Memorandum

From: Edward Glover and Harvey Michaels

Assessment and Standards Division, Office of Transportation and Air Quality

To: Docket EPA-HQ-OAR-2011-0135

Subject: Sulfate, SO2, and OC Updates to MOVES for the Tier 3 NPRM

Date: 26 February 2013

ABSTRACT

This document describes the data and methodology used to develop the Post MOVES2010A 

model sulfate, gaseous SO2 and Organic Carbon (OC) emission factors. The gasoline vehicle 

sulfate emission rates are based on 2004-2005 calendar year vehicle testing done in Kansas City, 

Missouri. The diesel sulfate rates for 1960 through 2006 model year diesel vehicles were taken 

from predecessor model - MOBILE6.2 because no new data were available. However, the 2007 

and later model year, trap equipped vehicles were modeled with new data collected by Southwest 

Research Institute under contract with the Coordinating Research Council (CRC) as part of the 

Phase 1 of the Advanced Collaborative Emissions Study (ACES). These data allowed for 

revised modeling of SO4, SO2 and OC emission rates in MOVES on 2007 and later model year 

diesel vehicles. The gasoline vehicle sulfate rates were obtained from a least squares linear 

regression of the data. 

The data and results of the analysis are shown tabular and graphical format. The gasoline sulfate 

emission rates are 2.004e-07 and 1.4807e-08 grams SO4 / (g fuel * ppm S) for the pre-1981 and 

1981+ model year groups, respectively. The rate is 1.371e-07 grams SO4 / (g fuel * ppm S) for 

pre-2007 diesel vehicles, and 3.143e-06 grams SO4 / (g fuel * ppm S) for the 2007 and later 

model years. 

The corresponding SO2 emission rates are: 2.0e-06 grams SO2 / (g fuel * ppm S) for gasoline 

vehicles, and 1.97e-06 and 1.083e-06 grams SO2 / (g fuel * ppm S) for pre and post 2007 model 

year diesel vehicles. Gaseous SO2 emission rates now represent 54 percent of the total fuel 

sulfur (mass basis) rather than the 98 percent assumption of previous versions of MOVES. 

The Organic Carbon (OC) emission rates for 2007 and later model year diesels were also 

modified and are set equal to 1.61 times the Elemental Carbon (EC) emission rates. This value 

was chosen because it leaves the Total PM2.5 unchanged for a National MOVES run in calendar 

year 2040 using 11 ppm sulfur diesel fuel. Pre-2007 model year diesel particulate rates and 

gasoline rates remain unchanged from previous MOVES versions.

BACKGROUND and INTRODUCTION
Gasoline Vehicles

Sulfate particulate matter (PM) emissions have been estimated by EPA vehicle emission 

factor models since the development of the PART5 model in 1995. In 2002, the PART5 model 

was updated with new methodologies and incorporated into the MOBILE6.2 emission factor 

model (see EPA report EPA420-R-03-001 “MOBILE6.2 Particulate Emission Factor Model 

Technical Description” for details regarding the transition from PART5 to MOBILE6.2). The 

new model changed the calculation methodology by adding a fuel sulfur mass balance to the 

equation. However, the update did not involve a new data collection or analysis effort, nor did it 

substantially change the sulfate PM emission factors. As a result, even the new MOBILE6.2 

model is based almost entirely on data collected prior to 1995, and most of these data consist of 

tests on pre-1990 model year vehicles.

The PART5 / MOBILE6.2 (MOBILE6.2) sulfate emission factors are a function of 

several detailed vehicle parameters. These are catalyst availability, catalyst type, air injection 

availability, average vehicle speed over a cycle and vehicle fuel economy. The calculations 

require three parameters: the basic sulfate emission rates (which depend on speed), the 

technology weighting factors (air injection type, catalyst type, etc.), and the vehicle fuel 

economy values. The basic sulfate emission factors are shown in Table 1. These were taken 

from the PART5 model, and were not updated for MOBILE6.2. The vehicle fleet technology 

weighting factors and the fuel economy values are from MOBILE6. Separate sulfate emission 

factors were developed for two speed bins: 19.6 MPH and 34.8 MPH. Sulfate emission levels at 

intermediate speeds are calculated by linear interpolation between these two speeds.

