EPA420-R-00-022
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
ANN ARBOR, Ml 48105
OFFICE OF
AIR AND RADIATION
MEMORANDUM
DATE:November 17, 2000
SUBJECT: Summary and Analysis of Comments for Notice of Proposed Finding: Control of
Emissions from New Nonroad Spark-Ignition Engines Rated above 19 Kilowatts and
New Land-Based Recreational Spark-Ignition Engines
FROM: John Mueller, Mechanical Engineer
Assessment and Standards Division
THRU: Glenn Passavant, Nonroad Center Director
Assessment and Standards Division
TO: Docket A-98-01
We published a Notice of Proposed Finding in the Federal Register on February 8, 1999
regarding emissions from new land-based nonrecreational nonroad spark-ignition engines rated
above 19 kilowatts and new land-based recreational spark-ignition engines.a In that notice we
requested comments from all interested parties on all aspects of the notice and its supporting
documentation. We received comments from 12 entities including industry groups, government
agencies, private citizens, and environmental groups. The purpose of this memorandum is to
summarize, analyze and respond to the comments we received.
List of Commenters
The following entities provided written comments on the Notice of Proposed Finding.
American Motorcyclist Association (AMA)
Bluewater Network
California Motorcycle Dealers Association (CMDA)
Industrial Truck Association (ITA)
International Snowmobile Manufacturers Association (ISMA)
Steven K. Lyda
Motorcycle Industry Council and the Specialty Vehicle Institute of America (MIC/SVIA)
a 64 FR 6008, February 8, 1999.
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Orbital Combustion Process - For A Cleaner Tomorrow (OCP-FACT)
Magaly Rosas
Southwest Research Institute (SwRI)
State of Wyoming, Office of Federal Land Policy
United States Department of the Interior (DOI)
Summary and Analysis of Comments
This summary and analysis of comments is divided into several general subject areas. The
first section deals with general issues concerning the proposed finding and the conclusions we
reached in the proposal. The second section deals with comments pertaining to the seasonal and
geographic nature of recreational vehicle usage and emissions. The third section deals with the
potential impact of future standards and the technologies that may be employed to meet any future
standards. The fourth and fifth sections deal separately with the emissions modeling used to support
the conclusions in the proposed finding for recreational and nonrecreational vehicles and engines.
1. Finding - General
Summary of Comments:
California Motorcycle Dealers Association (CMDA) commented that we based our finding
on emissions inventories which were derived using erroneous information. CMDA is concerned
that this will lead to unwarranted regulations.
The Motorcycle Industry Council, the Specialty Vehicle Institute of America (MIC/SVIA)
and S. Lyda all suggested that our emissions inventories were substantially overstated. They, along
with the International Snowmobile Manufacturers Association (ISMA), suggested that we need to
refine our modeling further before we can make a finding of contribution.
S. Lyda commented that section 213(a)(3) of the Clean Air Act allows us to exercise
judgement in determining whether a class or category of new nonroad engines and new nonroad
vehicles contribute to air pollution described in section 213(a)(2). He stated that this discretion
allows us to decide when carbon monoxide (CO) or ozone precursor emissions from a class or
category of new nonroad vehicles or engines are insignificant enough that regulating them would be
a waste of time.
M. Rosas and the U.S. Department of Interior (DOI) expressed general support for the
finding. DOI expressed concern about the impact of snowmobile use in national parks, especially
Yellowstone National Park (YNP). DOI submitted a variety of information, including estimates of
snowmobile use in YNP and its impacts on air quality and an investigation of snowmobile driver
exposure to CO while traveling in the wake of another snowmobile. DOI also informed us of
several studies they have underway in this area.
The American Motorcyclist Association (AMA) and S. Lyda opposed including recreational
vehicles and industrial equipment in the same finding. AMA stated that off-road motorcycles and
ATVs are generally discretionary purchases that are used in rural areas, in contrast to industrial
equipment which is more of a mandatory purchase and tends to be used more in urban areas. AMA
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stated that, while it supports reasonable emission controls for off-road motorcycles and ATVs, this
is not the proper place to initiate such controls. AMA did not, however, recommend an alternative.
S. Lyda commented that recreational engines are subject to much higher transient load conditions
and have higher power to weight ratios than industrial equipment. These factors, he added, would
make it much harder to reduce emissions from recreational engines than from industrial engines.
Both AMA and S. Lyda commented that the off-road motorcycle and ATV industry is
moving away from 2-stroke engines in favor of 4-stroke engines. They suggested that this alone
serves to reduce emissions from off-road motorcycles and ATVs.
