Risk Reduction Plan to Reduce

Particulate Matter Emissions from

Diesel-Fueled Engines and Vehicles

Stationary Source Division

Mobile Source Control Division

October 2000
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Prepared by

Stationary Source Division

Mobile Source Control Division

Contributors

Compliance Division

Mobile Source Operations Division

Planning and Technical Support Division

Research Division

Office of Environmental Health Hazard Assessment

Acknowledgements:

In appreciation of their participation, the Air Resources Board staff extends its

appreciation to the members of the Advisory Committee, Risk Management

Subcommittee, Stationary Source Subcommittee, Mobile Source Subcommittee, and

Fuels Subcommittee.
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TABLE OF CONTENTS

Contents Page

I. Executive Summary ..............................................................................................1

II. Background...........................................................................................................3

A. How is this report structured?.....................................................................4

B. What does this report contain and how was it developed? ........................5

III. Diesel-Fueled Engines: Definition and Uses........................................................6

A. How is “diesel-fueled engine” defined? ......................................................6

B. What categories of diesel-fueled engines and vehicles

were evaluated in this report? ....................................................................6

C. What are mobile engines? .........................................................................8

D. What are stationary engines?.....................................................................8

IV. Summary of Existing and Proposed Regulations..................................................9

A. What current federal, state, or local regulations address diesel PM

emissions from mobile diesel-fueled engines?...........................................9

B. What current federal, state, or local regulations address diesel PM

emissions from stationary and portable diesel-fueled engines?...............10

C. What current federal, state or local regulations address diesel fuel

formulation? .............................................................................................10

V. Emission Inventory and Risk...............................................................................11

A. What are the estimated diesel PM emissions for

1990, 2000, 2010, and 2020? ..................................................................11

B. What are the estimated statewide potential cancer risks

associated with diesel PM emissions? .....................................................13

C. How much of the estimated statewide potential cancer risk

level from air toxics is due to diesel PM emissions? ................................15

D. What are the potential cancer risks associated with some

typical activities where diesel-fueled engines are used?..........................16

VI. Control Technology and Fuel Options.................................................................19

A. Has ARB identified control technology options that can further

reduce diesel PM emissions from diesel-fueled engines and vehicles?...19

B. What are the costs associated with the control technology options? .......20

VII. Alternative Technologies.....................................................................................22

A. What alternatives to diesel-fueled engines and vehicles exist

today that would result in lower diesel PM emissions? ............................22
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TABLE OF CONTENTS (cont.)

Contents Page

VIII. Staff’s Recommendation.....................................................................................23

A. What measures does ARB recommend be developed to further

reduce diesel PM emissions from mobile diesel-fueled engines

and vehicles? ...........................................................................................24

B. What measures does ARB recommend be developed to further

reduce diesel PM emissions from stationary and off-road portable

diesel-fueled engines? .............................................................................27

C. What measures does ARB recommended regarding diesel fuel

reformulation? ..........................................................................................30

D. What impact will the recommended measures have on diesel PM

emissions and risk?..................................................................................31

E. What other expected benefits are associated with implementing

the recommended measures ?.................................................................33

F. What possible adverse impacts may be associated with the

recommended measures?........................................................................33

G. What actions should the U.S. EPA pursue to support the

ARB staff’s recommended measures?.....................................................33

Appendix I: Glossary of Terms and Acronyms

Appendix II: Stationary and Portable Diesel-Fueled Engines: Appendix to the Diesel

Risk Reduction Plan, September 2000

Appendix III: Mobile Diesel-Fueled Engines: Appendix to the Diesel Risk Reduction

Plan, September 2000

Appendix IV: Fuels Report: Appendix to the Diesel Risk Reduction Plan, 

September 2000

Appendix V: Summary of Existing Regulations

Appendix VI: Methodology for Estimating the Ambient Concentrations of Particulate

Matter from Diesel-Fueled Engines and Vehicles

Appendix VII: Risk Characterization Scenarios

Appendix VIII: Health and Safety Code Section 39665

Appendix IX: Diesel PM Control Technologies
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I. EXECUTIVE SUMMARY

Particulate matter emissions from diesel-fueled vehicles and engines are about

28,000 tons per year in California. These emissions come from a wide variety of

sources including over one million on-road and off-road vehicles, about

16,000 stationary engines, and close to 50,000 portable engines. On-road engines

account for about 27 percent of the emissions, off-road engines about 66 percent, with

the remaining 7 percent from stationary and portable engines. With full implementation

of the current vehicle standards on the books and vehicle turnover, diesel particulate

matter (diesel PM) will still be about 22,000 tons per year in 2010 and about 19,000 tons

per year in 2020.

In 1998, following an exhaustive 10-year scientific assessment process, the Air

Resources Board (ARB or Board) identified particulate matter from diesel-fueled

engines as a toxic air contaminant (TAC). On a statewide basis, the average potential

cancer risk associated with these emissions is over 500 potential cases per million. In

the South Coast Air Basin, the potential risk associated with diesel PM emissions is

estimated to be 1,000 per million people. Compared to other air toxics the Board has

identified and controlled, diesel PM emissions are estimated to be responsible for about

70 percent of the total ambient air toxics risk. In addition to these general risks, diesel

PM can also present elevated localized or near-source exposures. Depending on the

activity and nearness to receptors, these potential risks can range from small to 1,500

per million or more. As a result of this significant potential risk, when the Board

identified diesel PM as a TAC, it directed staff to convene an advisory committee of

interested parties to engage in a dialogue on the steps that can be taken to reduce

these emissions.

This plan, the Diesel Risk Reduction Plan or Diesel RRP, represents the staff’s

proposal for a comprehensive plan to significantly reduce diesel PM emissions. The

basic premise behind the staff proposal is simple: to require all new diesel-fueled

vehicles and engines to use state-of-the-art catalyzed diesel particulate filters (DPFs)

and very low-sulfur diesel fuel. Further, all existing vehicles and engines should be

evaluated, and wherever technically feasible and cost-effective, retrofitted with DPFs.

As with new engines, very low-sulfur diesel fuel should be used by retrofitted vehicles

and engines. In short, the staff’s proposed plan contains the following

three components:

1. New regulatory standards for all new on-road, off-road, and stationary

diesel-fueled engines and vehicles to reduce diesel PM emissions by

about 90 percent overall from current levels;

2. New retrofit requirements for existing on-road, off-road, and stationary

diesel-fueled engines and vehicles where determined to be technically

feasible and cost-effective; and
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3. New Phase 2 diesel fuel regulations to reduce the sulfur content levels of

diesel fuel to no more than 15 ppm to provide the quality of diesel fuel

needed by the advanced diesel PM emission controls.

Diesel PM filter control technology is now available and has been demonstrated

in over 40,000 applications worldwide. It is staff’s vision that well before the end of this

decade these filters will become as commonplace on diesel-fueled engines as catalysts

are now on gasoline-fueled vehicles.

Upon the Board’s approval of this comprehensive plan with its various control

measures, staff will begin the full regulatory process to develop the actual regulations

envisioned by this plan. During the regulatory development process, the details

associated with each specific regulation will be fully developed. Over the next several

years, staff will be developing these regulations and bringing them to the Board for

consideration of adoption. To assist staff in evaluating retrofit applications and provide

technical advice to staff, the Board created an Advisory Committee on Toxic Air

Contaminant Emissions from Diesel-Fueled Engines and Vehicles.

