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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 79, 80, 85, 86, 600, 1036, 1037, 1039, 1042, 1048, 1054, 1065, and 

1066

[EPA–HQ–OAR–2011–0135; FRL_XXXX-X]

RIN 2060-AQ86

Control of Air Pollution from Motor Vehicles: Tier 3 Motor Vehicle Emission 

and Fuel Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final Rule.

SUMMARY: This action establishes more stringent vehicle emissions standards 

and will reduce the sulfur content of gasoline beginning in 2017, as part of a 

systems approach to addressing the impacts of motor vehicles and fuels on air 

quality and public health. The gasoline sulfur standard will make emission control 

systems more effective for both existing and new vehicles, and will enable more 

stringent vehicle emissions standards. The vehicle standards will reduce both 

tailpipe and evaporative emissions from passenger cars, light-duty trucks, mediumduty passenger vehicles, and some heavy-duty vehicles. This will result in 

significant reductions in pollutants such as ozone, particulate matter, and air toxics 

across the country and help state and local agencies in their efforts to attain and 

maintain health-based National Ambient Air Quality Standards. Motor vehicles are 

an important source of exposure to air pollution both regionally and near roads. 

These vehicle standards are intended to harmonize with California’s Low Emission 

Vehicle program, thus creating a federal vehicle emissions program that will allow 

automakers to sell the same vehicles in all 50 states. The vehicle standards will be 

implemented over the same timeframe as the greenhouse gas/fuel efficiency

standards for light-duty vehicles (promulgated by EPA and the National Highway

Safety Administration in 2012), as part of a comprehensive approach toward 

regulating emissions from motor vehicles. 

DATES: This final rule is effective on [Insert date 60 days after publication in 

the Federal Register]. The incorporation by reference of certain publications listed 

in this regulation is approved by the Director of the Federal Register as of [Insert 

date 60 days after publication in the Federal Register].
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ADDRESSES: EPA has established a docket for this action under Docket ID No. 

EPA–HQ–OAR–2011–0135. All documents in the docket are listed on the 

www.regulations.gov web site. Although listed in the index, some information is 

not publicly available, e.g., CBI or other information whose disclosure is restricted 

by statute. Certain other material, such as copyrighted material, is not placed on the 

Internet and will be publicly available only in hard copy form. Publicly available 

docket materials are available either electronically in www.regulations.gov or in 

hard copy at the Air and Radiation Docket and Information Center, EPA/DC, EPA 

West, Room 3334, 1301 Constitution Ave., NW, Washington, DC. The Public 

Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, 

excluding legal holidays. The telephone number for the Public Reading Room is 

(202) 566-1744, and the telephone number for the Air Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: JoNell Iffland, Office of 

Transportation and Air Quality, Assessment and Standards Division (ASD), 

Environmental Protection Agency, 2000 Traverwood Drive, Ann Arbor MI 48105; 

Telephone number: (734) 214-4454; Fax number: (734) 214-4816; E-mail address: 

iffland.jonell@epa.gov.

SUPPLEMENTARY INFORMATION:

I. General Information

A. Does this Action Apply to Me?

Entities potentially affected by this rule include gasoline refiners and 

importers, ethanol producers, ethanol denaturant producers, butane and pentane 

producers, gasoline additive manufacturers, transmix processors, terminals and fuel 

distributors, light-duty vehicle manufacturers, independent commercial importers, 

alternative fuel converters, and manufacturers and converters of vehicles between 

8,500 and 14,000 lbs gross vehicle weight rating (GVWR). 

Potentially regulated categories include:

Category NAICSa Code SIC

b Code Examples of Potentially Affected Entities

Industry 324110 2911 Petroleum refineries (including importers)

Industry 325110 2869 Butane and pentane manufacturers

Industry 325193 2869 Ethyl alcohol manufacturing

Industry 324110,

211112

2911,

1321

Ethanol denaturant manufacturers

Industry 211112 1321 Natural gas liquids extraction and fractionation

Industry 325199 2869 Other basic organic chemical manufacturing
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Industry 486910 4613 Natural gas liquids pipelines, refined petroleum 

products pipelines

Industry 424690 5169 Chemical and allied products merchant 

wholesalers

Industry 325199 2869 Manufacturers of gasoline additives

Industry 424710 5171 Petroleum bulk stations and terminals.

Industry 493190 4226 Other warehousing and storage- bulk petroleum 

storage

Industry 336111,

336112 3711

Light-duty vehicle and light-duty truck 

manufacturers

Industry 811111, 

811112, 

811198

7538, 

7533, 

7534 Independent commercial importers

Industry 335312,

336312,

336322,

336399,

811198

3621, 

3714, 

3519, 

3599, 

7534 Alternative fuel converters

Industry 333618,

336120,

336211,

336312

3699, 

3711, 

3713, 

3714

On-highway heavy-duty engine & vehicle 

(>8,500 lbs GVWR) manufacturers

a North American Industry Classification System (NAICS).

b

Standard Industrial Classification (SIC).

This table is not intended to be exhaustive, but rather provides a guide for 

readers regarding entities likely to be regulated by this action. This table lists the 

types of entities that EPA is now aware could potentially be regulated by this 

action. Other types of entities not listed in the table could also be regulated. To 

determine whether your activities are regulated by this action, you should carefully

examine the applicability criteria in 40 CFR parts 79, 80, 85, 86, 600, 1036, 1065, 

and 1066 and the referenced regulations. If you have any questions regarding the 

applicability of this action to a particular entity, consult the person listed in the 

preceding FOR FURTHER INFORMATION CONTACT section.

B. Did EPA Conduct a Peer Review before Issuing this Action?

This regulatory action was supported by influential scientific information. 

Therefore, EPA conducted peer reviews in accordance with OMB’s Final 

Information Quality Bulletin for Peer Review. EPA conducted several peer 

reviews in connection with data supporting the Tier 3 program, including new 

research on the effects of fuel properties changes (including sulfur effects) on 
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exhaust and evaporative emissions of Tier 2 vehicles. The refinery-by-refinery cost 

model was also peer reviewed. The peer review reports are located in the docket 

for today's action, as well as the agency's response to the peer review comments.

Table of Contents

I. Executive Summary and Program Overview 

A. Introduction

In this action, EPA is finalizing a major program designed to reduce air 

pollution from passenger cars and trucks. This program includes new standards for 

both vehicle emissions and the sulfur content of gasoline, considering the vehicle 

and its fuel as an integrated system. We refer to this program as the “Tier 3” vehicle 

and fuel standards. 

This rule is part of a comprehensive approach to address the impacts of 

motor vehicles on air quality and public health. Over 149 million Americans are 

currently experiencing unhealthy levels of air pollution, which are linked with 

respiratory and cardiovascular problems and other adverse health impacts that lead 

to increased medication use, hospital admissions, emergency department visits, and 

premature mortality.

1

 Motor vehicles are a particularly important source of 

exposure to air pollution, especially in urban areas. By 2018, we project that in 

many areas that are not attaining health-based ambient air quality standards (i.e., 

“nonattainment areas”), passenger cars and light trucks will contribute 10-25

percent of total nitrogen oxides (NOX) emissions, 15-30 percent of total volatile 

organic compound (VOC) emissions, and 5-10 percent of total direct particulate 

matter (PM2.5) emissions.2 These compounds form ozone, PM, and other air 

pollutants, whose health and environmental effects are described in more detail in 

Section II. Cars and light trucks also continue to be a significant contributor to air 

pollution directly near roads, with gasoline vehicles accounting for more than 50 

percent of near-road concentrations of some criteria and toxic pollutants.3 More 

 

1 Data come from Summary Nonattainment Area Population Exposure Report, current as of 

December 5, 2013 at: http://www.epa.gov/oar/oaqps/greenbk/popexp.html and contained in Docket 

EPA-HQ-OAR-2011-0135.

2 Mobile source contributions derived from inventories developed for this rule. For more 

information on these inventories see the Emissions Inventory Technical Support Document (TSD) 

for the final Tier 3 Rule, Docket ID No. EPA-HQ-OAR-2011-0135.

3

For example, see Fujita, E.M; Campbell, D.E.; Zielinska, B.; Arnott, W.P.; Chow, J.C. (2011) 

Concentrations of Air Toxics in Motor Vehicle-Dominated Environments. Health Effects Institute 

Research Report 156. Available at http://www.healtheffects.org
Page 5 of 88

than 50 million people live, work, or go to school in close proximity to high-traffic 

roadways, and the average American spends more than one hour traveling along 

roads each day.

4,5 Almost 90 percent of daily trips use personal vehicles or other 

motor vehicles.

6

The standards set forth in this rule will significantly reduce levels of 

multiple air pollutants (such as ambient levels of ozone, PM, nitrogen dioxide 

(NO2), and mobile source air toxics (MSATs)) across the country, with immediate 

benefits from the gasoline sulfur control standards starting in 2017. These 

reductions will help state and local agencies in their effort to attain and maintain 

health-based National Ambient Air Quality Standards (NAAQS). Few other 

national strategies exist that will deliver the same magnitude of multi-pollutant 

reductions and associated public health protection that is projected to result from 

the Tier 3 standards. Without this action to reduce nationwide motor vehicle 

emissions, areas would have to adopt other, less cost-effective measures to reduce 

emissions from other sources under their state or local authority. In the absence of 

additional controls, certain areas would continue to have ambient ozone 

concentrations exceeding the NAAQS in the future. See Section III.C for more 

details.

The Clean Air Act authorizes EPA to establish emissions standards for 

motor vehicles to address air pollution that may reasonably be anticipated to 

endanger public health or welfare (section 202). EPA also has authority to establish 

fuel controls to address such air pollution (section 211). These statutory authorities 

are described in Section II.A. 

The vehicle and gasoline sulfur standards we are finalizing represent a 

“systems approach” to reducing vehicle exhaust and evaporative emissions by

addressing the vehicle and fuel as a system. The systems approach enables emission 

reductions that are both technologically feasible and cost-effective beyond what 

would be possible looking at vehicle and fuel standards in isolation. We first 

applied such an approach with our Tier 2 vehicle/gasoline sulfur standards 

 

4 U.S. Census Bureau (2011). Current Housing Reports, Series H150/09, American Housing Survey 

for the United States: 2009. U.S. Government Printing Office, Washington, DC. Available at 

http://www.census.gov/hhes/www/housing/ahs/ahs09/ahs09.html. (Note that this survey includes 

estimates of homes within 300 feet of highways with four or more lanes, railroads, and airports.)

5 Drago, R. (2011). Secondary activities in the 2006 American Time Use Survey. U.S. Bureau of 

Labor Statistics Working Paper 446. Available at http://www.bls.gov

6 U.S. Department of Transportation, Bureau of Transportation Statistics (2003). National 

Household Travel Survey 2001 Highlights Report. Government Printing Office, Washington, DC. 

Available at 

http://www.bts.gov/publications/highlights_of_the_2001_national_household_travel_survey/
Page 6 of 88

(finalized in 2000).7 We believe that a similar approach for the Tier 3 standards is a 

cost-effective way to achieve substantial additional emissions reductions. 

The Tier 3 standards include new light- and heavy-duty vehicle emission 

standards for exhaust emissions of VOC (specifically, non-methane organic gases, 

or NMOG), NOX, and PM, as well as new evaporative emissions standards. The 

fully phased-in standards for light-duty vehicle, light-duty truck, and medium-duty

passenger vehicle tailpipe emissions are an 80 percent reduction in fleet average 

NMOG+NOX compared to current standards, and a 70 percent reduction in pervehicle PM standards. The fully phased-in Tier 3 heavy-duty vehicle tailpipe 

emissions standards for NMOG+NOX and PM are on the order of 60 percent lower 

than current standards. Finally, the fully phased-in evaporative emissions standards 

represent a 50 percent reduction from current standards.

The vehicle emission standards, combined with the reduction of gasoline 

sulfur content from the current 30 parts per million (ppm) average down to a 10

ppm average, will result in dramatic emissions reductions for NOX, VOC, direct 

PM2.5, carbon monoxide (CO) and air toxics. For example, in 2030, when Tier 3 

vehicles will make up the majority of the fleet as well as vehicle miles traveled, 

NOX and VOC emissions from on-highway vehicles will be reduced by about 21 

percent, and CO emissions will be reduced by about 24 percent. National emissions 

of many air toxics from on-highway vehicles will also be reduced by 10 to nearly 

30 percent. Reductions will continue beyond 2030 as more of the fleet is composed 

of vehicles meeting the fully phased-in Tier 3 standards. For example, the Tier 3 

program will reduce on-highway emissions of NOX and VOC nearly 31 percent by 

2050, when vehicles meeting the fully phased-in Tier 3 standards will comprise 

almost the entire fleet.

Gasoline vehicles depend to a great degree on catalytic converters to reduce 

levels of pollutants in their exhaust, including NMOG and NOX, as well as PM 

(specifically, the volatile hydrocarbon fraction), CO, and most air toxics. The 

catalytic converters become significantly less efficient when exposed to sulfur. The 

Tier 2 rulemaking required refiners to take steps to reduce sulfur levels in gasoline 

by approximately 90 percent, to an average of 30 ppm. As discussed in Section 

IV.A.6, subsequent research provides a compelling case that even this level of 

sulfur not only degrades the emission performance of vehicles on the road today, 

but also inhibits necessary further reductions in vehicle emissions performance to 

reach the Tier 3 standards. Thus, the 10 ppm average sulfur standard for Tier 3 is 

significant in two ways: it enables vehicles designed to the Tier 3 tailpipe exhaust 

standards to meet these standards in-use for the duration of their useful life, and it 

facilitates immediate emission reductions from all the vehicles on the road at the 

 

7

65 FR 6698 (February 10, 2000)
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time the fuel sulfur controls are implemented. EPA is not the first regulatory agency

to recognize the need for lower-sulfur gasoline. Agencies in Europe and Japan have 

already imposed gasoline sulfur caps of 10 ppm, and the State of California is 

already averaging 10 ppm sulfur with a per gallon cap of 20 ppm. Other states are 

preempted by the Clean Air Act from adopting new fuel programs to meet air 

quality objectives. Consequently, they could not receive the air quality benefits of 

lower sulfur gasoline without federal action. 

This action is one aspect of a comprehensive national program regulating 

emissions from motor vehicles. EPA’s final rule for reducing greenhouse gas 

(GHG) emissions from light-duty (LD) vehicles starting with model year (MY) 

2017 (referred to here as the “2017 LD GHG” standards) is another aspect of this 

comprehensive program.8 The Tier 3 program addresses interactions with the 2017 

LD GHG rule in a manner that aligns implementation of the two actions, to achieve 

significant criteria pollutant and GHG emissions reductions while providing 

regulatory certainty and compliance efficiency. As vehicle manufacturers introduce 

new vehicle platforms for compliance with the GHG standards, they will be able to 

design them for compliance with the Tier 3 standards at the same time. The Tier 3 

standards are also closely coordinated with California’s Low Emission Vehicle 

(LEV) III program to create a vehicle emissions program that will allow automakers 

to sell the same vehicles in all 50 states. (In December 2012 EPA approved a 

waiver of Clean Air Act preemption for the California Air Resources Board’s 

(CARB’s) LEV III program with compliance beginning in 2015. Twelve states 

adopted the LEV III program under Section 177 of the Clean Air Act.9) We have 

worked closely with individual vehicle manufacturers and their trade associations, 

who have emphasized the importance of a harmonized national program. Together, 

the Tier 3, 2017 LD GHG, and LEV III standards will provide significant 

reductions in GHGs, criteria pollutants and air toxics from motor vehicles while 

streamlining programs and enabling manufacturers to design a single vehicle for 

nationwide sales, thus reducing their costs of compliance. In this way, the Tier 3 

program responds to the May 21, 2010 Presidential Memorandum that requested 

that EPA develop a comprehensive approach toward regulating motor vehicles, 

including consideration of non-GHG emissions standards.10

As part of the systems approach to this program, we have considered the 

types of fuels on which vehicles will be operating in the future. In particular, the 

 

8 EPA’s GHG standards are part of a joint National Program with the National Highway Traffic 

Safety Administration, which also set coordinated standards for Corporate Average Fuel Economy 

(CAFE). 77 FR 62623 (October 15, 2012).

9 These states include Connecticut, Delaware, Maryland, Maine, Massachusetts, New Jersey, New 

York, Oregon, Pennsylvania, Rhode Island, Washington, and Vermont.

10 The Presidential Memorandum is found at: http://www.whitehouse.gov/the-pressoffice/presidential-memorandum-regarding-fuel-efficiency-standards.
Page 8 of 88

renewable fuels mandate that was revised by the Energy Independence and Security

Act (EISA) and is being implemented through the Renewable Fuel Standards 

program (RFS2)11 is resulting in the use of significant amounts of ethanol-blended

gasoline. We are updating the specifications of the emissions test fuel with which 

vehicles demonstrate compliance with emissions standards, in order to better reflect 

the ethanol content and other properties of gasoline that is in use today and is 

expected in future years.

Section I provides an overview of the vehicle and fuel standards we are 

finalizing as well as the impacts of the standards. The public health issues and 

statutory requirements that have prompted this action are described in Section II, 

and our discussion of how the Tier 3 standards will reduce emissions and air 

pollution is presented in Section III. Details of the standards and how they will be 

implemented can be found in Sections IV through VI. Sections VII through X 

contain our discussion of the standards’ technological feasibility and costs, benefits, 

and economic impacts. Sections XI through XIII address public participation, 

statutory and executive orders, and statutory provisions and legal authority under 

the Clean Air Act covered in this rulemaking. 

This final rule is based on extensive public input received in response to 

EPA’s Tier 3 proposal. The proposal was signed and posted on the EPA website on 

March 29, 2013, and published in the Federal Register on May 21, 2013. EPA held 

two public hearings in Philadelphia and Chicago in April 2013. In response to 

stakeholder requests, EPA extended the public comment period to July 1, 2013. We 

received more than 200,000 public comments. A broad range of stakeholders 

provided comments, including state and local governments, auto manufacturers, 

emissions control suppliers, refiners, fuel distributors and others in the petroleum 

industry, renewable fuels providers, environmental organizations, consumer groups, 

labor groups, private citizens, and others. Some of the issues raised in comments 

included leadtime and the program’s start date, the vehicle manufacturers’ support 

for a 50-state program harmonized with California, the need for and degree of 

gasoline sulfur control (including the level of the sulfur cap), the ethanol content of 

vehicle certification test fuel, and various details on the flexibilities and other 

program design features of both the vehicle and fuels standards.

B. Overview of the Tier 3 Program

In the 14 years since EPA established the Tier 2 Vehicle Program, 

manufacturers of light-duty vehicles and automotive technology suppliers have 

continued to develop a wide range of improved technologies capable of reducing 

vehicle emissions. The California LEV II program has been instrumental in the 

 

11 75 FR 14670 (March 26, 2010).
Page 9 of 88

continuous technology improvements by requiring year after year reductions in fleet 

average hydrocarbon levels, in addition to requiring the introduction of advanced 

exhaust and evaporative emission controls in partial zero emission vehicles 

(PZEVs). This technological progress has made it possible for manufacturers to 

achieve emission reductions well beyond the requirements of the Tier 2 program if 

gasoline sulfur levels are lowered further. 

As a result, in conjunction with lower gasoline sulfur standards, we are 

establishing new Tier 3 standards for exhaust emissions of NMOG, NOX, and PM, 

as well as for evaporative hydrocarbon emissions. These vehicle emissions 

standards will phase in beginning with MY 2017. The structure of the Tier 3 

standards is very similar to that of the existing Tier 2 program. As with the Tier 2 

program, the standards will apply to all light-duty vehicles (LDVs, or passenger 

cars), light-duty trucks (LDT1s, LDT2s, LDT3s, and LDT4s) and Medium-Duty

Passenger Vehicles (MDPVs). We also are establishing separate but closely related 

standards for heavy-duty vehicles up to 14,000 lbs Gross Vehicle Weight Rating 

(GVWR).12 We have concluded that the vehicle emissions standards, in 

conjunction with the reductions in fuel sulfur also required by this action, are 

feasible across the fleet in the timeframe provided. 

Auto manufacturers have stressed the importance of being able to design,

produce, and sell a single fleet of vehicles in all 50 states that complies with both 

the Tier 3 and California LEV III programs, as well as the greenhouse gas

(GHG)/Corporate Average Fuel Economy (CAFE) programs in the same 

timeframe. To that end, we worked closely with the California Air Resources 

Board and vehicle manufacturers to align the two programs as closely as possible. 

This consistency among the federal and California programs means that 

manufacturers do not need to design unique versions of vehicles with different 

emission control hardware and calibrations for different geographic areas. This 

allows manufacturers to avoid the additional costs of parallel design, development, 

calibration, and manufacturing. We also have designed the Tier 3 program to be 

implemented in the same timeframe as the GHG emissions and fuel economy

standards for model years 2017-2025. We expect that in response to these 

programs, manufacturers will be developing entirely new powertrains for most of 

their vehicles. Because the Tier 3 standards will phase in over the same timeframe, 

manufacturers are in a better position to simultaneously respond to all of these 

requirements.

Overall, the final Tier 3 program is very similar to the program we 

proposed. As discussed below and throughout this preamble, the program phases in 

 

12 These heavy-duty vehicles were not included in the Tier 2 program but were subject to standards 

in a subsequent rule covering the heavy-duty sector (66 FR 5002, January 18, 2001). 
Page 10 of 88

over several years – with the primary vehicle emission standards starting in Model 

Year (MY) 2017 (2018 for heavier vehicles) and the gasoline sulfur control 

provisions beginning in 2017. 

As discussed above, we received a large number and wide range of 

comments on the proposed rule. Several comments raise particularly significant 

issues concerning some fundamental components of the Tier 3 program, including 

when the vehicle-related and fuel-related requirements begin. We briefly discuss 

these key issues in this section, and in more detail later in this preamble. The 

Summary and Analysis of Comments document provides our responses to the 

comments we received; it is located in the docket for this rulemaking and also on 

EPA’s website at www.epa.gov/otaq/tier3.htm.

1. Major Public Comments and Key Changes from the Proposal

a. Start Date and Lead Time Issues

(1) Gasoline Sulfur Control Program

Many stakeholders commented on the proposed 2017 start date of the Tier 3 

program, with state and NGO organizations supporting finalizing the standards as 

proposed. Conversely, refiners, importers, and others in the fuel industry

commented that they believed the proposed start date would not provide a sufficient 

amount of lead time to meet the requirements of the Tier 3 program, and that EPA 

has historically provided at least four years of lead time in previous fuels 

rulemakings. These commenters noted that five years of lead time is needed to 

allow for necessary refinery changes to be made during a refinery’s normal 

turnaround/shutdown schedule (these occur every four years, on average) and to 

allow adequate time for the permitting process. These commenters also stated that, 

given the proposed flexibility provisions for vehicles, that a 2017 fuel program start 

date was not truly needed to enable the vehicle technology. Further, these 

commenters stated that they believed insufficient lead time would drive up the costs 

for regulated entities as they would need to do unscheduled shutdowns to install 

and/or revamp equipment to meet the proposed standards. Lastly, they stated that 

the uncertainty regarding the potential availability of credits would make meeting a 

2017 start date more challenging.

As discussed in greater detail in Section V below, we are finalizing the 

proposed start date of January 1, 2017. We understand refiners’ concerns, including 

their concerns over the necessary capital investments and potential off-cycle 

turnarounds/shutdowns to make refinery modifications for Tier 3. Especially in 

light of the additional flexibilities we are finalizing beyond those already in the 

proposal, we are confident that the program being finalized today addresses these 

concerns. The magnitude of the investments necessary to comply with Tier 3 is 

much smaller than what was required for Tier 2 or ultra-low sulfur diesel. 
Page 11 of 88

Considering all the flexibilities offered to regulated parties, there is, in effect, nearly 

6 years of lead time provided for those refineries that may need it. As discussed in 

Section V.D, we are finalizing a credit averaging, banking, and trading (ABT) 

program that will allow for a smooth transition from the Tier 2 to Tier 3 ABT 

programs (including provisions for early credit generation beginning in 2014). 

These early credit provisions, coupled with the ability to carry over credits from 

Tier 2 into Tier 3 (an additional flexibility being finalized today that was not part of 

the proposal), will allow for early actions to reduce sulfur levels by some refineries 

to be used to delay the need for actions at other refineries until 2020. This structure 

of the ABT program allows refiners and importers the flexibility to choose the most 

economical compliance strategy – investment in technology, use of credits, or both 

– for meeting the Tier 3 average gasoline sulfur standard. In addition, approved 

small refiners and small volume refineries are given an additional three years from 

the January 1, 2017, Tier 3 program start date to comply (January 1, 2020).

We proposed that the Tier 2 ABT program would not only be separate from 

the Tier 3 ABT program, but that it would also end at the start of the Tier 3 program 

in 2017. The implications of this meant that any Tier 2 credits generated after 2012 

would run the risk of expiring before the end of their full five-year life if they were 

not used before January 1, 2017. Commenters requested that EPA consider 

allowing such Tier 2 “banked” credits to receive their full five-year life. This 

would eliminate any incentive refiners may have to use these credits prior to the end 

of the Tier 2 program to raise their in-use sulfur levels. The ABT program that we 

are finalizing today enables a seamless transition from Tier 2 to Tier 3, including an 

allowance for Tier 2 banked credits to be used for their full five-year life or through 

December 31, 2019, whichever is earlier. Not only does this provision effectively

provide more lead time and flexibility for refiners and importers, but we believe 

these banked credits will help to provide certainty of the availability of credits for 

refiners and importers who may want to rely on them for compliance.

Finally, as discussed in Section V.E.2, we are also finalizing hardship 

provisions that allow refiners to petition for delayed compliance, on a case-by-case 

basis, for situations of extreme hardship or extreme unforeseen circumstances. 

These provisions, similar to those implemented in past fuel rulemakings, provide a 

safety valve should all the other flexibilities provided prove insufficient. As part of 

these hardship provisions, we are finalizing the ability for refiners to carry a deficit 

for up to 3 years, providing them with yet additional flexibility during the transition 

to Tier 3 should it prove necessary.

(2) Vehicle Emission Control Program

There were no major concerns raised for the proposed MY 2017 start date 

for lighter light-duty vehicles, although commenters from the auto manufacturing 

industry raised concerns about the lead time we proposed for heavier light-duty

vehicles. Specifically, commenters pointed to the Clean Air Act requirement that, 
Page 12 of 88

for vehicles over 6,000 lbs GVWR, EPA emission standards provide at least four 

years of lead time and three years of regulatory stability. 

In light of this statutory requirement, in addition to the primary declining 

fleet average standards starting in MY 2018 for heavier vehicles, EPA proposed an 

alternative phase-in schedule for any manufacturer that prefers a longer lead time 

and annual stability for these vehicles in lieu of the declining fleet average 

standards option. The commenters stated that the proposed alternative pathway

would be too difficult to take advantage of in comparison to the primary program 

and thereby failed to comply with the Clean Air Act. 

In considering these comments, EPA also considered that during the 

development of the Tier 3 program and in their comments, the same auto industry

commenters consistently urged EPA to design the Tier 3 program to harmonize 

with the California LEV III standards as closely and as early as possible. As 

discussed in detail below in Section IV.A, extensive data that EPA has generated or 

received continue to support the conclusion that the primary fleet-average standards 

provide a compliance path that is feasible across the industry and that closely

harmonizes with LEV III. EPA believes that we have reasonably resolved these 

somewhat competing concerns -- early harmonization vs. additional lead time -- by

finalizing the primary declining fleet average standards as proposed while also 

finalizing revised alternative phase-in compliance schedules (see Section IV.A.2.c). 

In response to the comments on this topic, we have revised the alternative phase-in 

schedules to reduce their associated burden for manufacturers, while still 

maintaining environmental benefits that are equivalent to the primary program. We 

also include provisions in the percent-of-sales phase-in alternatives that allow 

manufacturers to exclude vehicle models that begin their 2019 model year 

production early in 2018, in order to provide four years of lead time. 

b. Emissions Test Fuel

In-use gasoline has changed considerably since EPA last revised 

specifications for the test gasoline used in emissions testing of light- and heavyduty vehicles. Perhaps most importantly, gasoline containing 10 percent ethanol by

volume (E10) has replaced non-oxygenated gasoline (E0) across the country. As a 

result, we are updating federal emissions test fuel specifications to better match inuse fuel. 