Bluewater Network commented that snowmobiles are one of the largest sources of
unchecked pollution nationwide, and urged us to consider regulating their emissions as soon as
possible. Bluewater pointed out that snowmobiles emit very high levels of PM compared to other
vehicle types, and there are numerous PM nonattainment areas in which snowmobiles are a
significant contributor to respiratory problems, asthma and premature mortality. Bluewater also
cited studies showing high CO and PM levels in parts of Yellowstone National Park and high CO
exposures to riders in trailing snowmobiles, pointing out that it is common for snowmobiles to
travel in groups, exposing riders to high CO levels for extended periods of time.
U.S. DOT commented that our finding should go beyond considering nonattainment areas
and address snowmobile emissions in the context of regional haze regulations and other regulations
that protect air quality in Class I areas across the United States. DOT pointed out that reducing
snowmobile emissions would contribute to air quality improvements and haze reductions in some
Wilderness areas near national parks.
Response to Comments:
As a result of the information provided by the commenters and additional information we
have uncovered since the proposal, we have been able to improve the accuracy of our emissions
modeling estimates for recreational vehicles. As discussed later in this memorandum, we have
revised our emission inventory estimates through a more rigorous evaluation of the information we
had at the time of the proposed finding and have evaluated further information that was submitted to
us in response to that proposal as well as additional information we collected. The details of the
revised recreational modeling estimates (including all of the information we considered and our
conclusions regarding how to use that information) are contained in a separate memorandum to the
docket.b We believe that these revised emissions inventory estimates are justified considering all of
the information currently available. While we have confidence in the accuracy of these new
estimates, we intend to continue pursuing additional data and further refine our recreational vehicle
emissions inventories in the future.
The result of the improvements to our modeling is that our total estimates for recreational
and nonrecreational applications have changed. Our estimates of hydrocarbons (HC), carbon
monoxide (CO) and particulate matter (PM) have decreased by 44 percent, 20 percent, and 63
b "Emission Modeling for Recreational Vehicles," EPA memorandum from Line Wehrly
to docket A-98-01, November 14, 2000.
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percent, respectively, while our estimate of total oxides of nitrogen (NOx) has increased by 32
percent. Our estimates of snowmobile emissions inventories were reduced by 76 percent for HC, 77
percent for CO, 45 percent for NOx and 66 percent for PM, as compared to those in the proposed
finding. In contrast, off-road motorcycle and ATV emissions inventories of HC and NOx increased
by 83 percent and five percent, respectively, while their inventories of CO and PM were reduced by
two percent and 63 percent, respectively. The net result of these changes is that total recreational
vehicle emissions inventories decreased by 48 percent, 30 percent, and 65 percent for HC, CO and
PM, respectively, while NOx inventories remain essentially unchanged compared to those in the
proposed finding. For Large SI, our new estimates represent reductions of five percent for HC and
48 percent for PM, and increases of 11 percent for CO and 35 percent for NOx. While these new
inventories represent a change from those in the proposed finding, these changes do not
fundamentally change the conclusions we reached in that proposal, namely that, in our judgement,
nonroad spark-ignition (SI) engines rated above 19 kilowatts (kW), as well as land-based
recreational nonroad spark-ignition engines, cause or contribute to air quality nonattainment in more
than one ozone or carbon monoxide (CO) nonattainment area, and that particulate matter (PM)
emissions from these engines cause or contribute to air pollution that may reasonably be anticipated
to endanger public health or welfare.
We disagree with AMA and S. Lyda's comments that it is inappropriate to consider all large
SI nonroad engines and vehicles together when determining emissions contribution. The legislative
history of the Act indicates that we should not subdivide categories of nonroad engines into small
subcategories.c This is because Congress did not want us to subdivide source categories into such
small divisions that each subcategory by itself would have minimal contribution, despite the fact
that nonroad engines as a whole contribute significantly to pollution. This is likely the reason why
the final version of the Act does not require a finding of "significant contribution," but merely
"contribution," for individual categories of nonroad engines. In general, we chose to group engines
and equipment together based on common characteristics such as combustion cycle, fuel, usage
patterns, power rating, and equipment type. By dividing nonroad engines and equipment into
separate categories based on these characteristics we are able to devise the most appropriate
regulatory programs for each category which take into account the specific characteristics of the
engines and equipment, as well as the unique traits and needs of the affected vehicle and equipment
manufacturing industries and the end users of the vehicles and equipment. In addition, it avoids the
danger recognized in the legislative history of dividing nonroad engines into small categories.
Large SI nonroad engines, both recreational and nonrecreational, do have similar emissions
characteristics, though there are also significant differences in usage and design. We will take these
differences into account in designing the regulatory requirements for these engines, as indicated in
the accompanying Advance Notice of Proposed Rulemaking. However, we believe that the
emissions characteristics of all large SI nonroad engines are sufficiently similar that they can be
reviewed as one category in making this finding.
