United States Air and Radiation EPA420-R-01-017
Environmental Protection June 2001
Agency
vxEPA VOC Adjustment Rule:
Response to Comments
> Printed on Recycled Paper
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EPA420-R-01-017
June 2001
to
Transportation and Regional ProgramsDivision
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
Document II.B-3
Docket A-99-3 2
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TABLE OF CONTENTS
I. COST 1
A. References 1
B. The cost of complying with the Phase IIVOC standard for ethanol RFG 2
1. Background 2
2. Comments on cost 3
C. Market effects of an adjustment in the Midwest 4
D. Market effects of an adjustment outside the Midwest 5
II. SELECTION OF ADJUSTMENT LEVEL AND EXPECTED AIR QUALITY
IMPACTS OF THE RULE IN THE MIDWEST 7
A. Background and summary 7
B. Description of IEPA photochemical modeling analysis 10
C. EPA's reasons for not accepting the adjustment of 0.5 psi 12
D. How lEPA's photochemical modeling supports an adjustment equivalent to an
increase in RVP of 0.3 psi 13
E. Consideration of other approaches 16
F. Calculation of ratios of CO emission decreases to VOC increases 17
G. Other comments on the adjustment level 17
H. Discussion of the emissions impact of the VOC adjustment 18
1. NOx and permeation 18
2. Comparison of emission impacts with and without the adjustment 19
3. Calculation of onroad VOC and CO emissions for the "rule" and "no-rule"
scenarios 20
4. Commingling 22
a. Background 22
b. Further evaluation of commingling in response to comments 24
5. Toxics 25
6. Nonroad emissions 26
a. Effect of VOC adjustment on VOC nonroad emissions 26
b. Commingling effect for off-road emissions 27
c. Effect of rule on CO nonroad emissions 27
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III. EXPECTED AIR QUALITY IMPACTS (OUTSIDE MIDWEST) 29
IV. EFFECT OF NEWER VEHICLES AND LOW SULFUR GASOLINE ON
ADJUSTMENT VALUE 31
V. OTHER COMMENTS 32
A. Applicability of adjustment to ethanol RFG at less than 10 volume percent 32
B. Stranded cost of investments to comply with Phase II RFG 32
LIST OF TABLES
Table 1: VOC emission increases and ratios of CO decrease to VOC increases for Chicago and
Milwaukee as a function of RVP 34
Table 2: VOC emission reductions calculated by the Complex Model as a function of RVP . 35
Table 3: Comparison of emissions with and without the rule in Chicago and Milwaukee ... 36
Table 4: Detailed breakdown of emissions with and without the rule in Chicago and
Milwaukee 37
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I. COST
A. References
Information in the proposed rule regarding the cost of producing MTBE and ethanol RFG
was derived from previous cost studies. These studies are included in Docket A-99-32:
II.D-1: March 17, 1999 report prepared by Jerry Hadder of Oakridge National Laboratory
(ORNL) estimating the economic impacts of Phase 2 gasoline reformulation on the value
of ethanol.
II.D-2: June 14, 1999 memo from Jerry Hadder of ORNL regarding the impact of Phase 2
gasoline reformulation requirements on the cost of using ethanol in PADD II.
We also used information contained in EPA's Final Regulatory Impact Analysis for
Reformulated Gasoline (December 13, 1993).
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B. The cost of complying with the Phase II VOC standard for ethanol RFG
1. Background
Section 21 l(k)(3) of the Clean Air Act requires that for the year 2000 and beyond, EPA's
regulations for RFG must include a VOC performance standard which must be at least equal to a
25 percent reduction from baseline emissions. An exception to the 25 percent reduction can be
allowed for factors such as technical feasibility and cost, but in no case can the reduction be less
than 20 percent.
According to the cost study on ethanol RFG blends conducted by DOE (referenced in
Section LA), the change in average manufacturing cost of reducing the RVP of blendstock
intended for ethanol-blended RFG to a level that ensures compliance with the current Phase n
VOC performance standard is approximately $0.01 per gallon of RFG for refiners currently using
ethanol. Based on DOE's modeled 1.4 psi increase, this cost reflects the 1.4 psi RVP reduction
necessary to offset the RVP increase associated with the use of ethanol as an oxygenate. (DOE
derived its cost impact estimates by comparing the cost of reducing the RVP in Phase I RFG
with 10 volume percent ethanol, to the RVP level necessary to comply with the Phase n RFG
performance standard for VOC.)
Based on the above, it would cost refiners approximately $0.01 per gallon to reduce the
RVP of blendstock used to make ethanol RFG by 1.4 psi. Since our adjustment of the VOC
performance standard by 2.0 percentage points is equivalent to an increase in RVP of
approximately 0.3 psi of the blendstock, we calculate the reduction in cost associated with this
adjustment as follows: the ratio of the 0.3 psi to 1.4 psi is 21.4 percent; this ratio is then applied
to the $0.01 per gallon to yield a cost reduction of approximately $0.002 per gallon.
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2. Comments on cost
Comments stated that the adjustment (at an equivalent increase in RVP of 0.2 psi, as
proposed) would be too small to offer relief to refiners. One commenter suggested that an
adjustment equivalent to as much as 1.0 psi would not result in a change in ambient ozone that
could be detected via monitoring or photochemical modeling. The commenter stated that since
the Clean Air Act allows EPA to adjust the performance standard downward to as low as 20
percent, taking into account technical feasibility and cost, that such an adjustment could be
allowed. Other commenters also raised the 20 percent lower limit as a possibility that EPA
should consider.
We do not agree, in light of the serious air quality consequences associated with such an
adjustment, that cost considerations related to making RFG with ethanol justify an adjustment
equivalent to a 1.0 psi RVP increase. The statutory basis for the adjustment, per Sections
21 l(k)(l) and 21 l(k)(3), authorizes EPA to consider the additional cost associated with making
Phase n RFG with 10 volume percent ethanol and the water quality impacts of any potential
increase in use of MTBE, and EPA believes it also appropriate to consider the impact of any such
adjustment on the air quality benefits that are the primary aim of the RFG requirements.1 Thus,
the amount of the adjustment should be limited by considerations related to the impact that an
adjustment might have on the air quality benefits of the Phase II RFG program. As discussed in
Section HI below, we believe that the adjustment should be no larger than that which can be
reasonably expected to result in overall air quality benefits comparable to the benefits achieved
Unlike EPA's renewable oxygen requirement (see Am. Petroleum Inst. v. Browner, 52 F.3d 1113, (D.C. Cir
1995)), today's rulemaking does not impose any additional restrictions on RFG. Rather, today's action
preserves the goals of the RFG program while taking into consideration the factors enumerated in sections
21 l(k)(l) and (k)(3) to identify the appropriate VOC reduction requirement for certain types of fuels."
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by Phase II of the RFG program generally. We believe that a downward adjustment of 2.0
percentage points (rather than the proposed 1.0 percentage point) from the current standard is
appropriate, based largely on photochemical modeling that Illinois Environmental Protection
Agency (IEPA) submitted to EPA.