In the NPRM, EPA proposed that the specified gasoline for emissions 

testing be changed from E0 to E15 as a forward-looking approach. Since then, 

several factors have led EPA to reconsider that approach, including minimal 

proliferation on a national scale of stations offering E15 and the complexities that 

E15 would introduce for long-term harmonization with California’s use of E10 in 

their LEVIII program. We received comments from a broad set of stakeholders 

including the auto and oil industries, states, and NGOs with a general consensus 
Page 13 of 88

that E15 would not be appropriate as the official test fuel at this time. Ethanol 

industry commenters supported E15 certification fuel, but provided no timeline by

which this blend level would be representative of in-use fuel. In light of the 

comments received and EPA’s assessment of the current and projected levels of 

ethanol in gasoline in use, we are finalizing E10 as the new emissions test fuel.

In deciding to finalize E10 test fuel, EPA considered whether to change the 

volatility of the test fuel, typically expressed as pounds per square inch (psi) Reid 

Vapor Pressure (RVP). As discussed in detail in Section IV.F, after considering 

technical and policy implications as well as stakeholder comments, we have 

concluded that the most appropriate approach is to maintain an RVP of 9 psi for the 

E10 emissions test fuel at this time. EPA considered raising test fuel RVP to 10 psi, 

but decided to leave it unchanged at 9 psi based on what would have been the 

associated increase in stringency of the Tier 3 evaporative standard with 10 psi and 

the loss of regulatory harmony on evaporative emissions with California’s LEV III 

program. 

As a result, after reassessing market trends and considering comments, EPA 

concludes that the most appropriate approach is to finalize an ethanol content of 10 

percent and an RVP of 9 psi for emissions test gasoline. We will continue to 

monitor ethanol trends in the gasoline market, as discussed later in this preamble. 

c. Gasoline Sulfur Caps

As described in more detail in Section V.C. we proposed two options for the

Tier 3 per-gallon sulfur caps—maintaining the Tier 2 refinery gate sulfur cap of 80 

ppm (with a 95 ppm downstream sulfur cap), and lowering to a 50 ppm refinery

gate sulfur cap beginning January 1, 2020 (with a 65 ppm downstream cap). We 

received comments supporting lower per-gallon caps which noted potential 

environmental benefits, greater certainty that vehicles would see lower and more

uniform gasoline sulfur levels, and the ability to enable new vehicle technologies 

requiring very low sulfur levels. Conversely, comments received in support of 

maintaining the Tier 2 per-gallon caps cited concerns on cost, flexibility for 

turnarounds/unplanned shutdowns (due to refinery fires, natural disasters, etc.), and 

gasoline supply and/or price impacts.

Analysis performed since the time of the proposal found that a lower 

refinery gate cap would likely result in higher costs to the fuels industry and a 

decreased ability to handle off-spec product (potentially impacting gasoline supply

and pricing), without any significant increase in the nationwide emissions 

reductions provided by the Tier 3 program. Thus, in today’s action we are retaining 

the Tier 2 per-gallon sulfur caps. The 80 ppm refinery gate cap will provide 

refiners needed flexibility in allowing for naturally-occurring fuel batch variability, 

as well as more certainty that they will be able to continue producing and 

distributing gasoline during turnarounds/upsets to avoid a total shutdown. It will 
Page 14 of 88

also provide more certainty for transmix processors, additive manufacturers, and 

other downstream parties in producing gasoline.

However, we do understand commenters’ concerns that retaining the Tier 2 

sulfur caps might create regional differences in the benefits of the Tier 3 program. 

Therefore we will continue to monitor in-use sulfur levels and their impact on 

vehicle emissions to ascertain whether a future reduction in the per-gallon cap may

be necessary.

d. Effect of Gasoline Sulfur on Tier 3 Vehicle Emissions

The need for and level of gasoline sulfur control was a key issue raised in 

public comments. The petroleum industry raised concerns that there was 

insufficient basis for the proposed 10 ppm average sulfur level, while auto 

manufacturers and emissions control equipment manufacturers stressed that the 

feasibility of the Tier 3 vehicle standards was dependent on near-zero gasoline 

sulfur levels. This issue is discussed in detail below in Section IV.A.6. In sum, 

EPA believes that the range of studies conducted by EPA and others in recent years, 

along with the comments submitted by the auto industry and emissions control 

manufacturers during the comment period and more recently, strongly reinforce our 

conclusion that the impact of gasoline sulfur poisoning on exhaust catalyst 

performance is significant. 

Sulfur is a well-known catalyst poison. The nature of sulfur’s interactions 

with active catalytic materials is complex and varies with catalyst composition, 

exhaust gas composition, and exhaust temperature. Thus, even if a manufacturer 

were able to certify a new vehicle to the new stringent standards, the manufacturer’s 

ability to maintain the emission performance of that vehicle in-use is greatly

jeopardized if the vehicle is being operated on gasoline sulfur levels greater than 10 

ppm. In fact, due to the variation in actual vehicle operation, any amount of 

gasoline sulfur will deteriorate catalyst efficiency. Vehicle manufacturers and 

suppliers, both individually and through their trade associations, stressed the need 

for gasoline sulfur to be reduced to near zero levels in order for them to meet the 

proposed standards. However, we believe that a 10 ppm average sulfur level is 

sufficiently low to enable compliance with the Tier 3 vehicle standards, and as 

described below and in Section V, reducing sulfur levels further would cause sulfur 

control costs to quickly escalate. 

Taken together, this information provides a compelling argument that the

fleetwide Tier 3 vehicle standards are achievable only with a reduction of gasoline 

sulfur content from the current 30 ppm average down to a 10 ppm average. 
Page 15 of 88

e. SFTP (US06) PM Standard for Light-Duty Vehicles

The final Tier 3 vehicle standards are largely unchanged from their proposed 

levels. One change from the proposal is the PM emissions standards as measured 

on the US06 test cycle. The US06 cycle is part of the composite Supplemental 

Federal Test Procedure (SFTP) and simulates aggressive driving. The US06 PM 

standards are part of the suite of Tier 3 tailpipe standards that limit emissions under 

a wide range of common vehicle driving conditions. Newer emissions test data 

presented in the NPRM, as well as more recent additional test data submitted in 

public comments, show that a numerically lower US06 PM standard is feasible and 

appropriately reflects the actual emissions performance achieved by many vehicles 

in the fleet today while preventing increased emissions in the future. 

Taken together, the test results clearly show that most current light-duty 

vehicles – regardless of engine technology, emission control strategy, or vehicle 

size – are performing at much lower US06 emission levels than previously 

documented. Based on these newer data, we believe that it is appropriate to 

finalize a numerically lower US06 PM emission standard for LDVs, LDTs, and 

MDPVs, and to set a single standard for both lighter and heavier vehicles in this 

vehicle segment. In general, the final US06 PM standard for these vehicles begins 

to phase in at a level of 10 mg/mi in MYs 2017 and 2018, stepping down to a level 

of 6 mg/mi in MY2019. See Section IV.A.4.b for additional discussion of the US06 

standards and how they will phase in. 

2. Key Components of the Tier 3 Program

a. Tailpipe Standards for Light-Duty Vehicle, Light-Duty Truck, and 

Medium-Duty Passenger Vehicle Tailpipe Emissions

We are establishing a comprehensive program that includes new fleetaverage standards for the sum of NMOG and NOX tailpipe emissions (presented as 

NMOG+NOX) as well as new per-vehicle standards for PM.13 These standards, 

when applied in conjunction with reduced gasoline sulfur content, will result in very

significant improvements in vehicle emissions from the levels of the Tier 2 

program. For these pollutants, the standards are measured on test procedures that 

represent a range of vehicle operation, including the Federal Test Procedure (or 

FTP, simulating typical driving) and the Supplemental Federal Test Procedure (or 

SFTP, a composite test simulating higher ambient temperatures, higher vehicle 

speeds, and quicker accelerations). In addition to the standards, we are extending

the regulatory useful life period during which the standards apply (see Section 

 

13A discussion of the reasons for combining NMOG and NOX for this purpose is in Section IV.A.3.a 

below.
Page 16 of 88

IV.A.7.b below) and making test fuel more representative of expected real-world 

fuel (see Section I.B.2.e below). The final standards are in most cases identical to 

those of California’s LEVIII program, which provides the 50-state harmonization 

strongly supported by the auto industry. 

As proposed, the new Tier 3 FTP and SFTP NMOG+NOX standards are

fleet-average standards, meaning that a manufacturer calculates the average 

emissions of the vehicles it sells in each model year and compares that average to 

the applicable standard for that model year. The manufacturer certifies each of its 

vehicles to a per-vehicle “bin” standard (see Section IV.A.2) and sales-weights

these values to calculate its fleet-average NMOG+NOX emissions for each model 

year. Table I-1 summarizes the fleet average standards for NMOG+NOX evaluated 

over the FTP. The standards for light-duty vehicles begin in MY 2017 at a level 

representing a 46 percent reduction from the Tier 2 requirements. For the light-duty 

fleet over 6000 lbs GVWR, and MDPVs, the standards apply beginning in MY 

2018. As shown, these fleet-average standards decline during the first several years 

of the program, becoming increasingly stringent until ultimately reaching an 81 

percent reduction when the transition is complete. The FTP NMOG+NOX program 

includes two separate sets of declining fleet-average standards, with LDVs and 

small light trucks in one grouping and heavier light trucks and MDPVs in a second 

grouping, that converge at 30 milligrams per mile (mg/mi) in MY 2025 and later. 

As mentioned above, we are also providing alternative percent phase-in schedules 

for this and the other light-duty standards. 

Table I-1 Tier 3 LDV, LDT, and MDPV Fleet Average FTP NMOG+NOX

Standards (mg/mi) 

Model Year

2017a2018 2019 2020 2021 2022 2023 2024 2025 

and later

LDV/LDT1b86 79 72 65 58 51 44 37 30

LDT2,3,4 and 

MDPV

101 92 83 74 65 56 47 38 30

a For LDV and LDTs above 6000 lbs GVWR and MDPVs, the fleet average standards apply 

beginning in MY 2018.

b These standards apply for a 150,000 mile useful life. Manufacturers can choose to certify some or 

all of their LDVs and LDT1s to a useful life of 120,000 miles. If a vehicle model is certified to the 

shorter useful life, a proportionally lower numerical fleet-average standard applies, calculated by 

multiplying the respective 150,000 mile standard by 0.85 and rounding to the nearest mg. See 

Section IV.A.7.c. 

Similarly, as proposed, the NMOG+NOX standards measured over the SFTP 

are fleet-average standards, declining from MY 2017 until MY 2025, as shown in 

Table I-2. In this case, the same standards apply to both lighter and heavier 
Page 17 of 88

vehicles in the light-duty fleet. In MY 2025, the SFTP NMOG+NOX standard 

reaches its final fleet average level of 50 mg/mi.

Table I-2 Tier 3 LDV, LDT, and MDPV Fleet Average SFTP NMOG+NOX

Standards (mg/mi)

Model Year

2017a2018 2019 2020 2021 2022 2023 2024 2025 

and later

NMOG + NOX 103 97 90 83 77 70 63 57 50

a For LDVs and LDTs above 6000 lbs GVWR and MDPVs, the fleet average standards apply 

beginning in MY 2018. 

As proposed, manufacturers can also earn credits if their fleet average 

NMOG+NOX performance is better than the applicable standard in any model year. 

Credits that have been previously banked or obtained from other manufacturers can

be used, or credits can be traded to other manufacturers. Manufacturers would 

also be allowed to carry forward deficits in their credit balance. (See Sections

IV.A.7.a and IV.A.7.m).

We are also establishing PM standards as part of the Tier 3 program, for 

both the FTP and US06 cycles (as described above, US06 is a component of the 

SFTP test). Research has demonstrated that the level of PM from gasoline lightduty vehicles is more significant than previously thought.14

 Although many 

vehicles today are performing at or near the levels of the new standards, the data 

indicate that improvements, especially in high-load fuel control and in the durability

of engine components, are possible. 

Under typical driving, as simulated by the FTP, the PM emissions of most 

current-technology gasoline vehicles are fairly low at certification and in use, well 

below the Tier 2 PM standards. At the same time we see considerable variation in 

PM emissions among vehicles of various makes, models, and designs. As a result, 

as proposed, we are setting the new FTP PM standard at a level that will ensure that 

all new vehicles perform at the level already being achieved by well-designed Tier 

2 vehicles. The PM standards apply to each vehicle separately (i.e., not as a fleet 

average). Also, in contrast to the declining NMOG+NOX standards, the PM 

standard on the FTP for certification testing is 3 mg/mi for all vehicles and for all 

model years. As for the NMOG+NOX standards, for vehicles over 6000 lbs 

 

14 Nam, E.; Fulper, C.; Warila, J.; Somers, J.; Michaels, H.; Baldauf, R.; Rykowski, R.; and Scarbro, 

C. (2008). Analysis of Particulate Matter Emissions from Light-Duty Gasoline Vehicles in Kansas 

City, EPA420-R-08-010. Assessment and Standards Division Office of Transportation and Air 

Quality U.S. Environmental Protection Agency Ann Arbor, MI, April 2008.
Page 18 of 88

GVWR, the FTP PM standard applies beginning in MY 2018. Manufacturers can

phase in their vehicle models as a percent of U.S. sales through MY 2022. Most 

vehicles are already performing at this stringent PM level, and the primary intent of 

the standard is to bring all light-duty vehicles to the typical level of PM 

performance being demonstrated by many of today’s vehicles. 

As proposed, the Tier 3 program also includes a temporary in-use FTP PM 

standard of 6 mg/mi for the testing of in-use vehicles that applies during the percent 

phase-in period only. This in-use standard will address the in-use variability and

durability uncertainties that accompany the introduction of new technologies. Table 

I-3 presents the FTP certification and in-use PM standards and the phase-in 

percentages. 

Table I-3 Phase-In for Tier 3 FTP PM Standards 

2017a2018 2019 2020 2021 2022 and 

later

Phase-In

(percent of U.S. sales)

20b20 40 70 100 100

Certification 

Standard (mg/mi)

3 3 3 3 3 3

In-Use Standard 

(mg/mi)

6 6 6 6 6 3

a

For LDVs and LDTs above 6000 lbs GVWR and MDPVs, the FTP PM standards apply beginning 

in MY 2018.

b Manufacturers comply in MY 2017 with 20 percent of their LDV and LDT fleet under 6,000 lbs 

GVWR, or alternatively with 10 percent of their total LDV, LDT, and MDPV fleet. 

Finally, as discussed in Section I.B.1.e above, the Tier 3 program includes 

PM standards evaluated over the US06 driving cycle (the US06 is one part of the 

SFTP procedure) of 10 mg/mi through MY 2018 and of 6 mg/mi for 2019 and later 

model years, for light-duty vehicles. As in the case of the FTP PM standards, the 

intent of the US06 PM standard is to bring the emission performance of all vehicles 

to that already being demonstrated by many vehicles in the current light-duty fleet. 

b. Heavy-Duty Vehicle Tailpipe Emissions Standards

As discussed in detail in Section IV.B, we are setting Tier 3 exhaust 

emissions standards for complete heavy-duty vehicles (HDVs) between 8,501 and 

14,000 lbs GVWR. Vehicles in this GVWR range are often referred to as Class 2b 

(8,501-10,000 lbs) and Class 3 (10,001-14,000 lbs) vehicles, and are typically

heavy-duty pickup trucks and work or shuttle vans. Most are built by companies 

with even larger light-duty truck markets, and as such they frequently share major 

design characteristics and emissions control technologies with their LDT 

counterparts. However, in contrast to the largely gasoline-fueled LDT fleet, 
Page 19 of 88

roughly half of the heavy-duty pickup and van fleet in the U.S. is diesel-fueled. 

This is an important consideration in setting emissions standards, as diesel engine 

emissions control strategies differ from those of gasoline engines.

As proposed, the key elements of the Tier 3 program for HDVs parallel 

those being adopted for passenger cars and LDTs, with adjustments in standard 

levels, emission test requirements, and implementation schedules appropriate to this 

sector. These key elements include combined NMOG+NOX declining fleet average 

standards, a phase-in of PM standards, adoption of a new emissions test fuel for 

gasoline-fueled vehicles, extension of the regulatory useful life to 150,000 miles or 

15 years (whichever occurs first), and a first-ever requirement for HDVs to meet 

standards over an SFTP drive cycle that addresses real-world driving modes not 

well-represented by the FTP cycles.

We are adopting the Class 2b and Class 3 fleet average NMOG+NOX

standards shown in Table I-4, as proposed. The standards become more stringent in 

successive model years from 2018 to 2022, with voluntary standards made available 

in 2016 and 2017, all of which are set at levels that match those of California’s LEV 

III program for these classes of vehicles. Each covered HDV sold by a 

manufacturer in each model year contributes to this fleet average based on the 

mg/mi NMOG+NOX standard level of the “bin” declared for it by the manufacturer, 

who chooses from a set of seven discrete Tier 3 bins specified in the regulations. 

These bin standards then become the compliance standards for the vehicle over its 

useful life, with some adjustment provided for in-use testing in the early model 

years of the program.

As proposed, manufacturers can also earn credits for fleet average 

NMOG+NOX levels below the standard in any model year. Tier 3 credits that were 

previously banked, obtained from other manufacturers, or transferred across the 

Class 2b/Class 3 categories can be used to help demonstrate compliance. Unused 

credits expire after 5 model years. Manufacturers will also be allowed to carry

forward deficits in their credit balance for up to 3 model years.

Table I-4 Tier 3 HDV Fleet Average FTP NMOG+NOX Standards (mg/mi)

Voluntary Required Program

Model 

Year 2016 2017 2018 2019 2020 2021 2022 and later

Class 2b 333 310 278 253 228 203 178

Class 3 548 508 451 400 349 298 247

 
Page 20 of 88

We are adopting the proposed FTP PM standards of 8 mg/mi and 10 mg/mi 

for Class 2b and Class 3 HDVs, respectively, phasing in as an increasing percentage 

of a manufacturer’s sales per year. We are adopting the same phase-in schedule as 

for the light-duty sector during model years 2018-2019-2020-2021: 20-40-70-100 

percent, respectively, and a more flexible but equivalent alternative PM phase-in is 

also being adopted. Tier 3 HDVs will also be subject to CO and formaldehyde 

exhaust emissions standards that are more stringent than the existing standards.

Finally, we are setting first-ever nationwide SFTP standards for HDVs to 

ensure a robust overall control program that precludes high off-FTP cycle emissions 

by having vehicle designers consider them in their choice of compliance strategies. 

As for light-duty vehicles, we are requiring that SFTP compliance be based on a 

weighted composite of measured emissions from testing over the FTP cycle, the 

SC03 cycle, and an aggressive driving cycle, with the latter tailored to various HDV 

sub-categories: the US06 cycle for most HDVs, the highway portion of the US06 

cycle for low power-to-weight Class 2b HDVs, and the LA-92 (or “Unified”) cycle 

for Class 3 HDVs. The SFTP standards are the same as those adopted for 

California LEV III vehicles, and apply to NMOG+NOX, PM, and CO emissions.

The HDV program outlined above and described in detail in Section IV.B is 

substantially what we proposed. Commenters generally supported the scope, 

stringency, and implementation phase-in of this program. However, some industry

commenters requested changes to some specific provisions of the proposal, and the 

program we are adopting reflects improvements we have made in response. These 

are: (1) a limited allowance for engine certification of Class 3 complete diesel 

vehicles to avoid a potential need for dual chassis- and engine-based certification 

and to better harmonize with LEV III, (2) relaxed interim in-use testing standards to 

facilitate a smooth transition to the Tier 3 standards and to better harmonize with 

LEV III, (3) adoption of combined NMOG+NOx standards for the two highest 

(interim) bins, with a restriction placed on NOx levels in certification testing, to 

enhance the utility of these bins and to better harmonize with LEV III, and (4) a 

provision in the percent-of-sales phase-in alternative to allow manufacturers to 

exclude vehicle models that begin their 2019 model year production early in 2018, 

in order to provide four years of lead time. Commenters also requested relaxed 

standards for testing at high altitudes and changes to the credits program structure 

for generation of early credits and use of LEV III-based “vehicle emission credits”, 

but we did not adopt these for reasons explained in Section IV.B.

Overall, we expect the Tier 3 program we are adopting for HDVs to result in 

substantial reductions in harmful emissions from this large fleet of work trucks and 

vans. The fully-phased in Tier 3 standards levels for NMOG+NOX and PM are on 

the order of 60 percent lower than the current standards that took full effect in the 

2009 model year.
Page 21 of 88

c. Evaporative Emission Standards

Gasoline vapor emissions from vehicle fuel systems occur when a vehicle is 

in operation, when it is parked, and when it is being refueled. These evaporative 

emissions, which occur on a daily basis from gasoline-powered vehicles, are 

primarily functions of temperature, fuel vapor pressure, and activity. EPA first 

instituted evaporative emission standards in the early 1970s to address emissions 

when vehicles are parked after being driven. These are commonly referred to as hot 

soak plus diurnal emissions. Over the subsequent years the test procedures have 

been modified and improved and the standards have become more numerically

stringent. We have addressed emissions which arose from new fuel system designs 

by putting in place new requirements such as running loss emission standards and 

test procedure provisions to address permeation emissions. Subsequently standards 

were put in place to control refueling emissions from all classes of gasolinepowered motor vehicles up to 10,000 lbs GVWR. Evaporative and refueling 

emission control systems have been in place for most of these vehicles for many

years. These controls have led to significant reductions, but evaporative and 

refueling emissions still constitute 30-40 percent of the summer on-highway mobile 

source hydrocarbon inventory. These fuel vapor emissions are ozone and PM 

precursors, and also contain air toxics such as benzene. 

To control evaporative emissions, EPA is establishing more stringent 

standards that will require covered vehicles to have essentially zero fuel vapor 

emissions in use. These include more stringent evaporative emissions standards, 

new test procedures, and a new fuel/evaporative system leak emission standard. 

The program also includes refueling emission standards for all complete heavy-duty 

gasoline vehicles (HDGVs) over 10,000 lbs GVWR. EPA is including phase-in 

flexibilities as well as credit and allowance programs. The standards, harmonized 

with California’s “zero evap” standards, are designed to allow for a use of common 

technology in vehicle models sold throughout the U.S. The level of the standard 

remains above zero to account for nonfuel background emissions from the vehicle 

hardware.

Requirements to meet the Tier 3 evaporative emission regulations phase in 

over a six model year period. We are finalizing three options for the 2017 model 

year, but after that the sales percentage requirements are 60 percent for MYs 2018 

and 2019, 80 percent for model years 2020 and 2021, and 100 percent for model 

years 2022 and later. In Table I-5 we present the Tier 3 evaporative hot soak plus

diurnal emission standards by vehicle class. The standards are approximately a 50 

percent reduction from the existing standards. To enhance flexibility and reduce 

costs, EPA is finalizing provisions that allow manufacturers to generate allowances 

through early certifications (basically before the 2017 model year) and to 

demonstrate compliance using averaging concepts. Manufacturers may comply on 

average within each of the four vehicle categories, but not across these categories. 

EPA is not making any changes to the existing light-duty running loss or refueling 
Page 22 of 88

emission standards, with the exception of the certification test fuel requirement 

discussed in Section I.B.2. below.

Table I-5 Tier 3 Evaporative Emission Standards (g/test)

Vehicle Class Highest Hot Soak + Diurnal Level

(over both 2-day and 3-day diurnal tests)

LDV, LDT1 0.300

LDT2 0.400

LDT3, LDT4, MDPV 0.500

HDGVs 0.600

Flexible Fuel Vehicles (FFVs) must meet the same evaporative emission 

standards as non-FFVs using Tier 3 emissions certification test fuel. However, 

FFVs must meet the refueling emission standards using 10 psi RVP fuel to account 

for emissions resulting from commingling with non-E85 blends that may be in the 

vehicle’s fuel tank.

EPA is establishing the canister bleed emission test procedure and emission 

standard to help ensure fuel vapor emissions are eliminated. Under this provision, 

manufacturers are required to measure diurnal emissions over the 2-day diurnal test 

procedure from just the fuel tank and the evaporative emission canister and comply

with a 0.020 gram per test (g/test) standard for all LDVs, LDTs, and MDPVs, 

without averaging. The corresponding canister bleed test standard for HDGVs is

0.030 g/test. The Tier 3 evaporative emission standards will be phased in over a 

period of six model years between MY 2017 and MY 2022, with the leak test 

phasing in beginning in 2018.

Data from in-use evaporative emissions testing indicates that vapor leaks 

from vehicle fuel/evaporative systems are found in the fleet and that even very

small leaks have the potential to make significant contributions to the mobile source 

VOC inventory. To help address this issue, we are also adding a new standard and 

test procedure to control vapor leaks from vehicle fuel and vapor control systems. 

The standard will prohibit leaks with a cumulative equivalent diameter of 0.02 

inches or greater. We are adding this simple and inexpensive test and emission 

standard to help ensure vehicles maintain zero fuel vapor emissions over their full 

useful life. New LDV, LDT, MDPV, and HDGV equal to or less than 14.000 lbs 

GVWR meeting the Tier 3 evaporative emission regulations are also required to 

meet the leak standard beginning in the 2018 model year. Manufacturers must 

comply with the leak standard phase-in on the same percentage of sales schedule as 

that for the Tier 3 evaporative emission standards. Manufacturers will comply with 

the leak emission standard during certification and in use. The leak emission 

standard does not apply to HDGVs above 14,000 lbs GVWR.
Page 23 of 88

EPA is also establishing new refueling emission control requirements for all 

complete HDGVs equal to or less than 14,000 lbs GVWR (i.e., Class 2b/3 

HDGVs), starting in the 2018 model year, and for all larger complete HDGVs by

the 2022 model year. The existing refueling emission control requirements apply to 

complete Class 2b HDGVs, and EPA is extending those requirements to other 

complete HDGVs, since the fuel and evaporative control systems on these vehicles 

are very similar to those on their lighter-weight Class 2b counterparts.

 

d. Onboard Diagnostic Systems (OBD)

EPA and CARB both have OBD regulations applicable to the vehicle 

classes covered by the Tier 3 emission standards. In the past the requirements have 

been very similar, so most manufacturers have met CARB OBD requirements and, 

as permitted in our regulations, EPA has generally accepted compliance with 

CARB’s OBD requirements as satisfying EPA’s OBD requirements. Over the past 

several years CARB has upgraded its requirements to help improve the 

effectiveness of OBD in ensuring good in-use exhaust and evaporative system 

emissions performance. We have reviewed these provisions and agree with CARB 

that these revisions will help to improve in-use emissions performance, while at the 

same time harmonizing with the CARB program. Toward that end, we are adopting

and incorporating by reference the current CARB OBD regulations, effective for 

the 2017 MY, with a few minor differences including phase-in flexibility provisions 

and specific additions to enhance the implementation of the leak standard. EPA is 

retaining the provision that certifying with CARB’s program would permit 

manufacturers to seek a separate EPA certificate on that basis. 

e. Emissions Test Fuel

As described above, after reassessing market trends and considering 

comments, EPA is finalizing E10 as the ethanol blend level in emissions test 

gasoline for Tier 3 light-duty and heavy-duty gasoline vehicles. We will continue 

to monitor the in-use gasoline supply and based on such review may initiate 

rulemaking action to revise the specifications for emissions test fuel to include a 

higher ethanol blend level. EPA is also making additional changes that are 

consistent with CARB’s LEV III emissions test fuel specifications, including new 

specifications for octane, distillation temperatures, aromatics, olefins, sulfur and 

benzene. (See Section IV.F below for a detailed discussion of all the revised 

emission test fuel parameters.) 

As discussed in Sections IV.A.7.d (tailpipe emission testing) and IV.C.5.b 

(evaporative emission testing), we are requiring certification of all Tier 3 light-duty 

and chassis-certified heavy-duty gasoline vehicles on federal E10 test fuel. The 
Page 24 of 88

new test fuel specifications will apply to new vehicle certification, assembly line, 

and in-use testing. 