While the principal focus of this plan is the reduction in emissions of diesel PM,

staff are well aware that there are a number of viable alternative technologies, such as

compressed natural gas and electrification that in many cases could be used to

accomplish the same results. It is staff’s full intent, as it develops the regulations

proposed in this plan, to fully explore and engage in dialogue with interested parties

concerning opportunities for using these alternatives to reduce diesel PM emissions.

The projected emission benefits associated with the full implementation of this

plan, including proposed federal measures, are reductions in diesel PM emissions and

associated cancer risks of 75 percent by 2010 and 85 percent by 2020. The measures

recommended in this plan will have a great impact on reducing the localized risks

associated with activities that expose nearby individuals to diesel PM emissions.

Further, there are other benefits associated with reducing diesel PM emissions. These

include reduced ambient fine particulate matter levels, increased visibility, less material

damage due to soiling of surfaces, and reduced incidences of noncancer health effects,

such as bronchitis and asthma. Staff expects that the costs associated with carrying out

this plan will be significant and will be on the order of the costs associated with other

major ARB programs.
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II. BACKGROUND

The public’s exposure to TACs is a significant public health issue in California. In

1983, the California Legislature enacted a program to identify the health effects of TACs

and to reduce exposure to these contaminants to protect the public health (Assembly

Bill (AB) 1807: Health and Safety Code sections 39650-39674). The Legislature

established a two-step process to address the potential health effects from TACs. The

first step is the risk assessment (or identification) phase. The second step is the risk

management (or control) phase of the process.

In August 1998, the ARB identified diesel PM as a TAC, following a 10-year

review process. This marked the completion of the identification phase of the process

to address the potential for adverse health effects associated with diesel PM emissions.

This Diesel RRP is the first formal product of the risk management phase of the

AB 1807 process. This report presents information that identifies the available options

to reduce diesel PM, and identifies recommended control measures to achieve further

reductions. The recommended control measures would be developed as mobile source

regulations or stationary source airborne toxic control measures (ATCMs).

The next step in the AB 1807 process, following approval of this plan by the

Board, is the development of the specific ATCMs and fuel or vehicular emissions

regulations designed to reduce diesel PM emissions. The goal of each regulation is to

reduce diesel PM to the greatest extent feasible. These regulations must be technically

feasible and be cost-effective, and they will provide an opportunity to address issues

associated with the application of controls on a specific source categories. In

developing rules to implement the Diesel RRP, the staff will consider the availability and

cost of engine modifications, add-on control technology, changes in fuel parameters,

alternative fuels, and alternative methods of performing the function of the diesel engine

application. Thus, although most of the Board’s regulatory activities are expected to be

focused on emission controls that can be added to or built into diesel-fueled engines,

staff will also fully integrate alternative “non-diesel” technologies (e.g., electrification and

compressed natural gas (CNG)) as possible control options for reducing diesel PM

emissions.

ARB staff will develop the ATCMs and regulations with full public involvement

and dialogue through public workshops and meetings with groups and individuals. Draft

versions of the ATCMs and regulations will be presented to the public for review and

comment, and final draft versions will be presented to the Board for approval.

Public outreach is an essential element in the development of any ATCM or regulation

to ensure that all affected and interested parties have full opportunity to provide input

and shape rules that are both effective and workable.

As part of the identification process, the Office of Environmental Health Hazard

Assessment (OEHHA) evaluated the potential for diesel exhaust to affect human health.

The OEHHA found that exposures to diesel PM resulted in an increased risk of cancer

and an increase in chronic noncancer health effects including a greater incidence of
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cough, labored breathing, chest tightness, wheezing, and bronchitis. The OEHHA

estimated that based upon available studies, the potential cancer risk from exposure to

diesel PM in concentrations of one microgram per cubic meter ranged from 130 to

2400 excess cancers per million. The Scientific Review Panel (SRP) approved the

OEHHA’s determinations concerning health effects and approved the range of risk for

particulate matter from diesel-fueled engines. The SRP concluded that a value of

300 excess cancers per million people, per microgram per cubic meter of diesel PM,

was appropriate as a point estimate of unit risk for diesel PM.

The OEHHA also concluded that exposure to diesel PM in concentrations

exceeding 5 micrograms per cubic meter can result in a number of long-term (chronic)

noncancer health effects including greater incidence of cough, phlegm, and bronchitis.

The 5 microgram per cubic meter value is referred to as the Chronic Reference

Exposure Value (REL) for diesel PM. The SRP supported the OEHHA’s conclusion and

noted that the REL may need to be lowered further as more data emerge on potential

adverse noncancer effects of diesel PM.

As part of its formal identification of diesel PM as a TAC, the Board accepted the

OEHHA and SRP’s conclusions and directed the ARB staff to begin the risk

management process. The staff was directed to develop control measures to reduce

both diesel PM and other potentially harmful pollutants. The staff was also directed to

form a diesel risk management working group to advise the staff during its risk

management efforts. This working group, the Advisory Committee and subcommittees,

are discussed in Section B., below.

A. How is this report structured?

This report consists of a main report and appendices that summarize and discuss

the proposed Diesel RRP to reduce emissions, exposure, and potential cancer risk

associated with particulate matter from diesel-fueled engines.

The main report provides the following information:

♦ defines the term “diesel-fueled engine” and identifies the categories of

diesel-fueled engines and vehicles evaluated in this report;

♦ summarizes current regulations that address diesel PM emissions from

diesel-fueled engines and vehicles;

♦ presents diesel PM emission inventory estimates, estimated ambient

concentrations, and associated potential cancer risk information for the years

1990, 2000, 2010, and 2020;

♦ presents current near-source diesel PM emissions exposure and potential

cancer risk estimates;

♦ discusses available diesel PM emissions control technology options;

♦ present’s ARB staff’s recommendation, based upon the above information, to

further control particulate matter emissions from diesel-fueled engines and

vehicles;
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♦ estimates the reduction in diesel PM emissions, exposure, and risk by 2010

and 2020 that could be achieved if all recommended measures were

implemented; and

♦ recommends specific measures to be developed to further reduce diesel PM

emissions from diesel-fueled engines and vehicles.

Appendix I is a list of terms, definitions and acronyms used in both the main

report and appendices. Appendix II is a report on the need for further regulation of

stationary and portable diesel-fueled engines. Appendix III is a report on the need for

further regulation of mobile on-and off-road diesel-fueled engines (excluding portable

equipment, which is addressed in Appendix II). Appendix IV is a report on the need for

further regulation of diesel fuel. Appendix V is a summary of existing regulations

addressing diesel-fueled engines, vehicles, and diesel fuel. Appendix VI is a discussion

of the methodology for estimating the ambient concentrations of diesel PM emissions

from diesel-fueled engines and vehicles. Appendix VII is a discussion of the potential

risks associated with typical activities where diesel-fueled engines and vehicles are

used (risk characterization scenarios). Appendix VIII is Health and Safety Code

Section 39665, which identifies the requirements this report must meet. Appendix IX is

a discussion of diesel PM control technologies.

