis may consider alternative approaches more grounded in accepted theoretical or statistical methodology.
The logistic curves described above receive IMEP predictions from PERE to predict EC-TOT and OC-TOT emission rates (g/bhp-hr) for every second of a driving cycle.  Combined with real-time work estimates from PERE, emissions are expressed in g/s, the same units required for MOVES.
EC-TOT and OC-TOT emission rates are converted to TOR-equivalent rates for use in MOVES, using the TOT-TOR "calibration" relationships described above.  Alternatively, TOT-equivalent rates can be used to compare with data from studies employing TOT for carbon analysis.
It should be noted that these emission estimates are based on a single engine.  Therefore, predictions of EC and OC emission rates based on these relationships are insensitive to model year, although PERE-HD does vary frictional MEP as a function of model year.
 Organic Carbon to Organic Mass Conversion
Carbon is only one component of the organic material found in PM emission samples.  Hydrogen, oxygen, and nitrogen are also components of organic molecules found in exhaust PM.  For this study, a simple set of OC/OM conversion ratios were employed.
Heywood (1988) presents data on the chemical composition of diesel exhaust PM, presenting characterization of both the "extractable composition" and "dry soot" components of PM measured at idle and at 48 km/h.  The composition data is as follows:
                                       
Idle
48 km/h
Atomic formula
C23H29O4.7N0.21
C24H30O2.6N0.18
OM/OC Ratio
1.39
1.26

The data for the "extractable composition" is assumed to represent  the organic mass of particles.  The total molar weight to carbon molar weight ratio was used to convert OC to OM.  The idle data from Heywood were used when engine IMEP was 0.15 or under, corresponding to the idle mode of the cycle employed by Kweon et al. (2004).  All other engine conditions employed the ratio based on the 48 km/h sample in Heywood.

 Comparison of Predicted Emissions with Independent Measurements
To ensure that predicted EC and OC emission rates from this approach are reasonable prior to any application for MOVES, PERE-HD based EC and OC emission factors were compared with measured emission factors from an independent study.  Shah et al. (2004) report EC and OC emission factor and rates for a series of heavy heavy-duty diesel trucks (HHDT) in California.  Shah et al. report the results of emission testing using the CE-CERT Mobile Emissions Laboratory (MEL), a 53-foot combination truck trailer containing a full-scale dilution tunnel designed to meet Code of Federal Register (CFR) requirements.  The primary dilution tunnel is a full-flow constant volume sampler, with a double-wall insulated stainless steel snorkel that connects the MEL directly to the exhaust system of a diesel truck.  PM collection systems were designed to meet 2007 CFR specification, including a secondary dilution system (SDS).
The 11 trucks sampled in this study were all large HHDDTs with engine model years 1996-2000, odometers between approximately 9,000 and 547,000 miles, and rated powers from 360-475 hp.  It should be noted that these trucks, on average, have larger engines and higher rated power than "typical" trucks on the road.  Furthermore, they were loaded with only the MEL, which weighs 20,400 kg.  As a result, the emissions from these trucks do not reflect the expected variability in truck running weight described above and used in the PERE-HD runs for this study.
Shah et al. (2004) report emission data for each of the four modes of the CARB HHDDT cycle, including cold start/idle, creep, transient, and cruise.  The test cycle represents a wide range of driving patterns, as suggested in the table below.  Note that these test cycles are trip-based, so each begins and ends with the vehicle at stop.  

Cycle
Distance (mi)
Duration (s)
Average Speed (mph)
Maximum Speed (mph)
Maximum Acceleration (mph/s)
Cold start/idle
0
600
0
0
0
Creep
0.124
253
1.77
8.24
2.3
Transient
2.85
668
15.4
47.5
3.0
Cruise
23.1
2083
39.9
59.3
2.3

The following table presents the EC-TOT and OC-TOT emission rates reported in Table 6 of the study:
                                     Rate
                                     Idle
                                     Creep
                                   Transient
                                    Cruise
                                  EC (mg/mi)
                                       
                                   340+-140
                                   446+-115
                                   175+-172
                                  OC (mg/mi)
                                       
                                   607+-329
                                  182.9+-51.2
                                  74.7+-56.3
                                  EC (mg/min)
                                  4.10+-2.38
                                   10.4+-4.8
                                  110.7+-27.0
                                  93.0+-68.3
                                  OC (mg/min)
                                  20.9+-11.6
                                   17.0+-6.4
                                  45.5+-13.2
                                  42.3+-26.8

