Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards

Federal RegisterJan 24, 2023

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 2, 59, 60, 80, 85, 86, 600, 1027, 1030, 1031, 1033, 1036, 1037, 1039, 1042, 1043, 1045, 1048, 1051, 1054, 1060, 1065, 1066, 1068, and 1090

[EPA-HQ-OAR-2019-0055; FRL-7165-02-OAR]

RIN 2060-AU41

Control of Air Pollution From New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Final rule.

SUMMARY:

The Environmental Protection Agency (EPA) is finalizing a program to further reduce air pollution, including ozone and particulate matter (PM), from heavy-duty engines and vehicles across the United States. The final program includes new emission standards that are significantly more stringent and that cover a wider range of heavy-duty engine operating conditions compared to today's standards; further, the final program requires these more stringent emissions standards to be met for a longer period of when these engines operate on the road. Heavy-duty vehicles and engines are important contributors to concentrations of ozone and particulate matter and their resulting threat to public health, which includes premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. The final rulemaking promulgates new numeric standards and changes key provisions of the existing heavy-duty emission control program, including the test procedures, regulatory useful life, emission-related warranty, and other requirements. Together, the provisions in the final rule will further reduce the air quality impacts of heavy-duty engines across a range of operating conditions and over a longer period of the operational life of heavy-duty engines. The requirements in the final rule will lower emissions of NO

and other air pollutants (PM, hydrocarbons (HC), carbon monoxide (CO), and air toxics) beginning no later than model year 2027. We are also finalizing limited amendments to the regulations that implement our air pollutant emission standards for other sectors (

e.g.,

light-duty vehicles, marine diesel engines, locomotives, and various other types of nonroad engines, vehicles, and equipment).

DATES:

This final rule is effective on March 27, 2023. The incorporation by reference of certain material listed in this rule is approved by the Director of the Federal Register as of March 27, 2023.

ADDRESSES:

Docket: EPA has established a docket for this action under Docket ID No. EPA-HQ-OAR-2019-0055. Publicly available docket materials are available either electronically at

www.regulations.gov

or in hard copy at Air and Radiation Docket and Information Center, EPA Docket Center, EPA/DC, EPA WJC West Building, 1301 Constitution Ave., NW, Room 3334, Washington, DC. Out of an abundance of caution for members of the public and our staff, the EPA Docket Center and Reading Room are open to the public by appointment only to reduce the risk of transmitting COVID-19. Our Docket Center staff also continues to provide remote customer service via email, phone, and webform. Hand deliveries and couriers may be received by scheduled appointment only. For further information on EPA Docket Center services and the current status, please visit us online at

www.epa.gov/dockets

FOR FURTHER INFORMATION CONTACT:

Brian Nelson, Assessment and Standards Division, Office of Transportation and Air Quality, Environmental Protection Agency, 2000 Traverwood Drive, Ann Arbor, MI 48105; telephone number: (734) 214-4278; email address:

nelson.brian@epa.gov

SUPPLEMENTARY INFORMATION:

Does this action apply to me?

This action relates to companies that manufacture, sell, or import into the United States new heavy-duty highway engines. Additional amendments apply for gasoline refueling facilities and for manufacturers of all sizes and types of motor vehicles, stationary engines, aircraft and aircraft engines, and various types of nonroad engines, vehicles, and equipment. Regulated categories and entities include the following:

NAICS codes

NAICS title

326199

All Other Plastics Product Manufacturing.

332431

Metal Can Manufacturing.

333618

Manufacturers of new marine diesel engines.

335312

Motor and Generator Manufacturing.

336111

Automobile Manufacturing.

336112

Light Truck and Utility Vehicle Manufacturing.

336120

Heavy Duty Truck Manufacturing.

336211

Motor Vehicle Body Manufacturing.

336213

Motor Home Manufacturing.

336411

Manufacturers of new aircraft.

336412

Manufacturers of new aircraft engines.

333618

Other Engine Equipment Manufacturing.

336999

All Other Transportation Equipment Manufacturing.

423110

Automotive and Other Motor Vehicle Merchant Wholesalers.

447110

Gasoline Stations with Convenience Stores.

447190

Other Gasoline Stations.

454310

Fuel dealers.

811111

General Automotive Repair.

811112

Automotive Exhaust System Repair.

811198

All Other Automotive Repair and Maintenance.

NAICS Association. NAICS & SIC Identification Tools. Available online:

https://www.naics.com/search.

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 entity is regulated by this action, you should carefully examine the applicability criteria found in Sections XI and XII of this preamble. If you have questions regarding the applicability of this action to a particular entity, consult the person listed in the

FOR FURTHER INFORMATION CONTACT

section.

Public participation: Docket:

All documents in the docket are listed on the

www.regulations.gov

website. 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 through the EPA Docket Center at the location listed in the

ADDRESSES

section of this document.

What action is the agency taking?

The Environmental Protection Agency (EPA) is adopting a rule to reduce air pollution from highway heavy-duty vehicles and engines. The final rulemaking will promulgate new numeric standards and change key provisions of the existing heavy-duty emission control program, including the

test procedures, regulatory useful life, emission-related warranty, and other requirements. Together, the provisions in the final rule will further reduce the air quality impacts of heavy-duty engines across a range of operating conditions and over a longer period of the operational life of heavy-duty engines. Heavy-duty vehicles and engines are important contributors to concentrations of ozone and particulate matter and their resulting threat to public health, which includes premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. This final rule will reduce emissions of nitrogen oxides and other pollutants.

What is the agency's authority for taking this action?

Clean Air Act section 202(a)(1) requires that EPA set emission standards for air pollutants from new motor vehicles or new motor vehicle engines that the Administrator has found cause or contribute to air pollution that may endanger public health or welfare. See Sections I.D and XIII of this preamble for more information on the agency's authority for this action.

What are the incremental costs and benefits of this action?

Our analysis of the final standards shows that annual total costs for the final program relative to the baseline (or no action scenario) range from $3.9 billion in 2027 to $4.7 billion in 2045 (2017 dollars, undiscounted, see Table V-16). The present value of program costs for the final rule, and additional details are presented in Section V. Section VIII presents our analysis of the human health benefits associated with the final standards. We estimate that in 2045, the final rule will result in total annual monetized ozone- and PM

2.5

-related benefits of $12 and $33 billion at a 3 percent discount rate, and $10 and $30 billion at a 7 percent discount rate (2017 dollars, discount rate applied to account for mortality cessation lag, see Table VIII-3).

These benefits only reflect those associated with reductions in NO

emissions (a precursor to both ozone and secondarily-formed PM

2.5

) and directly-emitted PM

2.5

from highway heavy-duty engines. The agency was unable to quantify or monetize all the benefits of the final program, therefore the monetized benefit values are underestimates. There are additional human health and environmental benefits associated with reductions in exposure to ambient concentrations of PM

2.5

, ozone, and NO

that data, resource, or methodological limitations have prevented EPA from quantifying. There will also be benefits associated with reductions in air toxic pollutant emissions that result from the final program, but we did not attempt to monetize those impacts because of methodological limitations. More detailed information about the benefits analysis conducted for the final rule, including the present value of program benefits, is included in Section VIII and RIA Chapter 8. We compare total monetized health benefits to total costs associated with the final rule in Section IX. Our results show that annual benefits of the final rule will be larger than the annual costs in 2045, with annual net benefits of $6.9 and $29 billion assuming a 3 percent discount rate, and net benefits of $5.8 and $25 billion assuming a 7 percent discount rate.

The benefits of the final rule also outweigh the costs when expressed in present value terms and as equalized annual values (see Section IX for these values). See Section VIII for more details on the net benefit estimates

2045 is a snapshot year chosen to approximate the annual health benefits that occur when the final program will be fully implemented and when most of the regulated fleet will have turned over.

The range of benefits and net benefits reflects a combination of assumed PM

2.5

and ozone mortality risk estimates and selected discount rate.

Did EPA conduct a peer review before issuing this action?

This regulatory action was supported by influential scientific information. EPA therefore conducted peer review in accordance with OMB's Final Information Quality Bulletin for Peer Review. Specifically, we conducted peer review on five analyses: (1) Analysis of Heavy-Duty Vehicle Sales Impacts Due to New Regulation (Sales Impacts), (2) Exhaust Emission Rates for Heavy-Duty Onroad Vehicles in MOVES_CTI NPRM (Emission Rates), (3) Population and Activity of Onroad Vehicles in MOVES_CTI NPRM (Population and Activity), (4) Cost teardowns of Heavy-Duty Valvetrain (Valvetrain costs), and (5) Cost teardown of Emission Aftertreatment Systems (Aftertreatment Costs). All peer review was in the form of letter reviews conducted by a contractor. The peer review reports for each analysis are in the docket for this action and at EPA's Science Inventory

(https://cfpub.epa.gov/si/)

Table of Contents

I. Executive Summary

A. Introduction

B. Overview of the Final Regulatory Action

C. Impacts of the Standards

D. EPA Statutory Authority for This Action

II. Need for Additional Emissions Control

A. Background on Pollutants Impacted by This Proposal

B. Health Effects Associated With Exposure to Pollutants Impacted by This Rule

C. Environmental Effects Associated With Exposure to Pollutants Impacted by This Rule

D. Environmental Justice

III. Test Procedures and Standards

A. Overview

B. Summary of Compression-Ignition Exhaust Emission Standards and Duty Cycle Test Procedures

C. Summary of Compression-Ignition Off-Cycle Standards and Off-Cycle Test Procedures

D. Summary of Spark-Ignition HDE Exhaust Emission Standards and Test Procedures

E. Summary of Spark-Ignition HDV Refueling Emission Standards and Test Procedures

IV. Compliance Provisions and Flexibilities

A. Regulatory Useful Life

B. Ensuring Long-Term In-Use Emissions Performance

C. Onboard Diagnostics

D. Inducements

E. Fuel Quality

F. Durability Testing

G. Averaging, Banking, and Trading

V. Program Costs

A. Technology Package Costs

B. Operating Costs

C. Program Costs

VI. Estimated Emissions Reductions From the Final Program

A. Emission Inventory Methodology

B. Estimated Emission Reductions From the Final Program

C. Estimated Emission Reductions by Engine Operations and Processes

VII. Air Quality Impacts of the Final Rule

A. Ozone

B. Particulate Matter

C. Nitrogen Dioxide

D. Carbon Monoxide

E. Air Toxics

F. Visibility

G. Nitrogen Deposition

H. Demographic Analysis of Air Quality

VIII. Benefits of the Heavy-Duty Engine and Vehicle Standards

IX. Comparison of Benefits and Costs

A. Methods

B. Results

X. Economic Impact Analysis

A. Impact on Vehicle Sales, Mode Shift, and Fleet Turnover

B. Employment Impacts

XI. Other Amendments

A. General Compliance Provisions (40 CFR Part 1068) and Other Cross-Sector Issues

B. Heavy-Duty Highway Engine and Vehicle Emission Standards (40 CFR Parts 1036 and 1037)

C. Fuel Dispensing Rates for Heavy-Duty Vehicles (40 CFR Parts 80 and 1090)

D. Refueling Interface for Motor Vehicles (40 CFR Parts 80 and 1090)

E. Light-Duty Motor Vehicles (40 CFR Parts 85, 86, and 600)

F. Large Nonroad Spark-Ignition Engines (40 CFR Part 1048)

G. Small Nonroad Spark-Ignition Engines (40 CFR Part 1054)

H. Recreational Vehicles and Nonroad Evaporative Emissions (40 CFR Parts 1051 and 1060)

I. Marine Diesel Engines (40 CFR Parts 1042 and 1043)

J. Locomotives (40 CFR Part 1033)

K. Stationary Compression-Ignition Engines (40 CFR Part 60, subpart IIII)

L. Nonroad Compression-Ignition Engines (40 CFR Part 1039)

XII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

B. Paperwork Reduction Act (PRA)

C. Regulatory Flexibility Act (RFA)

D. Unfunded Mandates Reform Act (UMRA)

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

G. Executive Order 13045: Protection of Children From Environmental Health and Safety Risks

H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use

I. National Technology Transfer and Advancement Act (NTTAA) and 1 CFR Part 51

J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations

K. Congressional Review Act

L. Judicial Review

XIII. Statutory Provisions and Legal Authority

I. Executive Summary

A. Introduction

1. Summary of the Final Criteria Pollutant Program

In this action, the EPA is finalizing a program to further reduce air pollution, including pollutants that create ozone and particulate matter (PM), from heavy-duty engines and vehicles across the United States. The final program includes new, more stringent emissions standards that cover a wider range of heavy-duty engine operating conditions compared to today's standards, and it requires these more stringent emissions standards to be met for a longer period of time of when these engines operate on the road.

This final rule is part of a comprehensive strategy, the “Clean Trucks Plan,” which lays out a series of clean air and climate regulations that the agency is developing to reduce pollution from large commercial heavy-duty trucks and buses, as well as to advance the transition to a zero-emissions transportation future. Consistent with President Biden's Executive Order (E.O.) 14037, this final rule is the first step in the Clean Trucks Plan.

We expect the next two steps of the Clean Trucks Plan will take into consideration recent Congressional action, including the recent Inflation Reduction Act of 2022, that we anticipate will spur significant change in the heavy-duty sector.

We are not taking final action at this time on the proposed targeted updates to the existing Heavy-Duty Greenhouse Gas Emissions Phase 2 program (HD GHG Phase 2); rather, we intend to consider potential changes to certain HD GHG Phase 2 standards as part of a subsequent rulemaking.

President Joseph Biden. Executive Order on Strengthening American Leadership in Clean Cars and Trucks. 86 FR 43583, August 10, 2021.

For example, both the 2021 Infrastructure Investment and Jobs Act (commonly referred to as the “Bipartisan Infrastructure Law” or BIL) and the Inflation Reduction Act of 2022 (“Inflation Reduction Act” or IRA) include many incentives for the development, production, and sale of zero emissions vehicles (ZEVs) and charging infrastructure. Infrastructure Investment and Jobs Act, Public Law 117-58, 135 Stat. 429 (2021) (“Bipartisan Infrastructure Law” or “BIL”), available at

https://www.congress.gov/117/plaws/publ58/PLAW-117publ58.pdf

; Inflation Reduction Act of 2022, Public Law 117-169, 136 Stat. 1818 (2022) (“Inflation Reduction Act” or “IRA”), available at

https://www.congress.gov/117/bills/hr5376/BILLS-117hr5376enr.pdf.

Across the United States, heavy-duty engines emit oxides of nitrogen (NO

) and other pollutants that are significant contributors to concentrations of ozone and PM

2.5

and their resulting adverse health effects, which include death, respiratory illness (including childhood asthma), and cardiovascular problems.

5 6 7

Without this final rule, heavy-duty engines would continue to be one of the largest contributors to mobile source NO

emissions nationwide in the future, representing 32 percent of the mobile source NO

emissions in calendar year 2045.

Furthermore, we estimate that without this final rule, heavy-duty engines would represent 90 percent of the onroad NO

inventory in calendar year 2045.

Reducing NO

emissions is a critical part of many areas' strategies to attain and maintain the National Ambient Air Quality Standards (NAAQS) for ozone and PM; many state and local agencies anticipate challenges in attaining the NAAQS, maintaining the NAAQS in the future, and/or preventing nonattainment.

