AIR QUALITY BENEFITS OF ALTERNATIVE FUELS
Prepared for the
Alternative Fuels Working Group
of the
President's Task Force on Regulatory Relief
July 1987
Office of Mobile Sources
OfHce of Air and Radiation
Environmental Protection Agency
-------
Table of Contents
I. Introduction and Background 1
A. Health and Welfare Impacts
(Ozone and Carbon Monoxide) 1
B. Contribution of Mobile Sources 2
II. Attainment Status and Projections ............ 3
III. Air Quality Impact of Alternative Fuels ......... 3
A. Vehicle Emission Effects .............. 3
1. Methanol .................... 4
2. Compressed Natural Gas ............. 8
3. Oxygenated Blends: Ethanol .
Methanol, MTBE ................. 10
B. Potential Impact on Attainment ............ 11
1. Overview .................... 11
2. Methanol Vehicle Scenario - Current
Technology (1991-1995) ............. 12
3. Methanol Vehicle Scenario - Advanced
Technology (1995-2000) ............. 13
4. Methanol Vehicle Scenarios
(Steady State) ................. 14
5. Oxygenated Blends Scenario .......... 15
-------
I. Introduction and Background
This paper s inarizes EPA’s current best esti ates of the
potential for a ].: quality improvements available if various
alternative fuels scenarios were implemented. Inc ded in this
evaluation are methanol (for current technology,
flexible—fueled, a-.d advanced technology venicles). compressed
natural gas (CNG), and blends of gasoline w::h ethanol,
methanol, a d met:y1 tertiary butyl ether (MTBE). The primary
air quality conce:ns relate to ozone and carbon mc oxide (CO);
thus the mczor vehicle pollutants which receive rr:st emphasis
here are voaatile ::ganic compounds (VOCs) and CO.
A. Health and Welfare Impacts
The Naziona Ambient Air Quality Standard (N QS) for
ozone is presently a maximum one hour level of 0.12 ppm, not to
be exceeded more than three times in a three-year period.
Several fac:ors we:e cited as a basis for settinc the current
ozone standard. .rnong these were: (1) ozone is a pulmonary
irritant that affeots respiratory mucous me .branes as well as
other lung tissue and impairs respiratory function at levels as
low as 0.15 pm fc: exercising persons, (2) elevated numbers of
asthma attacks c::ur when peak hourly ozone c: centrations
reach about 0.25 :=i, (3) increased susceptibility to bacterial
infection is noze± in laboratory animals exposed ozone plus
a bacterial cha1.e ge , (4) premature aging symptc s have been
reported in rabb::s, (5) apparent synergistic effe:zs exist on
pulmonary f nCtic from exposure to 0.37 ppm ozone and 0.37 ppm
sulfur diox:de, a:..d (6) the adverse health effe:: threshold
could not be iden::fied with certainty. Since the ozone NAAQS
standard was esta iished in the late 1970s, a r ther of new
health stud:es ha.-e been completed conE irr:ng t.tese earlier
findings and show: g that alterations in pui onary function can
occur for healthy adults and children during exerc:se at levels
as low as 0.12 EPA is presently reviewin; these new
studies and deter=:ning whether a change should be :roposed for
the ozone standa:d. The EPA Science Advisor : Board has
supported a EPA staff recommendation that a rev:sed one hour
ozone standard be somewhere in the range of 0.08 :0 0.14 ppm
based on th:s new :nformation.
In add::ion :o these health effects, ambie : ozone has
been shown to case crop yield reductions, forest Injury, and
damage to ma:eria.s such as rubber and dyes. There s no known
threshold for these welfare effects.
The N QS for carbon monoxide (CO) was estab .:shed in 1971
as a 9 ppm eight hour average and 35 ppm one hour average not
to be exceeded r::e than once a year. In 1980, ?A proposed
retaining the ei h: hour standard and tightening :ne one hour
-------
—2--
standard to 25 ppm but this proposal has not been finalized.
The 1971 NAAQS was based on work showing 2 to 3 percent
carboxyhemoglobin (which is the product formed froci reaction of
carbon monoxide absorbed into the lungs and hemoglobin which
carries oxygen in the blood stream) impairs the ability to
discriminate time intervals by affecting the central nervous
system. Since then. further work has shown this type of effect
occurs only at higher carboxyhemoglobin levels.
However, newer studies (some of which have been recently
disputed) show that 2.7 to 3 percent carboxyhemcglobin levels
shorten the time before the onset of pain for heart patients
with angina pectoras (a heart disease associated with decreased
oxygen to the heart). A 1984 EPA reevaluation of available
health information indicates that chronic angina patients (who
are presently viewed as the most sensitive group for carbon
monoxide exposure) show aggravation of pain at levels of 2.9 to
4.5 percent carboxyhemoglobin. Based on this evidence, EPA has
decided to retain the present carbon monoxide NAAQS although
high priority has been given to obtain additional data on
angina patients so that the NAAQS can be reevaluated as needed;
EPA expects to be able to propose any necessary changes in the
carbon monoxide NAAQS based on the new angina studies in about
3 years.
Other groups at risk for carbon onox:de exosure include
fetuses and young infants, the elderly (especially those with
compromised cardiopulmonary functior.s), younger individuals
with severe cardiac or respiratory disease, and individuals
with genetically unusual forms of hemoglobin that affect oxygen
carrying capacity.
B. Contribution of Mobile Sources
Since alternative fuels strategies would pr:narily affect
notor vehacle emissions, it is important to estimate the
magnitude of the emissions contribution of motc: vehicles to
overall urban emissions under likely scenarios. For CO, more
than two thirds of all emissions today come from rotor vehicles
(see Figure 1); for many urban areas the percentage is 80
percent or more. This fraction will continue to decrease in
the foreseeable f iture as the current Federal otor Vehicle
Control Program (FMVCP) reduces CO from motor venicles. since
new r vehicles em:t CO at much lower levels :nan the older
vehicles they are replacing.
