EPA-AA-TSS-PA-8 7-4
Technical Report
Guidance on Estimating Motor
Vehicle Emission Reductions From the
Use of Alternative Fuels
and Fuel Blends
January 29, 1988
Emission Control Technology Division
Office of Mobile Sources
Office of Air and Radiation
U. S. Environmental Protection Agency
2565 Plymouth Road
Ann Arbor, MI 48105
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EPA-AA-TSS-PA-87-4
Technical Report
Guidance on Estimating Motor
Vehicle Emission Reductions From the
Use of Alternative Fuels
and Fuel Blends
January 29, 1988
Emission Control Technology Division
Office of Mobile Sources
Office of Air and Radiation
U. S. Environmental Protection Agency
2565 Plymouth Road
Ann Arbor, MI 48105
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Table of Contents
Section Title
1.0 INTRODUCTION 1
1.1 Purpose 1
1.2 Alternative Fuels Addressed 2
1.3 Usage Scenarios Addressed; Tracking 2
1.4 Organization 6
2.0 BACKGROUND ON SIP INVENTORIES FOR MOTOR 7
VEHICLE EMISSIONS
3.0 PER-VEHICLE EMISSION REDUCTIONS WITH 10
ALTERNATIVE FUELS
3.1 Oxygenated Gasoline Blends 10
3.1.1 10% Ethanol blends (3.7% Oxygen) 10
3.1.1.1 Exhaust HC, CO and NOx Emissions 10
3.1.1.2 Evaporative HC Emissions 12
3.1.2 Methanol Blends with 3.7% Oxygen 14
3.1.2.1 Exhaust HC, CO and NOx Emissions 15
3.1.2.2 Evaporative HC Emissions 15
3.1.3 11% MTBE Blends (2% Oxygen) 16
3.1.3.1 Exhaust HC, CO and NOx Emissions 16
3.1.3.2 Evaporative HC Emissions 17
3.1.4 Simultaneous Marketing of Ethanol, Methanol 17
and MTBE Blends
3.2 Fuels Requiring Special Vehicles 18
3.2.1 Compressed Natural Gas (CNG) Vehicles 18
3.2.2 Methanol Fueled Vehicles (FFVs, M85, 20
Mioo, etc.)
3.2.2.1 City-Specific Ozone Reduction Determinations 21
3.2.2.2 Default Ozone Reduction Estimates for 22
Vehicles Just Meeting the EPA Standards
for Methanol Vehicles
3.2.2.3 Default Ozone Reduction Estimates for 24
Vehicles With Emissions Well Below
the EPA Standards
3.2.2.4 Default Ozone Reduction Estimates for 25
Vehicles with Intermediate Emission Levels
4.0 CALCULATION OF FLEET EFFECTS 27
4.1 General Approach and Model Year-Specific 27
Adjustment Factor
4.2 Partial Penetration by One Blend or 29
Vehicle Type
4.3 Simultaneous Marketing of MTBE, Ethanol, 30
and/or Methanol Blends
4.4 Blends and CNG, FFV, M85 and/or MIOO in Same 30
Model Year
5.0 OBTAINING SPECIAL MOBILES OUTPUT 31
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Table of Contents (continued)
List of References
Tables 3-1 to 3-4
Tables 4-1 to 4-17
Appendix A Formula for Quadratic Interpolation Based
on Blend Market Share
Appendix B Commingling Calculations with Nonoxygenated
Gasoline and Two Blends in the Market
Simultaneously
32
Appendix C
Appendix D
Examples of Calculations
Calculation Procedure Estimating the Effects of
Gasoline/Oxygenate Blends Use on Fleetwide Emissions
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1.0 INTRODUCTION
1.1 Purpose
This document provides methods and assumptions for
estimating the impact of use of alternative fuels and fuel
blends on motor vehicle emissions including HC, CO, and NOx*.
The information is presented in a format which assumes it will
be used by State and local air quality planning agencies in
preparing current and future emissions inventories and emission
reduction strategies during 1988, 1989, and 1990. Such
planning efforts will be necessary in areas which receive calls
from EPA for revisions to their ozone** or CO State
Implementation Plans (SIP) following their failure to attain
(or in a few cases following their failure to provide for
attainment in a prospective sense) the National Ambient Air
Quality Standards (NAAQS) for these pollutants. EPA has
recently proposed requirements applicable to these SIP calls
(52 FR 45044, November 24, 1987), and many affected areas will
need to estimate current and future year motor vehicle
emissions. Use of alternative fuels and fuel blends is likely
to be part of future scenarios that will be examined in many
areas.
Adherence to the methods and assumptions in this document
when preparing SIP revisions will facilitate EPA review and
avoid the need for States to justify those aspects of their
analysis. Differing assumptions and methods, if used, will be
subject to closer and more questioning EPA review. in all
cases, final EPA approval or disapproval of a particular
State's SIP revision occurs only after notice and opportunity
for public comment, including any comments on the methods and
assumptions recommended here.
While not specifically addressed, the information in this
document may be useful for estimating the emissions impact of
smaller scale use of alternative fuels than might be
contemplated in a SIP revision.
* Some studies have suggested that particulate emissions may
also be affected with alternative fuels; when sufficient data
are available in this area, EPA may want to include provisions
for the effect of alternative fuels on particulate emissions.
** Areas receiving ozone SIP calls and considering adoption of
an alternative fuels program should account for its impact on
both hydrocarbon and CO emission inventories, since both are
inputs to the latest model for predicting future ozone
attainment. Directionally, CO emission reductions from
alternative fuels will assist in attaining the ozone NAAQS, but
the strength of this effect has not yet been documented for the
range of local conditions which affect ozone formation.
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The reader is warned that the methods described in this
document have not been cast into the form of a self-contained
computer model or single look-up table. At the present time,
hand calculation and transcription of intermediate results is
necessary. The resourceful planner may be able to automate
these steps, however.
This document is not intended to be an all-inclusive
manual on alternative fuel implementation issues. For
instance, it does not address pump labeling, consumer
education, incentives such as state tax exemptions, or specific
methods to monitor and track actual fuel usage trends.
1.2 Alternative Fuels Addressed
Separate information is provided for the following fuels
or types of fuels. In some cases cross references are made
between fuels to avoid repetition of numerical information that
can apply to more than one fuel.
o 10% ethanol blends (gasohol).
o Methanol blends (including DuPont and Oxinol).
o Methyl Tertiary Butyl Ether (MTBE) blends.
o Retrofit of gasoline vehicles to achieve dual-fuel
gasoline/compressed natural gas (CNG) capability and
new CNG vehicles.
o Newly manufactured vehicles designed for operation
on methanol fuel, such as 85% methanol / 15%
gasoline or 100% methanol. These vehicles can be
designed with different emission levels. The
emission reduction credit given is a function of the
actual emission levels of the vehicles as discussed
later.
1.3 Usage Scenarios Addressed; Tracking
This document addresses only the issue of individual
vehicle effects when operating on an alternative fuel. A
government program on alternative fuels could take a variety of
forms with respect to requiring or encouraging the use of
alternative fuels. A regulatory mandate to require certain
vehicles to use one specific fuel is one approach. The
following are some of the other forms a government program
might take:
o A requirement that all fuel sold for use in gasoline
vehicles have a minimum oxygen content. (Up to a
certain point, increasing oxygen content results in
proportional reductions in tailpipe CO emissions.)
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Depending on the nature of the oxygen content
requirement, ethanol blends (gasohol), methanol
blends, and MTBE blends might all compete and
achieve a market share mix that depends on relative
cost and local consumer attitudes and other
conditions. There are basically two approaches.
First, require a minimum oxygen content for all
fuel, without allowing any trading. Presently, any
such minimum oxygen content requirements that
exceeds 2% would preclude marketing of MTBE blends
in unleaded fuel, since 2% oxygen is the limit of
EPA's "substantially similar" regulation. Under
this approach, environmental regulators must be able
to predict with reasonable confidence the future
market share mix in order to calculate the net
effect on emissions since each of these three blends
affects emissions differently. If any gasohol is
sold, the average oxygen content will exceed the
program's minimum requirement, for example.
A second approach would set a minimum average oxygen
level, but allow fuel suppliers to purchase and sell
"oxygen credits." This would permit states to set a
much higher average oxygen content requirement* than
under the first approach, since the market for
oxygen credits eventually will automatically adjust
the mix to achieve the targeted level of emission
reductions yet still permit different blends (and
straight gasoline) to share in the market mix.
(Achieving a 2.5% oxygen average in a program which
only sets a minimum requirement of 2% would require
that 30% of consumers voluntarily select gasohol
over MTBE. Such a large market share now exists in
a few markets with sizable state tax exemptions.)
Fuel blenders could satisfy the 2.5% average oxygen
requirement by a combination of MTBE and by
purchasing oxygen credits to make up the difference
between MTBE's 2% oxygen content and the 2.5%
requirement. Those credits would be supplied by
alcohol fuel blenders, whose 3.7% oxygen content
earns a surplus against the 2.5% standard. Using
this example, any number of market mixes would
achieve the 2.5% average oxygen content
requirement: for example, MTBE 45%, gasohol 45% and
straight gasoline (oxygen free) 10%. Even a 3%
oxygen content standard could be achieved by a
market mix of MTBE 18%, gasohol 72%, and straight
gasoline 10%.
*Some areas may find it necessary (or desirable) to set higher
oxygen content requirements in order to meet the CO reduction
targets to be established in EPA's non-attainment strategy for
CO and ozone. Alternative CO reduction measures may be much
more costly or non-existent. For instance, a state could
require a 2.5% minimum average oxygen level.
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The second approach is superior to the first from
several perspectives. It allows states to achieve a
greater level of CO reduction, while preserving the
possibility of consumer choice between MTBE and
alcohol blends. At a very high average oxygen
content requirement the possible market shares for
straight gasoline and MTBE blends might be so small
that some fuel distributors and retailers choose not
to carry them due to the disproportionate handling
and overhead costs, if consumers' willingness to pay
is not commensurate. It internalizes the relative
environmental costs and benefits of the various
fuels via the payments by straight gasoline refiners
and by MTBE blenders to alcohol blenders. This
results in a closer correspondence between what
vehicle owners pay to drive and the environmental
and public health damage caused by their driving.
It also provides greater environmental certainty and
eliminates the need for regulators to predict the
market share mix, since the market will result in a
mix which achieves the necessary emission
reductions. States could design their own oxygen
trading system using EPA's lead trading rules as a
model, or they could propose a better system subject
to EPA's approval of it as adequate to enforce the
oxygen level on which emission reduction estimates
are based.
It should be noted that the averaging approach has
some of the advantages mentioned here even when
applied at oxygen levels of 2% or less, for example
it would allow some sales of straight gasoline.
Planners must also be alert to the possibility that
older, higher emitting vehicles may use the lower
oxygen content fuels disproportionately more than
others. If so, the average oxygen content may vary
by model year, affecting the overall emission
reductions adversely.
A requirement that certain types of fleets retrofit
all newly purchased vehicles to operate on
compressed natural gas.
An initially voluntary but by agreement irrevocable
and enforceable commitment by a large fleet to use
an alternative fuel. This might be part of an
emissions trade, offset, or netting agreement, for
example.
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o An incentive program for use of one fuel or a group
of fuels based on differences in State or local fuel
taxes or vehicle sales taxes.
o A promotional program based solely on voluntary
participation.
Predicting how many and which types of vehicles will use
each type of fuel in response to a specific planned government
program is an important step in estimating its effect on motor
vehicle fleet emissions. This document does not attempt to
provide standard assumptions on usage of alternative fuels.
Instead, States must demonstrate a reasonable basis for their
own estimates of fuel use by type. EPA technical staff are
available to discuss such estimates before States invest
heavily in analysis or planning based on them. Purely
promotional programs may be difficult to assess prior to actual
start up.
EPA's policy on post-1987 nonattainment requires affected
areas to both adopt emission reduction measures and to report
periodically to EPA on the status of their implementation
efforts and on the year-to-year changes in their emission
inventory. If this inventory tracking system shows significant
differences between the expected inventory trend and the trend
that actually occurs, EPA will require corrective or offsetting
action by the area as a condition for avoiding federal funding
and/or new source permitting restrictions. States which adopt
an alternative fuels program, and receive EPA approval for
emission reduction estimates based on predicted future usage
levels as a result of that program, will be required to track
and report on actual usage levels. Significant errors in
prediction may require further revision of the SIP.
A final usage issue relates to seasonal requirements or
incentives for alternative fuels and how to predict usage in
the off season when use is not required or subsidized. For
example, an area might require all gasoline-type fuels to
contain a certain minimum level of oxygen only in winter
months, but this may indirectly result in substantially higher
use of oxygenated blends in summer months. Depending on a
number of factors, summer time VOC emissions may be increased
or decreased as a result. Areas adopting winter time
alternative fuels programs should explicitly predict their
effect, if any, on summer time VOC and hence on VOC reduction
targets. This document can be used to estimate summer VOC
effects, but only given an external prediction of fuel use by
type. Each state must demonstrate a reasonable expectation
that its prediction is accurate. EPA may require actual use in
summer to be tracked and reported.
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1.4 Organization
This document is organized as follows.
Section 2.0 provides some background on how motor vehicle
emission inventories are estimated apart from the complications
posed by alternative fuels.
Section 3.0 presents the core technical assumptions about
the effect of each alternative fuel on various types of
vehicles. These assumptions are for the most part not fully
derived or defended in this document, but appropriate
references to other documents are provided.
Section 4.0 explains how these core assumptions can be
used to adjust the output of MOBILES or MOBILE4* to reflect
an alternative fuel usage scenario of interest.
Section 5.0 gives instructions on how to obtain and use a
special version of MOBILES's or MOBILE4's Fortran code so as to
achieve in practice the steps described in principle in Section
4.0.
* MOBILES is a computer model designed to predict fleet
average emissions by calendar year given various inputs that
describe the local fleet make-up and operating conditions.
MOBILE4 will be an updated version of this model and is
expected to be released shortly after this document.
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2.0 BACKGROUND ON SIP INVENTORIES FOR MOTOR VEHICLE EMISSIONS
Except for California areas, EPA requires the motor
vehicle emission inventories in all ozone, CO, and N02 SIP
revisions to be based on the most recent available version of
EPA's mobile source emission factor computer model. The
current version is MOBILES; MOBILE4 is under development and
expected to be released early in 1988, for use in preparing the
SIP revision for which EPA will call in early 1988. MOBILE4
will be updated internally with new information, and will also
allow planners to account for the influence of some factors not
addressed by MOBILES. Externally, MOBILE4 will resemble
MOBILES and will be used in the same manner by planners. The
discussion that follows will refer mostly to MOBILES, but will
apply to MOBILE4 also.
The function of MOBILES is to provide estimates of the
average emission levels of in-use motor vehicles, expressed in
grams per mile. The normal output provides average levels for
each of HC (either total or non-methane at the user's
direction), CO, and NOx for each vehicle type and for all
vehicle types averaged together. The following vehicle types
are used.:
o light-duty gasoline vehicles (LDGV)
o light-duty gasoline trucks below 6000 GVWR (LDGT1)
o light-duty gasoline trucks between 6000 and 8500
GVWR (LDGT2)
o light-duty diesel vehicles (LDDV)
o light-duty diesel trucks below 8500 GVWR (LDDT)
o heavy-duty gasoline vehicles (HDGV)
o heavy-duty diesel vehicles (HDDV)
o motorcycles (MC)
A planner typically wishes to estimate motor vehicle
emissions of a given pollutant for a certain city, an
individual roadway, or a collection of similar roadway segments
for a year, a day, or an hour. He or she would do this by
making or obtaining an estimate of the number of vehicle miles
traveled (VMT) in the geographic area and time period of
interest and multiplying it by the gram per mile "emission
factor" produced by MOBILES.