B. What does this report contain and how was it developed?

In accordance with California Health and Safety Code Section 39665 (see

Appendix VIII), this report includes the following information:

♦ number (population) and categories of diesel-fueled engines and vehicles;

♦ consideration of all past and current measures for reducing diesel PM;

♦ emissions and associated ambient and near-source potential risk levels for

diesel PM;

♦ available technologies for reducing diesel PM;

♦ initial estimates for the costs of reducing diesel PM;

♦ alternative methods of emission reductions;

♦ recommended measures to be developed to reduce emissions and potential

risk;

♦ potential adverse health, safety, or environmental impacts from

implementation of the recommended measures; and

♦ impact of the recommended measures on diesel PM emissions and potential

risk.

While the above items are addressed in this plan, staff will further refine and

update this information as it develops the various control measures identified in this

plan.

To ensure full opportunity for public consultation and input in developing this

report, an Advisory Committee was created to serve as a forum for on-going

communication, cooperation, and coordination in identifying opportunities to reduce
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diesel PM emissions. The Advisory Committee consists of the Stationary Source,

Fuels, Mobile Source/Alternative Strategies, and Risk Management subcommittees.

The Advisory Committee and each of the four subcommittees include representatives

from industry, local districts, environmental organizations, ARB, the United States

Environmental Protection Agency (U.S. EPA), and the public.

ARB staff presented a draft of this document to each of the four subcommittees

and the Advisory Committee for review and comment. All comments were considered

and the draft report was revised in a number of ways to reflect these comments.

III. DIESEL-FUELED ENGINES: DEFINITION AND USES

A. How is “diesel-fueled engine” defined?

For purposes of this report, a diesel-fueled engine is defined as any internal

combustion, compression-ignition (diesel-cycle) engine. It is generally assumed that the

engine will be using diesel fuel. However, diesel-cycle engines using alternative fuels or

fuel reformulation (e.g., jet fuel, biodiesel, CNG, and diesel/water mixtures) will also be

addressed during the development of each specific ATCM or regulation.

B. What categories of diesel-fueled engines and vehicles were evaluated in

this report?

Staff’s goal in this plan was to address all diesel-fueled engines in California.

Figure 1 identifies the specific categories of diesel-fueled engines and vehicles

evaluated in this report. The following paragraphs provide a brief description of each

category. Detailed descriptions can be found in Appendix II for Stationary Engines and

in Appendix III for Mobile Engines.
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Cars

Trucks

Buses

On-Road

Off-Road

Vehicles &

Equipment

Portable

Prime Engines

Emergency/

Standby

Mobile

Stationary

Figure 1: Diesel-Fueled Engines and Vehicle Categories

Diesel Engines
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C. What are mobile engines?

Mobile engines can be divided into two categories: on-road vehicles and off-road

engines and vehicles.

On-Road Vehicles: Diesel-fueled engines are used in every category of on-road

vehicles except motorcycles, and include light to heavy-duty trucks, school buses, urban

buses, and passengers vehicles. In California, the majority of on-road diesel-fueled

engines are found in the heavy-duty vehicles with a gross vehicle weight rating (GVWR)

greater than 14,000 pounds. There are approximately 700,000 on-road diesel-fueled

vehicles currently in use in California.

Off-Road Engines and vehicles: Diesel-fueled off-road engines comprise over

100 individual off-road vehicle and equipment types classified into 17 equipment

categories. Engine sizes range from under 15 horsepower to over 10,000 horsepower.

These equipment categories include agriculture, airport ground support, construction

and mining, commercial, industrial, logging, transportation refrigeration units, lawn and

garden, commercial marine vessels, pleasure craft, and locomotives. Many of the

off-road categories contain equipment types that are classified as portable (equipment

of 25 horsepower or greater that is designed and capable of being carried or moved

from one location to another). There are approximately 550,000 off-road diesel-fueled

engines and vehicles currently in use in California. A more detailed breakdown is

presented in Appendix III.

D. What are stationary engines?

Stationary engines can be divided into two categories: emergency/standby

engines and prime engines.

Emergency/standby engine: Emergency/standby engines are typically used for

emergency back-up electric power generation or the emergency pumping of water.

Sizes range from 50 to 6,000 horsepower, depending on the needs of the user. There

are over 11,000 diesel-fueled emergency/standby engines in use in California.

Emergency/standby engines make up about 70 percent of the total number of stationary

engines throughout the State. Several local air pollution control and air quality

management districts (districts) have rules that regulate NOx and CO emissions, but not

PM from internal combustion engines. However, some districts currently exempt

emergency/standby engines from complying with these requirements.

Prime Engines: Prime engines are stationary engines that are not used in an

emergency back-up or standby mode. There are approximately 5,000 diesel-fueled

prime engines currently in use in California. Examples include diesel-fueled engines

that are used to power compressors, cranes, generators, pumps, and grinders. Prime

engines make up about 30 percent of the total stationary engine inventory throughout

the State.
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Of the prime engines operating throughout the State, about 70 percent are agricultural

irrigation pump engines.

IV. SUMMARY OF EXISTING AND PROPOSED REGULATIONS

The ARB has the responsibility for control of emissions from mobile sources.

The local air districts have the primary responsibility for control of air pollution for all

sources, other than emissions for mobile sources. State law, however, provides the

South Coast AQMD with the authority to require fleets of 15 or more vehicles to

purchase clean vehicles when adding or replacing vehicles, authority which they have

recently exercised.

There are certain categories of mobile sources, however, for which ARB lacks

direct authority to regulate. The federal Clean Air Act Amendments of 1990 (CAA)

preempt state and local authorities from the control of emissions from new farm and

construction equipment under 175 horsepower and from new locomotives or locomotive

engines (CAA Section 209(e)(1)(A)); only the U.S. EPA has the authority to establish

emission standards for those engines. In addition, heavy-duty diesel vehicles that travel

in California but are registered in other states are subject only to federal emission

certification standards; these vehicles contribute approximately 25 percent of the heavy

heavy-duty vehicle-miles-traveled in California.

The CAA also requires California to receive authorization from the U.S. EPA for

controls over on-road (CAA Section 209(b)(1)) and the non-preempted off-road sources

(CAA section 209(e)(2)(A)). Overall these provisions make the U.S. EPA an important

partner in control of emissions from diesel engines.

The following sections briefly describe the existing federal, state, and local

programs that currently apply to diesel-fueled engines and vehicles operating in

California. A more detailed summary of the statutes and regulations may be found in

the tables in Appendix V.

A. What current federal, state, or local regulations address diesel PM

emissions from mobile diesel-fueled engines?

Virtually all new diesel-fueled on-road and off-road motor engines and vehicles

sold in California are required to meet both federal and state emission certification

requirements. Preempted engines, as noted above, must meet only the federal

requirements. In most cases, California’s motor vehicle and diesel-fueled engine

programs are designed to be consistent with the federal programs. To ensure the

on-road engines continue to have functional controls and proper maintenance,

California has implemented Heavy-Duty Vehicle Inspection and Periodic Smoke

Inspection Programs to reduce excessive smoke emissions and tampering with on-road

diesel-fueled vehicles over 6,000 pounds gross vehicular weight for both in-state and

out-of-state registered heavy-duty diesel vehicles. Non-regulatory strategies, which
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include incentives and voluntary agreements with vehicle and engine manufacturers,

have also been implemented in California to accelerate reductions in certain criteria

pollutants.