For VOC (and hence ozone), motor veh:cles play a
significant role, although somewhat smaller than for CO (see
Figure 2). As Table 1 shows, the mobile source VOC emission
fraction also varies considerably from city to caty. As with
CO. the VOC mobile source fractions will decline in the near
term as newer, cleaner cars replace older ones. in any event,
the contribution of vehicles to overall VOC at any given time
is a key factor n assessing the potential impact of local or
national fuel—based emission control programs.
-------
—3—
II. Attainment Status and Projections
Non—attainment of the National Ambient Air Quality
Standards (NAAQSs) for ozone and CO is widespread and,
especially for ozone, is likely to remain so into the
foreseeable future. Figures 3 and 4 show how average ambient
CO and ozone levels, respectively 1 have exceeded the NAAQSs in
recent years. For ozone, 76 areas are currently in violation
of the standard, 11 of which are in California. For CO. 81
areas are in violation, 10 in California. Tables 2 and 3
present for the 30 most seriously affected cities for each
pollutant the 1983—1985 air quality design values and the
emission reduction required for attainment.
EPA has projected how emission control programs currently
in place or in the process of being implemented will affect the
status of ozone and CO non—attainment. Table 4 shows projected
numbers of non—attainment areas for the base year and for 1990,
1995, 2000, and 2010.
It can be seen from Table 4 that while the magnitude of
the non—attainment problem is similar for both ozone and CO at
the present time, projections of future non—attainment for the
two pollutants diverge substantially. The CO attainment
situation is expected to improve significantly through the end
of the century due primarily to fleet turnover, as new vehicles
with low CO emission factors continue to displace older
vehicles with much higher emission factors. We expect that by
1995 approximately 80 to 90 percent of the urban areas now in
non—attainment for CO will move into attainment. In
comparison, less than half of the urban areas now in
non—attainment for ozone are projected to comply by 1995. Of
even greater concern is the fact that, as Table 4 shows, the
ozone non—attainment problem is expected to begin to worsen in
the late 1990s. There are several reasons for this: 1) the
relative improvement due to newer vehicles is less for VOC than
for CO; 2) vehicle miles traveled in urban areas is expected to
continue to increase in the future, thus of fsettirTg and at some
point overwhelming the reduction in the emissions of each car;
and 3) it is expected that VOC emissions from stationary
sources will increase due to general economic growth.
III. Air Quality Impact of Alternative Fuels
A. Vehicle Emissions Effects
Table 5 presents EPA’s estimates of potential reductions
in VOC, CO, and NOx emissions for several types of light—duty
vehicles operating on methanol, CNG, and oxygenated blends.
These are per—vehicle estimates and appear as comparisons to
gasoline vehicles meeting current EPA emission standards. For
this analysis EPA assumes that light—duty gasoline trucks
operated on alternative fuels would exhibit similar emission
reductions.
-------
—4—
1. Methanol
Methanol has long been considered to be an excellent motor
vehicle fuel. Its simple molecular structure, high octane,
wide flammability limits, high flame speed, and low flame
temperature result in a fuel that can be burned in a very clean
and efficient way relative to petroleum fuels. Interest in
methanol vehicles has grown significantly in the last few
years, and several vehicle demonstrations are in progress
throughout the United States. Because methanol is such a
different (and generally superior) fuel than gasoline, it is
helpful to distinguish between two types of methanol vehicles
—— current technology and advanced technology methanol vehicles.
Current technology methanol vehicles utilize engines that
are very similar to engines used in today’s gasoline vehicles,
with modifications to allow the engine to operate well, but not
optimally, on a blend of 85 percent methanol, 15 percent
gasoline (M85). These are the types of methanol vehicles
currently involved in demonstration programs, and these
vehicles would have emissions and efficiency characteristics
very similar to flexible fuel vehicles (FFVs) when FFVs are
operated on M85. Such vehicles generally have emissions
similar to those of gasoline vehicles, with the primary
difference being the reactivity of the VOC emissions (this will
be discussed in much greater detail later in this section).
Because methanol has a low flame temperature, it has been
claimed that current technology methanol vehicles should reduce
NOx emissions. We do not believe this to be the case. Vehicle
emissions are a function of many factors, including fuel type,
engine type, emission control system design, etc. With current
NOx emission standards, manufacturers will likely trade off
methanol’s low—NOx characteristic to gain other benefits such
as fuel economy, performance, or a less expensive catalytic
converter.
Advanced technology methanol vehicles would be designed
and optimized specifically for methanol fuel. Such an engine
should include, at minimum, high compression, lean combustion,
advanced fuel injection, and an emission control system
optimized for formaldehyde reduction. From an emissions
perspectives the most interesting aspect of methanol fuel is
its potential to operate successfully under lean burn
.conditions. Gasoline engines cannot operate at high air—fuel
ratios both because of engine misfire and because of high NOx.
emissions (the NOX reduction function of the catalytic
converter cannot operate well at high exhaust oxygen levels).
Methanol’s fuel properties suggest that methanol can operate at
very lean conditions while still maintaining good
driveability. If NOx emissions can be maintained below EPA
standards without catalytic reduction, then significant
benefits in terms of fuel consumption and Co emissions can be
achieved through lean combustion. Again, however, we believe
-------
—5—
that there will not be NOx benefits with advanced technology
methanol vehicles, although it is methanol’s low—NOx
characteristic that permits lean combustion with corresponding
Co and fuel economy benefits.
With regard to VOC emissions, estimating potential
reductions is complicated by the fact that the composition of
methanol VOC emissions is fundamentally different from that of
gasoline vehicles. In its August 29, 1986 Notice of Proposed
Rulemaking to establish emission standards for methanol
vehicles, EPA has considered this problem in detail and
determined that the organic compounds of primary concern are
methanol, formaldehyde and non—oxygenated hydrocarbons (HC).
With gasoline vehicles, the organic compounds are primarily
non-oxygenated HC. As mentioned previously, the various
components of methanol vehicle organic emissions have differing
tendencies to form ozone; that is, different degrees of
reactivity. Thus, in order to evaluate the potential ozone
reductions associated with methanol vehicles, EPA has developed
a methodology for estimating the relative reactivities of the
different emission components and using them to weight the
expected emissions. The weighted sum can be compared to the
organic emissions of a gasoline vehicle. The resulting ratio
represents the ozone—producing potential of a methanol vehicle
relative to that of a gasoline vehicle.