With a change in the ethanol content of the test fuel, EPA also needed to 

consider whether a change is warranted in the volatility of the test fuel, typically 

expressed as pounds per square inch (psi) Reid Vapor Pressure (RVP). As 

discussed in detail in Section IV.F below, after considering several technical and 

policy implications as well as stakeholder comments, EPA has concluded that the 

most appropriate approach is to maintain an RVP of 9 psi for the E10 certification 

fuel at this time. 

In addition to finalizing a new E10 emissions test fuel, we are also finalizing

detailed specifications for the E85 emissions test fuel used for flexible fuel vehicle 

(FFV) certification, as discussed in Section IV.F.3.

15

 This will resolve uncertainty

and confusion in the certification of FFVs designed to operate on ethanol levels up 

to 83 percent. Furthermore, we allow vehicle manufacturers to request approval for 

an alternative certification fuel such as a high-octane 30 percent ethanol by volume

blend (E30) for vehicles that may be optimized for such fuel. 

f. Fuel Standards

Under the Tier 3 fuel program, gasoline must contain no more than 10 ppm 

sulfur on an annual average basis beginning January 1, 2017. Similar to the Tier 2 

gasoline program, the Tier 3 program will apply to gasoline in the U.S. and the U.S. 

territories of Puerto Rico and the Virgin Islands, excluding California. The 

program will result in gasoline that contains, on average, two-thirds less sulfur than 

it does today. In addition, following discussions with numerous refiners and other 

segments of the fuel market (e.g., pipelines, terminals, marketers, ethanol industry

representatives, transmix processors, additive manufacturers, etc.), the Tier 3 fuel 

program contains considerable flexibility to ease both initial and long-term 

implementation of the program. The program that we are finalizing today includes

an averaging, banking, and trading (ABT) program that allows refiners and 

importers to spread out their investments over nearly a 6 year period through the 

use of an early credit program and then rely on ongoing nationwide averaging to 

meet the 10 ppm sulfur standard. In addition there is a three-year delay for small 

refiners and “small volume refineries”. As a result of the early credit program, we 

anticipate considerable reductions in gasoline sulfur levels prior to 2017, with a 

complete transition to the 10 ppm average occurring by January 1, 2020. For more 

information on the gasoline sulfur program flexibilities, refer to Section V.E. 

 

15 Flexible fuel vehicles are currently required to meet emissions certification requirements using 

both E0 and E85 test fuels. However, there were no detailed regulatory specifications regarding the

composition of E85 test fuels before those finalized today.
Page 25 of 88

Under today’s Tier 3 gasoline sulfur program, we are maintaining the 

current 80 ppm refinery gate and 95 ppm downstream per-gallon caps. We also 

evaluated and sought comment on the potential of lowering the per-gallon caps.

While there are advantages and disadvantages with each of the sulfur cap options 

that we proposed, we believe that retaining the current Tier 2 sulfur caps is prudent 

at this time, as explained in more detail in Section V.C. Further, the stringency of 

the 10 ppm annual average standard will result in reduced gasoline sulfur levels 

nationwide. Today’s program requires that manufacturers of gasoline additives that 

are used downstream of the refinery at less than 1 volume percent must limit the 

sulfur contribution to the finished gasoline from the use of their additive to less than 

3 ppm when the additive is used at the maximum recommended treatment rate (see 

Section V.C.2). This requirement will preclude the unnecessary use of high sulfur 

content additives in gasoline.

The vehicle emissions standards finalized today are fuel-neutral (i.e., they

are applicable regardless of the type of fuel that the vehicle is designed to use). 

There currently are no sulfur standards for the fuel used in compressed natural gas 

(CNG) and liquid propane gas (LPG) vehicles. We requested comment on whether 

it is necessary for EPA to establish sulfur standards for CNG and LPG to enable 

them meeting more stringent vehicle emissions standards. EPA is deferring 

finalizing in-use sulfur requirements for CNG/LPG in this final rule to provide 

additional time to work with stakeholders to collect data on current CNG/LPG 

sulfur content, to determine whether additional control of in-use CNG/LPG sulfur 

content is needed, and to evaluate the feasibility and costs associated with potential 

additional sulfur controls (see Section V.J). Given that the information provided 

suggests that CNG/LPG sulfur levels tend to be low already, the vehicle emissions 

standards finalized today will apply to CNG/LPG vehicles in addition to vehicles 

fueled on gasoline, diesel fuel, or any other fuel. The sulfur content of highway

diesel fuel is already required to meet a 15 ppm sulfur cap, which is sufficient for 

diesel fuel vehicles to meet the Tier 3 emissions standards.

As the number of flex-fuel vehicles (FFVs) in the in-use fleet increases, it is 

becoming increasingly important that all fuels used in FFVs, not just gasoline, meet 

fuel quality standards. A lack of clarity regarding the standards that apply to fuels 

used in FFVs could also act to impede the further expansion of ethanol blended 

fuels with concentrations greater than 15 volume percent, which is important to 

satisfying the requirements of the RFS2 program. Hence, we sought comment on 

appropriate regulatory mechanisms to implement in-use quality standards for E51-

83 and E16-50 in the Tier 3 proposal. Additional work is needed on some issues 

that could not be accommodated within the timeline for this Tier 3 final rule. 

Therefore, we are choosing not to finalize these provisions at this time. We intend 

to finalize in-use fuel quality standards for E51-83 and perhaps E16-50 as well in a 

follow-up final rule.
Page 26 of 88

g. Regulatory Streamlining and Technical Amendments

This action also includes a number of items to help streamline the in-use 

fuels regulations at 40 CFR parts 79 and 80. The majority of these items involve 

clarifying vague or inconsistent language, removal or updating of outdated 

provisions, and decreasing in frequency and/or volume of reporting burden where 

data are no longer needed or are redundant with other EPA fuels programs. In 

general, we believe that these changes will reduce the burden on industry and allow 

the standards and resulting environmental benefits to be achieved as early as 

possible with no expected loss in environmental control. In some cases, these 

regulatory streamlining items are non-substantive amendments that correct minor 

errors or inconsistencies in the regulations.

The regulatory streamlining items that we are finalizing for the in-use fuels 

regulations are changes that we believe are straightforward and should be made 

quickly. 

This action also includes a variety of technical amendments to certificationrelated requirements for engine and vehicle emission standards; adjusting the fuel 

economy label provisions to correspond to the new Tier 3 standards, removing

obsolete regulatory text, and making several minor corrections and clarifications. 

Please refer to Section VI for a complete discussion of technical 

amendments and regulatory streamlining provisions and issues.

C. What Will the Impacts of the Standards Be?

The final Tier 3 vehicle and fuel standards together will reduce dramatically 

emissions of NOX, VOC, PM2.5, and air toxics. The gasoline sulfur standards, 

which will take effect in 2017, will provide large immediate reductions in emissions 

from existing gasoline vehicles and engines. NOX emissions are projected to be 

reduced by about 260,000 tons, or about 10 percent of emissions from on-highway

vehicles, in 2018, and these emission reductions will increase over time as newer 

vehicles become a larger percentage of the fleet. In 2030, when 70 percent of the 

miles travelled are projected to be from vehicles that meet the fully phased-in Tier 3 

standards, we expect the NOX and VOC emissions to be reduced by about 330,000

tons and 170,000 tons, respectively, or 25 percent and 16 percent of emissions from 

on-highway vehicles compared to their 2030 levels without the Tier 3 program. 

Emissions of CO are projected to decrease by almost 3.5 million tons, or 24 percent 

of emissions from on-highway vehicles. Emissions of many air toxics will also be 

reduced, including benzene, 1,3-butadiene, acetaldehyde, formaldehyde, acrolein 

and ethanol, with reductions projected to range from 10 to nearly 30 percent of 

national emissions from on-highway vehicles. We expect these reductions to 

continue beyond 2030 as more of the fleet continues to turn over to Tier 3 vehicles; 

for example, by 2050, when nearly all of the fleet will have turned over to vehicles 
Page 27 of 88

meeting the fully phased-in Tier 3 standards, we estimate the Tier 3 program will

reduce on-highway emissions of NOX and VOC nearly 31 percent from the level of 

emissions projected without Tier 3 controls.16 

These reductions in emissions of NOX, VOC, PM2.5 and air toxics from the 

Tier 3 standards are projected to lead to significant decreases in ambient 

concentrations of ozone, PM2.5 and air toxics (including notable nationwide 

reductions in benzene concentrations) by 2030, and will immediately reduce ozone 

in 2017 when the sulfur controls take effect. Additional information on the 

emission and air quality impacts of the final Tier 3 program is presented in Sections 

III.B and C. 

Exposure to ambient concentrations of ozone, PM2.5, and air toxics is linked 

to adverse human health impacts such as premature deaths as well as other 

important public health and environmental effects (see Section II.B). The final Tier 

3 standards are expected to reduce these adverse impacts and yield significant 

benefits, including those we can monetize and those we are unable to quantify. We 

estimate that by 2030, the emission reductions of the Tier 3 standards will annually

prevent between 660 and 1,500 PM-related premature deaths, between 110 and 500

ozone-related premature deaths, 81,000 work days lost, 210,000 school absence 

days, and approximately 1.1 million minor restricted-activity days. The estimated 

annual monetized health benefits of the Tier 3 standards in 2030 (2011$) is between 

$7.4 and $19 billion, assuming a 3-percent discount rate (or between $6.7 billion 

and $18 billion assuming a 7-percent discount rate). We project the final fuel 

standards to cost on average 0.65 cent (i.e., less than a penny) per gallon of 

gasoline, and the final vehicle standards to have an average cost that increases in 

proportion to the increase in stringency during the phase-in period, from $28 per 

vehicle in 2017 to $72 per vehicle in 2025, when the standards are fully phased in. 

We estimate the annual cost of the overall program in 2030 will be approximately 

$1.5 billion, and the 2030 benefits will be between 4.5 and 13 times the costs of the 

program. 

The estimated benefits in Table I-6 include all of the human health impacts 

we are able to quantify and monetize at this time. However, the full complement of 

human health and welfare effects associated with PM, ozone and air toxics remain 

unquantified because of current limitations in methods and/or available data. As a 

result, the health benefits quantified in this section are likely underestimates of the 

total benefits attributable to the final standards. See Sections VII and VIII for 

detailed descriptions of the costs and benefits of this action. 

 

16 To estimate the benefits of the final Tier 3 rule, we performed air quality modeling for the year 

2030. 
Page 28 of 88

Table I-6 Summary of Estimated Annual Benefits and Costs Associated with 

the Final Tier 3 Program (Billions, 2011$)a

Description 2030

Vehicle Program Costs

Fuels Program Costs

Total Estimated Costsb

$0.76

$0.70

$1.5

Total Estimated Health Benefitsc,d,e,f

 3 percent discount rate

 7 percent discount rate

$7.4 - $19

$6.7 - $18

Annual Net Benefits (Total Benefits – Total Costs)

 3 percent discount rate

 7 percent discount rate

$5.9 - $18

$5.2 - $17

Notes:

a All estimates represent annual benefits and costs anticipated for the year 2030. Totals are rounded 

to two significant digits and may not sum due to rounding.

b The calculation of annual costs does not require amortization of costs over time. Therefore, the 

estimates of annual cost do not include a discount rate or rate of return assumption (see Section VII 

of the preamble for more information on vehicle and fuel costs).

c Total includes ozone and PM2.5 estimated benefits. Range was developed by adding the estimate 

from the Bell et al., 2004 ozone premature mortality function to PM2.5-related premature mortality 

derived from the American Cancer Society cohort study (Krewski et al., 2009) for the low estimate 

and ozone premature mortality derived from the Levy et al., 2005 study to PM2.5-related premature 

mortality derived from the Six-Cities (Lepeule et al., 2012) study for the high estimate.

d Annual benefits analysis results reflect the use of a 3 percent and 7 percent discount rate in the 

valuation of premature mortality and nonfatal myocardial infarctions, consistent with EPA and OMB 

guidelines for preparing economic analyses. 

e Valuation of premature mortality based on long-term PM exposure assumes discounting over the 

SAB recommended 20-year segmented lag structure described in the Regulatory Impact Analysis for 

the 2012 PM National Ambient Air Quality Standards (December, 2012). 

f Not all possible benefits are quantified and monetized in this analysis; the total monetized benefits 

presented here may therefore be underestimated. Potential benefit categories that have not been 

quantified and monetized, due to current limitations in methods and/or data availability, are listed in 

Table VIII-2. For example, we have not quantified a number of known or suspected health and 

welfare effects linked with reductions in ozone and PM (e.g., reductions in heart rate variability, 

reduced material damage to structures and cultural monuments, and reduced eutrophication in 

coastal areas). We are also unable to quantify health and welfare benefits associated with reductions 

in air toxics.

II. Why Is EPA Taking this Action? 

The Clean Air Act authorizes EPA to establish emissions standards for 

motor vehicles to address air pollution that may reasonably be anticipated to 

endanger public health or welfare. EPA also has authority to establish fuel controls 

to address such air pollution. These statutory requirements are described in Section 

II.A.
Page 29 of 88

Emissions from motor vehicles and their fuels contribute to ambient levels 

of ozone, PM, NO2, sulfur dioxide (SO2) and CO, which are all pollutants for which 

EPA has established health-based NAAQS. These pollutants are linked with 

respiratory and/or cardiovascular problems and other adverse health impacts leading 

to increased medication use, hospital admissions, emergency department visits, and 

premature mortality. Over 149 million people currently live in areas designated 

nonattainment for one or more of the current NAAQS.17 

Motor vehicles also emit air toxics, and the most recent available data 

indicate that the majority of Americans continue to be exposed to ambient 

concentrations of air toxics at levels which have the potential to cause adverse 

health effects, including cancer, immune system damage, and neurological, 

reproductive, developmental, respiratory, and other health problems.18 A more 

detailed discussion of the health and environmental effects of these pollutants is 

included in Section II.B. 

Cars and light trucks also continue to be a significant contributor to air 

pollution directly near roads, with gasoline vehicles accounting for more than 50 

percent of near-road concentrations of some criteria and toxic pollutants.19 More 

than 50 million people live, work, or go to school in close proximity to high-traffic 

roadways, and the average American spends more than one hour traveling each day, 

with nearly 90 percent of daily trips occurring by personal vehicle.20,21,22,23,24 

Exposure to traffic-related pollutants has been linked with adverse health impacts 

 

17 Data come from Summary Nonattainment Area Population Exposure Report, current as of 

December 5, 2013 at: http://www.epa.gov/oar/oaqps/greenbk/popexp.html and contained in Docket 

EPA-HQ-OAR-2011-0135.

18 U.S. EPA. (2011) Summary of Results for the 2005 National-Scale Assessment. 

www.epa.gov/ttn/atw/nata2005/05pdf/sum_results.pdf.

19 For example, see Fujita, E.M; Campbell, D.E.; Zielinska, B.; Arnott, W.P.; Chow, J.C. (2011) 

Concentrations of Air Toxics in Motor Vehicle-Dominated Environments. Health Effects Institute 

Research Report 156. Available at http://www.healtheffects.org

20 Rowangould, G.M. (2013) A census of the US near-roadway population: public health and 

environmental justice considerations. Transportation Research Part D 25: 59-67.

21 U.S. Census Bureau (2011). Current Housing Reports, Series H150/09, American Housing Survey 

for the United States: 2009. U.S. Government Printing Office, Washington, DC. Available at 

http://www.census.gov/hhes/www/housing/ahs/ahs09/ahs09.html

22 Drago, R.(2011). Secondary activities in the 2006 American Time Use Survey. U.S. Bureau of 

Labor Statistics Working Paper 446. Available at http://www.bls.gov

23 U.S. Department of Transportation, Bureau of Transportation Statistics. (2003) National 

Household Travel Survey 2001 Highlights Report. Government Printing Office, Washington, DC. 

Available at 

http://www.bts.gov/publications/highlights_of_the_2001_national_household_travel_survey/

24 Santos, A.; McGuckin, N, Yukiko Nakamoto, H.; Gray, D.; Liss, S. (2011) Summary of Travel 

Trends: 2009 National Household Travel Survey. Federal Highway Administration report no 

FHWA-PL-11-022. Available at http://nhts.ornl.gov/publications.shtml.
Page 30 of 88

such as respiratory problems (particularly in asthmatic children) and cardiovascular 

problems. 

In the absence of additional controls such as Tier 3 standards, many areas 

will continue to have ambient ozone and PM2.5 concentrations exceeding the 

NAAQS in the future. States and local areas are required to adopt control measures 

to attain the NAAQS and, once attained, to demonstrate that control measures are in 

place sufficient to maintain the NAAQS for ten years (and eight years later, a 

similar demonstration is required for another ten-year period). The Tier 3 standards 

will be a critical part of many areas’ strategies to attain and maintain the NAAQS. 

Maintaining the NAAQS has been challenging for some areas in the past, 

particularly those where high population growth rates lead to significant annual 

increases in vehicle trips and vehicle miles traveled. Our air quality modeling for 

this final rule, which is described in more detail in Section III.C, projects that in 

2018 a significant number of counties outside CA will be within 10 percent of the 

2008 ozone NAAQS, in the absence of additional controls. These counties in 

particular will benefit from the Tier 3 standards as they work to ensure long-term 

maintenance of the NAAQS. 

Section III provides more detail on how we expect this action will reduce 

motor vehicle emissions and ambient levels of pollution. We project that the Tier 3 

program will meaningfully reduce ozone concentrations as early as 2017 (the first 

year of the program), and even more significantly in 2030. The estimated 

reductions are of significant enough magnitude to bring ozone levels in some 

counties from above the standard to below the standard, even without any additional 

controls. We also project that the Tier 3 standards will reduce ambient PM2.5 

concentrations. 

Without this action to reduce nationwide motor vehicle emissions, areas 

would have to adopt other measures to reduce emissions from other sources under 

their state or local authority. Few other measures exist for providing multi-pollutant 

reductions of the same magnitude and cost-effectiveness as those expected from the 

Tier 3 standards. Furthermore, most states do not have the authority to lower the 

sulfur in gasoline, which is needed to immediately reduce emissions from the 

existing fleet and also enable new vehicles to meet the Tier 3 emissions standards 

throughout their useful life. 

The projected reductions in ambient ozone and PM2.5 that will result from 

the Tier 3 standards will provide significant health benefits. We estimate that by 

2030, the standards will annually prevent between 660 and 1,500 PM-related 

premature deaths, between 110 and 500 ozone-related premature deaths, 81,000

work days lost, 210,000 school absence days, and approximately 1.1 million minor 

restricted-activity days (see Section VIII for more details). This action will also 

reduce air toxics; for example, we project that in 2030, the Tier 3 standards will

decrease ambient benzene concentrations by 10 - 25 percent in some urban areas. 
Page 31 of 88

Furthermore, the Tier 3 standards will reduce traffic-associated pollution near major 

roads.

EPA is finalizing Tier 3 vehicle and fuel standards as part of a 

comprehensive nationwide program for regulating all types of air pollution from 

motor vehicles. EPA recently finalized standards to reduce GHG emissions from 

light-duty vehicles, starting with model year 2017.25 The Tier 3 standards in this 

final rule, which address non-GHGs, will be implemented on the same timeframe, 

thus allowing manufacturers to optimize their vehicle redesigns over both sets of 

standards. Furthermore, the Tier 3 vehicle and fuel standards are also closely

aligned with California’s LEV III program, in such a way that manufacturers will 

be able to design a single vehicle for nationwide sales. This reduces the cost of 

compliance for auto manufacturers.

This Tier 3 rulemaking responds to the President’s request in his May 2010 

memorandum for EPA to review the adequacy of its existing non-GHG standards 

for new motor vehicles and fuels, and to promulgate new standards, if necessary, as 

part of a comprehensive approach to regulating motor vehicles.26 Based on our 

review, we have concluded that improved vehicle technology, combined with lower 

sulfur gasoline, make it feasible and cost-effective to reduce emissions well below 

the current Tier 2 levels. These emission reductions are necessary to reduce air 

pollution that is (and projected to continue to be) at levels that endanger public 

health and welfare.

A. Basis for Action under the Clean Air Act

1. Clean Air Act Section 202

We are setting motor vehicle emission standards under the authority of 

section 202 of the Clean Air Act. Section 202(a) provides EPA with general 

authority to prescribe vehicle standards, subject to any specific limitations 

elsewhere in the Act. EPA is setting standards for larger light-duty trucks and 

MDPVs under the general authority of section 202(a)(1) and under section 

202(a)(3), which requires that standards applicable to emissions of hydrocarbons, 

NOX, CO and PM from heavy-duty vehicles27 reflect the greatest degree of 

 

25 77 FR 62623 (October 15, 2012).

26 The Presidential Memorandum is found at: http://www.whitehouse.gov/the-pressoffice/presidential-memorandum-regarding-fuel-efficiency-standards.

27 LDTs that have gross vehicle weight ratings above 6000 lbs and all MDPVs are considered 

‘‘heavy-duty vehicles’’ under the CAA. See section 202(b)(3)(C). For regulatory purposes, we 

generally refer to those LDTs which are above 6000 lbs GVWR and at or below 8500 lbs GVWR as 

‘‘heavy light-duty trucks’’ made up of LDT3s and LDT4s, and we have defined MDPVs primarily 

as vehicles between 8500 and 10000 lbs GVWR designed primarily for the transportation of persons. 

See 40 CFR 86.1803-01
Page 32 of 88

emission reduction available for the model year to which such standards apply, 

giving appropriate consideration to cost, energy, and safety. In addition, section 

202(k) provides EPA with authority to issue and revise regulations applicable to 

evaporative emissions of hydrocarbons from all gasoline-fueled motor vehicles 

during: (1) operation, and (2) over 2 or more days of nonuse; under ozone-prone 

summertime conditions. Regulations under section 202(k) shall take effect as 

expeditiously as possible and shall require the greatest degree of emission reduction 

achievable by means reasonably expected to be available for production during any

model year to which the regulations apply, giving appropriate consideration to fuel 

volatility, and to cost, energy, and safety factors associated with the application of 

the appropriate technology. Further, section 206 and in particular section 206(d) of 

the Clean Air Act authorizes EPA to establish methods and procedures for testing 

whether a motor vehicle or motor vehicle engine conforms with section 202 

requirements.

2. Clean Air Act Section 211

We are adopting gasoline sulfur controls pursuant to our authority under 

section 211(c)(1) of the CAA. This section allows EPA to establish a fuel control if 

at least one of the following two criteria is met: (1) The emission products of the 

fuel cause or contribute to air pollution which may reasonably be anticipated to 

endanger public health or welfare; or (2) the emission products of the fuel will 

impair to a significant degree the performance of any emissions control device or 

system which is either in general use or which the Administrator finds has been 

developed to a point where in a reasonable time it will be in general use were the 

fuel control to be adopted. We are finalizing gasoline sulfur controls based on both 

of these criteria. Under the first criterion, we believe that gasoline with current 

levels of sulfur contributes to ambient levels of air pollution that endanger public 

health and welfare, as described in Section II.B. Under the second criterion, we 

believe that gasoline sulfur impairs the emissions control systems of vehicles, as 

discussed in Section III.A.2. 

B. Overview of Public Health Impacts of Motor Vehicles and Fuels 

Motor vehicles emit pollutants that contribute to ambient concentrations of 

ozone, PM, NO2, SO2, CO, and air toxics. Motor vehicles are significant 

contributors to emissions of VOC and NOX, which contribute to the formation of 

both ozone and PM2.5. Over 149 million people currently live in counties 

designated nonattainment for one or more of the NAAQS, and this figure does not 

include the people living in areas with a risk of exceeding the NAAQS in the 
Page 33 of 88

future.28 The majority of Americans continue to be exposed to ambient 

concentrations of air toxics at levels which have the potential to cause adverse 

health effects.29 In addition, populations who live, work, or attend school near 

major roads experience elevated exposure concentrations to a wide range of air 

pollutants.30

EPA has already adopted many emission control programs that are expected 

to reduce ambient pollution concentrations. As a result of these programs, the 

number of areas that continue to violate the ozone and PM2.5 NAAQS or have high 

levels of air toxics is expected to continue to decrease. However, the baseline air 

quality modeling completed for this rule predicts that without additional controls 

there will continue to be a need for reductions in ozone, PM2.5 and air toxics 

concentrations in some locations in the future. Section III.C of this preamble 

presents the air quality modeling results for this action. 

1. Ozone 

a. Background

Ground-level ozone pollution is typically formed through reactions 

involving VOC and NOX in the lower atmosphere in the presence of sunlight. 

These pollutants, often referred to as ozone precursors, are emitted by many types 

of pollution sources, such as highway and nonroad motor vehicles and engines, 

power plants, chemical plants, refineries, makers of consumer and commercial 

products, industrial facilities, and smaller area sources.

The science of ozone formation, transport, and accumulation is complex. 

Ground-level ozone is produced and destroyed in a cyclical set of chemical 

reactions, many of which are sensitive to temperature and sunlight. When ambient 

temperatures and sunlight levels remain high for several days and the air is 

relatively stagnant, ozone and its precursors can build up and result in more ozone 

than typically occurs on a single high-temperature day. Ozone and its precursors 

can be transported hundreds of miles downwind from precursor emissions, resulting 

in elevated ozone levels even in areas with low local VOC or NOX emissions.

 

28 Data come from Summary Nonattainment Area Population Exposure Report, current as of 

December 5, 2013 at: http://www.epa.gov/oar/oaqps/greenbk/popexp.html and contained in Docket 

EPA-HQ-OAR-2011-0135.

29 U.S. EPA. (2011) Summary of Results for the 2005 National-Scale Assessment. 

www.epa.gov/ttn/atw/nata2005/05pdf/sum_results.pdf. 

30

 Health Effects Institute Panel on the Health Effects of Traffic-Related Air Pollution. (2010) 

Traffic-related air pollution: a critical review of the literature on emissions, exposure, and health 

effects. HEI Special Report 17. Available at http://www.healtheffects.org] 
Page 34 of 88

b. Health Effects of Ozone

This section provides a summary of the health effects associated with 

exposure to ambient concentrations of ozone.

31

 The information in this section is 

based on the information and conclusions in the February 2013 Integrated Science 

Assessment for Ozone (Ozone ISA) prepared by EPA’s Office of Research and 

Development (ORD).

32 The Ozone ISA concludes that human exposures to 

ambient concentrations of ozone are associated with a number of adverse health 

effects and characterizes the weight of evidence for these health effects. 33 The 

discussion below highlights the Ozone ISA’s conclusions pertaining to health 

effects associated with both short-term and long-term periods of exposure to ozone.

For short-term exposure to ozone, the Ozone ISA concludes that respiratory

effects, including lung function decrements, pulmonary inflammation, exacerbation 

of asthma, respiratory-related hospital admissions, and mortality, are causally

associated with ozone exposure. It also concludes that cardiovascular effects, 

including decreased cardiac function and increased vascular disease, and total 

mortality are likely to be causally associated with short-term exposure to ozone and 

that evidence is suggestive of a causal relationship between central nervous system 

effects and short-term exposure to ozone. 

For long-term exposure to ozone, the Ozone ISA concludes that respiratory

effects, including new onset asthma, pulmonary inflammation and injury, are likely

to be a causally related with ozone exposure. The Ozone ISA characterizes the 

evidence as suggestive of a causal relationship for associations between long-term 

ozone exposure and cardiovascular effects, reproductive and developmental effects, 

central nervous system effects and total mortality. The evidence is inadequate to 

infer a causal relationship between chronic ozone exposure and increased risk of 

lung cancer.

Finally, interindividual variation in human responses to ozone exposure can 

result in some groups being at increased risk for detrimental effects in response to 

 

31

 Human exposure to ozone varies over time due to changes in ambient ozone concentration and 

because people move between locations which have notable different ozone concentrations. Also, 

the amount of ozone delivered to the lung is not only influenced by the ambient concentrations but 

also by the individuals breathing route and rate.