B. What current federal, state, or local regulations address diesel PM

emissions from stationary and portable diesel-fueled engines?

In California, the local air pollution control and air quality management districts

(Districts) establish rules and regulations for controlling emissions from new and

existing stationary sources of air contaminants. These rules and regulations address

both criteria and toxic air contaminant emissions.

District preconstruction and operating permit programs implement the local,

State, and federal air pollution control requirements applicable to new or modified

sources of air pollution. Larger new or modified sources located in a nonattainment

area must apply the Lowest Achievable Emission Rate control technology to minimize

emissions, and they must “offset” the remaining emissions with reductions from other

sources when appropriate. A new or modifying source located in an attainment or

unclassified area must apply the Best Available Control Technology and meet additional

requirements aimed at maintaining the region’s clean air. In addition, “major sources” of

air pollution must obtain federal Title V operating permits that govern continuing

operation.

Many Districts have also adopted, pursuant to the California Health and Safety

Code, Reasonably Available Control Technology/Best Available Retrofit Control

Technology requirements that apply to existing sources located in nonattainment,

attainment, and unclassified areas. These requirements are also implemented through

the district’s permit program.

Pursuant to State law, the ARB has established the Portable Equipment

Registration Program (PERP) which is a voluntary program for the registration and

regulation of portable engines and associated equipment. Several Districts have

implemented similar registration programs. Portable equipment not registered through

the ARB or a local district may be subject to District stationary source permit

requirements, depending on the size of the engine. In addition, the U.S. EPA and ARB

have established engine certification standards for new off-road engines (of which

portable engines are a subset). These engines are available for use in portable

equipment.

C. What current federal, state or local regulations address diesel fuel

formulation?

Current federal U.S. EPA regulations establish fuel registration and formulation

requirements. All diesel fuels and all additives for on-road motor vehicles are required

to be registered with the U.S. EPA. The ARB has established California fuel formulation

requirements, applicable to all motor vehicles, that either meet or exceed existing
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federal formulation requirements. In addition, ASTM D 975 specifies standards which

diesel fuels should meet to ensure safety, reliability, and performance. Generally,

alternative diesel fuels do not meet all of the ASTM specifications.

Since 1993, the sulfur content limit of California diesel (as well as diesel fuel sold

to on-road vehicles nationwide) has been set at a maximum 500 parts per million by

weight (ppmw). However, the average sulfur content of complying fuel formulations

currently being sold in California is about 140 ppmw.1 Further, California’s diesel fuel

specifications include an aromatics limit and the fuel specifications apply to both

on-road and off-road vehicles (EPA’s fuel sulfur requirements only apply to on-road

vehicles). Although stationary engines are not required to use fuel that meets California

Air Resources Board diesel (CARB diesel) formulation requirements, virtually all use

complying fuel because of California’s single fuel distribution network. Also, under state

law, districts have the authority to establish formulation requirements for fuels to be

used in stationary engines. To date, several districts have established diesel-fueled

engine best available control technology requirements specifying the use of CARB

diesel. Portable engines registered under ARB’s Statewide Portable Equipment

Registration program are required to use CARB diesel. Beginning July 1, 2002,

medium and larger transit agencies must use diesel fuel with a sulfur content no greater

than 15 ppmw in all diesel buses.

V. EMISSION INVENTORY AND RISK

This section summarizes the statewide diesel PM emissions inventory from

diesel-fueled engines and provides ambient and near-source potential cancer risk

estimates for those emissions. A detailed description of how the inventory, ambient

concentration, and ambient risk values listed in Tables 1 through 5 of this chapter were

determined is presented in Appendix VI.

A. What are the estimated diesel particulate matter emissions for 1990, 2000,

2010, and 2020?

Table 1 lists the estimates for the statewide diesel PM emissions inventory from

diesel-fueled engines and vehicles for 1990. Tables 2, 3, and 4 provide similar

estimates for 2000, 2010, and 2020. The relative contribution of the major

subcategories of engines and vehicles that comprise the stationary and mobile

categories are also shown. All tables take into account growth in engines due to

population and economic growth and emission reductions due to both federal and state

regulations in effect at the time of the inventory estimate. These estimates do not

include proposed recommended measures discussed in Chapter VIII, including the

recently proposed 2007 federal on-road and diesel fuel standards.

 

1

141 ppmw is the volume-weighted average determined by the California Energy Commission’s

1997 California refiner survey. (See Appendix IV.)
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Table 1: Estimated Statewide Diesel PM Emissions Inventory –

Diesel-Fueled Engines and Vehicles (1990)

Category

Engine

Population

Diesel PM

(tons per year)

% of Total

Diesel PM

Emissions

STATIONARY

 Prime 4,600 400 0.9

 Emergency Stand-by 10,200 124 0.3

MOBILE

 On-road 606,700 18,400 39.7

 Off-road (Excluding Portable Equipment) 476,300 25,300 54.5

 Portable 47,600 2,200 4.7

TOTAL 1,145,300 46,400 100.0

Table 2: Estimated Statewide Diesel PM Emissions Inventory –

Diesel-Fueled Engines and Vehicles (2000)

Category

Engine

Population

Diesel PM

(tons per year)

% of Total

Diesel PM

Emissions

STATIONARY

 Prime 4,800 420 1.5

 Emergency Stand-by 11,300 138 0.5

MOBILE

 On-road 687,200 7,500 26.8

 Off-road (Excluding Portable Equipment) 498,200 18,500 66.1

 Portable 49,200 1,400 5.0

TOTAL 1,250,700 28,000 100.0

Table 3: Estimated Statewide Diesel PM Emissions Inventory –

Diesel-Fueled Engines and Vehicles (2010)

Category

Engine

Population

Diesel PM

(tons per year)

% of Total

Diesel PM

Emissions

STATIONARY

 Prime 4,400 360 1.6

 Emergency/Standby 12,300 143 0.6

MOBILE

 On-road 643,900 5,200 22.9

 Off-road (Excluding Portable Equipment) 521,300 15,900 70.0

 Portable 53,600 1,100 4.9

TOTAL 1,235,500 22,700 100.0
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Table 4: Estimated Statewide Diesel PM Emissions Inventory –

Diesel-Fueled Engines and Vehicles (2020)

Category

Engine

Population

Diesel PM

(tons per year)

% of Total

Diesel PM

Emissions

STATIONARY

 Prime 4,400 350 1.9

 Emergency/Standby 13,200 149 0.8

MOBILE

 On-road 610,200 4,900 26.0

 Off-road (Excluding Portable Equipment) 527,800 12,800 67.9

 Portable 55,200 660 3.5

TOTAL 1,210,800 18,900 100.0

The current inventory of diesel PM emissions in Table 2 shows that there are

about 28,000 tons per year of diesel PM that can potentially be reduced from a variety

of sources. The inventory also shows that the sources are numerous, with over

1.25 million diesel-fueled engines operating statewide. Comparing the statewide diesel

PM emissions in Table 1 (1990) and Table 2 (2000), shows that significant progress has

been made to reduce diesel PM emissions in California.