This type of analysis has two key elements. First,
atmospheric photochemistry modeling is required in order to
develop reactivity factors for the relevant emissions. Second,
emission factors must be estimated. The following discussion
presents these analyses as well as important caveats that must
accompany their use. It must be emphasized that this
methodology presented below is still under development and
should be considered very preliminary at this time.
a. Relative Reactivity
Various methods can be used to characteriZe ’ the relative
reactivities of organic compounds. One common approach is to
measure the reaction rates of the organic compound of interest
when introduced into a chamber containing one or two common
atmospheric reactants such as hydroxyl radicals or NOx. This
approach is often useful for ranking organics in terms of
reactivity but may be less reliable when attempting to
establish a more absolute quantification of a compound’s
reactivity in a real urban environment.
Within the last few years several computer simulation
studies have been performed to model the effect of mobile
source methanol fuel substitution in a number of urban areas.
These studies simulate the air chemistry and transport within
the urban area, and account for the entrainment and dilution of
local pollutant inventories into the airshed. It should be
noted that none of the studies actually utilized emission
-------
—6—
factors for methanol vehicles which EPA believes to be wholly
consistent with the available data base, nor did they model
substitution scenarios for methanol vehicles similar to the
scenarios developed for this document, as presented in Section
IV.B. below.
It is also extremely important to bear in mind that the
reactivity factors will vary not only city—to—city, as the data
in Table 6 demonstrate, but also within a given city from day
to day. This is because the chemistry of ozone formation is
sensitive to changes in the makeup of the pollutant inventory,
variations in the boundary and aloft conditions (related to
inter—city transport), shifts in the wind field (the less wind,
the less flushing of the airshed, the higher the local
pollutant concentrations, and the more ozone is likely to be
formed), solar intensity, and numerous other transient factors.
EPA is not confident that the available modeling base is
sufficient to adequately characterize methanol and formaldehyde
reactivity on a national average; a city specific
characterization is even more problematic. Great care must be
exercised in using the results from past modeling as the basis
for regulatorily binding decisions which presume environmental
effects that may or may not actually occur.
Nevertheless, the data may and should be used to evaluate
relative policy options. EPA therefore has analyzed the
results of these studies and developed reactivity factors from
them for each relevant pollutant. To date, three modeling
studies have been performed which can be used in the desired
fashion. One study modeled the Los Angeles airshed, under
contract for ARCO and other companies. Another study modeled
the Philadelphia airshed, under contract for EPA. Finally,
Ford Motor Company did a study which, though less detailed than
the previous two, considered methanol substitution in 20 ozone
non—attainment cities. Using the results of these studies, EPA
has developed reactivity factors for methanol and formaldehyde
relative to non—oxygenated HC. These factors are presented in
Table 6.
b. Emission Factors——Current Technoloqy Methanol
Vehicles
Emission testing has been performed on many different
prototype methanol vehicles by a number of different
organizations. EPA has evaluated the methodology used by these
organizations and, as appropriate, included the data in a
master data base. This data base was discussed briefly in the
Regulatory Support Document that accompanied the Notice of
Proposed Rulemaking (NPRM) for methanol vehicle emission
standards. Since that time the data base has been expanded and
will be presented in detail with the Final Rule. For the
purposes of this discussion only the relevant details of the
analysis are presented.
-------
—7—
To develop exhaust emission factors for methanol vehicles,
the following approach was used. EPA proposed and will likely
finalize Co and NOx standards for methanol vehicles equivalent
to those for gasoline and diesel vehicles. Therefore, the data
base was sorted to pull out all emission tests where CO and NOx
met the current standards. For these vehicles, a typical ratio
of methanol to formaldehyde was established. A methanol to
hydrocarbon ratio was developed using much more limited data
(the HC measurement techniques used by most researchers to date
were found inappropriate for EPA’s purposes). These ratios
were then applied to the proposed organic emission standards
for methanol vehicles in order to determine likely
certification exhaust emissions of methanol, formaldehyde, and
HC (the proposed standards allow roughly the same amount of
carbon to be present in methanol vehicle VOC emissions as is
allowed by current standards for gasoline and diesel HC
emissions). In order to estimate in—use exhaust emissions of
methanol vehicle VOCs, offsets were developed based on the
in—use performance of gasoline vehicles. A similar procedure
was used with regard to evaporative emissions, both for
carbureted and fuel—injected engines. The resulting in—use
exhaust and evaporative emission factors are given in Table 7.
The present analysis accounts for refueling emissions
based on very recent and as yet unpublished test data performed
by EPA’S Office of Research and Development (ORD). This
testing involved only one methanol veh.cle. The results are
given in Table 7 and assume that no refueling controls are
applied to 49—state methanol vehicles and that refueling
controls in California are as effective for methanol vehicles
as for gasoline vehicles (86% control efficiency is assumed).
c. Emission Factors——Advanced Technology Methanol
Vehicles
As mentioned earlier, there is great potential for
emissions and efficiency benefits with engines designed and
optimized for methanol fuel. The data for vehicles
representative of this future technology are extremely
limited. The one prototype vehicle that incorporates many of
the potential design features of an advanced technology
methanol vehicle is a Toyota Car:na that is currently
undergoing evaluatipn by EPA. Thus, the emission factors given
in Table 7 are based on engineering judgment as well as
preliminary test results from the Carina obtained by both
Toyota and EPA. In general, methanol-optimized technology is
expected to lower the overall mass of organic emissions and to
selectively lower formaldehyde levels. Additionally, these
vehicles must operate on pure methanol (M100) in order to
achieve the maximum environmental benefit. With M100 ,
relatively less HC (which is related to fuel gasoline content)
and more methanol are found in the emissions. The numbers
given in Table 7 reflect these effects. With regard to
-------
—8—
evaporative emissions, the estimates are based on the
assumption that all organic evaporants are methanol (since
there is no HC in the fuel) and that the vehicles emit only the
equivalent of 1.0 gram per test, which is half of the standard
currently applicable. Refueling emissions are again based on
the recent ORD test of only one vehicle, this time operated on
MlOO.