Some nonattainment areas have already been “bumped up” to higher classifications because of challenges in attaining the NAAQS.

Oxides of nitrogen (NO

) refers to nitric oxide (NO) and nitrogen dioxide (NO

Zawacki et al, 2018. Mobile source contributions to ambient ozone and particulate matter in 2025. Atmospheric Environment, Vol 188, pg 129-141. Available online:

https://doi.org/10.1016/j.atmosenv.2018.04.057

Davidson et al, 2020. The recent and future health burden of the U.S. mobile sector apportioned by source. Environmental Research Letters. Available online:

https://doi.org/10.1088/1748-9326/ab83a8.

Sectors other than onroad and nonroad were projected from 2016v1 Emissions Modeling Platform.

https://www.epa.gov/air-emissions-modeling/2016v1-platform

U.S. EPA (2020) Motor Vehicle Emission Simulator: MOVES3.

https://www.epa.gov/moves

See Section II for additional detail.

For example, in September 2019 several 2008 ozone nonattainment areas were reclassified from moderate to serious, including Dallas, Chicago, Connecticut, New York/New Jersey and Houston, and in January 2020, Denver. Also, on September 15, 2022, EPA finalized reclassification of 5 areas in nonattainment of the 2008 ozone NAAQS from serious to severe and 22 areas in nonattainment of the 2015 ozone NAAQS from marginal to moderate. The 2008 NAAQS for ozone is an 8-hour standard with a level of 0.075 ppm, which the 2015 ozone NAAQS lowered to 0.070 ppm.

In addition, emissions from heavy-duty engines can result in higher pollutant levels for people living near truck freight routes. Based on a study EPA conducted of people living near truck routes, an estimated 72 million people live within 200 meters of a truck freight route.

Relative to the rest of the population, people of color and those with lower incomes are more likely to live near truck routes.

This population includes children; childcare facilities and schools can also be in close proximity to freight routes.

See discussion in Section II.B.7.

See Section VII.H for additional discussion on our analysis of environmental justice impacts of this final rule.

Kingsley, S., Eliot, M., Carlson, L. et al. Proximity of U.S. schools to major roadways: a nationwide assessment. J Expo Sci Environ Epidemiol 24, 253-259 (2014).

https://doi.org/10.1038/jes.2014.5

The final rulemaking will promulgate new numeric standards and change key provisions of the existing heavy-duty emission control program, including the test procedures, regulatory useful life, emission-related warranty, and other requirements. Together, the provisions in the final rule will further reduce the air quality impacts of heavy-duty engines across a range of operating conditions and over a longer portion of the operational life of heavy-duty engines.

The requirements in the final

rule will lower emissions of NO

and other air pollutants (PM, hydrocarbons (HC), carbon monoxide (CO), and air toxics) beginning no later than model year (MY) 2027. The emission reductions from the final rule will increase over time as more new, cleaner vehicles enter the fleet.

Note that the terms useful life and operational life are different, though they are related. As required by Clean Air Act (CAA) section 202(a), the useful life period is when manufacturers are required to meet the emissions standards in the final rule; whereas, operational life is the term we use to describe the duration over which an engine is operating on roadways. We are finalizing useful life periods that cover a greater portion of the operational life. We consider operational life to be the average mileage at rebuild for compression-ignition engines and the average mileage at replacement for spark-ignition engines (see preamble Section IV.A for details).

We estimate that the final rule will reduce NO

emissions from heavy-duty vehicles in 2040 by more than 40 percent; by 2045, a year by which most of the regulated fleet will have turned over, heavy-duty NO

emissions will be almost 50 percent lower than they would have been without this action. These emission reductions will result in widespread decreases in ambient concentrations of pollutants such as ozone and PM

2.5

. We estimate that in 2045, the final rule will result in total annual monetized ozone- and PM

2.5

-related benefits of $12 and $33 billion at a 3 percent discount rate, and $10 and $30 billion at a 7 percent discount rate. These widespread air quality improvements will play an important role in addressing concerns raised by state, local, and Tribal governments, as well as communities, about the contributions of heavy-duty engines to air quality challenges they face such as meeting their obligations to attain or continue to meet NAAQS, and to reduce other human health and environmental impacts of air pollution. This rule's emission reductions will reduce air pollution in close proximity to major roadways, where concentrations of many air pollutants are elevated and where people of color and people with low income are disproportionately exposed.

In EPA's judgment, our analyses in this final rule show that the final standards will result in the greatest degree of emission reduction achievable starting in model year 2027, giving appropriate consideration to costs and other factors, which is consistent with EPA's statutory authority under Clean Air Act (CAA) section 202(a)(3)(A).

CAA section 202(a)(3)(A) requires standards for emissions of NO

, PM, HC, and CO emissions from heavy-duty vehicles and engines to “reflect the greatest degree of emission reduction achievable through the application of technology which the Administrator determines will be available for the model year to which such standards apply, giving appropriate consideration to cost, energy, and safety factors associated with the application of such technology.” Throughout this notice we use terms like “maximum feasible emissions reductions” to refer to this statutory requirement to set standards that “reflect the greatest degree of emission reduction achievable . . .'.

CAA section 202(a)(1) requires the EPA to “by regulation prescribe (and from time to time revise) . . . standards applicable to the emission of any air pollutant from any class or classes of new motor vehicles or new motor vehicle engines . . . , which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” CAA section 202(a)(3)(C) requires that NO

, PM, HC, and CO (hereafter referred to as “criteria pollutants”) standards for certain heavy-duty vehicles and engines apply for no less than 3 model years and apply no earlier than 4 years after promulgation.

See Sections I.D and XIII for additional discussion on EPA's statutory authority for this action, including our authority under CAA sections 202(d) and 207.

Although heavy-duty engines have become much cleaner over the last decade, catalysts and other technologies have evolved such that harmful air pollutants can be reduced even further. The final standards are based on technology improvements that have become available over the 20 years since the last major rule was promulgated to address emissions of criteria pollutants and toxic pollutants from heavy-duty engines, as well as projections of continued technology improvements that build on these existing technologies. The criteria pollutant provisions we are adopting in this final rule apply for all heavy-duty engine (HDE) classes: Spark-ignition (SI) HDE, as well as compression-ignition (CI) Light HDE, CI Medium HDE, and CI Heavy HDE.

This final rule includes new criteria pollutant standards for engine-certified Class 2b through 8 heavy-duty engines and vehicles. Class 2b and 3 vehicles with a Gross Vehicle Weight Rating (GVWR) between 8,500 and 14,000 pounds are primarily commercial pickup trucks and vans and are sometimes referred to as “medium-duty vehicles.” The majority of Class 2b and 3 vehicles are chassis-certified vehicles, and EPA intends to include them in a future combined light-duty and medium-duty rulemaking action, consistent with E.O, 14037, Section 2a. SI HDE are typically fueled by gasoline, whereas CI HDE are typically fueled by diesel; note that the Heavy HDE class, which is largely CI engines, does include certain SI engines that are generally natural gas-fueled engines intended for use in Class 8 vehicles. See 40 CFR 1036.140 for additional description of the primary intended service classes for heavy-duty engines. Heavy-duty engines and vehicles are also used in nonroad applications, such as construction equipment; nonroad heavy-duty engines and vehicles are not the focus of this final rule. As outlined in I.B of this Executive Summary and detailed in Section XI, this final rule also includes limited amendments to regulations that implement our air pollutant emission standards for other industry sectors, including light-duty vehicles, light-duty trucks, marine diesel engines, locomotives, and various types of nonroad engines, vehicles, and equipment. See 40 CFR 1036.140 for a description of the primary intended service classes for heavy-duty engines.

As described in Section III, the final standards will reduce emissions during a broader range of operating conditions compared to the current standards, such that nearly all in-use operation will be covered. Available data indicate that emission levels demonstrated for certification are not currently achieved under the broad range of real-world operating conditions.

19 20 21 22

In fact, less than ten percent of the data collected during a typical test while the vehicle is operated on the road is subject to EPA's current on-the-road emission standards.

These testing data further show that NO

emissions from heavy-duty CI engines are high during many periods of vehicle operation that are not subject to current on-the-road emission standards. For example, “low-load” engine conditions occur when a vehicle operates in stop-and-go traffic or is idling; these low-load conditions can result in exhaust temperature decreases that then lead to the diesel engine's selective catalytic reduction (SCR)-based emission control system becoming less effective or ceasing to function. Test data collected as part of EPA's manufacturer-run in-use testing program indicate that this low-load operation could account for more than half of the NO

emissions from a vehicle during a typical workday.

Similarly, heavy-duty SI engines also operate in conditions where their catalyst technology becomes less effective, resulting in higher levels of air pollutants; however, unlike CI engines, it is sustained medium-to-high load operation where emission levels are less certain. To address these concerns, as part of our comprehensive approach, the final standards include both revisions to our existing test procedures and new test procedures to reduce emissions

from heavy-duty engines under a broader range of operating conditions, including low-load conditions.

Hamady, Fakhri, Duncan, Alan. “A Comprehensive Study of Manufacturers In-Use Testing Data Collected from Heavy-Duty Diesel Engines Using Portable Emissions Measurement System (PEMS).” 29th CRC Real World Emissions Workshop, March 10-13, 2019.

Sandhu, Gurdas, et al. “Identifying Areas of High NO

Operation in Heavy-Duty Vehicles”. 28th CRC Real-World Emissions Workshop, March 18-21, 2018.

Sandhu, Gurdas, et al. “In-Use Emission Rates for MY 2010+ Heavy-Duty Diesel Vehicles”. 27th CRC Real-World Emissions Workshop, March 26-29, 2017.

As noted in Section I.B and discussed in Section III, testing engines and vehicles while they are operating without a defined duty cycle is referred to as “off-cycle” testing; as detailed in Section III, we are finalizing new off-cycle test procedures and standards as part of this rulemaking.

Heavy-duty CI engines are currently subject to off-cycle standards that are not limited to specific test cycles; throughout this notice we use the terms “on-the-road”, “over the road”, or “real world” interchangeably to refer to off-cycle standards.

Sandhu, Gurdas, et al. “Identifying Areas of High NO

Operation in Heavy-Duty Vehicles”. 28th CRC Real-World Emissions Workshop, March 18-21, 2018.

Data also show that tampering and mal-maintenance of the engine's emission control system after the useful life period is projected to result in NO

emissions that would represent a substantial part of the HD emissions inventory in 2045.

To address this problem, as part of our comprehensive approach, the final rule includes longer regulatory useful life and emission-related warranty requirements to ensure the final emissions standards will be met through more of the operational life of heavy-duty vehicles.

26 27

Further, the final rule includes requirements for manufacturers to better ensure that operators keep in-use engines and emission control systems working properly in the real world. We expect these final provisions to improve maintenance and serviceability will reduce incentives to tamper with the emission control systems on MY 2027 and later engines, which would avoid large increases in emissions that would impact the reductions projected from the final rule. For example, we estimate NO

emissions will increase more than 3000 percent due to malfunction of the NO

emissions aftertreatment on a MY 2027 and later heavy heavy-duty vehicle. To address this, the final rule requires manufacturers to meet emission standards with less frequent scheduled maintenance for emission-related parts and systems, and to provide more information on how to diagnose and repair emission control systems. In addition, the final rule requires manufacturers to demonstrate that they design their engines to limit access to electronic controls to prevent operators from reprogramming the engine to bypass or disable emission controls. The final rule also specifies a balanced approach for manufacturers to design their engines with features to ensure that operators perform ongoing maintenance to keep SCR emission control systems working properly, without creating a level of burden and corresponding frustration for operators that could increase the risk of operators completely disabling emission control systems. These provisions combined with the longer useful life and warranty periods will provide a comprehensive approach to ensure that the new, much more stringent emissions standards are met during in use operations.

See Section VI for more information on projected inventory contributions from each operating mode or process, as well as discussion on the emissions impacts of tampering and mal-maintenance.

Emission standards set under CAA section 202(a) apply to vehicles and engines “for their useful life.” CAA section 202(d) directs EPA to prescribe regulations under which the useful life of vehicles and engines shall be determined, and for heavy-duty vehicles and engines establishes minimum values of 10 years or 100,000 miles, whichever occurs first, unless EPA determines that greater values are appropriate. CAA section 207(a) further requires manufacturers to provide emission-related warranty, and EPA set the current emission-related warranty periods for heavy-duty engines in 1983 (48 FR 52170, November 16, 1983). See Section I.D for more discussion on the statutory authority for the final rule.

See Section IV for more discussion on the final useful life and warranty requirements.

The final standards and requirements are based on further consideration of the data included in the proposed rule, as well as additional supporting data from our own test programs, and consideration of the extensive public input EPA received in response to the proposed rule. The proposal was posted on the EPA website on March 7, 2022, and published in the

Federal Register

on March 28, 2022 (87 FR 17414, March 28, 2022). EPA held three virtual public hearings in April 2022. We received more than 260,000 public comments.

A broad range of stakeholders provided comments, including state and local governments, heavy-duty engine manufacturers, emissions control suppliers and others in the heavy-duty industry, environmental organizations, environmental justice organizations, state, local, and Tribal organizations, consumer groups, labor groups, private citizens, and others. Some of the issues raised in comments included the need for new, more stringent NO

standards, particularly in communities already overburdened by pollution; the feasibility and costs of more stringent NO

standards combined with much longer useful life periods; the longer emissions-related warranty periods; a single- vs. two-step program; and various details on the flexibilities and other program design features of the proposed program. We briefly discuss several of these key issues in Section I.B, with more detail in later sections in this preamble and in the Response to Comments document that is available in the public docket for this rule.

Of these comments, 1,860 were unique letters, many of which provided data and other detailed information for EPA to consider; the remaining comments were mass mailers sponsored by 30 different organizations, nearly all of which urged EPA to take action to reduce emissions from trucks or to adopt more stringent limits.

U.S. EPA, “Control of Air Pollution from New Motor Vehicles: Heavy-Duty Engine and Vehicle Standards—Response to Comments”, Docket EPA-HQ-OAR-2019-0055.

This Section I provides an overview of the final program, the impacts of the final program, and how the final program is consistent with EPA's statutory requirements. The need for additional emissions control from heavy-duty engines is described in Section II. We describe the final standards and compliance flexibilities in detail in Sections III and IV. We discuss our analyses of estimated emission reductions, air quality improvements, costs, and monetized benefits of the final program in Sections V through X. Section XI describes limited amendments to the regulations that implement our air pollutant emission standards for other sectors (

e.g.,

light-duty vehicles, marine diesel engines, locomotives, and various types of nonroad engines, vehicles, and equipment).

2. EPA Will Address HD GHG Emissions in a Subsequent Rulemaking

Although we proposed targeted revisions to the MY2027 GHG Phase 2 standards as part of the same proposal in which we laid out more stringent NO

standards, in this final rule we are not taking final action on updates to the GHG standards. Instead, we intend to consider potential changes to certain HD GHG Phase 2 standards as part of a subsequent rulemaking.

B. Overview of the Final Regulatory Action

We are finalizing a program that will begin in MY 2027, which is the earliest year that these new criteria pollutant standards can begin to apply under CAA section 202(a)(3)(C).