The bulk of the 30 percent decrease in diesel PM emissions from 2000 to 2020 is

due to currently adopted on-road standards and fleet turn-over as new vehicles with

controls replace older vehicles with little or far less effective controls. Proposed federal

standards for diesel-fueled engines are not considered in this inventory, but would

reduce total diesel PM in California by approximately 3,500 tons per year (or an

additional 15 percent when compared to year 2000 emissions) in 2020. Some reduction

in diesel PM emissions is due to a slight decrease in the on-road engine population.

B. What are the estimated statewide potential cancer risks associated with

diesel PM emissions?

Table 5 lists the estimates for the statewide population-weighted annual outdoor

average diesel PM concentrations and corresponding percent change in the

concentration for the years 1990, 2000, 2010, and 2020 resulting from diesel PM

emissions. These estimates are based on the emission inventory estimates presented

in Tables 1 through 4.

The Proposed Identification of Diesel Exhaust as a Toxic Air Contaminant,

Appendix III, Part A, Exposure Assessment2 (ID Report) reported the statewide

population–weighted annual outdoor average diesel PM concentration as 3.0 μg/m3 for

1990. The ARB staff reviewed studies conducted in the San Joaquin Valley, the South

 

2 As approved by the Scientific Review Panel on April 22, 1998.
14

Coast Air Basin, and the city of San Jose to obtain more complete PM10 ambient data.

These data, along with routinely collected ambient PM10 monitoring network data and

the 1990 PM10 emissions inventory, were used in a receptor model to estimate the

statewide outdoor concentration of diesel PM in 1990.

We estimated the statewide outdoor concentration of diesel PM for 1990, 2000,

2010, and 2020 by assuming that the ambient concentration is proportional (linearly) to

the statewide emissions. The ratio of the ambient concentration to statewide emissions

was assumed to remain constant for the years 1990, 2000, 2010, and 2020. For 1990,

this ratio was determined by using the ambient concentration from the ID report

(3.0 μg/m3) and the statewide emission estimate for 1990 from Table 1 (46,400 TPY).

Using the 1990 ratio and the statewide emissions estimates for 2000, 2010, and 2020

from Tables 2, 3, and 4, the ambient concentration estimates for 2000, 2010, and 2020

were estimated. These are presented in Table 5.

Table 5: Statewide Population-Weighted Annual Outdoor

Average Diesel PM Concentration for 1990, 2000,

2010, and 2020

1990 2000 2010 2020

Concentration (μg/m3)

3.0 1.8 1.5 1.2

Percent Reduction in

Diesel PM from 1990

Concentration

N/A 40% 50% 60%

The ID Report provided estimates of indoor and total exposure to diesel PM.

Applying the 1990 ratio to the estimated population-weighted annual outdoor average

diesel PM concentrations for 2000, 2010, and 2020 results in the following indoor

exposure estimates, respectively: 1.2 μ/m3, 1.0 μ/m3, and 0.8 μ/m3. Total exposure

estimates for 2000, 2010, and 2020 are 1.3 μ/m3, 1.1 μ/m3, and 0.84 μ/m3. The

potential risk was estimated by multiplying the statewide ambient concentration by the

unit risk factor of 300 excess cancers per million people per microgram per cubic meter

of diesel PM.3 This information, along with the estimated potential cancer risk values, is

summarized in Table 6.

 

3 The full range of unit risk factors identified by the SRP is 130 to 2400 excess cancers per million per

microgram per cubic meter of diesel particulate matter. The 300 value was recommended by the

SRP for use as a point estimate of the unit risk.
15

Table 6: Estimated Exposure of Californians to Diesel PM for 2000, 2010

and 2020

Estimated Average Air Exposure Concentration

(μg/m3 ) and Potential Risk

(excess cancers/million)

2000 2010 2020

Estimated

Average Air

Exposure

Concentration

– 1990 μg/m3

1990

Ratio

Conc. Risk Conc. Risk Conc. Risk

Outdoor

Ambient

Estimate

3.0 1.8 540 1.5 450 1.2 360

Total Indoor

Exposure

Estimate

2.0 2.0/3.0 1.2 360 1.0 300 0.8 240

Total

Exposure

Estimate

2.1 2.1/3.0 1.26 380 1.05 315 0.84 252

C. How much of the estimated statewide potential cancer risk level from air

toxics is due to diesel PM emissions?

To provide a perspective on the contribution that diesel PM has on the overall

statewide average ambient air toxics potential cancer risk, ARB staff evaluated risks

from other compounds using data from ARB’s ambient monitoring network. ARB

maintains a 21 site air toxics monitoring network which measures outdoor ambient

concentration levels for approximately 60 air toxics.

Table 7 shows the potential cancer risk from the top ten inhalation risk

contributors that the State of California has identified as TACs and routinely monitors.

The diesel PM values are calculated based on the procedure discussed in the previous

section. The risk values for the other compounds are based on the annual average

concentration (determined from ambient monitoring) multiplied by the unit risk factor for

each compound. Table 7 also shows that for the top ten risk contributors, diesel PM

contributes over 70 percent of the state estimated potential cancer risk levels.
16

Table 7: Estimated Statewide Average Potential Cancer Risk from

Outdoor Ambient Levels of Air Toxics for the year 2000

Compound

Potential Cancer Risk1,2

Excess Cancers/Million

Percent Contribution to

Total Risk

Diesel Exhaust PM10 540 71.2

1,3-Butadiene 74 9.8

Benzene 57 7.5

Carbon Tetrachloride 30 4.0

Formaldehyde 19 2.5

Hexavalent Chromium 17 2.2

para-Dichlorobenzene 9 1.2

Acetaldehyde 5 0.7

Perchloroethylene 5 0.7

Methylene Chloride 2 0.3

TOTAL 758 100

1. Diesel exhaust PM10 potential cancer risk based on 2000 emission inventory estimates presented in Table 5. All other

potential cancer risks based on air toxics network data. Used 1997 data for para-Dichlorobenzene. Used 1998

monitoring data for all others.

2. Assumes measured concentrations are equivalent to annual average concentrations and duration of exposure is

70 years, inhalation pathway only.

The South Coast Air Quality Management District also conducted a study of air

toxics in the South Coast Air Basin (Multiple Air Toxics Exposure Study II (MATES-II)) in

1998 and 1999. The MATES-II study estimated that the average basin wide potential

cancer risk from diesel PM was about 1,000 excess cancers per million, or 71 percent of

the average cancer risk from all air toxics in the South Coast Air Basin.

ARB staff’s findings are consistent with the MATES-II study in that diesel PM is a

major contributor to potential ambient risk levels and accounts for approximately 70

percent of the ambient air toxics cancer risk. Our analysis also indicates that average

ambient concentrations of air toxics are higher in the South Coast Air Basin than

elsewhere in the state, resulting in higher estimates of risk for residents of that air basin.

Staff concludes that reducing the risk from diesel PM is an essential element in reducing

the public’s overall ambient exposure to air toxics.