With respect to the comment that the 1 percentage point adjustment was too small, we
note that during last summer, refiners supplied RFG with ethanol to the Chicago and Milwaukee
RFG areas. The ethanol industry originally feared that the increased stringency of the Phase II
VOC standard would result in ethanol being "locked out" of the RFG market. Last summer's
RFG market proved otherwise, however. This suggests that with economic conditions similar to
last summer's the current Phase II standard should not prevent refiners from making RFG with
ethanol. More importantly, however, it suggests that an adjustment will offer increased
flexibility to refiners. Thus even if market conditions change, we believe an adjustment will
provide an incentive to make more RFG with ethanol than without such adjustment. Finally, one
refiner commented that the 1 percentage point adjustment would result in that refiner making
approximately 5 percent more RFG with ethanol than without the adjustment. We believe,
therefore that the 2 percentage point adjustment will allow even greater flexibility to refiners
supplying RFG to Chicago and Milwaukee.
C. Market effects of an adjustment in the Midwest
While ethanol maintained its market share in the Chicago and Milwaukee RFG programs
during the summer of 2000, for the future it continues to be difficult to predict with certainty the
geographic distribution of specific oxygenates in the Phase n RFG program. EPA wishes to
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ensure the stability of the RFG program in the Midwest and to avoid any significant disincentive
for the use of ethanol. Related to this, one refiner supplying the Chicago area commented that
the VOC adjustment could result in an increase at the commenter's refinery of approximately one
to two thousand barrels per day of ethanol-RFG during the summer blending season. Although
this is a nominal increase, it was an estimate made on the basis of the proposed adjustment of 1.0
percentage point. We believe that today's adjustment of 2.0 percentage points will provide an
incentive for the continued use of ethanol in Chicago and Milwaukee.
D. Market effects of an adjustment outside the Midwest
Outside the Midwest, where MTBE is the predominant oxygenate used in RFG, we agree
with commenters who suggested that an adjustment to the VOC performance standard may have
little or no impact on ethanol use. This is because ethanol use outside of the Midwest is
influenced primarily by ethanol availability and cost. While an adjusted standard, if it were to
apply in such areas, could provide some cost relief to refiners choosing to make ethanol-RFG, it
would probably not provide sufficient incentive to cause refiners who would not otherwise do so
to switch from MTBE to ethanol. Therefore, to the extent that conditions favorable to increased
ethanol use arise in areas outside of the Midwest, refiners may decide to switch to ethanol, but
any such decisions are unlikely to be strongly influenced by a small adjustment to the VOC
standard. Even if an adjustment of the VOC performance standard would result in some
additional ethanol use in these areas, however, we believe that in areas where there is current
ethanol use would not preserve the benefits of the RFG program. This is discussed in further
detail in Section n.H.4. below on commingling effects.
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II. SELECTION OF ADJUSTMENT LEVEL AND EXPECTED AIR QUALITY
IMPACTS OF THE RULE IN THE MIDWEST
In deciding to promulgate the final VOC adjustment rule, we concluded that in the
Chicago and Milwaukee RFG areas the adjustment would preserve the air quality benefits of the
RFG program and provide an incentive for continued use of ethanol. In this section we discuss
how we established the adjustment level, and compare the emission impacts of the rule to that of
a "no-rule" scenario. We believe that the overall effect of the adjustment on emissions will not
adversely impact the overall benefits of Phase II RFG. While there will be greater mass VOC
emissions with the rule than without it, RFG with 10 volume percent ethanol (3.5 weight percent
oxygen) achieves significantly greater CO emission reductions than RFG with 2.0 weight percent
oxygen. We believe that the ratio of CO reduction to VOC increase associated with ethanol use
provides a reasonable degree of assurance that the ozone air quality impacts of RFG in Chicago
and Milwaukee will result in benefits similar to those generally expected from the Phase n RFG
program.
A. Background and summary
RFG blended withlO percent ethanol by volume, the typical blending level of ethanol,
achieves significant reductions in CO emissions compared to non-ethanol RFG blends because of
higher oxygen content (3.5 weight percent oxygen vs. 2.0 weight percent oxygen). It is well
recognized that CO contributes to ozone formation. CO is present in ambient concentrations due
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in large part to the large volume of emissions from mobile sources. The Urban Airshed Model
(UAM), relied on by states in their State Implementation Plan (SIP) submissions, includes
inventories of CO emissions as well as volatile organic compounds (VOC) and oxides of
nitrogen (NOx). While the role of CO in the formation of ozone is limited when compared to the
effect of VOC and NOx, the volume of CO emissions from motor vehicles is comparatively large
and therefore is not ignored in photochemical modeling demonstrations.
RFG with 3.5 weight percent oxygen results in a level of CO emission reductions that is
greater than at 2.0 weight percent - the minimum amount of oxygen required by the statute -
with correspondingly greater ozone benefits. Thus, at appropriate levels an adjustment to the
VOC performance standard for such blends can still preserve the level of ozone air quality
benefits generally expected to be achieved by the statutory RFG program. We have concluded
that such an adjustment is appropriate in this case, based on cost and water quality
considerations, so long as we can be reasonably confident that the expected benefits of the RFG
program will be preserved. We are therefore adjusting the VOC performance standard by 2.0
percentage points for 10 volume percent ethanol RFG in the Chicago and Milwaukee areas. In
order to provide reasonable assurance that the benefits of the RFG program will be preserved, we
used the following process to determine the appropriate level for the adjustment:
1) We calculated the CO decrease in tons per day for Chicago and Milwaukee (the RFG
areas that use ethanol) associated with the increase from 2.0 to 3.5 weight percent
oxygen in the fuel;
2) We calculated the VOC increase in tons per day in Chicago and Milwaukee
associated with varying increases in RVP in increments of 0.1 psi;
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3) We calculated the ratio of CO decrease to VOC increase for each of the RVP
increments for both Chicago and Milwaukee;
4) We selected the RVP increment yielding a ratio of CO decrease to VOC increase that
we believe will result in similar ozone air quality benefits as currently achieved by the
Phase IIRFG program in the Chicago and Milwaukee areas.
The first three steps are detailed in the draft Technical Support Document (see Document
II-B-2 in Docket A-99-32). The fourth step involved using the results of photochemical
modeling that Illinois Environmental Protection Agency (IEPA) conducted for the Chicago
region, and which was submitted to EPA for our consideration.
The proposed adjustment to the VOC performance standard of 1.0 percentage point
(equivalent to an increase in RVP of approximately 0.2 psi) would have resulted in a ratio of CO
emission decrease to VOC emission increase of 45:1. At the time, EPA was generally confident
that this level of adjustment would protect the air quality benefits of the RFG program.
Comments criticized and questioned our selection of this adjustment value; some commenters
believed that the adjustment was not large enough and others believed it could result in adverse
ozone air quality impacts.
In the proposed rule we solicited comment on a photochemical modeling analysis that
IEPA provided to EPA. IEPA submitted an analysis that it believed supported an adjustment
equivalent to an increase in RVP of 0.5 psi in the Chicago area. (A report analyzing lEPA's
submission is Document IV-A-1 in Docket A-99-32.) While we do not accept the adjustment
level of 0.5 psi for reasons detailed below, we believe that the photochemical modeling that
IEPA conducted provides information about the relationship between CO and VOC emissions
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and ozone formation that reasonably supports a VOC adjustment equivalent to 0.3 psi in the
Chicago and Milwaukee areas.