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To allow the planner to get an "emission factor" that is
representative of the geographic area and time period under
investigation, MOBILE3 allows the user to specify a number of
input parameters to reflect local conditions. The more
important of these factors are the following:
o whether the area is at low or high altitude
o the VMT split by vehicle type
o for each vehicle type, the age mix of vehicle
registrations
o for each vehicle type, the mileage accumulation rate
by age of vehicle
o ambient temperature
o average speed of the traffic in the area
o the mix of cold versus warmed up vehicles
o the features of any periodic vehicle inspection
program operating in the area of interest
o local tampering and misfueling rates
o the calendar year of interest
The last item is very important since it determines the
mix of vehicles designed to different emission standards and
their age, and therefore deterioration.
For every input parameter except calendar year, MOBILES
(or its user's manual) provides a default value for users not
wishing or able to use local conditions. The defaults
generally represent summer time nationwide urban conditions.
The influence of some input parameters is very strong, and
the overall emission factor output can vary by a factor of 3 or
4 or more by setting some inputs to extreme but still realistic
values. Speed, temperature, and cold/warm mix are particularly
influential. These inputs can affect the relative contribution
of different vehicle types and vintage to the overall emission
factor outputs, as well as its absolute level.
The default inputs to MOBILES are also the conditions of
the official Federal Test Procedure (FTP) for vehicle
emissions, which is used for regulatory purposes. The FTP
conditions are also used in nearly all research projects
involving vehicle emissions and factors that affect them. In
particular, virtually all reliable data on the emissions
effects of alternative fuels has been collected under these FTP
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conditions. An important issue in assessing the impact of
alternative fuels for SIP purposes is to provide a way to
bridge between test data collected under "default" FTP
conditions and the "local" conditions facing individual SIP
planners. This issue is addressed by the method presented in
subsequent sections. Basically, the bridging assumption is
that a percentage change observed during testing under FTP
conditions can be applied to emissions under non-FTP local
conditions, even if the base emission levels on ordinary fuel
are quite different under the two sets of conditions.
This document does not address how local inputs for
MOBILES should be estimated, or methods for estimating VMT in a
particular area and time period. EPA Regional Offices should
be contacted for guidance in these areas.
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3.0 PER-VEHICLE EMISSION REDUCTIONS WITH ALTERNATIVE FUELS
3.1 Oxygenated Gasoline Blends
3.1.1 10% Ethanol Blends (3.7% Oxygen)
Much of the information in Section 3 is summarized from
recent EPA reports on the effects of fuel volatility on vehicle
emissions.[1,2] Much of the information also comes from
analyses and test programs run by the Colorado Department of
Health for exhaust emissions of vehicles at high altitude
[3,4,5,6,7] and from statistical analyses of low altitude data
performed by the EPA Office of Mobile
Sources.[8,9,10,11,12,13] Much of the information in this
section for ethanol blends is applicable to methanol blends
and, to a lesser extent, MTBE blends both of which are
discussed in later Sections (3.1.2 and 3.1.3).
3.1.1.1 Exhaust HC, CO and NOx Emissions
The use of an oxygenated fuel blend such as gasoline with
10% ethanol (gasohol) results in an enleanment (i.e., more
oxygen for fuel combustion) due to the oxygen contained in the
blend itself. Fuel metering devices on vehicles such as
carburetors or fuel injectors (without an oxygen sensor or with
an oxygen sensor but operating in the "open loop" mode where
the sensor is not functional) usually meter fuel and air
volumetrically. Thus, the oxygen in the fuel results in less
fuel and more total oxygen reaching the engine for fuel
combustion since the amount of air is not diminished. If the
initial mixture when using gasoline is rich of stoichiometric,
this enleanment results in reduced exhaust HC and CO but causes
an increase in vehicle nitrogen oxide (NOx) emissions.
A closed-loop vehicle with an operating oxygen sensor in
control of the engine will try to compensate for the oxygen
present in the fuel by increasing the fuel flow until
stoichiometry is achieved. If its fuel system has the
necessary range of control authority, such a vehicle
experiences little or no enleanment due to the blend for those
portions of vehicle operation when the oxygen sensor is
functioning -and in control of the engine. Thus, one expects a
smaller absolute reduction in exhaust HC and CO emissions from
vehicles with oxygen sensors (generally 1981 and later model
years) than earlier model year vehicles and perhaps a smaller
proportional (percentage) reduction as well. It should be
noted, however, that a closed-loop vehicle produces most of its
CO during its occasional open-loop modes of operation.
HC and CO emissions are generally greater for vehicles at
high altitude since a given volume of air at high altitude has
lower density and less oxygen. Open-loop vehicles operate
richer more often and to a greater degree than they would at
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low altitude which results in greater grams per mile
emissions. The same holds for closed-loop vehicles during
their open-loop modes unless there is some compensation for
altitude in open-loop modes. One issue EPA has had to address
is how these differences in operation between altitudes affects
the reductions — both absolute and relative — that will occur
with use of oxygenated blends.
Various organizations have done extensive tests under low
altitude conditions on oxygenated blends providing a large but
somewhat disjointed data base that can be used to quantify the
effects of these blends on emissions. Only the Colorado
Department of Health has conducted and published data from
exhaust emission tests on numerous vehicles at high altitude.
EPA has reviewed the available data and performed several
statistical analyses to better quantify these emission
effects. A companion report[25] to this document will provide
more details on these analyses. An analysis of emission tests
of a group of vehicles tested with ethanol and methanol
gasoline blends shows similar results for both fuels when the
results are adjusted for RVP differences using the extensive
emission data base obtained by EPA. This suggests that the
most important factor is fuel oxygen content rather than the
type of alcohol. Accordingly, EPA has pooled exhaust emission
data from different types of oxygenated blends, using percent
oxygen content and RVP as the only important variables
influencing exhaust emission reductions.
Table 3-1 lists EPA's conclusions on the exhaust emission
changes with oxygenated blends for fuels with 3.7% oxygen
(gasohol or methanol blends) and 2% oxygen (an 11% MTBE
blend). Analysis of the separate low and high altitude data
bases indicates essentially the same effects of blends on a
percent basis, as shown in the table. HC and CO reductions on
an absolute basis are generally higher at high altitude. Both
CO and exhaust volatile organic compounds (VOC) decrease while
NOx increases. VOC, in effect, are the non-methane
hydrocarbons with adjustments made to account for the mix of
true hydrocarbons, alcohols, and aldehydes that is expected
with each blend. Because vehicle exhaust emissions with
oxygenated fuels -are still primarily true hydrocarbons, the
adjustment is small. Specifically, EPA assumes that the
effects of slightly increased alcohol and aldehyde emissions
balance each other.
One important point to note is that some, but not all,
newer closed-loop vehicles are equipped with "adaptive
learning." Properly functioning vehicles with adaptive
learning continuously adjust their open-loop fuel calibrations
based on the most recent period of closed-loop operation.
Thus, they can in theory compensate at least partially for
fuel-caused enleanment even when the oxygen sensor is not in
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control, such as during cold starts and heavy accelerations.
They may also not run as rich in failure modes as simpler
closed-loop vehicles. These vehicles have been expected by
some to have lower exhaust CO (and HC) reductions from
oxygenated blends than earlier closed-loop vehicles. These
lower reductions expected for the adaptive learning vehicles
are not reflected in the test data available. Thus, for the
purposes of this report, the same emission reduction is applied
to all closed-loop vehicles regardless of model year. The
emission reduction is based on the available emission data.
Also, increases in RVP from ASTM type levels (e.g., 11.5
psi in a moderate summer condition), as can occur with ethanol
blends that have not been adjusted to meet ASTM volatility
specifications, cause an increase in exhaust emissions. For
example, an increase in RVP of 1 psi results in carbon monoxide
increases of about 3.1% for pre-1981 vehicles and about 7.6%
for 1981 and newer vehicles for 75° ambient temperatures.
Also, a 1 psi RVP increase results in exhaust hydrocarbon
increases of about 1.8% from pre-1981 vehicles and 3.7% from
1981 and newer vehicles for 75° ambient temperatures. For
temperatures of 50° or below, RVP correction factors are
currently assumed to be zero. For temperatures between 50° and
75°, the percentage factor should be linearly interpolated.
The adjustments for 75° are reflected in the "+0.76 psi"
columns of Table 3-1 which give the emission changes with a
higher RVP ethanol blends; these numbers reflect an average
increase in volatility for ethanol blends of 0.76 psi. It
should be noted that EPA will continue to review emission data
at different temperatures and RVP and will develop updated
factors as needed.
3.1.1.2 Evaporative HC Emissions
Evaporative emissions consist of hot soak and diurnal
emissions. Hot soak emissions occur during the period
immediately following engine shut-down (i.e., at the end of
each vehicle trip). These losses will originate from both the
fuel metering system and from the fuel tank. These emissions
are greater for carbureted vehicles than for vehicles with fuel
injection. Diurnal emissions consist of hydrocarbons both
evaporated and displaced -from the vehicle's fuel tank as the
vehicle tracks the diurnal swing in ambient temperatures. Each
day, as the fuel in the tank and the vapor above the fuel heat
up, more of the liquid fuel evaporates and the vapor itself
expands, with both phenomena causing hydrocarbons to be
released into the atmosphere.
MOBILES outputs a single evaporative emission rate in
grams per mile by assuming that each vehicle makes 3.05 daily
trips totalling 31.1 miles per day, so that there ,are 3.05
incidences of hot soak emissions for every diurnal emission.
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However, in reality, the relative number of hot soak and
diurnal emissions vary with vehicle age since older vehicles
are used for fewer daily trips (and also fewer miles but not in
exact proportion) than newer vehicles. MOBILE4 will account
for these differences. Also, local areas may in MOBILE4 be
able to specify local factors. To account for this accurately
in assessing alternative fuels (which affect hot soak and
diurnal emissions differently) would be very difficult with
MOBILES and perhaps also in MOBILE4, and is beyond this
document. This document uses the fixed weighting from MOBILES
for all age vehicles.
Fuel volatility varies by season and from one part of the
country to another. For example, in most areas of the country,
the recommended ASTM RVP level during the summer months is
generally 11.5 psi, although some areas have lower ASTM RVP
limits but higher temperatures and/or higher altitude. MOBILE4
will explicitly account for any combination of fuel RVP and
ambient temperatures in calculating emissions on non-oxygenated
fuel. This report gives data on evaporative emissions with
both low and high volatility fuel, of 9 and 11.5 psi RVP
respectively. The correct case to use should be selected
carefully. For the purposes of this report, the percent
reduction values given under the 11.5 psi RVP headings should
be used whenever local RVP is about egual to the local ASTM
limit, i.e., nearly everywhere at present. The 9.0 psi RVP
values are provided because EPA has proposed a new limit of 9.0
psi that will apply in areas now having an 11.5 psi ASTM limit
for some years for which state and local planners will wish to
estimate blend effects. These two cases are evaluated
separately because evaporative emissions are a non-linear
function of RVP. Thus, the percentage reduction effects of
oxygenated fuels at one RVP level could not be easily evaluated
based on the effects at the other level.
Test data indicate that evaporative emissions from an
ethanol blend consist mostly of gasoline vapor with a small
amount of ethanol, roughly 15% ethanol. It is important to
note that gasohol of egual RVP to the gasoline it displaces is
assumed to result in equal moles of diurnal emissions; the
lower molecular weight of ethanol (46) versus the typical
evaporative hydrocarbon (64) results in slightly lower mass
emissions. This factor has been accounted for in the tables.
If no adjustments are made to compensate for it, use of
alcohol increases RVP compared to the base gasoline. Since a
blend of 10% ethyl alcohol (ethanol) in gasoline presently is
not subject to ASTM or any federal RVP limits, the final blend
will be about 0.76 psi higher in RVP and can exceed ASTM
levels. However, state or local governments might enforce ASTM
limits for gasohol and EPA may establish the same RVP limit for
gasohol as for gasoline when it finalizes the RVP reduction
proposal mentioned above. The tables contain separate columns
to reflect both cases.
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Addition of ethanol to gasoline also changes the
distillation curve of the fuel and, in particular, increases
the percent evaporated at 160°F. The increase in the 160°
point has been shown to result in an increase in hot soak
evaporative emissions even if the RVP of the gasohol is kept at
the same level as the displaced gasoline.[12]
Another important phenomenon to consider with ethanol
blends is "commingling" which refers to the mixing of
gasoline/alcohol blends with non-oxygenated gasolines in
vehicle fuel tanks whenever consumers switch from one fuel type
to the other when refueling their vehicles at different service
stations. The resultant commingled blend consisting of a
mixture of gasohol and gasoline will have a higher RVP level
than the simple volume weighted average of the gasohol and
gasoline. With 50% market penetration of gasohol and 50%
gasoline, a maximum amount of commingling of the two different
fuel types will occur. Table 3-2 gives these values for
ethanol blends.[30] If the market penetration of an ethanol
blend is other than 50%, a commingling value should be
determined by use of a quadratic equation through the three
points given for 0%, 50%, and 100% market share (see Appendix
A). Very limited data indicate that there may be no
commingling effect when ethanol blends and MTBE blends or
methanol blends are mixed; therefore, this document assumes no
commingling effect for MTBE blends.[27,28] This also means
that Table 3-2 cannot be used for commingling when MTBE and
ethanol blends are both sold along with base gasoline; see
Appendix B for more details.
A final factor has been raised for ethanol blends
concerning the relative contribution of ethanol emissions to
ozone formation compared to hydrocarbons in either exhaust or
evaporative emissions. Some smog chamber data have indicated
that on a mass basis ethanol may be less reactive than the
typical hydrocarbon compounds in exhaust and evaporative
emissions.[22] This lower reactivity in effect has been
incorporated into the evaporative VOC adjustment factors by
ignoring the mass of oxygen in the ethanol. The issue of
relative reactivity of ethanol on a per-carbon atom basis is
much less clear-cut and no further adjustment has been used in
this report. The available data indicate that at low HC/NOx
ratios there may be some reactivity benefit, but at higher
HC/NOx ratios this may not be true.[31]
3.1.2 Methanol Blends with 3.7% Oxygen
To date, two different waivers for methanol blends have
been approved. The first is the ARCO Oxinol waiver for up to
4.75% methanol and 4.75% t-butanol as a cosolvent alcohol.
This mixture has an oxygen content of 3.5%. Variations in the
amount of the two alcohols are permitted as long as the
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methanol to cosolvent ratio is not over one to one (i.e., more
methanol than cosolvent) and the total oxygen content does not
exceed 3.5%. The second waiver is the DuPont waiver for a
maximum of 5% methanol and a minimum of 2.5% cosolvent alcohol
with a maximum total oxygen content of 3.7%. The cosolvent
alcohols can be ethanol, propanols, or butanols. Use of 5%
methanol and 2.5% ethanol results in an oxygen level of 3.7%.
Use of propanols or butanols for cosolvents would result in
lower oxygen levels if only 2.5% cosolvent alcohol were used.
3.1.2.1 Exhaust HC, CO and NOx Emissions
As mentioned before, the exhaust emission effect depends
only on the fuel oxygen level and RVP. Therefore, Table 3-1
also applies to methanol blends. If it is anticipated that
fuels will be blended under waivers such as the DuPont or ARCO
waivers that do not specify a lower limit on oxygen content,
the program should take into account the possibility that
blending could be done at less than the maximum oxygen level
allowed by the EPA waiver. If the expected average oxygen
level is less than 3.7%, the reduction in exhaust HC and CO
emissions and the increase in NOx emissions should be adjusted
linearly from the values in Section 3.1.1.1 and Table 3-1.
As was done with ethanol blends, the potential increase in
exhaust aldehydes has been accounted for by assuming it would
increase exhaust ozone potential to the same degree as the
presence of exhaust alcohol would decrease the ozone
potential. In other words, the net effect of increases in
exhaust aldehydes and exhaust alcohol is assumed to be zero.