D. What are the potential cancer risks associated with some typical activities

where diesel-fueled engines are used?

ARB staff estimated the range of potential cancer risks from seven common

activities or situations to determine if the concentrated operation of diesel-fueled

engines could expose nearby individuals to locally elevated diesel PM concentrations

higher than average regional concentrations. The specific situations investigated

included idling school buses, truck stops, freeways, emergency and standby diesel

engine operations, prime engine operations, and warehouse distribution center

operations. Figure 2 shows the range of potential cancer risk, above background levels,

estimated for each type of activity. The risk estimate for each activity does not account

for the risk from any other diesel-fueled engines or vehicles and assumes a 70-year, or

lifetime, exposure. For more detailed information regarding each activity and the

methodology used to derive the estimates, see Appendix VII.
17

0 100 200 300 400 500 600 700 800 900

Potential Excess Cancers 

(Chances per million based on 70-years exposure)

Truck Stop

Idling School Buses

High Volume Freeway

Prime 

Engine

Emergency/Standby Engine

1,700

Distribution Center

The ranges within each activity result from 

variations of operating times and durations, 

stack parameters, facility sizes, numbers and 

sizes of equipment, and meteorological 

conditions. The estimated 70-year cancer 

risks occur at the point of maximum off-site 

impact (PMI). PMI is the off-site location 

closest to the emission source that shows the 

highest modeled concentration of diesel PM. 

PMI can be located as close as 20 meters 

from the emission source.

Low Volume Freeway

Figure 2: Potential Cancer Risk Range of Activities

Using Diesel-Fueled Engines
18

Risk is a function of the lifetime average daily dose and the carcinogenic potency

of the compound. The potential risks reported here were estimated by multiplying the

modeled concentration of a toxic compound by the carcinogenic potency value, also

known as the unit risk factor. The unit risk factor is defined as the estimated probability

of a person contracting cancer as a result of constant exposure to an ambient

concentration of 1 μg/m3 over a 70-year lifetime. This approach and the use of a

70-year lifetime is consistent with the OEHHA/ARB methodology for evaluating the

potential risk from exposure to air toxics.

We expect the estimated 70-year potential cancer risk range for each of these

activities will fall within the ranges in Figure 2. Each range assumes a 70-year

exposure to diesel PM emissions at current levels, and uses SRP’s diesel PM unit risk

factor point estimate of 300 excess cancers per million people per microgram per cubic

meter of diesel PM. The ranges within each activity result from variations in

assumptions of operating times and durations, stack parameters, facility sizes, numbers

and sizes of equipment, and meteorological conditions. For example, in the Idling

School Buses scenario the activity ranged from five buses idling two minutes each twice

per day to 20 buses idling 15 minutes each twice per day for 180 days per year.

The estimated 70-year potential cancer risks in Figure 2 are based on the

modeled diesel PM concentrations at the point of maximum impact (PMI). PMI is the

off-site location closest to the emission source that shows the highest modeled

concentration of diesel PM. The PMI can be located as close as 20 meters from the

emission point. The diesel PM concentrations and associated potential risk decreases

as one moves away from the point of maximum impact. For example, the potential

cancer risk at the point of maximum impact for the Low-Volume Freeway scenario is

estimated to be 200 excess cancers per million if a residence were located 20 meters

away. For a residence located 500 meters away, the estimated potential cancer risk

drops to 30 excess cancers per million.

The estimated risks presented in Figure 2, and the assumptions used to

determine these risks, are not based on a specific source of diesel PM. Instead,

general assumptions bracketing a fairly broad range of possible operating scenarios

were used. The estimated risks are based on the diesel PM concentration at the point

of maximum impact as determined using air dispersion modeling. The estimated risk

ranges are used to provide a “qualitative” assessment of potential risk levels near

sources of diesel PM. These estimates are based on the risk assessment methodology

and assumptions identified in Appendix VII. Actual risk levels from these types of

sources at any individual site will vary due to site specific parameters, including

equipment technologies and emission rates, fuel properties, operating schedules,

meteorology, and the actual location of off-site receptors.

Figure 2 shows that each of the investigated activities has the potential of

significant increases in potential cancer risk under certain circumstances. The potential

cancer risk associated with these activities, combined with the high statewide ambient
19

risk levels reported earlier, provide additional evidence that all categories of

diesel-fueled engines should be subject to further control requirements.

VI. CONTROL TECHNOLOGY AND FUEL OPTIONS

A. Has ARB identified control technology options that can further reduce

diesel PM emissions from diesel-fueled engines and vehicles?

Yes. The ARB has evaluated various types of control options identifying the

control efficiency, description of technology, cost, and source test data. Technical

evaluations of the control technologies, including summaries of the available emission

test information, are included in Appendix IX. Because emission test information was

deemed essential for a thorough evaluation of diesel PM control technologies, detailed

technical evaluations were not performed where the technology proponent did not

provide adequate emission test information. The most effective control technologies

evaluated by ARB staff are catalyst-based diesel particulate filters (catalyst-based

DPFs).

Catalyst-based DPFs use catalyst materials to reduce the temperature at which

collected diesel PM oxidizes. The catalyst material can either be directly incorporated

into the filter system, or can be added to the fuel as a fuel-borne catalyst (FBC-DPF).

Although catalyst-based DPFs can be used with diesel fuels of varying sulfur content,

the greatest reductions come from using very low-sulfur fuels. Used with very low-sulfur

(<15 ppmw sulfur) diesel fuel, catalyst-based DPFs have been reported to reduce diesel

PM emissions by over 85 percent.

Table 8 provides a description and range of control efficiencies of catalyst-based

DPFs and new diesel-fueled engines. The control efficiency information is based on

available test information summarized in Appendix IX. As shown, the range of control

efficiencies for catalyst-based DPFs is 85 to 97 percent.

Table 8: Control Technology Efficiencies

Control Technology

Diesel PM Control

Efficiency

Description

Catalyst-Based DPFs /

Very low-sulfur Fuel 85% - 97%

Particulate filter system where the

catalyst material is either

incorporated into the filter or added

to the fuel; Diesel fuel with a sulfur

content < 15 ppmw.

New Engine Up to 85%

Replaces existing engines with

engines certified to meet ARB/U.S.

EPA off-road engine emission

standards.
20

For existing diesel engine applications, catalyst-based DPFs have been shown to

be effective in reducing diesel PM emissions. Worldwide, DPFs have been used in over

20,000 applications. In several European countries, catalyst-based DPFs have been

installed on more than 6,500 buses, heavy-duty trucks, and municipal vehicles. In the

United States, the application of catalyst-based DPF’s is less prevalent, but several

demonstration projects have been initiated. In California, diesel-fueled school buses

and tanker trucks have been retrofitted with catalyzed DPFs as part of a program to

evaluate the effectiveness of a refiner’s low-sulfur diesel formulation. In New York, the

New York City Transit Authority’s fleet demonstration program will test the effectiveness

of catalyzed DPF’s on 50 diesel-fueled buses.