32

 U.S. EPA. Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Final 

Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-10/076F, 2013. The 

ISA is available at http://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=247492#Download

33 The ISA evaluates evidence and draws conclusions on the causal relationship between relevant 

pollutant exposures and health effects, assigning one of five “weight of evidence” determinations: 

causal relationship, likely to be a causal relationship, suggestive of a causal relationship, inadequate 

to infer a causal relationship, and not likely to be a causal relationship. For more information on 

these levels of evidence, please refer to Table II in the Preamble of the ISA. 
Page 35 of 88

exposure. The Ozone ISA identified several groups that are at increased risk for 

ozone-related health effects. These groups are people with asthma, children and 

older adults, individuals with reduced intake of certain nutrients (i.e., Vitamins C 

and E), outdoor workers, and individuals having certain genetic variants related to 

oxidative metabolism or inflammation. Ozone exposure during childhood can have 

lasting effects through adulthood. Such effects include altered function of the 

respiratory and immune systems. Children absorb higher doses (normalized to lung 

surface area) of ambient ozone, compared to adults, due to their increased time 

spent outdoors, higher ventilation rates relative to body size, and a tendency to 

breathe a greater fraction of air through the mouth. Children also have a higher 

asthma prevalence compared to adults. Additional children’s vulnerability and 

susceptibility factors are listed in Section XII.G.

c. Current and Projected Concentrations of Ozone 

Concentrations that exceed the level of the ozone NAAQS occur in many

parts of the country, including major population centers such as Atlanta, Baltimore, 

Chicago, Dallas, Houston, New York, Philadelphia, and Washington, D.C. In

addition, our modeling without the Tier 3 controls projects that in the future we will 

continue to have many counties that will have ambient ozone concentrations above 

the level of the NAAQS (see Section III.C.1). States will need to meet the standard 

in the 2015-2032 time frame for the 2008 ozone NAAQS. The emission reductions 

and significant ambient ozone improvements from this rule, which will take effect 

starting in 2017, will be helpful to states as they work to attain and maintain the 

ozone NAAQS.

The primary and secondary NAAQS for ozone are 8-hour standards with a 

level of 0.075 ppm. The most recent revision to the ozone standards was in 2008; 

the previous 8-hour ozone standards, set in 1997, had a level of 0.08 ppm. In 2004, 

the U.S. EPA designated nonattainment areas for the 1997 8-hour ozone 

NAAQS.34,35 As of December 5, 2013, there were 39 ozone nonattainment areas 

for the 1997 ozone NAAQS composed of 216 full or partial counties with a total 

population of over 112 million. Nonattainment designations for the 2008 ozone 

standard were finalized on April 30, 2012 and May 31, 2012.36 As of December 5, 

2013, there were 46 ozone nonattainment areas for the 2008 ozone NAAQS, 

composed of 227 full or partial counties, with a population of over 123 million. As 

 

34 69 FR 23858 (April 30, 2004).

35 A nonattainment area is defined in the Clean Air Act (CAA) as an area that is violating an ambient 

standard or is contributing to a nearby area that is violating the standard.

36 77FR 30088 (May 21, 2012) and 77 FR 34221 (June 11, 2012).
Page 36 of 88

of December 5, 2013, over 135 million people are living in ozone nonattainment 

areas.37 

States with ozone nonattainment areas are required to take action to bring 

those areas into attainment. The attainment date assigned to an ozone 

nonattainment area is based on the area’s classification. Most ozone nonattainment 

areas were required to attain the 1997 8-hour ozone NAAQS in the 2007 to 2013 

time frame and then to maintain it thereafter.38 The attainment dates for areas 

designated nonattainment for the 2008 8-hour ozone NAAQS are in the 2015 to 

2032 timeframe, depending on the severity of the problem in each area. In addition, 

EPA is currently working on a review of the ozone NAAQS. If EPA revises the 

ozone standards pursuant to that review, the attainment dates associated with areas 

designated nonattainment for that NAAQS would be 5 or more years after the final 

rule is promulgated, depending on the severity of the problem in each area. 

EPA has already adopted many emission control programs that are expected 

to reduce ambient ozone levels. As a result of these and other federal, state and 

local programs, 8-hour ozone levels are expected to improve in the future. 

However, even with the implementation of all current state and federal regulations, 

there are projected to be counties violating the ozone NAAQS well into the future. 

Thus additional federal control programs, such as Tier 3, can assist areas with 

attainment dates in 2018 and beyond in attaining the NAAQS as expeditiously as 

practicable and may relieve areas with already stringent local regulations from some 

of the burden associated with adopting additional local controls.

2. Particulate Matter

a. Background

Particulate matter is a highly complex mixture of solid particles and liquid 

droplets distributed among numerous atmospheric gases which interact with solid 

and liquid phases. Particles range in size from those smaller than 1 nanometer (10-9

meter) to over 100 micrometer (μm, or 10-6 meter) in diameter (for reference, a 

typical strand of human hair is 70 μm in diameter and a grain of salt is about 100 

μm). Atmospheric particles can be grouped into several classes according to their 

 

37 The 135 million total is calculated by summing, without double counting, the 1997 and 2008 

ozone nonattainment populations contained in the Summary Nonattainment Area Population 

Exposure report (http://www.epa.gov/oar/oaqps/greenbk/popexp.html). If there is a population 

associated with both the 1997 and 2008 nonattainment areas, and they are not the same, then the 

larger of the two populations is included in the sum.

38 The Los Angeles South Coast Air Basin 8-hour ozone nonattainment area and the San Joaquin 

Valley Air Basin 8-hour ozone nonattainment area are designated as Extreme and will have to attain 

before June 15, 2024. The Sacramento, Coachella Valley, Western Mojave and Houston 8-hour 

ozone nonattainment areas are designated as Severe and will have to attain by June 15, 2019. 
Page 37 of 88

aerodynamic and physical sizes, including ultrafine particles (<0.1 μm), 

accumulation mode or ‘fine’ particles (<1 to 3 μm), and coarse particles (>1 to 3 

μm).39 For regulatory purposes, fine particles are measured as PM2.5 and inhalable 

or thoracic coarse particles are measured as PM10-2.5, corresponding to their size 

(diameter) range in micrometers. The EPA currently has standards that measure 

PM2.5 and PM10.

40

 

Particles span many sizes and shapes and may consist of hundreds of 

different chemicals. Particles are emitted directly from sources and are also formed 

through atmospheric chemical reactions; the former are often referred to as 

“primary” particles, and the latter as “secondary” particles. Particle concentration 

and composition varies by time of year and location, and in addition to differences 

in source emissions, is affected by several weather-related factors, such as 

temperature, clouds, humidity, and wind. A further layer of complexity comes from 

particles’ ability to shift between solid/liquid and gaseous phases, which is 

influenced by concentration and meteorology, especially temperature. 

Fine particles are produced primarily by combustion processes and by 

transformations of gaseous emissions (e.g., sulfur oxides (SOX), oxides of nitrogen, 

and volatile organic compounds (VOC)) in the atmosphere. The chemical and 

physical properties of PM2.5 may vary greatly with time, region, meteorology, and 

source category. Thus, PM2.5 may include a complex mixture of different 

components including sulfates, nitrates, organic compounds, elemental carbon and 

metal compounds. These particles can remain in the atmosphere for days to weeks 

and travel hundreds to thousands of kilometers.

b. Health Effects of PM

Scientific studies show ambient PM is associated with a broad range of 

health effects. These health effects are discussed in detail in the December 2009

Integrated Science Assessment for Particulate Matter (PM ISA).

41

 The PM ISA 

summarizes health effects evidence associated with both short- and long-term 

exposures to PM2.5, PM10-2.5, and ultrafine particles. The PM ISA concludes that 

human exposures to ambient PM2.5 concentrations are associated with a number of 

adverse health effects and characterizes the weight of evidence for these health 

 

39 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. Figure 3-1.

40 Regulatory definitions of PM size fractions, and information on reference and equivalent methods 

for measuring PM in ambient air, are provided in 40 CFR Parts 50, 53, and 58. With regard to 

national ambient air quality standards (NAAQS) which provide protection against health and welfare 

effects, the 24-hour PM10 standard provides protection against effects associated with short-term

exposure to thoracic coarse particles (i.e., PM10-2.5).

41 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. 
Page 38 of 88

outcomes.42 The discussion below highlights the PM ISA’s conclusions pertaining 

to health effects associated with both short- and long-term PM exposures. Further 

discussion of health effects associated with PM2.5 can also be found in the 

rulemaking documents for the most recent review of the PM NAAQS completed in 

2012.

43,44

The EPA concludes that a causal relationship exists between both long- and

short-term exposures to PM2.5 and premature mortality and cardiovascular effects 

and a likely causal relationship exists between long- and short-term PM2.5 exposures 

and respiratory effects. Further, there is evidence suggestive of a causal 

relationship between long-term PM2.5 exposures and other health effects, including 

developmental and reproductive effects (e.g., low birth weight, infant mortality) and 

carcinogenic, mutagenic, and genotoxic effects (e.g., lung cancer mortality).45

As summarized in the Final PM NAAQS rule, and discussed extensively in 

the 2009 PM ISA, the scientific evidence available since the completion of the 2006 

PM NAAQS review significantly strengthens the link between long- and short-term 

exposure to PM2.5 and premature mortality, while providing indications that the 

magnitude of the PM2.5- mortality association with long-term exposures may be 

larger than previously estimated. 46,47 The strongest evidence comes from recent 

studies investigating long-term exposure to PM2.5 and cardiovascular-related 

mortality. The evidence supporting a causal relationship between long-term PM2.5

exposure and mortality also includes consideration of new studies that demonstrated 

 

42 The causal framework draws upon the assessment and integration of evidence from across 

epidemiological, controlled human exposure, and toxicological studies, and the related uncertainties 

that ultimately influence our understanding of the evidence. This framework employs a five-level 

hierarchy that classifies the overall weight of evidence and causality using the following 

categorizations: causal relationship, likely to be causal relationship, suggestive of a causal 

relationship, inadequate to infer a causal relationship, and not likely to be a causal relationship (U.S. 

EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F, Table 1–3). 

43 78 FR 3086 (January 15, 2013), pages 3103-3104.

44 77 FR 38890 (June 29, 2012), pages 38906-38911.

45 These causal inferences are based not only on the more expansive epidemiological evidence 

available in this review but also reflect consideration of important progress that has been made to 

advance our understanding of a number of potential biologic modes of action or pathways for PMrelated cardiovascular and respiratory effects (U.S. EPA. (2009). Integrated Science Assessment for 

Particulate Matter (Final Report). U.S. Environmental Protection Agency, Washington, DC, 

EPA/600/R-08/139F, chapter 5).

46 78 FR 3103-3104 (January 15, 2013).

47 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F, chapter 6 (Section 6.5) 

and chapter 7 (Section 7.6).
Page 39 of 88

an improvement in community health following reductions in ambient fine 

particles.48

Several studies evaluated in the 2009 PM ISA have examined the 

association between cardiovascular effects and long-term PM2.5 exposures in multicity studies conducted in the U.S. and Europe. While studies were not available in 

the 2006 PM NAAQS review with regard to long-term exposure and 

cardiovascular-related morbidity, studies published since then have provided new 

evidence linking long-term exposure to PM2.5 with an array of cardiovascular 

effects such as heart attacks, congestive heart failure, stroke, and mortality. This 

evidence is coherent with studies of short-term exposure to PM2.5 that have 

observed associations with a continuum of effects ranging from subtle changes in 

indicators of cardiovascular health to serious clinical events, such as increased 

hospitalizations and emergency department visits due to cardiovascular disease and 

cardiovascular mortality.

49

As detailed in the 2009 PM ISA, extended analyses of studies available in 

the 2006 PM NAAQS review as well as epidemiological studies conducted in the 

U.S. and abroad published since then provide stronger evidence of respiratoryrelated morbidity effects associated with long-term PM2.5 exposure. The strongest 

evidence for respiratory-related effects is from studies that evaluated decrements in 

lung function growth (in children), increased respiratory symptoms, and asthma 

development. The strongest evidence from short-term PM2.5 exposure studies has 

been observed for increased respiratory-related emergency department visits and 

hospital admissions for chronic obstructive pulmonary disease (COPD) and 

respiratory infections.50

The body of scientific evidence detailed in the 2009 PM ISA is still limited 

with respect to associations between long-term PM2.5 exposures and developmental 

and reproductive effects as well as cancer, mutagenic, and genotoxic effects, but is 

somewhat expanded from the 2006 review. The strongest evidence for an 

association between PM2.5 and developmental and reproductive effects comes from 

epidemiological studies of low birth weight and infant mortality, especially due to 

respiratory causes during the post-neonatal period (i.e., 1 month to 12 months of 

age). 51 With regard to cancer effects, ‘‘[m]ultiple epidemiologic studies have 

shown a consistent positive association between PM2.5 and lung cancer mortality, 

 

48 78 FR 3103 (January 15, 2013).

49 78 FR 3103 (January 15, 2013).

50 78 FR 3103-3104 (January 15, 2013).

51 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F, chapter 2 (section 2.3.1 

and 2.3.2) and chapter 7.
Page 40 of 88

but studies have generally not reported associations between PM2.5 and lung cancer 

incidence.’’53

Specific groups within the general population are at increased risk for 

experiencing adverse health effects related to PM exposures.54,55,56, 57 The evidence 

detailed in the 2009 PM ISA expands our understanding of previously identified atrisk populations and lifestages (i.e., children, older adults, and individuals with preexisting heart and lung disease) and supports the identification of additional at-risk 

populations (e.g., persons with lower socioeconomic status, genetic differences). 

Additionally, there is emerging, though still limited, evidence for additional 

potentially at-risk populations and lifestages, such as those with diabetes, people 

who are obese, pregnant women, and the developing fetus. 60

For PM10-2.5, the 2009 PM ISA concluded that available evidence was 

suggestive of a causal relationship between short-term exposures to PM10-2.5 and 

cardiovascular effects (e.g., hospital admissions and ED visits, changes in 

cardiovascular function), respiratory effects (e.g, ED visits and hospital admissions, 

increase in markers of pulmonary inflammation), and premature mortality. Data 

were inadequate to draw conclusions regarding the relationships between long-term 

exposure to PM10-2.5 and various health effects. 61,62,63

For ultrafine particles, the 2009 PM ISA concluded that the evidence was 

suggestive of a causal relationship between short-term exposures and cardiovascular 

effects, including changes in heart rhythm and vasomotor function (the ability of 

blood vessels to expand and contract). It also concluded that there was evidence 

suggestive of a causal relationship between short-term exposure to ultrafine 

particles and respiratory effects, including lung function and pulmonary

inflammation, with limited and inconsistent evidence for increases in ED visits and 

hospital admissions. Data were inadequate to draw conclusions regarding the 

 

53 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. pg 2-13

54 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. Chapter 8 and Chapter 2.

55 77 FR 38890 (June 29, 2012).

56 78 FR 3104 (January 15, 2013).

57 U.S. EPA. (2011). Policy Assessment for the Review of the PM NAAQS. U.S. Environmental 

Protection Agency, Washington, DC, EPA/452/R-11-003. section 2.2.1.

60 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. Chapter 8 and Chapter 2 

(Section 2.4.1).

61 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. Section 2.3.4 and Table 

2-6.

62 78 FR 3167-8 (January 15, 2013).

63 77 FR 38947-51 (June 29, 2012).
Page 41 of 88

relationship between short-term exposure to ultrafine particle and additional health 

effects including premature mortality as well as long-term exposure to ultrafine 

particles and all health outcomes evaluated.

64,65

c. Current and Projected Concentrations of PM2.5

There are two primary NAAQS for PM2.5: an annual standard (12.0

micrograms per cubic meter (μg/m3)) and a 24-hour standard (35 μg/m3), and two 

secondary NAAQS for PM2.5: an annual standard (15.0 μg/m3) and a 24-hour 

standard (35 μg/m3). The initial PM2.5 standards were set in 1997 and revisions to 

the standards were finalized in 2006 and in December 2012. The December 2012 

rule revised the level of the primary annual PM2.5 standard from 15.0 μg/m3to 12.0

μg/m3.

66

There are many areas of the country that are currently in nonattainment for 

the annual and 24-hour PM2.5 NAAQS. Our modeling without the Tier 3 controls 

projects that in the future we will continue to have many areas that will have 

ambient PM2.5 concentrations above the level of the NAAQS (see Section III.C.2). 

States will need to meet the 2006 24-hour standards in the 2015-2019 timeframe 

and the 2012 primary annual standard in the 2021-2025 timeframe. The emission 

reductions and improvements in ambient PM2.5 concentrations from this action, 

which will take effect starting in 2017, will be helpful to states as they work to 

attain and maintain the PM2.5 NAAQS.

In 2005 the EPA designated 39 nonattainment areas for the 1997 PM2.5

NAAQS.67 As of December 5, 2013, over 68 million people lived in the 24 areas 

that are still designated as nonattainment for the 1997 annual PM2.5 NAAQS. These 

PM2.5 nonattainment areas are comprised of 135 full or partial counties. EPA 

anticipates making initial area designation decisions for the 2012 primary annual 

PM2.5 NAAQS in December 2014, with those designations likely becoming 

effective in early 2015.68 On November 13, 2009 and February 3, 2011, the EPA 

designated 32 nonattainment areas for the 2006 24-hour PM2.5 NAAQS.69 As of 

December 5, 2013, 28 of these areas remain designated as nonattainment, and they

are composed of 104 full or partial counties with a population of over 65 million. 

 

64 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. Section 2.3.5 and Table 

2-6.

65 78 FR 3121 (January 15, 2013).

66 U.S. EPA (2012). National Ambient Air Quality Standards for Particulate Matter. 

http://www.epa.gov/PM/2012/finalrule.pdf. 78 FR 3164

67 70 FR 19844 (April 14, 2005).

68 U.S. EPA (2012). Fact Sheet: Implementing the Standards. 

http://www.epa.gov/airquality/particlepollution/2012/decfsimp.pdf

69 74 FR 58688 (November 13, 2009) and 76 FR 6056 (February 3, 2011).
Page 42 of 88

In total, there are currently 39 PM2.5 nonattainment areas with a population of over 

84 million people.70 

States with PM2.5 nonattainment areas will be required to take action to 

bring those areas into attainment in the future. Designated nonattainment areas not 

currently attaining the 1997 annual PM2.5 NAAQS are required to attain the 

NAAQS by 2015 and will be required to maintain the 1997 annual PM2.5 NAAQS 

thereafter. The 2006 24-hour PM2.5 nonattainment areas are required to attain the 

2006 24-hour PM2.5 NAAQS in the 2015 to 2019 time frame and will be required to 

maintain the 2006 24-hour PM2.5 NAAQS thereafter. Areas to be designated 

nonattainment for the 2012 primary annual PM2.5 NAAQS will likely be required to 

attain the 2012 NAAQS in the 2021 to 2025 time frame. The Tier 3 standards 

finalized here begin taking effect in 2017. 

The EPA has already adopted many mobile source emission control 

programs that are expected to reduce ambient PM concentrations. As a result of 

these and other federal, state and local programs, the number of areas that fail to 

meet the PM2.5 NAAQS in the future is expected to decrease. However, even with 

the implementation of all current state and federal regulations, there are projected to 

be counties violating the PM2.5 NAAQS well into the future. Thus additional 

federal control programs, such as Tier 3, can assist areas with attainment dates in 

2017 and beyond in attaining the NAAQS as expeditiously as practicable and may

relieve areas with already stringent local regulations from some of the burden 

associated with adopting additional local controls.

d. Current Concentrations of PM10

In the December 2012 action in which the EPA promulgated the revised 

primary annual PM2.5 NAAQS, the EPA also retained the existing primary and 

secondary 24-hour PM10 standards at 150 μg/m3. As of December 5, 2013, over 11

million people live in the 40 areas that are designated as nonattainment for the PM10

NAAQS. There are 33 full or partial counties that make up the PM10 nonattainment 

areas.

3. Oxides of Nitrogen and Sulfur

a. Background

Nitrogen dioxide (NO2) is a member of the NOX family of gases. Most NO2

is formed in the air through the oxidation of nitric oxide (NO) emitted when fuel is 

 

70

 Data come from Summary Nonattainment Area Population Exposure Report, current as of July

31, 2013 at: http://www.epa.gov/oar/oaqps/greenbk/popexp.html and contained in Docket EPA-HQOAR-2011-0135. 
Page 43 of 88

burned at a high temperature. Sulfur dioxide (SO2), a member of the sulfur oxide 

(SOX) family of gases, is formed from burning fuels containing sulfur (e.g., coal or 

oil derived), extracting gasoline from oil, or extracting metals from ore. 

SO2 and NO2 and their gas phase oxidation products can dissolve in water 

droplets and further oxidize to form sulfuric and nitric acid which react with 

ammonia to form sulfates and nitrates, both of which are important components of 

ambient PM. The health effects of ambient PM are discussed in Section II.B.2.b of 

this preamble. NOX and VOC are the two major precursors of ozone. The health 

effects of ozone are covered in Section II.B.2.1.b.

b. Health Effects of NO2

The most recent review of the health effects of oxides of nitrogen completed 

by the EPA can be found in the 2008 Integrated Science Assessment for Nitrogen 

Oxides (NOX ISA).

71

 The EPA concluded that the findings of epidemiologic, 

controlled human exposure, and animal toxicological studies provide evidence that 

is sufficient to infer a likely causal relationship between respiratory effects and 

short-term NO2 exposure. The 2008 NOX ISA concluded that the strongest 

evidence for such a relationship comes from epidemiologic studies of respiratory 

effects including increased respiratory symptoms, emergency department visits, and 

hospital admissions. Based on both short- and long-term exposure studies, the 2008 

NOX ISA concluded that individuals with preexisting pulmonary conditions (e.g., 

asthma or COPD), children, and older adults are potentially at greater risk of NO2-

related respiratory effects. Based on findings from controlled human exposure 

studies, the 2008 NOX ISA also drew two broad conclusions regarding airway

responsiveness following NO2 exposure. First, the NOX ISA concluded that NO2

exposure may enhance the sensitivity to allergen-induced decrements in lung 

function and increase the allergen-induced airway inflammatory response following

30-minute exposures of asthmatic adults to NO2 concentrations as low as 260 ppb. 

Second, exposure to NO2 has been found to enhance the inherent responsiveness of 

the airway to subsequent nonspecific challenges in controlled human exposure 

studies of healthy and asthmatic adults. Small but statistically significant increases 

in nonspecific airway hyperresponsiveness were reported for asthmatic adults 

following 30-minute exposures to 200-300 ppb NO2 and following 1-hour 

exposures of asthmatics to 100 ppb NO2. Enhanced airway responsiveness could 

have important clinical implications for asthmatics since transient increases in 

airway responsiveness following NO2 exposure have the potential to increase 

symptoms and worsen asthma control. Together, the epidemiologic and 

experimental data sets form a plausible, consistent, and coherent description of a 

 

71 U.S. EPA (2008). Integrated Science Assessment for Oxides of Nitrogen – Health Criteria (Final 

Report). EPA/600/R-08/071. Washington, DC: U.S.EPA. 
Page 44 of 88

relationship between NO2 exposures and an array of adverse health effects that 

range from the onset of respiratory symptoms to hospital admission. 

In evaluating a broader range of health effects, the 2008 NOX ISA 

concluded evidence was “suggestive but not sufficient to infer a causal relationship” 

between short-term NO2 exposure and premature mortality and between long-term 

NO2 exposure and respiratory effects. The latter was based largely on associations 

observed between long-term NO2 exposure and decreases in lung function growth 

in children. Furthermore, the 2008 NOX ISA concluded that evidence was 

“inadequate to infer the presence or absence of a causal relationship” between 

short-term NO2 exposure and cardiovascular effects as well as between long-term 

NO2 exposure and cardiovascular effects, reproductive and developmental effects, 

premature mortality, and cancer.72 The conclusions for these health effect 

categories were informed by uncertainties in the evidence base such as the 

independent effects of NO2 exposure within the broader mixture of traffic-related 

pollutants, limited evidence from experimental studies, and/or an overall limited 

literature base.

c. Health Effects of SO2

Information on the health effects of SO2 can be found in the 2008 Integrated 

Science Assessment for Sulfur Oxides (SO2 ISA).

73

 Short-term peaks of SO2 have

long been known to cause adverse respiratory health effects, particularly among 

individuals with asthma. In addition to those with asthma (both children and 

adults), potentially sensitive groups include all children and the elderly. During 

periods of elevated ventilation, asthmatics may experience symptomatic 

bronchoconstriction within minutes of exposure. Following an extensive evaluation 

of health evidence from epidemiologic and laboratory studies, the EPA concluded 

that there is a causal relationship between respiratory health effects and short-term 

exposure to SO2. Separately, based on an evaluation of the epidemiologic evidence 

of associations between short-term exposure to SO2 and mortality, the EPA 

concluded that the overall evidence is suggestive of a causal relationship between 

short-term exposure to SO2 and mortality.

d. Current Concentrations of NO2

The EPA most recently completed a review of the primary NAAQS for NO2

in January 2010. There are two primary NAAQS for NO2: an annual standard (53 

ppb) and a 1-hour standard (100 ppb). The EPA promulgated area designations in 

 

72 U.S. EPA (2008). Integrated Science Assessment for Oxides of Nitrogen – Health Criteria (Final 

Report). EPA/600/R-08/071. Washington, DC: U.S.EPA.

73 U.S. EPA. (2008). Integrated Science Assessment (ISA) for Sulfur Oxides – Health Criteria (Final 

Report). EPA/600/R-08/047F. Washington, DC: U.S. Environmental Protection Agency.
Page 45 of 88

the Federal Register on February 17, 2012. In this initial round of designations, all 

areas of the country were designated as “unclassifiable/attainment” for the 2010 

NO2 NAAQS based on data from the existing air quality monitoring network. The 

EPA and state agencies are working to establish an expanded network of NO2

monitors, expected to be deployed in the 2014-2017 time frame. Once three years 

of air quality data have been collected from the expanded network, the EPA will be 

able to evaluate NO2 air quality in additional locations.

74,75

e. Current Concentrations of SO2

The EPA most recently completed a review of the primary SO2 NAAQS in 

June 2010. The current primary NAAQS for SO2 is a 1-hour standard of 75 ppb. 

The EPA finalized the initial area designations for 29 nonattainment areas in 16 

states in a notice published in the Federal Register on August 5, 2013. In this first 

round of designations, EPA only designated nonattainment areas that were violating 

the standard based on existing air quality monitoring data provided by the states. 

The Agency did not have sufficient information to designate any area as 

“attainment” or make final decisions about areas for which additional modeling or 

monitoring is needed (78 FR 47191, August 5, 2013). EPA anticipates designating 

areas for the revised SO2 standard in multiple rounds.

4. Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas emitted from combustion 

processes. Nationally and, particularly in urban areas, the majority of CO emissions 

to ambient air come from mobile sources.

a. Health Effects of Carbon Monoxide

Information on the health effects of CO can be found in the January 2010

Integrated Science Assessment for Carbon Monoxide (CO ISA).

76

 The CO ISA 

concludes that ambient concentrations of CO are associated with a number of 

 

74 U.S. EPA. (2012). Fact Sheet – Air Quality Designations for the 2010 Primary Nitrogen Dioxide

(NO2) National Ambient Air Quality Standards. 

http://www.epa.gov/airquality/nitrogenoxides/designations/pdfs/20120120FS.pdf

75 U.S. Environmental Protection Agency (2013). Revision to Ambient Nitrogen Dioxide 

Monitoring Requirements. March 7, 2013. 

http://www.epa.gov/airquality/nitrogenoxides/pdfs/20130307fr.pdf

76 U.S. EPA, (2010). Integrated Science Assessment for Carbon Monoxide (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-09/019F, 2010. Available at

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=218686. 
Page 46 of 88

adverse health effects.77 This section provides a summary of the health effects 

associated with exposure to ambient concentrations of CO.78 

Controlled human exposure studies of subjects with coronary artery disease 

show a decrease in the time to onset of exercise-induced angina (chest pain) and 

electrocardiogram changes following CO exposure. In addition, epidemiologic 

studies show associations between short-term CO exposure and cardiovascular 

morbidity, particularly increased emergency room visits and hospital admissions for 

coronary heart disease (including ischemic heart disease, myocardial infarction, and 

angina). Some epidemiologic evidence is also available for increased hospital 

admissions and emergency room visits for congestive heart failure and 

cardiovascular disease as a whole. The CO ISA concludes that a causal relationship 

is likely to exist between short-term exposures to CO and cardiovascular morbidity. 

It also concludes that available data are inadequate to conclude that a causal 

relationship exists between long-term exposures to CO and cardiovascular 

morbidity. 

Animal studies show various neurological effects with in-utero CO 

exposure. Controlled human exposure studies report central nervous system and 

behavioral effects following low-level CO exposures, although the findings have 

not been consistent across all studies. The CO ISA concludes the evidence is 

suggestive of a causal relationship with both short- and long-term exposure to CO 

and central nervous system effects.