The IEPA analysis suggests the ratio of CO decrease to VOC increase necessary to
maintain similar ozone air quality benefits is lower than the 45 to 1 ratio upon which we based
the proposed adjustment. Specifically, for the modeled region, the ratios of CO decrease to
VOC increase suggested by lEPA's modeling range from 12:1 to 23:1, for the four episode days
modeled.
As explained in further detail in Section II.B. below, EPA believes that based upon
lEPA's photochemical modeling, the proposed 0.2 psi equivalent adjustment level would be
overly conservative. EPA is reasonably confident that an adjustment equivalent to 0.3 psi will
maintain similar ozone air quality benefits as the current Phase IIRFG program.
B. Description of IEPA photochemical modeling analysis
IEPA performed an analysis of the ozone impacts of CO and VOC emissions from motor
vehicles in the lower Lake Michigan area. (See Documents II-D-4, 5 and 6 in Docket A-99-32).
IEPA ran the Urban Airshed Model-Version V (UAM-V) for a four day episode in 1991. The
analysis compared the reduction in peak predicted ozone concentrations from assumed reductions
of CO and VOC emissions from motor vehicles.
The baseline emissions inventory for lEPA's modeling analysis was the most recent
inventory developed by the Lake Michigan Air Directors Consortium (LADCO) for the Chicago
area for the year 2007. The inventory reflected all mandated CAA controls, motor vehicle
emissions at NLEV and RFG-II levels, and a NOx emissions rate of 0.25 Ib/MMBTU for large
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electric generating units. IEPA then ran a baseline scenario using the 2007 inventory and
meteorological and air quality data bases developed for the 16-21 July 1991 LMOS/OTAG
episode. We believe that this episode corresponds to the most prevailing type of episode for
Chicago and generally provides a reasonable basis for evaluating air quality impacts in this areas.
In addition to the year 2007 baseline, IEPA simulated additional hypothetical emissions
scenarios. These involved runs in which IEPA first reduced motor vehicle CO emissions,
producing an ozone differential of approximately 1 ppb. IEPA then used an iterative process to
determine how much VOC reductions in the on-road vehicle inventory in the greater Chicago
region in northeastern Illinois would be needed in the model to give the same ozone response.
No other changes to the modeling input files (including initial and boundary conditions) were
made.
IEPA next analyzed UAM-V results; i.e, ground level ozone concentrations for the 2007
baseline, the CO reduction scenario, and the VOC reduction scenario. For each modeling day,
IEPA tabulated the peak 1-hr ozone concentration predicted anywhere in the grid domain for the
baseline and the two hypothetical scenarios. IEPA normalized the impact of CO and VOC
emissions on ozone formation by computing, on a daily basis, the change in ozone (in ppb) for
each 1000 tons of CO and VOC emissions reduced. The result of the analysis was a table listing
the computed ratio of CO to VOC ozone changes per 1000 tons of emissions reductions.
IEPA concluded that the amount of ozone formed by CO emissions is 4 to 8 percent of
that for VOC for the episode modeled. The actual CO/VOC ratios of ozone formation derived
from UAM-V modeling for Chicago were 8.61, 4.30, 6.56 and 7.86 percent for the individual
days during the 18-21 July 2007 simulation period. IEPA used this modeling, in combination
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with certain emission assumptions (as described below), to conclude that EPA should adopt an
adjustment to the VOC performance standard equivalent to 0.5 psi.
C. EPA's reasons for not accepting the adjustment of 0.5 psi
After evaluating lEPA's analysis, EPA has decided that the IEPA study does not
reasonably support an adjustment of 0.5 psi RVP for RFG containing ethanol . lEPA's
methodology was internally inconsistent and used inaccurate emission estimates.
IEPA compared the emissions (expressed in mg/mi) of a "complying fuel" (assumed to
have an RVP of 6.8 psi and 2.0— see Document n-D-6 in Docket A-99-32) with an alternative
fuel consisting of a 7.3 psi RVP and 3.5 weight percent oxygen. IEPA calculated the ozone
impact from the "complying fuel" versus the 7.3 psi fuel using the ratios of CO and VOC ozone
formation derived from the photochemical modeling described above. Using this technique,
IEPA calculated that the ozone impact of complying fuel would be 4,289 mg ozone/mi and that
the ozone impact of the 7.3 psi fuel (with accompanying CO reductions due to the 3.5 weight
percent oxygen) would be 4,291 mg ozone/mi—comparable amounts.
We found several deficiencies in the emission calculations which IEPA used in its
justification of a 0.5 psi adjustment. Specifically, the motor vehicle VOC emission rates were
taken from the EPA Complex Model and represent emissions from solely 1990 model year
vehicles rather than those of the in-use fleet post-2000. IEPA then obtained the emission factor
for CO by multiplying the Complex Model-derived VOC emission factor by a ratio of nationwide
CO to VOC emissions for onroad vehicles, taken from the 1997 EPA Emissions Trends report
rather than using values contained in the emission inventory for this region. This method is
highly inaccurate, in that it represents a blend of emissions in areas with conventional and
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reformulated gasoline, summer and winter conditions, and a wide range of local emission control
programs, such as I/M, rather than the specific conditions existing in Chicago during the ozone
episodes. Finally, lEPA's estimate that 10 volume percent ethanol RFG (3.5 weight percent
oxygen) would provide a 10 percent reduction in CO emissions from motor vehicles (compared
to 2.1 weight percent oxygen RFG) is overstated. Using draft MOBILE62 methodology,
(described in the above referenced draft Technical Support Document) we estimate a reduction of
approximately 7 percent. We found that while the application of the modeling results was
mathematically correct, the emissions inventory assumptions that they used to apply the results
were inaccurate and inconsistent and therefore did not support an adjustment to the VOC
standard of 3.7 percentage points (0.5 psi).
Notwithstanding the inaccuracies of the inventory used, IEPA also relied upon the use of
relative reactivity factors for exhaust and evaporative VOC emissions. EPA does not support the
use of relative reactivity factors, for reasons stated in the preamble of the NPRM. See 65 FR
42924.
D. How lEPA's photochemical modeling supports an adjustment equivalent to an
increase in RVP of 0.3 psi
While we do not accept lEPA's recommendation for an adjustment equivalent to an
increase in RVP of 0.5 psi, we find that the photochemical modeling that IEPA conducted does
MOBILE is an integrated set of FORTRAN routines for use in the analysis of the air pollution impact of
gasoline-fueled and diesel-powered highway mobile sources. MOBILE is used in the preparation of all
projection year emission inventories required by the Clean Air Act Amendments of 1990 for non-California
areas. MOBILE calculates emission factors for gasoline-fueled light-duty vehicles (LDGVs), light-duty
trucks (LDGTs), heavy-duty vehicles (HDGVs), and motorcycles. MOBILE also contains provisions for
modeling the impact on emission factors of oxygenated fuels (i.e., gasoline/alcohol and gasoline/ether
blends) and of participation in the reformulated gasoline (RFG) program under the 1990 Clean Air Act
Amendments.