For new diesel engine applications, catalyst-based DPF technology is playing a

key role in both establishing and complying with new more stringent diesel PM

standards. The U.S. EPA recently announced its proposed regulation for heavy-duty

engine and vehicle standards and highway diesel fuel sulfur control requirements. A

diesel PM emission standard of 0.01 g/bhp/hr is proposed. This proposed standard is

based on the anticipated emission reductions from low-sulfur diesel fuel and the use of

a catalyst-based diesel particulate filter. To comply with a 2005 European Union (EU)

emission standard for diesel fueled vehicles, the French automaker, Peugeot Citroen,

recently unveiled a diesel PM catalyst-based DPF system which is expected to go into

production in the year 2000.

B. What are the costs associated with these control technology options?

Tables 9a through 9d present information on the costs associated with applying

catalyst-based DPFs4 to stationary, off-road, and on-road diesel engines, including both

retrofit and new engine applications. Table 9a provides information on the capital costs

associated with retrofitting stationary diesel engines with catalyst-based DPFs. This

information was obtained from representative catalyst-based DPF manufacturers and is

intended to represent the range in the retail costs at this time. These cost estimates are

mostly consistent with the $30 to $50 per horsepower range reported by the

Manufacturers of Emission Controls Association (MECA) in “Emission Control

Technology for Stationary Internal Combustion Engines” dated July 1997.

Table 9a: Stationary Engines - Current Catalyst-Based DPF Retrofit

Costs

Technology 40 hp 100 hp 275 hp 400 hp 1,400 hp

 Capital Cost $1,300 -

$5,000

$2,000 -

$7,500

$3,500 -

$9,000

$7,000 –

$10,500

$30,000 -

$44,000

 

4 Some Catalyst-Based DPFs require, and all Catalyst-Based DPF’s will benefit from, the use of very

low-sulfur fuel. The incremental cost of this fuel is projected to be less than $ 0.05 per gallon and is

discussed further in Appendix IV.
21

The costs associated with retrofitting off-road engines with catalyst-based DPFs

are presented in Table 9b. This information also assumes a cost of $30 to $50 per

horsepower, as reported by MECA representatives in “Exhaust Controls Available to

Reduce Emissions from Non-road Heavy-Duty Engines.”

Table 9b: Off-Road Engines - Current Catalyst-Based DPF Retrofit

Costs

Technology 190 hp5275 hp 475 hp

Catalyst-Based DPF $5,700-9,500 $8,250-13,750 $13,500- 23,750

Table 9c provides an estimate of the current cost to retrofit on-road engines and

vehicles with catalyst-based DPFs. This information assumes a cost of $10 to $20 per

horsepower, as reported by MECA in “Emission Control Retrofit of Diesel-Fueled

Vehicles” dated March 2000.

Table 9c: On-Road Engines - Current Catalyst-Based DPF Retrofit

Costs

Vehicle Class LHD MHD HHD

Average Horsepower6190 hp 250 hp 475 hp

 Capital Cost $1,900 - $3,800 $2,500 -

$5,000

$4,750 -

$9,500

In contrast to the retrofit costs presented in Tables 9a – 9c, Table 9d presents

the U.S. EPA’s estimate of the future (2007) costs of applying catalyst-based DPFs to

new on-road engines and vehicles. The U.S. EPA estimates are based on higher

production volumes, and they are similar to the future cost projections presented by

MECA in “Emission Control Retrofit of Diesel-Fueled Vehicles (March 2000).”

Table 9d: On-Road Engines - Future (2007) Catalyst-Based DPF Costs

Vehicle Class LHD MHD HHD

Average Horsepower7190 hp 250 hp 475 hp

Catalyst-Based DPF Costs8$670 $890 $1,100

 

5

The power range noted has been selected to facilitate comparison with on-road costs.

6

The average horsepower was derived from the U.S. EPA’s engine certification database for LHDD,

MHDD, and HHDD engines for model years 1999 and 2000.

7

The engine horsepower ranges were derived from the U.S. EPA’s engine certification database for

LHDD, MHDD, and HHDD engines for model years 1999 and 2000.

8

The U.S. EPA Catalyst Based-DPF cost estimates include both fixed costs (e.g., tooling, research

and development, and certification) and variable costs (e.g., hardware, assembly and markup).
22

There is a stark difference between the current costs associated with retrofitting

existing engines and the future costs associated with applying catalyst-based DPFs to

new engines and vehicles. However, we expect these costs to decline as production

volumes and experience increase. ARB staff expects that, over the next few years, the

retrofit costs presented in Tables 9a- 9c will approach the new engine costs presented

in Table 9d.

Detailed cost and cost-effectiveness analyses will be completed during the

preparation of each control measure. However, staff expects that the costs associated

with carrying out this plan will be significant and will be on the order of the costs

associated with other major ARB programs. In addition, ARB staff recognize that there

may be unique situations that require a special evaluation of the feasibility and/or

cost-effectiveness of applying catalyst-based DPF technology. These issues will be

fully investigated and considered during the development of the specific control

measures.

VII. ALTERNATIVE TECHNOLOGIES

A. What alternatives to diesel-fueled engines and vehicles exist today that

would result in lower diesel PM emissions?

Diesel-fueled engines are extensively used throughout California in equipment

and vehicles that provide for the transportation of goods, construction of homes, and

emergency power generation. (See Chapter III for more information on the uses of

diesel-fueled engines.) Diesels are the engines of choice for most “heavy-duty”

applications. However, for a significant number of applications, lower PM emitting

alternatives to existing diesel-fueled engines exist. As ARB staff develop the control

measures recommended in this report, the feasibility and cost of these alternatives will

be evaluated and considered. In most cases, it is expected that well controlled diesel

engines using very low-sulfur fuel will have equivalent PM emissions as benchmark

gasoline or CNG fueled engines. Where this is true, it is envisioned that regulations

would be structured to provide a choice of fuels. In cases where alternatively-fueled

engines offer emission performance that cannot be matched by diesel-fueled engines,

the feasibility and costs of setting standards based on the capability of alternatively

fueled engines will be assessed.

Current alternatives to diesel-fueled vehicles and equipment include:

♦ natural gas fueled vehicles and equipment;

♦ gasoline-fueled vehicles and equipment;

♦ dual-fueled vehicles and equipment;

♦ electrically-powered vehicles and equipment;

♦ fuel cell technology; and

♦ other alternatively fueled (e.g., Bio-diesel) vehicles and equipment.
23

The next step in the AB 1807 process, following approval of this report, is the

development of the specific ATCMs and regulations designed to reduce diesel PM

emissions from diesel-fueled engines and vehicles. Chapter VIII identifies the specific

control measures we currently recommend be developed. As part of the process in

developing these recommended measures, where appropriate, the ARB staff will

thoroughly evaluate available alternatives to diesel-fueled engines and diesel fuel.

Criteria evaluated by the ARB staff when considering the recommendation of alternative

technologies include:

♦ reduction in emissions of air toxics;

♦ the availability and quality of source test information;

♦ cost and cost-effectiveness of the alternative technology; and

♦ operation or design constraints associated with the alternative.

In summary, diesel-fueled engines have established themselves for a variety of

reasons as the preferred power source for many functions in our industrial society.

However, cleaner alternatives do exist which ARB staff will consider when developing

the measures recommended in this report.

ARB staff will develop the ATCMs and regulations in an open and public process.