A number of studies cited in the CO ISA have evaluated the role of CO 

exposure in birth outcomes such as preterm birth or cardiac birth defects. The 

epidemiologic studies provide limited evidence of a CO-induced effect on preterm 

births and birth defects, with weak evidence for a decrease in birth weight. Animal 

toxicological studies have found perinatal CO exposure to affect birth weight, as 

well as other developmental outcomes. The CO ISA concludes the evidence is

suggestive of a causal relationship between long-term exposures to CO and 

developmental effects and birth outcomes.

Epidemiologic studies provide evidence of associations between ambient 

CO concentrations and respiratory morbidity such as changes in pulmonary

 

77 The ISA evaluates the health evidence associated with different health effects, assigning one of 

five “weight of evidence” determinations: causal relationship, likely to be a causal relationship, 

suggestive of a causal relationship, inadequate to infer a causal relationship, and not likely to be a 

causal relationship. For definitions of these levels of evidence, please refer to Section 1.6 of the 

ISA. 

78 Personal exposure includes contributions from many sources, and in many different environments. 

Total personal exposure to CO includes both ambient and nonambient components; and both 

components may contribute to adverse health effects.
Page 47 of 88

function, respiratory symptoms, and hospital admissions. A limited number of 

epidemiologic studies considered copollutants such as ozone, SO2, and PM in twopollutant models and found that CO risk estimates were generally robust, although 

this limited evidence makes it difficult to disentangle effects attributed to CO itself 

from those of the larger complex air pollution mixture. Controlled human exposure 

studies have not extensively evaluated the effect of CO on respiratory morbidity. 

Animal studies at levels of 50-100 ppm CO show preliminary evidence of altered 

pulmonary vascular remodeling and oxidative injury. The CO ISA concludes that 

the evidence is suggestive of a causal relationship between short-term CO exposure 

and respiratory morbidity, and inadequate to conclude that a causal relationship 

exists between long-term exposure and respiratory morbidity. 

Finally, the CO ISA concludes that the epidemiologic evidence is suggestive 

of a causal relationship between short-term concentrations of CO and mortality. 

Epidemiologic studies provide evidence of an association between short-term 

exposure to CO and mortality, but limited evidence is available to evaluate causespecific mortality outcomes associated with CO exposure. In addition, the 

attenuation of CO risk estimates which was often observed in copollutant models 

contributes to the uncertainty as to whether CO is acting alone or as an indicator for 

other combustion-related pollutants. The CO ISA also concludes that there is not 

likely to be a causal relationship between relevant long-term exposures to CO and 

mortality.

b. Current Concentrations of CO

There are two NAAQS for CO: an 8-hour standard (9 ppm) and a 1-hour 

standard (35 ppm). The primary NAAQS for CO were retained in August 2011. 

There are currently no CO nonattainment areas; as of September 27, 2010, all CO 

nonattainment areas were redesignated to maintenance areas. The designations 

were based on the existing community-wide monitoring network. EPA is making 

changes to the ambient air monitoring requirements for CO. The new requirements 

are expected to result in approximately 52 CO monitors operating near roads within 

52 urban areas by January 2015 (76 FR 54294, August 31, 2011). 

5. Mobile Source Air Toxics

Light-duty vehicle emissions contribute to ambient levels of air toxics 

known or suspected as human or animal carcinogens, or that have noncancer health 

effects. The population experiences an elevated risk of cancer and other noncancer 

health effects from exposure to the class of pollutants known collectively as “air 

toxics.”79 These compounds include, but are not limited to, benzene, 1,3-butadiene, 

 

79 U.S. EPA. (2011) Summary of Results for the 2005 National-Scale Assessment. 

www.epa.gov/ttn/atw/nata2005/05pdf/sum_results.pdf. 
Page 48 of 88

formaldehyde, acetaldehyde, acrolein, polycyclic organic matter, and naphthalene. 

These compounds were identified as national or regional risk drivers or contributors 

in the 2005 National-scale Air Toxics Assessment and have significant inventory

contributions from mobile sources.80 

a. Health Effects of Air Toxics

i. Benzene

The EPA’s Integrated Risk Information System (IRIS) database lists 

benzene as a known human carcinogen (causing leukemia) by all routes of 

exposure, and concludes that exposure is associated with additional health effects, 

including genetic changes in both humans and animals and increased proliferation 

of bone marrow cells in mice.81,82,83 EPA states in its IRIS database that data 

indicate a causal relationship between benzene exposure and acute lymphocytic 

leukemia and suggest a relationship between benzene exposure and chronic nonlymphocytic leukemia and chronic lymphocytic leukemia. EPA’s IRIS 

documentation for benzene also lists a range of 2.2 x 10-6to 7.8 x 10-6as the unit 

risk estimate (URE) for benzene.84,85 The International Agency for Research on 

Carcinogens (IARC) has determined that benzene is a human carcinogen and the 

U.S. Department of Health and Human Services (DHHS) has characterized benzene 

as a known human carcinogen.86,87 

A number of adverse noncancer health effects including blood disorders, 

such as preleukemia and aplastic anemia, have also been associated with long-term 

 

80 U.S. EPA (2011) 2005 National-Scale Air Toxics Assessment. 

http://www.epa.gov/ttn/atw/nata2005. 

81 U.S. EPA. (2000). Integrated Risk Information System File for Benzene. This material is available 

electronically at: http://www.epa.gov/iris/subst/0276.htm. 

82 International Agency for Research on Cancer, IARC monographs on the evaluation of 

carcinogenic risk of chemicals to humans, Volume 29, Some industrial chemicals and dyestuffs, 

International Agency for Research on Cancer, World Health Organization, Lyon, France 1982. 

83 Irons, R.D.; Stillman, W.S.; Colagiovanni, D.B.; Henry, V.A. (1992). Synergistic action of the 

benzene metabolite hydroquinone on myelopoietic stimulating activity of granulocyte/macrophage 

colony-stimulating factor in vitro, Proc. Natl. Acad. Sci. 89:3691-3695. 

84 A unit risk estimate is defined as the increase in the lifetime risk of an individual who is exposed 

for a lifetime to 1 μg/m3 benzene in air.

85 U.S. EPA. (2000). Integrated Risk Information System File for Benzene. This material is 

available electronically at: http://www.epa.gov/iris/subst/0276.htm. 

86 International Agency for Research on Cancer (IARC). (1987). Monographs on the evaluation of 

carcinogenic risk of chemicals to humans, Volume 29, Supplement 7, Some industrial chemicals and 

dyestuffs, World Health Organization, Lyon, France.

87 U.S. Department of Health and Human Services National Toxicology Program. (2011). 12th 

Report on Carcinogens. Available at: http://ntp.niehs.nih.gov/?objectid=03C9AF75-E1BF-FF40-

DBA9EC0928DF8B15. 
Page 49 of 88

exposure to benzene.88,89 The most sensitive noncancer effect observed in humans, 

based on current data, is the depression of the absolute lymphocyte count in 

blood.90,91 EPA’s inhalation reference concentration (RfC) for benzene is 30 μg/m3. 

The RfC is based on suppressed absolute lymphocyte counts seen in humans under 

occupational exposure conditions. In addition, recent work, including studies 

sponsored by the Health Effects Institute, provides evidence that biochemical 

responses are occurring at lower levels of benzene exposure than previously

known.92,93,94,95 EPA’s IRIS program has not yet evaluated these new data. EPA 

does not currently have an acute reference concentration for benzene. The Agency

for Toxic Substances and Disease Registry (ATSDR) Minimal Risk Level (MRL) 

for acute exposure to benzene is 29 μg/m3for 1-14 days exposure.96,97

ii. Formaldehyde 

In 1991, EPA concluded that formaldehyde is a carcinogen based on nasal 

tumors in animal bioassays.98 An Inhalation Unit Risk for cancer and a Reference 

Dose for oral noncancer effects were developed by the Agency and posted on the 

IRIS database. Since that time, the National Toxicology Program (NTP) and 

 

88 Aksoy, M. (1989). Hematotoxicity and carcinogenicity of benzene. Environ. Health Perspect. 82: 

193-197. 

89 Goldstein, B.D. (1988). Benzene toxicity. Occupational medicine. State of the Art Reviews. 3: 

541-554.

90 Rothman, N., G.L. Li, M. Dosemeci, W.E. Bechtold, G.E. Marti, Y.Z. Wang, M. Linet, L.Q. Xi, 

W. Lu, M.T. Smith, N. Titenko-Holland, L.P. Zhang, W. Blot, S.N. Yin, and R.B. Hayes. (1996). 

Hematotoxicity among Chinese workers heavily exposed to benzene. Am. J. Ind. Med. 29: 236-246. 

91 U.S. EPA. (2002). Toxicological Review of Benzene (Noncancer Effects). Environmental 

Protection Agency, Integrated Risk Information System (IRIS), Research and Development, 

National Center for Environmental Assessment, Washington DC. This material is available 

electronically at http://www.epa.gov/iris/subst/0276.htm. 

92 Qu, O.; Shore, R.; Li, G.; Jin, X.; Chen, C.L.; Cohen, B.; Melikian, A.; Eastmond, D.; Rappaport, 

S.; Li, H.; Rupa, D.; Suramaya, R.; Songnian, W.; Huifant, Y.; Meng, M.; Winnik, M.; Kwok, E.; 

Li, Y.; Mu, R.; Xu, B.; Zhang, X.; Li, K. (2003). HEI Report 115, Validation & Evaluation of 

Biomarkers in Workers Exposed to Benzene in China.

93 Qu, Q., R. Shore, G. Li, X. Jin, L.C. Chen, B. Cohen, et al. (2002). Hematological changes among 

Chinese workers with a broad range of benzene exposures. Am. J. Industr. Med. 42: 275-285. 

94 Lan, Qing, Zhang, L., Li, G., Vermeulen, R., et al. (2004). Hematotoxically in Workers Exposed 

to Low Levels of Benzene. Science 306: 1774-1776.

95 Turtletaub, K.W. and Mani, C. (2003). Benzene metabolism in rodents at doses relevant to human 

exposure from Urban Air. Research Reports Health Effect Inst. Report No.113. 

96 U.S. Agency for Toxic Substances and Disease Registry (ATSDR). (2007). Toxicological profile 

for benzene. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service. 

http://www.atsdr.cdc.gov/ToxProfiles/tp3.pdf.

97 A minimal risk level (MRL) is defined as an estimate of the daily human exposure to a hazardous 

substance that is likely to be without appreciable risk of adverse noncancer health effects over a 

specified duration of exposure.

98 EPA. Integrated Risk Information System. Formaldehyde (CASRN 50-00-0) 

http://www.epa.gov/iris/subst/0419/htm
Page 50 of 88

International Agency for Research on Cancer (IARC) have concluded that 

formaldehyde is a known human carcinogen.99,100,101

The conclusions by IARC and NTP reflect the results of epidemiologic 

research published since 1991 in combination with previous animal, human and 

mechanistic evidence. Research conducted by the National Cancer Institute 

reported an increased risk of nasopharyngeal cancer and specific 

lymphohematopoietic malignancies among workers exposed to 

formaldehyde.102,103,104 A National Institute of Occupational Safety and Health 

study of garment workers also reported increased risk of death due to leukemia 

among workers exposed to formaldehyde.105 Extended follow-up of a cohort of 

British chemical workers did not report evidence of an increase in nasopharyngeal 

or lymphohematopoietic cancers, but a continuing statistically significant excess in 

lung cancers was reported.106 Finally, a study of embalmers reported formaldehyde 

exposures to be associated with an increased risk of myeloid leukemia but not brain 

cancer.107

Health effects of formaldehyde in addition to cancer were reviewed by the 

Agency for Toxics Substances and Disease Registry in 1999108 and supplemented in 

 

99 National Toxicology Program, U.S. Department of Health and Human Services (HHS), 12th 

Report on Carcinogens, June 10, 2011

100 IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Volume 88 (2006): 

Formaldehyde, 2-Butoxyethanol and 1-tert-Butoxypropan-2-ol

101 IARC Mongraphs on the Evaluation of Carcinogenic Risks to Humans Volume 100F (2012): 

Formaldehyde

102 Hauptmann, M..; Lubin, J. H.; Stewart, P. A.; Hayes, R. B.; Blair, A. 2003. Mortality from 

lymphohematopoetic malignancies among workers in formaldehyde industries. Journal of the 

National Cancer Institute 95: 1615-1623. 

103 Hauptmann, M..; Lubin, J. H.; Stewart, P. A.; Hayes, R. B.; Blair, A. 2004. Mortality from solid 

cancers among workers in formaldehyde industries. American Journal of Epidemiology 159: 1117-

1130. 

104 Beane Freeman, L. E.; Blair, A.; Lubin, J. H.; Stewart, P. A.; Hayes, R. B.; Hoover, R. N.; 

Hauptmann, M. 2009. Mortality from lymphohematopoietic malignancies among workers in 

formaldehyde industries: The National Cancer Institute cohort. J. National Cancer Inst. 101: 751-

761. 

105 Pinkerton, L. E. 2004. Mortality among a cohort of garment workers exposed to formaldehyde: 

an update. Occup. Environ. Med. 61: 193-200.

106 Coggon, D, EC Harris, J Poole, KT Palmer. 2003. Extended follow-up of a cohort of British 

chemical workers exposed to formaldehyde. J National Cancer Inst. 95:1608-1615.

107 Hauptmann, M,; Stewart P. A.; Lubin J. H.; Beane Freeman, L. E.; Hornung, R. W.; Herrick, R. 

F.; Hoover, R. N.; Fraumeni, J. F.; Hayes, R. B. 2009. Mortality from lymphohematopoietic 

malignancies and brain cancer among embalmers exposed to formaldehyde. Journal of the National 

Cancer Institute 101:1696-1708.

108 ATSDR. 1999. Toxicological Profile for Formaldehyde, U.S. Department of Health and Human 

Services (HHS), July 1999.
Page 51 of 88

2010,109 and by the World Health Organization.110 These organizations reviewed 

the literature concerning effects on the eyes and respiratory system, the primary

point of contact for inhaled formaldehyde, including sensory irritation of eyes and 

respiratory tract, pulmonary function, nasal histopathology, and immune system 

effects. In addition, research on reproductive and developmental effects and 

neurological effects were discussed.

EPA released a draft Toxicological Review of Formaldehyde – Inhalation 

Assessment through the IRIS program for peer review by the National Research 

Council (NRC) and public comment in June 2010.111 The draft assessment 

reviewed more recent research from animal and human studies on cancer and other 

health effects. The NRC released their review report in April 2011.112 The EPA is 

currently revising the draft assessment in response to this review.

iii.Acetaldehyde 

Acetaldehyde is classified in EPA’s IRIS database as a probable human 

carcinogen, based on nasal tumors in rats, and is considered toxic by the inhalation, 

oral, and intravenous routes.113 The URE in IRIS for acetaldehyde is 2.2 × 10-6per 

μg/m3.

114

 Acetaldehyde is reasonably anticipated to be a human carcinogen by the 

U.S. DHHS in the 12th Report on Carcinogens and is classified as possibly 

carcinogenic to humans (Group 2B) by the IARC.115,116 EPA is currently 

conducting a reassessment of cancer risk from inhalation exposure to acetaldehyde.

 

109 ATSDR. 2010. Addendum to theToxicological Profile for Formaldehyde. U.S. Department of 

Health and Human Services (HHS), October 2010.

110 IPCS. 2002. Concise International Chemical Assessment Document 40. Formaldehyde. World 

Health Organization.

111 EPA (U.S. Environmental Protection Agency). 2010. Toxicological Review of Formaldehyde 

(CAS No. 50-00-0) – Inhalation Assessment: In Support of Summary Information on the Integrated 

Risk Information System (IRIS). External Review Draft. EPA/635/R-10/002A. U.S. Environmental 

Protection Agency, Washington DC [online]. Available: 

http://cfpub.epa.gov/ncea/irs_drats/recordisplay.cfm?deid=223614

112 NRC (National Research Council). 2011. Review of the Environmental Protection Agency’s 

Draft IRIS Assessment of Formaldehyde. Washington DC: National Academies Press. 

http://books.nap.edu/openbook.php?record_id=13142

113 U.S. EPA (1991). Integrated Risk Information System File of Acetaldehyde. Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available electronically at http://www.epa.gov/iris/subst/0290.htm. 

114 U.S. EPA (1991). Integrated Risk Information System File of Acetaldehyde. This material is 

available electronically at http://www.epa.gov/iris/subst/0290.htm. 

115 NTP. (2011). Report on Carcinogens, Twelfth Edition. Research Triangle Park, NC: U.S. 

Department of Health and Human Services, Public Health Service, National Toxicology Program. 

499 pp.
Page 52 of 88

The primary noncancer effects of exposure to acetaldehyde vapors include 

irritation of the eyes, skin, and respiratory tract.117 In short-term (4 week) rat 

studies, degeneration of olfactory epithelium was observed at various concentration 

levels of acetaldehyde exposure.118,119 Data from these studies were used by EPA 

to develop an inhalation reference concentration of 9 μg/m3. Some asthmatics have 

been shown to be a sensitive subpopulation to decrements in functional expiratory

volume (FEV1 test) and bronchoconstriction upon acetaldehyde inhalation.120 The 

agency is currently conducting a reassessment of the health hazards from inhalation 

exposure to acetaldehyde. 

iv. Acrolein

EPA most recently evaluated the toxicological and health effects literature 

related to acrolein in 2003 and concluded that the human carcinogenic potential of 

acrolein could not be determined because the available data were inadequate. No 

information was available on the carcinogenic effects of acrolein in humans and the 

animal data provided inadequate evidence of carcinogenicity.

121

 The IARC 

determined in 1995 that acrolein was not classifiable as to its carcinogenicity in 

humans.122 

Lesions to the lungs and upper respiratory tract of rats, rabbits, and hamsters 

have been observed after subchronic exposure to acrolein.123 The Agency has 

 

116 International Agency for Research on Cancer (IARC). (1999). Re-evaluation of some organic 

chemicals, hydrazine, and hydrogen peroxide. IARC Monographs on the Evaluation of 

Carcinogenic Risk of Chemical to Humans, Vol 71. Lyon, France.

117 U.S. EPA (1991). Integrated Risk Information System File of Acetaldehyde. This material is 

available electronically at http://www.epa.gov/iris/subst/0290.htm. 

118 U.S. EPA. (2003). Integrated Risk Information System File of Acrolein. Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available electronically at http://www.epa.gov/iris/subst/0364.htm. 

119 Appleman, L.M., R.A. Woutersen, and V.J. Feron. (1982). Inhalation toxicity of acetaldehyde in 

rats. I. Acute and subacute studies. Toxicology. 23: 293-297. 

120 Myou, S.; Fujimura, M.; Nishi K.; Ohka, T.; and Matsuda, T. (1993) Aerosolized acetaldehyde 

induces histamine-mediated bronchoconstriction in asthmatics. Am. Rev. Respir.Dis.148(4 Pt 1): 

940-943. 

121 U.S. EPA. (2003). Integrated Risk Information System File of Acrolein. Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available at http://www.epa.gov/iris/subst/0364.htm. 

122 International Agency for Research on Cancer (IARC). (1995). Monographs on the evaluation of 

carcinogenic risk of chemicals to humans, Volume 63. Dry cleaning, some chlorinated solvents and 

other industrial chemicals, World Health Organization, Lyon, France. 

123 U.S. EPA. (2003). Integrated Risk Information System File of Acrolein. Office of Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available at http://www.epa.gov/iris/subst/0364.htm. 
Page 53 of 88

developed an RfC for acrolein of 0.02 μg/m

3 and an RfD of 0.5 μg/kg-day.124

 EPA 

is considering updating the acrolein assessment with data that have become 

available since the 2003 assessment was completed.

Acrolein is extremely acrid and irritating to humans when inhaled, with 

acute exposure resulting in upper respiratory tract irritation, mucus hypersecretion 

and congestion. The intense irritancy of this carbonyl has been demonstrated 

during controlled tests in human subjects, who suffer intolerable eye and nasal 

mucosal sensory reactions within minutes of exposure.125 These data and additional 

studies regarding acute effects of human exposure to acrolein are summarized in 

EPA’s 2003 IRIS Human Health Assessment for acrolein.126 Studies in humans 

indicate that levels as low as 0.09 ppm (0.21 mg/m3) for five minutes may elicit 

subjective complaints of eye irritation with increasing concentrations leading to 

more extensive eye, nose and respiratory symptoms. Acute exposures in animal 

studies report bronchial hyper-responsiveness. Based on animal data (more 

pronounced respiratory irritancy in mice with allergic airway disease in comparison 

to non-diseased mice127) and demonstration of similar effects in humans (e.g., 

reduction in respiratory rate), individuals with compromised respiratory function 

(e.g., emphysema, asthma) are expected to be at increased risk of developing 

adverse responses to strong respiratory irritants such as acrolein. EPA does not 

currently have an acute reference concentration for acrolein. The available health 

effect reference values for acrolein have been summarized by EPA and include an 

ATSDR MRL for acute exposure to acrolein of 7 μg/m3for 1-14 days exposure; 

and Reference Exposure Level (REL) values from the California Office of 

Environmental Health Hazard Assessment (OEHHA) for one-hour and 8-hour 

exposures of 2.5 μg/m3and 0.7 μg/m3, respectively.128

 

124 U.S. EPA. (2003). Integrated Risk Information System File of Acrolein. Office of Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available at http://www.epa.gov/iris/subst/0364.htm. 

125 U.S. EPA. (2003) Toxicological review of acrolein in support of summary information on 

Integrated Risk Information System (IRIS) National Center for Environmental Assessment, 

Washington, DC. EPA/635/R-03/003. p. 10. Available online at: 

http://www.epa.gov/ncea/iris/toxreviews/0364tr.pdf. 

126 U.S. EPA. (2003) Toxicological review of acrolein in support of summary information on 

Integrated Risk Information System (IRIS) National Center for Environmental Assessment, 

Washington, DC. EPA/635/R-03/003. Available online at: 

http://www.epa.gov/ncea/iris/toxreviews/0364tr.pdf. 

127 Morris JB, Symanowicz PT, Olsen JE, et al. (2003). Immediate sensory nerve-mediated 

respiratory responses to irritants in healthy and allergic airway-diseased mice. J Appl Physiol 

94(4):1563-1571. 

128 U.S. EPA. (2009). Graphical Arrays of Chemical-Specific Health Effect Reference Values for 

Inhalation Exposures (Final Report). U.S. Environmental Protection Agency, Washington, DC, 

EPA/600/R-09/061, 2009. http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003 
Page 54 of 88

v. 1,3-Butadiene

EPA has characterized 1,3-butadiene as carcinogenic to humans by

inhalation.129,130 The IARC has determined that 1,3-butadiene is a human 

carcinogen and the U.S. DHHS has characterized 1,3-butadiene as a known human 

carcinogen.131,132,133 There are numerous studies consistently demonstrating that 

1,3-butadiene is metabolized into genotoxic metabolites by experimental animals 

and humans. The specific mechanisms of 1,3-butadiene-induced carcinogenesis are 

unknown; however, the scientific evidence strongly suggests that the carcinogenic 

effects are mediated by genotoxic metabolites. Animal data suggest that females 

may be more sensitive than males for cancer effects associated with 1,3-butadiene 

exposure; there are insufficient data in humans from which to draw conclusions 

about sensitive subpopulations. The URE for 1,3-butadiene is 3 × 10-5per μg/m3.

134

1,3-butadiene also causes a variety of reproductive and developmental effects in 

mice; no human data on these effects are available. The most sensitive effect was 

ovarian atrophy observed in a lifetime bioassay of female mice.135 Based on this 

critical effect and the benchmark concentration methodology, an RfC for chronic 

health effects was calculated at 0.9 ppb (approximately 2 μg/m3).

vi. Ethanol

 

129 U.S. EPA. (2002). Health Assessment of 1,3-Butadiene. Office of Research and Development, 

National Center for Environmental Assessment, Washington Office, Washington, DC. Report No. 

EPA600-P-98-001F. This document is available electronically at 

http://www.epa.gov/iris/supdocs/buta-sup.pdf. 

130 U.S. EPA. (2002). “Full IRIS Summary for 1,3-butadiene (CASRN 106-99-0)” Environmental 

Protection Agency, Integrated Risk Information System (IRIS), Research and Development, 

National Center for Environmental Assessment, Washington, DC

http://www.epa.gov/iris/subst/0139.htm. 

131 International Agency for Research on Cancer (IARC). (1999). Monographs on the evaluation of 

carcinogenic risk of chemicals to humans, Volume 71, Re-evaluation of some organic chemicals, 

hydrazine and hydrogen peroxide and Volume 97 (in preparation), World Health Organization, 

Lyon, France. 

132 International Agency for Research on Cancer (IARC). (2008). Monographs on the evaluation of

carcinogenic risk of chemicals to humans, 1,3-Butadiene, Ethylene Oxide and Vinyl Halides (Vinyl 

Fluoride, Vinyl Chloride and Vinyl Bromide) Volume 97, World Health Organization, Lyon, France. 

133 NTP. (2011). Report on Carcinogens, Twelfth Edition. Research Triangle Park, NC: U.S. 

Department of Health and Human Services, Public Health Service, National Toxicology Program. 

499 pp.

134 U.S. EPA. (2002). “Full IRIS Summary for 1,3-butadiene (CASRN 106-99-0)” Environmental 

Protection Agency, Integrated Risk Information System (IRIS), Research and Development, 

National Center for Environmental Assessment, Washington, DC

http://www.epa.gov/iris/subst/0139.htm. 

135 Bevan, C.; Stadler, J.C.; Elliot, G.S.; et al. (1996). Subchronic toxicity of 4-vinylcyclohexene in 

rats and mice by inhalation. Fundam. Appl. Toxicol. 32:1-10.
Page 55 of 88

EPA is planning to develop an assessment of the health effects of exposure 

to ethanol, a compound which is not currently listed on EPA’s IRIS database. 

Extensive health effects data are available for ingestion of ethanol, while data on 

inhalation exposure effects are sparse. In developing the assessment, EPA is 

evaluating pharmacokinetic models as a means of extrapolating across species 

(animal to human) and across exposure routes (oral to inhalation) to better 

characterize the health hazards and dose-response relationships for low levels of 

ethanol exposure in the environment.

vii. Polycyclic Organic Matter

The term polycyclic organic matter (POM) defines a broad class of 

compounds that includes the polycyclic aromatic hydrocarbon compounds (PAHs). 

One of these compounds, naphthalene, is discussed separately below. POM 

compounds are formed primarily from combustion and are present in the 

atmosphere in gas and particulate form. Cancer is the major concern from exposure 

to POM. Epidemiologic studies have reported an increase in lung cancer in humans 

exposed to diesel exhaust, coke oven emissions, roofing tar emissions, and cigarette 

smoke; all of these mixtures contain POM compounds.136,137 Animal studies have 

reported respiratory tract tumors from inhalation exposure to benzo[a]pyrene and 

alimentary tract and liver tumors from oral exposure to benzo[a]pyrene.138 In 1997 

EPA classified seven PAHs (benzo[a]pyrene, benz[a]anthracene, chrysene, 

benzo[b]fluoranthene, benzo[k]fluoranthene, dibenz[a,h]anthracene, and 

indeno[1,2,3-cd]pyrene) as Group B2, probable human carcinogens.139 Since that 

time, studies have found that maternal exposures to PAHs in a population of 

pregnant women were associated with several adverse birth outcomes, including 

low birth weight and reduced length at birth, as well as impaired cognitive 

development in preschool children (3 years of age).140,141 These and similar studies 

 

136 Agency for Toxic Substances and Disease Registry (ATSDR). (1995). Toxicological profile for 

Polycyclic Aromatic Hydrocarbons (PAHs). Atlanta, GA: U.S. Department of Health and Human 

Services, Public Health Service. Available electronically at 

http://www.atsdr.cdc.gov/ToxProfiles/TP.asp?id=122&tid=25. 

137 U.S. EPA (2002). Health Assessment Document for Diesel Engine Exhaust. EPA/600/8-90/057F 

Office of Research and Development, Washington DC. 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=29060. 