2. Compressed Natural Gas (CNG )
Compressed natural gas (CNG) consists primarily of methane
thit also contains smaller quantities of other compounds such as
ethane and propane. Sharing many of the same fuel
characteristics of methancl (simple molecular structure, high
octane, ability to combust under lean conditions, etc.) 1 CNG
has long been considered to be an environmentally attractive
engine fuel. Two characteristics of CNG distinguish it from
methanol. The most obvious difference is that CNG is a gaseous
fuel. This is an advantage in that it is an excellent cold
starting fuel, and thus has the potential to significantly
reduce cold start emissions. Its gaseous nature also poses
problems however, in that it is much more difficult to store
large amounts of energy onboard the vehicle, and engine power
output is usually decreased. A second difference is CNG’s
relatively high flame temperature 1 which results in relatively
high NOx emissions. This characteristic makes the possibility
of a high compression 1 lean burn CNG engine which could meet
stringent NOx standards without the aid of a NOx reduction
catalyst more difficult than for methanol (such catalysts are
not effective under the high-oxygen regime of lean burn
combustion). As with methanol, it is helpful to distinguish
between near—term current technology and the potential for
optimized 1 advanced technology CNG vehicles.
a. Relative Reactivity
Since methane is the primary component of CNG fuel, a high
percentage of the fuel—related emissions from CNG vehicles is
methane. Test data from EPA and Ford suggest that typically
between 80 to 90 percent of the hydrocarbon emissions from CNG
vehicles are methane, with small amounts of ethane, propane,
and other hydrocarbon compounds. Methane has long been
considered to be photochemically nonreactive, so much so that
•the California Air Resources Board permits vehicle
manufacturers to certify to noninethane hydrocarbon standards
and EPA has proposed such standards inthe past, though the
change was not finalized. Since the relative reactivity of CNG
vehicle exhaust has not been modeled as extensively as that of
methanol vehicle exhaust, the practice has been to assume that
the methane component of CNG emissions has zero reactivity
while the remaining hydrocarbons have an overall reactivity
similar to gasoline vehicle hydrocarbons. Though this
methodology is rather simplistic 1 it has been widely practiced
and will be used in this analysis as well.
-------
—9—
b. Emission Factors——Dual—Fuel Retrofit CNG
Most of the vehicles currently operating in the U.S. on
CNG fuel are gasoline vehicles retrofitted with a conversion
kit to allow the vehicles to operate on either CNG or
gasoline. It is very difficult to estimate the overall
emissions impacts of such vehicles for several reasons:
1) there has been little reliable emission testing performed,
particularly on conversions of recent computer—controlled
vehicles, 2) the performance of conversion kits can vary
greatly depending on kit manufacturer, the expertise of the
installer, the quality of maintenance, etc., 3) the fact that
the vehicle can operate on either CNG or gasoline means that
overall emissions depend on the fuel that is actua]ly used, and
4) the conversion process itself sometimes interferes with the
gasoline combustion process leading to increased emissions on
gasoline. It should also be obvious that an engine that must
be able to operate on fuels as different as CNG and gasoline
cannot be optimized for either fuel.
EPA has recently examined emissions data from dual—fuel
CNG retrofit vehicles tested by the California Air Resources
Board, Colorado Department of Health, the Canadian Ministry of
Energy, Mines and Resources, as well as EPA. As might be
expected in view of the caveats listed above, there is
considerable scatter in the data. Nevertheless, there are
clear trends in the data, and ranges for likely emission
impacts compared to gasoline vehicles are shown in Table 5.
Nonxnethane exhaust HC were typically 40 to 60 percent lower,
which when combined with zero evaporative and refueling HC,
lead to overall VOC reductions of 50 to 80 percent compared to
gasoline vehicles. CO emissions were typically between 50 and
90 percent lower on CNG. NOx emission impacts of CNG fueling
are auite variable, :anging from small decreases to large
increases. It should also be noted that there are usually
significant power losses associated with dual—fuel CNG retrofit
kits, as well as somewhat reduced energy efficiencies.
c. Emission Factors —— Advanced Technology CNG
As with methanol, it is possible to take full advantage of
CNG’s fuel properties only by utilizing it in engines dedicated
and optimized for its use. To date there has been very little
work done to identify the proper design of such an engine, so
the overall emissions impacts are very speculative. The
primary issue that needs to be addressed is whether it will be
possible to reap the CO and efficiency benefits of high—
compression/lean—burn operation while maintaining NOx emissions
within acceptable levels (again, the NOx reduction part of the
catalytic converter would not be effective under lean burn
conditions). CNG, with a high flame temperature, faces a more
difficult task in this regard than methanol (which is an
inherently low—NOx fuel due to its low flame temperature).
-------
—10—
Ford Motor Company has built several dedicated CNG Ranger
pickup trucks that are being operated by gas utilities
throughout the country. Ford’s zero—mile emission data showed
a 40 percent decrease in exhaust HC, a 99 percent decrease in
CO, and an 80 percent increase in NOx emissions. The NOx
emissions level of 1.96 grams per mile was still slightly below
the applicable light—duty truck NOx standard of 2.3 gpm, but
beginning in 1988 the light-duty truck Wax standard drops below
that value. Thus, it is still unclear whether NOx levels will
be a problem on advanced technology CNG vehicles. EPA is
currently in the process of obtaining a high-mileage CNG Ranger
for emissions testing. For the time being, Table 5 asswnes
that advanced technology CNG vehicles will have emissions
characteristics similar to those of dual—fuel vehicles when the
latter are operating on CNG.