The final NO

standards are a single-step program that reflect the greatest degree of emission reduction achievable starting in MY2027, giving appropriate consideration to costs and other factors. The final rule establishes not only new, much more stringent NO

standards compared to today's standards, but also requires lower NO

emissions over a much wider range of testing conditions both in the laboratory and when engines are operating on the road. Further, the final standards include longer useful life periods, as well as significant increases in the emissions-related warranty periods. The longer useful life and emissions warranty periods are particularly important for ensuring continued emissions control when the engines are operating on the road. These final standards will result in significant reductions in emissions of NO

, PM

2.5

, and other air pollutants across the country, which we project will meaningfully decrease ozone

concentrations across the country. We expect the largest improvements in both ozone and PM

2.5

to occur in areas with the worst baseline air quality. In a supplemental demographic analysis, we also found that larger numbers of people of color are projected to reside in these areas with the worst baseline air quality.

Section 202(a)(3)(C) requires that standards under 202(a)(3)(A), such as the standards in this final rule, apply no earlier than 4 years after promulgation, and apply for no less than 3 model years. See Section I.D for additional discussion on the statutory authority for this action.

The final standards and requirements are based on further consideration of the data included in the proposed rule, as well as additional supporting data from our own test programs, and consideration of the extensive public input EPA received in response to the proposed rule. As required by CAA section 202(a)(3), the final new numeric NO

standards will result in the greatest degree of emission reduction achievable for a national program starting in MY 2027 through the application of technology that the Administrator has determined will be available starting in MY 2027, after giving appropriate consideration to cost, energy, and safety factors associated with the application of such technology. The EPA proposal included two options for the NO

program. Proposed Option 1 was the more stringent option, and it included new standards and other program elements starting in MY 2027, which were further strengthened in MY 2031. Proposed Option 2 was the less stringent option, with new standards and requirements implemented fully in MY 2027. The final numeric NO

standards and testing requirements are largely consistent with the proposed Option 1 in MY 2027. The final numeric standards and regulatory useful life values will reduce NO

emissions not only when trucks are new, but throughout a longer period of their operational life under real-world conditions. For the smaller engine service-class categories, we are finalizing the longest regulatory useful life and emissions warranty periods proposed, and for the largest engines we are finalizing requirements for useful life and emissions aftertreatment durability demonstration that are significantly longer than required today.

As previously noted in this Section I, we received a large number and wide range of comments on the proposed rule. Several comments raised particularly significant issues related to some fundamental components of the proposed program, including the level of the numeric standards and feasibility of lower numeric standards combined with longer useful life periods. We briefly discuss these key issues in this Section I.B, with more detail in later sections in this preamble. The Response to Comments document provides our responses to the comments we received; it is located in the docket for this rulemaking.

1. Key Changes From the Proposal

i. Feasibility of More Stringent NO

Standards Combined With Much Longer Useful Life Periods

Many stakeholders commented on the proposed numeric NO

standards, and the feasibility of maintaining those numeric standards over the proposed useful life periods. Environmental organizations and other commenters, including suppliers to the heavy-duty industry, generally urged EPA to adopt the most stringent standards proposed, or to finalize even more stringent standards by fully aligning with the California Air Resources Board (CARB) Low NO

Omnibus program.

In contrast, most engine manufacturers, truck dealers, fleets, and other members of the heavy-duty industry stated that even the less stringent proposed numeric standards and useful life periods would be extremely challenging to meet, particularly for the largest heavy-duty engines. Some of these commenters provided data that they stated showed the potential for large impacts on the purchase price of a new truck if EPA were to finalize the most stringent proposed numeric standards and useful life periods for the largest heavy-duty engines.

EPA is reviewing a waiver request under CAA section 209(b) from California for the Omnibus rule. For more information on the California Air Resources Board Omnibus rule see, “Heavy-Duty Engine and Vehicle Omnibus Regulation and Associated Amendments,” December 22, 2021.

https://ww2.arb.ca.gov/rulemaking/2020/hdomnibuslownox

. Last accessed September 21, 2022. See also

“

California State Motor Vehicle Pollution Control Standards and Nonroad Engine Pollution Control Standards; The “Omnibus” Low NO

Regulation; Request for Waivers of Preemption; Opportunity for Public Hearing and Public Comment” at 87 FR 35765 (June 13, 2022).

As summarized in I.B.2 and detailed in preamble Section III, we are finalizing numeric NO

standards and useful life periods that are largely consistent with the most stringent proposed option for MY 2027. For all heavy-duty engine classes, the final numeric NO

standards for medium- and high-load engine operations match the most stringent standards proposed for MY 2027; for low-load operations we are finalizing the most stringent standard proposed for any model year (see I.B.1.ii for discussion).

For smaller heavy-duty engines (

i.e.,

light and medium heavy-duty engines CI and SI heavy-duty engines), the numeric standards are combined with the longest useful life periods we proposed. The final numeric NO

emissions standards and useful life periods for smaller heavy-duty engines are based on further consideration of data included in the proposal from our engine demonstration programs that show the final NO

emissions standards are feasible at the final useful life periods applicable to these smaller heavy-duty engines. Our assessment of the data available at the time of proposal is further supported by our evaluation of additional information and public comments stating that the proposed standards are feasible for these smaller engine categories. For the largest heavy-duty engines (

i.e.,

heavy heavy-duty engines), the final numeric standards are combined with the longest useful life mileage that we proposed for MY 2027. The final useful life periods for the largest heavy-duty engines are 50 percent longer than today's useful life periods, which will play an important role in ensuring continued emissions control while the engines operate on the road.

As proposed, we are finalizing a new test procedure for heavy-duty CI engines to demonstrate emission control when the engine is operating under low-load and idle conditions; this new test procedure does not apply to heavy-duty SI engines (see Sections I.B.2 and III for additional discussion).

After further consideration of the data included in the proposal, as well as information submitted by commenters and additional data we collected since the time of proposal, we are finalizing two updates from our proposed testing requirements in order to ensure the greatest degree of emission reduction achievable are met throughout the final useful life periods; these updates are tailored to the larger engine classes (medium and heavy heavy-duty engines), which have longer useful life periods and more rigorous duty-cycles compared to the smaller engine classes. First, we are finalizing a requirement for manufacturers to demonstrate before heavy heavy-duty engines are in-use that the emissions control technology is durable through a period of time longer than the final useful life mileage.

For these largest engines with the longest useful life mileages, the extended laboratory durability demonstration will better ensure the final standards will be met throughout the regulatory useful life

under real-world operations where conditions are more variable. Second, we are finalizing an interim compliance allowance that applies when EPA evaluates whether the heavy or medium heavy-duty engines are meeting the final standards after these engines are in use in the real world. When combined with the final useful life values, we believe the interim compliance allowance will address concerns raised in comments from manufacturers that the more stringent proposed MY 2027 standards would not be feasible to meet over the very long useful life periods of heavy heavy-duty engines, or under the challenging duty-cycles of medium heavy-duty engines. This interim, in-use compliance allowance is generally consistent with our past practice (for example, see 66 FR 5114, January 18, 2001); also consistent with past practice, the interim compliance allowance is included as an interim provision that we may reassess in the future through rulemaking based on the performance of emissions controls over the final useful life periods for medium and heavy heavy-duty engines. To set standards that result in the greatest emission reductions achievable for medium and heavy heavy-duty engines, we considered additional data that we and others collected since the time of the proposal; these data show the significant technical challenge of maintaining very low NO

emissions throughout very long useful life periods for heavy heavy-duty engines, and greater amounts of certain aging mechanisms over the long useful life periods of medium heavy-duty engines. In addition to these data, in setting these standards, we gave appropriate consideration to costs associated with the application of technology to achieve maximum emissions reductions in MY 2027 (

i.e.,

cost of compliance for manufacturers associated with the standards) and other factors. We determined that for heavy heavy-duty engines the combination of: (1) The most stringent MY 2027 standards proposed, (2) longer useful life periods compared to today's useful life periods, (3) targeted, interim compliance allowance approach to in-use compliance testing, and (4) the extended durability demonstration for emissions control technologies is appropriate, feasible, and consistent with our authority under the CAA to set technology-forcing NO

pollutant standards for heavy-duty engines for their useful life.

Similarly, for medium heavy-duty engines we determined that the combination of the first three elements (

i.e.,

most stringent MY 2027 standards proposed, increase in useful life periods, and interim compliance allowance for in-use testing) is appropriate, feasible, and consistent with our CAA authority to set technology-forcing NO

pollutant standards for heavy-duty engines for their useful life.

Manufacturers of any size heavy-duty engine must demonstrate that the emission control technology is durable through a period equivalent to the useful life period of the engine, and may be subject to recall if EPA subsequently determines that properly maintained and used engines do not conform to our regulations over the useful life period (as specified in our regulations and consistent with CAA section 207). As outlined here, the extended laboratory durability demonstration in the final program will require manufacturers of the largest heavy-duty engines to demonstrate emission control durability for a longer period to better ensure that in-use engines will meet emission standards throughout the long regulatory useful life of these engines.

CAA section 202(a)(3)(A) is a technology-forcing provision and reflects Congress' intent that standards be based on projections of future advances in pollution control capability, considering costs and other statutory factors. See

National Petrochemical & Refiners Association

EPA

, 287 F.3d 1130, 1136 (D.C. Cir. 2002) (explaining that EPA is authorized to adopt “technology-forcing” regulations under CAA section 202(a)(3));

NRDC

Thomas,

805 F.2d 410, 428 n.30 (D.C. Cir. 1986) (explaining that such statutory language that “seek[s] to promote technological advances while also accounting for cost does not detract from their categorization as technology-forcing standards”); see also

Husqvarna AB

EPA

, 254 F.3d 195 (D.C. Cir. 2001) (explaining that CAA sections 202 and 213 have similar language and are technology-forcing standards). In this context, the term “technology-forcing” has a specific legal meaning and is used to distinguish standards that may require manufacturers to develop new technologies (or significantly improve existing technologies) from standards that can be met using existing off-the-shelf technology alone. Technology-forcing standards such as those in this final rule do not require manufacturers to use specific technologies.

ii. Test Procedures To Control Emissions Under a Broader Range of Engine Operations

Many commenters supported our proposal to update our test procedures to more accurately account for and control emissions across a broader range of engine operation, including in urban driving conditions and other operations that could impact communities already overburdened with pollution. Consistent with our proposal, we are finalizing several provisions to reduce emissions from a broader range of engine operating conditions. First, we are finalizing new standards for our existing test procedures to reduce emissions under medium- and high-load operations (

e.g.,

when trucks are traveling on the highway). Second, we are finalizing new standards and a corresponding new test procedure to measure emissions during low-load operations (

i.e.,

the low-load cycle, LLC). Third, we are finalizing new standards and updates to an existing test procedure to measure emissions over the broader range of operations that occur when heavy-duty engines are operating on the road (

i.e.,

off-cycle).

Duty-cycle test procedures measure emissions while the engine is operating over precisely defined duty cycles in an emissions testing laboratory and provide very repeatable emission measurements. “Off-cycle” test procedures measure emissions while the engine is not operating on a specified duty cycle; this testing can be conducted while the engine is being driven on the road (

e.g.,

on a package delivery route), or in an emission testing laboratory. Both duty-cycle and off-cycle testing are conducted pre-production (

e.g.,

for certification) or post-production to verify that the engine meets applicable duty-cycle or off-cycle emission standards throughout useful life (see Section III for more discussion).

The new, more stringent numeric standards for the existing laboratory-based test procedures that measure emissions during medium- and high-load operations will ensure significant emissions reductions from heavy-duty engines. Without this final rule, these medium- and high-load operations are projected to contribute the most to heavy-duty NO

emissions in 2045.

We are finalizing as proposed a new LLC test procedure, which will ensure demonstration of emission control under sustained low-load operations. After further consideration of data included in the proposal, as well as additional information from the comments summarized in this section, we are finalizing the most stringent numeric LLC standard proposed for any model year. As discussed in our proposal, data from our CI engine demonstration program showed that the lowest numeric NO

standard proposed would be feasible for the LLC throughout a useful life period similar to the useful life period we are finalizing for the largest heavy-duty engines. After further consideration of this data, and additional support from data collected since the time of proposal, we are finalizing the most stringent standard proposed for any model year.

We are finalizing new numeric standards and revisions to the proposed off-cycle test procedure. We proposed updates to the current off-cycle test procedure that included binning emissions measurements based on the type of operation the engine is performing when the measurement data is being collected. Specifically, we proposed that emissions data would be grouped into three bins, based on whether the engine was operating in idle (Bin 1), low-load (Bin 2), or medium-to-high load (Bin 3). Given the different operational profiles of each of the three bins, we proposed a separate standard for each bin. Based on further consideration of data included in the proposal, as well as additional support from our consideration of data provided by commenters, we are finalizing off-cycle standards for two bins, rather than three bins; correspondingly, we are finalizing a two-bin approach for grouping emissions data collected during off-cycle test procedures. Our evaluation of available information shows that two bins better represent the

differences in engine operations that influence emissions (

e.g.,

exhaust temperature, catalyst efficiency) and ensure sufficient data is collected in each bin to allow for an accurate analysis of the data to determine if emissions comply with the standard for each bin. Preamble Section 0 further discusses the final off-cycle standards with additional detail in preamble Section III.

iii. Lengthening Emissions-Related Warranty

EPA received general support from many commenters for the proposal to lengthen the emissions-related warranty beyond existing requirements. Some commenters expressed support for one of the proposed options, and one organization suggested a warranty period even longer than either proposed option. Several stakeholders also commented on the costs of lengthened warranty periods and potential economic impacts. For instance, one state commenter supported EPA's cost estimates and agreed that the higher initial cost will be offset by lower repair costs; further, the commenter expects the resale value of lengthened warranty will be maintained for subsequent owners. In contrast, stakeholders in the heavy-duty engine and truck industry (

e.g.,

engine and vehicle manufacturers, truck dealers, suppliers of emissions control technologies) commented that the proposed warranty periods would add costs to vehicles, and raised concerns about these cost impacts on first purchasers. Many commenters indicated that purchase price increases due to the longer warranty periods may delay emission reductions, stating that high costs could incentivize pre-buy and reduce fleet turnover from old technology.

After further consideration of data included in the proposal, and consideration of additional supporting information from the comments summarized in this Section I.B.1.iii, we are finalizing a single-step increase for new, longer warranty periods to begin in MY 2027. Several commenters recommended we pull ahead the longest proposed warranty periods to start in MY 2027. We agree with that approach for the smaller heavy-duty engine classes, and our final warranty mileages match the longest proposed warranty periods for these smaller engines (

i.e.,

Spark-ignition HDE, Light HDE, and Medium HDE). However, we are finalizing a different approach for the largest heavy-duty engines (

i.e.,

Heavy HDE). We are finalizing a warranty mileage that matches the MY 2027 step of the most stringent proposed option to maximize the emission control assurance and to cover a percentage of the final useful life that is more consistent with the warranty periods of the smaller engine classes. The final emissions warranty periods are approximately two to four times longer than today's emissions warranty periods. The durations of the final emissions warranty periods balance two factors: First, the expected improvements in engine emission performance from longer emissions warranty periods due to increases in maintenance and lower rates of tampering with emissions controls (see preamble Section IV.B for more discussion); and second, the potential, particularly for the largest heavy-duty engines, for very large increases in purchase price due to much longer warranty periods to slow fleet turnover through increases in pre- and low-buy, and subsequently result in fewer emissions reductions. We are finalizing emissions warranty periods that in our evaluation will provide a significant increase in the emissions warranty coverage while avoiding large increases in the purchase price of a new truck.

iv. Model Year 2027 Single-Step Program

Many stakeholders expressed support for a single-step program to implement new emissions standards and program requirements beginning in model year 2027, which is consistent with one of the proposed options. Stakeholders in the heavy-duty engine and truck industry, including suppliers of emissions controls technologies, truck dealers, and engine manufacturers, generally stated that a single-step program avoids technology disruptions and allows industry to focus on research and development for zero-emissions vehicle technologies for model years beyond 2027. Some of these commenters further noted that a two-step approach would result in gaps in available technology for some vehicle types and could exacerbate slower fleet turnover from pre- and low-buy associated with new standards. The trade association for truck dealers noted that a two-step approach would significantly compromise expected vehicle performance characteristics, including fuel economy. Other commenters also generally supported a single-step approach in order for the most stringent standards to begin as soon as possible, which would lead to larger emissions reductions earlier than a two-step approach. Several of these stakeholders noted the importance of early emissions reductions in communities already overburdened with pollution.

