Proposed Determination for
Renewable Fuels and Air Quality
Pursuant to Clean Air Act
Section 211(v)
United States
Environmental Protection
^1	Agency

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Proposed Determination for
Renewable Fuels and Air Quality
Pursuant to Clean Air Act
Section 211(v)
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
£%	United States
Environmental Protection
^1	Agency
EPA-420-D-20-003
May 2020

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Proposed Determination for Renewable Fuels and Air Quality
Pursuant to Clean Air Act Section 211(v)
Summary
EPA proposes to determine that no additional fuel control measures are necessary under
Clean Air Act section 21 l(v) to mitigate adverse air quality impacts of required renewable fuel
volumes.
Introduction
The Renewable Fuel Standard (RFS) program (Clean Air Act (CAA) section 21 l(o)) was
created by the Energy Policy Act of 2005 (EPAct) and expanded by the Energy Independence
and Security Act (EISA) in 2007. The RFS program was designed to "increase the production of
clean renewable fuels" by requiring increasing volumes of renewable fuel to be introduced into
the United States' supply of transportation fuel each year.1
The amendments added by EISA included section 21 l(v) of the CAA, which requires
EPA to take two actions. First, section 21 l(v) states that:
the Administrator shall complete a study to determine whether the renewable fuel
volumes required by this section will adversely impact air quality as a result of changes
in vehicle and engine emissions of air pollutants regulated under this chapter.
This study, commonly known as the "anti-backsliding study," must include consideration of
different blend levels, types of renewable fuels, and available vehicle technologies, as well as
appropriate national, regional, and local air quality control measures, according to section
21 l(v)(l)(B). EPA has completed the required study,2 and it is described in further detail below.
Second, section 21 l(v) states that:
the Administrator shall—
(A)	promulgate fuel regulations to implement appropriate measures to mitigate, to the
greatest extent achievable, considering the results of the study under paragraph (1), any
adverse impacts on air quality, as the result of the renewable volumes required by this
section; or
(B)	make a determination that no such measures are necessary.
1	Pub. L. No. 110-140, §§ 201-202, 121 Stat. 1492, 1492 (2007).
2	Report No. EPA-420-R-20-008. Available at https://www.epa.gov/renewable-fuel-standard-program/anti-
backsliding-determination-and-studv.
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The general purpose of this provision prompts EPA to study and address, as appropriate,
potential adverse effects on air quality caused by the implementation of the RFS program. In
fulfilling its obligation under this section, EPA has had to exercise its technical judgment in
designing the anti-backsliding study, in assessing the results, and in determining a course of
action. We describe below, and in the study, the judgments we made and the conclusions we
reached.
In addition, EPA interprets section 21 l(v) as providing authority to take action to
mitigate any adverse impacts of the RFS program subject to two crucial limitations established
by section 21 l(v)(2). First, EPA may only promulgate "fuel regulations" in response to any
adverse impacts, which narrows the range of possible regulatory actions (section 21 l(v)(2)(A)).
While EPA retains broad discretion to regulate vehicle emissions under section 202, and is
considering the mitigating impacts of certain vehicle standards adopted since the enactment of
Sections 21 l(o) and 21 l(v), EPA is not directed to do so to mitigate any adverse impacts of the
RFS program resulting from changes in vehicle and engine emissions. Second, EPA must only
promulgate such fuel regulations if the agency believes they are appropriate measures necessary
to mitigate any adverse impacts of the RFS program (section 21 l(v)(2)(A)-(B)). If there are no
necessary, appropriate measures, EPA is not directed to promulgate regulations.
These limitations also serve to highlight the role of EPA's technical judgment under
section 21 l(v)(2). The measures that EPA puts in place must be "appropriate." As the Supreme
Court has stated, the "term [appropriate] leaves agencies with flexibility," although agencies
must consider "all the relevant factors" when deciding whether regulation is "appropriate,"
including the cost of those regulations.3 To comply with section 21 l(v)(2), then, EPA must
consider whether there are any potential fuel regulations that are both "necessary" to mitigate
adverse impacts of the RFS program as a result of the renewable volumes required by section
21 l(o) and are "appropriate" measures to do so. EPA is taking comment on an initial
determination that there are no fuel regulations that are both "necessary" and "appropriate" to
mitigate any of the adverse impacts identified after consideration of the section 21 l(v)(l) study
discussed further below.
Section 21 l(o) lays out the renewable fuel volume requirements for the RFS program,
which are designed to increase over time. For total renewable fuel, the CAA establishes
increasing annual nationally applicable volume targets through 2022 (section 21 l(o)(2)(B)(i)(I)).