3.1.2.2 Evaporative HC Emissions
Table 3-3 contains the evaporative emission effects of
methanol blends, which do not depend on exact oxygen content.
Addition of methanol to a base gasoline generally results
in an increase of 2-3 psi RVP. However, the resultant blend is
subject to ASTM volatility parameters unlike gasohol. Thus,
the volatility of the blend is adjusted (e.g., by prior butane
removal) to decrease the volatility. For the purposes of this
document, it can be assumed that the RVP of a methanol blend
will be the same as that of the gasoline it displaces in the
market place if gasoline in the area is on average about at the
ASTM RVP limit. However, if various fuel surveys (such as the
MVMA or NIPER summer surveys) show that gasoline in that area
is under the ASTM limit (e.g., by about 0.76 psi), then the
numbers in the tables for +0.76 psi RVP for either the 9 or
11.5 psi RVP cases should be used. Larger or smaller RVP
margins can be approximated by linear interpolation or
extrapolation. EPA assumes that methanol blend refiners will
utilize all of the RVP allowed by the ASTM limit, even if for
various reasons refiners of the gasoline now sold in the same
area do not.
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The lower molecular weight of methanol versus gasoline
evaporative hydrocarbons (32 versus 64) reduces the mass of
diurnal evaporative emissions. Evaporative emissions from a
vehicle using a methanol blend consist of about 15% methanol,
so the molecular weight adjustment (for diurnal emissions) has
been applied to this fraction of the evaporative emissions in
Table 3-3 and the subsequent adjustment factor tables.
Methanol, like ethanol, increases the percentage of fuel
evaporated at 160°F. This has also been accounted for in the
values shown in Table 3-3. Molecular differences between
methanol and true hydrocarbons with respect to ozone formation
have also been reflected in the adjustment factor tables, on
the same basis as for methanol fueled vehicles in Section 3.2.2
below.
If the market penetration of a methanol blend is other
than 50% or 100%, a commingling value should be determined by
use of a quadratic equation through the three points given for
0%, 50%, and 100% market share. Based on limited data, it is
assumed that methanol blends have no commingling effects with
either ethanol blends or MTBE blends. Thus, if methanol blends
are sold with ethanol blends and/or MTBE blends, commingling
effects should be calculated as described in Appendix B.
3.1.3 11% MTBE Blends (2% Oxygen)
While EPA has granted a waiver for use of 7% MTBE, EPA
subsequently issued rules permitting use of all alcohol and
ether-type oxygenates other than methanol in gasoline up to a
level corresponding to 2% oxygen, ruling that such levels would
be substantially similar to gasoline.[14] A 2% oxygen level
would permit use of. an 11% MTBE blend, which is therefore the
maximum level presently permitted. A new waiver application
would have to be submitted to EPA and approved for use of
higher MTBE levels.
3.1.3.1 Exhaust HC, CO, and NOx Emissions
It is assumed that the changes in exhaust emissions from
use of 11% MTBE with a 2% oxygen level will be directly
proportional to the amount of oxygen present. Thus, the values
are a linear proportion of the earlier values for ethanol -and
methanol blends in Sections 3.1.1.1 and 3.1.2.1 and are shown
in Table 3-1. The basis for this assumption is as follows.
An 11% MTBE blend has less oxygen and, therefore, less
potential for enleanment of the air/fuel mixture. Among a
large group of vehicles, the actual reductions should logically
show a trend of diminishing returns from higher and higher
oxygen levels as more and more cars are pushed into the lean
region for more of their operation, so that further oxygen has
less or no effect. Most of the existing data on oxygenated
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blends is for fuels in the 3.5% - 3.7% oxygen range, and if a
linear effect is assumed from zero up to 3.7%, it will provide
a conservative estimate of the effect of 2.0% oxygen. Since
the issue is whether a substantially greater than linear
emission reduction occurs at 2.0% oxygen, EPA has reviewed the
data on vehicles tested with both 2.0% and 3.7% oxygen fuels,
and its judgment is that the available data are currently
neither extensive enough, consistent enough, nor dramatic
enough, in showing a clear departure from linearity to risk
overestimating the benefits at this time. Therefore, EPA
assumes a linear relationship between exhaust emissions and
oxygen content in the zero to 3.7% range of fuel oxygen. For a
more detailed discussion of this data and its analysis, refer
to the technical support report that will be released soon
after this document.[25] This issue is being investigated
further in EPA and industry programs designed to obtain more
data with both fuels.
3.1.3.2 Evaporative HC Emissions
Addition of MTBE to gasoline does not result in increased
RVP; in fact, some limited evidence indicates that there may be
a slight decrease in RVP. However, 11% MTBE will increase the
160°F distillation point.[15] This is expected to result in
increased evaporative emissions as mentioned in Section
3.1.1.2.[2] Values for this emission impact are given in Table
3.4.
3.1.4 Simultaneous Marketing of Ethanol, Methanol and MTBE
Blends
The exhaust and evaporative emission impacts of partial
marketing of only a single blend can be calculated easily as
explained above using the appropriate tables. The factor for
commingling included in the tables is relatively
straightforward for a single blend.
However, simultaneous marketing of several different types
of blends with or without gasoline also being sold raises the
possibility of different types of commingling, such as of one
blend with another. However, most of the available data on
commingling effects are for mixtures of individual oxygenate
blends with gasoline with only a small amount of data on
mixtures of ethanol blends with MTBE blends or methanol
blends. Based on the few data points available, it will be
assumed that mixtures of ethanol blends with MTBE blends or
with methanol blends act linearly. In other words, there is no
commingling effect, and emission effects in an all-blends
program can be calculated by doing a simple market share
weighting of the individual blend effects.
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If non-oxygenated gasoline is expected to be sold at the
same time as more than one type of blend, non-linear
commingling effects on the gasoline will occur but a more
complicated calculation is required to account for the absence
of commingling effects among the blends. The required
calculation is described in Appendix B.
3.2 Fuels Repairing Special Vehicles
The following fuels cannot be used in typical current
technology gasoline fueled vehicles without some degree of
mechanical modifications to the vehicles. Therefore, these
fuels would more likely be used initially in fleet applications
(with new vehicles) rather than in area-wide applications with
typical in-use (both old and new) vehicles.
Due to the limited quantity of available emissions data on
these fuels and the fact that the vehicle technologies for use
of these fuels are undergoing rapid advances, the emission
benefits that follow are subject to change as new information
arises. Given the anticipated pace of research and EPA's
desire to provide a stable set of assumptions through the
upcoming cycle of SIP development, review, and approval, it is
unlikely that EPA will revise these benefit estimates downward
by a significant degree prior to completion of this planning
cycle.
3.2.1 Compressed Natural Gas (CNG) Vehicles
Compressed Natural Gas (CNG) consists mainly of methane
with smaller quantities of ethane and propane. Very, limited
data suggest a large fraction (approximately 80%) of the
exhaust consists of methane. Since methane is photochemically
non-reactive except over long periods, a potential exists for
lower urban ozone formation from the exhaust emission
products. Also, the combustion characteristics of CNG (e.g.,
leaner flammability limits, better mixing with the intake air
for combustion) could lead to both lower HC and CO emissions.
The limited data from several different studies on NOx
emissions with CNG are conflicting. While some data indicate
that a decrease of NOx up to 20% might occur, the majority of
the data'indicate an increase (up to 80%) with CNG. Due to the
leaner combustion as well as methane's relatively high flame
temperature, an increase in NOx would be expected.
Most of the work done so far has been on retrofitting
gasoline fueled vehicles to operate on CNG. Limited
consideration has been given to manufacturing new vehicles
designed to operate specifically on CNG. This section
discusses factors affecting the retrofit scenario in some
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detail. The changes in emissions for CNG vehicles given later
though may be applied to either new or retrofitted vehicles.
Very limited data are available on emissions from CNG vehicles,
however, so EPA would consider using different credits if
adequate data are provided to support them. It is likely that
new dedicated CNG vehicles would be able to achieve lower
emission rates than those presented here.
While numerous firms produce and market kits for
converting gasoline vehicles to operate on either gasoline or
CNG, very little reliable data on emissions of converted
vehicles on CNG and gasoline have been obtained. There is some
reason to suspect that some kits, when installed improperly,
may result in increases in emissions when operated on gasoline,
and emissions on CNG which are not significantly lower if at
all. However, if an area were to make CNG conversions a
significant part of its attainment strategy, it would be
appropriate and quite feasible to ensure that only
proven-effective kits are used and that only competent
mechanics install them.
Also, CNG can result in a deterioration of driveability
and a power loss. Fleet operators may re-adjust the vehicles
for richer operation to improve driveability. Thus, it would
be necessary to have a procedure implemented with CNG use
assuring that vehicles remain correctly adjusted. EPA would be
available to give advice in this regard, and may at a later
date even require or recommend specific safeguards and
specifications for large-scale conversion programs if they are
to be part of an approvable SIP.
The following estimates may be used to predict the
emission changes expected when operating vehicles on CNG. The
base for applying the exhaust HC change is the MOBILE3 estimate
of non-methane HC from gasoline-fueled vehicles. Due to lack
of high altitude data, it may be assumed for now that the same
percentage changes apply to both low and high altitude, as has
been found for low level gasoline-oxygenate blends.
HC Exh: -40% (Includes effect of reduced
reactivity due to high methane
fraction)
CO: -50%
NOx: +40% (NOx emissions generally increase
with CNG and this number is an
average of the data range)
HC Evap: -100% (assumes no evaporative emissions)
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EPA will allow areas to assume that, when operating dual fuel
vehicles on gasoline, emissions are not affected by
conversion. Table 4-18 summarizes the multiplicative
adjustment factors corresponding to these reductions.
In any practical conversion program most conversions will
likely be of new or fairly young vehicles, since these are the
types operated by self-fueling fleets and since the economics
of conversion are more favorable as the length of time in
service increases. Although the available data are mostly from
light-duty trucks and vehicles, EPA believes that the above
percentage reductions may be reasonably appropriate for
conversions of recent and future technology gasoline-fueled
passenger cars, light-duty trucks and vans, and heavy-duty
trucks and buses. Furthermore, these percentage reductions are
assumed to apply at all ages.
3.2.2 Methanol Fueled Vehicles (FFV's, M85, M100, etc.)
The use of methanol as an alternative fuel has received
increasing interest in recent months from legislative,
environmental, and automotive groups, as well as the methanol
supply industry. Numerous prototype vehicles, fleet
demonstrations, and legislative proposals have been initiated.
EPA has started a rulemaking to set standards to provide
planning stability for the automakers. The proposed standards
will in effect regulate a weighted sum of hydrocarbons,
methanol, and formaldehyde. The numerical standards for the
weighted sum of "organics" will be equivalent to the existing
hydrocarbon standards for gasoline-fueled vehicles in terms of
the total amount of carbon which can be emitted in the form of
partially burned or unburned fuel. The CO and NOx standards
will be the same as for gasoline-fueled vehicles. These
standards will apply to methanol-fueled vehicles and to
flexible fueled vehicles (FFV's) when running on methanol.[29]
EPA believes that lower emission levels than required by the
proposed standards are possible, and promising technology for
even lower levels is under development.
This section will describe the range of emission effects
expected from use of fuels with high concentrations of methanol
(or possibly ethanol) in vehicles designed or modified to use
such fuels. A SIP mandate for such vehicles could take a
variety of forms as to the type of vehicles required. For
instance, it might state (explicitly or by having no other
provision) that the methanol fueled vehicles that will displace
gasoline fueled vehicles would just meet the proposed EPA
standard for methanol fueled vehicles, or it could provide
assurance that the vehicles will be designed for lower emission
levels than would result just from the proposed EPA standards.
Therefore, the cases to be presented include ones that go
beyond just meeting the proposed EPA standard. the details of
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how this would be accomplished (assuring that vehicles would be
cleaner than the EPA standard) technically, legally, and
administratively are beyond the scope of this document. ,
Regarding the feasibility/availability of dedicated
methanol vehicles^ it should be noted that some comments were
received by EPA stating that production of such vehicles for
consumer use is not expected in the near future. Planners
wishing to incorporate the use of such vehicles in air quality
projections are cautioned to make sure vehicle technology
projections are realistic in terms of which technologies are
actually available.
The actual credits to be applied would depend on the
emission levels of whatever vehicle technology is proposed by a
locality, with adequate supporting data. For scenarios other
than the three presented here, credits can be determined
through individual consultation with EPA.
The use of a high concentration of methanol or neat
methanol results in exhaust and evaporative emissions that are
primarily methanol. The exhaust may also contain elevated
levels of formaldehyde. However, the presence of any gasoline
in the blend results in significant hydrocarbon emissions too.
The impact of this changed mix and amount of emitted species is
addressed in the following sections.
Data are not sufficient to indicate that either CO or NOx
emissions are changed with use of a dedicated or flexible
fueled vehicle.[16,17,18,19,20] In fact, at low temperatures
current technology dedicated vehicles and FFV's may have poorer
CO performance than gasoline vehicles in the absence of low
temperature standards for either vehicle type. Since this is
currently an area of uncertainty, however, EPA will allow
states to assume equal CO and NOx emissions for methanol and
gasoline vehicles.
3.2.2.1 City-specific Ozone Reduction Determinations
The photochemical reactions of normal auto exhaust
hydrocarbons, methanol, and formaldehyde can vary from city to
city depending on the HC/NOx ratio, atmospheric conditions, and
other parameters. Due to the city-specific nature of emissions
reactivity, ideally a planner would use a photochemical
dispersion model for the urban area of interest to determine
potential ozone reductions from use of dedicated methanol
vehicles and/or flexible fueled vehicles. EPA endorses the
superiority of this approach and recommends its use by areas
capable of following it. However, planning realities require
the availability of more workable or default assumptions and
approaches, such as are made available for other aspects of the
planning task. Default benefits representing EPA's best
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judgment of an average case are presented in the following
sections, and these may be used with no city-specific defense
of their applicability. Areas wishing to conduct the more
accurate city-specific analysis should consult with EPA at each
step. These default values are considered an interim approach,
and city specific photochemical dispersion models (e.g.,
Airshed) should be used as they become available.
3.2.2.2 Default Ozone Reduction Estimates for Vehicles Just
Meeting The EPA Standards For Methanol Vehicles
The first case to be examined is for light duty vehicles
that just meet the proposed EPA carbon-based organics emissions
standard for methanol fueled vehicles. This standard is based
on the fact that 0.41 g/mile HC represents 0.354 g/mile carbon
assuming a carbon:hydrogen ratio of 1:1.85, and a
methanol-fueled vehicle would, therefore, also emit no more
than 0.354 g/mile carbon. This is expected to be the most
likely case that planners could have available to them in the
next few years. For instance, it would probably apply to FFV's
operating on M85 as well as dedicated methanol vehicles
operating on M85.
A dedicated methanol vehicle is one that uses only fuel
composed of at least 85% methanol. Even though the comments
EPA received in response to its proposed methanol rulemaking
indicated that such vehicles could realize most cost and
performance advantages by using as little as 50% methanol, the
vehicles currently being designed and built use from 85% to
100% methanol. Flexible fueled vehicles (FFVs) can use either
gasoline fuel or an alcohol/gasoline blend up to 85% or 100%
methanol (or ethanol). The vehicles are designed to sense how
much alcohol is in the mixture and make appropriate engine
adjustments for proper combustion.
There are a number of issues specifically related to use
of FFV's that a SIP would need to cover if FFV use is to be
part of the SIP. For instance, FFV's would probably be
designed to need M85 in the winter for cold driveability, and
thus would not be expected to be able to achieve the low or
intermediate emission levels that follow this section. In the
summer months, however, EPA will allow the assumption of M100
fuel in FFV's if MlOO fuel is mandated in the SIP. This would
increase the likelihood of FFV's being able to meet the
intermediate and possibly even the low emission estimates that
follow.