All of the emission test data used in the MOBILE6.2 sulfate emission factors were 

collected based on an underlying gasoline fuel sulfur level of approximately 340 ppm sulfur 

(0.034 wt%). In order to model other fuel sulfur levels, a simple linear versus fuel sulfur level 

equation was constructed by assuming that a 0 ppm gasoline fuel sulfur level will produce zero 

sulfate emissions (assumes no contribution from the lubricating oil). Although the effect may be 

nonlinear, the linear model was also extrapolated to 1000 ppm fuel sulfur to allow estimates to 

be generated for historical high sulfur fuel. The linear sulfur function was used because no data 

were available to develop any other functional response. 

Diesel Vehicles

No new data were available for 1960 – 2006 model year diesel vehicles so as a result, the 

existing MOBILE6.2 emission rates were carried over into MOVES. For the 2007 and later 

model years, a limited sample of four new, trap equipped vehicles was available for analysis 

from the Coordinating Research Council (CRC) funded test program - Advanced Collaborative 

Emissions Study (ACES). The results from this test program suggested that the current data and 

assumptions regarding sulfate (SO4), gaseous sulfur dioxide emissions (SO2) and organic carbon 

(OC) formation in the presence of traps were incorrect. As a result, the emission rates for these 

particulate constituents were revised, accordingly.
DATA

A new study conducted by EPA and others conducted in Kansas City, Missouri in 

calendar year 2004 forms the basis of the gasoline SO4 and SO2 emission rates. In this study, 

several hundred gasoline vehicles (cars and trucks) were recruited and tested for a range of 

pollutants (HC, CO, NOx, and PM) using several test procedures. A several reports and the 

complete data set are available at the link:

http://www.epa.gov/otaq/emission-factors-research/index.htm

Fuel sulfur measurements and sulfate emission measurements were also performed on a 

subset of the vehicles. It is this limited subset of vehicles on which this analysis of vehicle 

sulfate emissions is based. All of the data are shown in Table 2 entitled “Vehicle Sulfate and 

Fuel Sulfur Data from the Kansas City Test Program”. It is shown at the end of this document.

In the Kansas City test program, 75 vehicles were tested for sulfate emissions, and fuel 

samples from 48 vehicles were tested for fuel sulfur levels. Unfortunately, there were only 

sixteen (16) vehicles which received both the LA92 sulfate exhaust emission test and fuel 

composition sulfur test measurements. Only the vehicles which received both tests were used in 

the analysis. The remaining vehicles which received only the sulfate emission test or the fuel 

sulfur test were used to confirm the results. 

The report entitled “CRC Report: ACES Phase 1 of the Advanced Collaborative 

Emissions Study, June, 2009. Contains describes all of the instrumentation, produces and 

contains the primary data collected during the study. None of this information will be repeated 

in the this document. The interested reader is referred to the original documentation. It can be 

obtained at the following link.

http://www.crcao.org/reports/recentstudies2009/ACES%20Phase%201/ACES%20P

hase1%20Final%20Report%2015JUN2009.pdf

ANALYSIS

1.0 Sulfate Emission Calculation for Gasoline Vehicles

The gasoline vehicle test sample was divided into two strata based on model year. The 

larger sample that consisted of 44 vehicles was the 1981 and later model years. A small subsample of 9 pre-1981 vehicles was also analyzed. This separation was done because of the 

considerable differences in technology between the two strata, and an expected difference in the 

magnitude of the sulfate emission factors. 

Previous research (from PART5 model analysis) suggests significant differences in 

sulfate emissions exist between vehicles with oxidation only catalysts (or no catalyst) and air 
injection systems and the more modern closed loop three-way catalysts that are typical of the 

1981 and later vehicles. The differences likely arise from the different catalytic chemistry that 

occurs in the oxidation-only catalyst versus the three-way catalysts. Also, the presence of excess 

air in the older systems with air injection may allow for greater production of sulfate (SO4) 

particulate versus other forms of gaseous sulfur compounds (i.e., SO2). 

Model year group stratification is required in the MOVES model because specific 

technology stratification by catalyst type (oxidation, three-way, or three-way plus oxidation) and 

supplemental air injection presence is not available. These parameters are not included in 

MOVES model because data on the frequencies of occurrence in the vehicle population of 

specific vehicle technology items are usually difficult to obtain and update in sufficient detail, 

and are mostly irrelevant anyway for modern vehicles. The auto industry has long standardized 

on the closed loop three-way catalyst technology with only limited application of supplemental 

air injection or other similar strategies. The MOVES2006 model also has a limited scope of 

calendar year coverage with a focus on calendar years of 1990 through 2050.