3. oxygenated Blends
EPA’S estimates of the emissions effects of switching
gasoline vehicles to various oxygenated blends are also
presented in Table 5. The VOC estimates were developed by
modeling all the factors that affect hydrocarbon emissions
(evaporative emissions, exhaust emissions, and the effect of
commingling of fuels when straight gasoline and a blend are
mixed in—use), summing these factors, and applying reactivity
weightings so that all results appear on an ozone—eqi.iivalent
basis.
co reductions are estimated on the basis of tests
collected on vehicles tested at low and high altitudes. The
high—altitude data on non—catalyst and open—loop vehicles,
developed by the Colorado Department of Health, are similar to
the available low—altitude data; EPA has chosen values
representative of the entire body of data. The closed—loop
reduction presented 1 however (10 percent for a 3.7 percent
oxygen fuel), is smaller than the test data indicated.
Colorado and EPA have reduced that value to reflect the fact
that theory and very limited test data ind .cate that the CO
benefit may actually be less if the recently-introduced
“adaptive—learning” closed—loop technology becomes widespread
(such systems are designed to optimize the individual vehicle’s
operation for the specific climate, altitude, and usage
patterns theoretically reducing the potential CO reductions
•available from blends to near zero). While older vehicles
operated at high altitude emit more CO than at lower altitudes-
(the thinner air causes a richer air—fuel mixture), the
percentage reduction available through blend usage is about the
same regardless of altitude.
The estimated NOx increases were developed by EPA from the
low—altitude data that were a part of the data base f or the CO
reduction estimates above.
-------
—11—
The potential improvement in Co emissions over straight
gasoline that would result from the use of blends in current
gasoline vehicles could be significant. However,
ozone—equivalent VOC emissions show’no clear benefit; if they
were sold at a Reid Vapor Pressure (RVP) higher than for
gasoline during the summer, ethanol and methanol blends would
cause considerably more ozone. NOx emissions are worse in all
scenarios.
B. Potential Impact on Attainment
1. Overview
In order to analyze how the current ozone and Co
attainment situation might respond to large scale alternative
fuel initiatives, EPA has defined and evaluated three major
scenarios.
a. Methanol Scenarios
In the first two scenarios a significant number of
methanol-fueled passenger cars and light-duty trucks would be
introduced into three urban ozone non—attainment areas——Los
ngeles , New York, and Washington, DC. Fleetwide composite
emission estimates are made for the short—term (assuming
current technology and flexible—fueled vehicles) arid in the
longer term (assuming advanced methanol technology). The
analysis then translates the emission estimates into overall
estimates of how ambient ozone levels would be affected.
Since, as stated above, compressed natural gas (CNG) vehicles
would probably have ozone—equivalent VOC emissions falling
somewhere between current technology/FFV methanol vehicles and
advanced technology methanol vehicles, qualitative conclusions
about CNG vehicles can also be drawn from this analysis.
In these methanol—vehicle scenarios, the effect on ozone
is roughly proportional to the number of methanol vehicles
assumed to be introduced in an area. Therefore, in order to
translate potential per—vehicle VOC reductions into percent
ozone reductions in an area, EPA needed to make assumptions of
how many methanol vehicles might be introduced into an area
each year, and for how many years this replacement would
occur. In the current technology/FFV scenario, introduction of
vehicles begins iii 1991 (the earliest prcjected date for
vehicle availability of any manufacturer) and continues through
1995; advanced technology vehicles would require additional
time for development and are assumed to be introduced from 1995
through the year 2000. Methanol vehicles are assumed to
replace all fleet vehicles first, with the remainder replacing
vehicles in general use. Table 8 presents the numbers of
vehicles assumed to be replaced each year and the total number
reached by 1995 and by 2000.
-------
—12—
Based on a comprehensive 1978 study of U.S. vehicle
distribution, EPA has estimated that there are 80,000 vehicles
sold each year in Los Angeles for use in vehicle fleets of 10
or more vehicles (very small fleets would not be any more
likely to utilize alternative fuels than general public
vehicles). For the New York and Washington areas, fleet
vehicles assumed to be replaced annually are estimated as
proportional fractions of the total vehicle populations of
those cities.
b. Blend Scenarios
The final scenario evaluated by EPA for this paper
estimates the effect of mandating oxygenated blend usage in two
Co non—attainment areas, one at low altitude (Phoenix) and one
at high altitude (Denver). Unlike the methanol vehicle
scenarios, in which only a segment of the vehicle population is
assumed to use an alternative fuel, in this blend scenario all
gasoline vehicles in an area would switch to blend fuels. This
distinction means that the per-vehicle CO reductions in Table 5
can be converted into estimates of fleetwide effect much more
directly than could the methanol vehicle reduction numbers.
The single analytical step required is to estimate the fleet
mix of emission control technologies that would exist in a
given year (non—catalyst, open-loop 1 and closed loop) and
weight the effect of each type of vehicle if it were to switch
to oxygenated blends.
Another way in which the blends scenario differs from the
methanol vehicle scenarios is that while new fuels could be
introduced sooner than could new vehicles, the largest Co
reductions would only be available for the relatively near
future. As suggested in the discussion of CO attair r ent above,
most of the reduction in CO would come from older vehicles,
which are steadily being replaced by much cleaner closed—loop
vehicles. For this reason, the blends scena:io focuses on CO
reductions in the near term —— 1990 and 1995 (as well as for a
future date when the entire fleet has turned over to
closed—loop vehicles —— probably between 2000 and 2010).
2. Methanol Vehicles Replacing Gasoline Vehicles—
( 1991—1995 )
In this scenario, significant numbers of current
technology methanol light—duty vehicles •and light—duty trucks.
(and/or flexible—fueled vehicles operating on M85) would
replace gasoline fleet vehicles as well as some vehicles in
general use in the New York, Washington, DC. and LOS Angeles
metropolitan areas. EPA’s analysis of the effect on ozone
levels of such a replacement of gasoline vehicles with methanol
vehicles is calculated from composite projections for future
years of gasoline vehicle emission performance and of expected
annual vehicle miles traveled (WIT). Fleet vehicles are
-------
—13—
assumed to average 33,000 miles per year (taken from DOT
figures that are on the high end of available estimates), while
vehicles in general use are assumed to average 13,000 miles per
year (from EPA’S MOBILE3 data base for light—duty vehicles and
light—duty trucks in their early years of use).