It is important when estimating future emission reductions
for flexible fueled vehicles to credibly predict what fraction
of the time the vehicles will operate on a methanol mixture
versus gasoline, since no emission reductions occur with use of
gasoline. It is also important to confirm what percentage
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methanol is being used. Predicting future fuel composition and
use is easiest when the SIP contains regulations with specific
mandates for both aspects. Items such as methanol sales
records should be used for tracking purposes to determine the
mileage accumulated with the methanol blends. If the SIP
allows less than M85 and the vehicles in question match one of
the certification emission levels only on M85, the SIP must
justify an estimate of the average methanol content and
percentage of time operated on that fuel and then proportion
the benefit accordingly. For tracking methanol use
retrospectively, the two aspects (methanol content and time it
is used) can be combined, and all that needs to be determined
is the percent of total fuel used that was methanol.
0
The following are the individual emission levels which EPA
predicts would be exhibited under certification conditions
(e.g., properly maintained and used) for a vehicle certified to
meet the proposed combined organics standard, CO standard, and
NOx standard. This prediction is subject to uncertainty, since
EPA will not directly regulate the amounts of HC, methanol, and
formaldehyde individually.
Just Meeting the Proposed EPA Organics Standard
For Methanol Fueled Light Duty Vehicles
Certification Certification
Exhaust Evaporative
HC 0.15 g/mile 1.08 g/test
(0.07 g/mile)
Methanol 0.55 g/mile 2.19 g/test
(0.16 g/mile)
Formaldehyde 0.048 g/mile none
In selecting default estimates for the ozone reduction
achieved by methanol vehicles with these certification emission
levels, EPA considered several factors each of which causes
some uncertainty. First, the engine designs and emission
control system designs which manufacturers would use to achieve
these emission levels are not yet known with certainty. FFV's
may dominate, but perhaps not to the exclusion of dedicated
vehicles. Fuel injection will most likely be used on all
vehicles, but other features may vary. Second, the
relationship between certification emission levels and in-use
emission levels may be different from the relationship with
gasoline vehicles, which is itself not fully known for the most
recent designs. Dedicated methanol vehicles should be less
exposed to lead in their fuel, and FFV's may be also, which
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will limit catalyst deactivation relative to gasoline
vehicles. Deliberate catalyst removal may also be less
frequent, since much of the catalyst removal problem on
gasoline vehicles is associated with deliberate misuse of
leaded fuel. Third, EPA considered the results of the
available studies of the photochemical effects of methanol
vehicle emissions relative to gasoline vehicle emissions.
These studies vary in their sophistication and in their
results, but on the whole support an assumption of a
substantial difference in overall contribution to ozone
formation.
In light of the above factors, EPA will accept the use of
the following estimates of the equivalent HC reductions for
vehicles just meeting the EPA standards. These percentages
should be applied to the non-methane HC output for MOBILES, and
the results treated as non-methane.
VOC Exhaust - 34%
VOC Evaporative - 71%
(compared to 11.5
psi summer gasoline)
VOC Evaporative - 32%
(compared to 9.0
psi summer gasoline)
Methanol-fueled light-duty trucks and heavy-duty vehicles just
meeting the proposed standards for their classes may claim the
same percentage reduction credits.
3.2.2.3 Default Ozone Reduction Estimates for Vehicles With
Emissions Well Below the EPA Standards
The following are the individual emission levels under
certification conditions (e.g., properly maintained and used)
which define this scenario.
Emissions Well Below the EPA Standards
Certification Certification
Exhaust Evaporative
HC 0.020 g/mile 0.0 g/test
Methanol 0.20 g/mile 1.0 g/test
(0.07 g/mile)
Formaldehyde 0.010 g/mile none
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In order to meet these emission levels a methanol vehicle
would most likely incorporate engine design features optimized
to take full advantage of pure methanol's excellent combustion
characteristics (high octane, wide flammability limits, high
flame speed, low flame temperature, etc.). Design features
would likely include high compression, lean burn combustion,
and an advanced fuel injection system, and could include
concepts such as turbocharging or supercharging, methanol
dissociation, cooling system modification, etc. Also, the
vehicle would have very low formaldehyde emissions possibly due
to use of a modified catalyst configuration (size, composition,
or location). The vehicle would have to be designed to have
good driveability even though it would be leaned out enough to
have sufficiently low NOx emissions without the use of a
reduction catalyst. EPA expects that dedicated M100 vehicles
are the most likely technology to achieve these levels, but if
FFV or M85 vehicles are certified with test results this low,
the same credits would apply.
However, comments received from the California Air
Resources Board point out that in some areas the control of NOx
emissions is important enough to ozone control that such
vehicles may need to operate at stoichiometry to allow use of
3-way catalysts for maximum NOx control.
A low emitting vehicle meeting the above emission criteria
may claim the following default non-methane HC reduction
credits, calculated as in the prior example.
VOC Exhaust - 83%
VOC Evaporative - 93%
(compared to 11.5
psi gasoline)
VOC Evaporative - 85%
(compared to 9.0
psi gasoline)
3.2.2.4 Default Ozone Reduction Estimates for Vehicles With
Intermediate Emission Levels
This case could apply to vehicles that could not meet the
very low emission levels in the previous section, but were still
capable of substantially lower emissions than vehicles just able
to meet the standard. This could include FFV's and dedicated
methanol (e.g., M85 or M100) vehicles.
The following are the individual emission levels under
certification conditions (e.g., properly maintained and used)
which define this scenario.
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Certification Certification
Exhaust Evaporative
HC 0.09 g/mile 0.35 g/test
(0.02 g/mile)
Methanol 0.34 g/mile 1.5 g/test
(O.ll g/mile)
Formaldehyde 0.023 g/mile
The default reduction credits for this case are as follows:
VOC Exhaust - 68%
VOC Evaporative - 78%
(compared to 11.5
psi gasoline)
VOC Evaporative - 48%
(compared to 9.0
psi gasoline)
Table 4-18 summarizes the adjustment factors for CNG
vehicles (given in Section 3.2.1) and methanol vehicles.
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4.0 CALCULATION OF FLEET EFFECTS
4.1 General Approach and Model Year-Specific Adjustment Factors
The general approach for calculating emission changes due
to use of alternative fuels is based on MOBILES which is the
model the States use to calculate the mobile source emission
portion of their SIPs. MOBILES calculates emissions from
in-use motor vehicles for the calendar year of interest. The
purpose of this section is to present factors to adjust a
special version of the MOBILES output to account for
alternative fuels. Detailed examples of this method are
provided in Appendix C. Appendix D provides an in-depth
explanation of (a) the calculation procedure used to create
Tables 4-1 to 4-17 and (b) how to combine the appropriate
information for a given scenario; this can also be used to
automate the full calculation procedure.
Before discussing the adjustment factors for MOBILES, it
is important to -determine the technology split in the various
vehicle classes. This technology split is important since the
change in vehicle emissions with oxygenated fuels depends on
the vehicle technology as mentioned in Section 3. Table 4-1
lists the technology splits for vehicles from the pre-1975
through 1990+ model years. The different technologies
considered in Table 4-1 are non-catalyst, open-loop oxidation
catalyst vehicles with carburetors, open-loop oxidation
catalysts with fuel injection, closed-loop 3-way catalyst
vehicles with carburetors, and closed loop 3-way catalyst
vehicles with fuel injection. For exhaust emissions, it is a
reasonable approximation to assume that a technology type's
share of the model year's emissions is the same as its share of
that year's sales. However, carbureted and fuel injected
vehicles have quite different evaporative emissions. Greater
accuracy can be achieved without undue complication by
recognizing and accounting for this difference. Table 4-2
presents EPA's current best estimates of evaporative emissions
from carbureted and fuel injected vehicles on 11.5 psi and 9.0
psi non-oxygenated gasoline.
Table 3-1 already listed the general percentage changes
assigned to each technology class for exhaust emissions for
ethanol, methanol, and MTBE blends. On a percentage basis
these numbers are the same for low and high altitude, but since
high altitude CO emissions are greater than low altitude, the
g/mile changes would be greater at high altitude. Table 3-2
lists the evaporative emission assumptions by technology for
ethanol blends. These changes were determined for each
technology by adding the effects of RVP on diurnal and hot soak
emissions as well as the effect of distillation curve (%
evaporated at 160°F) on hot soak mass emissions. The
distillation effect has been adjusted so as not to double count
any RVP-only effect on hot soak emissions.
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Ethanol Blends - The final results for ethanol blends are given
in Tables 4-3 to 4-9, in the form of adjustment factors to be
applied to individual model year emission levels of individual
vehicle types (e.g., LDGV, LDGT, etc.). Table 4-3 contains the
percentage change in exhaust "volatile organic compounds" (or,
for the purposes of MOBILES, exhaust non-methane HC) for
vehicles in model years pre-1975 through 1990+. Tables 4-4
through 4-7 list similar information for vehicles in these
model years for vehicle evaporative emissions when using
ethanol blends. Factors such as the RVP level of the blend and
percent market share of the blend (i.e., the commingling effect
for either 50% or 100% market share) are included in these
tables. Tables 4-8 and 4-9 give exhaust CO and NOx emissions
changes with ethanol blends.
These tables were constructed using the individual
technology effects from Tables 3-1 and 3-2 and weighting those
effects by the technology mix (non-catalyst/OL/CL for exhaust,
Carb/FI for evap) for each model year for each vehicle category
(LDGV, LDGT1, LDGT2, and HDGV).
Methanol Blends - Since the exhaust effects of methanol blends
are the same as for ethanol blends at a given RVP, Tables 3-1,
4-3, 4-8, and 4-9 also apply to methanol blends. Regarding
evaporative emission effects, Tables 3-3 and 4-10 through 4-13
give similar information for methanol blends.
MTBE Blends - Tables 3-1, 3-4 and 4-14 through 4-17 give the
corresponding exhaust and evaporative emission information for
MTBE blends.
CNG and Methanol - Table 4-18 provides adjustment factors for
CNG and methanol fueled vehicles. Because the adjustments for
CNG vehicles, FFV's, and current technology and advanced
technology dedicated methanol vehicles do not depend on the
technology mix of gasoline vehicles, they do not depend on
model year. The general approach is the same, however.
Appropriate adjustment factors for each affected model year
have been derived from the relevant reductions given in the
text in Section 3.2.
These -calculations apply to both low and high altitude
areas. However, for high altitude areas, the high altitude
input flag of MOBILES should be used.
To use the information in, for example, Table 4-8 to
calculate an overall fleet effect, it is necessary to first
obtain a special MOBILES output showing model year-specific
g/mile emission levels and VMT weighting factors. (This
MOBILES run should include the vehicle inspection program, if
any, that is or will be in operation on the evaluation date.)
Then the model year adjustment factors from the appropriate
-28-
-------
table should be applied to the individual model year output for
oxygenated blends. This must be repeated for each vehicle
type. The model year factors should then be recombined across
model years and then vehicle types. For both steps, VMT
weighting factors are used. This adjustment and recombination
procedure requires hand calculation.
This methodology will work for 100% of one or some model
years using CNG, FFV, 85% methanol, or 100% methanol. It will
also work for the oxygenated blends for the cases for which
there are tables. These cases include 100% market share of one
of the three oxygenate blends or 50% market share of either the
ethanol or methanol blends. Other cases are covered in
Appendix A.
4.2 Partial Penetration by One Blend or Vehicle Type
For market shares of oxygenated blends not listed in the
table, the effects of. the blends on evaporative emissions must
be calculated. This calculation is simplest for MTBE where one
can interpolate linearly for the effects between 0% and 100%,
since there are no commingling effects. For either the ethanol
or methanol blends with gasoline, one must make a quadratic
interpolation using the 0%, 50%, and 100% points since this
relationship is not linear due to commingling effects.
It is important to note that the 50% market penetration of
an ethanol or methanol blend with gasoline results in a greater
per-vehicle effect on evaporative VOC for the blend fueled
fraction of the fleet than the 100% market share case. This
can be seen by comparing Tables 4-4 and 4-6. The reason for
this is that with an ethanol or methanol blend market share of
less than 100% some degree of commingling is expected from
consumers mixing the alcohol blend with non-oxygenated gasoline
(such as by filling their tank with non-oxygenated gasoline
when the previous fill-up was with an ethanol blend).
Therefore, a program with no such commingling would yield the
greatest benefits.
If the blend market share varies by model year or vehicle
type, the user must interpolate the adjustment factors before
they are applied to the model year g/mile emission levels. If
it is the same for each model year and vehicle type, a single
interpolation on the overall fleet emission level is
acceptable.
If one blend or vehicle type (e.g., CNG, methanol) is used
for only some model years, the adjustment should be .applied
only for those model years. Interpolation may be needed for
that model year if there is less than 100% usage.
-29-
-------
For partial penetration of alternative fuel vehicles
(e.g., CNG, methanol), one can proportion the adjustment
factors or the final fleet g/mile value accordingly.
4.3 Simultaneous Marketing of MTBE, Ethanol, and/or Methanol
Blends
Based on the limited amount of test data that has been
collected on commingling of these oxygenates, it appears that
no significant non-linear RVP increase results from mixtures of
MTBE, ethanol, or methanol blends.[27,28] Therefore, any
all-blends scenario can be analyzed by market share weighting
the individual blends' "100% Use" adjustment factors from
Tables 4-3 to 4-17.
A scenario in which non-oxygenated gasoline is marketed at
the same time as two blends can be analyzed using the method
described in Appendix B.
4.4 Blends and CNG, FFV, M85 and/or M100 in Same Model Year
Here each model year should be divided into two or more
groups based on the sales split between gasoline vehicles and
alternative fuel vehicles. An adjustment factor should be
selected (or calculated if necessary) for the gasoline portion
based on expected blend use. This adjustment factor should be
combined with the standard adjustment factors for CNG, FFV,
current technology methanol vehicles, and advanced technology
methanol vehicles using the new vehicle sales mix.
-30-
-------
5.0 OBTAINING SPECIAL MOBILE3 OUTPUT
To use the method and numerical adjustment factors provided
in earlier sections, it is necessary to have more detailed
output than can be obtained with the standard MOBILES (or
MOBILE4) program. Specifically, output is needed which shows
for a given pollutant the emission factor for each model
year/vehicle type, and that model year's share of the VMT from
that vehicle type. VMT shares among vehicle types are also
needed but are available in the standard MOBILES output. For
VOC, exhaust and evaporative emissions must be shown separately
for each model year so that the separate adjustments can be made.
While it is possible for a user to modify the MOBILES (or
MOBILE4) code to generate the required output, EPA believes it
will be more convenient and less error prone for most users to
obtain from EPA a magnetic tape containing the Fortran source
code for a modified MOBILES (or MOBILE4) which can produce both
the standard types of output and the special version required
for using this method. Users should contact Joseph H. Somers or
Jonathan Adler, U.S. Environmental Protection Agency, 2565
Plymouth Road, 48105, (Telephone 313-668-4321) for more
information.
-31-
-------
List of References
1. "Study of Gasoline Volatility and Hydrocarbon Emissions
from Motor Vehicles," U.S. EPA, Office of Air and
Radiation, Office of Mobile Sources, Emission Control
Technology Division Report, EPA-AA-SDSB-85-05, November
1985.
2. Draft Regulatory Impact Analysis, "Control of Gasoline
Volatility and Evaporative Emissions from New Motor
Vehicles," U.S. EPA, Office of Air and Radiation, Office of
Mobile Sources, May 1987.
3. "The Effects of Two Different Oxygenated Fuels on Exhaust
Emissions at High Altitude," Colorado Department of Health
Report, 1987.
4. Overheads for Presentation by Colorado Department of Health
personnel for EPA meeting with Rocky Mountain Oil and Gas
Association personnel, January 28, 1987.
5. "Report and Recommendations of the Oxygenated Fuels Task
Force," Report to Richard D. Lamm, Governor, State of
Colorado, October 29, 1986
6. "Ethanol-Blended Fuel as a CO Reduction Strategy at High
Altitude," Colorado Department of Health Report, August
1985.