138 International Agency for Research on Cancer (IARC). (2012). Monographs on the Evaluation of 

the Carcinogenic Risk of Chemicals for Humans, Chemical Agents and Related Occupations. Vol. 

100F. Lyon, France.

139 U.S. EPA (1997). Integrated Risk Information System File of indeno(1,2,3-cd)pyrene. Research 

and Development, National Center for Environmental Assessment, Washington, DC. This material is 

available electronically at http://www.epa.gov/ncea/iris/subst/0457.htm. 

140 Perera, F.P.; Rauh, V.; Tsai, W-Y.; et al. (2002). Effect of transplacental exposure to 

environmental pollutants on birth outcomes in a multiethnic population. Environ Health Perspect. 

111: 201-205. 
Page 56 of 88

are being evaluated as a part of the ongoing IRIS assessment of health effects 

associated with exposure to benzo[a]pyrene.

viii. Naphthalene

Naphthalene is found in small quantities in gasoline and diesel fuels. 

Naphthalene emissions have been measured in larger quantities in both gasoline and 

diesel exhaust compared with evaporative emissions from mobile sources, 

indicating it is primarily a product of combustion. Acute (short-term) exposure of 

humans to naphthalene by inhalation, ingestion, or dermal contact is associated with 

hemolytic anemia and damage to the liver and the nervous system.142 Chronic (long 

term) exposure of workers and rodents to naphthalene has been reported to cause 

cataracts and retinal damage.143 EPA released an external review draft of a 

reassessment of the inhalation carcinogenicity of naphthalene based on a number of 

recent animal carcinogenicity studies.144 The draft reassessment completed external 

peer review.145 Based on external peer review comments received, a revised draft 

assessment that considers all routes of exposure, as well as cancer and noncancer 

effects, is under development. The external review draft does not represent official 

agency opinion and was released solely for the purposes of external peer review and 

public comment. The National Toxicology Program listed naphthalene as 

"reasonably anticipated to be a human carcinogen" in 2004 on the basis of bioassays 

reporting clear evidence of carcinogenicity in rats and some evidence of 

carcinogenicity in mice.146 California EPA has released a new risk assessment for 

 

141 Perera, F.P.; Rauh, V.; Whyatt, R.M.; Tsai, W.Y.; Tang, D.; Diaz, D.; Hoepner, L.; Barr, D.; Tu, 

Y.H.; Camann, D.; Kinney, P. (2006). Effect of prenatal exposure to airborne polycyclic aromatic 

hydrocarbons on neurodevelopment in the first 3 years of life among inner-city children. Environ 

Health Perspect 114: 1287-1292. 

142 U. S. EPA. 1998. Toxicological Review of Naphthalene (Reassessment of the Inhalation Cancer 

Risk), Environmental Protection Agency, Integrated Risk Information System, Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available electronically at http://www.epa.gov/iris/subst/0436.htm.

143 U. S. EPA. 1998. Toxicological Review of Naphthalene (Reassessment of the Inhalation Cancer 

Risk), Environmental Protection Agency, Integrated Risk Information System, Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available electronically at http://www.epa.gov/iris/subst/0436.htm.

144 U. S. EPA. (1998). Toxicological Review of Naphthalene (Reassessment of the Inhalation 

Cancer Risk), Environmental Protection Agency, Integrated Risk Information System, Research and 

Development, National Center for Environmental Assessment, Washington, DC. This material is 

available electronically at http://www.epa.gov/iris/subst/0436.htm. 

145 Oak Ridge Institute for Science and Education. (2004). External Peer Review for the IRIS 

Reassessment of the Inhalation Carcinogenicity of Naphthalene. August 2004. 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=84403. 

146 NTP. (2011). Report on Carcinogens, Twelfth Edition. Research Triangle Park, NC: U.S. 

Department of Health and Human Services, Public Health Service, National Toxicology Program. 

499 pp.
Page 57 of 88

naphthalene, and the IARC has reevaluated naphthalene and re-classified it as 

Group 2B: possibly carcinogenic to humans.147 

Naphthalene also causes a number of chronic non-cancer effects in animals, 

including abnormal cell changes and growth in respiratory and nasal tissues.148 The 

current EPA IRIS assessment includes noncancer data on hyperplasia and 

metaplasia in nasal tissue that form the basis of the inhalation RfC of 3 μg/m3.

149

 

The ATSDR MRL for acute exposure to naphthalene is 0.6 mg/kg/day.

ix. Other Air Toxics

In addition to the compounds described above, other compounds in gaseous 

hydrocarbon and PM emissions from motor vehicles will be affected by this action. 

Mobile source air toxic compounds that will potentially be impacted include 

ethylbenzene, propionaldehyde, toluene, and xylene. Information regarding the 

health effects of these compounds can be found in EPA’s IRIS database.150

b. Current Concentrations of Air Toxics 

The most recent available data indicate that the majority of Americans 

continue to be exposed to ambient concentrations of air toxics at levels which have 

the potential to cause adverse health effects.151 The levels of air toxics to which 

people are exposed vary depending on where people live and work and the kinds of 

activities in which they engage, as discussed in detail in U.S. EPA’s most recent 

Mobile Source Air Toxics Rule.152 According to the National Air Toxic 

Assessment (NATA) for 2005,153 mobile sources were responsible for 43 percent of 

outdoor toxic emissions and over 50 percent of the cancer risk and noncancer 

hazard associated with primary emissions. Mobile sources are also large 

contributors to precursor emissions which react to form secondary concentrations of 

 

147 International Agency for Research on Cancer (IARC). (2002). Monographs on the Evaluation of 

the Carcinogenic Risk of Chemicals for Humans. Vol. 82. Lyon, France. 

148 U. S. EPA. (1998). Toxicological Review of Naphthalene, Environmental Protection Agency, 

Integrated Risk Information System, Research and Development, National Center for Environmental 

Assessment, Washington, DC. This material is available electronically at 

http://www.epa.gov/iris/subst/0436.htm 

149 U.S. EPA. (1998). Toxicological Review of Naphthalene. Environmental Protection Agency, 

Integrated Risk Information System (IRIS), Research and Development, National Center for 

Environmental Assessment, Washington, DC http://www.epa.gov/iris/subst/0436.htm. 

150 U.S. EPA Integrated Risk Information System (IRIS) database is available at: www.epa.gov/iris 

151 U.S. EPA. (2011) Summary of Results for the 2005 National-Scale Assessment. 

www.epa.gov/ttn/atw/nata2005/05pdf/sum_results.pdf.

152 U. S. Environmental Protection Agency (2007). Control of Hazardous Air Pollutants from Mobile 

Sources; Final Rule. 72 FR 8434, February 26, 2007. 

153 U. S. EPA. (2011). 2005 National-Scale Air Toxics Assessment. 

http://www.epa.gov/ttn/atw/nata2005/. 
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air toxics. Formaldehyde is the largest contributor to cancer risk of all 80 pollutants

quantitatively assessed in the 2005 NATA. Mobile sources were responsible for 

over 40 percent of primary emissions of this pollutant in 2005, and are major 

contributors to formaldehyde precursor emissions. Benzene is also a large 

contributor to cancer risk, and mobile sources account for over 70 percent of 

ambient exposure. Over the years, EPA has implemented a number of mobile 

source and fuel controls which have resulted in VOC reductions, which also 

reduced formaldehyde, benzene and other air toxic emissions.

6. Near-Roadway Pollution

Locations in close proximity to major roadways generally have elevated 

concentrations of many air pollutants emitted from motor vehicles. Hundreds of 

such studies have been published in peer-reviewed journals, concluding that 

concentrations of CO, NO, NO2, benzene, aldehydes, particulate matter, black 

carbon, and many other compounds are elevated in ambient air within 

approximately 300-600 meters (about 1,000-2,000 feet) of major roadways. 

Highest concentrations of most pollutants emitted directly by motor vehicles are 

found at locations within 50 meters (about 165 feet) of the edge of a roadway’s 

traffic lanes.

A recent large-scale review of air quality measurements in vicinity of major 

roadways between 1978 and 2008 concluded that the pollutants with the steepest 

concentration gradients in vicinities of roadways were CO, ultrafine particles, 

metals, elemental carbon (EC), NO, NOX, and several VOCs.154 These pollutants 

showed a large reduction in concentrations within 100 meters downwind of the 

roadway. Pollutants that showed more gradual reductions with distance from 

roadways included benzene, NO2, PM2.5, and PM10. In the review article, results 

varied based on the method of statistical analysis used to determine the trend.

For pollutants with relatively high background concentrations relative to 

near-road concentrations, detecting concentration gradients can be difficult. For 

example, many aldehydes have high background concentrations as a result of 

photochemical breakdown of precursors from many different organic compounds. 

This can make detection of gradients around roadways and other primary emission 

sources difficult. However, several studies have measured aldehydes in multiple 

weather conditions, and found higher concentrations of many carbonyls downwind 

 

154 Karner, A.A.; Eisinger, D.S.; Niemeier, D.A. (2010). Near-roadway air quality: synthesizing the 

findings from real-world data. Environ Sci Technol 44: 5334-5344.
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of roadways.155,156 These findings suggest a substantial roadway source of these 

carbonyls.

In the past 15 years, many studies have been published with results reporting

that populations who live, work, or go to school near high-traffic roadways 

experience higher rates of numerous adverse health effects, compared to 

populations far away from major roads.157 In addition, numerous studies have 

found adverse health effects associated with spending time in traffic, such as 

commuting or walking along high-traffic roadways.158,159,160,161 The health 

outcomes with the strongest evidence linking them with traffic-associated air 

pollutants are respiratory effects, particularly in asthmatic children, and 

cardiovascular effects.

Numerous reviews of this body of health literature have been published as 

well. In 2010, an expert panel of the Health Effects Institute (HEI) published a 

review of hundreds of exposure, epidemiology, and toxicology studies.162 The 

panel rated how the evidence for each type of health outcome supported a 

conclusion of a causal association with traffic-associated air pollution as either 

“sufficient,” “suggestive but not sufficient,” or “inadequate and insufficient.” The 

panel categorized evidence of a causal association for exacerbation of childhood 

asthma as “sufficient.” The panel categorized evidence of a causal association for 

new onset asthma as between “sufficient” and as “suggestive but not sufficient.” 

“Suggestive of a causal association” was how the panel categorized evidence 

 

155 Liu, W.; Zhang, J.; Kwon, J.l; et l. (2006). Concentrations and source characteristics of airborne 

carbonyl compounds measured outside urban residences. J Air Waste Manage Assoc 56: 1196-

1204.

156 Cahill, T.M.; Charles, M.J.; Seaman, V.Y. (2010). Development and application of a sensitive 

method to determine concentrations of acrolein and other carbonyls in ambient air. Health Effects 

Institute Research Report 149.Available at http://dx.doi.org

157 In the widely-used PubMed database of health publications, between January 1, 1990 and August 

18, 2011, 605 publications contained the keywords “traffic, pollution, epidemiology,” with 

approximately half the studies published after 2007. 

158 Laden, F.; Hart, J.E.; Smith, T.J.; Davis, M.E.; Garshick, E. (2007) Cause-specific mortality in 

the unionized U.S. trucking industry. Environmental Health Perspect 115:1192-1196.

159 Peters, A.; von Klot, S.; Heier, M.; Trentinaglia, I.; Hörmann, A.; Wichmann, H.E.; Löwel, H. 

(2004) Exposure to traffic and the onset of myocardial infarction. New England J Med 351: 1721-

1730.

160 Zanobetti, A.; Stone, P.H.; Spelzer, F.E.; Schwartz, J.D.; Coull, B.A.; Suh, H.H.; Nearling, B.D.; 

Mittleman, M.A.; Verrier, R.L.; Gold, D.R. (2009) T-wave alternans, air pollution and traffic in 

high-risk subjects. Am J Cardiol 104: 665-670.

161 Dubowsky Adar, S.; Adamkiewicz, G.; Gold, D.R.; Schwartz, J.; Coull, B.A.; Suh, H. (2007) 

Ambient and microenvironmental particles and exhaled nitric oxide before and after a group bus trip. 

Environ Health Perspect 115: 507-512.

162 Health Effects Institute Panel on the Health Effects of Traffic-Related Air Pollution. (2010). 

Traffic-related air pollution: a critical review of the literature on emissions, exposure, and health 

effects. HEI Special Report 17. Available at http://www.healtheffects.org
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linking traffic-associated air pollutants with exacerbation of adult respiratory

symptoms and lung function decrement. It categorized as “inadequate and 

insufficient” evidence of a causal relationship between traffic-related air pollution 

and health care utilization for respiratory problems, new onset adult asthma, chronic 

obstructive pulmonary disease (COPD), nonasthmatic respiratory allergy, and 

cancer in adults and children. Other literature reviews have been published with 

conclusions similar to the HEI panel’s.163,164,165 Health outcomes with few 

publications suggest the possibility of other effects still lacking sufficient evidence 

to draw definitive conclusions. Among these outcomes with a small number of 

positive studies are neurological impacts (e.g., autism and reduced cognitive 

function) and reproductive outcomes (e.g., preterm birth, low birth 

weight).166,167,168,169

In addition to health outcomes, particularly cardiopulmonary effects, 

conclusions of numerous studies suggest mechanisms by which traffic-related air 

pollution affects health. Numerous studies indicate that near-roadway exposures 

may increase systemic inflammation, affecting organ systems, including blood 

vessels and lungs.170,171,172,173 Long-term exposures in near-road environments have 

 

163 Boothe, V.L.; Shendell, D.G. (2008). Potential health effects associated with residential proximity 

to freeways and primay roads: review of scientific literature, 1999-2006. J Environ Health 70: 33-

41.

164 Salam, M.T.; Islam, T.; Gilliland, F.D. (2008). Recent evidence for adverse effects of residential 

proximity to traffic sources on asthma. Curr Opin Pulm Med 14: 3-8.

165 Raaschou-Nielsen, O.; Reynolds, P. (2006). Air pollution and childhood cancer: a review of the 

epidemiological literature. Int J Cancer 118: 2920-9.

166 Volk, H.E.; Hertz-Picciotto, I.; Delwiche, L.; et al. (2011). Residential proximity to freeways and 

autism in the CHARGE study. Environ Health Perspect 119: 873-877.

167 Franco-Suglia, S.; Gryparis, A.; Wright, R.O.; et al. (2007). Association of black carbon with 

cognition among children in a prospective birth cohort study. Am J Epidemiol. doi: 

10.1093/aje/kwm308. [Online at http://dx.doi.org]

168 Power, M.C.; Weisskopf, M.G.; Alexeef, S.E.; et al. (2011). Traffic-related air pollution and 

cognitive function in a cohort of older men. Environ Health Perspect 2011: 682-687.

169 Wu, J.; Wilhelm, M.; Chung, J.; et al. (2011). Comparing exposure assessment methods for 

traffic-related air pollution in and adverse pregnancy outcome study. Environ Res 111: 685-6692.

170 Riediker, M. (2007). Cardiovascular effects of fine particulate matter components in highway 

patrol officers. Inhal Toxicol 19: 99-105. doi: 10.1080/08958370701495238 Available at 

http://dx.doi.org

171 Alexeef, S.E.; Coull, B.A.; Gryparis, A.; et al. (2011). Medium-term exposure to traffic-related 

air pollution and markers of inflammation and endothelial function. Environ Health Perspect 119: 

481-486. doi:10.1289/ehp.1002560 Available at http://dx.doi.org

172 Eckel. S.P.; Berhane, K.; Salam, M.T.; et al. (2011). Traffic-related pollution exposure and

exhaled nitric oxide in the Children’s Health Study. Environ Health Perspect (IN PRESS). 

doi:10.1289/ehp.1103516. Available at http://dx.doi.org

173 Zhang, J.; McCreanor, J.E.; Cullinan, P.; et al. (2009). Health effects of real-world exposure 

diesel exhaust in persons with asthma. Res Rep Health Effects Inst 138. [Online at 

http://www.healtheffects.org]
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been associated with inflammation-associated conditions, such as atherosclerosis 

and asthma.174,175,176 

Several studies suggest that some factors may increase susceptibility to the 

effects of traffic-associated air pollution. Several studies have found stronger 

respiratory associations in children experiencing chronic social stress, such as in 

violent neighborhoods or in homes with high family stress.177,178,179 

The risks associated with residence, workplace, or schools near major roads 

are of potentially high public health significance due to the large population in such 

locations. According to the 2009 American Housing Survey, over 22 million 

homes (17.0 percent of all U.S. housing units) were located within 300 feet of an 

airport, railroad, or highway with four or more lanes. This corresponds to a 

population of more than 50 million U.S. residents in close proximity to high-traffic 

roadways or other transportation sources. Based on 2010 Census data, a 2013 

publication estimated that 19% of the U.S. population (over 59 million people) 

lived within 500 meters of roads with at least 25,000 annual average daily traffic 

(AADT), while about 3.2% of the population lived within 100 meters (about 300 

feet) of such roads.180 Another 2013 study estimated that 3.7% of the U.S. 

population (about 11.3 million people) lived within 150 meters (about 500 feet) of 

interstate highways, or other freeways and expressways.181 As discussed in Section 

III, on average, populations near major roads have higher fractions of minority

residents and lower socioeconomic status. Furthermore, on average, Americans 

 

174 Adar, S.D.; Klein, R.; Klein, E.K.; et al. (2010). Air pollution and the microvasculatory: a crosssectional assessment of in vivo retinal images in the population-based Multi-Ethnic Study of 

Atherosclerosis. PLoS Med 7(11): E1000372. doi:10.1371/journal.pmed.1000372. Available at 

http://dx.doi.org

175 Kan, H.; Heiss, G.; Rose, K.M.; et al. (2008). Proxpective analysis of traffic exposure as a risk 

factor for incident coronary heart disease: the Atherosclerosis Risk in Communities (ARIC) study. 

Environ Health Perspect 116: 1463-1468. doi:10.1289/ehp.11290. Available at http://dx.doi.org

176 McConnell, R.; Islam, T.; Shankardass, K.; et al. (2010). Childhood incident asthma and trafficrelated air pollution at home and school. Environ Health Perspect 1021-1026.

177 Islam, T.; Urban, R.; Gauderman, W.J.; et al. (2011). Parental stress increases the detrimental 

effect of traffic exposure on children’s lung function. Am J Respir Crit Care Med (In press) 

178 Clougherty, J.E.; Levy, J.I.; Kubzansky, L.D.; et al. (2007). Synergistic effects of traffic-related 

air pollution and exposure to violence on urban asthma etiology. Environ Health Perspect 115: 

1140-1146.

179 Chen, E.; Schrier, H.M.; Strunk, R.C.; et al. (2008). Chronic traffic-related air pollution and stress 

interact to predict biologic and clinical outcomes in asthma. Environ Health Perspect 116: 970-5.

180 Rowangould, G.M. (2013) A census of the US near-roadway population: public health and 

environmental justice considerations. Transportation Research Part D 25: 59-67.

181 Boehmer, T.K.; Foster, S.L.; Henry, J.R.; Woghiren-Akinnifesi, E.L.; Yip, F.Y. (2013) 

Residential proximity to major highways – United States, 2010. Morbidity and Mortality Weekly 

Report 62(3);46-50.
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spend more than an hour traveling each day, bringing nearly all residents into a 

high-exposure microenvironment for part of the day.

In light of these concerns, EPA has required and is working with states to 

ensure that air quality monitors be placed near high-traffic roadways for 

determining NAAQS compliance for CO, NO2, and PM2.5 (in addition to those 

existing monitors located in neighborhoods and other locations farther away from 

pollution sources). Near-roadway monitors for NO2 begin operation between 2014 

and 2017 in Core Based Statistical Areas (CBSAs) with population of at least 

500,000. Monitors for CO and PM2.5 begin operation between 2015 and 2017. 

These monitors will further our understanding of exposure in these locations.

EPA continues to research near-road air quality, including the types of 

pollutants found in high concentrations near major roads and health problems 

associated with the mixture of pollutants near roads. 

7. Environmental Impacts of Motor Vehicles and Fuels

a. Plant and Ecosystem Effects of Ozone

The welfare effects of ozone can be observed across a variety of scales, i.e. 

subcellular, cellular, leaf, whole plant, population and ecosystem. Ozone effects 

that begin at small spatial scales, such as the leaf of an individual plant, when they

occur at sufficient magnitudes (or to a sufficient degree) can result in effects being 

propagated along a continuum to larger and larger spatial scales. For example, 

effects at the individual plant level, such as altered rates of leaf gas exchange, 

growth and reproduction can, when widespread, result in broad changes in 

ecosystems, such as productivity, carbon storage, water cycling, nutrient cycling, 

and community composition.

Ozone can produce both acute and chronic injury in sensitive species 

depending on the concentration level and the duration of the exposure.182 In those 

sensitive species, ozone effects also tend to accumulate over the growing season of 

 

182 Only a small percentage of all the plant species growing within the U.S. (over 43,000 species 

have been catalogued in the USDA PLANTS database) have been studied with respect to ozone

sensitivity (U.S. EPA. Review of the National Ambient Air Quality Standards for Ozone: Policy 

Assessment of Scientific and Technical Information. OAQPS Staff Paper. U.S. Environmental 

Protection Agency, Washington, DC, EPA-452/R-07-007, 2007. p.7-7). Thus, ozone impacts could 

be occurring in areas where plant species sensitive to ozone have not yet been studied or identified.

In addition, the concentration at which ozone levels overwhelm a plant’s ability to detoxify or 

compensate for oxidant exposure varies (U.S. EPA. Welfare Risk and Exposure Assessment for 

Ozone. Second External Review Draft. EPA-452/P-14-003a, 2014. Figure 6-2, p. 6-5). Thus, 

whether a plant is classified as sensitive or tolerant depends in part on the exposure levels being 

considered.
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the plant, so that even low concentrations experienced for a longer duration have 

the potential to create chronic stress on vegetation. Ozone damage to sensitive 

species includes visible injury to leaves and impaired photosynthesis, both of which 

can lead to reduced plant growth and reproduction, resulting in reduced crop yields, 

forestry production, and use of sensitive ornamentals in landscaping. In addition, 

the impairment of photosynthesis, the process by which the plant makes 

carbohydrates (its source of energy and food), can lead to a subsequent reduction in 

root growth and carbohydrate storage below ground, resulting in other, more subtle 

plant and ecosystems impacts. These latter impacts include increased susceptibility

of plants to insect attack, disease, harsh weather, interspecies competition and 

overall decreased plant vigor. The adverse effects of ozone on areas with sensitive 

species could potentially lead to species shifts and loss from the affected 

ecosystems, resulting in a loss or reduction in associated ecosystem goods and 

services. Lastly, visible ozone injury to leaves can result in a loss of aesthetic value 

in areas of special scenic significance like national parks and wilderness areas. 

The Integrated Science Assessment (ISA) for Ozone presents more detailed 

information on how ozone effects vegetation and ecosystems.183 The ISA 

concludes that ambient concentrations of ozone are associated with a number of 

adverse welfare effects and characterizes the weight of evidence for different effects 

associated with ozone.184 The ISA concludes that visible foliar injury effects on 

vegetation, reduced vegetation growth, reduced productivity in terrestrial 

ecosystems, reduced yield and quality of agricultural crops, and alteration of belowground biogeochemical cycles are causally associated with exposure to ozone. It 

also concludes that reduced carbon sequestration in terrestrial ecosystems, alteration 

of terrestrial ecosystem water cycling, and alteration of terrestrial community

composition are likely to be causally associated with exposure to ozone. 

b. Visibility

Visibility can be defined as the degree to which the atmosphere is 

transparent to visible light.185 Visibility impairment is caused by light scattering 

 

183 U.S. EPA. Integrated Science Assessment of Ozone and Related Photochemical Oxidants (Final 

Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-10/076F, 2013. The 

ISA is available at http://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=247492#Download

184 The Ozone ISA evaluates the evidence associated with different ozone related health and welfare

effects, assigning one of five “weight of evidence” determinations: causal relationship, likely to be a 

causal relationship, suggestive of a causal relationship, inadequate to infer a causal relationship, and 

not likely to be a causal relationship. For more information on these levels of evidence, please refer 

to Table II of the ISA. 

185 National Research Council, (1993). Protecting Visibility in National Parks and Wilderness 

Areas. National Academy of Sciences Committee on Haze in National Parks and Wilderness Areas. 
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and absorption by suspended particles and gases. Visibility is important because it 

has direct significance to people’s enjoyment of daily activities in all parts of the 

country. Individuals value good visibility for the well-being it provides them 

directly, where they live and work, and in places where they enjoy recreational 

opportunities. Visibility is also highly valued in significant natural areas, such as 

national parks and wilderness areas, and special emphasis is given to protecting 

visibility in these areas. For more information on visibility see the final 2009 PM 

ISA.186

EPA is working to address visibility impairment. In 1999, EPA finalized

the regional haze program to protect the visibility in Mandatory Class I Federal 

areas.187 There are 156 national parks, forests and wilderness areas categorized as 

Mandatory Class I Federal areas.188 These areas are defined in CAA section 162 as 

those national parks exceeding 6,000 acres, wilderness areas and memorial parks 

exceeding 5,000 acres, and all international parks which were in existence on 

August 7, 1977. EPA has also concluded that PM2.5 causes adverse effects on 

visibility in other areas that are not protected by the Regional Haze Rule, depending 

on PM2.5 concentrations and other factors that control their visibility impact 

effectiveness such as dry chemical composition and relative humidity (i.e., an 

indicator of the water composition of the particles). EPA revised the PM2.5

standards in December 2012 and established a target level of protection that is 

expected to be met through attainment of the existing secondary standards for 

PM2.5. 

 

National Academy Press, Washington, DC. This book can be viewed on the National Academy 

Press Website at http://www.nap.edu/books/0309048443/html/

186 U.S. EPA. (2009). Integrated Science Assessment for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, Washington, DC, EPA/600/R-08/139F. 

187 64 FR 35714 (July 1, 1999). 

188 62 FR 38680-38681 (July 18, 1997).
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i. Current Visibility Levels

As mentioned in Section II.B.2.c, millions of people live in nonattainment 

areas for the PM2.5 NAAQS. These populations, as well as large numbers of 

individuals who travel to these areas, are likely to experience visibility impairment. 

In addition, while visibility trends have improved in mandatory class I federal areas, 

the most recent data show that these areas continue to suffer from visibility 

impairment. In summary, visibility impairment is experienced throughout the U.S., 

in multi-state regions, urban areas, and remote mandatory class I federal areas.

c. Atmospheric Deposition

Wet and dry deposition of ambient particulate matter delivers a complex 

mixture of metals (e.g., mercury, zinc, lead, nickel, aluminum, cadmium), organic 

compounds (e.g., polycyclic organic matter, dioxins, furans) and inorganic 

compounds (e.g., nitrate, sulfate) to terrestrial and aquatic ecosystems. The 

chemical form of the compounds deposited depends on a variety of factors 

including ambient conditions (e.g., temperature, humidity, oxidant levels) and the 

sources of the material. Chemical and physical transformations of the compounds 

occur in the atmosphere as well as the media onto which they deposit. These 

transformations in turn influence the fate, bioavailability and potential toxicity of 

these compounds. Atmospheric deposition has been identified as a key component 

of the environmental and human health hazard posed by several pollutants including 

mercury, dioxin and PCBs.189

Adverse impacts on water quality can occur when atmospheric contaminants 

deposit to the water surface or when material deposited on the land enters a 

waterbody through runoff. Potential impacts of atmospheric deposition to 

waterbodies include those related to both nutrient and toxic inputs. Adverse effects 

to human health and welfare can occur from the addition of excess nitrogen via 

atmospheric deposition. The nitrogen-nutrient enrichment contributes to toxic algae 

blooms and zones of depleted oxygen, which can lead to fish kills, frequently in 

coastal waters. Deposition of heavy metals or other toxics may lead to the human 

ingestion of contaminated fish, impairment of drinking water, damage to freshwater 

and marine ecosystem components, and limits to recreational uses. Several studies 

have been conducted in U.S. coastal waters and in the Great Lakes Region in which 

the role of ambient PM deposition and runoff is investigated.190,191,192,193,194 

 

189 U.S. EPA. (2000). Deposition of Air Pollutants to the Great Waters: Third Report to Congress. 

Office of Air Quality Planning and Standards. EPA-453/R-00-0005. 