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support a larger adjustment to the VOC standard than we originally proposed when more recent
information on emissions inventory of CO and VOC from onroad vehicles is used.
As described in the above referenced draft Technical Support Document, we calculated
changes in emissions associated for each 0.1 psi increment of RVP above complying fuel as
determined via the Mobile Model.3 (Table 1 provides a summary of the VOC emission increases
and ratios of CO decrease to VOC increase for Chicago and Milwaukee for RVP values from 6.7
to 7.7 in increments of 0.1 psi; Table 2 provides a summary of the VOC emission reductions
calculated by the Complex Model as a function of these varying RVP levels, with all other
parameters held constant. Table 2 is included here as a reference to show how the ratio of CO
decrease to VOC increase of 15:1 relates to a downward adjustment to the VOC performance
standard by 2.0 percentage points.) As shown in Table 1, at a 0.2 psi adjustment level, the
reduction of CO emissions relative to the increase in VOC emissions is 45:1. At a 0.3 psi
adjustment, the ratio of CO decrease to VOC increase drops to 15:1. Having determined the CO
and VOC emission consequences of different levels of adjustment, we evaluated what the ozone
consequences might be, in order to identify a level of adjustment at which we could be generally
confident that the ozone benefit of Phase n RFG would be preserved in the Chicago and
Mobile 6 is currently under review and has not as yet been released to the public. As a result, we felt that the
computation of VOC increases associated with the adjustment should be based on Mobile 5b, which is
publicly available. The equations for computation of CO in Mobile 6, however, were peer reviewed and
available to the public. We chose to use the Mobile 6-derived equation for CO, rather than relying on
Mobile 5b, primarily because newer and more relevant data was used in Mobile 6 to arrive at the relationship
between fuel oxygen and CO. MOBILESb oxygen-based CO benefits have been questioned for some time
because dispersion modeling of Mobile 5b-derived CO inventories have not matched monitored ambient CO
levels. Mobile 5b overestimates the CO reduction benefit due to fuel oxygen, while Mobile 6, based on new
data, shows a reduction in oxygen-based CO benefits for many vehicle classes and essentially a zero-benefit
for post-tier 1 (1994 and later) vehicles. Therefore because of the public availability of the CO calculation
method for Mobile 6 and the increased accuracy in prediction of oxygen-based CO benefits, we felt the
Mobile 6 estimation method for CO provided a better more conservative estimate for these emissions than
Mobile 5b.
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Milwaukee areas.
The single episode UAM analysis performed by IEPA indicated that, ton for ton, CO
would form 4.30, 6.56, 7.86 and 8.61 percent as much ozone as VOC, respectively, over the four
days of the modeled episode. The mean value of the CO to VOC ozone formation ratios
obtained from lEPA's analysis is 6.8 percent, at which level the ratio of CO reductions to VOC
increase needed to maintain ozone levels is 14.7:1. Moreover, looking at the IEPA modeling
results on a daily basis, the results indicate that for each ton of VOC increase, the decreases in
CO emissions necessary to maintain ozone levels are 23, 15, 13, and 12 tons, respectively.
Thus, on two of the days that IEPA modeled, the ratio was better than the 15:1 associated with a
VOC adjustment equivalent to 0.3 psi (an ozone benefit), and on one of the days the modeled
ratio was approximately 15:1 (ozone neutral). On only one of the four days modeled was the
ratio worse (i.e., greater) than 15:1. Significantly, the modeled day producing the ratio of 15:1
yielded the highest ozone concentration of the four days modeled. Because the highest ozone
concentration is associated with the 15:1 ratio, adjustments based on lower ratios (i.e., 12:1 and
13:1) should not be used. We believe, therefore, that lEPA's analysis provides reasonable
assurance that the 0.3 psi adjustment level is appropriate and would tend to preserve the ozone
air quality benefits of the Phase n RFG program.
Finally, we note that the photochemical analysis for Chicago can be said to be generally
representative of the Milwaukee area to due to the similarity in fuel formulations (100 percent
ethanol blended RFG), their geographical proximity (less than 100 miles apart), and the fact that
lake effects on local meteorology would be expected to be similarly important in the formation
of ozone in these two areas.
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E. Consideration of other approaches
Both the Renewable Fuels Association (RFA) and the National Corn Growers
Association (NCGA) submitted comments on the proposed rule, suggesting that a larger
adjustment be adopted. (See items IV-D-10 and IV-G-01 in Docket A-99-32). RFA's analysis
was based in part on reactivity factors, as well as photochemical modeling runs. We do not
accept the use of reactivity factors as discussed in further detail below. RFA's consultant
prepared the photochemical modeling analyses for RFA, and also prepared photochemical
analyses for IEPA which they used in the studies which they submitted to EPA. The report
prepared by our consultant on lEPA's study addresses the photochemical modeling conducted by
RFA's consultant (see document IV-A-1 in Docket A-99-32). Briefly, for the reasons stated in
the report on lEPA's analysis, we believe that assumptions and approach adopted by RFA's
consultant in the photochemical modeling analysis contain similar technical problems as those
that were in the consultant's analyses for IEPA. We found that lEPA's own photochemical
analysis, however, while possessing some problems, were generally valid for use in establishing
the adjustment that we are promulgating.
NCGA's analysis was based entirely on the use of reactivity factors to support a larger
adjustment. Our position on the use of reactivity factors is the same as we stated in the proposed
rulemaking. Specifically, we agree with the National Research Council in its 1999 report (page
5) in which it states '' So-called reactivity factors * * * are often uncertain and of limited utility
for comparing similar RFG blends." EPA continues to believe that the reactivity factors that
have been developed to date may not accurately reflect actual photochemical reactivity of various
ozone precursors. In recent regulatory decisions, EPA has expressed these concerns and others
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related to the use of relative reactivity factors [63 FR 48792, September 11, 1998]. In particular,
EPA is concerned that the factors do not represent the wide variation in atmospheric conditions
that exist across the country or across any individual airshed and which have a large influence on
ozone formation.
F. Calculation of ratios of CO emission decreases to VOC increases
Some commenters criticized the procedure we used to establish ratios of CO emission
decreases to VOC increases for the various incremental RVP values and questioned our use of
Mobile 5b for calculation of VOC emissions while using an equation derived from Mobile 6 for
calculating CO decreases. At this time, the Mobile 6 equation for CO has been peer reviewed
and is thus appropriate for use, while the equations for VOC in Mobile 6 are still undergoing
review. We do not believe that use of Mobile 5b for VOC and the Mobile 6 equation for CO
represents an inconsistency. Rather, Mobile 6 provides a more accurate method for estimating
CO as a function of oxygen in the fuel. Mobile 5b would have overestimated the CO decrease,
suggesting an inappropriate adjustment for VOC. Thus, while we believe that there is no
inconsistency in our approach, we note that any potential effect of using Mobile 6 to evaluate CO
emissions would tend to make our analysis more accurate.