However, even if we were to agree with the commenters that we should review recreational
vehicles separately from nonrecreational equipment, our result would be the same. As indicated in
the tables presented in the preamble, large SI nonrecreational equipment are modeled to contribute
Senate Report 101-228, pp. 104-105.
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306,000 tons of NOx, 125,000 tons of HC, 2,294,000 tons of CO and 1.6 tons of PM to this year's
national inventories. Similarly, recreational SI contributed 587,000 tons of HC, 4,231,000 tons of
CO and 5.6 tons of PM to national inventories. Review of the local inventories show similar results.
Table 3 in the preamble shows substantial emission totals both for recreational and nonrecreational
engines in all emission categories. Off-road motorcycles and ATVs alone account for a
considerable amount of emissions, as do snowmobiles. It is clear from these totals that even if, as
suggested, we reviewed recreational vehicles separately, they would still contribute to emission
contributions in more than one ozone or CO nonattainment area and would contribute to PM
pollution that may reasonably be anticipated to endanger public health or welfare, and the
Administrator has explicitly, using the authority of section 213(a)(3) and (4), made that finding in
this action.
Regarding comments that the off-road motorcycle and ATV industries are moving away
from 2-stroke engines in favor of 4-stroke engines, the current populations already include
significant numbers of 4-stroke engines, and we believe that further shifts away from 2-stroke
engines would not change the finding that these engines contribute to air pollution. It is true that 4-
stroke engines tend to have lower HC and PM emissions than 2-strokes. However, off-road
motorcycles and ATVs would not stop emitting HC, in particular, or even PM, if these engines all
became 4-stroke. Moreover, CO emissions tend to be similar, and 4-strokes generally have higher
NOx emissions than 2-strokes. In any case, speculation about the possible future populations of
these engines does not detract from the fact that these engines currently contribute to air pollution.
In addition, there is no evidence that 2-stroke engines are going to be eliminated voluntarily from
the market, especially for off-road motorcycles. Currently, 4-stroke engines account for more than
70 percent of the total off-road motorcycle/ATV population. Seventeen percent of the current ATV
population is currently 2-stroke. The off-road motorcycle population is currently 67 percent 2-
stroke. While the manufacturers have indicated to us that they intend to offer more 4-stroke models
in the future, it remains to be seen whether these additional offerings will be at the expense of 2-
stroke sales, or whether 4-strokes will maintain their current share of the market, but with more
different models available. We also believe it is notable that none of the manufacturers submitted
comments suggesting that the populations would move toward a higher fraction of 4-strokes. The
commenters may in fact have shown that emission standards may be useful to provide further
encouragement for manufacturers to develop more 4-stroke engines for these vehicles.
We agree with the comments of M. Rosas and have finalized the proposed finding. We also
agree with DOI and Bluewater Network that emissions of snowmobiles appear to be responsible for
elevated levels of CO and decreased visibility in Yellowstone National Park. While this area is not
a CO nonattainment area, it does appear that increased levels of CO, sometimes above the national
ambient air quality standard (NAAQS), have been measured, adding to our belief that snowmobile
emissions in areas of concentrated snowmobile use can dramatically increase pollution levels in
those areas. DOI also notes that 27 other units of the National Park system allow snowmobiles and
that these concerns also apply in these areas as well. Bluewater also notes that snowmobiles
contribute to PM levels in several nonattainment areas, which appears to be consistent with our
modeling results, which show snowmobiles contributing to PM levels in PM nonattainment areas
such as Denver County, CO and Spokane County, WA. Although we recognize that recreational
vehicles do contribute to PM emissions, we have not yet decided on the appropriateness of PM
standards for these vehicles.
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2. Seasonal and Geographic Nature of Emissions
Summary of Comments:
ISMA stated that snowmobile use is limited to cold weather and therefore doesn't contribute
to ozone nonattainment. AMA pointed out that snowmobiles account for 75 percent of recreational
vehicle emissions and considering that they are generally only used when it snows, their
contribution to the recreational category is irrelevant in the scheme of national emission reductions,
especially for ozone. CMDA stated that snowmobiles are used in climatic conditions and altitudes
where there are no ozone violations. Finally, MIC/SVIA stated that our modeling does not
distinguish between cold weather (i.e., non-ozone causing) and warm weather emissions.
MIC/SVIA added that snowmobiles dominate the recreational HC emissions inventory but do not
contribute to ozone and should be removed when considering an ozone strategy.