190 U.S. EPA. (2004). National Coastal Condition Report II. Office of Research and Development/ 

Office of Water. EPA-620/R-03/002. 
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Atmospheric deposition of nitrogen and sulfur contributes to acidification, 

altering biogeochemistry and affecting animal and plant life in terrestrial and 

aquatic ecosystems across the United States. The sensitivity of terrestrial and 

aquatic ecosystems to acidification from nitrogen and sulfur deposition is 

predominantly governed by geology. Prolonged exposure to excess nitrogen and 

sulfur deposition in sensitive areas acidifies lakes, rivers and soils. Increased 

acidity in surface waters creates inhospitable conditions for biota and affects the 

abundance and nutritional value of preferred prey species, threatening biodiversity

and ecosystem function. Over time, acidifying deposition also removes essential 

nutrients from forest soils, depleting the capacity of soils to neutralize future acid 

loadings and negatively affecting forest sustainability. Major effects include a 

decline in sensitive forest tree species, such as red spruce (Picea rubens) and sugar 

maple (Acer saccharum), and a loss of biodiversity of fishes, zooplankton, and 

macro invertebrates.

In addition to the role nitrogen deposition plays in acidification, nitrogen 

deposition also leads to nutrient enrichment and altered biogeochemical cycling. In 

aquatic systems increased nitrogen can alter species assemblages and cause 

eutrophication. In terrestrial systems nitrogen loading can lead to loss of nitrogen 

sensitive lichen species, decreased biodiversity of grasslands, meadows and other 

sensitive habitats, and increased potential for invasive species. For a broader 

explanation of the topics treated here, refer to the description in Section 6.3.2 of the 

RIA.

Adverse impacts on soil chemistry and plant life have been observed for 

areas heavily influenced by atmospheric deposition of nutrients, metals and acid 

species, resulting in species shifts, loss of biodiversity, forest decline, damage to 

forest productivity and reductions in ecosystem services. Potential impacts also 

include adverse effects to human health through ingestion of contaminated 

vegetation or livestock (as in the case for dioxin deposition), reduction in crop 

yield, and limited use of land due to contamination. 

 

191 Gao, Y., E.D. Nelson, M.P. Field, et al. (2002). Characterization of atmospheric trace elements 

on PM2.5 particulate matter over the New York-New Jersey harbor estuary. Atmos. Environ. 36: 

1077-1086. 

192 Kim, G., N. Hussain, J.R. Scudlark, and T.M. Church. (2000). Factors influencing the 

atmospheric depositional fluxes of stable Pb, 210Pb, and 7Be into Chesapeake Bay. J. Atmos. 

Chem. 36: 65-79. 

193 Lu, R., R.P. Turco, K. Stolzenbach, et al. (2003). Dry deposition of airborne trace metals on the 

Los Angeles Basin and adjacent coastal waters. J. Geophys. Res. 108(D2, 4074): AAC 11-1 to 11-

24. 

194 Marvin, C.H., M.N. Charlton, E.J. Reiner, et al. (2002). Surficial sediment contamination in 

Lakes Erie and Ontario: A comparative analysis. J. Great Lakes Res. 28(3): 437-450. 
Page 67 of 88

Atmospheric deposition of pollutants can reduce the aesthetic appeal of 

buildings and culturally important articles through soiling, and can contribute 

directly (or in conjunction with other pollutants) to structural damage by means of 

corrosion or erosion. Atmospheric deposition may affect materials principally by

promoting and accelerating the corrosion of metals, by degrading paints, and by

deteriorating building materials such as concrete and limestone. Particles contribute 

to these effects because of their electrolytic, hygroscopic, and acidic properties, and 

their ability to adsorb corrosive gases (principally sulfur dioxide). 

i. Current Nitrogen and Sulfur Deposition

Over the past two decades, the EPA has undertaken numerous efforts to 

reduce nitrogen and sulfur deposition across the U.S. Analyses of long-term 

monitoring data for the U.S. show that deposition of both nitrogen and sulfur 

compounds has decreased over the last 19 years.195 The data show that reductions 

were more substantial for sulfur compounds than for nitrogen compounds. In the 

eastern U.S., where data are most abundant, total sulfur deposition decreased by

about 44 percent between 1990 and 2007, while total nitrogen deposition decreased 

by 25 percent over the same time frame.196 These numbers are generated by the 

U.S. national monitoring network and they likely underestimate nitrogen deposition 

because neither ammonia nor organic nitrogen is measured. Although total nitrogen 

and sulfur deposition has decreased over time, many areas continue to be negatively 

impacted by deposition. Deposition of inorganic nitrogen and sulfur species 

routinely measured in the U.S. between 2005 and 2007 were as high as 9.6 

kilograms of nitrogen per hectare (kg N/ha) averaged over three years and 20.8 

kilograms of sulfur per hectare (kg S/ha) averaged over three years.197

d. Environmental Effects of Air Toxics

Emissions from producing, transporting and combusting fuel contribute to 

ambient levels of pollutants that contribute to adverse effects on vegetation. 

Volatile organic compounds, some of which are considered air toxics, have long 

 

195 U.S. EPA. (2013). U.S. EPA’s Report on the Environment. Data accessed online November 25, 

2013 at: 

http://cfpub.epa.gov/eroe/index.cfm?fuseaction=detail.viewInd&lv=list.listBySubTopic&r=216610

&subtop=341&ch=46. 

196 U.S. EPA. (2012). U.S. EPA’s Report on the Environment. Data accessed online February 15, 

2012 at: 

http://cfpub.epa.gov/eroe/index.cfm?fuseaction=detail.viewPDF&ch=46&lShowInd=0&subtop=341

&lv=list.listByChapter&r=216610. 

197 U.S. EPA. (2012). U.S. EPA's Report on the Environment. Data accessed online February 15, 

2012 at: 

http://cfpub.epa.gov/eroe/index.cfm?fuseaction=detail.viewPDF&ch=46&lShowInd=0&subtop=341

&lv=list.listByChapter&r=216610. 
Page 68 of 88

been suspected to play a role in vegetation damage.198 In laboratory experiments, a 

wide range of tolerance to VOCs has been observed.199 Decreases in harvested seed 

pod weight have been reported for the more sensitive plants, and some studies have 

reported effects on seed germination, flowering and fruit ripening. Effects of 

individual VOCs or their role in conjunction with other stressors (e.g., acidification, 

drought, temperature extremes) have not been well studied. In a recent study of a 

mixture of VOCs including ethanol and toluene on herbaceous plants, significant 

effects on seed production, leaf water content and photosynthetic efficiency were 

reported for some plant species.200

Research suggests an adverse impact of vehicle exhaust on plants, which has 

in some cases been attributed to aromatic compounds and in other cases to nitrogen 

oxides.201,202, 203

III. How Would This Rule Reduce Emissions and Air

Pollution?

A. Effects of the Vehicle and Fuel Changes on Mobile Source Emissions

The Tier 3 vehicle and fuel standards will significantly reduce the tailpipe 

and evaporative emissions of light- and heavy-duty vehicles in several ways, as 

described in this section. In addition, the gasoline sulfur standard will reduce 

emissions of SO2 from existing gasoline-powered vehicles and equipment. As 

described in Section II, all of these emission reductions will in turn improve air 

quality nationwide and reduce the health effects associated with air pollution from 

mobile sources.

As with the Tier 2 program, EPA is implementing closely-coordinated 

requirements for both automakers and refiners in the same rulemaking action. The 

Tier 3 vehicle emission standards and gasoline sulfur standards represent a “systems 

 

198 U.S. EPA. (1991). Effects of organic chemicals in the atmosphere on terrestrial plants. 

EPA/600/3-91/001. 

199 Cape JN, ID Leith, J Binnie, J Content, M Donkin, M Skewes, DN Price AR Brown, AD Sharpe. 

(2003). Effects of VOCs on herbaceous plants in an open-top chamber experiment. Environ. Pollut. 

124:341-343. 

200 Cape JN, ID Leith, J Binnie, J Content, M Donkin, M Skewes, DN Price AR Brown, AD Sharpe. 

(2003). Effects of VOCs on herbaceous plants in an open-top chamber experiment. Environ. Pollut. 

124:341-343. 

201 Viskari E-L. (2000). Epicuticular wax of Norway spruce needles as indicator of traffic pollutant 

deposition. Water, Air, and Soil Pollut. 121:327-337. 

202 Ugrekhelidze D, F Korte, G Kvesitadze. (1997). Uptake and transformation of benzene and 

toluene by plant leaves. Ecotox. Environ. Safety 37:24-29. 

203 Kammerbauer H, H Selinger, R Rommelt, A Ziegler-Jons, D Knoppik, B Hock. (1987). Toxic 

components of motor vehicle emissions for the spruce Picea abies. Environ. Pollut. 48:235-243. 
Page 69 of 88

approach” to reducing vehicle-related exhaust and evaporative emissions. By

recognizing the relationships among the various sources of emissions addressed by

this action, we have been able to integrate the provisions into a single, coordinated 

program. 

1. How Do Vehicles Produce the Emissions Addressed in this Action?

The degree to which vehicles produce exhaust and evaporative emissions 

depends on the design and functionality of the engine and the associated exhaust 

and evaporative emission controls, in concert with the properties of the fuel on 

which the vehicle is operating. In the following paragraphs, we discuss how lightand heavy-duty vehicles produce each of these types of emissions, both from the

tailpipe and from the fuel system. 

a. Tailpipe (Exhaust) Emissions

The pollutants emitted at the vehicle’s tailpipe and their quantities depend 

on how the fuel is combusted in the engine and how the resulting gases are treated 

in the exhaust system. Historically, much of tailpipe emission control has focused 

on hydrocarbon compounds (HC) and NOX. The portion of hydrocarbons that is 

methane is minimally reactive in forming ozone. Thus, for emission control 

purposes, the focus is generally on non-methane hydrocarbons (NMHC), which are 

also expressed as non-methane organic gases (NMOG) in order to account for 

oxygenates (usually ethanol) now usually present in the fuel. 

Tailpipe hydrocarbon emissions also include several toxic pollutants, 

including benzene, acetaldehyde, and formaldehyde. To varying degrees, the mass 

emissions of these pollutants are reduced along with other hydrocarbons by the 

catalytic converter and improved engine controls. 

Light- and heavy-duty gasoline vehicles also emit PM and CO. PM forms 

directly as a combustion product (as elemental carbon or soot) and indirectly as 

semi-volatile hydrocarbon compounds that form particles in the exhaust system or 

soon after exiting the tailpipe. CO is a product of incomplete fuel combustion.

When operating properly, modern exhaust emission controls (centering on 

the catalytic convertor) can reduce much of the HC (including toxics), NOX and CO 

exiting the engine. However, tailpipe emissions are increased during periods of 

vehicle startup, as catalytic convertors must warm up to be effective; during 

subsequent operation due to the interference of sulfur in the gasoline; during high 

load operating events, as the catalyst is overwhelmed or its operation is modified to 

protect against permanent damage; and as a vehicle ages, as the catalyst degrades in 

performance due to the effects of high temperature operation and contaminants in 

the fuel and lubricating oil. 
Page 70 of 88

b. Evaporative Emissions

Gasoline vehicles also produce vapors in the fuel tank and fuel system that 

can be released as evaporative emissions. These vapors are primarily the lighter, 

more volatile hydrocarbon compounds in gasoline. As discussed in Section IV 

below, vehicle evaporative (“evap”) control systems are designed to block or 

capture vapors as they are generated. Vapors are generated in the vehicle fuel tank 

and fuel system (and released to the atmosphere if not adequately controlled) as fuel 

heats up due to ambient temperature increase and/or vehicle operation. Fuel vapors 

are also released when they permeate through elastomers in the fuel system, when 

they leak at connections or due to damaged components, and during refueling 

events. 

In general, the evap emission controls on current vehicles (and that will be 

improved under this action) consist of a canister filled with activated charcoal and 

connected by hoses to the fuel system. The hoses direct generated vapors to the 

canister, which collects the vapors on the carbon and stores them until the system 

experiences a “purge” event. During purge, the engine draws fresh air through the 

canister, carrying vapors released by the carbon to the engine to be combusted and 

restoring the capacity of the canister. Evaporative emissions occur when vapors are 

emitted to the atmosphere because the evap system is compromised, the carbon 

canister is overwhelmed, or vapors permeate or leak. As such, evaporative 

emission controls also involve proper material selection for fuel system 

components, careful design of these components, and onboard diagnostics to check 

the system for failure. 

2. How Will the Changes to Gasoline Sulfur Content Affect Vehicle 

Emissions?

Gasoline vehicles rely on highly efficient aftertreatment catalysts to control 

tailpipe emissions of harmful pollutants like CO and NOX, as well as VOCs that 

include air toxics and precursor compounds to ozone and secondary PM in the 

atmosphere. These catalysts utilize finely-dispersed precious metals that are 

susceptible to deactivation by sulfur compounds in the exhaust. Studies have 

repeatedly demonstrated that the presence of even a tiny amount of sulfur in fuel 

has a measurable impact on the ability of the catalyst to control emissions, and that 

emission levels of most pollutants, especially NOx, are very sensitive to fuel 

sulfur.204,205 

 

204 The Effects of Ultra-Low Sulfur Gasoline on Emissions from Tier 2 Vehicles in the In-Use Fleet, 

EPA-420-R-14-002.
Page 71 of 88

Sulfur naturally occurs in crude oil and is carried through the refining 

process into gasoline. EPA’s Tier 2 rulemaking for light-duty vehicles, published 

in 2000, required refiners to reduce sulfur levels in gasoline to an average of 30 

ppm, a reduction of about 90 percent from the in-use baseline. At the time, there 

were indications that sulfur reductions below 30 ppm may provide additional 

emission benefits. However, the data was insufficient to quantify the benefits to the

existing fleet, and the Tier 2 vehicle standards could be achieved without lowering 

sulfur below 30 ppm.

206

As discussed in Section IV.A.6, subsequent research provides a compelling

case that even this level of sulfur degrades the emission performance of vehicles on 

the road today and inhibits necessary further reductions in vehicle emissions 

performance, which depend on optimum catalyst performance to reach emission 

targets. A study conducted by EPA and the auto industry in support of the Mobile 

Source Air Toxics (MSAT) rule found significant reductions in NOX, CO and total 

HC when nine Tier 2 vehicles were tested on ultra-low sulfur fuel.207 In particular, 

the study found a 32 percent decrease in NOX when sulfur was reduced from 32

ppm to 6 ppm (equivalent to a 25% decrease if sulfur levels were reduced from 30 

to 10 ppm, assuming a linear effect). Another recent study by Umicore showed 

reductions of 41 percent for NOX and 17 percent for hydrocarbons on a PZEV 

operating on fuel with 33 ppm and 3 ppm fuel (equivalent to reductions of 27% and 

11%, respectively, if sulfur levels were reduced from 30 to 10 ppm, assuming a 

linear effect).208 

A larger study of Tier 2 vehicles recently completed by EPA confirmed 

these results, showing significant reductions in FTP-composite NOX (14 percent), 

CO (10 percent) and total HC (15 percent) on the 5 ppm fuel, relative to 28 ppm 

fuel (equivalent to 12%, 9%, and 13% reduction, respectively, if sulfur levels were 

reduced from 30 to 10 ppm, assuming a linear effect).

209

 For NOX, the majority of 

overall reductions were driven by large reductions on warmed-up periods of the test 

cycle (Bag 2), which showed a 52% reduction using 5 ppm fuel relative to 28 ppm 

fuel (equivalent to 45% reduction if sulfur levels were reduced from 30 to 10 ppm, 

assuming a linear effect), consistent with the role of sulfur in catalyst degradation 

 

205 Durbin, T., “The Effect of Fuel Sulfur on NH3 and Other Emissions from 2000-2001 Model Year 

Vehicles”, May 2003. Published as Report E-60 by the Coordinating Research Council, Alpharetta, 

GA.

206 65 FR 6698 (February 10, 2000)

207 Regulatory Impact Analysis for the Control of Hazardous Air Pollutants from Mobile Sources 

Final Rule, EPA 420-R-07-002, Chapter 6

208 Ball D., Clark D., Moser D. (2011), Effects of Fuel Sulfur on FTP NOx Emissions from a PZEV 

4 Cylinder Application. SAE 2011 World Congress Paper 2011-01-0300

209 The Effects of Ultra-Low Sulfur Gasoline on Emissions from Tier 2 Vehicles in the In-Use Fleet, 

EPA-420-R-14-002. 
Page 72 of 88

discussed above. For additional details regarding these results, please see Section 

IV.A.6.c.

Our application of these study results assumes a linear effect of sulfur level 

on catalyst efficiency between the high and low sulfur test fuels. This is reasonable 

given that the mass flow rate of sulfur in exhaust gas changes in proportion to its 

concentration in the fuel, and that the chemical kinetics of adsorption of sulfur to 

the precious metal sites is approximately first order. Linearity of effect is also 

supported by past studies with multiple fuel sulfur levels such as the CRC E-60 and 

2000 AAM/AIAM/Oil Industry emission test programs.

210,211

Based on these analyses, the benefits of the Tier 3 sulfur standard are 

significant in two ways: they enable vehicles designed to the Tier 3 tailpipe exhaust 

standards to meet these standards for the duration of their useful life, and they 

facilitate immediate emission reductions from all the vehicles on the road at the 

time the sulfur controls are implemented. 

B. How Will Emissions Be Reduced?

The Tier 3 standards will reduce emissions of VOC, NOX (including NO2), 

direct PM2.5, CO, SO2, and air toxics. The sulfur standards will reduce emissions 

from the on-road fleet immediately upon implementation in calendar year 2017. 

The vehicle standards will begin to reduce emissions as the cleaner cars and trucks 

begin to enter the fleet in model year 2017 and model year 2018, respectively. The 

magnitude of reduction will grow as more Tier 3 vehicles enter the fleet. We

present emission reductions in calendar year 2018 to reflect the early reductions 

expected from the Tier 3 standards, and in calendar year 2030, when 70 percent of 

the miles travelled are from vehicles that meet the fully phased-in Tier 3 standards. 

Although 2030 is the farthest year that is feasible for air quality modeling, the full 

reduction of the vehicle program will be realized after 2030, when the fleet has fully

turned over to vehicles that meet the fully phased-in Tier 3 standards; thus we 

present emission reductions projected in 2050 as well (see Chapter 7 of the RIA). 

Emission reductions are estimated on an annual basis, for all 50 U.S. states 

plus the District of Columbia, Puerto Rico and the U.S. Virgin Islands. The 

reductions were estimated using a version of EPA’s MOVES model updated for this 

analysis, as described in detail in Chapter 7 of the RIA. This version of MOVES 

includes our most recent data on how vehicle emissions are affected by changes in 

 

210 Durbin, T., “The Effect of Fuel Sulfur on NH3 and Other Emissions from 2000-2001 Model Year 

Vehicles”, May 2003. Published as Report E-60 by the Coordinating Research Council, Alpharetta, 

GA.

211 “AAM/AIAM/Oil Industry Low Sulfur & Oxygenate Test Program”, 2000, last accessed on 

01/15/14 at the following URL: http://www.arb.ca.gov/fuels/gasoline/carfg3/aam_prstn.pdf.
Page 73 of 88

sulfur, ethanol, RVP, and other fuel properties. We estimated emission reductions 

compared to a reference case that assumed renewable fuel volumes and ethanol 

blends based on the U.S. Energy Information Administration’s Annual Energy

Outlook 2013 (AEO2013).212 As described in Chapter 7 of the RIA, the reference 

and control scenarios based on AEO2013 reflect a mix of E10, E15, and E85 in

both 2018 and 2030. The reference case assumed an average sulfur level of 30 ppm 

(10 ppm in California) and continuation of the Tier 2 vehicle program indefinitely, 

with the exception of California and Section 177 states that have adopted the LEV 

III program.

The analysis described here accounts for the following national onroad 

rules:

 Tier 2 Motor Vehicle Emissions Standards and Gasoline Sulfur 

Control Requirements (65 FR 6698, February 10, 2000)

 Heavy-Duty Engine and Vehicle Standards and Highway Diesel Fuel 

Sulfur Control Requirements (66 FR 5002, January 18, 2001)

 Mobile Source Air Toxics Rule (72 FR 8428, February 26, 2007)

 Regulation of Fuels and Fuel Additives: Changes to Renewable Fuel 

Standard Program (75 FR 14670, March 26, 2010)

 Light-Duty Vehicle Greenhouse Gas Emission Standards and 

Corporate Average Fuel Economy Standards for 2012-2016 (75 FR 

25324, May 7, 2010)

 Greenhouse Gas Emissions Standards and Fuel Efficiency Standards 

for Medium- and Heavy-Duty Engines and Vehicles (76 FR 57106, 

September 15, 2011)

 2017 and Later Model Year Light-Duty Vehicle Greenhouse Gas 

Emissions and Corporate Average Fuel Economy Standards (77 FR 

62623, October 15, 2012)

The analysis also accounts for many other national rules and standards. In addition, 

the modeling accounts for state and local rules including California’s most recent 

Low Emission Vehicle (LEV III) program adopted in California and twelve other 

states (also referred to as Section 177 states),213 local fuel standards, 

 

212 U.S. Energy Information Administration, Annual Energy Outlook (April 15, 2013)

213 These states include Connecticut, Delaware, Maryland, Maine, Massachusetts, New Jersey, New 

York, Oregon, Pennsylvania, Rhode Island, Washington, and Vermont.
Page 74 of 88

Inspection/Maintenance programs, Stage II refueling controls, the National Low 

Emission Vehicle Program (NLEV), and the Section 177 states LEV and LEV II 

programs. See the Tier 3 emissions modeling TSD for more detail.

A summary of emission reductions projected to result from Tier 3, relative 

to the reference case, is shown in calendar years 2018 and 2030 for NOX, VOC, 

direct PM2.5, CO, SO2, and total air toxics in Table III-1. For many pollutants, the 

immediate reductions in 2018 are significant; for example, combined NOX and 

VOC emissions will be reduced by over 300,000 tons. By 2030, combined NOX

and VOC emissions will be reduced by roughly 500,000 tons, one quarter of the 

onroad inventory. Many of the modeled air toxics will be significantly reduced as 

well, including benzene, 1,3-butadiene, acetaldehyde, acrolein and ethanol (ranging 

from 10 to nearly 30 percent of the national onroad inventory by 2030). The 

relative reduction in overall emissions will continue to increase beyond 2030 as 

more of the fleet continues to turn over to Tier 3 vehicles; for example, by 2050, 

when nearly all of the fleet will have turned over to vehicles meeting the fully

phased-in Tier 3 standards, we estimate the Tier 3 program will reduce onroad 

emissions of NOX and VOC nearly 31 percent from the level of emissions projected 

without Tier 3 controls. 

Table III-1 Estimated Emission Reductions from the Tier 3 Standards 

(Annual U.S. short tons)

2018 2030

Tons % of 

Onroad 

Inventory

Tons % of 

Onroad 

Inventory

NOX 264,369 10% 328,509 25%

VOC 47,504 3% 167,591 16%

CO 278,879 2% 3,458,041 24%

Direct PM2.5 130 0.1% 7,892 10%

Benzene 1,916 6% 4,762 26%

SO2 14,813 56% 12,399 56%

1,3-Butadiene 257 5% 677 29%

Formaldehyde 513 2% 1,277 10%

Acetaldehyde 600 3% 2,067 21%

Acrolein 40 3% 127 15%

Ethanol 2,704 2% 19,950 16%

 
Page 75 of 88

Reductions for each pollutant are discussed in the following sections, 

focusing on the contribution of program elements to the total reductions 

summarized above. 

1. NOX

The Tier 3 sulfur standards will significantly reduce NOX emissions 

immediately upon implementation of the program. As discussed above, recent 

research on the impact of sulfur on Tier 2 technology vehicles shows the potential 

for significant reductions in NOX emissions from the existing fleet of Tier 2 

vehicles by lowering sulfur levels to 10 ppm. Prior research shows that NOX

emissions will also be expected to decrease from the fleet of older (pre-Tier 2) 

light-duty vehicles as well as heavy-duty gasoline vehicles,214 although to a lesser 

extent than for Tier 2 vehicles. 

Table III-2 shows the reduction in NOX emissions, in annual short tons, 

projected in calendar years 2018 and 2030. The reductions are split into those 

attributable to the introduction of low sulfur fuel in the pre-Tier 3 fleet (defined for 

this analysis as model years prior to 2017); and reductions attributable to vehicle 

standards enabled by low sulfur fuel (model year 2017 and later). As shown, upon 

implementation of the Tier 3 sulfur standards, total onroad NOX emissions are 

projected to drop 10 percent. This is primarily due to large reductions from Tier 2 

gasoline vehicles, which contribute about one-quarter of the NOX emissions from 

the on-road fleet in 2018. The relative reduction grows as cleaner vehicles turn 

over into the fleet. By 2030, we project that the reduction in overall onroad NOX

inventory will be 25 percent.

Table III-2 Projected NOX Reductions from Tier 3 Program (Annual U.S. 

Tons)

2018 2030

Total reduction 264,369 328,509

Reduction from pre-Tier 3 

fleet due to sulfur standard

242,434 56,324

Reduction from Tier 3 fleet 

due to vehicle and sulfur 

standards 

21,934 272,185

Percent reduction in 

onroad NOX emissions

10% 25%

 

214 Rao, V. (2001), Fuel Sulfur Effects on Exhaust Emissions: Recommendations for MOBILE6, 

EPA-420-R-01-039
Page 76 of 88

2. VOC

Table III-3 shows the reduction in VOC emissions, in annual short tons,

projected in calendar years 2018 and 2030 resulting from the Tier 3 standards. In 

2018, as with NOX, we project reductions from the pre-Tier 3 fleet with the fuel 

standards. By 2030, the reduction in overall onroad VOC emissions will be 16

percent, the majority of this from the vehicles meeting the fully phased-in Tier 3 

standards. The evaporative standards are projected to account for roughly one third

of the overall vehicle program reduction in 2030. 

Table III-3 Projected VOC Reductions from Tier 3 Program (Annual U.S. 

Tons)

2018 2030

Total reduction 47,504 167,591

Reduction from pre-Tier 3 

fleet due to sulfur standard

38,786 11,249

Reduction from Tier 3 

fleet due to vehicle and 

sulfur standards 

8,718 156,343

Exhaust 43,009 105,253

Evaporative 4,495 62,339

Percent reduction in 

onroad VOC emissions

3% 16%

3. CO

Table III-4 shows the reductions for CO, broken down by pre- and post-Tier 

3 in the manner described for NOX and VOC above. In contrast to NOx and VOC,

the immediate CO reductions in the onroad fleet from sulfur control in 2018 are 

small, based on research showing that fuel sulfur level has a minimal impact on CO 

emissions from Tier 2 vehicles. The CO exhaust standards are projected to reduce 

onroad CO emissions by 24 percent in 2030. 

Table III-4 Projected CO Reductions from Tier 3 Program (Annual U.S. Tons)

2018 2030

Total reduction 278,879 3,458,041

Reduction from pre-Tier 3 

fleet due to sulfur 

standard

122,171 17,734

Reduction from Tier 3 

fleet due to vehicle and 

sulfur standards

156,708 3,440,307

Percent reduction in 

onroad CO emissions

2% 24%
Page 77 of 88

4. Direct PM2.5

Reductions in direct emissions of PM2.5 are projected to result solely from 

the vehicle tailpipe standards, so meaningful reductions are realized mainly as the 

fleet turns over. By 2030, we project a reduction of about 7,900 tons annually, 

which represents approximately 10 percent of the onroad direct PM2.5 inventory. 

The relative reduction in onroad emissions is projected to grow to 28 percent in 

2050, when nearly all of the fleet will have turned over to vehicles meeting the fully 

phased-in Tier 3 standards. Reductions in NOX and VOC emissions will also 

reduce secondary PM formation, which is quantified as part of the air quality

analysis described in Section III.C. 

5. Air Toxics

Emissions of air toxics also will be reduced by the sulfur, exhaust and 

evaporative standards. Air toxics are generally a subset of compounds making up 

VOC, so the reduction trends tend to track the VOC reductions presented above, for 

most air toxics. Table III-5 presents reductions for certain key air toxics, and Table 

III-6 presents reductions for the sum of 71 different toxic compounds. 