The following graph illustrates the comparison between predicted EC-TOT and OC-TOT emission factors predicted by PERE-HD and those reported by Shah et al. (2004).  The letters "H," "M," and "L" refer to high, medium, and low accessory loads employed in the PERE-HD runs with IMEP-based emission rates.  As shown in the graph, it appears that for transient and cruise conditions, PERE-HD predicts the general between-cycle trends in EC-TOT and OC-TOT emission factors.  It appears that for the low-speed "creep cycle," PERE-HD or the IMEP-based emission rates underpredict total carbon (EC+OC) emission factors, but that the general trend in the EC/OC ratio is directionally correct.

Variability in Predicted EC and OC Emission Rates
Through the modeling approach used here the influence of variability in vehicle weight and engine displacement on heavy-duty EC and OC emission rates can be assessed.  It should be noted that these relationships are contingent on the particular algorithms employed in PERE-HD for estimating power and IMEP, as well as on the functional form of the IMEP-based emission relationship described above.  As such, the analysis of variability in EC and OC emission rates is constrained within the functional forms of all models employed.
The graph below depicts the TOR-specific ratios of the total amount of EC and OM emitted across the transient driving cycle.  As is apparent, increasing running weight per unit of engine displacement is associated with an increased EC/OC ratio.  The highest EC/OM ratios, located in the upper right-hand-quadrant of the graph, correspond to vehicles loaded with extreme weight relative to the total available engine displacement.  

In general, these results reflect the role that running weight has on IMEP in a truck.  Since IMEP correlates highly with the air/fuel ratio (or equivalence ratio φ), the data suggest that EC/OC partitioning is driven by the pyrolysis that occurs in engines under load.  
Very few weight/displacement pairings are greater than 3,300 kg/L.  The following graph depicts the cumulative frequency distribution (CFD) of simulated weight/displacement ratios in PERE-HD.

For a 12 L engine, 3,000 kg/L would correspond to a running weight of 39600 kg (87,302 lb).  Such vehicle loadings are infrequent, as they exceed Federal and state limits for vehicle weights on highways.  The graph below presents the cumulative distribution of simulated weights, based on the VIUS microdata.  Furthermore, the graph presents cumulative frequency distributions for several broad weight categories reported by Ahanotu (1999) for trucks in the Atlanta metropolitan area.  Note that in the graph, the highest weight category reported by Ahanotu (1999) is represented as 100%, although the actual maxima of observed trucks are unknown.

In general, the sensitivity of EC/OM ratios to the weight/displacement ratio suggest that properly capturing the variability in both inputs is key to developing representative inputs for MOVES.

Calculating EC/OC fraction by Operating Mode 
The modeling described in the previous sections has been employed to create second-by-second estimates of EC-TOR and OC-TOR emission factors for use in the MOVES emissionRateByAge table.  The next step of consists of appropriately binning the outputs to fit the MOVES operating-mode structure.  EC and nonECPM emission rates, , are the inputs to the MOVES model for PM inventory calculations.  To convert the total PM rates calculated from heavy-duty emissions analysis into EC and nonECPM rates, we must calculate EC and nonECPM fractions by operating modes.  Then, the total PM rate can be multiplied by the EC and nonECPM fractions to obtain EC and NonECPM input emission rates. 
PM emissions contain additional inorganic species. However, the total carbon (TC =EC + OC) composes almost all the PM2.5 emissions from conventional diesel emissions. As such, we use the EC/TC as a surrogate for the EC/PM emissions in MOVES. 

One of PERE's outputs for heavy-duty vehicles is the track road-load coefficients.  For each individual weight in the distribution, PERE outputs a set of A/B/C coefficients similar to the ones used to calculate VSP in the HC, CO, and PM emission rate analysis.  We used these coefficients and weights to calculate VSP for each second using the equation below.
                                       