G. Other comments on the adjustment level
The California Air Resources Board (CARB) commented on our proposed rule and stated
that our ratio of CO decrease to VOC increase associated with the adjustment (45:1) is similar to
theirs, but "must not be further decreased." While we had proposed a nationwide adjustment to
the VOC performance standard, we believe for the reasons explained in the preamble to the rule
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that the adjustment should be restricted to the Chicago and Milwaukee areas. Thus, while
CARS's comment might have merit for a rule of national applicability, it is not specifically
relevant to Chicago and Milwaukee and does not provide a basis for rejection of lEPA's
photochemical modeling results for the modeled region.
Another comment suggested that the effect on ozone from an adjustment equivalent to an
RVP increase of 1.0 psi would be impossible to detect via monitoring or modeling and therefore
the adjustment should be made at such level. We agree that the effect of small VOC adjustments
on ozone generally would be too small to be measured via ambient ozone monitoring or
modeling due to the lack of sensitivity of such measurement and predictive tools. Given the
numerous factors (e.g., other stationary and mobile source air quality control strategies,
meteorology, traffic patterns, geography and other factors) that affect ambient air measurements,
it is difficult to discern the impact of any one air quality control strategy through ambient
monitoring or photochemical modeling. Notwithstanding the difficulty of discerning the changes
due to any one air quality strategy, this does not mean there is no impact on ozone or that a 1.0
psi adjustment would preserve the benefit of the Phase n RFG program. This benefit comes
from the actual impact of the RFG emissions reductions on ozone and the role these reductions
play in combination with many other necessary regulatory programs to obtain overall reductions
in ozone. We do not believe that the size of the CO reduction relative to a VOC increase
associated with a 1.0 psi adjustment would preserve the benefit of the Phase II RFG program.
Furthermore, we do not consider the benefits of the Phase n RFG program to be inconsequential.
H. Discussion of the emissions impact of the VOC adjustment
1. NOx and permeation
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Some commenters raised issues regarding the impact of the proposed VOC adjustment
on NOx emissions and permeation. Commenters stated that the higher oxygen levels associated
with the use of ethanol in RFG at 10 volume percent (3.5 weight percent oxygen) lead to
increased NOx emissions, and result in a loss of overcompliance with the NOx performance
standard. Commenters also suggested that the proposed VOC adjustment would result in an
increase in permeation. Specifically, commenters observed that soft fuel components of
automotive fuel systems tend to be more permeable to ethanol than to other hydrocarbons in
gasoline. Thus, they argued, any increase in ethanol use attributable to an adjustment of the VOC
performance standard would be accompanied by an increase in permeation-related emissions.
There is a high level of uncertainty regarding the overall impact of the VOC adjustment
on NOx emissions, given the variety of other fuel parameters such as aromatics, olefms, and
other gasoline components that can affect NOx emissions. Specifically, there is no adequate
basis to conclude what the effect on NOx would be absent information about what impact this
rule-or oxygen levels-will have on how refineries reformulate their gasoline for all of the fuel
parameters relevant to NOx. There is also uncertainty regarding permeation since currently there
is little information on the level of permeation emissions associated with ethanol. The California
Air Resources Board is undertaking a study to quantify permeation losses, but the study will not
be released until the fall of 2001. Moreover, because the rule is restricted to the Chicago and
Milwaukee RFG areas, in which the penetration of ethanol-RFG is 100 percent, the NOx and
permeation emissions would not change from their current levels if there is no change in ethanol
use.
2. Comparison of emission impacts with and without the adjustment
19
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We believe that without the VOC adjustment a limited potential exists for refiners to use
more MTBE in RFG in the Chicago and Milwaukee areas than with the adjustment.
Accordingly, we have examined the effect of the adjustment on emissions for both scenarios (i.e.,
rule and no rule) and compared the results. We believe that the ratio of CO reduction to VOC
increase associated with ethanol use will remain at a level that provides a reasonable assurance
that the benefits of the Phase n RFG program will be preserved, even with the adjustment.
Therefore, the rule will not sacrifice the general benefits of Phase n RFG.
Table 3 summarizes the emission impacts of today's action, as compared to the emission
consequences of no action, in both the Chicago and Milwaukee RFG areas with respect to CO
and VOC. The no-rule scenario assumes that the VOC standard remains as it is currently, and
that there would be a 5 percent market penetration of MTBE as an oxygenate for RFG in the
Chicago and Milwaukee areas.4 Table 4 provides a detailed breakdown of the emission effects
for the rule and no-rule scenarios for commingling and nonroad vehicles.
Calculation methods and assumptions are described in the sections below. Also
discussed below is the effect on the parameters of commingling, nonroad vehicles, and toxics.
3. Calculation of onroad VOC and CO emissions for the "rule" and "no-rule" scenarios
The above-referenced draft Technical Support Document for the proposed rulemaking
contains the calculation procedures that we used to estimate the CO reduction associated with 3.5
weight percent oxygen in the gasoline, and the VOC emission changes as a function of RVP
increases associated with an adjustment to the VOC performance standard.
We believe that this 5 percent level is a conservative estimate of the most MTBE-blended RFG we
might expect to see in Chicago and Milwaukee over the short term. We use this level for purposes
of this analysis to illustrate the potential impact of today's rule if the rule has the intended effect.
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For the no-rule scenario, there would be no VOC increase since there would be no
adjustment. The calculation of CO for the no-rule scenario assumes that 5 percent of the ethanol-
RFG market share is displaced by MTBE-RFG. This increase in MTBE use would result in a
loss of some of the CO reduction benefits associated with 10 volume percent ethanol RFG.
Specifically, for the 5 percent share of ethanol RFG that is displaced, the oxygen content
of the RFG decreases from 3.5 to 2.1 weight percent; it is necessary then to calculate the CO
emissions increase for that market share. CO emissions at 2.1 weight percent oxygen are
approximated by the Mobile 6-derived equation used in the draft Technical Support Document.
We converted the CO emission rate (10636.7 mg/mi) to tons/day and multiplied by the MTBE
market share (5 percent) and the VMT for Chicago and Milwaukee to yield 76.39 tons/day and
18.6 tons/day, respectively. We then compared these values with CO emissions assuming 3.5
weight percent oxygen in the fuel, also approximated by the Mobile 6-derived equation. Using
this same approach we estimate these emissions to be 9906 mg/mi which, based on the Vehicle
Miles Traveled (VMT) for each area, equates to 71.14 and 17.28 tons/day for Chicago and
Milwaukee, respectively. Thus we estimate the increase in CO from a displacement of 5 percent
of ethanol RFG at 3.5 weight percent oxygen by MTBE RFG at 2.1 weight percent oxygen to be
5.25 tons/day (76.39 - 71.14) and 1.27 tons/day (18.6-17.28), for Chicago and Milwaukee,
respectively.
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4. Commingling
a. Background
In comparing the rule and no-rule scenarios, a model that estimates commingling effects
(described in more detail below) suggests that the adjustment will have a modest beneficial
impact on VOC emissions because the adjustment would preserve the current 100 percent
penetration of ethanol RFG in the Chicago and Milwaukee areas. Therefore, no emission
increases associated with the mixture of ethanol and non-ethanol blends of gasoline in
automobile gasoline tanks would occur in the rule scenario. Since the presence of ethanol causes
an increase in the volatility of gasoline (as measured by Reid Vapor Pressure or RVP), such
commingling in automobile gas tanks would contribute to an increase in VOC emissions in the
no-rule scenario.