The final NO

standards are a single-step program that reflect the greatest emission reductions achievable starting in MY 2027, giving appropriate consideration to costs and other factors. In this final rule, we are focused on achieving the greatest emission reductions achievable in the MY 2027 timeframe, and have applied our judgment in determining the appropriate standards for MY 2027 under our CAA authority for a national program. As the heavy-duty industry continues to transition to zero-emission technologies, EPA could consider additional criteria pollutant standards for model years beyond 2027 in future rules.

v. Averaging, Banking, and Trading of NO

Emissions

The majority of stakeholders supported the proposed program to allow averaging, banking, and trading (ABT) of NO

emissions, although several suggested adjustments for EPA to consider in the final rule. Stakeholders provided additional input on several specific aspects of the proposed ABT program, including the proposed family emissions limit (FEL) caps, the proposed Early Adoption Incentives, and the proposed allowance for manufacturers to generate NO

emissions credits from Zero Emissions Vehicles (ZEVs). In this Section we briefly discuss stakeholder perspectives on these specific aspects of the proposed ABT program, as well as our approach for each in the final rule.

a. Family Emissions Limit Caps

A wide range of stakeholders urged EPA to finalize a lower FEL cap than proposed; there was broad agreement that the FEL cap in the final rule should be 100 mg/hp-hr or lower, with commenters citing various considerations, such as the magnitude of reduction between the current and proposed standards, as well as the desire to prevent competitive disruption.

After further consideration, including consideration of public comments, we are finalizing lower FEL caps than proposed. The FEL caps in the final rule are 65 mg/hp-hr for MY 2027 through 2030, and 50 mg/hp-hr for MY 2031 and later. Our rationale for the final FEL caps includes two main factors. First, we agree with commenters that the difference between the current standard (approximately 200 mg/hp-hr) and the standards we are finalizing for MY 2027 and later suggests that FEL caps lower than the current standard are

appropriate to ensure that available emissions control technologies are adopted. This is consistent with our past practice when issuing rules for heavy-duty onroad engines or nonroad engines in which there was a substantial (

e.g.,

greater than 50 percent) difference between the numeric levels of the existing and new standards (69 FR 38997, June 29, 2004; 66 FR 5111, January 18, 2001). Specifically, by finalizing FEL caps below the current standards, we are ensuring that the vast majority of new engines introduced into commerce include updated emissions control technologies compared to the emissions control technologies manufacturers use to meet the current standards.

As discussed in Section IV.G.9, we are finalizing an allowance for manufacturers to continue to produce a small number (5 percent of production volume) of engines that meet the current standards for a few model years (

i.e.,

through MY 2030); thus, the vast majority of, but not all, new engines will need to include updated emissions control technologies compared to those used to meet today's standards until MY 2031, when all engines will need updated emissions control technologies to comply with the final standards or use credits up to the FEL cap. See Section IV.G.9 for details on our approach and rationale for including this allowance in the final rule.

Second, finalizing FEL caps below the current standard is consistent with comments from manufacturers stating that a FEL cap of 100 mg/hp-hr or between 50 and 100 mg/hp-hr would help to prevent competitive disruptions (

i.e.,

require all manufacturers to make improvements in their emissions control technologies).

The FEL caps for the final rule have been set at a level to ensure sizeable emission reductions from the current 2010 standards, while providing manufacturers with flexibility in meeting the final standards. When combined with the other restrictions in the final ABT program (

i.e.,

credit life, averaging sets, expiration of existing credit balances), we determined the final FEL caps of 65 mg/hp-hr in MYs 2027 through 2030, and 50 mg/hp-hr in MY 2031 and later avoid potential adverse effects on the emissions reductions expected from the final program.

b. Encouraging Early Adoption of New Emissions Controls Technologies

Several stakeholders provided general comments on the proposed Early Adoption Incentive program, which included emissions credit multipliers of 1.5 or 2.0 for meeting all proposed requirements prior to the applicable model year. Although many of the stakeholders in the heavy-duty engine industry generally supported incentives such as emissions credit multipliers to encourage early investments in emissions reductions technology; other industry stakeholders were concerned that the multipliers would incentivize some technologies (

e.g.,

hybrid powertrains, natural gas engines) over others (

e.g.,

battery-electric vehicles). Environmental organizations and other commenters were concerned that the emissions credit multipliers would result in an excess of credits that would undermine some of the benefits of the rule.

After consideration of public comments, EPA is not finalizing the proposed Early Adoption Incentives program, and in turn we are not including emissions credit multipliers in the final program. Rather, we are finalizing an updated version of the proposed transitional credit program under the ABT program. As described in preamble Section IV.G.7, the transitional credit program that we are finalizing provides four pathways to generate straight NO

emissions credits (

i.e.,

no credit multipliers) in order to encourage the early introduction engines with NO

-reducing technology.

c. Heavy-Duty Zero Emissions Vehicles and NO

Emissions Credits

Numerous stakeholders provided feedback on EPA's proposal to allow manufacturers to generate NO

emissions credits from ZEVs. Environmental organizations and other commenters, as well as suppliers of heavy-duty engine and vehicle components, broadly oppose allowing manufacturers to generate NO

emissions credits from ZEVs. These stakeholders present several lines of argument, including the potential for: (1) Substantial impacts on the emissions reductions expected from the proposed rule, which could also result in disproportionate impacts in disadvantaged communities already overburdened with pollution; and (2) higher emissions from internal combustion engines, rather than further incentives for additional ZEVs (further noting that other State and Federal actions are providing more meaningful and less environmentally costly HD ZEV incentives). In contrast, heavy-duty engine and vehicle manufacturers generally support allowing manufacturers to generate these credits. These stakeholders also provided several lines of argument, including: (1) The potential for ZEVs to help meet emissions reductions and air quality goals; (2) an assertion that ZEV NO

credits are essential to the achievability of the standards for some manufacturers; and (3) ZEV NO

credits allow manufacturers to manage investments across different products that may ultimately result in increased ZEV deployment.

After further consideration, including consideration of public comments, we are not finalizing the allowance for manufacturers to generate NO

emissions credits from heavy-duty ZEVs. Our decision is based on two primary considerations. First, the standards in the final rule are technology-forcing, yet achievable for MY 2027 and later internal combustion engines without this flexibility. Second, because the final standards are not based on projected utilization of ZEV technology, and because we believe there will be increased penetration of ZEVs in the heavy-duty fleet by MY 2027 and later,

we are concerned that allowing ZEVs to generate NO

emissions credits would result in fewer emissions reductions than intended from this rule. For example, by allowing manufacturers to generate ZEV NO

credits, EPA would be allowing higher emissions (through internal combustion engines using credits to emit up to the FEL cap) in MY 2027 and later, without requiring commensurate emissions reductions (through additional ZEVs beyond those already entering the market without this rule). This erosion of emissions benefits could have particularly adverse impacts in communities already overburdened by pollution. In addition, we continue to believe that testing requirements to ensure continued battery and fuel cell performance over the useful life of a ZEV may be important to ensure the zero-emissions tailpipe performance for which they are generating NO

credits; however, after further consideration, including consideration of public comments, we believe it is appropriate to take additional time to work with industry and other stakeholders on any test procedures and other specifications for ZEV battery and fuel cell performance over the useful life period of the ZEV.

For example, the recently passed Inflation Reduction Act (IRA) has many incentives for promoting zero-emission vehicles, see Sections 13403 (Qualified Clean Vehicles), 13404 (Alternative Fuel Refueling Property Credit), 60101 (Clean Heavy-Duty Vehicles), 60102 (Grants to Reduce Air Pollution at Ports), and 70002 (United States Postal Service Clean Fleets) of H. R. 5376.

2. Summary of the Key Provisions in the Regulatory Action

i. Controlling Criteria Pollutant Emissions Under a Broader Range of Operating Conditions

The final rule provisions will reduce emissions from heavy-duty engines

under a range of operating conditions through revisions to our emissions standards and test procedures. These revisions will apply to both laboratory-based standards and test procedures for both heavy-duty CI and SI engines, as well as the off-cycle standards and test procedures for heavy-duty CI engines. These final provisions are outlined immediately below and detailed in Section III.

a. Final Laboratory Standards and Test Procedures

For heavy-duty CI engines, we are finalizing new standards for laboratory-based tests using the current duty cycles, the transient Federal Test Procedure (FTP) and the steady-state Supplemental Emission Test (SET) procedure. These existing test procedures require CI engine manufacturers to demonstrate the effectiveness of emission controls when the engine is transitioning from low-to-high loads or operating under sustained high load, but do not include demonstration of emission control under sustained low-load operations. As proposed, we are finalizing a new, laboratory-based LLC test procedure for heavy-duty CI engines to demonstrate emission control when the engine is operating under low-load and idle conditions. The addition of the LLC will help ensure lower NO

emissions in urban areas and other locations where heavy-duty vehicles operate in stop-and-go traffic or other low-load conditions. As stated in Section I.B.1, we are finalizing the most stringent standard proposed for any model year for low-load operations based on further evaluation of data included in the proposal, and supported by information received during the comment period. We are also finalizing as proposed the option for manufacturers to test hybrid engines and powertrains together using the final powertrain test procedure.

For heavy-duty SI engines, we are finalizing new standards for laboratory-based testing using the current FTP duty cycle, as well as updates to the current engine mapping procedure to ensure the engines achieve the highest torque level possible during testing. We are also finalizing the proposed addition of the SET duty-cycle test procedure to the heavy-duty SI laboratory demonstrations; it is currently only required for heavy-duty CI engines. Heavy-duty SI engines are increasingly used in larger heavy-duty vehicles, which makes it more likely for these engines to be used in higher-load operations covered by the SET.

Our final NO

emission standards for all defined duty cycles for heavy-duty CI and SI engines are detailed in Table I-1. As shown, the final NO

standards will be implemented with a single step in MY 2027 and reflect the greatest emission reductions achievable starting in MY 2027, giving appropriate consideration to costs and other factors. As discussed in I.B.1.i, for the largest heavy-duty engines we are finalizing two updates to our testing requirements to ensure the greatest emissions reductions technically achievable are met throughout the final useful life periods of the largest heavy-duty engines: (1) A requirement for manufacturers to demonstrate before heavy heavy-duty engines are in-use that the emissions control technology are durable through a period of time longer than the final useful mileage, and (2) a compliance allowance that applies when EPA evaluates whether medium or heavy heavy-duty engines are meeting the final standards after these engines are in-use in the real world. We requested comment on an interim compliance allowance, and it is consistent with our past practice (for example, see 66 FR 5114, January 18, 2001); the interim compliance allowance is shown in the final column of Table I-1. See Section III for more discussion on feasibility of the final standards. Consistent with our existing, MY 2010 standards for criteria pollutants, the final standards, presented in Table 1, are numerically identical for SI and CI engines.

See Section III for our final PM, HC, and CO standards.

Table I-1—Final NO

Emission Standards for Heavy-Duty CI and SI Engines on Specific Duty Cycles

[milligrams/horsepower-hour (mg/hp-hr)]

Current

All HD

engines

Model years 2027 and later

Spark

ignition HDE, light HDE, medium HDE,

and heavy HDE

Medium and

heavy HDE

with interim in-use

compliance

allowance

Federal Test Procedure (transient mid/high load conditions)

200

Supplemental Emission Test (steady-state conditions)

200

Low Load Cycle (low-load conditions)

N/A

b. Final On-the-Road Standards and Test Procedures

In addition to demonstrating emission control over defined duty cycles tested in a laboratory, heavy-duty CI engines must be able to demonstrate emission control over operations experienced while engines are in use on the road in the real world (

i.e.,

“off-cycle” testing).

We are finalizing with revisions the proposed updates to the procedure for off-cycle testing, such that data collected during a wider range of operating conditions will be valid, and therefore subject to emission standards.

As discussed in Section III, “off-cycle” testing measures emissions while the engine is not operating on a specified duty cycle; this testing can be conducted while the engine is being driven on the road (

e.g.,

on a package delivery route), or in an emission testing laboratory.

Similar to the current approach, emission measurements collected during off-cycle testing will be collected on a second-by-second basis. As proposed, we are finalizing that the emissions data will be grouped into 300-second windows of operation. Each 300-second window will then be binned based on the type of operation that the engine performs during that 300-second period. Specifically, the average power of the engine during each 300-second window will determine whether the emissions during that window are binned as idle (Bin 1), or non-idle (Bin 2).

Due to the challenges of measuring engine power directly on in-use vehicles, we are finalizing as proposed the use of the CO

emission rate (grams per second) as a surrogate for engine power; further, we are finalizing as proposed to normalize CO

emission rates relative to the nominal maximum CO

rate of the engine (

e.g.,

when an engine with

a maximum CO

emission rate of 50 g/sec emits at a rate of 10 g/sec, its normalized CO

emission rate is 20 percent).

Our final, two-bin approach covers a wide range of operations that occur in the real world—significantly more in-use operation than today's requirements. Bin 1 includes extended idle and other very low-load operations, where engine exhaust temperatures may drop below the optimal temperature where SCR-based aftertreatment works best. Bin 2 includes a large fraction of urban driving conditions, during which engine exhaust temperatures are generally moderate, as well as higher-power operations, such as on-highway driving, that typically results in higher exhaust temperatures and high catalyst efficiencies.

Given the different operational profiles of each of these two bins, we are finalizing, as proposed, a separate standard for each bin. As proposed, the final structure follows that of our current not-to-exceed (NTE) off-cycle standards where testing is conducted while the engine operates on the road conducting its normal driving patterns, however, the final standards apply over a much broader range of engine operation.

Because the final approach considers time-averaged power, either of the bins could include some idle operation and any of the bins could include some high-power operation.

Table I-2 presents our final off-cycle standards for NO

emissions from heavy-duty CI engines. As discussed in I.B.1.i, for the medium and heavy heavy-duty engines we are also finalizing an interim compliance allowance that applies to non-idle (Bin 2) off-cycle standard after the engines are in-use. This interim compliance allowance is consistent with our past practice (for example, see 66 FR 5114, January 18, 2001) and is shown in the final column of Table I-2. See Section III for details on the final off-cycle standards for other pollutants.