Table III-5 Reductions for Certain Individual Compounds (Annual U.S. Tons)

Tons 

Reduced in 

2018

% Reduction

in Onroad 

Emissions

Tons Reduced 

in 2030

% Reduction in 

Onroad 

Emissions

Benzene 1,916 6% 4,762 26%

Acetaldehyde 600 3% 2,067 21%

Formaldehyde 513 2% 1,277 10%

1,3-Butadiene 257 5% 677 29%

Acrolein 40 3% 127 15%

Naphthalene 99 3% 269 15%

Ethanol 2,704 2% 19,950 16%

The totals shown in Table III-6 represent the sum of 71 species including the 

toxics in Table III-5, 15 polycyclic aromatic hydrocarbon (PAH) compounds in gas 

and particle phase, and additional gaseous compounds such as toluene, xylenes, 

styrene, hexane, 2,2,4-trimethylpentane, n-hexane, and propionaldehyde (see 

Appendix 7A of the RIA). As shown, in 2030, the overall onroad inventory of total 

toxics will be reduced by 15 percent, with nearly one half of the vehicle program 

reductions coming from the evaporative standards. 

Table III-6 Reductions in Total Mobile Source Air Toxics (Annual U.S. Tons)

2018 2030
Page 78 of 88

Total reduction 15,583 64,558

Reduction from pre-Tier 3 

fleet due to sulfur standard

11,981 3,517

Reduction from Tier 3 

fleet due to vehicle and 

sulfur standards

3,602 61,041

Exhaust 13,340 34,595

Evaporative 2,243 29,963

Percent reduction in 

onroad toxics emissions

3% 15%

6. SO2

SO2 emissions from mobile sources are a direct function of sulfur in the 

fuel, and reducing sulfur in gasoline will result in immediate reductions in SO2 from 

the on and off-road fleet. The reductions, shown in Table III-7, are a function of the 

sulfur level and fuel consumption. This is reflected in the relative contribution of 

on-road vehicles and off-road equipment, where off-road gasoline consumption 

accounts for approximately 5 percent of overall gasoline use.215

Table III-7 Projected SO2 Reductions from Tier 3 Program (Annual U.S. Tons)

2018 2030

Total reduction 15,565 13,261

Reduction from onroad 

vehicles due to sulfur 

standard

14,813 12,399

Reduction from off-road 

equipment due to sulfur 

standard

752 862

Percent reduction in 

onroad SO2 emissions

56% 56%

7. Greenhouse Gases

Reductions in nitrous oxide (N2O) emissions and methane (CH4) emissions, 

both potent greenhouse gas emissions, are projected for gasoline cars and trucks as 

a result of the sulfur and tailpipe standards. A study conducted by the University

of California-Riverside found a 29 percent reduction in N2O emissions over the 

FTP when sulfur was reduced from 30 to 5 ppm,216 while EPA research described in 

 

215 U.S. Energy Information Administration, Annual Energy Outlook 2013 (April 15, 2013)

216 Huai, et al. (2004), Estimates of the emission rates of nitrous oxide from light-duty vehicles using 

different chassis dynamometer test cycles, Atmospheric Environment 6621-6629 
Page 79 of 88

Section IV.A.6 on sulfur effects found a 26 percent reduction in CH4 emissions 

when sulfur was reduced from 28 to 5 ppm.

217

 

Several studies have established correlations between reductions in tailpipe 

NOX emissions and reductions in N2O from gasoline cars and trucks,218,219,220,221 as 

well as correlations between reductions in tailpipe HC emissions and reductions in 

CH4.

222,223 Studies by Winer, et al (2005) and Behrentz et al (2004) reported N2O: 

NOX ratios of 0.06 and 0.095, respectively, and supported the application of N2O: 

NOX ratios to NOX emissions as a reasonable method for estimating N2O emission 

inventories. CARB has also used N2O: NOX ratio to develop the N2O emissions 

inventories for the LEV III program, based on a regression analysis suggesting 

N2O: NOX ratio of 0.04, on average.224 

As detailed in Chapter 7.3 of the RIA, the N2O reductions are estimated by 

employing two different methodologies, resulting in a range of reductions. The first 

method applies the relationship between N2O and NOX from a regression model225

to NOX inventories from both Tier 3 and pre-Tier 3 vehicles. The second method 

applies the regression of N2O and NOX only to Tier 3 vehicles and uses the UC 

Riverside sulfur results to estimate the N2O reductions from pre-Tier 3 vehicles. 

Using a 100-year global warming potential of 298 for N2O according to the 2007 

IPCC AR4,

226 the estimated N2O reduction is 2.2 million metric tons of carbon 

 

217 The Effects of Ultra-Low Sulfur Gasoline on Emissions from Tier 2 Vehicles in the In-Use Fleet, 

EPA-420-R-14-002,

218 Michaels, H. (1998) Emissions of Nitrous Oxide from Highway Mobile Sources, U.S. EPA 

EPA420-R-98-009 

219 Behrentz, et al. (2004), Measurements of nitrous oxide emissions from light-duty motor vehicles: 

a pilot study, Atmospheric Environment 4291-4303 

220 Meffert, et. al (2000) Analysis of Nitrous Oxide Emissions from Light Duty Passenger Cars, SAE 

2000-01-1952

221 Winer, et al. (2005) Estimates of Nitrous Oxide Emissions and the Effects of Catalyst 

Composition and Aging, State of California Air Resources Board 02-313

222 Meszler, D. (2004), Light Duty Vehicle Methane and Nitrous Oxide Emissions: Greenhouse Gas 

Impacts, Study for Northeast States Center for a Clean Air Future

223 Graham, L., Greenhouse Gas Emissions from 1997-2005 Model Year Light Duty Vehicles, 

Environment Canada ERMD Report #04-44 

224 LEV III Moblie Source Emissions Inventory Technical Support Document – Appendix T, 

January 2012, last accessed on 01/15/14 at the following URL: 

http://www.arb.ca.gov/regact/2012/leviiighg2012/levappt.pdf

225 U.S. EPA, 2014, Memorandum to Docket: Regression Analysis of Nitrous Oxide and Oxides of 

Nitrogen from Motor Vehicles.

226 The global warming potentials (GWP) used in this rule are consistent with the 100-year time 

frame values in the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment 

Report (AR4). At this time, the 1996 IPCC Second Assessment Report (SAR) 100-year GWP 

values are used in the official U.S. greenhouse gas inventory submission to the United Nations 

Framework Convention on Climate Change (per the reporting requirements under that international 
Page 80 of 88

dioxide equivalent (MMTCO2e) in 2018, growing to the range between 3.8 to 4.0 

MMTCO2e in 2030. For 2018, there was an agreement between the two 

methodologies described above, resulting in a single estimate. MOVES can be used 

to directly estimate CH4 reductions from the sulfur and vehicle standards, 

estimating an additional 0.1 MMTCO2e reduction in 2018, growing to 0.3

MMTCO2e in 2030. The total GHG reduction from the Tier 3 rule is 2.3

MMTCO2e in 2018, and between 4.1 and 4.3 MMTCO2e in 2030. 

These reductions will be partially offset by CO2 emissions associated with 

higher energy use required in the process of removing sulfur within the refinery. As 

an extension of our refinery-by-refinery cost modeling described in Section VII.B.,

we calculated the CO2 emission impacts of Tier 3 gasoline sulfur control. We 

estimated refinery-specific changes in process energy and then applied emission 

factors that correspond to those changes, on a refinery-by-refinery basis. As 

described in Chapter 4.5 of the RIA, the results showed an increase of up to 1.9

MMTCO2e in 2018 and 1.6 MMTCO2e in 2030 for all U.S. refineries complying 

with the lower sulfur standards assuming that the sulfur standards are fully phasedin. In 2018, the combined impact of CH4 and N2O emission reductions from the 

vehicles and CO2 emission increases from the refineries shows a slight net decrease 

on a CO2 equivalent basis. While still small, this net decrease grows to a range 

between 2.5 to 2.7 MMTCO2e by 2030.

We do not expect the Tier 3 vehicle standards to result in any discernible 

changes in vehicle CO2 emissions or fuel economy. Emissions of the pollutants that 

are controlled by the Tier 3 program – NMOG, NOX, and PM – are not a function 

of the amount of fuel consumed, since manufacturers need to design their catalytic 

emission control systems to reduce these emissions regardless of their engine-out 

levels. 

C. How Will Air Pollution Be Reduced? 

Reductions in emissions of NOX, VOC, PM2.5 and air toxics expected as a 

result of the Tier 3 standards are projected to lead to significant improvements in air 

quality. The air quality modeling predicts significant improvements in ozone 

concentrations due to the Tier 3 st`andards. Ambient PM2.5 and NO2 concentrations 

are also expected to improve as a result of the Tier 3 program. Decreases in 

ambient concentrations of air toxics are projected with the Tier 3 standards, 

including notable nationwide reductions in benzene concentrations. Our air quality

modeling also predicts improvements in visibility and sulfur deposition, as well as 

substantial decreases in nitrogen deposition as a result of the Tier 3 standards. The 

 

convention, which were last updated in 2006). N2O has a 100-year GWP of 298 and CH4 has a 100-

year GWP of 25 according to the 2007 IPCC AR4.
Page 81 of 88

results of our air quality modeling of the impacts of the Tier 3 rule are summarized 

in the following section. 

1. Ozone

The air quality modeling done for this action projects that in 2018, with all 

current and required controls in effect but excluding the emissions changes 

expected to occur as a result of the Tier 3 standards or any other additional controls, 

at least 19 counties, with a projected population of over 37 million people, would 

have projected design values above the level of the 2008 8-hour ozone standard of 

75 ppb. In 2030 the modeling projects that in the absence of Tier 3 standards or any

other additional controls there will be 6 counties with a population of over 19

million people with projected design values above the level of the 2008 8-hour 

ozone standard of 75 ppb. An additional 37 million people will be living in the 43 

counties that will be close to (within 10% of) the level of the ozone standard. 

Air quality modeling indicates that this action will meaningfully decrease 

ozone design value concentrations in many areas of the country, including those 

that are projected to be exceeding, or close to exceeding, the ozone standard. In

2018, the majority of the design value decreases are between 0.5 and 1.0 ppb. In 

2030, the Tier 3 rule will result in larger decreases in ozone design values, with the 

majority of counties projecting decreases of between 0.5 and 1.0 ppb, and over 250 

more counties with decreases greater than 1.0 ppb. Since the Tier 3 standards go 

into effect during the period when some areas are still working to attain the ozone 

NAAQS, the projected air quality changes will help state and local agencies in their 

effort to attain and maintain the ozone standard. 

2. Particulate Matter

The air quality modeling conducted for this action projects that in 2018, 

with all current controls in effect but excluding the emissions changes expected to 

occur as a result of Tier 3 standards or any other additional controls, at least 14

counties, with a projected population of over 20 million people, would have 

projected design values above the level of the annual standard of 12 μg/m3 and at 

least 24 counties, with a projected population of over 18 million people, would have 

projected design values above the level of the 24-hour standard of 35 μg/m3. In 

2030, the modeling projects that in the absence of Tier 3 standards or any other 

additional controls there will be 13 counties, with a projected population of over 21

million people, with projected design values above the level of the annual standard 

of 12 μg/m3 and 18 counties, with a projected population of over 12 million people,

with projected design values above the level of the 24-hour standard of 35 μg/m3.

Since the Tier 3 standards go into effect during the period when some areas are still 

working to attain the 2006 and 2012 PM2.5 NAAQS, the projected air quality
Page 82 of 88

changes will be useful to state and local agencies in their effort to attain and 

maintain the PM2.5 standards. 

The Tier 3 standards will reduce 24-hour and annual PM2.5 design values 

due to projected tailpipe reductions in primary PM2.5, SO2, NOX and VOCs from 

reductions in fuel sulfur and engine controls. In 2018 the standards will have a 

small impact on annual PM2.5 design values in the majority of modeled counties. 

However, in over 200 counties annual PM2.5 design values are projected to decrease 

by greater than 0.01 μg/m

3

. In 2030 annual PM2.5 design values in the majority of 

modeled counties will decrease by between 0.01 and 0.05 μg/m3 and in over 140 

additional counties design values are projected to decrease by greater than 0.05 

μg/m3. In addition, in 2018 24-hour PM2.5 design values in over 200 counties are 

projected to decrease by between 0.05 and 0.15 μg/m

3

and in 2030 24-hour PM2.5

design values in over 180 counties decrease by at least 0.15 μg/m3. 

3. Nitrogen Dioxide

Although our modeling indicates that by 2030 the majority of the country 

will experience decreases of less than 0.1 ppb in their annual NO2 concentrations 

due to this rule, annual NO2 concentrations are projected to decrease by more than 

0.3 ppb in most urban areas. These emissions reductions would also likely decrease 

1-hour NO2 concentrations and help any potential nonattainment areas to attain and 

maintain the standard. Additional information on the emissions reductions that are 

projected with this rule is available in Section 7.2.1 of the RIA. 

4. Air Toxics

Our modeling indicates that the impacts of final Tier 3 standards include 

notable nationwide reductions in benzene and generally small decreases in ambient 

concentrations of other air toxics, mainly in urban areas. Although reductions are 

greater in 2030 (when 70 percent of the miles travelled are from vehicles that meet 

the fully phased-in Tier 3 standards) than in 2017 (the first year of the final

program), our modeling projects there will be small immediate reductions in 

ambient concentrations of air toxics due to the Tier 3 sulfur controls. Furthermore, 

the full reduction of the vehicle program will be realized after 2030, when the fleet 

has fully turned over to vehicles meeting the fully phased-in Tier 3 standards. Air 

toxics pollutants dominated by primary emissions (or a decay product of a directly

emitted pollutant), such as benzene, are impacted more than air toxics that primarily

result from photochemical transformation. 

Specifically, in 2030, our modeling projects that the Tier 3 rule will

decrease ambient benzene concentrations across much of the country on the order 

of 1 to 5 percent, with reductions ranging from 10 to 25 percent in some urban 

areas. Our modeling also shows reductions of 1,3-butadiene and acrolein 

concentrations in 2030 ranging between 1 and 25 percent and 1 and 10 percent 
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respectively, with 1,3-butadiene decreases of at least 0.005 μg/m3 in urban areas. 

These toxics are national risk drivers and the reductions in ambient concentrations 

from this rule will result in reductions in risks from cancer and noncancer health 

effects. In some parts of the country (mainly urban areas), ethanol and 

formaldehyde concentrations are projected to decrease on the order of 1 to 10

percent and 1 to 2.5 percent respectively in 2030 as a result of the Tier 3 rule. 

Decreases in ethanol concentrations are expected due to reductions in VOC as a 

result of the Tier 3 standards. Changes in ambient acetaldehyde concentrations are 

generally less than 1 percent across the U.S., although the Tier 3 rule may decrease 

acetaldehyde concentrations in some urban areas by 1 to 2.5 percent in 2030. 

Changes in ambient naphthalene concentrations are generally between 1 and 10 

percent in 2030 with absolute decreases of up to 0.005 μg/m3. 

Although the reductions in ambient air toxics concentrations expected from 

the Tier 3 standards are generally small, they are projected to benefit the majority of 

the U.S. population. As shown in Table III-8, over 75 percent of the total U.S. 

population is projected to experience a decrease in ambient benzene and 1,3-

butadiene concentrations of at least 1 percent. Over 60 percent of the U.S 

population is projected to experience at least a 1 percent decrease in ambient 

ethanol and acrolein concentrations, and over 35 percent would experience a similar 

decrease in ambient formaldehyde concentrations with the Tier 3 standards. 

Table III-8 Percent of Total Population Experiencing Changes in Annual 

Ambient Concentrations of Toxic Pollutants in 2030 as a Result of the Tier 3

Standards

Percent Change Benzene Acrolein 1,3-Butadiene Formaldehyde Ethanol Acetaldehyde Naphthalene

≤ -50

> -50 to ≤ -25

> -25 to ≤ -10 2.29% 0.75% 19.07% 10.74%

> -10 to ≤ -5 20.63% 12.72% 27.29% 5.39% 31.56%

> -5 to ≤ -2.5 27.50% 25.17% 15.37% 0.60% 24.08% 20.58%

> -2.5 to ≤ -1 28.60% 24.62% 18.33% 35.34% 34.10% 11.77% 14.98%

> -1 to < 1 20.97% 36.74% 19.93% 64.06% 36.43% 88.23% 22.14%

≥ 1 to < 2.5

≥ 2.5 to < 5

≥ 5 to < 10

≥ 10 to < 25

≥ 25 to < 50

≥ 50 
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In addition, as described in Section 7.2.4.4.2 of the RIA, our modeling 

projects that acrolein concentrations would decrease to levels below the inhalation 

reference concentration for acrolein (0.02 μg/m3) for over 5 million people in 2030, 

meaning that as a result of the Tier 3 standards, 5 million fewer Americans will be 

exposed to ambient levels of acrolein high enough to present a potential for adverse 

health effects. 

5. Visibility

Air quality modeling conducted for this final action was used to project 

visibility conditions in 137 mandatory class I federal areas across the U.S. The 

results show that in 2030 all the modeled areas will continue to have annual average 

deciview levels above background and the Tier 3 rule will improve visibility in all 

these areas.227 The average visibility at all modeled mandatory class I federal areas 

on the 20 percent worst days is projected to improve by 0.02 deciviews, or 0.16

percent, in 2030. Section 7.2.5.5 of the RIA contains more detail on the visibility

portion of the air quality modeling.

6. Nitrogen and Sulfur Deposition

Our air quality modeling projects substantial decreases in nitrogen 

deposition as a result of the Tier 3 standards. The standards will result in annual 

percent decreases of greater than 2.5 percent in most major urban areas and greater 

than 5 percent in a few areas. In addition, smaller decreases, in the 1 to 2.5 percent 

range, will occur over much of the rest of the country. The impacts of the Tier 3

standards on sulfur deposition are smaller, ranging from no change to decreases of 

over 2.5 percent in some areas. For maps of 2030 deposition impacts and additional 

information on these impacts see Section 7.2.5.6 of the RIA. 

7. Environmental Justice

Environmental justice (EJ) is a principle asserting that all people deserve 

fair treatment and meaningful involvement with respect to environmental laws, 

regulations, and policies. EPA seeks to provide the same degree of protection 

from environmental health hazards for all people. As referenced below, numerous 

studies have found that some environmental hazards are more prevalent in areas 

with high population fractions of racial/ethnic minorities and people with low 

 

227 The level of visibility impairment in an area is based on the light-extinction coefficient and a 

unitless visibility index, called a “deciview,” which is used in the valuation of visibility. The 

deciview metric provides a scale for perceived visual changes over the entire range of conditions, 

from clear to hazy. Under many scenic conditions, the average person can generally perceive a 

change of one deciview. The higher the deciview value, the worse the visibility. Thus, an 

improvement in visibility is a decrease in deciview value.
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socioeconomic status (SES), as would be expected on the basis of those areas’ 

share of the general population.

As discussed in Section II of this document, concentrations of many air 

pollutants are elevated near high-traffic roadways. If minority populations and 

low-income populations disproportionately live near such roads, then an issue of 

EJ may be present. Such disparities may be due to multiple factors.228

People with low SES often live in neighborhoods with multiple stressors and 

health risk factors, including reduced health insurance coverage rates, higher 

smoking and drug use rates, limited access to fresh food, visible neighborhood 

violence, and elevated rates of obesity and some diseases such as asthma, diabetes, 

and ischemic heart disease. Although questions remain, several studies find 

stronger associations between air pollution and health in locations with such 

chronic neighborhood stress, suggesting that populations in these areas may be 

more susceptible to the effects of air pollution.229,230,231,232 Household-level 

stressors such as parental smoking and relationship stress also may increase 

susceptibility to the adverse effects of air pollution.233,234

To address the existing conditions in areas near major roadways, in 

comparison with other locations, we reviewed existing scholarly literature 

examining the topic, and conducted our own evaluation of two national datasets: 

 

228 Depro, B.; Timmins, C. (2008) Mobility and environmental equity: do housing choices 

determine exposure to air pollution? North Caroline State University Center for Environmental and 

Resource Economic Policy

229 Clougherty, J.E.; Kubzansky, L.D. (2009) A framework for examining social stress and 

susceptibility to air pollution in respiratory health. Environ Health Perspect 117: 1351-1358. 

Doi:10.1289/ehp.0900612 [Online at http://dx.doi.org]

230 Clougherty, J.E.; Levy, J.I.; Kubzansky, L.D.; Ryan, P.B.; Franco Suglia, S.; Jacobson Canner, 

M.; Wright, R.J. (2007) Synergistic effects of traffic-related air pollution and exposure to violence 

on urban asthma etiology. Environ Health Perspect 115: 1140-1146. doi:10.1289/ehp.9863 [Online 

at http://dx.doi.org]

231 Finkelstein, M.M.; Jerrett, M.; DeLuca, P.; Finkelstein, N.; Verma, D.K.; Chapman, K.; Sears, 

M.R. (2003) Relation between income, air pollution and mortality: a cohort study. Canadian Med 

Assn J 169: 397-402.

232 Shankardass, K.; McConnell, R.; Jerrett, M.; Milam, J.; Richardson, J.; Berhane, K. (2009) 

Parental stress increases the effect of traffic-related air pollution on childhood asthma incidence. 

Proc Natl Acad Sci 106: 12406-12411. doi:10.1073/pnas.0812910106 [Online at http://dx.doi.org]

233 Lewis, A.S.; Sax, S.N.; Wason, S.C.; Campleman, S.L (2011) Non-chemical stressors and 

cumulative risk assessment: an overview of current initiatives and potential air pollutant 

interactions. Int J Environ Res Public Health 8: 2020-2073. Doi:10.3390/ijerph8062020 [Online at 

http://dx.doi.org]

234 Rosa, M.J.; Jung, K.H.; Perzanowski, M.S.; Kelvin, E.A.; Darling, K.W.; Camann, D.E.; 

Chillrud, S.N.; Whyatt, R.M.; Kinney, P.L.; Perera, F.P.; Miller, R.L (2010) Prenatal exposure to 

polycyclic aromatic hydrocarbons, environmental tobacco smoke and asthma. Respir Med (In 

press). doi:10.1016/j.rmed.2010.11.022 [Online at http://dx.doi.org]
Page 86 of 88

the U.S. Census Bureau’s American Housing Survey for calendar year 2009 and 

the U.S. Department of Education’s database of school locations.

Existing publications that address EJ issues generally report that populations 

living near major roadways (and other types of transportation infrastructure) tend 

to be composed of larger fractions of nonwhite residents. People living in 

neighborhoods near such sources of air pollution also tend to be lower in income 

than people living elsewhere. Numerous studies evaluating the demographics and 

socioeconomic status of populations or schools near roadways have found that they

include a greater percentage of minority residents, as well as lower SES (indicated 

by variables such as median household income). Locations in these studies include 

Los Angeles, CA; Seattle, WA; Wayne County, MI; Orange County, FL; and the 

State of California 235,236,237,238,239,240 

More recently, three publications report nationwide analyses that compare 

the demographic patterns of people who do or do not live near major 

roadways.241,242,243 All three of these studies found that people living near major 

roadways are more likely to be minorities or low in SES. They also found that the 

outcomes of their analyses varied between regions within the U.S. However, only

one such study looked at whether such conclusions were confounded by living in a 

location with higher population density and how demographics differ between 

 

235 Marshall, J.D. (2008) Environmental inequality: air pollution exposures in California’s South 

Coast Air Basin.

236 Su, J.G.; Larson, T.; Gould, T.; Cohen, M.; Buzzelli, M. (2010) Transboundary air pollution and 

environmental justice: Vancouver and Seattle compared. GeoJournal 57: 595-608. 

doi:10.1007/s10708-009-9269-6 [Online at http://dx.doi.org]

237 Chakraborty, J.; Zandbergen, P.A. (2007) Children at risk: measuring racial/ethnic disparities in 

potential exposure to air pollution at school and home. J Epidemiol Community Health 61: 1074-

1079. doi: 10.1136/jech.2006.054130 [Online at http://dx.doi.org]

238 Green, R.S.; Smorodinsky, S.; Kim, J.J.; McLaughlin, R.; Ostro, B. (2003) Proximity of 

California public schools to busy roads. Environ Health Perspect 112: 61-66. 

doi:10.1289/ehp.6566 [http://dx.doi.org]

239 Wu, Y; Batterman, S.A. (2006) Proximity of schools in Detroit, Michigan to automobile and 

truck traffic. J Exposure Sci & Environ Epidemiol. doi:10.1038/sj.jes.7500484 [Online at 

http://dx.doi.org]

240 Su, J.G.; Jerrett, M.; de Nazelle, A.; Wolch, J. (2011) Does exposure to air pollution in urban 

parks have socioeconomic, racial, or ethnic gradients? Environ Res 111: 319-328.

241 Rowangould, G.M. (2013) A census of the US near-roadway population: public health and 

environmental justice considerations. Transportation Research Part D; 59-67.

242 Tian, N.; Xue, J.; Barzyk. T.M. (2013) Evaluating socioeconomic and racial differences in trafficrelated metrics in the United States using a GIS approach. J Exposure Sci Environ Epidemiol 23: 

215-222.

243 Boehmer, T.K.; Foster, S.L.; Henry, J.R.; Woghiren-Akinnifesi, E.L.; Yip, F.Y. (2013) 

Residential proximity to major highways – United States, 2010. Morbidity and Mortality Weekly 

Report 62(3): 46-50. 
Page 87 of 88

locations nationwide. In general, it found that higher density areas have higher 

proportions of low income and minority residents.

We analyzed two national databases that allowed us to evaluate whether 

homes and schools were located near a major road. One database, the American 

Housing Survey (AHS), includes descriptive statistics of over 70,000 housing units 

across the nation. The study is conducted every two years by the U.S. Census 

Bureau. We analyzed data from the 2009 AHS. The second database we analyzed 

was the U.S. Department of Education’s Common Core of Data, which includes 

enrollment and location information for schools across the U.S.

In analyzing the 2009 AHS, we focused on whether or not a housing unit 

was located within 300 feet of “4-or-more lane highway, railroad, or airport.”244 

We analyzed whether there were differences between houses and householders in 

such locations and those not in them.245 We included other variables, such as land 

use category, region of country, and housing type. We found that homes with a 

nonwhite householder were 22-34 percent more likely to be located within 300 feet 

of these large transportation facilities, while homes with a Hispanic householder 

were 17-33 percent more likely. Households near large transportation facilities 

were, on average, lower in income and educational attainment, more likely to be a 

rental property and located in an urban area.

In examining schools near major roadways, we examined the Common Core 

of Data (CCD) from the U.S. Department of Education, which includes 

information on all public elementary and secondary schools and school districts 

nationwide.246 To determine school proximities to major roadways, we used a 

geographic information system (GIS) to map each school and roadways based on 

the U.S. Census’s TIGER roadway file.247 We found that minority students were 

overrepresented at schools within 200 meters of the largest roadways, and that 

schools within 200 meters of the largest roadways also had higher than expected 

numbers of students eligible for free or reduced-price lunches. For example, Black 

students represent 21.57 percent of students at schools located within 200 meters 

of a primary road, whereas Black students represent 16.62 percent of students in all 

U.S. schools. Hispanic students represent 30.13 percent of students at schools 

 

244 This variable primarily represents roadway proximity. According to the Central Intelligence 

Agency’s World Factbook, in 2010, the United States had 6,506,204 km or roadways, 224,792 km of 

railways, and 15,079 airports. Highways thus represent the overwhelming majority of transportation 

facilities described by this factor in the AHS.

245 Bailey, C. (2011) Demographic and Social Patterns in Housing Units Near Large Highways and 

other Transportation Sources. Memorandum to docket.

246 http://nces.ed.gov/ccd/

247 Pedde, M.; Bailey, C. (2011) Identification of Schools within 200 Meters of U.S. Primary and 

Secondary Roads. Memorandum to the docket.
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located within 200 meters of a primary road, whereas Hispanic students represent 

21.93 percent of students in all U.S. schools.

Overall, there is substantial evidence that people who live or attend school 

near major roadways are more likely to be of a minority race, Hispanic ethnicity, 

and/or low SES. The emission reductions from this rule will result in widespread 

air quality improvements, but the impact on pollution levels in close proximity to 

roadways will be most direct. Thus, this rule is likely to help in mitigating the

disparity in racial, ethnic, and economically-based exposures.