The analysis of the vehicle sulfate data consisted of a least squares linear regression of 

the sulfate emission versus the gasoline fuel sulfur levels. A regression was performed on both 

the pre-1981 model year sample and the 1981 and later sample. The product of the regression 

was a sulfate emission slope versus fuel sulfur level in units of ppm. The regression was forced

through the origin by assuming that sulfate emission will be zero at a gasoline fuel sulfur level of 

zero. 

Both Figures 1 and 2 were taken directly from an EPA contractor (Sierra Research) report 

“Development of Emission Rates for the MOVES Model – March 3, 2010”. These figures are 

based on an updated analysis that Sierra Research performed on the full set of EPA’s Kansas 

City Study data. The Original analysis done by EPA included only a sample of the full dataset 

and the individual points are labeled “Original” with solid square points in Figures 1 and 2. The 

additional data points are labeled “New Data” with ‘X’ points, and the regression analysis is 

based on the full data sample. 

A regression was performed to determine the slope of the equation:

SO4 (g/mi) = slope × fuel S (ppm) (forcing zero intercept)
Figure 1 

Exhaust SO4 vs. Fuel S – 1981 and Newer

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0 100 200 300 400 500

Fuel S (ppm)

Exhaust SO4 (g/mi)

Original

New Data

Linear (Original)

Linear (New Data)

The newly developed combined slope was slightly more than half of that developed with 

the original limited sample. This Updated slope was used subsequently in the analysis; the 

Original slope was not used.

Original 0.000002952

Update 0.000001597 grams/mile SO4 / ppm fuel sulfur

Also, only four of the more modern vehicles had SO4 emissions results above 0.0005 

g/mi, with little response to varying sulfur level in the fuel. The average SO4 emission rate for 

this group of vehicles was 0.000344.
Figure 2

Exhaust SO4 vs. Fuel S – 1980 and Older

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0 50 100 150 200

Fuel S

Exhaust SO 4 - g/mi

Original

New Data

Linear (Original)

Linear (New Data)

The results obtained with 1980 and older vehicles were similar and are displayed in 

Figure 2. The original analysis included only three vehicles. The slope was determined by 

averaging the three Exhaust SO4 measurements and dividing by the average fuel S for those tests. 

In the updated analysis, several additional vehicle tests were found, and a slope was determined 

using linear regression.

Original 0.00002892

Update 0.00001907 grams/mile SO4 / ppm fuel sulfur

The slope developed with the combined data set for older vehicles is more than 10X the 

slope obtained with the 1981 and newer vehicles. This Updated slope was used subsequently in 

the analysis; the Original slope was not used. The same factors were used for ethanol fuel, with 

the assumption that the sulfur level used as an input will be the level measured in the diluted fuel 

plus the ethanol blend used on the road, not just in the blend fuel. Lacking other information, the 

same factors were used for starting, running, and extended idle.

The sulfate emission factors in units of gram/mile / ppm fuel sulfur are transformed into 

MOVES model usnits of grams SO4 / (gram fuel * ppm fuel Sulfur) using Equation 1

grams SO4 / (gram fuel*ppm fuel Sulfur) = SULF * FE / Fuel Density Eq 1
Where,

SULF is the sulfate emission factor in grams/mile SO4 / ppmS.

1981+ 0.000001597 grams/mile SO4 / ppm fuel sulfur

Pre-1981 0.00001907 grams/mile SO4 / ppm fuel sulfur

FE (fuel economy) is 13.97 miles/gallon for Pre-1981 model years and 19.31 miles/gallon for 

1981+ model years. These were the mean fuel economy values for the vehicle samples in the 

test program. It reflects a mixture of cars and light trucks.

Fuel Density is 2819 grams fuel / gallon fuel for gasoline. This value is MOVES default 

gasoline density.

Use of Equation 1 produces the gasoline vehicle sulfate emission factors which are found 

in the MOVES database.

1981+ MY 1.597-06 * 19.31 / 2819 = 1.094e-08 gSO4/(gfuel-ppmS)

Pre-1981 1.907-05 * 13.97 / 2819 = 9.457e-08 gSO4/(gfuel-ppmS)
2.0 Theoretical Maximum Sulfate Emission Rate for Gasoline Vehicles

The theoretical maximum sulfate emission rate as calculated in EPA’s PART5 model is 

used as a first step is estimating the sulfur dioxide (SO2) emission factor. This method is used 

because gaseous sulfur dioxide (SO2) emissions were not measured as part of the EPA Kansas 

City test program. These equations are based on a mass balance of fuel sulfur (i.e., all the sulfur 

contained in the fuel is exhausted as either sulfate (SO4) or SO2.), and excludes lube oil 

contributions which were not measured.