Table I-2—Final Off-Cycle NO

Standards for Heavy-Duty CI Engines

Model years 2027 and later

Light HDE,

medium HDE,

heavy HDE

Medium HDE

and heavy HDE

with in-use

compliance

allowance

Bin 1: Idle (g/hr)

10.0

Bin 2: Low/medium/high load (mg/hp-hr)

The standards reflected in Table I-2 are applicable at 25 °C and above; at lower temperatures the numerical off-cycle Bin 1 and Bin 2 standards for NO

adjust as a function of ambient air temperature (see preamble Section III.C for details).

The interim compliance allowance we are finalizing for medium and heavy heavy-duty engines does not apply to the Bin 1 (Idle) off-cycle standard (see preamble Section III for details).

In addition to the final standards for the defined duty cycle and off-cycle test procedures, the final standards include several other provisions for controlling emissions from specific operations in CI or SI engines. First, we are finalizing, as proposed, to allow CI engine manufacturers to voluntarily certify to idle standards using a new idle test procedure that is based on an existing California Air Resources Board (CARB) procedure.

13 CCR 1956.8 (a)(6)(C)—Optional NO

idling emission standard.

We are also finalizing two options for manufacturers to control engine crankcase emissions. Specifically, manufacturers will be required to either: (1) As proposed, close the crankcase, or (2) measure and account for crankcase emissions using an updated version of the current requirements for an open crankcase. We believe that either will ensure that the total emissions are accounted for during certification testing and throughout the engine operation during useful life. See Section III.B for more discussion on both the final idle and crankcase provisions.

For heavy-duty SI, we are finalizing as proposed a new refueling emission standard for incomplete vehicles above 14,000 lb GVWR starting in MY 2027.

The final refueling standard is based on the current refueling standard that applies to complete heavy-duty gasoline-fueled vehicles. Consistent with the current evaporative emission standards that apply for these same vehicles, we are finalizing a requirement that manufacturers can use an engineering analysis to demonstrate that they meet our final refueling standard. We are also adopting an optional alternative phase-in compliance pathway that manufacturers can opt into in lieu of being subject to this implementation date for all incomplete heavy-duty vehicles above 14,000 pounds GVWR (see Section III.E for details).

Some vehicle manufactures sell their engines or “incomplete vehicles” (

i.e.,

chassis that include their engines, the frame, and a transmission) to body builders who design and assemble the final vehicle.

ii. Ensuring Standards Are Met Over a Greater Portion of an Engine's Operational Life

In addition to reducing emissions under a broad range of engine operating conditions, the final program also includes provisions to ensure emissions standards are met over a greater portion of an engine's operational life. These final provisions include: (1) Lengthened regulatory useful life periods for heavy-duty engines, (2) revised requirement for the largest heavy-duty engines to demonstrate that the emissions control technology is durable through a period of time longer than the final useful life mileage, (3) updated methods to more accurately and efficiently demonstrate the durability of emissions controls, (4) lengthened emission warranty periods, and (5) increased assurance that emission controls will be maintained properly through more of the service life of heavy-duty engines. Each of these final provisions is outlined immediately below and detailed in Section IV.

a. Final Useful Life Periods

Consistent with the proposal, the final useful life periods will cover a significant portion of the engine's operational life.

The longer useful life periods, in combination with the durability demonstration requirements we are finalizing in this rule, are expected to lead manufacturers to further improve the durability of their

emission-related components. After additional consideration of data included in the proposal, as well as additional data provided in public comments, we are modifying our proposed useful life periods to account for the combined effect of useful life and the final numeric standards on the overall stringency and emissions reductions of the program (see Section IV.A for additional details).

We consider operational life to be the average mileage at rebuild for CI engines and the average mileage at replacement for SI engines (see preamble Section IV.A for details).

For smaller heavy-duty engines (

i.e.,

Spark-ignition HDE, Light HDE, and Medium HDE) we are finalizing the longest useful life periods proposed (

i.e.,

MY 2031 step of proposed option 1), to apply starting in MY 2027. The final useful life mileage for Heavy HDE, which has a distinctly longer operational life than the smaller engine classes, is approximately 50 percent longer than today's useful life mileage for these engines and matches the longest useful life we proposed for MY 2027. Our final useful life periods for all heavy-duty engine classes are presented in Table I-3. We are also increasing the years-based useful life from the current 10 years to values that vary by engine class and match the respective proposed options. After considering comments, we are also adding hours-based useful life values to all engine categories based on a 20 mile per hour speed threshold and the corresponding final mileage values.

As noted in this I.B.2, we are finalizing, as proposed, refueling standards for certain HD SI engines that apply for a useful life of 15 years or 150,000 miles. See 40 CFR 1037.103(f) and preamble Section IV.A for more details.

Table I-3—Current and Final Useful Life Periods for Heavy-Duty CI and SI Engines

Primary intended service class

Current

Miles

Years

Hours

MY 2027 and later

Miles

Years

Hours

Spark-ignition HDE

110,000

200,000

10,000

Light HDE

110,000

270,000

13,000

Medium HDE

185,000

350,000

17,000

Heavy HDE

435,000

22,000

650,000

32,000

Current useful life period for Spark-ignition HDE and Light HDE for GHG emission standards is 15 years or 150,000 miles; we are not revising these useful life periods in this final rule. See 40 CFR 1036.108(d).

As discussed in Section I.B.2.ii.c, we are finalizing a requirement for manufacturers to demonstrate at the time of certification that the emissions controls on these largest heavy-duty engines are durable through the equivalent of 750,000 miles.

b. Extended Laboratory Demonstration of Emissions Control Durability for the Largest Heavy-Duty Engines

As discussed in Section I.B.1.i, for the largest heavy-duty engines we are finalizing two updates to our proposed testing requirements in order to ensure the greatest emissions reductions technically achievable are met throughout the final useful life periods of these engines. One of the approaches (an in-use interim compliance allowance for medium and heavy heavy-duty engines) was noted in Section I.B.2.i; here we focus on the requirement for manufacturers to demonstrate before the largest heavy-duty engines are in use that the emissions control technology is durable through a period of time longer than the final useful mileage. Specifically, we are finalizing a requirement for manufacturers to demonstrate before the largest heavy-duty engines are in use that the emissions controls on these engines are durable (

e.g.,

capable of controlling NO

emissions over the FTP duty-cycle at a level of 35 mg/hp-hr) through the equivalent of 750,000 miles. The extended durability demonstration in a laboratory environment will better ensure the final standards will be met throughout the longer final regulatory useful life mileage of 650,000 miles when these engines are operating in the real world where conditions are more variable.

As discussed immediately below in Section I.B.2.ii.c, we are also finalizing provisions to improve the accuracy and efficiency of emissions control durability demonstrations for all heavy-duty engine classes.

Once these engines are in use, EPA can require manufacturers to submit test data, or can conduct our own testing, to verify that the emissions control technologies continue to control emissions through the 650,000 mile useful life period (or the equivalent hours or years requirements as applicable).

c. Final Durability Demonstration

EPA regulations require manufacturers to include durability demonstration data as part of an application for certification of an engine family. Manufacturers typically complete this demonstration by following regulatory procedures to calculate a deterioration factor (DF). The final useful life periods outlined in Table I-4 will require manufacturers to extend their durability demonstrations to show that the engines will meet applicable emission standards throughout the lengthened useful life.

To address the need for accurate and efficient emission durability demonstration methods, EPA worked with manufacturers and CARB to address this concern through guidance for MY 2020 and later engines.

Consistent with the recent guidance, we proposed three methods for determining DFs. We are finalizing two of the three proposed methods; we are not finalizing the option to perform a fuel-based accelerated DF determination, noting that it has been shown to underestimate emission control system deterioration. The two methods we are finalizing include: (1) Allowing manufacturers to continue the current practice of determining DFs based on engine dynamometer-based aging of the complete engine and aftertreatment system out to regulatory useful life, and (2) a new option to bench-age the aftertreatment system at an accelerated rate to limit the burden of generating a DF over the final lengthened useful life periods. If manufacturers choose the second option (accelerated bench-aging of the aftertreatment system), then they may also choose to use an accelerated aging test procedure that we are codifying in this final rule; the test procedure is, based on a test program that we introduced in the proposal to evaluate a rapid-aging protocol for diesel catalysts. We are also finalizing with revisions two of the three proposed DF verification options to confirm the accuracy of the DF values submitted by manufacturers for certification. After further consideration of data included in the proposal, as well as supported by

information provided in public comments, we are finalizing that, upon EPA request, manufacturers would be required to provide confirmation of the DF accuracy through one of two options.

U.S. EPA. “Guidance on Deterioration Factor Validation Methods for Heavy-Duty Diesel Highway Engines and Nonroad Diesel Engines equipped with SCR.” CD-2020-19 (HD Highway and Nonroad). November 17, 2020.

d. Final Emission-Related Warranty Periods

We are updating and significantly strengthening the emission-related warranty periods, for model year 2027 and later heavy-duty engines.

We are finalizing most of the emission-related warranty provisions of 40 CFR 1036.120 as proposed. Following our approach for useful life, we are revising the proposed warranty periods for each primary intended service class to reflect the difference in average operational life of each class and in consideration of the information provided by commenters (see preamble Section IV and the Response to Comments document for details).

Components installed to control only criteria pollutant emissions or both greenhouse gas (

i.e.,

, N

O, and CH

) and criteria pollutant emissions would be subject to the final warranty periods of 40 CFR 1036.120. See 40 CFR 1036.150(w).

EPA's current emissions-related warranty periods for heavy-duty engines range from 22 percent to 54 percent of the current regulatory useful life. Notably, these percent values have decreased over time given that the warranty periods have not changed since 1983 even as the useful life periods were lengthened.

The revised warranty periods are expected to result in better maintenance, including maintenance of emission-related components, and less tampering, which would help to ensure the benefits of the emission controls in-use. In addition, longer regulatory warranty periods may lead engine manufacturers to simplify repair processes and make them more aware of system defects that need to be tracked and reported to EPA.

The useful life for heavy heavy-duty engines was increased from 290,000 miles to 435,000 miles for 2004 and later model years (62 FR 54694, October 21, 1997).

Our final emission-related warranty periods for heavy-duty engines are presented in Table I-4. The final warranty mileages that apply starting in MY 2027 for Spark-ignition HDE, Light HDE, and Medium HDE match the longest warranty mileages proposed (

i.e.,

MY 2031 step of proposed Option 1) for these primary intended service classes. For Heavy HDE, which has a distinctly longer operational life, the final warranty mileage matches the longest warranty mileage proposed to apply in MY 2027 (

i.e.,

MY 2027 step of proposed Option 1), and is more than four times longer than today's warranty mileage for these engines. We are also increasing the years-based warranty from the current 5 years to 10 years for all engine classes. After considering comments, we are also adding hours-based warranty values to all primary intended service classes based on a 20 mile per hour speed threshold and the corresponding final mileage values. Consistent with current warranty provisions, the warranty period would be whichever warranty value (

i.e.,

mileage, hours, or years) occurs first.

Table I-4—Current and Final Emission-Related Warranty Periods for Heavy-Duty CI and SI Engines Criteria Pollutant Standards

Primary intended service class

Current

Mileage

Years

Hours

Model year 2027 and later

Mileage

Years

Hours

Spark-Ignition HDE

50,000

160,000

8,000

Light HDE

50,000

210,000

10,000

Medium HDE

100,000

280,000

14,000

Heavy HDE

100,000

450,000

22,000

e. Provisions To Ensure Long-Term Emissions Performance

We proposed several approaches for an enhanced, comprehensive strategy to increase the likelihood that emission controls will be maintained properly through more of the operational life of heavy-duty engines, including beyond their useful life periods. These approaches include updated maintenance provisions, revised requirements for the owner's manual and emissions label, codified engine derates or “inducements” regulations, and updated onboard diagnostics (OBD) regulations.

Our final updates to maintenance provisions include defining the type of maintenance manufacturers may choose to recommend to owners in maintenance instructions, updating minimum maintenance intervals for certain critical emission-related components, and outlining specific requirements for maintenance instructions provided in the owner's manual.

We are finalizing changes to the owner's manual and emissions label requirements to ensure access to certain maintenance information and improve serviceability. We expect this additional maintenance information to improve factors that contribute to mal-maintenance, which would result in better service experiences for independent repair technicians, specialized repair technicians, owners who repair their own equipment, and possibly vehicle inspection and maintenance technicians. We also believe improving owner experiences with operating and maintaining heavy-duty engines can reduce the likelihood of tampering.

In addition, we are adopting inducement regulations that are an update to and replace existing guidance regarding recommended methods for manufacturers to reduce engine performance to induce operators to maintain appropriate levels of high-quality diesel emission fluid (DEF) in their SCR-based aftertreatment systems and discourage tampering with such systems. See Section IV.D for details on the principles we followed to develop multi-step derate schedules that are tailored to different operating characteristics, as well as changes in the final rule inducement regulations from the proposal.

We are also finalizing updated OBD regulations both to better address newer diagnostic methods and available technologies, and to streamline provisions where possible. We are incorporating by reference the current CARB OBD regulations, updated in 2019, as proposed.

Specifically, manufacturers must comply with OBD requirements as referenced in the CARB

OBD regulations starting in model year 2027, with optional compliance based on the CARB OBD regulations for earlier model years. After considering comments, many of which included specific technical information and requests for clarification, we are finalizing certain provisions with revisions from proposal and postponing others for consideration in a future rulemaking (see Section IV.C for details).

CARB's 2019 Heavy-duty OBD Final Regulation Order was approved and became effective October 3, 2019. Title 13, California Code of Regulations sections 1968.2, 1968.5, 1971.1, and 1971.5, available at

https://ww2.arb.ca.gov/rulemaking/2018/heavy-duty-board-diagnostic-system-requirements-2018

iii. Averaging, Banking, and Trading of NO

Emissions Credits

In addition the key program provisions, EPA is finalizing an averaging, banking, and trading (ABT) program for heavy-duty engines that provides manufacturers with flexibility in their product planning while encouraging the early introduction of emissions control technologies and maintaining the expected emissions reductions from the program. Several core aspects of the final ABT program are consistent with the proposal, but the final ABT program also includes several updates after consideration of public comments. In particular, EPA requested comment on and agrees with commenters that a lower family emission limit (FEL) cap than proposed is appropriate for the final rule. Further, after consideration of public comments, EPA is choosing not to finalize at this time the proposed Early Adoption Incentives program, and in turn we are not including emissions credit multipliers in the final program. Rather, we are finalizing an updated version of the proposed transitional credit program under the ABT program. The revised transitional credit program that we are finalizing provides four pathways to generate NO

emissions credits in MYs 2022 through 2026 that are valued based on the extent to which the engines generating credits comply with the requirements we are finalizing for MY 2027 and later (

e.g.,

credits discounted at a rate of 40 percent for engines meeting a lower numeric standard but none of the other MY 2027 and later requirements). Specifically, the four transitional credit pathways in the final rule are: (1) In MY 2026, for heavy heavy-duty or medium heavy-duty engine service classes, certify all engines in the manufacturer's respective service class to a FEL of 50 mg/hp-hr or less and meet all other EPA requirements for MYs 2027 and later to generate undiscounted credits that have additional flexibilities for use in MYs 2027 and later (2026 Service Class Pull Ahead Credits); (2) starting in MY 2024, certify one or more engine family(ies) to a FEL below the current MY 2010 emissions standards and meet all other EPA requirements for MYs 2027 and later to generate undiscounted credits based on the longer UL periods included in the 2027 and later program (Full Credits); (3) starting in MY 2024, certify one or more engine family(ies) to a FEL below the current MY 2010 emissions standards and several of the key requirements for MYs 2027 and later, while meeting the current useful life and warranty requirements to generate undiscounted credits based on the shorter UL period (Partial Credits); (4) starting in MY 2022, certify one or more engine family(ies) to a FEL below the current MY 2010 emissions standards, while complying with all other MY2010 requirements, to generate discounted credits (Discounted Credits). We note that the transitional credit and main ABT program we are finalizing does not allow engines certified to state standards that are different than the Federal EPA standards to generate Federal EPA credits.