Several commenters provided comment on the geographic nature of recreational vehicle
emissions. ISMA simply stated that snowmobiles are not used in or around nonattainment areas and
don't contribute to nonattainment. ISMA provided trail maps to further this argument. AMA stated
that, while off-road motorcycle and ATV owners may live in nonattainment areas, the majority of
off-road motorcycle and ATV use is in rural areas. AMA mentioned examples of areas of high use
of off-road motorcycles and ATVs. The vast majority of these areas, according to AMA, are
attainment areas. Thus, AMA commented, unlike industrial equipment, off-road motorcycles and
ATVs have little impact on emissions in nonattainment areas. MIC/SVIA stated that recreational
emissions occur predominantly in rural and attainment areas, and therefore it is not appropriate to
compare them to nationwide on-highway emissions.
Response to Comments:
Regarding the contribution of snowmobile emissions to ozone, snowmobiles are not a
separate category of nonroad engines and will be regulated as part of a broader category. Whether
we view snowmobiles as part of the full large SI category, or even if we view them as part of the
recreational vehicles category, they clearly are part of a category of engines that contributes to ozone
concentrations in more than one nonattainment area. No commenter stated that snowmobiles should
have been placed in its own separate category of nonroad engines, nor would that be appropriate,
given the similarities in usage and design between snowmobiles and, at the very least, off-road
motorcycles and ATVs. Moreover, even reviewing snowmobile emissions themselves, they emit
substantial amounts of HC in several nonattainment areas, which would certainly increase ozone
levels in those areas.d Further, the evidence in the docket also shows that snowmobile emissions
contribute to concentrations of CO in several CO nonattainment areas. Given the statutory language
regarding the categories of new nonroad engines subject to regulation, categories "which, in the
Administrator's judgment cause or contribute to [ozone or carbon monoxide concentrations in more
than one area that has failed to attain the national ambient air quality standards for ozone or carbon
monoxide]," snowmobiles are part of such a category, and in fact would be such a category were it
d "Additional Detail on Revised Recreational Vehicle Emissions Inventories," EPA
memorandum from John Mueller to docket A-98-01, November 15, 2000, and the inventories
provided for the 1991 Nonroad Study (Docket No. A-91-24, Document No. U-B-4).
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looked at separately.
We recognize that snowmobiles' contribution to ozone concentrations is less important if it
occurs solely during portions of the year when exceedences of the ozone NAAQS are unlikely to
occur. We will bear this issue in mind as we move forward with emission regulations for these
vehicles. In the Advance Notice of Proposed Rulemaking (ANPRM) accompanying this Final
Finding, we specifically request comment on whether we should distinguish snowmobiles from
other recreational vehicles in regulating ozone precursors.
Regarding the comments of AMA and MIC/SVIA that snowmobile emissions dominate the
HC emissions inventory, our revised estimates indicate that off-road motorcycles and ATVs are
actually a larger source of HC and other pollutants than snowmobiles and, in any case, clearly
contribute to both national and local inventories.
Regarding the assertion that emissions from recreational vehicles occur most often in rural
areas, this assertion is not relevant for our finding. The test under the statute is whether a category
of engines contributes to ozone or CO contributions in more than one nonattainment area, not
whether it contributes even more pollution in rural areas. Moreover, though there is a strong
correlation between nonattainment areas and urban areas, particularly for ozone, there are many
counties that are part of nonattainment areas that may be considered rural or suburban in character -
in fact, there is not much correlation between PM nonattainment areas and urban areas. In any case,
the evidence, including the particular site information provided by AMA, shows that recreational
vehicles are used in numerous nonattainment areas around the country and in fact contribute sizable
emissions in such areas. Our local modeling information, with geographical distribution of
recreational vehicles based on the presence of areas to ride them in (such as recreational vehicle
parks), indicates considerable usage of these vehicles in nonattainment areas6. The inventories
provided for the 1991 Nonroad Study (Docket No. A-91-24, Document No. II-B-4) contain
numerous examples of nonattainment areas with populations of recreational vehicles.
3. Future Standards and Technology
Summary of Comments:
We received a variety of comments on recreational vehicles concerning the availability of
emissions control technology, concerns about the use of particular technologies, and potential
impacts of future standards on the affected industries.
Supporters of Orbital Combustion Process-For A Cleaner Tomorrow (OCP-F ACT)
commented that the Orbital Combustion Process technology is available and that we should
consider its capabilities as we develop new emission standards. OCP-F ACT submitted a variety of
information which details the operation and capabilities of the OCP technologies and listed several
e Further details of the growth and geographical allocation methodologies are covered in
the paper, "Geographic Allocation and Growth in EPA's NONROAD Emission Inventory
Model," by Gary Dolce, Greg Janssen, and Richard Wilcox, presented at the 1998 Air and Waste
Management Association Conference.