This equation is implemented slightly differently than the one used for analysis of the chassis dynamometer testing for PM, HC, and CO since the road load coefficients (A, B, and C) and weight (or mass) m were specific to each individual vehicle, not general to the regulatory class.  In the PM, HC, and CO equation, the road load coefficients and denominator mass were not specific to the vehicle and the numerator mass was specific to the vehicle.  We felt confident in using vehicle-specific numbers because we performed the analysis using a full representative distribution of weights and displacements.  Also, since we are interested in the EC and nonECPM fractions rather than the actual rates themselves, normalizing by the actual weight provides a more accurate picture.  For example, a large engine operating at 90% of rated power (high VSP) would have a similar EC fraction as a smaller engine operating at 90% of rated power, even though the large engine would likely be hauling a proportionally greater amount of weight.  This is also supported by the previous research and analysis that relates EC fraction to IMEP and not power itself. The large engine would, however, emit a larger EC rate than the smaller engine, but this difference in rates is captured by our PM emission rate analysis.
We separated vehicles into two different regulatory classes based on running weight (we did not have GVWR information).  The weight distribution used in the analysis is shown below.

      Representative distribution of weights used in the EC/OC analysis.
                                       
Based on this weight distribution, we considered all vehicles weighing more than 40,000 lb to be HHD vehicles and all vehicles less than 40,000 to be MHD vehicles.  This was a very simple approach to stratifying by regulatory class.  
As EC and nonECPM rates were also computed for each second during each cycle, we were able to average the EC and nonECPM rates by operating mode.  Then, we calculated the fractions of EC and nonECPM for each operating mode.  For the LHD classes, we used the MHD fractions, and for buses, we used the HHD fractions. 
                                      , 

The resulting EC fractions by operating mode are shown in Figure 2-18 in the main body of this report.

Heavy-duty Gasoline Start Emissions Analysis Figures
Figure F-1.  Cold-Start Emissions (FTP, g)  for Heavy-Duty Gasoline Vehicles,  averaged by Model-year and Age Groups
                                       
Figure F-2.  Cold-Start FTP Emissions for Heavy-Duty Gasoline Vehicles, GEOMETRIC MEANS by Model-year and Age Groups
                                       
Figure F-3.  Cold-start FTP Emissions for Heavy-Duty Gasoline Trucks: LOGARITHMIC STANDARD DEVIATION by Model-year and Age Groups.
Figure F-4.  Cold-Start Emissions for Heavy-Duty Gasoline Trucks:  RECALCULATED ARITHMETIC MEANS by Model-year and Age Groups.
                                       
                                       
                                       
  Table F-1. Emission Standards for Heavy-Duty Spark-Ignition On-road Engines
Regulatory Class
Model Year
                         Emissions Standards (g/hp-hr)

                                      CO
                                      THC
                                     NMHC
                                      NOx
                                  NMHC + NOx
LHD2b3
1990
                                     14.4
                                      1.1
                                       
                                      6.0
                                       

1991-1997
                                     14.4
                                      1.1
                                       
                                      5.0
                                       

1998-2004
                                     14.4
                                      1.1
                                       
                                      4.0
                                       

2005-2007
                                     14.4
                                       
                                       
                                       
                                      1.0

2008+

                                     14.4
                                       
                                     0.14
                                     0.20
                                       
LHD45, MHD
1990
                                     37.1
                                      1.9
                                       
                                      6.0
                                       

1991-1997
                                     37.1
                                      1.9
                                       
                                      5.0
                                       

1998-2004
                                     37.1
                                      1.9
                                       
                                      4.0
                                       

2005-2007
                                     37.1
                                       
                                       
                                       
                                      1.0

2008+
                                     14.4
                                       
                                     0.14
                                     0.20
                                       

Heavy-duty CNG Bus Emissions Supplemental Figures
In our analysis, we found for model year group 1994-2001 that whether or not the bus was equipped with after-treatment technology did not greatly affect its emissions, so we decided to group all the buses together regardless, as shown in the figures below.
Figure G-1. NOx emissions of vehicles with after-treatment versus no after-treatment tested on the CBD cycle.

                                       

Figure G-2. CO emissions of vehicles with after-treatment versus no after-treatment tested on the CBD cycle.

Figure G-3. PM emissions of vehicles with after-treatment versus no after-treatment tested on the CBD cycle.

Figure G-4. THC emissions of vehicles with after-treatment versus no after-treatment tested on the CBD cycle.

 

Figure G-5. CH4 emissions of vehicles with after-treatment versus no after-treatment tested on the CBD cycle.
                                       

Figure G-6. Total energy consumption of vehicles with after-treatment versus no after-treatment tested on the CBD cycle.

 References