When ethanol is mixed with gasoline, a non-linear increase in RVP occurs. For example,
if gasoline with an RVP of 8.0 psi is mixed with non-denatured ethanol (which alone has an RVP
of 2.4 psi) in a 90 percent gasoline/10 percent ethanol mixture, the RVP of the resulting mixture
is approximately 9.1 psi, a 1.1 psi RVP increase.5 Because of this RVP boost associated with
ethanol blending, a blendstock with a sufficiently low RVP must be used to achieve the desired
RVP in the ethanol-blended gasoline.
An RVP boost will also occur when ethanol-blended gasoline is mixed with non-
oxygenated or ether-oxygenated gasoline. For example, the RVP of a mixture containing equal
volumes of a 7 psi ethanol-oxygenated RFG blend and a 7 psi non-oxygenated RFG blend would
5 SAE paper 940765, "In-Use Volatility Impact of Commingling Ethanol and Non-Etnanol Fuels"
Peter J. Caffrey and Paul A. Machiele, US EPA.
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be greater than 7 psi. When an ethanol-oxygenated gasoline is mixed with an MTBE-
oxygenated gasoline the resulting increase in RVP is somewhat smaller than it is when an
ethanol-oxygenated gasoline is mixed with a non-oxygenated gasoline. Mixing of ethanol-
oxygenated gasoline with other gasoline is called commingling and the associated RVP boost is
called the commingling effect. While federal regulations prohibit or restrict commingling in the
distribution system, these restrictions do not apply to commingling in vehicle fuel tanks.
Several models exist to assist in estimating the commingling effect under differing input
assumptions about the amount of ethanol used, base RVP of the fuels, and consumer refueling
habits. Perhaps the most important factors in predicting the commingling effect in an
ethanol/MTBE market are brand loyalty (i.e., the extent to which consumers refuel with one
brand, several brands, or many brands)6, and the market share of ethanol-blended RFG in that
market.
EPA developed a model (SAE paper 940765; see footnote 2) that predicts emission
increases based on commingling. The California Air Resources Board developed a similar
probability model, formulated by Dr. D.M. Rocke of University of California at Davis. Both
models indicate that when "loyalty" is held constant, the commingling effect peaks at or near 50
percent ethanol market share. With the EPA model, the commingling effect peaks at 30 to 50
percent market share, depending on the model parameters selected Increases in the ethanol RFG
The significance of brand loyalty in prediction of the commingling effect is the underlying assumption that
oxygenate usage would be consistent within a given brand in a given area. Thus a specific brand of
oxygenated gasoline sold in a given area would be entirely ether-oxygenated or entirely ethanol-oxygenated.
While this is generally true, we have seen some exceptions to this assumption, although extremely limited. If
the assumption of dedicated oxygenate use per brand is not generally valid, then significant commingling
could occur even in vehicles whose owners do not switch brands, and the emission increase associated with
commingling would be even higher than what the models predict.
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market share above the critical mixing point for commingling would reduce the RVP increase
that occurs from commingling. These models also show that as loyalty decreases at a constant
market share (i.e., as consumer refueling choices become more random), the commingling effect
increases.
The commingling effect can result in an overall increase in the RVP of the gasoline pool
ranging from 0.1 to 0.3 psi. (Such increases in RVP would be beyond the equivalent RVP
increase of 0.3 psi associated with this rule.) Increases in the ethanol RFG market share in an
area where ethanol is already used at or above the critical percentage for commingling (e.g.,
above 50 percent market share) could reduce commingling-related emissions, however.
Although these models may accurately predict the magnitude of the commingling effect
for a given set of input conditions, the conditions that would be specifically applicable to RFG
areas in any given area of the country outside of Chicago and Milwaukee are unknown. Outside
Chicago and Milwaukee, it is more difficult to predict market share. However, states and state
associations expressed concern about the possibility of increased VOC emissions due to
commingling. For example, the Northeast States for Coordinated Air Use Management pointed
out that where both MTBE- and ethanol-blended RFG are available, commingling in automobile
gasoline tanks cannot be controlled by regulation and will result in VOC increases. The
California Air Resources Board similarly expressed concern that EPA's proposal did not address
commingling.
b. Further evaluation of commingling in response to comments
For the "no rule" scenario, we assumed a 95 percent market penetration of ethanol RFG
and 5 percent penetration of MTBE RFG. The blend not containing ethanol would then be
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subject to a commingling RVP increase due its presence in a market along with ethanol RFG. .
The above-referenced EPA commingling model estimates an increase in RVP of 0.08 psi (0.07 to
0.09 psi) for a displacement of 5 percent of RFG using ethanol by RFG using MTBE.
Emissions of VOC are derived from the RVP increase by using results from EPA's
MOBILE 5b model. MOBILE 5b yields emissions of VOC as a function of fuel RVP. Estimates
of the VOC emission increases resulting from the adjustment rule were calculated for RVP levels
varying from 6.7 to 7.7 in increments of 0.1 psi for Chicago and Milwaukee. (See Table 3.)
Using these values, we then calculated the effect of commingling for the "no-rule" scenario, by
prorating the tonnages in Table 3. Specifically, we calculated the VOC emission increase
associated with an RVP of 6.78 psi, which represents the baseline RVP with the additional
increase due to commingling (0.08 psi). We estimated the increase in VOC emissions associated
with an increase in RVP of 0.08 psi (i.e., an increase from 6.7 to 6.78 psi) due to commingling to
be 0.7 tons/day for Chicago and 0.17 tons/day for Milwaukee.
5. Toxics
Comments suggest that an adjustment would result in an increase in toxics because of the
slight increase in VOC; although there is a toxics performance standard, commenters were
concerned that toxics overcompliance would be lost.
Since the time that the VOC adjustment rule was proposed, EPA promulgated a final rule
(66 FR 17230; March 29, 2001) to prevent backsliding of air toxics. The rule establishes a
performance standard for toxics that must not exceed the average toxics performance for years
1998, 1999 and 2000 on a refinery by refinery basis. Thus, commenters' concerns that the VOC
adjustment would result in a diminishing of toxics overcompliance is addressed in large part by
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the new rule which would assure that refiners maintain whatever toxics overcompliance has been
achieved based over the above mentioned three year period. There is a possibility of additional
overcompliance in the absence of the VOC adjustment of 2 percentage points (i.e, equivalent
increase in RVP of 0.3 psi) but we believe this would have been very small.
Given the size of the VOC adjustment, we believe that the resulting increase in VOC
emissions will not make it noticeably more expensive to comply with the new toxics standard.
We believe that the impact of VOC emission increases on toxics performance will not diminish
any cost benefit associated with the VOC adjustment rule.