7. "Effects of Ethanol-Blended Fuel on Motor Vehicles at High
Altitude," Colorado Department of Health Report, September
1983.
8. "Further Analyses of the Effects of Fuel Oxygen Content on
Exhaust Emissions," EPA Memo from Jonathan Adler, Technical
Support Staff to Phil Lorang, Chief, Technical Support
Staff, March 9, 1987.
9. "Meeting with RMOGA Representatives on Blends," EPA Memo
from Phil Lorang, Chief, Technical Support Staff to the
Record, February 20, 1987.
10. EPA Letter on Oxygenated Fuels from Jonathan Adler,
Technical Support Staff to Nancy C. Wrona, Air Quality
Advisor, City of Phoenix, March 13, 1987.
11. EPA Letter on Oxygenated Fuels with supplemental memo from
Jonathan Adler, Technical Support Staff to Nancy C. Wrona,
Air Quality Advisor, City of Phoenix, January 7, 1987.
-32-
-------
12. "Effects of Distillation Point at 160°F on Hot Soak
Emissions," EPA Memo from Jonathan Adler, Technical Support
Staff to Charles L. Gray, Jr., Director, Emission Control
Technology Division, December 9, 1986.
13. "Analysis of the Effects on Exhaust Emissions of the Use of
Methanol Blends; A Summary of Several Studies," EPA Memo
from Jonathan Adler, Technical Support Staff to Phil
Lorang, Chief, Technical Support Staff, August 13, 1986.
14. Fuels and Fuel Additives; Revised Definition of
Substantially Similar, Federal Register, 46, 144, 38582,
July 28, 1981.
15. "Distillation of Fuels Containing MTBE," EPA memo from Carl
Scarbro, Testing Programs Branch to Jonathan Adler,
Technical Support Staff, March 27, 1987.
16. "Organic Emission Standards for Light-Duty Methanol-Fueled
Vehicles: A Methodology," Michael D. Gold (U.S. EPA), Air
Pollution Control Association Paper 85-38.6, June 1985.
17. "Assessment of Emissions from Methanol-Fueled Vehicles:
Implications for Ozone Air Quality," R.J. Nichols and J.M.
Norbeck, Air Pollution Control Association Paper 85-38.3,
June 1985.
18. EPA Regulatory Support Document, "Proposed Organic Emission
Standards and Test Procedures for 1986 and Later Methanol
Vehicles and Engines," U.S. EPA, Office of Air and
Radiation, Office of Mobile Sources, July 1986.
19. "Impact of Methanol on Smog: A Preliminary Estimate," Gary
Z. Whitten and Henry Hogo, Systems Applications, Inc.,
Publication tt 83044 prepared for ARCO Petroleum Products
Company, February 1983.
20. "Photochemical Modeling of Methanol-Use Scenarios in
Philadelphia," Gary Z. Whitten, N. Yonkow, and T.C. Myers,
Systems Applications, Inc., EPA Contract Report
460/3-86-001, March 1986, NTIS Order No. PB 87-164372/AS.
21. ARCO Letter on Commingling and Fuel Volatility from W.J.
Wostl to Charles L. Gray, EPA, February 4, 1985.
22. "Reactivity/Volatility Classification of Selected Organic
Chemicals: Existing Data," EPA Report 600/3-84-082, H. B.
Singh, et al, 1984.
-33-
-------
23. "Ethanol Reactivity - Comments of the Ad Hoc Ethanol
Committee," memo from Penny Carey to Phil Lorang, EPA
Technical Support Staff, December 16, 1987.
24. "Guideline For Use Of City-specific EKMA In Preparing Ozone
SIPs," EPA Monitoring and Data Analysis Division, Report
No. EPA-450/4-80-027, March 1981, NTIS Order No.
PB83-140251.
25. (Technical support document for this SIP credit guidance
document)
26. Robert L. Furey, "Volatility Characteristics of
Gasoline-Alcohol and Gasoline-Ether Fuel Blends," SAE Paper
852116, October 1985.
27. Robert L. Furey and Kevin L. Perry, "Vapor Pressures of
Mixtures of Gasolines and Gasoline-Alcohol Blends," SAE
Paper 861557, October 1986.
28. G. E. Crow and B. C. Davis, "Environmental Effects of
Oxygenates," Presentation given at the 1987 National
Conference on Fuel Alcohol and Oxygenates, September 30 -
October 1, 1987.
29. Standards for Emissions From Methanol-Fueled Motor Vehicles
and Motor Vehicle Engines; Notice of Proposed Rulemaking,
Federal Register, 51, 168, August 29, 1986.
30. "Ethanol Commingling," EPA Memo from Craig Harvey,
Technical Support Staff to Phil Lorang, Chief, Technical
Support Staff, December 21, 1987.
31. "Ethanol Reactivity - Comments of the Ad Hoc Ethanol
Committee," EPA Memo from Penny M. Carey, Technical Support
Staff to Phil Lorang, Chief, Technical Support Staff,
December 18, 1987.
32. ARCO waiver application for Oxinol.
-34-
-------
Technology
Table 3-1
Technology-Specific
Exhaust Effects of Blends
Percent Change from Gasoline
(low and high altitude)
3.7% Oxygen
(10% Ethanol or 5%
Methanol/Cosolvent Blends)
CO VOC
Same +0.76
RVP PSI
NOx
Same +0.76
RVP PSI
Non-Catalyst
Open-Loop Catalyst
Closed-Loop
-24.5% -22.8% +3.8% -5.5% -4.2%
-34.9 -33.4 +4.0 -15.6 -14.5%
-21.4 -17.2 +8.1 -5.1 -2.4%
2.0% Oxygen
(11% MTBE Blends)
CO
Same
RVP
NOx
VOC
Same
RVP
-13.2% +2.1% -3.0%
-18.9 +2.2 -8.4
-11.6 +4.4 -2.8%
1/7/88
-35-
-------
Table 3-2
Evaporative VOC Technology-Specific
Effects of 10% Ethanol Blends*
Percent Change From Gasoline
100% Share
(no commingling)
Diurnal
Carb
F.I.
11.5 RVP Base
Same RVP RVP +0.76
-9.66
-9.66
-1-80.1
+122.2
9.0 RVP Base
Same RVP RVP +0.76
-9.66
-9.66
+41.13
+42.67
H. S.
Carb +14.85
F. I. -5.70
50% Share
(max commingling)
Diurnal
Carb +20.97
F. I. +33.92
+35.28
+20.18
+96.21
+144.9
+14.85
-5.70
-2.39
-3.32
+25.52
+34.01
+51.72
+55.10
H. S.
Carb
F. I.
+18.18
+ 1.57
+39.57
+24.97
+16.20
+0.30
+28.47
+42.36
a These effects include adjustments for lower molecular
weight of ethanol and lower number of carbons/gram relative to
gasoline vapor. For hot soak, adjustments for molecular weight
are not used, but for carbureted vehicles an adjustment for
distillation (% evap @160°F) is included.
1/7/88
-36-
-------
Table 3-3
Technology-Specific Effects of 3.7% Oxygen
Methanol/Cosolvent Blends: Evaporative VOCa
(percent change including reactivity adjustment)
100% Share
(no commingling)
Diurnal
Carb
F.I.
11.5 RVP Base
9.0 RVP Base
Same RVP
-18.79
-18.79
RVP +0.76
+61.89
+99.76
Same RVP RVP +0.76
-18.79
•18.79
+26.88
+28.26
H.S.
Carb.
F.I.
-3.19
-12.20
+12.45
+11.90
-3. 19
-12.20
+3.37
+24.77
50% Share
(Max Commingling)
Diurnal
Carb.
F.I.
H.S.
Carb.
F.I.
+28.60
+50.69
+6.90
+0.05
+111.4
+189.1
+24.93
+25.92
-2.94
-1.64
+ 1.69
+ 6.25
+58.94
+68.28
+12.33
+48.66
a These effects include adjustments for lower molecular
weight of methanol and lower number of carbons/gram relative to
gasoline vapor. For hot soak, adjustments for molecular weight
are not used, but for carbureted vehicles an adjustment for
distillation (% evap @160°F) is included. The no commingling
scenarios are based on Reference 2, and the maximum commingling
scenarios adjust the no commingling estimates per Reference 21
assuming 20% full tanks at refueling and a reasonable degree of
brand loyalty.
1/7/88
-37-
-------
Table 3-4
Technology-Specific Effects of
11% MTBE Blends: Evaporative VOC*
(percent change, matched to any base RVP)
Diurnal
Carbureted +1.78
Fuel Injected +1.78
H.S.
Carbureted +12.82
Fuel Injected -1.90
a These effects include adjustments for greater molecular
weight of MTBE and lower number of carbons/gram relative to
gasoline vapor. For hot soak, adjustments for molecular weight
are not used, but for carbureted vehicles an adjustment for
distillation (% evap @160°F) is included.
1/7/88
-38-
-------
Table 4-1
Exhaust and Evaporative Emissions
Technology Mix (Sales-Based)
Model
Year
pre-1975
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
LDGV
A/B/C/D/E
100/0/0/0/0
20/75/5/0/0
15/80/5/0/0
15/80/5/0/0
10/85/5/0/0
10/85/5/0/0
5/83/7/5/0
0/28/0/63/9
0/33/0/50/17
0/24/0/48/28
0/6/0/55/39
0/6/0/39/55
0/7/0/26/67
0/1/0/24/75
0/1/0/20/79
0/1/0/15/84
0/1/0/10/89
Technology
LDGT1
A/B/C/D/E
100/0/0/0/0
30/70/0/0/0
20/80/0/0/0
25/75/0/0/0
25/75/0/0/0
20/80/0/0/0
20/79/1/0/0
0/96/1/3/0
0/79/1/20/0
0/70/0/30/0
0/72/0/26/2
0/63/0/25/12
0/41/9/15/35
0/14/5/13/68
0/14/5/13/68
0/14/5/13/68
0/14/5/13/68
Mix*
LDGT2
A/B/C/D/E
100/0/0/0/0
100/0/0/0/0
100/0/0/0/0
100/0/0/0/0
100/0/0/0/0
0/100/0/0/0
0/100/0/0/0
0/100/0/0/0
0/100/0/0/0
0/90/0/10/0
0/72/0/26/2
0/63/0/25/12
0/41/9/15/35
0/14/5/13/68
0/14/5/13/68
0/14/5/13/68
0/14/5/13/68
HDGV
A/B
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
26/74
26/74
26/74
26/74
A Non-catalyst
B Open-loop carbureted
C Open-loop fuel injected
D Closed-loop carbureted
E Closed-loop fuel injected,
1/12/88
-39-
-------
Table 4-2
Baseline Non-Oxygenated
Gasoline Evaporative HC Emissions
RVP ..
9.0 9.76 11.5 12.26
Carbureted
Hot Soak, g 2.46 2.77 4.27 5.25
Diurnal, g 2.65 4.14 9.09 18.12
Total, g/mile 0.326 0.405 0.711 1.098
Fuel Injected
Hot Soak, g 0.95 1.35 2.66 3.39
Diurnal, g 1.83 2.89 7.94 19.53
Total, g/mile 0.152 0.225 0.516 0.960
1/7/88
-40-
-------
Table 4-3
Low and High Altitude Adjustment Factors for 10% Ethanol or
3.7 Oxygen Methanol Blends by Model Year and Type: Exhaust VOC
Ratio of Blend to Base Exh
(3.7% 02, Matched RVP)
Matched RVP
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
LDGV
0.9450
0.8642
0.8592
0.8592
0.8541
0.8541
0.8543
0.9196
0.9144
0.9238
0.9427
0.9427
0.9417
0.9480
0 .9480
0.9480
0.9480
LDGT1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.9450
.8743
.8642
.8693
.8693
.8642
.8642
.8472
.8650
.8755
.8734
.8829
.8965
.9291
.9291
.9291
.9291
LDGT2
0.9450
0.9450
0.9450
0.9450
0.9450
0.8440
0.8440
0.8440
0.8440
0.8545
0.8734
0.8829
0.8965
0.9291
0.9291
0.9291
0.9291
VOC
HDGV
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.9450
.9450
.9450
.9450
.9450
.9450
.9450
.9450
.9450
.9450
.9450
.9450
.9450
.8703
.8703
.8703
.8703
Ratio of
(3.7%
LDGV
0.9580
0.8756
0.8705
0.8705
0.8653
0.8653
0.8662
0.9421
0.9361
0.9470
0.9687
0.9687
0.9675
0.9748
0.9748
0.9748
0.9748
Blend to Base Exh VOC
02, RVP + 0.76 psi)
RVP -1-0.76 RVP
LDGT1
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
9580
8859
8756
8808
8808
8756
8756
8586
8792
8913
8889
8998
9155
9530
9530
9530
9530
LDGT2
0.9580
0.9580
0.9580
0.9580
0.9580
0.8550
0.8550
0.8550
0.8550
0.8671
0.8889
0.8998
0.9155
0.9530
0.9530
0.9530
0.9530
HDGV
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.9580
0.8818
0.8818
0.8818
0.8818
1/11/88
-41-
-------
Table 4-4
Low and High Altitude Adjustment Factors for
Ethanol Blends by Model Year and Type: Evaporative VOC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
9.0
LDGV
1.0845
1.0808
1.0808
1.0808
1.0808
1.0808
1.0792
1.0776
1.0709
1.0605
1.0485
1.0276
1.0083
0.9931
0.9847
0.9732
0.9606
(100%
Use of Blend)
psi (matched RVP)
LDGT1
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0838
1.0838
1.0838
1.0845
1.0830
1.0751
1.0425
0.9971
0.9971
0.9971
0.9971
LDGT2
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0830
1.0751
1.0425
0.9971
0.9971
0.9971
0.9971
HDGV
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
1.0845
11
LDGV
1.0477
1.0432
1.0432
1.0432
1.0432
1.0432
1.0413
1.0394
1.0316
1.0204
1.0083
0.9893
0.9737
0.9625
0.9567
0.9493
0.9415
.5 psi (matched RVP)
LDGT1
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0468
1.0468
1.0468
1.0477
1.0459
1.0365
1.0026
0.9654
0.9654
0.9654
0.9654
LDGT2
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0459
1.0365
1.0026
0.9654
0.9654
0.9654
0.9654
HDGV
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1.0477
1/11/88
-42-
-------
Table 4-5
Low and High Altitude Adjustment Factors for 10%
Ethanol Blends by Model Year and Type: Evaporative VOC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
LDGV
1.2960
1.2978
1.2978
1.2978
1.2978
1.2978
1,2986
1.2994
1.3027
1.3079
1.3138
1.3241
1.3337
1.3412
1.3454
1.3511
T.3573
9.0 + 0
LDGT1
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2963
1.2963
1.2963
1.2960
1.2967
1.3006
1.3168
1.3392
1.3392
1.3392
1.3392
( 100%
.76 psi
LDGT2
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2967
1.3006
1.3168
1.3392
1.3392
1.3392
1.3392
Use of Blend)
HDGV
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
1.2960
LDGV
1.5370
1.5432
1.5432
1.5432
1.5432
1.5432
1.5458
1.5483
1.5589
1.5743
1.5907
1.6167
1.6379
1.6531
1.6610
1.6712
1.6818
11.5 + 0.