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companies which have announced plans to introduce engines with the OCP fuel system. DOT
suggested that we base our standards on emerging, rather than existing technology. DOT noted that
the Society of Automotive Engineers has sponsored a "Clean Snowmobile Challenge" intended to
allow student engineers the opportunity to develop cleaner and quieter snowmobiles.
Both AMA and S. Lyda suggested that there are safety concerns with some technology likely
to be used on off-road motorcycles and ATVs. S. Lyda commented that any technology that
increased weight the of a motorcycle would impact its handling. He added that emission standards
which require complex fuel management technology may leave riders stranded, whereas current
carburetors can easily be fixed on the trail. Both AMA and S. Lyda commented that catalysts would
increase the risk of burns and fires. S. Lyda also commented that we must consider the cost and
availability of technology before promulgating standards. He claimed that some technologies may
be too costly or complex to mass produce. AMA suggested that the use of alternative fuels (such as
gasohol) and lubricants in the existing fleet should be aggressively explored before requiring
engine-based technologies.
CMDA commented that any unwarranted regulations would hurt motorcycle and ATV
dealers. AMA stated that any regulations should not hurt the recreational industry, which provides
jobs and stress relieving benefits for many citizens.
The Industrial Truck Association (ITA) provided detailed comments regarding possible EPA
approaches for regulating Large SI engines. ITA states that it favors harmonization with California
and opposes federal standards that are more stringent than California's. ITA also opposes use of
any test cycles beyond the California steady-state cycle. ITA also provided comments regarding
lead time, fuel specifications and evaporative emissions.
Response to Comments:
Comments on applicable technologies and safety and cost concerns with those technologies
are not relevant to this finding. Nor are comments related to the specifics of possible approaches by
EPA in regulating these engines. The purpose of the finding is to determine whether emissions
from the vehicles and engines being considered contribute to air pollution, as required under
sections 213(a)(3) and (4) of the Act. Such a finding provides authority for us to set appropriate
emissions standards for these vehicles and engines. All of these comments, however, are very
relevant to the development of such emissions regulations. Thus, we will consider the availability
of technology as well as its cost, safety and other factors, including appropriate fuel requirements, as
we develop a proposed regulatory scheme for these vehicles and engines. There will be further
opportunities for public input as we go through the process of developing the regulations.
We do not agree with CMDA that any regulations we put into place would hurt the
recreational industry. Without knowing the levels of the standards and the nature of the compliance
program it is impossible to predict the impact of regulations on an industry. We do share AMA's
opinion that any regulations we put into place for the vehicles and engines covered by the final
finding not unnecessarily impact the affected industries. As we work to propose regulations for
these vehicles and engines we will take into account the nature of the affected industries and will
attempt to structure a regulatory program that minimizes the impact on those industries. During the
rulemaking process we invite any interested parties to submit comments on the potential impact of
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those proposed regulations on the affected industries.
4. Emissions Modeling - Recreational
Summary of Comments:
We received a variety of comments on our recreational vehicle emissions modeling. In
general, the commenters stated that we overestimated recreational vehicle emissions through
incorrect or inappropriate inputs to our emissions model. CMDA stated that erroneous load factors,
usage and inventories will be used to determine whether the vehicles and engines under
consideration should be regulated. AMA commented that our modeling does not account for
emissions reductions expected from regulations in the state of California.
MIC/SVIA commented that our HC emission factor for off-road motorcycles and ATVs is
high for engines operated at high loads. ISMA provided new industry average snowmobile
emission factors for HC and CO based on recent testing by the snowmobile manufacturers.
ISMA commented that our snowmobile load factor is too high. ISMA cited recent testing
and analysis done by Southwest Research Institute in support of a snowmobile emission factor of
0.337, significantly lower than our estimate of 0.81. S. Lyda commented that, based on an informal
survey he conducted at off-road motorcycle races, the off-road motorcycle load factor is 0.28. He
stated that this load factor may be on the high side given that it was based on a survey of motorcycle
racers, and the majority of trail riders do not ride as hard as racers, but that it was more realistic than
our load factor of 0.72. MIC/SVIA commented that the on-highway load factor is less that 0.10
based on an analysis of the federal test procedure for on-highway motorcycles. MIC/SVIA argued
that, even if off-road motorcycles were operated at twice the load of on-highway motorcycles, the
off-road motorcycle load factor would still be less than 0.20.
MIC/SVIA stated that we did not provide information on what average rated horsepower
(hp) was assumed in the analysis, but that 35 hp appears close to our estimate. ISMA also stated
that average hp was not provided in the proposal.