An estimate of the VOC effect of using methanol vehicles
to replace gasoline vehicles can be derived for each city from
the per—vehicle emission factors in Table 7, and the
city—specific reactivity factors from Table 6 (New York’s value
was approximated by averaging the values for Boston,
Philadelphia, Baltimore, Scranton, and Allentown). The VOC
effects for each city can be applied to city—specific voc
inventory projections for a specified year——1995 in this case.
In this way different motor vehicle VOC fractions are
incorporated for each city. For the New York and Washington
area estimates, fleetwide composite emission factors and
projected VOC inventories developed by EPA were used; for the
Los Angeles area estimate, EPA used California Air Resources
Board emission factors and inventories. The results presented
in Table 9 are percent reductions in. total
mobile—plus—stationary source VOC emissions on an
ozone—eqi.iivalent basis. Because of the ozone equivalence,
these estimated reductions can also be interpreted as percent
reductions in the ambient ozone levels expected in each city.
For comparison. Table 9 presents results for the case in which
the only vehicles that were replaced with methanol vehicles
were those sold to centralized fleets of 10 or more vehicles,
as well as for a broader case including a number of general use
vehicles.
3. Methanol Vehicles Replacing Gasoline Vehicles
( 1995—2000 )
The second scenario is similar to the first but is
designed to evaluate the effect of advanced technology methanol
vehicles. The same annual replacement rates for fleet vehicles
used for the first scenario are used here as well. Table 8
summarizes the numbers of fleet and general use vehicles in use
by the year 2000. Again, every new vehicle in a fleet of 10 or
more vehicles is assumed to be a methanol vehicle; additional
methanol vehicles in general use are also included in the
analysis.
Table 9 presents the percent reduction in ozone—equivalent
VOC emissions-—and hence in ambient ozone——for each city in the
year 2000. As for the first scenario, results are presented
both for a case of fleet—vehicle only replacement as well as
the case in which general—use methanol vehicles are also
included.
-------
—14—
4. Methanol Vehicles Replacing Gasoline Vehicles — Steady
State
The foregoing discussions have considered the effect that
methanol vehicles might have on ozone levels after a few years
of implementation. For two reasons, however, this sort of
analysis gives an incomplete understanding of the potential
impact of a methanol program.
The first is related to the fact that methanol vehicles
are assumed to displace newer, cleaner gasoline vehicles, which
are responsible for less than a proportional share of the voc
inventory. This is because their emission are less
deteriorated with regard to their emissions standards and
because they may have been certified to tighter emission
standards than the “average” gasoline vehicle was. Thus after
only five years of fleet integration, a significant portion of
the fleet is still composed of older gasoline vehicles which
account for a greater fraction of total emissions than their
VMT percentage would suggest. As a result, methanol’s impact
on total fleet emissions is significantly less than it is on
the emissions of each model year’s fleet into which methanol
vehicles have penetrated. By extension, it is also
significantly less than it would be on the emissions of an
entire fleet in which methanol vehicles are given an eçuivalent
age distribution to gasoline vehicles. Carrying forward an
implementation scenario until the entire gasoline fleet is able
to turn over will provide a demonstration of the maximum
potential impact of methanol on mobile source emissions.
The second factor that comes into play in a longer term
implementation is related to the changing mobile and stationary
source fractions of the VOC inventory. Since mobile source
fractions are generally expected to decline over time (see
Table 10) the potential impact of a methanol fleet on overall
ambient ozone levels is decreased. This second factor will
directionally work to offset the impact of the first.
In the steady stat scenarios, therefore, it is assumed
that sufficient time has elapsed to allow methanol vehicles to
integrate with the fleet as a fraction of the sales of every
model year that is present in the total fleet. According to
National Highway Traffic Safety Administration scrap rate data,
98 percent of the gasoline vehicle fleet turns over in 20
years, 83 percent in 15. To calculate steady state impacts of -
the two methanol scenarios considered, therefore, one would
ideally take the current technology program out 20 years to
2011 and the advanced technology program to 2015.
(Admittedly, private fleets may turn .over more guickly than the
overall fleet, but the scenarios considered all involve a
substantial portion of private vehicles as well.) Since the
mobile source fractions shown in Table 10 remain fairly stable
-------
—15—
after 2010. and since later data are unavailable, year 2010
data for New York and Washington and year 2000 data for Los
Angeles are used to represent later years.
For these scenarios it is assumed that methanol vehicles
are responsible for 30 percent of all VMT. This assumption
implies that methanol vehicles constitute 30 percent of the
total urban fleet and, to reiterate the above discussion, are
distributed through it in an age and use distribution identical
to that for gasoline vehicles.
Table 11 shows the results of this analysis. Phoenix is
included in this table along with the other cities which have
been used throughout this analysis because it has a high mobile
source VOC fraction into the early 21st century and represents
an upper limit on the potential impact of methanol
implementation. The effect of methanol on mobile source VOC is
distinguished in this table from its effect on total urban VOC
to provi.de an illustration of the relevance of the
mobile/stationary breakdown to this analysis. In this table,
current technology methanol vehicles are seen to provide a
potential 3 to 4 percent impact on urban VOC and advanced
technology could reduce urban VOC by 6 to 11 percent.
5. Oxygenated Blends Replacing Gasoline in All Vehicles
The final scenario evaluated in this paper projects the
effect of a mandated oxygenated blends program on ambient Co
levels. EPA’s analysis is based on an assumption that fuels
would contain about 3.7 percent oxygen. This approximate level
of oxygen content can be achieved with gasohol . (ten percent
ethanol), Oxinol (4.75 percent methanol and 4.75 percent
t—butyl alcohol), or the DuPont methanol blend (five percent
methanol with 2.5 percent cosolvent alcohol). A blend of MTBE
and gasoline would need to be 20 percent by volume to reach 3.7
percent oxygen; currently MTBE can only be used at levels up to
11 percent by volume (two percent oxygen). Co reduction
estimates for a program mandating two percent oxygen fuel are
assumed to be proportional to the 3.7 percent oxygen values.