However, Congress authorized EPA to reduce those statutory volumes in limited circumstances.
First, if EPA's projection of cellulosic biofuel production is lower than the statutory volume laid
out in section 21 l(o)(2)(B)(i)(III), EPA must lower the cellulosic biofuel volume, and has broad
discretion to decide whether to lower the applicable volume for total renewable fuel as well
(section 21 l(o)(7)(D)(i)).4 Second, if EPA determines there is "inadequate domestic supply" or
the volumes "would severely harm the economy or environment of a State, a region, or the
United States," then EPA may exercise its discretion to lower the required volumes (section
3	Michigan v. EPA, 135 S.Ct. 2699, 2707 (2015).
4	Cellulosic biofuels are a subset of total renewable fuel. See 21 l(o)(l)(E).
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21 l(o)(7)(a)). Those two authorities are often known as the "cellulosic waiver provision" and the
"general waiver provision," respectively.
From 2010 to 2019, EPA has exercised one or both of its waiver authorities, replacing the
volumes in the statutory table with new required total renewable fuel volumes.5 The statute
requires EPA to analyze the impacts of "the renewable fuel volumes required by this section."
This phrase could refer to the statutory volumes set forth in CAA section 21 l(o)(2)(B) or to the
volumes actually used in calculating the percentage standards under section 21 l(o)(3)(B) which
apply to obligated parties and result in renewable fuels being used in transportation fuels. EPA
notes that actual volumes have fallen well short of the statutory volumes6 and concludes it is
more reasonable and appropriate to use the volumes which represent actual fuel consumed and
actual impacts on emissions to the air, rather than hypothetical statutory volumes. Thus, EPA
completed the antibacksliding study by comparing the volumes of renewable fuel actually used
under the RFS to the volumes of renewable fuel in the fuel supply before the RFS program was
implemented.7
In particular, EPA chose to use 2016 as the year for assessing the effects on air quality of
renewable fuel volumes. EPA compared two scenarios for calendar year 2016, one with actual
renewable fuel volumes (the "with-RFS" scenario) and another with renewable fuel use
approximating 2005 levels (the "pre-RFS" scenario). By analyzing calendar year 2016, EPA
was able to use an existing modeling platform that includes known renewable fuel volumes and
fuel properties based on actual data. The "pre-RFS" scenario used 2005 renewable fuel usage,
because that is the year EPAct was signed into law. Other potential study approaches would have
involved highly uncertain estimates of fuel volumes and would have been less informative.
By analyzing calendar year 2016, EPA was also able to analyze a year where the non-
cellulosic renewable fuel volumes (e.g., ethanol and biodiesel volumes) were substantially
phased in and not dramatically different from today's volumes. In keeping with this, the "with-
RFS" scenario assumed 10 percent ethanol (E10) was used nationwide in all onroad and nonroad
gasoline-fueled vehicles and engines, and biodiesel was used at a five percent blend (B5) in all
onroad diesel vehicles nationwide. This was compared to the "pre-RFS" scenario, which
assumed E10 usage only in the 2016 reformulated gasoline (RFG) areas and no biodiesel usage.
Fuels in California were assumed to be the same in both scenarios. Consistent with the statutory
focus on the impact of renewable fuel volumes on "changes in vehicle and engine emissions of
air pollutants," EPA only varied the fuel supplies for onroad and nonroad engines between the
5	75 FR 14670 (March 26, 2010), 75 FR 76790 (December 9, 2010), 77 FR 1320 (January 9, 2012), 78 FR 49794
(August 15, 2013), 79 FR 25025 (May 2, 2014), 80 FR 77420 (December 14, 2015), 81 FR 89746 (December 12,
2016), 82 FR 58486 (December 12, 2017), 83 FR 63704 (December 11, 2018), 85 FR 7016 (February 6, 2020).
6	The shortfall has been primarily in the mandated cellulosic volumes which have remained a very small fraction of
the statutory volumes and the vast majority of which has been biogas replacing fossil natural gas, not liquid fuels
replacing gasoline or diesel fuel.
7	Report No. EPA-420-R-20-008. Available at https://www.epa.gov/renewable-fuel-standard-program/anti-
backsliding-determination-and-studv.
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two scenarios—everything else, including "upstream" emissions from producing, storing, and
transporting fuels and feedstocks, was held constant in both scenarios at 2016 levels.8
The study assessed the changes in emissions from motor vehicles and nonroad engines
and equipment using the MOtor Vehicle Emission Simulator (MOVES). Air quality modeling
was done using the Community Multiscale Air Quality model (CMAQ) to estimate the resulting
impacts on concentrations of ozone, particulate matter (PM), nitrogen dioxide (NO2), carbon
monoxide (CO), and some air toxics (including acetaldehyde, acrolein, benzene, 1,3-butadiene,
formaldehyde, and naphthalene).