ISMA commented that our snowmobile usage estimates are too high. ISMA cited some
state studies which showed snowmobile usage to be no more than 50 hours per year, rather than the
121 hour estimate in the proposed finding. MIC/SVIA commented that its own survey data
suggested that off-road motorcycle usage is 84 percent lower than our estimate. Finally, S. Lyda
commented that, based on an informal survey he conducted at off-road motorcycle races, off-road
motorcycle usage is about 84 hours per year. He also stated that our usage rates are overstated
because many riders have more than one motorcycle or ATV, and our modeling did not account for
this.
ISMA agreed with our snowmobile population estimates, but stated that the industry will not
maintain double-digit growth rates in the future.
S. Lyda claimed that the combined errors of our model inputs result in off-road
motorcycle/ATV inventories that are eight times higher than reality. MIC/SVIA claimed that once
the modeling problems they discussed are corrected, recreational vehicles would be estimated to
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contribute less than one half percent to mobile source HC emissions, about 1.2 percent of our
original estimate.
Response to Comments:
We have undertaken a very thorough review of all of the data, information and judgements
that went into our emissions modeling. We have considered all of the information submitted by the
commenters and have gathered additional information for consideration as well. As discussed
earlier in this document, we have significantly revised our emissions estimates as a result of this
review. We have documented all of the information we considered as well as our rationale for
choosing the inputs we did in a separate memorandum/ Although our updated modeling took into
account information beyond that submitted by the commenters, the following responses deal
specifically with the comments we received.
CMDA provided no details regarding their claims of erroneous information. However, we
have revised certain of these factors based on other information received during the rulemaking
process.
It is true that our emissions model does not take into account the emissions control program
in California. However, the impacts of this are minimal. First, California does not have any
emission regulations in place for snowmobiles. Second, California allows the sale of non-compliant
off-road motorcycles and ATVs, which are allowed to operate in specific geographic areas during
certain times of the year. As a result, a sizable percentage of off-road motorcycles and ATVs in
California do not meet any emission standards. Third, a reduction in modeled emissions to take into
account California's regulations would not have an appreciable effect on the total emissions forecast
and would not affect the clear evidence that these engines contribute to air pollution. Finally, our
finding is based on the contribution to ozone and CO in nonattainment areas, as well as the
contribution to total PM inventories, both nationwide and in specific areas. Numerous areas that we
considered in making this finding are outside of California. Thus, although our modeling may
marginally overstate the national emissions inventories from recreational vehicles because it does
not account for California's emissions regulations, this issue in no way compromises the validity of
our conclusion regarding the finding itself.
Regarding the HC emission factor for off-road motorcycles and ATVs, although MIC/SVIA
questioned our emission factor, they did not provide any rationale as to why they believed it was too
high. Nor did they provide any additional data or analysis from which a new emission factor could
be derived. We used data on actual off-road motorcycles and ATVs provided by a manufacturer to
develop our off-road motor cycle/AT V emission factors.
Regarding the emission factors for snowmobiles, ISMA did not provide the actual analysis it
used to derive its industry average emission factors. Lacking such supporting information we do not
believe that it is appropriate to adopt ISMA's recommended emission factors. However, we
performed our own analysis of data from a variety of sources, including tests of individual
f "Emission Modeling for Recreational Vehicles," EPA memorandum from Line Wehrly
to docket A-98-01, November 14, 2000.
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snowmobiles provided by ISMA as well as from several test programs performed by Southwest
Research Institute (SwRI). The majority of the snowmobile engines tested were new or nearly new
and represented recent model year snowmobiles (1990 and later), although a few of the tests were
on older snowmobiles. Our analysis of this data yielded snowmobile emission factors of 111 grams
per horsepower hour (g/hp-hr) for HC, 296 g/hp-hr for CO, 0.86 g/hp-hr for NOx, and 2.7 g/hp-hr
for PM. Our HC emission factor is slightly higher than ISMA's recommendation of 104 g/hp-hr,
while our CO emission factor is lower than ISMA's recommendation of 331 g/hp-hr. These
differences are not substantial, and we have confidence that our snowmobile emission factors are
reasonable given the data available to us.
Regarding the snowmobile load factor, we agree with ISMA that the snowmobile load factor
we used in the proposed finding is too high. Further, we believe that the SwRI testing program cited
by ISMA provided a fairly robust examination of snowmobile operation through the actual in-use
testing of snowmobiles. Thus, we have adopted the load factor developed by SwRI for our
modeling of snowmobile emissions.