The Sulfate Equation is shown in Equation 2.

DSulf = 13.6078 * (1.0 + Water) * FDNSTY * SWGHTD * DCNVRT / FE Eq 2

Where

Dsulf g/mi Sulfate emission factor

DCNVRT fraction fuel sulfur converted to Sulfate

FDNSTY 2857 g/gallon fuel density

FE miles/gal average fuel economy

SWGHTD 0.0344 fuel sulfur concentration (parts per hundred) or 344 ppm. 

A typical fuel sulfur concentration prior to sulfur control.

WATER 1.2857 The weight ratio of seven water molecules to sulfate 

(7*18/ 98 = 1.2857)

Constant 13.6078 Unit conversion factor (453.592 * 3)/100. Where 3 is the 

weight ratio of SO4 to sulfur. 453.592 grams per pound. A 

value of 100 is to correct for the weight percent of sulfur in 

SWGHTD.

For more information, please see reference (EPA-AA-AQAB-94-2) for more details on 

the PART5 and MOBILE6.2 vehicle emission data and the development of the equations. 

Substituting the variables into Equation 2 and setting DCNVRT equal to 1.00 to simulate 

100 percent conversion of all fuel sulfur to SO4 produces a value of 0.3444 g/mi SO4 as a 

theoretical maximum SO4 (MAX(SO4)) value for the 1981 and later model years. A value of 

0.476 g/mi is obtained as the theoretical maximum for the 1980 and earlier model years. These 

values are completely theoretical because in practice less than two percent of the fuel sulfur is 

converted to SO4 particulate in a gasoline vehicle. They are used as a basis for determining 

sulfur to SO4 conversion as represented by the sulfate emission factors produced by Equation 1.

0.344 g/mi = 13.6078 * (1+1.2857) * (2819/453.593) * 0.0344 * 1 /19.31 1981+ MY

0.476 g/mi = 13.6078 * (1+1.2857) * (2819/453.593) * 0.0344 * 1 /13.97 1980- MY
The actual conversion of fuel sulfur into SO4 based on the MOVES sulfate emission rates 

is computed by dividing the MOVES rate by the theoretical maximum values.

SO4 Conversion = SULF * SWGHTD (in ppm) / MAX(SO4) Eq 3

1981+ MY SO4 Conversion = 1.597e-06 * 344 / 0.344 = 0.1595 %

1980- MY SO4 Conversion = 1.907e-05 * 344 / 0.476 = 1.378 %

3.0 Gaseous Sulfur Dioxide Emission Calculation for Gasoline Vehicles

The SO4 conversion percentage is used to calculate the SO2 conversion percentage using 

the simple formula.

SO4 conversion + SO2 conversion = 1.0 Eq 4

1981+ MY SO2 Conversion = 99.85 %

1980- MY SO2 Conversion = 98.62 %

The values for SO2 conversion are used in the calculation of gaseous SO2 emissions. 

This is done using Equation 5a. The following algebraic steps are used in the transformation.

SO2 = 9.072 * FDNSTY * SWGHTD * DCNVRTSO2 / FE Eq 5a

SO2 * FE = 9.072 * FDNSTY * SWGHTD * DCNVRTSO2 Eq 5b

SO2 = Constant * FDNSTY * (SO2 Conversion) / FDNSTY* 453.592 * (1,000,000 / 100)

1.9968e-06 = 9.072 * 6.982 * 0.9984 / (6.982*453.592*10000) 1981+ MY

1.9725e-06 = 9.072 * 6.982 * 0.9862 / (6.982*453.592*10000) 1980 - MY

Where SO2 EF is the gaseous SO2 emission factor in units (g/mileSO2 / (g-fuel * ppm S)

4.0 Sulfate Emission Calculation for Diesel Vehicles

The sulfate emission rates for diesel vehicles as subject to the same theoretical equations 

as those used for gasoline vehicles. In case of diesel vehicles there were no data available on 

pre-2006 model year vehicles so the theoretical equations and an assumption of low sulfate 

conversion were used. However, some limited data from the CRC ACES test program on 2007 

and later trap equipped vehicles were available (four vehicles and multiple tests), and these were 

used to generate an alternative fuel sulfur to sulfate conversion for the new technology. 
Diesel Sulfate from 2006 and Earlier Vehicles

DSulf = 13.6078 * (1.0 + Water) * FDNSTY * SWGHTD * DCNVRT / FE Eq 6

Dsulf g/mi Sulfate emission factor

DCNVRT 0.02 fraction fuel sulfur converted to Sulfate

FDNSTY 6.982 lb/gallon fuel density

FE miles/gal average fuel economy

SWGHTD 0.0500 fuel sulfur concentration (parts per hundred) or 500 ppm. 