LDGT1
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5382
1.5382
1.5382
1.5370
1.5395
1.5522
1.5985
1.6492
1.6492
1.6492
1.6492
.76 psi
LDGT2
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5395
1.5522
1.5985
1.6492
1.6492
1.6492
1.6492
HDGV
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1.5370
1/11/88
-43-
-------
Table 4-6
Low and High Altitude Adjustment Factors for 10\
Ethanol Blends by Model Year and Type: Evaporative VQC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
9.0
LDGV
1.1135
1.1105
1.1105
1.1105
1.1105
1.1105
1.1093
1.1080
1.1026
1.0944
1.0849
1.0683
1.0530
1.0409
1.0342
1.0251
1.0151
(50% Use
psi (matched RVP)
LDGT1
1.1135
1.1135
1.1135
1.1135
1.1135
1.1135
1.1129
1.1129
1.1129
1.1135
1.1123
1.1060
1.0801
1.0441
1.0441
1.0441
1.0441
LDGT2
1.1135
1.1135
1.1135
1.1135
1.1135
1.1135
1.1135
1.1135
1.1135
1.1135
1.1123
1.1060
1.0801
1.0441
1.0441
1.0441
1.0441
of Blend)
11.5
HDGV
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1135
1135
1135
1135
1135
1135
1135
1135
1135
1135 .
1135
1135
1135
1135
1135
1135
1135
LDGV
1.1933
1.1920
1.1920
1.1920
1.1920
1.1920
1.1915
1.1910
1.1889
1.1859
1.1827
1.1775
1.1733
1.1704
1.1688
1.1668
1.1647
psi
(matched RVP)
LDGT1
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1933
1933
1933
1933
1933
1933
1930
1930
1930
1933
1928
1903
1811
1711
1711
1711
1711
LDGT2
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1933
1933
1933
1933
1933
1933
1933
1933
1933
1933
1928
1903
1811
1711
1711
1711
1711
HDGV
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1.1933
1/11/88
-44-
-------
Table 4-7
Low and High Altitude Adjustment Factors for 10%
Ethanol Blends by Model Year and Type: Evaporative VOC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
LDGV
1.3454
1.3485
1.3485
1.3485
1.3485
1.3485
1.3497
1.3510
1.3565
1.3650
1.3747
1.3917
1.4074
1.4197
1.4266
1.4359
1.4462
9.0 + 0.
LDGT1
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3460
1.3460
1.3460
1.3454
1.3466
1.3530
1.3796
1.4165
1.4165
1.4165
1.4165
(50%
76 psi
LDGT2
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3466
1.3530
1.3796
1.4165
1.4165
1.4165
1.4165
Use of Blend)
HDGV
1.3454
1.3454
1.3454,
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
1.3454
LDGV
1.6285
1.6364
1.6364
1.6364
1.6364
1.6364
1.6396
1.6429
1.6563
1.6757
1.6965
1.7294
1.7563
1.7755
1.7855
1.7984
1.8118
11.5 + 0.
LDGT1
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6301
1.6301
1.6301
1.6285
1.6317
1.6478
1.7064
1.7706
1.7706
1.7706
1.7706
.76 psi
LDGT2
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6317
1.6478
1.7064
1.7706
1.7706
1.7706
1.7706
HDGV
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1.6285
1/11/88
-45-
-------
Table 4-8
Low and High Altitude Adjustment Factors for 10% Ethanol
or 3.7% Oxygen Methanol Blends by Model Year and Type: CO
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
Ratio of Blend to Base CO
(3.7% 02, Matched RVP)
LDGV LDGT1 LDGT2 HDGV
0.7550
0.6718
0.6666
0.6666
0.6614
0.6614
0.6630
0.7482
0.7415
0.7536
0.7779
0.7779
0.7766
0.7847
0.7847
0.7847
0.7847
0.7550
0.6822
0.6718
0.6770
0.6770
0.6718
0.6718
0.6551
0.6780
0.6915
0.6888
0.7010
0.7185
0.7604
0.7604
0.7604
0.7604
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.7550
.7550
.7550
.7550
.7550
.6510
.6510
.6510
.6510
.6645
.6888
.7010
.7185
.7604
.7604
.7604
.7604
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.7550
0.6780
0.6780
0.6780
0.6780
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Ratio of Blend to Base CO
(3.7% 02, RVP + 0.76 psi)
LDGV LDGT1 LDGT2 HDGV
.7720
.6872
.6819
.6819
.6766
.6766
.6794
.7826
.7745
.7891
.8183
.8183
.8167
.8264
.8264
.8264
.8264
0.7720
0.6978
0.6872
0.6925
0.6925
0.6872
0.6872
0.6709
0.6984
0.7146
0.7114
0.7259
0.7470
0.7972
0.7972
0.7972
0.7972
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.7720
.7720
.7720
.7720
.7720
.6660
.6660
.6660
.6660
.6822
.7114
.7259
.7470
.7972
.7972
.7972
.7972
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.7720
0.6936
0.6936
0.6936
0.6936
1/11/88
-46-
-------
Table 4-9
Low and High Altitude Adjustment Factors for 10% Ethanol
or 3.7% Oxygen Methanol Blends by Model Year and Type: NOx
Ratio of Blend to Base NOx
(3.7% 02, Any RVP)
MY
LDGV
LDGT1
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90+
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
.0380
.0396
.0397
.0397
.0398
.0398
.0420
.0695
.0675
.0712
.0785
.0785
.0781
.0806
.0806
.0806
.0806
1.0380
1.0394
1.0396
1.0395
1.0395
1.0396
1.0396
1.0412
1.0482
1.0523
1.0515
1.0552
1.0605
1.0732
1.0732
1.0732
1.0732
LDGT2
0380
0380
0380
0380
0380
0400
0400
0400
0400
0441
1.0515
1.0552
0605
0732
0732
0732
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1.0732
HDGV
0380
0380
0380
0380
0380
0380
0380
0380
0380
0380
0380
0380
,0380
,0395
,0395
,0395
1.0395
1/11/88
-47-
-------
Table 4-10
Low and High Altitude Adjustment Factors for 3.7\ Oxygen
Methanol Blends by Model Year and Type; Evaporative VOC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
9.0
LDGV
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.9274
.9256
.9256
.9256
.9256
.9256
.9248
.9241
.9209
.9159
.9102
.9002
.8910
.8837
.8797
.8742
.8682
(100% Use of Blend)
psi (matched RVP) 11.5
LDGT1
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9270
0.9270
0.9270
0.9274
0.9267
0.9229
0.9073
0.8857
0.8857
0.8857
0.8857
LDGT2
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9267
0.9229
0.9073
0.8857
0.8857
0.8857
0.8857
HDGV
0.9274
0.9274
0.9274
0.9274
0.9274'
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
0.9274
LDGV
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
9040
9018
9018
9018
9018
9018
9010
9001
8964
8911
8854
8765
8691
8639
8611
8576
8539
psi
(matched RVP)
LDGT1
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
9040
9040
9040
9040
9040
9040
9036
9036
9036
9040
9031
8987
8827
8652
8652
8652
8652
LDGT2
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9031
0.8987
0.8827
0.8652
0.8652
0.8652
0.8652
HDGV
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
0.9040
1/11/88
-48-
-------
Table 4-11
Low and High Altitude Adjustment Factors for 3.7% Oxygen
Methanol Blends by Model Year and Type: Evaporative VOC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
9.0
LDGV
1.0950
1.0990
1.0990
1.0990
1.0990
1.0990
1.1007
1.1024
1.1095
1.1205
1.1332
1.1553
1.1758
1.1919
1.2008
1.2130
1.2263
+ 0.76
LDGT1
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0958
1.0958
1.0958
1.0950
1.0966
1.1050
1.1396
1.1876
1.1876
1.1876
1.1876
(100%
psi RVP
LDGT2
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0966
1.1050
1.1396
1.1876
1.1876
1.1876
1.1876
Use of Blend)
11
HDGV
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
1.0950
LDGV
1.3278
1.3361
1.3361
1.3361
1.3361
1.3361
1.3395
1.3429
1.3570
1.3775
1.3993
1.4339
1.4623
1.4825
1.4930
1.5066
1.5207
.5 + 0.76 psi RVP
LDGT1
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3294
1.3294
1.3294
1.3278
1.3311
1.3481
1.4098
1.4774
1.4774
1.4774
1.4774
LDGT2
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3311
1.3481
1.4098
1.4774
1.4774
1.4774
1.4774
HDGV
1.3278
1.3278
•1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1.3278
1/11/88
-49-
-------
Table 4-12
Low and High Altitude Adjustment Factors for 3.7% Oxygen
Methanol Blends by Model Year and Type; Evaporative VOC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88-
89
90 +
9.0
LDGV
1.0202
1.0208
1.0208
1.0208
1.0208
1.0208
1.0210
1.0213
1.0223
1.0239
1.0258
1.0291
1.0321
1.0345
1.0358
1.0376
1.0395
(50%
Use of Blend)
psi (matched RVP)
LDGT1
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0203
1.0203
1.0203
1.0202
1.0204
1.0216
1.0267
1.0338
1.0338
1.0338
1.0338
LDGT2
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0204
1.0216
1.0267
1.0338
1.0338
1.0338
1.0338
HDGV
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
1.0202
11.5
LDGV
1.1582
1.1616
1.1616
1.1616
1.1616
1.1616
1.1630
1.1644
1.1702
1.1786
1.1876
1.2018
1.2135
1.2218
1.2261
1.2317
1.2375
osi (matched RVP)
LDGT1
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1589
1.1589
1.1589
1.1582
1.1596
1.1666
1.1919
1.2196
1.2196
1.2196
1.2196
LDGT2
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1596
1.1666
1.1919
1.2196
1.2196
1.2196
1.2196
HDGV
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1.1582
1/11/88
-50-
-------
Table 4-13
Low and High Altitude Adjustment Factors for 3.7% Oxygen
Methanol Blends by Model Year and Type: Evaporative VQC
MY
<75
75
76
77
78
79
80
81
82
83 •
84
85
86
87
88
89
90 +
9.0
LDGV
1.2449
1.2525
1.2525
1.2525
1.2525
1.2525
1.2557
1.2589
1.2726
1.2936
1.3178
1.3601
1.3993
1.4300
1.4471
1.4704
1.4959
+ 0.76
LDGT1
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2464
1.2464
1.2464
1.2449
1.2479
1.2639
1.3300
1.4220
1.4220
1.4220
1.4220
(50%
psi RVP
LDGT2
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2479
1.2639
1.3300
1.4220
1.4220
1.4220
1.4220
Use of Blend)
HDGV
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
1.2449
11
LDGV
1.6048
1.6217
1.6217
1.5217
1.6217
1.6217
1.6287
1.6357
1.6645
1.7064
1.7510
1.8217
1.8797
1.9210
1.9425
1.9703
1.9991
.5 + 0.76 psi RVP
LDGT1
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6081
1.6081
1.6081
1.6048
1.6115
1.6463
1.7724
1.9105
1.9105
1.9105
1.9105
LDGT2
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6115
1.6463
1.7724
1.9105
1.9105
1.9105
1.9105
HDGV
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.604.8
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1.6048
1/11/88
-51-
-------
Table 4-14
Low and High Altitude Adjustment Factors for
11% MTBE Blends by Model Year and Type: Exhaust VOC
Ratio of Blend to Base Exh VOC
(2.0% 02, Matched RVP)
MY
LDGV
LDGT1
LDGT2
HDGV
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90+
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.9703
.9266
.9239
.9239
.9211
.9211
.9212
.9565
.9537
.9588
.9690
.9690
.9685
.9719
.9719
.9719
.9719
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.9703
.9321
.9266
.9293
.9293
.9266
.9266
.9174
.9270
.9327
.9316
.9367
.9441
.9616
.9616
.9616
.9616
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.9703
.9703
.9703
.9703
.9703
.9157
.9157
.9157
.9157
.9214
.9316
.9367
.9441
.9616
.9616
.9616
.9616
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.9703
.9703
.9703
.9703
.9703
.9703
.9703
.9703
.9703
.9703
.9703
.9703
.9703
.9299
.9299
.9299
.9299
1/11/88
-52-
-------
Table 4-15
Low and High Altitude Adjustment Factors for
11% MTBE Blends by Model Year and Type: Exhaust CO
Ratio of Blend to Base CO
(2.0% 02, Matched RVP)
LDGV
LDGT1
LDGT2
HDGV
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.8676
.8226
.8198
.8198
.8170
.8170
.8178
.8639
.8602
.8668
.8799
.8799
.8792
.8836
.8836
.8836
.8836
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.8676
.8282
.8226
.8254
.8254
.8226
.8226
.8135
.8259
.8332
.8318
.8384
.8478
.8705
.8705
.8705
.8705
0
0
0.8676
0.8676
0.8676
0.8676
0.8676
0.8114
8114
8114
0.8114
0.8186
0.8318
0.8384
0.8478
0.8705
0.8705
0.8705
0.8705
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8676
0.8260
0.8260
0.8260
0.8260
1/11/88
-53-
-------
Table 4-16
Low and High Altitude Adjustment Factors for
11% MTBE Blends by Model Year and Type: Exhaust NOx
Ratio of Blend to Base NOx
(2.0% 02, Any RVP)
LDGV
LDGT1
LDGT2
HDGV
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90+
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
.0205
.0214
.0215
.0215
.0215
.0215
.0227
.0376
.0365
.0385
.0425
.0425
.0422
.0436
.0436
.0436
.0436
1.
1.
1.
1.
1.
1.
• 1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
1.
0205
0213
0214
0214
0214
0214
0214
0223
0261
0283
0278
0298
0327
0396
0396
0396
0396
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
.0205
.0205
.0205
.0205
.0205
.0216
.0216
.0216
.0216
.0238
.0278
.0298
.0327
.0396
.0396
.0396
.0396
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
.0205
.0205
.0205
.0205
.0205
.0205
.0205
.0205
.0205
.0205
.0205
.0205
.0205
.0213
.0213
.0213
.0213
1/11/88
-54-
-------
Table 4-17
Low and High Altitude Adjustment Factors for
11% MTBE Blends by Model Year and Type: Evaporative VQC
MY
<75
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90 +
9.0
•LDGV
1.0993
1.0969
1.0969
1.0969
1.0969
1.0969
1.0958
1.0948
1.0903
1.0834
1.0755
1.0616
1.0488
1.0387
1.0331
1.0255
1.0171
psi (matched RVP)
LDGT1
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0989
1.0980
1.0989
1.0993
1.0984
1.0931
1.0715
1.0413
1.0413
1.0413
1.0413
LDGT2
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0984
1.0931
1.0715
1.0413
1.0413
1.0413
1.0413
HDGV
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
1.0993
11.5
LDGV
1.0828
1.0797
1.0797
1.0797
1.0797
1.0797
1.0785
1.0772
1.0720
1.0644
1.0563
1.0435
1.0330
1.0255
1.0216
1.0166
1.0114
psi (matched RVP)
LDGT1
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0822
1.0822
1.0822
1.0828
1.0816
1.0753
1.0524
1.0274
1.0274
1.0274
1.0274
LDGT2
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0816
1.0753
1.0524
1.0274
1.0274
1.0274
1.0274
HDGV
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1.0828
1/11/88
-55-
-------
Table 4-18
Adjustments for Emission Factors Associated with Alternate
Fuels CNG, Methanol, and Flexible Fueled 1990+ Vehicles*
Methanol Vehicles
HC Exhaust
CO
NOx
HC Evap**
CNG . :
Vehicles
0.60
0.50
1.40
0.0
0.0
Just Meeting
EPA Emission
Standard
0.66
Emissions
Well Below
EPA Standard
0.17
Intermediate
Emission
Level
0.32
0.68
0.29
0.15
0.07
0.52
0.22
**
Reductions may be claimed only for the periods during which
alternate fuels are used. Factors are for LDGV, LDGT1,
LDGT2, and HDGV.
The first row is for the adjustment factor for comparing to
a 9 psi RVP gasoline fuel while the second is row for
comparison to a 11.5 psi RVP gasoline.