We agree with S. Lyda and MIC/SVIA that the proposed off-road motorcycle/ATV load
factor is unreal!stically high, considering the power to weight ratio of these vehicles. In the absence
of specific measured load factor data for off-road motorcycles and ATVs we have used the
snowmobile load factor of 0.34 for both off-road motorcycles and ATVs. The snowmobile load
factor was developed using instrumented vehicles under actual driving conditions, and we believe
that snowmobile and off-road motorcycle/ATV operations are similar enough that using a load
factor that has its basis in actual testing is the most appropriate approach given the information
available to us. This is a significant reduction of the load factor compared to what we proposed, and
we believe this is the most reasonable value given the data available to us. This load factor is close
to and generally supported by the estimate provided by S. Lyda per his informal survey of several
off-road motorcycle racers. We acknowledge Mr. Lyda's significant individual effort in gathering
and providing this information. We have chosen to use this specific load factor for off-road
motorcycles and ATVs due to its basis on actual measured load during engine operation. We do not
believe that on-highway and off-road motorcycle riding are similar enough to draw any reasonable
conclusions about the load factor of one from the load factor of another.
In our emissions modeling for recreational vehicles we use horsepower (hp) ranges for 4-
stroke motorcycles and ATVs, as well as snowmobiles. However, because our 2-stroke emission
factors for off-road motorcycles and ATVs are in terms of grams per mile, we have no need for hp
information in modeling these groups. In modeling, rather than use a single average hp to represent
an entire group of vehicles, we break to total hp range into separate bands, each with its own
population. This allows us to more accurately model future in the makeup of the vehicle population.
However, to answer MIC/SVIA's and ISMA's questions about average hp, we calculated, based in
the inputs to our emissions model, the population-weighted average hp of 4-stroke motorcycles to
be 10.5, 4-stroke ATVs to be 21.2, and snowmobiles to be 48.3. It is difficult to assess how these
numbers relate to the 35 hp number that MIC/SVIA provided because, for reasons previously
discussed, we do not have average hp estimates for 2-stroke motorcycles or 2-stroke ATVs.
We agree with ISMA that our annual operating hours for snowmobiles were too high. While
we have reduced our snowmobile operating hours estimate, we do not agree with ISMA that it
should be less than 50 hours per year. Using information from studies done on the economic impact
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of snowmobile operation for eight different states, as well as consumer satisfaction survey results
from the snowmobile industry, and survey results from Bluewater Network and Power Systems
Research we have developed an estimate of 57 hours per year for typical snowmobile operation.
Regarding the estimated annual hours of usage for off-road motorcycles and ATVs, new
information we considered suggested that off-road motorcycle and ATV use differ dramatically, and
that it is not appropriate to use a single annual usage rate for both. For off-road motorcycles we
considered data from two sources. The first source is a survey done by MIC. This survey was done
using two different methods which resulted in two very different estimates of annual usage, with
one estimate being almost six times higher than the other. Because the results of the two methods
are so dramatically different, we have concerns about the results of the MIC survey. The second
source of information we considered for off-road motorcycle usage was a study of recreational fuel
usage done by Oak Ridge National Laboratory (ORNL). Using the information on fuel usage in this
study, along with fuel economy information from California and SwRI, we derived an annual usage
rate of 120 hours per year for off-road motorcycles. While this value is not nearly as low as MIC
suggested it should be, it is somewhat lower than the value we used in the proposed finding.
For ATV usage we relied on a study done by the Consumer Product Safety Commission
(CPSC). This study was fairly robust, and from it we derived the value of 350 hours per year for
ATVs. Contrary to what S. Lyda claimed about the number of motorcycles a given rider owns, the
CPSC study suggested that a given ATV is used by more than one rider. Thus, the annual ATV
hours of usage developed from the CPSC report represents usage per ATV. A given rider tends to
ride about 100 hours per year less than this per-ATV estimate.
Regarding ISMA's comment concerning snowmobile population growth, we based our
future population estimates on extrapolations from historical snowmobile population estimates. We
agree with ISMA that large snowmobile population increases are not likely to continue. We
estimated that total snowmobile population will increase less than eight percent between 2000 and
2010, with similar growth projected beyond thatg.
Our current estimates of recreational vehicle emissions are reasonable when considering all
the information available to us. While our estimates of recreational vehicle emissions did go down
from the proposal, as discussed earlier in this memorandum, they did not go down nearly as much as
S. Lyda and MIC/SVIA suggested they might or should.
5. Emissions Modeling - Nonrecreational
Summary of Comments:
The Industrial Truck Association (ITA) noted several concerns with the details of the
emission modeling published with the proposed finding. ITA noted that the Nonroad Model
predicts about a 10 percent growth in population between 2000 and 2010, but that NOx emissions
increase by 27 percent over this period, CO emissions increase by 18 percent, and HC emissions
decrease by 24 percent. These figures appeared to be inconsistent and anomolous.