In addition, we are finalizing an optional production volume allowance for MYs 2027 through 2029 that is consistent with our request for comment in the proposal but different in several key aspects, including a requirement for manufacturers to use NO

emissions credits to certify heavy heavy-duty engines compliant with MY 2010 requirements in MYs 2027 through 2029. Finally, we have decided not to finalize an allowance for manufacturers to generate NO

emissions credits from heavy-duty ZEVs (see Section IV.G for details on the final ABT program).

iv. Migration From 40 CFR Part 86, Subpart A

Heavy-duty criteria pollutant regulations were originally codified into 40 CFR part 86, subpart A, in the 1980s. As discussed in the proposal, this rulemaking provides an opportunity to clarify and improve the wording of our existing heavy-duty criteria pollutant regulations in plain language and migrate them to 40 CFR part 1036.

Part 1036, which was created for the Phase 1 GHG program, provides a consistent, updated format for our heavy-duty regulations, with improved organization. In general, this migration is not intended to change the compliance program specified in part 86, except as specifically stated in this final rulemaking. See our summary of the migration in Section III.A. The final provisions of part 1036 will generally apply for model years 2027 and later, unless noted, and manufacturers will continue to use part 86 in the interim.

We are also adding and amending some provisions in parts 1065 and 1068 as part of the migration from part 86 for heavy-duty highway engines; these provisions in part 1065 and 1068 will apply to other sectors that are already subject to part 1065 and 1068. Additionally, some current vehicle provisions in part 1037 refer to part 86 and, as proposed, the final rule updates those references in part 1037 as needed.

v. Technical Amendments to Regulatory Provisions for Mobile Source Sectors

EPA has promulgated emission standards for highway and nonroad engines, vehicles, and equipment. Section XI of this final rule describes several amendments to correct, clarify, and streamline a wide range of regulatory provisions for many of those different types of engines, vehicles, and equipment. Section XI.A includes technical amendments to compliance provisions that apply broadly across EPA's emission control programs to multiple industry sectors, including light-duty vehicles, light-duty trucks, marine diesel engines, locomotives, and various other types of nonroad engines, vehicles, and equipment. Some of those amendments are for broadly applicable testing and compliance provisions in 40 CFR parts 1065, 1066, and 1068. Other cross-sector issues involve making the same or similar changes in multiple standard-setting parts for individual industry sectors. The rest of Section XI describes amendments we are finalizing that apply uniquely for individual industry sectors. Except as specifically identified in this rulemaking, EPA did not reopen any of the underlying provisions across these standard setting parts.

We are finalizing amendments in two areas of note for the general compliance provisions in 40 CFR part 1068. First, we are finalizing, with updates from proposal, a comprehensive approach for making confidentiality determinations related to compliance information that companies submit to or is collected by EPA. These provisions apply for highway, nonroad, and stationary engine, vehicle, and equipment programs, as well as aircraft and portable fuel containers.

Second, we are finalizing, with updates from proposal, provisions that include clarifying text to establish what qualifies as an adjustable parameter and to identify the practically adjustable range for those adjustable parameters. The adjustable-parameter provisions in the final rule also include specific provisions related to electronic controls that aim to deter tampering.

C. Impacts of the Standards

1. Projected Emission Reductions and Air Quality Improvements

Our analysis of the estimated emission reductions, air quality improvements, costs, and monetized benefits of the final rule is outlined in this section and detailed in Sections V through X. The final standards, which are described in detail in Sections III and IV, are expected to reduce emissions from highway heavy-duty engines in several ways. We project the final emission standards for heavy-duty CI engines will reduce tailpipe emissions of NO

; the combination of the final low-load test cycle and off-cycle test procedure for CI engines will help to ensure that the reductions in tailpipe emissions are achieved in-use, not only under high-speed, on-highway conditions, but also under low-load and idle conditions. We also project reduced tailpipe emissions of NO

from the final emission standards for heavy-duty SI engines, as well as reductions of CO, PM, VOCs, and associated air toxics, particularly under cold-start and high-load operating conditions. The final emissions warranty and regulatory useful life requirements for heavy-duty CI and SI engines will also help maintain emissions controls of all pollutants beyond the existing useful life periods, which will result in additional emissions reductions of all pollutants from both CI and SI engines, including primary exhaust PM

2.5

. The onboard refueling vapor recovery requirements for heavy-duty SI engines will reduce VOCs and associated air toxics. Table I-5 summarizes the projected reductions in heavy-duty emissions from the final standards in 2045 and shows the significant reductions in NO

emissions. Section VI and Regulatory Impact Analysis (RIA) Chapter 5 provide more information on our projected emission reductions for the final rule.

Table I-5—Projected Heavy-Duty Emission Reductions in 2045 From the Final Standards

Pollutant

Percent

reduction

in highway

heavy-duty

emissions

(percent)

Primary PM

2.5

VOC

The final standards will also reduce emissions of other pollutants. For instance, the final rule will result in a 28 percent reduction in benzene from highway heavy-duty engines in 2045. Leading up to 2045, emission reductions are expected to increase over time as the fleet turns over to new, compliant engines.

We expect this rule will decrease ambient concentrations of air pollutants, including significant improvements in ozone concentrations in 2045, as demonstrated in the air quality modeling analysis. We also expect reductions in ambient PM

2.5

, NO

and CO due to this rule. The emission reductions provided by the final standards will be important in helping areas attain and maintain the NAAQS and prevent future nonattainment. This rule's emission reductions will also reduce air pollution in close proximity to major roadways, reduce nitrogen deposition and improve visibility.

Our consideration of environmental justice literature indicates that people of color and people with low income are disproportionately exposed to elevated concentrations of many pollutants in close proximity to major roadways. We also used our air quality data from the proposal to conduct a demographic analysis of human exposure to future air quality in scenarios with and without the rule in place. Although the spatial resolution of the air quality modeling is not sufficient to capture very local heterogeneity of human exposures, particularly the pollution concentration gradients near roads, the analysis does allow estimates of demographic trends at a national scale. To compare demographic trends, we sorted 2045 baseline air quality concentrations from highest to lowest concentration and created two groups: Areas within the contiguous United States with the worst air quality and the rest of the country. We found that in the 2045 baseline, the number of people of color living within areas with the worst air quality is nearly double that of non-Hispanic Whites. We also found that the largest predicted improvements in both ozone and PM

2.5

are estimated to occur in areas with the worst baseline air quality, where larger numbers of people of color are projected to reside. An expanded analysis of the air quality impacts experienced by specific race and ethnic groups found that non-Hispanic Blacks will receive the greatest improvement in PM

2.5

and ozone concentrations as a result of the standards. More details on our air quality modeling and demographic analyses are included in Section VII and RIA Chapter 6.

2. Summary of Costs and Benefits

Our estimates of reductions in heavy-duty engine emissions and the associated air quality impacts are based on manufacturers adding emissions-reduction technologies and making emission control components more durable in response to the final standards and longer regulatory useful life periods; our estimates of emissions reductions also account for improved repair of emissions controls by owners in response to the longer emissions-related warranty periods and other provisions in the final rule.

Our program cost analysis includes both the total technology costs (

i.e.,

manufacturers' costs to add or update emissions control technologies) and the operating costs (

i.e.,

owners' costs to maintain and operate MY 2027 and later vehicles) (see Section V and RIA Chapter 7). Our evaluation of total technology costs of the final rule includes direct costs (

i.e.,

cost of materials, labor costs) and indirect manufacturing costs (

e.g.,

warranty, research and development). The direct manufacturing costs include individual technology costs for emission-related engine components and for exhaust aftertreatment systems. Importantly, our analysis of direct manufacturing costs includes the costs of the existing emission control technologies, because we expect the emissions warranty and regulatory useful life provisions in the final standards to have some impact on not only the new technology added to comply with the standards, but also on any existing emission control components. The cost estimates thus account for existing engine hardware and aftertreatment systems for which new costs will be incurred due to the new warranty and useful life provisions, even absent any changes in the level of emission standards. The indirect manufacturing costs in our analysis include the additional costs—research and development, marketing, administrative costs, etc.—incurred by manufacturers in running the company.

As part of our evaluation of operating costs, we estimate costs truck owners incur to repair emission control system components. Our repair cost estimates are based on industry data showing the amount spent annually by truck owners on different types of repairs, and our estimate of the percentage of those repairs that are related to emission control components. Our analysis of this data shows that extending the useful life and emission warranty periods will lower emission repair costs during several years of operation for several vehicle types. More discussion on our

emission repair costs estimates is included in Section V, with additional details presented in RIA Chapter 7.

We combined our estimates of emission repair costs with other operating costs (

i.e.,

urea/DEF, fuel consumption) and technology costs to calculate total program costs. Our analysis of the final standards shows that total costs for the final program relative to the baseline (or no action scenario) range from $3.9 billion in 2027 to $4.7 billion in 2045 (2017 dollars, undiscounted, see Table V-16). The present value of program costs for the final rule, and additional details are presented in Section V.

Section VIII presents our analysis of the human health benefits associated with the final standards. We estimate that in 2045, the final rule will result in total annual monetized ozone- and PM

2.5

-related benefits of $12 and $33 billion at a 3 percent discount rate, and $10 and $30 billion at a 7 percent discount rate.

These benefits only reflect those associated with reductions in NO

emissions (a precursor to both ozone and secondarily-formed PM

2.5

) and directly-emitted PM

2.5

from highway heavy-duty engines.

2045 is a snapshot year chosen to approximate the annual health benefits that occur when the final program will be fully implemented and when most of the regulated fleet will have turned over.

There are additional human health and environmental benefits associated with reductions in exposure to ambient concentrations of PM

2.5

, ozone, and NO

that EPA has not quantified due to data, resource, or methodological limitations. There will also be health benefits associated with reductions in air toxic pollutant emissions that result from the final program, but we did not attempt to quantify or monetize those impacts due to methodological limitations. Because we were unable to quantify and monetize all of the benefits associated with the final program, the monetized benefits presented in this analysis are an underestimate of the program's total benefits. More detailed information about the benefits analysis conducted for the final rule, including the present value of program benefits, is included in Section VIII and RIA Chapter 8.

We compare total monetized health benefits to total costs associated with the final rule in Section IX. Table I-6 shows that annual benefits of the final rule will be larger than the annual costs in 2045, with annual net benefits of $6.9 and $29 billion assuming a 3 percent discount rate, and net benefits of $5.8 and $25 billion assuming a 7 percent discount rate.

The benefits of the final rule also outweigh the costs when expressed in present value terms and as equalized annual values (see Section IX for these values).

The range of benefits and net benefits reflects a combination of assumed PM

2.5

and ozone mortality risk estimates and selected discount rate.

EPA's analysis of costs and benefits does not include California's Omnibus rule or actions by other states to adopt it. EPA is reviewing a waiver request under CAA section 209(b) from California for the Omnibus rule; until EPA grants the waiver, the HD Omnibus program is not enforceable. EPA's analysis also does not include the recent IRA of 2022, which we anticipate will accelerate zero emissions technology in the heavy-duty sector.

Table I-6—Final Costs, Benefits and Net Benefits in 2045

[billions, 2017$]

3% Discount

7% Discount

Benefits

$12-$33

$10-$30

Costs

$4.7

Net Benefits

$6.9-$29

$5.8-$25

3. Summary of Economic Impacts

Section X examines the potential impacts of the final rule on heavy-duty vehicles (sales, mode shift, fleet turnover) and employment in the heavy-duty industry. The final rule may impact vehicle sales due to both changes in purchase price and longer emission warranty mileage requirements. The final rule may impact vehicle sales by increasing purchases of new vehicles before the final standards come into effect, in anticipation of higher prices after the standards (“pre-buy”). The final rule may also reduce sales after the final standards are in place (“low-buy”). In this final rule, we outline an approach to quantify potential impacts on vehicle sales due to new emission standards. Our illustrative analysis for this final rule, discussed in RIA Chapter 10.1, suggest pre- and low-buy for Class 8 trucks may range from zero to approximately 2 percent increase in sales over a period of up to 8 months before the 2027 standards begin (pre-buy), and a decrease in sales from zero to approximately 3 percent over a period of up to 12 months after the 2027 standards begin (low-buy). We expect little mode shift due to the final rule because of the large difference in cost of moving goods via trucks versus other modes of transport (

e.g.,

planes or barges).

Employment impacts of the final rule depend on the effects of the rule on sales, the share of labor in the costs of the rule, and changes in labor intensity due to the rule. We quantify the effects of costs on employment, and we discuss the effects due to sales and labor intensity qualitatively. In response to comments, we have added a discussion in Chapter 10 of the RIA describing a method that could be used to quantitatively estimate a demand effect on employment, as well as an illustrative application of that method. The partial quantification of employment impacts due to increases in the costs of vehicles and parts, holding labor intensity constant, shows an increase in employment by 1,000 to 5,300 job-years in 2027.

See Section X for further detail on limitations and assumptions of this analysis.

A job-year is, for example, one year of full-time work for one person, or one year of half-time work for two people.

D. EPA Statutory Authority for This Action

This section briefly summarizes the statutory authority for the final rule. Title II of the Clean Air Act provides for comprehensive regulation of mobile sources, authorizing EPA to regulate emissions of air pollutants from all mobile source categories. Specific Title II authorities for this final rule include: CAA sections 202, 203, 206, 207, 208, 213, 216, and 301 (42 U.S.C. 7521, 7522, 7525, 7541, 7542, 7547, 7550, and 7601). We discuss some key aspects of these sections in relation to this final action immediately below (see also Section XIII of this preamble), as well as in each of the relevant sections later in this preamble. As noted in Section I.B.2.v, the final rule includes confidentiality determinations for much of the information collected by EPA for certification and compliance under Title II; see Section XI.A. for discussion of

relevant statutory authority for these final rule provisions.

Statutory authority for the final NO

, PM, HC, and CO emission standards in this action comes from CAA section 202(a), which states that “the Administrator shall by regulation prescribe (and from time to time revise) . . . standards applicable to the emission of any air pollutant from any class or classes of new . . . motor vehicle engines, which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.” Standards under CAA section 202(a) take effect after such period as the Administrator finds necessary to permit the development and application of the requisite technology, giving appropriate consideration to the cost of compliance within such period.”

Section 202(a)(3) further addresses EPA authority to establish standards for emissions of NO

, PM, HC, and CO from heavy-duty engines and vehicles. Section 202(a)(3)(A) requires that such standards “reflect the greatest degree of emission reduction achievable through the application of technology which the Administrator determines will be available for the model year to which such standards apply, giving appropriate consideration to cost, energy, and safety factors associated with the application of such technology.” Section 202(a)(3)(B) allows EPA to take into account air quality information in revising such standards. Section 202(a)(3)(C) provides that standards shall apply for a period of no less than three model years beginning no earlier than the model year commencing four years after promulgation. CAA section 202(a)(3)(A) is a technology-forcing provision and reflects Congress' intent that standards be based on projections of future advances in pollution control capability, considering costs and other statutory factors.