The results of this analysis were that, compared to the "pre-RFS" scenario, the 2016
"with-RFS" scenario increased ozone concentrations (eight-hour maximum daily average) across
the eastern U.S. and in some areas in the western U.S., with some decreases in localized areas.
In the 2016 "with-RFS" scenario, concentrations of annual average fine particulate matter
(PM2.5) were relatively unchanged in most areas, with increases in some areas and decreases in
some localized areas. The 2016 "with-RFS" scenario increased annual average concentrations of
NO2 across the eastern U.S. and in some areas in the western U.S., with larger increases in some
urban areas. The 2016 "with-RFS" scenario decreased annual average concentrations of CO
across the eastern U.S. and in some areas in the western U.S., with larger decreases in some
areas.
Compared to the "pre-RFS" scenario, the 2016 "with-RFS" scenario increased annual
average concentrations of acetaldehyde across much of the eastern U.S. and some areas in the
western U.S. and resulted in widespread increases in annual average formaldehyde
concentrations. The 2016 "with-RFS" scenario decreased annual average benzene
concentrations across most of the U.S., as compared to the "pre-RFS" scenario. The 2016 "with-
RFS" scenario also resulted in decreased annual average concentrations of 1,3-butadiene in many
urban areas. The 2016 "with-RFS" scenario resulted in small, geographically limited increases
and decreases in annual average concentrations of acrolein and naphthalene.
Necessity and Availability of Appropriate Control Measures to Address Modeled
Adverse Impacts
Having characterized the potential adverse impacts of the renewable fuel volumes
required by the RFS, we next considered whether it is necessary to implement appropriate fuel
control measures to address those impacts. First, we examined the impact of the Tier 3 motor
vehicle emissions and fuel standards, promulgated in 2014.9 These standards post-date the
adoption of the RFS and section 21 l(v) and likewise are not reflected in the antibacksliding
study's comparison of "pre-RFS" to "with-RFS" scenarios. The Tier 3 sulfur standard was
implemented in 2017, and the vehicle standards are phasing in between 2017 and 2025. Benefits
8	More explanation of the assumptions, their rationale, and the potential impacts on the results can be found in the
Clean Air Act Section 211(v)(l) Anti-backsliding Study, EPA-420-R-20-0008. Available at
https://www.epa.gov/renewable-fuel-standard-program/anti-backsliding-determination-and-studY.
9	Control of Air Pollution from Motor Vehicles: Tier 3 Motor Vehicle Emission and Fuel Standards, 79 FR 23414 (April 28,
2014). Although these standards were authorized under section 202 and 211 of the Clean Air Act, they were not adopted to fulfill
any specific statutory direction.
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of the vehicle standards will further increase over time as the fleet turns over. The Tier 3 rule
imposes fleet-wide exhaust emission standards for non-methane organic gases (NMOG) and
nitrogen oxides (NOx) that are 80% lower than the previous standards; PM exhaust emissions
standards for light and medium-duty vehicles that are 70% lower than previous standards; and
standards for heavy-duty pick-ups and vans that are on the order of 60% lower than previous
standards. It also imposes tighter evaporative emission standards for gasoline-powered vehicles
that represent a 50% reduction from previous standards. The tighter exhaust standards are
enabled by gasoline sulfur reductions of over 60%, allowing for more efficient and durable
emission control systems. The Tier 3 motor vehicle emission and fuel standards require recent
advances in vehicle and refining technology to be broadly applied across the industries. The
vehicle emission standards combined with the reduction of gasoline sulfur content are reducing
motor vehicle emissions, including nitrogen oxides (NOx), volatile organic compounds (VOC),
direct particulate matter (PM2.5), carbon monoxide (CO) and air toxics. Significantly, EPA
changed the longstanding primary certification fuel for light-duty vehicles from non-oxygenated
gasoline (E0) to gasoline containing 10 percent ethanol (E10) to better match in-use fuel after
implementation of the RFS program. In this way, the Tier 3 program was designed to control
vehicle emissions taking into consideration the nationwide shift to E10 under the RFS program.
A comparison of the air quality impacts estimated by the anti-backsliding study for 2016
and the Tier 3 regulatory analysis for 2018 and 2030 demonstrates the mitigating impact of the
Tier 3 program. Our comparison uses maps to depict the impacts modeled in the anti-
backsliding study and the impacts modeled for the Tier 3 rule. Although there are differences in
modeling assumptions between the two analyses, they are similar enough to allow meaningful
comparisons. For example, while the Tier 3 rule relied on a modified version of MOVES2010,10
the fuel effects updates in that Tier 3 model were incorporated into MOVES2014, giving similar
results for fuel impacts. Also, while Tier 3 was modeled using the NONROAD model, the data
and algorithms used were largely unchanged in the version of NONROAD incorporated in
MOVES2014, and the fuel effects are the same.