8 See footnote e
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ITA shared forklift shipment statistics to suggest an improved estimate of 390,907 forklifts
operating in the U.S. (compared with our estimate of 442,00). ITA's figure was based on an
average forklift life of 8 years. ITA recommended an estimate of 1250 hours annually, rather than
1500 hours, to characterize forklift usage rates. ITA noted that average rated horsepower should be
between 45 and 55 for forklifts powered by spark-ignition engines. These figures could not be
compared to the Nonroad Model, because the analogous figures were not published with the
proposed finding.
Southwest Research Institute (SwRI) also found various aspects of our emission modeling
worthy of note. SwRI suggested deleting leaf blower/vacuum from the population listing for Large
SI engines, expecting that all these engines would be have rated power below 19 kW. SwRI
commented that our estimate of the population of airport ground-service equipment was too low,
based on their earlier published estimates of these vehicles in California. SwRI reported that they
had been generally unable to find gasoline-fueled generators rated above 19 kW, either from the in-
use population or from new models from various manufacturers.
Analysis of Comments:
The apparent discrepancy in population and emission changes between 2000 and 2010 is
caused by the model's use of fuel-specific growth rates, in conjunction with a mistake we made in
the calculation of volatile organic compounds (VOC) in the proposal.11 We inadvertently used VOC
emission rates for natural gas engines to represent LPG engines in the proposal. The effect of this
was that per-engine HC emissions from LPG engines were dramatically underestimated. Also, the
model projects a faster growth in sales for LPG-fueled engines than for gasoline-fueled engines. In
fact, we projected that gasoline equipment populations will actually decrease in the future due to
decreasing sales in favor of LPG equipment. Since the proposed emission factors for LPG engines
are higher for NOx emissions, lower for CO emissions, and dramatically lower for HC emissions
relative to gasoline engines, the long-term emissions picture shows a NOx emissions increasing
faster than the population growth, CO increasing at a rate less than population growth, and HC
emissions actually decreasing over time. Having corrected the problem with the LPG emission
factor for VOC, our final inventory estimates for Large SI equipment increase over time for all
pollutants, as would be expected. However, the different growth rates for LPG and gasoline
engines, as previously discussed, mean that the growth rate in the inventories is different for the
different pollutants, and does not directly track engine population.
To arrive at the estimate of 442,000 forklifts operating with SI engines, we relied on an
industry report that showed not just population estimates, but additional information about how the
population is distributed among different industry sectors (retail, wholesale, manufacturing,
h Hydrocarbon (HC) and volatile organic compounds (VOC) tend to correlate fairly well
and are often used interchangeably. However, in the case of natural gas vehicles, VOC emissions
tend to be very low compared to HC emissions due to the fact that a large percentage of natural
gas vehicle HC emissions are methane, a compound with very low ozone-forming potential
compared to most other HC compounds in vehicle exhaust.
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construction, utilities, and services) and among companies with different fleet sizes.1 These figures
fit together to provide a detailed picture of forklift operations in the U.S. consistent with the original
population estimate. In contrast, ITA provides no basis for its estimate of an 8-year average lifetime
for forklifts. The industry report on forklifts described above estimates a 17-year life. As a result,
we believe that the original estimate may be too low, but is nevertheless a very defensible estimate.
We have updated our estimates of annual operating rates for forklifts using the industry
report referenced above. The new estimate increases to 1800 hours. Again, the report characterized
the information separately for different industry sectors in compiling a single, average estimate.
This detailed approach provides a compelling argument for its conclusion. ITA provided no
information supporting its lower estimate of forklift operating rates.
The Nonroad Model computes an emission contribution from each engine model, rather than
relying on a calculation based on average values (for load factor, average horsepower, hours per
year, etc.). Based on the population figures for each engine model, the weighted average power
level for forklifts with spark-ignition engines is 69 hp. This figure is 25 percent higher than ITA's
upper estimate. While these figures are quite close, they could nevertheless be reconciled by
comparing population counts of individual engine and forklift models.
Some leaf blower/vacuums use a 65-horsepower air-cooled engine. These units are used for
clearing leaves and small branches from large municipal parks. We therefore did not change these
figures in the model.
We agree that the estimated population of airport ground-service equipment is too low. We
have been actively pursuing an improved estimate for this figure, but have not been able to fully
resolve the issue. In the absence of better information, however, we have chosen to leave our
airport ground service equipment population estimate unchanged.
We recognize that there are few gasoline-fueled generators. We have therefore adjusted the
model to change the population of generators thought to be operating on gasoline to be LPG-fueled.
1 "The Role of Propane in the Fork Lift/Industrial Truck Market: A Study of its Status,
Threats, and Opportunities," by Robert Myers for the National Propane Gas Association,
December 1996.
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