56 57

CAA section 202(a)(3) neither requires that EPA consider all the statutory factors equally nor mandates a specific method of cost-analysis; rather EPA has discretion in determining the appropriate consideration to give such factors.

See

National Petrochemical & Refiners Association

EPA

, 287 F.3d 1130, 1136 (D.C. Cir. 2002) (explaining that EPA is authorized to adopt “technology-forcing” regulations under CAA section 202(a)(3));

NRDC

Thomas

, 805 F.2d 410, 428 n.30 (D.C. Cir. 1986) (explaining that such statutory language that “seek[s] to promote technological advances while also accounting for cost does not detract from their categorization as technology-forcing standards”); see also

Husqvarna AB

EPA

, 254 F.3d 195 (D.C. Cir. 2001) (explaining that CAA sections 202 and 213 have similar language and are technology-forcing standards).

In this context, the term “technology-forcing” has a specific legal meaning and is used to distinguish standards that may require manufacturers to develop new technologies (or significantly improve existing technologies) from standards that can be met using off-the-shelf technology alone. Technology-forcing standards such as those in this final rule do not require manufacturers to use specific technologies.

See,

e.g.,

Sierra Club

EPA

, 325 F.3d 374, 378 (D.C. Cir. 2003) (explaining that similar technology-forcing language in CAA section 202(l)(2) “does not resolve how the Administrator should weigh all [the statutory] factors in the process of finding the ‘greatest emission reduction achievable’ ”);

Husqvarna AB

EPA

, 254 F.3d 195, 200 (D.C. Cir. 2001) (explaining that under CAA section 213's similar technology-forcing authority that “EPA did not deviate from its statutory mandate or frustrate congressional will by placing primary significance on the ‘greatest degree of emission reduction achievable’ ” or by considering cost and other statutory factors as important but secondary).

CAA section 202(d) directs EPA to prescribe regulations under which the useful life of vehicles and engines are determined and establishes minimum values of 10 years or 100,000 miles, whichever occurs first, unless EPA determines that a period of greater duration or mileage is appropriate. EPA may apply adjustment factors to assure compliance with requirements in use throughout useful life (CAA section 206(a)). CAA section 207(a) requires manufacturers to provide emissions-related warranty, which EPA last updated in its regulations for heavy-duty engines in 1983 (see 40 CFR 86.085-2).

48 FR 52170, November 16, 1983.

EPA is promulgating the final emission standards pursuant to its authority under CAA section 202(a), including 202(a)(3)(A). Section II and Chapter 4 of the RIA describe EPA's analysis of information regarding heavy-duty engines' contribution to air pollution and how that pollution adversely impacts public health and welfare. Sections III and IV discuss our feasibility analysis of the emission standards and useful life periods in the final rule, with more detail in Chapter 3 of the RIA. Our analysis shows that the final emission standards and useful life periods are feasible and will result in the greatest emission reductions achievable for the model years to which they will apply, pursuant to CAA section 202(a)(3), giving appropriate consideration to costs, lead time, and other factors. Our analysis of the final standards includes providing manufacturers with sufficient time to ensure that emission control components are durable enough for the longer useful life periods in the final program. In setting the final emission standards, EPA appropriately assessed the statutory factors specified in CAA section 202(a)(3)(A), including giving appropriate consideration to the cost associated with the application of technology EPA determined will be available for the model year the final standards apply (

i.e.,

cost of compliance for the manufacturer associated with the application of such technology). EPA's assessment of the relevant statutory factors in CAA section 202(a)(3)(A) justify the final emission standards. We also evaluated additional factors, including factors to comply with E.O. 12866; our assessment of these factors lend further support to the final rule.

As proposed, we are finalizing new emission standards along with new and revised test procedures for both laboratory-based duty-cycles and off-cycle testing. Manufacturers demonstrate compliance over specified duty-cycle test procedures during pre-production testing, as well as confirmatory testing during production, which is conducted by EPA or the manufacturer. Test data and other information submitted by the manufacturer as part of their certification application are the basis on which EPA issues certificates of conformity pursuant to CAA section 206. Under CAA section 203, sales of new vehicles are prohibited unless the vehicle is covered by a certificate of conformity. Compliance with engine emission standards is required throughout the regulatory useful life of the engine, not only at certification but throughout the regulatory useful life in-use in the real word. In-use engines can be tested for compliance with duty-cycle and off-cycle standards, with testing over corresponding specific duty-cycle test procedures and off-cycle test procedures, either on the road or in the laboratory (see Section III for more discussion on for testing at various stages in the life of an engine).

Also as proposed, we are finalizing lengthened regulatory useful life and emission warranty periods to better reflect the mileages and time periods over which heavy-duty engines are driven today. These and other provisions in the final rule are further discussed in the preamble sections that follow. The proposed rule (87 FR 17414, March 28, 2022) includes additional information relevant to the development of this rule, including: History of Emissions Standards for Heavy-duty Engines and Vehicles; Petitions to EPA for Additional NO

control; the California Heavy-Duty Highway Low NO

Program Development; and the Advance Notice of Proposed Rulemaking.

II. Need for Additional Emissions Control

This final rule will reduce emissions from heavy-duty engines that contribute to ambient levels of ozone, PM, NO

and CO, which are all pollutants for which EPA has established health-based NAAQS. These pollutants are linked to premature death, respiratory illness (including childhood asthma), cardiovascular problems, and other adverse health impacts. Many groups are at greater risk than healthy people from these pollutants, including people with heart or lung disease, outdoor workers, older adults and children. These pollutants also reduce visibility and negatively impact ecosystems. This final rule will also reduce emissions of air toxics from heavy-duty engines. A more detailed discussion of the health and environmental effects associated with the pollutants affected by this rule is included in Sections II.B and II.C and Chapter 4 of the RIA.

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. We note that there is substantial evidence that people who live or attend school near major roadways are more likely to be people of color, Hispanic ethnicity, and/or low socioeconomic status.

Across the United States, NO

emissions from heavy-duty engines are important contributors to concentrations of ozone and PM

2.5

and their resulting threat to public health.

60 61

The emissions modeling done for the final rule (see Chapter 5 of the RIA) indicates that without these standards, heavy-duty engines will continue to be one of the largest contributors to mobile source NO

emissions nationwide in the future, representing 32 percent of the mobile source NO

in calendar year 2045.

Furthermore, it is estimated that heavy-duty engines would represent 90 percent of the onroad NO

inventory in calendar year 2045.

The emission reductions that will occur from the final rule are projected to reduce air pollution that is (and is projected to continue to be) at levels that endanger public health and welfare. For the reasons discussed in this Section II, EPA concludes that new standards are warranted to address the emissions of these pollutants and their contribution to national air pollution. We note that in the summer of 2016 more than 20 organizations, including state and local air agencies from across the country, petitioned EPA to develop more stringent NO

emission standards for on-road heavy-duty engines.

64 65

Among the reasons stated by the petitioners for such an EPA rulemaking was the need for NO

emission reductions to reduce adverse health and welfare impacts and to help areas attain the NAAQS. EPA responded to the petitions on December 20, 2016, noting that an opportunity exists to develop a new national NO

reduction strategy for heavy-duty highway engines.

We subsequently initiated this rulemaking and issued an Advanced Notice of Proposed Rulemaking in January 2020.

This final rule culminates the rulemaking proceeding and is responsive to those petitions.

Zawacki et al., 2018. Mobile source contributions to ambient ozone and particulate matter in 2025. Atmospheric Environment, Vol 188, pg 129-141. Available online:

https://doi.org/10.1016/j.atmosenv.2018.04.057

Davidson et al., 2020. The recent and future health burden of the U.S. mobile sector apportioned by source. Environmental Research Letters. Available online:

https://doi.org/10.1088/1748-9326/ab83a8

Sectors other than onroad and nonroad were projected from 2016v1 Emissions Modeling Platform.

https://www.epa.gov/air-emissions-modeling/2016v1-platform

U.S. EPA (2020) Motor Vehicle Emission Simulator: MOVES3.

https://www.epa.gov/moves

Brakora, Jessica. “Petitions to EPA for Revised NO

Standards for Heavy-Duty Engines” Memorandum to Docket EPA-HQ-OAR-2019-0055. December 4, 2019.

87 FR 17414, March 28, 2022.

U.S. EPA. 2016. Memorandum in Response to Petition for Rulemaking to Adopt Ultra-Low NO

Standards for On-Highway Heavy-Duty Trucks and Engines. Available at

https://19january2017snapshot.epa.gov/sites/production/files/2016-12/documents/nox-memorandum-nox-petition-response-2016-12-20.pdf

The Agency published an ANPR on January 21, 2020 to present EPA's early thinking on this rulemaking and solicit feedback from stakeholders to inform this proposal (85 FR 3306).

Many state and local agencies across the country commented on the NPRM and have asked the EPA to reduce NO

emissions, specifically from heavy-duty engines, because such reductions will be a critical part of many areas' strategies to attain and maintain the ozone and PM NAAQS. These state and local agencies anticipate challenges in attaining the NAAQS, maintaining the NAAQS in the future, and/or preventing nonattainment. Some nonattainment areas have already been “bumped up” to higher classifications because of challenges in attaining the NAAQS; others say they are struggling to avoid nonattainment.

Others note that the ozone and PM NAAQS are being reconsidered so they could be made more stringent in the future.

69 70

Many state and local agencies commented on the NPRM that heavy-duty vehicles are one of their largest sources of NO

emissions. They commented that without action to reduce emissions from heavy-duty vehicles, they will have to adopt other potentially more burdensome and costly measures to reduce emissions from other sources under their state or local authority, such as local businesses. More information on the projected emission reductions and air quality impacts that will result from this rule is provided in Sections VI and VII.

For example, in September 2019 several 2008 ozone nonattainment areas were reclassified from moderate to serious, including Dallas, Chicago, Connecticut, New York/New Jersey and Houston, and in January 2020, Denver. Also, on September 15, 2022, EPA finalized reclassification, bumping up 5 areas in nonattainment of the 2008 ozone NAAQS from serious to severe and 22 areas in nonattainment of the 2015 ozone NAAQS from marginal to moderate. The 2008 NAAQS for ozone is an 8-hour standard with a level of 0.075 ppm, which the 2015 ozone NAAQS lowered to 0.070 ppm.

https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone

https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm

In their comments on the NPRM, many nonprofit groups, citizen groups, individuals, and state, local, and Tribal organizations emphasized the role that emissions from trucks have in harming communities and that communities living near truck routes are disproportionately people of color and those with lower incomes. They supported additional NO

reductions from heavy-duty vehicles to address concerns about environmental justice and ensuring that all communities benefit from improvements in air quality. In addition, many groups and commenters noted the link between emissions from heavy duty trucks and harmful health effects, in particular asthma in children. Commenters also supported additional NO

reductions from heavy-duty vehicles to address concerns about regional haze, and damage to terrestrial and aquatic ecosystems. They mentioned the impacts of NO

emissions on numerous locations, such as the Chesapeake Bay, Long Island Sound, the Rocky Mountains, Sierra Nevada Mountains, Appalachian Mountains, Southwestern Desert ecosystems, and other areas. For further detail regarding these comments and EPA's responses, see Section 2 of the Response to Comments document for this rulemaking.

A. Background on Pollutants Impacted by This Proposal

1. Ozone

Ground-level ozone pollution forms in areas with high concentrations of ambient nitrogen oxides (NO

) and

volatile organic compounds (VOCs) when solar radiation is strong. Major U.S. sources of NO

are highway and nonroad motor vehicles, engines, power plants and other industrial sources, with natural sources, such as soil, vegetation, and lightning, serving as smaller sources. Vegetation is the dominant source of VOCs in the United States. Volatile consumer and commercial products, such as propellants and solvents, highway and nonroad vehicles, engines, fires, and industrial sources also contribute to the atmospheric burden of VOCs at ground-level.

The processes underlying ozone formation, transport, and accumulation are complex. Ground-level ozone is produced and destroyed by an interwoven network of free radical reactions involving the hydroxyl radical (OH), NO, NO

, and complex reaction intermediates derived from VOCs. Many of these reactions are sensitive to temperature and available sunlight. High ozone events most often occur when ambient temperatures and sunlight intensities remain high for several days under stagnant conditions. Ozone and its precursors can also be transported hundreds of miles downwind, which can lead to elevated ozone levels in areas with otherwise low VOC or NO

emissions. As an air mass moves and is exposed to changing ambient concentrations of NO

and VOCs, the ozone photochemical regime (relative sensitivity of ozone formation to NO

and VOC emissions) can change.

When ambient VOC concentrations are high, comparatively small amounts of NO

catalyze rapid ozone formation. Without available NO

, ground-level ozone production is severely limited, and VOC reductions would have little impact on ozone concentrations. Photochemistry under these conditions is said to be “NO

-limited.” When NO

levels are sufficiently high, faster NO

oxidation consumes more radicals, dampening ozone production. Under these “VOC-limited” conditions (also referred to as “NO

-saturated” conditions), VOC reductions are effective in reducing ozone, and NO

can react directly with ozone, resulting in suppressed ozone concentrations near NO

emission sources. Under these NO

-saturated conditions, NO

reductions can actually increase local ozone under certain circumstances, but overall ozone production (considering downwind formation) decreases. Even in VOC-limited areas, NO

reductions are not expected to increase ozone levels if the NO

reductions are sufficiently large—large enough to become NO

-limited.

The primary NAAQS for ozone, established in 2015 and retained in 2020, is an 8-hour standard with a level of 0.07 ppm.

EPA announced that it will reconsider the decision to retain the ozone NAAQS.

The EPA is also implementing the previous 8-hour ozone primary standard, set in 2008, at a level of 0.075 ppm. As of August 31, 2022, there were 34 ozone nonattainment areas for the 2008 ozone NAAQS, composed of 141 full or partial counties, with a population of more than 90 million, and 49 ozone nonattainment areas for the 2015 ozone NAAQS, composed of 212 full or partial counties, with a population of more than 125 million. In total, there are currently, as of August 31, 2022, 57 ozone nonattainment areas with a population of more than 130 million people.

https://www.epa.gov/ground-level-ozone-pollution/ozone-national-ambient-air-quality-standards-naaqs

https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone

The population total is calculated by summing, without double counting, the 2008 and 2015 ozone nonattainment populations contained in the Criteria Pollutant Nonattainment Summary report (

https://www.epa.gov/green-book/green-book-data-download

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. 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. Attainment dates for areas designated nonattainment for the 2015 ozone NAAQS are in the 2021 to 2038 timeframe, again depending on the severity of the problem in each area.

The final NO

standards will take effect starting in MY 2027 and will assist areas with attaining the NAAQS and may relieve areas with already stringent local regulations from some of the burden associated with adopting additional local controls.