With respect to a mandated fuel substitution program, the
per—vehicle CO reductior s in Table 5 essentially represent
fleetwide CO reductions as well because all gasoline vehicles
would in effect become blend—fueled vehicles. To convert this
mobile source CO reduction to a total Co reduction, an
assumption about the mobile source fraction of CO emissions is
needed. We have used values of 90 percent for Phoenix and 75
percent for Denver (the Denver fraction is lower due to the
extensive use of wood stoves there).
Table 9 presents both the percent reduction in mobile
source CO that EPA would expect in 1990, 1995, and in a
steady—state (100 percent closed—loop) year in an area
-------
—16—
implementing an oxygenated fuels program. Specific total
stationary—plus mobile—source Co reductions are presented for
Denver and Phoenix.
Finally, EPA has calculated rough estimates of the Co
effect of requiring a retrofit conversion of all vehicles in an
area to operate on CNG. The estimates are based on the low end
of the range of potential CO reductions presented in Table 5.
Overall ambient CO reductions from a total fleetwide CNG
retrofit program appear in Table 9.
-------
Fiqure 1
NA11ONAL TREND IN CARBON MONOXIDE EMISSIONS
1976-1985
CO EMISSIONS, 10 METRIC TONSIYEAR
1984 1985
120
100
80
60
40
20
0
76
1977 1978 1979 1980 1981 1982 1983
Source: EPA 1985 Trends Document
-------
Fiqure 2
NATIONAL TI ND VOLA11LE ORGANIC COMPOUMi 1Js o S
1976-1985
VOC EMISSIONS, 10’ METRIC TONS/YEAR
35-—
30
25
20
15
1Q
5
0.
W6
SOURCE CATEGORY
SOUD WASTE & MISC
D NX6T PROc
WA POR
1g77 1978 1979 1980 1981 1982 1983 1984 1985
Source: IPA 1 H3S Trends Document
-------
.itjure 3
CARBON MONOXIDE TREND. 1976 -1985
(ANNUAL 2ND MAX &-+IR NONOVERIAPPING AVG)
cON EN AT PPM
1976 1977 1978 1979 1980 1981 1982 1983 1984 1985
16351115
Source: EPA 1985 Trends Document
-------
urn 4
C ONE TREND. 1976-1985
(ANNUAL 4D DAILY MAX HOt*)
ON B41RA OR P
183 SiTES
1976 1g77 1978 1979 1980 1981 1982 1983 1984 1985
0.30
0.10
0.05
0.00
Source: EP 1985 Trends Document
-------
Table 1
Mobile Source voc Fractions
for Selected Non—Attainment Areas (Percent)
City 1983 2000
Houston 35 16
Chicago 43 25
New York City 49 28
Milwaukee 51 29
Washington, DC 55 32
Phoenix 64 40
-------
Table 2
Top 30 Ozone Non—Attainment Areas
1982—84 Percentage Reduction
Area Name Design Value (ppm) Required
Beaumont-Port Arthur, TX .21 87
LOS Angeles, CA .36 72
Houston, TX .25 70
Greater Connecticut .23 64
Oxnard—Venturi, CA .21 60
Chicago Metro. .20 60
Baton Rouge, LA .17 59
San Diego, CA .20 59
Atlantic City, NJ .19 57
Boston Metro., MA .19 57
El Paso, TX .17 56
Sacramento, CA .18 54
Baltimore, MD .17 51
Galveston, TX .17 51
Dallas—Ft.WOrth, TX .16 51
San Francisco, CA .17 50
Atlanta, GA .17 48
Bakersfield, CA .16 46
Fresno, CA .16 46
Birmingham, AL .15 38
Allentown-Bethlehem, PA .15 38
Modesto, Ck .15 38
Cincinnati, OH .15 32
Denver—Boulder, CO .14 29
Brazoria, TX .14 27
Detroit, M I .14 27
Huntington, WV .14 27
Vallejo—Fairfield, CA .14 27
Santa Barbara, CA .14 25
Kansas City, MO .14 23
-------
Table 3
Top 30 Co Non-Attainment Areas
1983—85 Percentage Reduction
Area Name Design Value (ppm) Req uired
Los Angeles—Long Beach 27.4 67
Denver 24.0 63
Phoenix 20.3 56
Provo—Orem 19.1 53
Anchorage 18.0 50
Ft. Collins, CO 17.8 49
Fairbanks 17.7 49
Newark 17.7 49
Albuquerque 17.2 48
Raleigh—Durham 16.6 46
Medford, OR 16.3 45
Sacramento 16.3 45
Las Vegas 16.3 45
Reno 16.2 44
Greeley , CO 16.2 44
Nashua, NH 16.0 44
New York City 16.0 44
Boise City, ID 15.5 42
Spokane, WA 15.4 42
Syracuse NY 14.7 39
San Jose, CA 14.3 37
Boston 14.1 36
Baltimore 13.9 35
Yakima, WA 13.9 35
Washington, DC 13.8 35
Jersey City, NJ 13.7 34
Chicago 13.3 32
El Paso 13.3 32
Charlotte, NC 13.2 32
Colorado Springs 13.2 32
-------
Table 4
Nationwide Non—California Attainment Projections
1983 1990 1995 2000 2010
Ozone Non-Attainment
Non—California Areas 61(11 40 38 41 51
California Areas 11 —— —— —— ——
co Non-Attainment
Non—California Areas(21 7113] 17—23 7—15 6—14
California Areas 10 —— —— ——
[ 11 projections based on 1982—84 data; recent 1983—85 data show
65 non—California areas and ii California areas
(2) Ranges show sensitivity to assumptions about temperature and
driving patterns
(3] unchanged for 1983—85
-------
Table 5
Emission Reduction Potential of Light—Duty Vehicles
(Per—vehicle basis compared to gasoline
vehicles meeting current standards)
VOC NOx
Methanol
FFV (M85) —(20 to 50)% 0 0
Current Technology —(20 to 50)% 0 0
Advanced Technology* —(85 to 95)% —(30 to 90)% 0
CNG
FFV/Retrofit* —(50 to 80)% —(50 to 90)% —20% to +80%
Advanced Technology* —(50 to 90)% —(50 to 90)% —20% to +80%
OXYGENATED BLENDS
VOC Ethanol Methanol MTBE
Constant RVP —2% to +5% —5% to +5% —1%
1 Psi Higher +15% to +35% +9% to +30% Not Applicable**
CO Ethanol, Methanol (3.7% Oxygen) MTBE (2.0% Oxygen )
Non—Catalyst —18% —10%
Open Loop —30% —16%
Closed Loop —10% —5%
NOx
Open Loop +5% +3%
Closed Loop +6% ÷3%
* Projections based on very small data bases; CNG vehicles would
also typically experience a loss in power and performance.