A typical fuel sulfur concentration prior to sulfur control.

WATER 1.2857 The weight ratio of seven water molecules to sulfate 

(7*18/ 98 = 1.2857)

Constant 13.6078 Unit conversion factor (453.592 * 3)/100. Where 3 is the 

weight ratio of SO4 to sulfur. 453.592 grams per pound. A 

value of 100 is to correct for the weight percent of sulfur in 

SWGHTD.

Dsulf * FE * (1gal/6.982 lbfuel) * (1 lbfuel/453.592 gfuel) = XConstant * SWGTD / (6.982 lb * 453.592 g)

Where 

XConstant = 13.6078*(1+Water)*FDNSTY*DCNVRT = 4.3433

Msulfate = XConstant / FDNSTY * 453.592*(1000000/100)

Msulfate = 1.37142E-07 g SO4 / gfuel- ppmS

The variable Msulfate is the MOVES model sulfate emission factor for 2006 and earlier 

diesel vehicles. It is in units of grams of SO4 particulate per gram fuel and per ppm fuel sulfur. 

It is based the PART5 assumption of a 2 percent conversion of fuel sulfur to SO4 particulate.

Diesel Sulfate from 2007 and Later Vehicles

The strict EPA particulate standards, as promulgated for the 2007 and later model year 

diesel vehicles, has forced the introduction of trap equipped vehicles in the in-use fleet. Recent 

testing by CRC ACES has strongly suggested that vehicles equipped with trap systems have 

much higher conversions of fuel sulfur to sulfate particulate than previous technology. The data 

also suggests that sulfate particulate in some cases may comprise the majority of total particulate 

of less than 2.5 microns.
An analysis is the available ACES data suggests a SO4 conversion of 45.84 percent 

should be used on trap equipped vehicles rather than a 2 percent conversion. Substituting this 

higher SO4 conversion into Equation 6 yields a MOVES diesel sulfate factor of:

Msulfate = 3.1433e-06 g SO4 / gfuel- ppmS

This factor was used for all 2007 model year diesel vehicles even though in the fleet 

some of these vehicles may not be trap equipped due to banking and trading credits, light-duty 

applications or other factors. MOVES does not contain phase-in fractions for such technology 

and other factors.

5.0 Sulfur Dioxide Emission Calculation for Diesel Vehicles

Diesel Sulfur Dioxide from 2006 and Earlier Vehicles

The calculation of the SO2 emission factors for diesel vehicles uses the same equation as 

used for gasoline vehicles. It is repeated as Equation 7. For the 2006 and earlier vehicles the 

conversion from fuel sulfur to gaseous sulfur dioxide is assumed to be 98 percent.

SO2 = 9.072 * FDNSTY * SWGHTD * (DCNVRT SO2) / FE Eq 7

SO2 g/mi SO2 emission factor

DCNVRT SO2 0.98 fraction fraction fuel sulfur converted to SO2

FDNSTY 6.982 lbs/gallon fuel density

FE miles/gal average fuel economy

SWGHTD parts per hundred fuel sulfur concentration

WATER 1.2857 (7*18 / 98)

Constant 9.072 (453.592*2)/100

SO2 * FE * (1gal/6.982 lbfuel) * (1 lbfuel/453.592 gfuel) = 62.07389 * SWGHTD / (6.982 lb * 453.592g)

MOVES SO2 = 62.07389 / 6.982*453.592*(1000000/100)

MOVES SO2 = 1.96003E-06 g SO2 / gfuel- ppmS
Diesel Sulfur Dioxide from 2007 and Later Vehicles

The calculation of the SO2 emission factors for diesel vehicles uses Equation 7. The only 

difference for the 2007 and later vehicles the conversion from fuel sulfur to gaseous sulfur 

dioxide which is 54.16 percent (i.e., unity minus the SO2 conversion). Given this conversion 

percentage the MOVES SO2 factor is:

MOVES SO2 = 1.0832E-06 g SO2 / gfuel- ppmS

6.0 Organic Carbon Particulate Emission Factors from Trap Equipped Vehicles

New Organic Carbon (OC) particulate emission factors for the 2007 and later model year 

diesel vehicles were developed in conjunction with the new sulfate emission factors. These new 

OC emission factors were developed because the new CRC ACES data suggests a much different 

split between the three principal constituents of total particulate at 2.5 microns (PM2.5) than the 

split MOVES currently uses.