The rule will also provide assistance to counties with ambient concentrations near the level of the NAAQS who are working to ensure long-term attainment or maintenance of the NAAQS.

https://www.epa.gov/ground-level-ozone-pollution/ozone-naaqs-timelines

While not quantified in the air quality modeling analysis for this rule, elements of the Averaging, Banking, and Trading (ABT) program could encourage manufacturers to introduce new emission control technologies prior to the 2027 model year, which may help to accelerate some emission reductions of the final rule (See Preamble Section IV.G for more details on the ABT program in the final rule). In RIA Chapter 5.5 we also include a sensitivity analysis that shows allowing manufacturers to generate NO

emissions credits by meeting requirements of the final rule one model year before required would lead to meaningful, additional reductions in NO

emissions in the early years of the program compared to the emissions reductions expected from the final rule (see preamble Section IV.G.7 and RIA Chapter 5.5 for additional details).

2. Particulate Matter

Particulate matter (PM) is a complex mixture of solid particles and liquid droplets distributed among numerous atmospheric gases which interact with solid and liquid phases. Particles in the atmosphere range in size from less than 0.01 to more than 10 micrometers (μm) in diameter.

Atmospheric particles can be grouped into several classes according to their aerodynamic diameter and physical sizes. Generally, the three broad classes of particles include ultrafine particles (UFPs, generally considered as particles with a diameter less than or equal to 0.1 μm [typically based on physical size, thermal diffusivity or electrical mobility]), “fine” particles (PM

2.5

; particles with a nominal mean aerodynamic diameter less than or equal to 2.5 μm), and “thoracic” particles (PM

; particles with a nominal mean aerodynamic diameter less than or equal to 10 μm). Particles that fall within the size range between PM

2.5

and PM

, are referred to as “thoracic coarse particles” (PM

−2.5

, particles with a nominal mean aerodynamic diameter greater than 2.5 μm and less than or equal to 10 μm). EPA currently has NAAQS for PM

2.5

and PM

U.S. EPA. Policy Assessment (PA) for the Review of the National Ambient Air Quality Standards for Particulate Matter (Final Report, 2020). U.S. Environmental Protection Agency, Washington, DC, EPA/452/R-20/002, 2020.

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 NAAQS which provide protection against health and welfare effects, the 24-hour PM

standard provides protection against effects associated with short-term exposure to thoracic coarse particles (

i.e.,

-2.5).

Most particles are found in the lower troposphere, where they can have residence times ranging from a few hours to weeks. Particles are removed from the atmosphere by wet deposition, such as when they are carried by rain or snow, or by dry deposition, when particles settle out of suspension due to gravity. Atmospheric lifetimes are generally longest for PM

2.5

, which often remains in the atmosphere for days to weeks before being removed by wet or dry deposition.

In contrast,

atmospheric lifetimes for UFP and PM

−2.5

are shorter. Within hours, UFP can undergo coagulation and condensation that lead to formation of larger particles, or can be removed from the atmosphere by evaporation, deposition, or reactions with other atmospheric components. PM

−2.5

are also generally removed from the atmosphere within hours, through wet or dry deposition.

U.S. EPA. Integrated Science Assessment (ISA) for Particulate Matter (Final Report, 2019). U.S.

Environmental Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-1.

U.S. EPA. Integrated Science Assessment (ISA) for Particulate Matter (Final Report, 2019). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Table 2-1.

Particulate matter consists of both primary and secondary particles. Primary particles are emitted directly from sources, such as combustion-related activities (

e.g.,

industrial activities, motor vehicle operation, biomass burning), while secondary particles are formed through atmospheric chemical reactions of gaseous precursors (

e.g.,

sulfur oxides (SO

), NO

, and VOCs).

There are two primary NAAQS for PM

2.5

: An annual standard (12.0 micrograms per cubic meter (μg/m

)) and a 24-hour standard (35 μg/m

), and there are two secondary NAAQS for PM

2.5

: An annual standard (15.0 μg/m

) and a 24-hour standard (35 μg/m

). The initial PM

2.5

standards were set in 1997 and revisions to the standards were finalized in 2006 and in December 2012 and then retained in 2020. On June 10, 2021, EPA announced that it will reconsider the decision to retain the PM NAAQS.

https://www.epa.gov/pm-pollution/national-ambient-air-quality-standards-naaqs-pm

There are many areas of the country that are currently in nonattainment for the annual and 24-hour primary PM

2.5

NAAQS. As of August 31, 2022, more than 19 million people lived in the 4 areas that are designated as nonattainment for the 1997 PM

2.5

NAAQS. Also, as of August 31, 2022, more than 31 million people lived in the 14 areas that are designated as nonattainment for the 2006 PM

2.5

NAAQS and more than 20 million people lived in the 5 areas designated as nonattainment for the 2012 PM

2.5

NAAQS. In total, there are currently 15 PM

2.5

nonattainment areas with a population of more than 32 million people.

The final NO

standards will take effect in MY 2027 and will assist areas with attaining the NAAQS and may relieve areas with already stringent local regulations from some of the burden associated with adopting additional local controls.

The rule will also assist counties with ambient concentrations near the level of the NAAQS who are working to ensure long-term attainment or maintenance of the PM

2.5

NAAQS.

The population total is calculated by summing, without double counting, the 1997, 2006 and 2012 PM

2.5

nonattainment populations contained in the Criteria Pollutant Nonattainment Summary report (

https://www.epa.gov/green-book/green-book-data-download

3. Nitrogen Oxides

Oxides of nitrogen (NO

) refers to nitric oxide (NO) and nitrogen dioxide (NO

). Most NO

is formed in the air through the oxidation of NO emitted when fuel is burned at a high temperature. NO

is a criteria pollutant, regulated for its adverse effects on public health and the environment, and highway vehicles are an important contributor to NO

emissions. NO

, along with VOCs, are the two major precursors of ozone and NO

is also a major contributor to secondary PM

2.5

formation. There are two primary NAAQS for NO

: An annual standard (53 ppb) and a 1-hour standard (100 ppb).

In 2010, EPA established requirements for monitoring NO

near roadways expected to have the highest concentrations within large cities. Monitoring within this near-roadway network began in 2014, with additional sites deployed in the following years. At present, there are no nonattainment areas for NO

The statistical form of the 1-hour NAAQS for NO

is the 3-year average of the yearly distribution of 1-hour daily maximum concentrations.

4. Carbon Monoxide

Carbon monoxide (CO) is a colorless, odorless gas emitted from combustion processes. Nationally, particularly in urban areas, the majority of CO emissions to ambient air come from mobile sources.

There are two primary NAAQS for CO: An 8-hour standard (9 ppm) and a 1-hour standard (35 ppm). There are currently no CO nonattainment areas; as of September 27, 2010, all CO nonattainment areas have been redesignated to attainment. The past designations were based on the existing community-wide monitoring network. EPA made an addition to the ambient air monitoring requirements for CO during the 2011 NAAQS review. Those new requirements called for CO monitors to be operated near roads in Core Based Statistical Areas (CBSAs) of 1 million or more persons, in addition to the existing community-based network (76 FR 54294, August 31, 2011).

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.

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=218686

. See Section 2.1.

5. Diesel Exhaust

Diesel exhaust is a complex mixture composed of particulate matter, carbon dioxide, oxygen, nitrogen, water vapor, carbon monoxide, nitrogen compounds, sulfur compounds and numerous low-molecular-weight hydrocarbons. A number of these gaseous hydrocarbon components are individually known to be toxic, including aldehydes, benzene and 1,3-butadiene. The diesel particulate matter present in diesel exhaust consists mostly of fine particles (<2.5 μm), of which a significant fraction is ultrafine particles (<0.1 μm). These particles have a large surface area which makes them an excellent medium for adsorbing organics and their small size makes them highly respirable. Many of the organic compounds present in the gases and on the particles, such as polycyclic organic matter, are individually known to have mutagenic and carcinogenic properties.

Diesel exhaust varies significantly in chemical composition and particle sizes between different engine types (heavy-duty, light-duty), engine operating conditions (idle, acceleration, deceleration), and fuel formulations (high/low sulfur fuel). Also, there are emissions differences between on-road and nonroad engines because the nonroad engines are generally of older technology. After being emitted in the engine exhaust, diesel exhaust undergoes dilution as well as chemical and physical changes in the atmosphere. The lifetime of the components present in diesel exhaust ranges from seconds to days.

Because diesel particulate matter (DPM) is part of overall ambient PM, varies considerably in composition, and lacks distinct chemical markers that enable it to be easily distinguished from overall primary PM, we do not have direct measurements of DPM in the ambient air.

DPM concentrations are

estimated using ambient air quality modeling based on DPM emission inventories. DPM emission inventories are computed as the exhaust PM emissions from mobile sources combusting diesel or residual oil fuel. DPM concentrations were estimated as part of the 2018 national Air Toxics Screening Assessment (AirToxScreen).

Areas with high concentrations are clustered in the Northeast and Great Lake States, with a smaller number of higher concentration locations in Western states. The highest impacts occur in major urban cores, and are also distributed throughout the rest of the United States near high truck traffic, coasts with marine diesel activity, construction sites, and rail facilities. Approximately half of the average ambient DPM concentration in the United States can be attributed to heavy-duty diesel engines, with the remainder attributable to nonroad engines.

DPM in exhaust from a high-load, high-speed engine (

e.g.,

heavy-duty truck engines) without aftertreatment such as a diesel particle filter (DPM) is mostly made of “soot,” consisting of elemental/black carbon (EC/BC), some organic material, and trace elements. At low loads, DPM in high-speed engine exhaust is mostly made of organic carbon (OC), with considerably less EC/BC. Low-speed diesel engines' (

e.g.,

large marine engines) exhaust

PM is comprised of more sulfate and less EC/BC, with OC contributing as well.

U.S. EPA (2022) Technical Support Document EPA Air Toxics Screening Assessment. 2018AirToxScreen TSD.

https://www.epa.gov/AirToxScreen/airtoxscreen-technical-support-document

6. Air Toxics

The most recent available data indicate that millions of Americans live in areas where air toxics pose potential health concerns.

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 EPA's 2007 Mobile Source Air Toxics Rule.

According to EPA's Air Toxics Screening Assessment (AirToxScreen) for 2018, mobile sources were responsible for 40 percent of outdoor anthropogenic toxic emissions and were the largest contributor to national average cancer and noncancer risk from directly emitted pollutants.

89 90

Mobile sources are also significant contributors to precursor emissions which react to form air toxics.

Formaldehyde is the largest contributor to cancer risk of all 71 pollutants quantitatively assessed in the 2018 AirToxScreen. Mobile sources were responsible for 26 percent of primary anthropogenic emissions of this pollutant in 2018 and are significant contributors to formaldehyde precursor emissions. Benzene is also a large contributor to cancer risk, and mobile sources account for about 60 percent of average exposure to ambient concentrations.

U.S. EPA (2022) Technical Support Document EPA Air Toxics Screening Assessment. 2017AirToxScreen TSD.

https://www.epa.gov/system/files/documents/2022-03/airtoxscreen_2017tsd.pdf

U.S. Environmental Protection Agency (2007). Control of Hazardous Air Pollutants from Mobile Sources; Final Rule. 72 FR 8434, February 26, 2007.

U.S. EPA. (2022) Air Toxics Screening Assessment.

https://www.epa.gov/AirToxScreen/2018-airtoxscreen-assessment-results

AirToxScreen also includes estimates of risk attributable to background concentrations, which includes contributions from long-range transport, persistent air toxics, and natural sources; as well as secondary concentrations, where toxics are formed via secondary formation. Mobile sources substantially contribute to long-range transport and secondarily formed air toxics.

Rich Cook, Sharon Phillips, Madeleine Strum, Alison Eyth & James Thurman (2020): Contribution of mobile sources to secondary formation of carbonyl compounds, Journal of the Air & Waste Management Association, DOI: 10.1080/10962247.2020.1813839.

B. Health Effects Associated With Exposure to Pollutants Impacted by This Rule

Heavy-duty engines emit pollutants that contribute to ambient concentrations of ozone, PM, NO

, CO, and air toxics. This section of the preamble discusses the health effects associated with exposure to these pollutants.

Additionally, because children have increased vulnerability and susceptibility for adverse health effects related to air pollution exposures, EPA's findings regarding adverse effects for children related to exposure to pollutants that are impacted by this rule are noted in this section. The increased vulnerability and susceptibility of children to air pollution exposures may arise because infants and children generally breathe more relative to their size than adults do, and consequently may be exposed to relatively higher amounts of air pollution.

Children also tend to breathe through their mouths more than adults and their nasal passages are less effective at removing pollutants, which leads to greater lung deposition of some pollutants, such as PM.

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Furthermore, air pollutants may pose health risks specific to children because children's bodies are still developing.

For example, during periods of rapid growth such as fetal development, infancy, and puberty, their developing systems and organs may be more easily harmed.

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EPA's America's Children and the Environment is a tool which presents national trends on air pollutants and other contaminants and environmental health of children.

EPA (2009) Metabolically-derived ventilation rates: A revised approach based upon oxygen consumption rates. Washington, DC: Office of Research and Development. EPA/600/R-06/129F.

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=202543

U.S. EPA Integrated Science Assessment for Particulate Matter (Final Report, 2019). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-19/188, 2019. Chapter 4 “Overall Conclusions” p. 4-1.

Foos, B.; Marty, M.; Schwartz, J.; Bennet, W.; Moya, J.; Jarabek, A.M.; Salmon, A.G. (2008) Focusing on children's inhalation dosimetry and health effects for risk assessment: An introduction. J Toxicol Environ Health 71A: 149-165.

Children's environmental health includes conception, infancy, early childhood and through adolescence until 21 years of age as described in the EPA Memorandum: Issuance of EPA's 2021 Policy on Children's Health. October 5, 2021. Available at

https://www.epa.gov/system/files/documents/2021-10/2021-policy-on-childrens-health.pdf

EPA (2006) A Framework for Assessing Health Risks of Environmental Exposures to Children. EPA, Washington, DC, EPA/600/R-05/093F, 2006.

U.S. Environmental Protection Agency. (2005). Supplemental guidance for assessing susceptibility from early-life exposure to carcinogens. Washington, DC: Risk Assessment Forum. EPA/630/R-03/003F.

https://www3.epa.gov/airtoxics/childrens_supplement_final.pdf

U.S. EPA. America's Children and the Environment. Available at:

https://www.epa.gov/americaschildrenenvironment

Information on environmental effects associated with exposure to these pollutants is included in Section II.C, and information on environmental justice is included in Section VII.H. Information on emission reductions and air quality impacts from this rule are included in Section VI and VII.

1. Ozone

This section provides a summary of the health effects associated with exposure to ambient concentrations of ozone.

The information in this section is based on the information and conclusions in the April 2020 Integrated Science Assessment for Ozone (Ozone ISA).

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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.

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The following discussion highlights the Ozone ISA's

conclusions pertaining to health effects associated with both short-term and long-term periods of exposure to ozone.

Human exposure to ozone varies over time due to changes in ambient ozone concentration and because people move between locations which have notably different ozone concentrations. Also, the amount of ozone delivered to the lung is influenced not only by the ambient concentrations but also by the breathing route and rate.

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U.S. EPA. Integrated Science Assessment (ISA) for Ozone and Related Photochemical Oxidants (Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-20/012, 2020.

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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.

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 metabolic effects, including metabolic syndrome (

i.e.,

changes in insulin or glucose levels, cholesterol levels, obesity, and blood pressure) and complications due to diabetes are likely to be causally associated with short-term exposure to ozone. The evidence is also suggestive of a causal relationship between short-term exposure to ozone and cardiovascular effects, central nervous system effects, and total mortality.

For long-term exposure to ozone, the Ozone ISA conclu

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