** Unlike ethanol and methanol, MTBE does not appear to
significantly increase the RVP of gasoline.
-------
Table 6
Reactivities [ 1]
of Methanol and Formaldehyde
Methanol Formaldehyde
Study City Reactivity Reactivity
SAl Los Angeles [ 2] 0.02 2.95
SAl Philadelphia 0.413 5.873
Ford Allentown 0.350 4.600
Atlanta 0.375 4.125
Baltimore 0.533 3.867
Boston 0.232 5.180
Chicago 0.310 5.138
Cincinnati 0.600 4.600
Dallas 0.563 4.625
Detroit 0.372 4.490
El Paso 0.563 4.938
Ft. Worth 0.417 5.972
Houston 0.625 4.375
Milwaukee 0.500 3.833
Nashville 0.520 4.120
Philadelphia 0.441 4.588
Phoenix 0.421 5.158
Pittsburg 0.258 5.560
Scranton 0.375 4.875
st. Louis 0.215 5.754
Washington D.C. 0.444 4.611
Youngstown 0.500 5.500
Average [ 3] 0.430 4.826
[ 1) Amount of ozone produced relative to gasoline hydrocarbon
emissions.
[ 2] Methanol reactivity appears low compared with other data.
Further modeling reguired to verify.
[ 3] Average of 20 non—California cities (uses average values
from SAl and Ford for Philadelphia).
-------
Table 7
In-Use Emission Factors and Relative Ozone Potential
for Gasoline and Methanol Vehicles [ l]
Exhaust (g/mi) Evap (q/mi) [ 6] Refueling (g/mi)
HC MeOH Form EC MeOH HC MeOR
49 - State .
Gasolirie [ 2] 1.00 - — 0.51 — 0.21 —
Current Methanol (M85) [ 3] 0. 1.08 0.09 0.14 0.39 0.14 0.04
Advanced Methanol (Ml00)(3] 0.04 0.44 0.01 - 0.20 - 0.05
California
Gasoline [ 4] 0.58 - — 0.07 - 0.03 —
Current Methanol (M85)(5] 0.25 0.70 0.06 0.04 0.10 0.02 0.01
Advanced Methanol (Ml00) [ 3] 0.04 0.44 0.01 - 0.20 - 0.01
(1) Based on 50.300 mile performance. Ass .tmes carbon based standards apply to
current technology methanol vehicles.
(2] Based on l 90+ model year vehicle EPA data. No volatility or refueling
controls in place.
(3] Based on testing of prototype venicles. Assumes in-use versus standards
offsets of 2.2 and 2.3. fcr exhaust and evaporative emissions. Offsets
estimated 3ased n performance of current technology gasoline vehicles.
Refueling data based on test of Ofli one nethanol vehicle.
(4] CARB projections for future exhaust. evap emission factors. EPA estimate of
refueling emissions assumes percent c3ntrol efficiency of .A Stage II vapor
recovery systems.
(5] Based on testing of prototype venicies. Assumes in-use versus sstandards
offsets of 1.42 and .58 for exhaust and evaporative emissions offsets estimated
ased on performance of current technology California gasoline vehicles.
(6] Converted to g/mi by assuniing 3.05 trips and 31.1 miles per day.
-------
Table 8
Methanol Vehicle Distributions
Used in Analysis (Vehicles/Year )
1995 2000
1991 ( 1991—1995) ( 1995—2000 )
Total Vehicles
Replaced Per Year
New York 200,000 1,000,000 1,200,000
Washington 25,000 125,000 150,000
Los Angeles 275,000 1,375,000 1,650,000
Distribution With Maxi.murn Fleet Vehicle
Replacement (Vehicles/Year ) *
New York
Fleet Vehicles 130,500 652,500 783,000
General Use 69,500 347,500 417,000
Washington
Fleet Vehicles 24,000 120.000 144,000
General Use 1,000 5,000 6,000
Los Angeles
Fleet Vehicles 80,000 400,000 480,000
General Use 195,000 975,000 1,170,000
* Based on estimated maximum Los Angeles area fleet vehicle
replacement of 80,000 vehicles per year (for fleets of 10
or more vehicles). New York and Washington fleet
replacement estimates are proportional to the Los Angeles
ratio of 80,000 fleet vehicles to 7,300,000 total vehicles.
-------
Table 9
Estimated Percent voc Reduction
for Methanol Strategies
Fleets Plus Some
Fleets Only General Use Vehicles
°VOC Reduction °GVMT ° 0 VOC Reduction ° 0 VMT
Current (1995 )
New York City 1.1 15 1.4 18
Washington 1.2 14 1.2 15
Los Angeles 0. 14 1.7 26
Advanced (2000 )
New York City 3.5 16 4.2 20
Washington 3.8 16 3.8 16
Los Angeles 2.3 15 4.5 29
Estimated Fleetwide Percent CO Reductions
for Blends Strategies
2% Oxygen 3.7% 3xygen CNG Retrofit
Steady Steady
1990 1995 State 1990 1995 State
Mobile Source CO 12 10 5 22 18 10 50
Total CO (Denver) 9 8 4 17 14 8 38
Total CO
(Phoenix) 11 9 5 20 16 9 45
-------
Table 10
Mobile Source Percentages of Total VOC Inventories
Year
City* 1983 1995 2000 2010
New York 49 30 28 28
Washington 55 34 32 33
Los Angeles 50 27 24 NA**
* Data for New York and Washington from EPA. Data for Los
Angeles based on information provided by California Air
Resources Board.
** NA indicates data not available.
------- |