-56-
-------
Appendix A
Formula for Quadratic Interpolation Based
on Different Blend Market Share
-------
A-l
Appendix A
Formula for Quadratic Interpolation
Based on Different Blend Market Share
Use a quadratic equation of the form:
(1) y=Ax2+Bx+C
where y = Evaporative VOC adjustment factor (for
market share other than 0, 50 or 100%),
x = Market share of fuel of interest (0 - 100%),
A, B, C = Coefficients to be determined,
to fit a curve to the three points (0, 50, and 100% market
share) given in the tables in Section 4 for the blend of
interest. This means finding the coefficients A, B, and C for
the model year, vehicle type, and blend of interest. Once these
coefficients are found, the market share of interest (x) for
that blend is put into the equation and the equation is solved
for y, which is the adjustment factor to use for that specific
model year and vehicle type (e.g., MY 1985, LDGV) . This same
procedure then needs to be followed for each model year and each
vehicle type.
Determination of Coefficients A, B, and C
These equations provide an example of how to determine the
coefficients for a case with a 9.0 psi ethanol blend for the
1985 model year, LDGV, which uses adjustment values (x) from
Tables 4-4 and 4-6. In general, values for x for the 50% market
share cases will come from Tables 4-6 or 4-7 for ethanol blends
or Tables 4-12 or 4-13 for methanol/cosolvent blends. For the
100% market share cases values for x will come from Tables 4-4
or 4-5 for ethanol blends or Tables 4-10 or 4-11 for
methanol/cosolvent blends.
As shown in equation (2) below, the adjustment factor for
0% blend market share will always be 1.0, and therefore, the
coefficient, C, will always be 1.0.
(2) 0% market share: 1.00 = A(0)2 + B(0) + C
(3) 50% market .share: 0.9792 = A(50)2 + B(50) + C
(4) 100% market share: 0.8994 = A(100)2 + B(100) + C
To determine A and B, equations (3) and (4) are used, which
means solving two equations with two unknowns (since C is
already known to be 1.0). These can easily be solved by
multiplying each term of equation (3) by 2.0 and subtracting
equation (4) from it, as shown in equations (3a), (4a), and
(5).
-------
A-2
(3a) 1.9584 = A(5,000) + B(100) -I- 2.0
(4a) - 0.8994 = ACI.0,000) + B(100) + 1.0
(5) 1.0590 = -A(5,000) + 1.0*
(5a) A = -1.18 x 10's
The coefficient, B, can then be determined by substituting the
value of A from equation (5a) into equation (3a) and solving for
B. This is shown in equations (6) and (6a).
(6) 1.9584 = (-1.18 x 10'5)(5,000) -I- B(100) + 2.0
(6a) B = 1.74 x 10'4
Determination of Adjustment Factor
Using the values for A, B, and C determined as shown for a
given model year, vehicle type, and blend, the adjustment
factor, y, for any specific market share can be determined. To
continue with the same example using an ethanol blend market
share of 25%:
(7) y = (-1.18 x 10-s)(25)2 + (1.74 X 10-4)(25) + 1.0
(7a) y = 0.9970
Please note that this just gives the evaporative adjustment
factor for model year 1985, LDGV, with a 25% market 'share of a
10% ethanol blend (and 75% market share of oxygen-free gasoline
and/or gasoline-MTBE blends). The same type of calculations
would need to be done for each model year and vehicle type to
obtain factors for use with the modified MOBILES output by model
year.
-------
Appendix B
Commingling Calculations with Nonoxygenated Gasoline and
Two Blends in the Market Simultaneously
-------
B-l
Appendix B
Commingling Calculations with Nonoxygenated Gasoline and
Two Blends in the Market Simultaneously
Tables 4-3 through 4-17 can be used to calculate emission
impacts for any two of the various fuels including gasoline,
ethanol blends, MTBE blends, methanol blends or even all three
oxygenated blends. These tables cannot be directly used to
calculate emission effects of a market situation consisting of
two oxygenated blends with gasoline. The following methodology
must be used instead. Either an ethanol blend or a methanol
blend can be present (along with MTBE and nonoxygenated
gasoline) but not both for this methodology to work.
The market place contains the following fuels.
m% = ethanol blends
n% = methanol blends
p% = MTBE blends
q% = gasoline
where m% + n% + p% + q% = 100% with either m or n
being zero.
It is reasonably assumed that the RVP increase due to
commingling has a negligible effect on exhaust emissions of HC
and CO. Thus, one uses the appropriate factors for exhaust
emissions (linearly adjusted based on market share) from Tables
4-3, 4-8, and 4-9 for HC, CO, and NOx for ethanol or methanol
blends. For MTBE blends Tables 4-14, 4-15, 4-16 are used.
The evaporative emission factor adjustment for the
multi-blend case is more complicated. Basically, the strength
of the commingling effect of the alcohol must be reduced to
account for the fact that commingling with MTBE blends has no
non-linear effects. The overall equation for this calculation
is shown below for an ethanol blend.
E = (m/lOO)(100% gasohol case) + (p/100)(100% MTBE case) +
(q/[p + q])(m% gasohol case -
[m/100][100% gasohol case])
-------
B-2
where ra and p are as given above, the 100% gasohol case is the
adjustment factor given by Table 4-4 and the m% gasohol case
adjustment factor is calculated by the quadratic methodology
described in Section 4 and Appendix A. And, E is the new
adjustment factor for evaporative emissions for a given model
year.
The same general methodology can be used with methanol and
MTBE blends in the market place with gasoline with n% being the
methanol fraction and the 100% gasohol case coming from Table
4-10.
If both ethanol and methanol blends are in the market
place along with MTBE and gasoline, please contact EPA for
appropriate guidance.
-------
Appendix C
Examples of Calculations
-------
C-l
Appendix C
Examples of Calculations
The following examples demonstrate the procedures
described in Appendix D.
Example 1 - Calculate the emission changes from 100% use
of splash blended gasohol with a 12.26 psi average RVP level in
the calendar year 1990.
For this example, some of the work has already been done.
Tables 4-3, 4-5, 4-8, and 4-9 show adjustments to the emission
factors, as calculated for each vehicle type and model year
combination for the case of 100% market penetration of a 10%
ethanol blend with RVP of 12.26 psi and no volatility
adjustment (base gasoline RVP is 11.5 psi.)
The following pages show the special MOBILE3 printout,
which lists emission factors for exhaust HC, CO, NOx, and
evaporative HC for each model year and vehicle class. MOBILES
has already weighted each of these emission factors by the
travel fraction of the model year within the vehicle class. To
perform the hand calculations, the appropriate adjustment
factors are chosen from the tables in Section 4 (i.e., Tables
4-3, 4-5, 4-8, and 4-9) and written to the left of the emission
factors on the MOBILES printout. The multiple of each emission
factor and the appropriate adjustment factor is written to the
left of the adjustment factor. For each column these multiples
are added together, and the sum is written at the bottom of the
column. This value is the adjusted emission factor for all
vehicles in that vehicle class. This process must be repeated
for sixteen combinations of vehicle class and pollutant. The
evaporative and exhaust HC are combined to yield a total HC
emission factor for each vehicle type.
The adjusted emission factors must now be weighted and
recombined with the emission factors of the vehicle classes
which were not adjusted (diesels and motorcycles) to form the
composite emission factor for the fleet. The first page of the
MOBILES output lists the unadjusted emission factors by vehicle
class and the travel fraction weights ("Composite emission
Factors" and "VMT Mix"). To find the adjusted emission factor
of a given pollutant for the whole fleet, multiply the adjusted
emission factor (or unadjusted emission factor, in the case of
motorcycles and diesel fueled vehicles) for each vehicle type
by the VMT mix for that type, and add the results for all types
together.
-------
C-2
Four pages which follow are photocopies of the special MOBILES
output. The results show a 15% increase in non-methane HC (from 2.54
to 2.92 g/mile), a 25% reduction in CO (from 18.19 to 13.71 g/mile),
and 4% increase in NOx.
Example 2 - Calculate the emission changes for the year 2005
which would result from substitution of methanol fueled vehicles for
30% of new sales of gasoline vehicles of all classes beginning in the
1997 model year. These methanol fueled vehicles are designed to have
emissions well below the EPA standards.
Section 3.2.2.3 and Table 4-18 of the report indicate HC
adjustment factors of 0.17 and 0.07 for exhaust and evaporative
emissions for methanol fueled vehicles with emissions well below the
standards. These adjustment factors are applied as described above
but for only 30% of the gasoline fleet beginning starting with the
1997 model year; the emission level for the remaining 70% of the
gasoline fleet remains unchanged. The net adjustments are therefore
0.751 for exhaust.
For evaporative emissions, the emissions of the fleet expected
to exist without methanol substitution should be compared with those
of the fleet which would exist if 30% of all gasoline fueled vehicles
were replaced by dedicated methanol fueled vehicles. The actual
percentages of carbureted and fuel injected vehicles for any model
year are listed in Table 4-1.
For this example, the fraction of the original fleet for any
model year that is composed of carbureted vehicles should, be denoted
as Y while that fraction for fuel injected vehicles would be Z. With
the 30% methanol fueled vehicle substitution, the remaining gasoline
carbureted vehicles would be 0.7 x Y% while it would be 0.3 x Z% for
the fuel injected vehicles. Assuming an 11.5 psi RVP gasoline, the
reference emission levels for these vehicles from Table 4-2 are 0.711
and 0.516 g/mile for carbureted and fuel injected vehicles
respectively. Assuming the methanol fueled vehicles have 93% lower
emissions than the fuel injected vehicles, their reference emission
levels would be 0.036 g/mile.
The ratio of the emissions of the two fleets for model years
1997 and beyond would be as follows.
(0.7xY%) x 0.711 q/mi + (0.7xZ%) x 0.516 q/mi + 30% x 0.036 q/mi
Y% x 0.711 g/mi + Z% x 0.516 g/mi
This ratio of the reference emission levels can be applied to
the actual emission levels in the MOBILES output as the adjustment
factor.
-------
C-3
for LDGV's, Y = 0.11, Z = 0.89
0.7 x 0.11 x 0.711 + 0.7 x 0.89 x 0.516 + 0.3 X 0.036 0.387
= 0.721
0.11 x 0.711 + 0.89 x 0.516 0.537
for LDGT1 and 2, Y = 0.27, Z = 0.73
0.7 X 0.27 X 0.711 + 0.7 x 0.73 X 0.516 + 0.3 X 0.036 0.409
0.27 x 0.711 + 0.73 x 0.516 0.569
= 0.719
for HDGV, Y = 1.0, Z = 0
0.7 X 1 x 0.711 + 0.3 X 0.036
0.711
= 0.715
The rest of the calculations are done as described for the
first example. These results show a 16% reduction in 2005
non-methane HC emissions (from 2.91 to 2.54 g/mile) due to
introduction of these methanol-fueled vehicles.
-------
Calculation example; default fleet with I/M program
I/M program selectedi
Start yaar (January 1)i 1983
Pre-1981 MVR stringency rate: 20%
Mechanic training program?: No
First model year covered: 1951
Last model year covered: 2020
Vehicle types covered: LDGV
1981 & later MYR test typai Idle
1981 & later MVR test cutpolntst 1.2% ICO / 220 ppm IHC
Non<-methane HC emission factors Include evaporative HC emission factors.
Cal. Year: 1990
I/M Program: Yes
Anti-tarn. Program: No
Ambient Temp: 75.0 (F)
Operating Mode: 20.6 / 27.3 / 20.6
Reg 1 on : Low
Altitude: 500.
Ft.
Veh. Type:
Veh. Speeds:
VMT Mix:
LDGV
19.6
0.635
LDGT1
19.6
0. 1 15
LOOT 2
19.6
0.086
LDGT
HDGV
19.6
0.041
UDDV
19.6
0.046
LDDT
19.6
0.021
HDDV
19.6
0.049
MC
A 1 1 Veh
19.6
0.007
Composite Emission Factors (Gm/Mtle)
Non-Math HC: 1.76 4.27 4.85
•Evap HC: 0.72 1.14 1.40
Exhaust CO: 11.77 34.84 37.39
Exhaust NOX: 1.49 2.80 3.01
(rw*
z //
f,?/ IS- H
4.52
1 .25
35.93
89
',J)
6.68
3.58
66.46
5.36
0.39
0.0
1 .32
1 . 10
0.61
0.0
1 .53
1 .28
3.40
0.0
11.11
15. 22
5.77
2.26
19.73
0.85
2.54
18. 19
2.57
C* /J- ^ *
*/«.*•
/«£/"-
''si ,, /.. -I <:.
ft>//0
.~f] ZJa«
^
-------
Product Of Travel Fraction Times The Emission Factor In Grams per Mile
Jan 1. 1990
Exhaust
HC:
SUM:
EvaporatIve
HC:
SUM:
Model
Year
LDGV
LDGT1
LDGT2
O.OOf
Q..J15J
ILJ15JE
JKQ6;
.D.
0.05f
.QJJ4E
_Q.Q5f
fl,_loa
o.oge
JMlBj; JJOt._
0, Q6?
197! .
1 .043
tt^5._.
.1*10
'&£.
0..2.4J
JLJL4S
0.224
0.22E
..Q...19E
_Q. !6£
.(?-?/-
:«i7ll
Q^13£,
._Q.Q8S
Q.Q7C
0.051
6. 10S
3.132
.17..':?.
.//g 0.12
..Q^J .1 2 .
0. 12
a-L3i .
.Z3.7 0.155,
0.!55 .
,7^2 Q_19S ,
.0.27C.
Q. 26C
^.^. ... .0.24i
,.2/j? 0.2651
^f * Q. 23
. /_3i 0. 26£t
Jl^L Q_._22
_Q. 18S
Si^\Sti
L/o.
f
3.45;
. _ J3U23g
-y^r
./?? JLJZfifi
a
HOGV
00
0.324
ilLH 0.304
./1.2
IV
. T.
-------
Product Of Travel Fraction
Times The Emission
Jan 1. 1990
Factor In Grams per Mile
CO:
SUM:
Model
Year
189Q_
_L9B3_
LDGV
0.067
1988 . 0.648._#^
1987 _ 0.764 tUH
1986^ O.B29.'3#7
'985 __- " ~"~ "~ ~~
1984
>983_ Q.722./3.?/
1982 0.658.77/5
J9BJL 0.645,7416?
19BOI 0.52a,*7J^
1979 ._ 1.1
1978."!". l.__ll (
.OSS
LDGT2
.63Z__
,fe77
!sB6!'7y72.' /-i^.. II
.570
2.402,
-2 - 2 7. 2
L1S>1~
LIlL ..
^347,^312
. 523J_57_2._
_ -Z25.2V.7g?
,685.72iy
2.026.7//V_
•ffzz
2.311 fc&iCi
A 773
62,0
3.039.772C
2.5B2 .
2^159
^L.Z.Z
.255
HDGV
0.0 j
i.cnv
4.285.6926
1.1CH
tselL-
3..147.M36
3.2O2./^y^,
/.jLi3_
/.y^/7 .
'•^4-
A$if;i
jf:5
3-882,77XjC
3_^725_
8.772
5.628
4.427
3.828
2-702 _
-? ^46
! =939
L..482 _
.L.1.76.
_J_JH2_
34.838
37.387
0,772
_.JL..524-77*3.
66.479
-2-47Z.
_.
T.. 1 t-l
~-&1lb
(.. 772
. VV/
-------
Product Of Travel Fraction Times The Emission Factor in Grams per Mile
Jan I. 1990
NOX:
SUM:
Model
Year
1990
1989
LDGV
0.02
Q.093',pfQt
'o"~ " -
0. 1.LJ./.0
0. __"
0- IQ7/Q7 SS
6..I03/.QZ»
Q.093/g7/
0.090/5.9/e>2f i iQtL
Q.Q42/.0W&,
iaz4
-19JL3
1972...
Q.026/.g3T4
./
-------
Calculation example; default fleet with I/M progran
I/M program selected:
Start year (January 1): 1983
Pre-1981 MVR stringency rate: 20X
Mechanic training program?: No
First model year covered: 1951
Last model year covered: 2020
Vehicle types covered: LOGV
1981 & later MVR test type: Idle
1981 & later MVR test outpoints: 1.2% ICO / 220 ppm IHC
Non-methane HC emission factors include evaporative HC emission factors.