Table 1 compares key modeling assumptions in the two efforts.11'12'13 Furthermore, the
limitations noted in the anti-backsliding study—including lack of data on spatial distribution of
biodiesel use, limited data on effects of renewable fuels on nonroad engines, uncertainties in
hydrocarbon speciation, and uncertainties in photochemical mechanisms used in CMAQ—are
similar for both analyses.14 The methodological differences and limitations of the analyses are
10	U.S. EPA. 2014. "Memorandum to Docket: Updates to MOVES for the Tier 3 FRM Analysis" Docket No. EPA-
HQ-OAR-2011-0135.
11	Report No. EPA-420-R-20-008. Available at https://www.epa.gov/renewable-fuel-standard-program/anti-
backsliding-determination-and-studv.
12	U. S. EPA. Emissions Modeling Technical Support Document: Tier 3 Motor Vehicle Emission and Fuel Standards. Air Quality
Assessment Division, Office of Air Quality Planning and Standards, Research Triangle Park, NC. Report No. EPA-454/R-14-
003, February 2014.
13	U. S. EPA. Air Quality Modeling Technical Support Document: Tier 3 Motor Vehicle Emission and Standards. Air Quality
Assessment Division, Office of Air Quality Planning and Standards, Research Triangle Park, NC. Report No. EPA-454/R-14-
002, February, 2014. Available at httPs://nepis.epa.gov/Exe/ZvPDF.cgi/P100HX23.PDF?Dockev=P100HX23.PDF
14	Report No. EPA-420-R-20-008. Available at https://www.epa.gov/renewable-fuel-standard-program/anti-
backsliding-determination-and-studv.
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not significant enough to change a conclusion that the Tier 3 standards mitigate the air quality
impacts of renewable fuel volumes suggested by the anti-backsliding study.
Table 1. Air Quality Modeling Assumptions for Anti-backsliding Study and Tier 3 Rule

Anli-liackslidinu Suidv
Tier 3 Rule
Mobile Source Inventory
Onroad and Nonroad:
MOVES2014b
Onroad: MOVES 2010b with
fuel effects updates; Nonroad:
National Mobile Inventory
Model, version
NMIM20090504a
Air Quality Model
CMAQ version 5.2.1
CMAQ version 5.0.1
Modeling Platform15
2016 Version 7.2
2007/8 Version 5
Grid Resolution
12 km, with 36 km for
boundary conditions
12 km, with 36 km for
boundary conditions
Scenarios Compared
2016 with actual fuel
volumes under RFS; 2016
with renewable fuel usage at
2005 levels (before RFS)
2018 with and without Tier 3
fuel and vehicle standards;
2030 with and without Tier 3
fuel and vehicle standards
Meteorological Inputs
Weather Research and
Forecasting Model (WRF)
version 3.8
Weather Research and
Forecasting Model (WRF)
version 3.3
Figures 1 through 15 below depict comparisons in absolute changes in concentrations of
ozone, PM2.5, NOx, acetaldehyde, and formaldehyde. Changes in absolute levels of acrolein and
naphthalene are not shown as they do not show up within the resolution of the smallest scale on
the maps.
Figures 1 through 3 show the offsetting impacts of the anti-backsliding study and Tier 3
for annual 8-hour maximum daily average ozone. The largest ozone increases identified by the
anti-backsliding study occur in the Southeast, with increases ranging from 0.25 to 0.75 ppb, with
a few locations over 0.75 ppb. However, decreases due to Tier 3 largely offset these increases in
2018, and by 2030 fully offset the increases at the vast majority of locations across the U.S.
Figures 4 through 6 show the offsetting impacts for annual average PM2.5. The anti-backsliding
study identifies small increases in PM2.5 at a few locations in the Pacific Northwest; these
increases range from 0.01 to 0.05 [j.g/m3. However, decreases due to Tier 3 largely offset these
increases in 2018, and more than offset them by 2030. Figures 7 through 9 show the offsetting
impacts for annual average NO2. While the anti-backsliding study identifies NO2 increases up to
0.3 ppb, reductions from Tier 3 are substantially larger by 2030. Calendar year 2030 is an
appropriate year of focus, because any new program EPA could promulgate under section 21 l(v)
would likely not be implemented until at least 2025, given the need for lead time.