In MOVES total PM2.5 is the sum of organic carbon (OC), elemental carbon (EC) and 

sulfate. Sulfur dioxide is not considered a particulate. This relationship is shown 

mathematically in Equation 8.

Total PM2.5 = OC + EC + Sulfate Eq 8

The development of the PREVIOUS MOVES particulate emission rate consisted of an 

analysis of real time total PM2.5 data to develop total PM2.5 emission rates. These were then 

apportioned into EC and OC using data from other test programs. The apportionment was done 

on a regulatory class and operating mode basis. Although present in the Total PM2.5 totals, and 

potentially double counted in the MOVES model, the sulfate emissions were unknown and 

assumed to be negligible because of the assumption of a very low (<2 percent) conversion based 

on non trap equipped vehicles, and a very low fuel sulfur level (i.e., < 15 ppm sulfur). Based on 

the CRC ACES study, this assumption was not correct – even at low fuel sulfur levels. In fact, 

the study strongly suggests that sulfate comprises anywhere from 30 to 60 percent of the total 

PM2.5 emissions, depending on the fuel sulfur level. Thus, it was determined that the 

distribution of Total PM2.5 emissions in terms of EC, OC and sulfate were incorrect in the 

MOVES model as of September, 2010.

Given the new heavy-duty diesel test data, it was decided for MOVES model 

development that at a diesel fuel sulfur level of 11 ppm, the Total PM2.5 emission level from 

2007 and later model year vehicles would remain the same, EC emission rates would remain the 

same and that OC emissions would be reduced at the same rate as sulfate emissions are 

increased. At higher levels of diesel fuel sulfur (i.e., 15 ppm sulfur regulation limit) the Total 

PM2.5 will increase as a result of this change to the MOVES model. At lower fuel sulfur levels 
the Total PM2.5 will be lower. The value of 11 ppm sulfur was chosen because it is currently 

the default diesel fuel sulfur level, and it is likely close to the actual fuel sulfur level used during 

vehicle certification. As a background reference, the existing MOVES 2007+ model year Total 

PM2.5 emission results were derived from an analysis of heavy-duty certification test results and 

data from in-use 1996-2006 model year diesel vehicles. Mathematically, the relationship

between Total PM2.5 and its constituents is shown in Equation 9.

Total PM2.5 = SO4 + EC + EC * OC factor Eq 9

The OC factor was computed using a standardized National and Yearly Aggregated 

MOVES run for all diesel processes (i.e., running, start and extended idle), source types and road

types. See the associated spreadsheet “DevelopmentOfTheOCFactorNational data.xls” for 

details. The value of the OC factor was computed to be 1.61.

The default MOVES organic carbon emission rates (pollutantID = 111) were computed 

for the 2007 and later model year (all regclasses – light-duty, light heavy, medium heavy, heavyheavy and buses) using Equation 10.

OC(g/hr) = 1.61 * EC (g/hr) Eq 10

Table 1 shows the relative contribution of each particulate constituent before and after the 

change to the MOVES model. The change to MOVES gives better agreement with the 

experimental data in terms of sulfate emissions, but still shows differences between the two in 

terms of OC and EC emission levels. The emission rates of metals are not currently accounted 

for in MOVES, but will be included in future updates.

Table 1

Relative Contribution of Each Particulate Constituent in MOVES

For 2007 and Later Diesel Vehicles

Particulate Constituent Old MOVES Revised MOVES ACES Study Results

Organic Carbon 88.2 % 50.5 % 32.97 %

Elemental Carbon 8.4 % 4.8 % 12.28 %

Sulfate 3.4 % 44.7% 50.68 %

Metals 4.07 %
7.0 References

1. EPA Kansas City Vehicle Testing Program in 2004-2005 Report

2. EPA-AA-AQAB-94-2, “Draft User’s Guide to Part5: A Program for Calculating Particle 

Emissions from Motor Vehicles”, February, 1995. 

3. EPA report EPA420-R-03-001 “ MOBILE6.2 Particulate Emission Factor Model 

Technical Description”, January, 2003.

4. Heywood, John B. “Internal Combustion Engine Fundamentals”, 1988, page 915

5. “Coordinating Research Council (CRC) Report: ACES Phase 1 of the Advanced 

Collaborative Emissions Study, June, 2009.