Cal. Vear: 2005 I/M
Ant 1 -tarn.
Veh. Type:
Veh. Speeds:
VMT Mix:
LDGV
19
0
Composite Emission
Non-Meth HC :
•Evap HC!
Exhaust CO:
Exhaust NOX:
1
0
8
1
.6
.605
Fac tors
. 18
.52
.77
. 29
Program: Yes
Program: No
LDGT1
19
0.
.6
.091
Ambient Temp:
Operating Mode:
LDGT2
19
0.
.6
.089
LDGT
75.0
20.5
HDGV
19
0
.6
.041
(F)
/ 27
.3 / 20.6
LDDV
19
0
.6
.078
Reg i on :
Al t i tude :
LDDT
19
0
.6
.046
: Low
: 500
HDDV
19.
0.
.6
.044
. Ft .
MC All Veh
19
0
.6
.007
(Gm/Mi le)
2.
0
20
1 .
.36
.72
.40
.93
2.
0.
20.
1 .
30
.64
.57
.95
2.
0.
20.
/) ' •
33
68
48
94.
4
2
24
5
. 17
.07
.49
.41
0
0
1 .
1
.42
.0
.37
.03
0
0
1
1
.70
.0
.61
. 16
2.
0
9,
1 1 .
64
.0
.93
.86
5
2
19.
0.
. 77
26
. 71
.85
1 .53
10. 74
.2.01
1.0,5
1.11
3.
l.*1
-------
Product Of Travel
Exhaust HC:
SUM:
Evaporative HC:
Fraction Times The Emission Factor 1n Grams per Mile
Jan 1. 2005
SUM:
Model
Year
2005
2004
2003
2002
2001
2000
1999
1998
1997
T99"6
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
0
0
0
0
0
0
0
0
0
u
0
0
0
0
0
0
0
0
0
0
0
0
0
0
. 0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
LOGV
.007
.038
.050
.057
.061
.061
.058
.054
• 050.75/ -327
. 0*4 ti
.040
.034
.029
.024
.019
.013
.009
.006
.005
.005 A - 2?
-------
Product Oi Travel Fraction Times The Emission Factor In Grants per Mile
Jan I. 2005
CO:
SUM:
Model
Vear
2005
2004
2003
2002
2001
2000
1999
1996
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
LOGV
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
a
070
460
658
766
816
825
783
724
661
594
524
454
383
313
244
176
1 12
080
059
064
768
LDGT1 LOGT2
0
1
1
1
1
0
0
0
0
0
0
0
0
0
20
.341 0.349
.500
.628
.682
.680
.637
.563
.467
.357
.239
.095
.544
.677
.731
.724
.673
.590
.486
.369
.243
.092
.986 0.979
.877 0.866
.768 0.755
.662 0.647
.560 0.544
.472 0.457
.389 0.374
.306 0.293
. 187 0. 179
.396 20.571
HDGV
0
4
3
3
2
2
1
1
1
0
0
0
0
0
0
0
0
0
0
0
24
.0
.074
.571
.056
.585
. 127
. 761
.434
. 153
.926
.753
.596
.483
.373
.310
.241
. 192
. 149
.112
.599
.494
-------
Product Of Travel Fraction Times The Emission Factor in Grams per Mile
Jan 1 . 2005
NOX:
Model
Year
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
19BB
1987
1986
LOGV
0
0
0
0
0
0
0
0
0
0
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
1 .
.022
.096
. 107
.112
.113
.111
. 107
. 101
.093
.084
.075
.065
.055
.045
.035
025
016
Oil
008
008
288
LDGT1
0
0
0
0
0
0
0
0
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
1 .
.043
. 177
. 176
.171
. 164
. 154
. 144
. 132
. 120
. 108
.094
.084
074
.064
. 0!i5
.046
.039
032
025
029
932
LOGT2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.
0.
0.
0.
0.
0.
1 .
.044
. 182
. 181
. 176
. 168
. 158
. 146
. 134
.121
.109
.094
.084
.073
.063
.054
.045
.038
031
024
028
953
HDGV
0
1
0
0
0
0
0
0
0
0
0.
0.
0.
0
0
0
0
0.
0.
0.
5.
.0
.044
.860
. 702
.572
.457
.369
. 295
. 233
185
. 148
. 1 16
.093
.071
.059
.047
.037
029
.021
067
406
SUM:
Comment: Current output unit numbers are IOUREP=6 IOUERR=6 IOUASK=2
-------
Appendix D
Calculation Procedure: Estimating the Effects of
Gasoline/Oxygenate Blend Use on Fleetwide Emissions
-------
D-l
Appendix D
Calculation Procedure: Estimating the Effects of
Gasoline/Oxygenate Blend Use on Fleetwide Emissions
This appendix provides additional details on the method
described in Section 4 and used in Appendix C. The first part
of this covers how the tables of adjustment factors (Tables 4-1
to 4-17) were calculated, and the second covers what is done
with those adjustment factors to calculate the fleetwide effect
of a given alternative fuel scenario. This information can be
used to automate the calculation process, if desired. Readers
choosing to do manual calculations, and not needing to
understand all aspects of how the tables of adjustment factors
were calculated need not read this Appendix.
The process of estimating the effects of
gasoline/oxygenate blends on fleetwide emissions includes two
phases. In the first phase, the planner considers how
emissions of vehicles from each model year and vehicle class
combination within the fleet will be affected by the new
fuel(s). If more than one fuel will be used, then these
effects should account for mixing of the fuels. The planner
must run the special version of the MOBILE3 (named M3.BYMY), or
MOBILE4 when available, to provide specific information about
the emissions of model year/vehicle class combinations within
the fleet when using pure gasoline fuels. The inputs to the
special version are the same as inputs to a standard MOBILES
run, and should represent the best available information
regarding the fleet. The second 'phase of the process involves
the repeated application of four weighting and summation
equations. This phase is suitable for computer processing.
1.0 Phase 1: Effects on Specific Technology/Fuel System Groups
1.1 Defining Technology and Fuel System Groups
A technology group is a group of vehicles whose emissions,
due to similar technology, could be expected to respond in
roughly the same way to -the use of alternative fuels. For
example, a typical gasoline fueled fleet can be divided into
subfleets by exhaust technology; one such group includes
vehicles without catalytic converters, another includes
vehicles with catalytic converters and open loop fuel control
systems, and a third group includes vehicles with closed loop
fuel control systems. This classification is used when
considering the effects of a given fuel on exhaust emissions.
-------
D-2
Another classification divides the fleet into two groups by
fuel system. One group contains the vehicles with carburetors,
and the other group contains vehicles with fuel injection. This
classification will be used when considering the fuel-related
effects of evaporative emissions. The terms, "technology
fraction" and "fuel system fraction" refer to the fraction of
the fleet, determined by sales data, which are part of the
technology or fuel system group. They are represented in
calculations by SFt,myr,cia,s and SFfs,myr; cjass,
respectively.
1.2 Technology-Specific Adjustment Factors
The planner must determine the effect of the alternate fuel
on the exhaust emissions of each technology group within the
fleet. This effect is expressed in terms of a technology
specific adjustment factor (AFt.poi) which will be multiplied
by the average emissions of the indicated pollutant from
vehicles within the group when using pure gasoline to find the
average emissions of the group when using the alternate fuels.
These calculations will proceed under the assumption that
the exhaust emissions from a fleet that is using more than one
fuel will egual the weighted average of the emissions of the
fleet when using the individual fuels (i.e., commingling does
not affect exhaust). For example, consider a fleet that uses
blend A 75% of the time and blend B 25% of the time. If the
closed loop vehicles achieve a 12% reduction (adjustment factor
of 0.88) in CO when operating on blend A and a 4% .reduction
(adjustment factor of 0.96) when operating on blend B, then the
emission change for the whole technology group is calculated as:
AFt,co = 0.75 * 0.88 + 0.25 * 0.96
CO blond = COgasoline * AF t , c o
Table 3-1 lists the adjustment factors for exhaust
emissions of each of the three technology groups when using two
different types of fuel. Note that the adjustment factors for
exhaust are dependent on the oxygen content and RVP of the
blend, and not necessarily on the species of the oxygenate.
-------
D-3
1.3 Fuel System Specific Adjustment Factors
Finding the fuel system specific adjustment factors
(AFfS) for evaporative emissions is more complicated than the
procedure for exhaust. The planner must determine the effects
of the fuels on both hot soak and diurnal emissions from each
technology group. These effects could include commingling if
more than one type of blend is used in the fleet or if blends
and gasoline are used in the fleet. The procedure for finding
the effects of commingling are described in Appendix A. The
effects must be weighted together to find the adjustment factor
for each fuel system group. This weighting process is done by
multiplying the evaporative emissions of vehicles using pure
gasoline by the appropriate adjustment factors (from Tables 3-2
to 3-4 or using a commingling calculation when appropriate),
and calculating the g/mi for both the reference case (pure
gasoline) and the fuel blend case. The equation which relates
hot soak and diurnal emissions in g/test to g/mi emission
factors is:
Evap VOC (g/mi) = 0.0981 * H.S. (g) + 0.0322 * Diurnal (g).
The adjustment factor, AFfs, can be found by dividing
the adjusted g/mi emissions by the reference case emissions.
For example, consider a city in which gasoline has an RVP of
11.5 psi, and which plans to implement a program of 100% use of
a gasohol blend (10% ethanol, no volatility adjustment). From
Table 4-2, the reference evaporative emissions from carbureted
vehicles in this fleet are 4.27 g/test hot soak, .and 9.09
g/test diurnal, yielding a 0.71 g/mi emission factor. From
Table 3-2, the appropriate emission changes for this vehicle
group and this fuel use scenario are +35.28% and +80.1% for hot
soak and diurnal, respectively, which indicate adjustment
factors of 1.353 and 1.801. Applying these adjustment factors:
H.S.biend = 4.27 g * 1.353 = 5.78 g
Diurnalbl.nd = 9.09 * 1.801 = 16.37 g
Evapbl8nd = 0.0981 * 5.78 + 0.0322 * 16.37 = 1.09 g/mi
AFfs = 1.09 / 0.71 = 1.5
1.4 Evaporative Emissions, Gram/Mile Reference Levels
The procedure uses the assumption that exhaust emission
levels from different technology groups within a given model
year and vehicle type are the same when fueled with gasoline.
-------
D-4
This reasonable assumption simplifies later calculations, since
the contribution of a technology group to the total exhaust
emissions of the model year/vehicle type are proportional to
the sales fraction of the group within the model year/vehicle
type.
This assumption is not used in the case of evaporative
emissions, because the evaporative emissions of the two fuel
system groups can be very different. The planner must
determine the relative levels of evaporative emissions (from
the reference case, in g/mi) so that the contribution of the
groups to the evaporative emissions of a given model
year/vehicle type can be determined. These levels are relative
to each other; the calculation procedure which uses them is
not sensitive to the absolute levels. For example, if the
reference levels are actually 0.5 g/mi for the fuel-injected
group and 1.0 g/mi for the carbureted group, then the results
will be the same if the levels are chosen at 2.0 g/mi and 4.0
g/mi, respectively.
One choice of the reference evaporative emission levels
will suffice for the whole fleet. The RVP of the. base fuel
determines which levels should be used. Table 4-2 lists
recommended levels for different fuels of four different
RVP's. If the modelled fleet uses fuel of an average RVP not
listed in Table 4-2, then the levels can be interpolated from
those listed.
2.0 Phase II: Calculations
Phase II of the procedure involves the repeated
application of four equations to the values chosen above, the-
sales fractions of the individual model years, and the output
from the special version of MOBILES (or MOBILE4). This version
of MOBILES lists the emission factors of each pollutant by each
model year of the four gasoline fueled vehicle classes. These
emission factors are already weighted by the travel fraction of
the model year within the vehicle class, so that the sum over
all model years equals the emission factor (on unblended
gasoline) for that vehicle class.
2.1 Adjustment Factors; Exhaust
The first equation finds the adjustment factor,
AFpoi ,myr, c i as s to the base exhaust emissions for each
pollutant, model year and vehicle class. The calculation is a
simple weighting of the technology-specific adjustment factors
by the sales fractions (SFt.myr,ci••«) of the technology
groups within the model year/vehicle class.
-------
D-5
"-C pol,myr, class = w OT t,myr,class AT t , p o 1
key
pol: pollutant indicator; exhaust HC, CO, NOx
class: vehicle class indicator; LDGV, LDGT1,
LDGT2, or HDGV
myr: model year indicator
t: technology indicator; no catalyst, catalyst
and open loop, or catalyst with closed loop
AFt.poi: technology-specific adjustment factor for
indicated pollutant
SFt,myr,ciass: sales fraction of technology group within
model year and vehicle class
AFpoi/myr/ciass : adjustment factor to pollutant of
model year/ vehicle class
This equation must be applied for each of the exhaust
pollutants to each vehicle class and model year.
2.2 Adjustment Factors; Evaporative VOC
The second equation finds the adjustment factor
AFpoi.myr . ciass to the base VOC evaporative emissions. The
calculation is a slightly more complicated weighting of the
fuel system-specific adjustment factors by the reference
emission levels and the sales fractions.
X - & SF fs,myr, class * RL f s
t s
Y = S. SFfs/myr
-------
D-6
Tables 4-1 to 4-17 list the adjustment factors for several
fuel use scenarios which were calculated using this method.
The planner may use these adjustment factors if the expected
fuel scenario in the area of interest fits one of the scenarios
listed.
2.3 Adjusted Emission Factors, by Model Year
Now that the adjustment factors have been determined for
all pollutants, model years, and relevant vehicle classes, the
planner must apply them to the emission factors listed by
M3.BYMY. M3.BYMY has a special section of output which lists
emission factors of exhaust HC, CO, and NOx, and evaporative HC
by model year for four gasoline-fueled vehicle classes. These
emission factors have already been weighted by the appropriate
travel fractions, and the sum of these values within a given
vehicle class equals the composite emission factor for that
class when using pure gasoline. To find the composite emission
factor for the class when using alternative fuels, the planner
multiplies each of the emission factors listed by the M3.BYMY
model by the adjustment factor for that pollutant, model year
and vehicle class, and sums the results within each vehicle
class as follows:
pol, class ~" C* -tJ-t pol,myr,class At pol.myr, class
my r
key:
myr: model year indicator
class: vehicle class indicator, LDGV, LDGT1,
LDGT2, HDGV
pol: pollutant indicator, in this eguation
indicates all four pollutants
EFpm ,myr. class emission factor listed by M3.BYMY model for
each pollutant, model year, and vehicle
class
AFpoi,myr,ciass adjustment to emission factor of indicated
pollutant from model year/vehicle class
CEFpoi.cias« emission factor of indicated pollutant for
given vehicle class after adjustment for
alternate fuel scenario
2.4 Fleetwide Emission Factors
The last step in the calculation procedure finds the
fleetwide emissions when the alternate fuels scenario is in
effect. This calculation is similar to the one which MOBILES
uses to weight by VMT mix and add together the vehicle class
emission factors, except that the original vehicle class
-------
D-7
emission factors for the four affected vehicle classes are
replaced by the new factors. The VMT mix and the original
emission factors by vehicle class are listed in the output of
M3.BYMY. The following equation summarizes the final step:
FEFpol = &
class
key:
pol: pollutant indicator, includes all four
pollutants
class: Vehicle class indicator, includes all eight
vehicle classes
CEFp0i,ci»,,: emission factor of indicated pollutant by
vehicle class, use values calculated in
earlier procedure for LDGV, LDGT1, LDGT2, and
HDGV classes, otherwise use values from
M3.BYMY output
VMTcla».: travel fraction of vehicle class within
fleet, as listed in model output
oi: fleetwide emission factor of indicated
pollutant
------- |