6. Nonroad emissions
Comments suggested that emissions from off-road vehicle would increase as a result of
the VOC adjustment. We have calculated and accounted for the emission changes associated
with both increased oxygen and the VOC adjustment for the scenario in which the rule is
implemented compared to no rule. The results of this analysis were considered in our overall
calculation of the ratio of CO decrease to VOC increase resulting from the rule. Inclusion of
nonroad vehicles results in a ratio greater than that for onroad vehicles only (19:1 versus 15:1).
Given the greater uncertainty associated with predicting nonroad compared to onroad emissions
in order to ensure that VOC adjustment still preserves the air quality benefits of the RFG
program, we relied upon the lesser ratio in establishing the adjustment level of 2.0 percentage
points (equivalent to an RVP increase of 0.3 psi).
a. Effect of VOC adjustment on VOC nonroad emissions
We employed EPA's nonroad model to estimate the VOC increase which would be
attributable to an 0.3 psi adjustment by setting the fuel RVP model inputs at 6.7 and 7.0 psi. The
26
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model estimated VOC emissions of 27.97 t/d and 11.9 t/d for Chicago and Milwaukee,
respectively, at 6.7 psi and estimated VOC emissions of 28.78 t/d and 12.64 t/d at 7.0 psi for
these respective areas. The difference in emissions between the varying RVP values, 0.81 t/d and
0.74 t/d for Chicago and Milwaukee, respectively, therefore provides an estimate of the VOC
emission increase which would be directly attributable to nonroad emissions for an adjustment of
0.3 psi in fuel RVP.
For the no-rule scenario, there would be no increase in VOC because the current Phase II
VOC standard would continue to apply for ethanol RFG.
b. Commingling effect for off-road emissions
For the rule scenario, we assumed that there will be no mixed market; hence, there would
be no commingling effect.
For the no-rule scenario, we assumed 5 percent market displacement of ethanol with
MTBE. EPA's commingling model (section ni.H.2 above) for onroad emissions predicted an
RVP increase of 0.08 psi for a 5 percent market displacement. We then applied the predicted
onroad RVP increase (0.08 psi) for commingling to the VOC emission estimates from nonroad
engines for Chicago and Milwaukee using the results from EPA's nonroad model as described
above (Section ni.H.S.a). We estimated the difference in VOC emissions associated with the
commingling effect (0.08 psi RVP increase) to be 0.7 tons/day for Chicago and 0.19 tons/day for
Milwaukee.
c. Effect of rule on CO nonroad emissions
We estimated the nonroad CO emissions using data for 2-cycle and 4-cycle nonroad
engines from the 1996 emission inventories. Based on a weighting of 2 stroke and 4 stroke
27
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engines, and using EPA's nonroad model, we derived a mathematical formula developed for
emissions as a function of the percent change oxygen increase (see Section ni.H.5 above). We
calculated a decrease of 6.33 percent CO emissions for each percent increase in fuel oxygen. We
then adjusted the emissions contained in the 1996 emission inventories from 3.5 to 2.0 oxygen by
weight, using the above mathematical relationship.
We estimated nonroad CO emissions of 1051 t/d and 261.1 t/d at 3.5 weight percent
oxygen for Chicago and Milwaukee, respectively. Employing the above oxygen-CO relationship
for nonroad engines, we calculated emissions of 1151 t/d and 285.9 t/d for Chicago and
Milwaukee, respectively, for the baseline of 2.0 percent by weight oxygen. The estimated
decrease in CO emissions from nonroad engines, previously unaccounted for, is therefore 100 t/d
and 24.8 t/d, respectively.
The no-rule scenario assumes 5 percent market displacement of ethanol RFG containing
3.5 percent by weight oxygen with MTBE RFG containing 2.0 percent by weight oxygen. In the
no-rule scenario, the 5 percent market penetration results in a reduction of the unaccounted for
CO benefit of 5.0 tons/day and 1.24 tons/day (0.05*100 t/d and 0.05*24.8t/d) for Chicago and
Milwaukee, respectively.
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III. EXPECTED AIR QUALITY IMPACTS (OUTSIDE MIDWEST)
This section addresses why we are restricting the adjustment to the Chicago and
Milwaukee areas. The reasons for restricting the adjustment to these areas is twofold: 1) the
IEPA photochemical modeling upon which the 0.3 psi equivalent RVP adjustment was selected
is representative only of the Chicago/Milwaukee areas, and cannot be extended to other areas,
and 2) a VOC adjustment outside these areas may not preserve the air quality benefits of the RFG
program, due to emissions increased associated with commingling.
Outside Chicago and Milwaukee, it is more difficult to predict market share. For
example, New York has enacted a ban on MTBE that will take effect in 2004. At the present
time, New Jersey has not enacted a ban on MTBE. Assuming New York's ban is implemented
as planned, we would expect that the market share of ethanol for RFG sold in the New York
City RFG area will be 100 percent starting in 2004, however, we don't know what it will be
between now and 2004, or the ethanol share for RFG sold in New Jersey. Assuming a worst case
of 30 to 50 percent in those states, using the commingling procedure discussed in Section JJ.H.2
above, the increase in VOC emissions will be approximately equivalent to an increase in the
RVP of 0.1 to 0.3 psi. In the New York City area, at 0.3 psi, the RVP increase from
commingling could increase VOC in an amount similar to the VOC adjustment-specifically
VOC could increase approximately 12 tons/day beyond the increase associated with the VOC
29
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adjustment alone. While we cannot say with certainty what portion of the 30 to 50 percent of the
market share might be attributable to the adjustment to the VOC performance standard, increases
in VOC from commingling would likely be exacerbated by such a rule.
In addition to questions regarding the effect on emissions that a VOC adjustment would
have regarding its potential effect on changes in market share and current and future levels of
commingling, all these localities lack the photochemical analysis of CO and VOC ozone
formation necessary to determine a ratio of CO to VOC emissions changes appropriate to
preserve the expected benefits of the RFG program. We therefore believe that the rule could
cause an inappropriate level of VOC increases compared to CO emissions which could have
adverse environmental effects on ozone in areas outside of the Midwest.
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IV. EFFECT OF NEWER VEHICLES AND LOW SULFUR GASOLINE ON
ADJUSTMENT VALUE
The rationale for selecting an VOC adjustment of 2.0 percentage points is the reduction in
CO emissions associated with the oxygen level of RFG containing 10 volume percent ethanol.
Some commenters pointed out that as newer vehicles enter the vehicle fleet, advanced engine
technology may reduce baseline CO emissions, so that the decrease in such emissions from the
use of ethanol RFG could be diminished. Additionally, the Tier 2/low sulfur gasoline regulations
which will take effect in future years, could also reduce CO emissions.
We agree with the commenters who pointed out that there might be changes in the ratio
of CO decrease to VOC increase because of new technology and the effect of lower sulfur on CO
emissions. The change in technology in the fleet over time could also affect the level of VOC
emissions associated with a change in the VOC performance standard for RFG. Comments did
not provide specific data to support a termination of or changes to the adjustment at any
particular time. We will continue to evaluate the potential impact of new technology and low
sulfur gasoline on the CO benefits associated with oxygen in gasoline as well as the performance
of the vehicle and the resulting ratios of CO decrease to VOC increase.