15 https://www.epa.gov/air-emissions-modeling/emissions-modeling-platforms
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The anti-backsliding study identified increases in formaldehyde concentrations in many
locations; however, reductions due to Tier 3 standards will offset these increases (Figures 13-15).
In contrast, in many locations Tier 3 standards will not fully offset the acetaldehyde increases
identified in the anti-backsliding study (Figures 10-12). Acetaldehyde is a primary byproduct of
the combustion of ethanol, which is the primary renewable fuel increased in the marketplace as a
result of section 21 l(o) implementation. EPA is not aware of a fuel control that would address
this pollutant without reducing ethanol use. Requiring reductions in ethanol use under section
21 l(v) would run directly counter to meeting the renewable fuel requirement of section 21 l(o).
Section 21 l(v) only seeks mitigation of the air quality impacts of the renewable fuel volumes
required under 21 l(o), not the reversal of those volumes. Moreover, EPA has already taken
action with the Tier 3 standards to broadly reduce pollutants to the extent technologically
achievable, and EPA is not aware of any vehicle or engine emissions control technology that
could specifically target acetaldehyde further.
Conclusion and Proposed Determination
Based on the results of the antibacksliding study, considered in conjunction with
pollution control measures EPA has already adopted and its evaluation of additional fuel control
measures that are currently available, EPA proposes to determine that no additional fuel control
measures are necessary to mitigate adverse air quality impacts of required renewable fuel
volumes. The Tier 3 rule has been promulgated and implemented, and these actions include fuel
and vehicle standards that reflect the shift of the gasoline pool from E0 to E10 while reducing
concentrations of ozone, PM2.5, NO2, and air toxics now and in the future. The analyses
supporting Tier 3 predict widespread reductions in 2018 and 2030 in ozone, PM, NO2, and
toxics, which mitigate the potential adverse air quality impacts identified in the anti-backsliding
study. For PM2.5, reductions from Tier 3 by 2030 are substantially larger than any adverse
impacts modeled in the anti-backsliding study. For other pollutants except acetaldehyde, Tier 3
reductions fully offset any adverse impacts from the anti-backsliding study at the vast majority of
locations across the U.S.
Therefore, based on these comparisons, and the lack of available controls which
specifically target acetaldehyde, EPA concludes that there are no additional appropriate measures
which are necessary to mitigate the potential adverse air quality impacts of required renewable
fuel volumes.
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Figure 1. Change in absolute concentrations of 8-hour maximum daily average 2016 ozone
between "pre-RFS" and "with-RFS" scenarios
jAnniat Oradierrt-Adjusled Oz
Figure 2. Change in absolute concentrations of 8-hour maximum daily average ozone in 2018
with and without Tier 3 standards
Figure 3. Change in absolute concentrations of 8-hour maximum daily average ozone in 2030
with and without Tier 3 standards
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ug/m3
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Hi -0.10 to-0.05
-0.05 to -0.01
-0.01 to 0.01
0.01 to 0.05
0.05 to 0.10
H >0.10
Figure 4. Absolute change in average annual 2016 PM2.5 concentrations between "pre-RFS" and
"with-RFS" scenarios
Figure 5. Change in absolute concentrations of annual average PM2.5 in 2018, with and without
Tier 3 standards
Figure 6. Change in absolute concentrations of annual average PM2.5 in 2030, with and without
Tier 3 standards
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Figure 7. Absolute change in average annual 2016 NO2 concentrations between "pre-RFS" and
"with-RFS" scenarios
1 Total NO1 Concentration
irg_clt minus 20l8rg_rcf2
Figure 8. Change in absolute concentrations of average NChin 2018, with and without Tier 3
standards
Figure 9. Change in absolute concentrations of average NO2 in 2030, with and without Tier 3
standards
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i ' . ' / '	./ ug/m3
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Figure 10. Absolute change in average annual 2016 acetaldehyde concentrations between "pre-
RFS" and "with-RFS" scenarios
IcTfiSws;
Figure 11. Change in absolute concentrations of annual average acetaldehyde in 2018, with and
without Tier 3 standards
Figure 12. Change in absolute concentrations annual average acetaldehyde in 2030, with and
without Tier 3 standards
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Figure 13. Absolute change in average annual 2016 formaldehyde concentrations between "pre-
RFS" and "with-RFS" scenarios
Absolute Difference for Formaldehyde -Ai
201Srg_cll minus mars
Figure 14. Change in absolute concentrations of annual average formaldehyde in 2018, with and
without Tier 3 standards
Absolut* Differ
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Figure 15. Change in absolute concentrations of annual average formaldehyde in 2030, with and
without Tier 3 standards
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