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V. OTHER COMMENTS
A. Applicability of adjustment to ethanol RFG at less than 10 volume percent
Some commenters objected to the adjustment not applying to RFG that might contain
less than 10 volume percent ethanol and suggested that lower adjustment levels apply, based on
the amount of ethanol. We understand that in areas outside Chicago and Milwaukee, refiners
may choose to blend less than 10 volume percent ethanol in RFG due to the supply and cost.
This point has become less of an issue since we are restricting the applicability of the adjustment
to the Chicago and Milwaukee areas, in which 10 volume percent is the prevailing amount of
ethanol in RFG. Notwithstanding the restriction of the adjustment to these areas, introducing
variable adjustment levels that correspond to different levels of ethanol in RFG would be
difficult to implement and enforce.
B. Stranded cost of investments to comply with Phase II RFG
Some of the refiners who commented expressed concern that the proposed change in the
VOC standard represents a change in the RFG II requirements that refiners relied upon when
making their investment decision. As such, refiners who fully invested to maintain RFG
production levels would not be able to benefit from the relaxation to as great an extent as refiners
who did not invest as fully since a portion of their costs for the new equipment would be
"stranded".
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We believe that the rule will not represent stranded costs for refiners. The purpose of the
adjustment is to provide refiners with greater flexibility in producing RBOB. The adjustment of
the VOC standard by 2.0 percentage points would reduce the cost of making Phase n RFG by
approximately 21 percent. As such, the reduction in costs associated with this greater flexibility
should enhance the opportunity for refiners to recover that portion of their investment that might
be stranded.
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Table 1:
VOC emission increases and ratios of CO decrease to VOC increases for Chicago and Milwaukee as a function of RVP
Increases in Chicago based on Mobile Runs
67 ......... | .......... II .............. i ......... II ............ 1 ............. 7 ................ i ........... 7V1 ......................... JJ ........................ 73 ............... 1 ........ JA_ ........... | .......... 7J5 .............. ] ......... T& ............ i ........... 77 ..............
[[[ 5JOO ....... t ................. Oil ............. Illl .............. pot ........... TpIT ....... JOI ............... MMI ...... lOpI ........... IIITl ........ OTpl ............ 47lT
_ .. gyyg-j 45^53-1 14^81 g-gg-.- g-^g-. 4~89| 3~gg| 3~3gj 2;89] 253'
Increases in Milwaukee based on Mobile Runs
JRVflpsi) [[[ 67 ........ | ........... O ............... | ........ Ill ............ i ............. 7 ................. | ........... 7VJ .......................... 73. ....................... 73 ............... I ........ TA ............ ! .......... TJ| .............. i ........ 7J| ............ i ........... 77 ............... '
[[[ CMJO ....... ! .................... (Til ............. l ............. CTPI .................. Til .................. ..................... IIF] ............. Off ................. 374J ............. -Oil ................. 4J9T
RFG: Rati^ofCO/VOC? ....... ~^_ [[[ n/a ............. [ .................... ............... Q2Q ..................... ................ 2~88i .................... Z52
3 The VOC emissions were calculated by first generating emission factors using the MobileSb model. In running Mobile 5b, default
values for vehicle mix and I/M programs were used. The Mobile model can be run in a conventional gasoline mode or RFC mode. In
the RFC mode, the model automatically assumes that the oxygen content is 2.0 weight percent and RVP cannot be varied. In order to
represent RFC with an oxygen content of 3.5 weight percent, for varying RVP values, Mobile was run in conventional gas mode, with
oxygen content set at 3.5 weight percent, varying the RVP from 6.7 to 7.7 by increments of 0. 1 psi. We then ran Mobile in RFC mode
and compared the exhaust VOC emissions with those from Mobile in conventional gasoline mode. In conventional gasoline mode,
Mobile yields 0.919 g/mi exhaust VOC; in RFC mode it yields 0.878. The difference, 0.041, was subtracted from the total VOC
emissions from the Mobile runs assuming 3.5 weight percent oxygen to yield total VOC reflecting exhaust VOC associated with RFC
and evaporative VOC reflecting varying RVP values.
b To calculate tons/day emissions, the VOC emission factors in grams per mile (g/mi) were multiplied by the average summer day
Vehicle Miles Traveled (VMT) for Chicago and Milwaukee, which were 1.58x 108 and 1.67 x 107, respectively. To convert to tons/day,
the product was multiplied by (lb/454 g) x (ton/2000 Ib). This yielded total emissions for each RVP level. To calculate increases, the
emissions at the 6.7 psi level were subtracted from the emissions for each RVP level.
c The ratio of CO/VOC was calculated by dividing the reduction in CO for each location by the respective VOC increase for each of the
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Table 2:
VOC emission reductions calculated by the Complex Model as a function of RVP
RVP(psi) 6.7 6.8 6.9 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7
VOC emission reduction3 -27.4 -26.7 -26.0 -25.3 -24.5 -23.7 -22.9 -22.0 -21.0 -20.1 -19.0
Difference from Phase 11 VOC 0 0.7 1.4 2.1 2.9 3.7 4.6 5.4 6.4 7.4 8.4
standard"
Incremental RVP increase (psi) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Calculated using the Complex Model, holding all parameters except RVP constant. The constant parameters are: Ethanol (wt%
oxygen): 3.5; MTBE: 0; TAME: 0; Sulfur (ppm): 150; E200(%): 46.9; E300(%): 83.3; Aromatics (vol%): 25.4; Olefins (vol%): 11.1,
Benzene (vol%) 0.8.
The Phase II standard for VOC is 27.4% emission reduction for northern areas.
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Table 3: Comparison of emissions with and without the rule in Chicago and Milwaukee
CO
voc
EMISSIONS (TONS/DAY)
CHICAGO
Rule
-219
8.7
No-rule
-209
0.93
Change due to rule
-10
7.8
MILWAUKEE
Rule
-54
2.6
No-rule
-51
0.4
Change
-3
2.2
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Table 4: Detailed breakdown of emissions with and without the rule in Chicago and Milwaukee
EMISSIONS (TONS/DAY)
CHICAGO
Rule
No-rule
Change due to
rule
MILWAUKEE
Rule
No-rule
Change due to
rule
CO Emissions3
Onroad
Nonroad
Total
-119
-100
-219
-114
-95
-209
-5
-5
-10
-29
-25
-54
-28
-23
-51
-1
-2
-3
VOC Emissions
Adjustment effect
on onroad vehicles
Adjustment effect
on nonroad engines
Commingling-
onroad
Commingling-
nonroad
Total
8.00
0.81
0.0
0.0
8.7
0.0
0.0
0.7
0.21
0.93
8.00
0.81
-0.7
-0.21
7.8
1.94
0.74
0.0
0.0
2.6
0.0
0.0
0.17
0.19
0.4
1.94
0.74
-0.17
-0.19
2.2
Represents decreases in CO emissions that were unaccounted for when the RFG program started in
1995 and oxygen levels in these areas increased from 2.0 to 3.5 weight percent. For the no-rule
scenario, the unaccounted for decreases in CO are adjusted by that portion of the fuel market (5
percent) which would use MTBE and for which oxygen levels would decrease from 3.5 to 2.0 weight
percent.
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