Draft versions of ATCMs and regulations will be presented to the public for review and

comment, and a final draft version will be presented to the Board for approval. Public

outreach is an essential element in the development of any ATCM or regulation to

ensure that all affected and interested parties have full opportunity to provide input and

shape rules that are both effective and workable.

VIII. STAFF’S RECOMMENDATION

In August 1998, the ARB identified particulate matter emissions from diesel

fueled engines as a TAC, and staff was directed to begin the risk management process.

A working group was convened to advise the staff with its risk management efforts.

Since October 1998, staff has been working with the advisory committee to develop this

report on the need for further control of particulate emissions from diesel engines. Staff

finds that:

1. The current inventory of diesel PM emissions, as presented in Chapter V of

this report, demonstrates that stationary and mobile diesel engines currently

emit over 28,000 tons per year of diesel PM in California;

2. The current statewide population-weighted annual outdoor and indoor risk

from exposure to diesel PM emissions, as presented in Chapter V of this

report, is estimated at over 500 and 350 potential excess cancers per million

people, respectively; and

3. The evaluation of available diesel PM control technologies and strategies, as

presented in Appendix II, Appendix III, and Appendix IX to this report,
24

demonstrates that technically feasible and commercially available diesel PM

control measures are available for diesel-fueled engines and vehicles.

Therefore, we recommend that the Board direct staff to develop measures to

reduce diesel PM emissions from all diesel-fueled engines and vehicles. Measures that

we recommend to be developed are presented below. None of the recommended

measures will result in an increase in NOx emissions above applicable NOx emission

certification levels.

The recommended measures for regulation development are discussed in

sections A, B, and C below. Section D discusses the actions we believe the U.S. EPA

needs to pursue to support our recommendations and to reduce diesel PM emissions in

California. Section E discusses possible adverse impacts associated with the

recommended measures. A more detailed description of each recommended measure

and the associated emission reduction, risk reduction, cost analysis, and proposed

implementation date for each measure can be found in Appendices II, III, and IV.

A. What measures does ARB recommend be developed to further reduce

diesel PM emissions from mobile diesel-fueled engines and vehicles?

Table 10 summarizes the recommended measures for all mobile sources except

for retrofit of off-road portable equipment, which is discussed in the next section.

Together, these measures comprise a comprehensive program to be implemented in

California to control and reduce potential cancer risk from exposure to diesel particulate

matter from mobile sources. These measures are further subcategorized for on-road

and off-road applications. Alternative strategy applications, which are non-regulatory,

are also part of the comprehensive program. They are discussed later in this section.

As discussed in Chapter II, the recommended measures will be developed in

accordance with the requirements of AB 1807. The specific control requirements of

each measure will be developed in an open and public process. Details concerning

each specific recommended measure, which include the cost and cost-effectiveness of

controls and the availability of alternative technologies, will be explored as each

recommended measure is developed.
25

Table 10: Recommended Measures to Reduce Diesel PM from Mobile Sources

Measures

Proposed

Board

Adoption

Date

Proposed

Implementation Date

Est. PM

Reduction,

tons per

year

Est. PM

Reduction,

tons per

year

Est. Cost

per Unit, $

On-Road Measures 2010 2020

Supplemental test

procedures HDV

certification

2000 2005 n/a n/a to be

determined

Lower emission

standards for new

HDV engines

2001 2007 1,600 3,500 670-1,100

Control of emissions

from existing engines

(retrofit)

2002 2002-2008 1,870 280 1,900-9,500

 Solid waste

collection vehicles 2002

 Other public

 HDV fleets 2002

 Other public &

 private HDV

 fleets

2003-2008

Control of HDV

in-use emissions 2003 2005 n/a n/a 130-150

Off-Road Measures

Lower emission

standards for new

engines

2002 2006-2008 910 3,600 1,300-1,800

Control of emissions

from existing engines

(retrofit)

2002 2002-2008 6,000 1,500 5,700-23,800

 Public fleets 2002-2003

 Other off-road

 fleets 2006-2008

Control of in-use

emissions 2003 2006-2008 n/a n/a to be

determined

PM standards for

new diesel pleasure

craft engines

2002 2005 9 24 to be

determined

Federal Measures

Locomotive retrofit 860 760 to be

determined

Commercial marine

vessels retrofit 3900 4500 to be

determined
26

On-Road

The recommended measures for diesel-fueled on-road mobile vehicles listed in

Table 10 address both new and existing vehicles. The proposed implementation dates

listed in Table 10 are tentative. The actual implementation dates may vary based on

engine type or service and on the availability of very low-sulfur fuel. For new vehicles,

ARB staff is proposing new engine diesel PM standards that will reduce diesel PM

emission by at least 90 percent from the current on-road standards. This proposal is

based upon the U.S. EPA’s proposed heavy-duty engine and vehicle standards and

highway diesel fuel sulfur control requirements rule, and the expected engine, fuel, and

control technology development needed to meet the proposed standards. For existing

vehicles, ARB staff is proposing diesel PM emissions be reduced, for almost all

(90 percent) engines, by at least 85 percent. This equates to an overall diesel PM

emission reduction of 75 percent from existing vehicles. This reduction can be achieved

through the addition of after-treatment technology, or replacement of existing engines

with new technology or alternatively fueled engines. The details of each of the

recommended measures will be addressed during the actual regulation development

process. In-use compliance programs will be implemented or enhanced to maintain the

diesel PM emission reductions achieved through cleaner new engine standards and

retrofits.

Off-Road

The recommended measures for diesel-fueled off-road engines are similar to

those for on-road vehicles: more stringent diesel PM standards, after-treatment control

retrofit requirements, and in-use compliance programs. In contrast, to on-road vehicles,

most off-road engines are not registered by the State, with the exception of portable

engines, boats, and off-highway motorcycles that are permitted and/or registered by

local districts or the State. Therefore, to ensure the application of recommended

measures such as inspection and maintenance programs, in-use compliance testing, or

mandatory retrofitting of older equipment, the ARB and district staff may rely on

mechanisms such as warranty registration, local operating permits, and contract

requirements.

Non-Regulatory Strategies

Non-regulatory strategies for mobile sources include guideline development,

voluntary memoranda of understanding, and non-regulatory incentive programs. A

variety of voluntary and incentive programs are being proposed to achieve reductions

beyond those California can achieve through regulatory action. These are activities the

ARB does not currently have the authority to regulate and for which regulations may not

be the most effective action. While pursuing these non-regulatory strategies, ARB staff

will work with the appropriate stakeholders to achieve voluntary reductions in diesel PM.

The non-regulatory strategies being considered by the ARB staff include:
27

♦ the voluntary application of diesel particulate filters for locomotives;

♦ the voluntary application of diesel particulate filters for commercial marine

vessels;

♦ developing a memorandum of understanding (MOU) for the retrofit of airport

ground support equipment;

♦ the voluntary retrofit of emergency vehicles; and

♦ implementing transportation control measures – idling restrictions;

B. What measures does ARB recommend be developed to further reduce

diesel PM emissions from stationary and off-road portable diesel-fueled

engines?

Table 11 summarizes the recommended measures designed to reduce diesel

PM emissions from stationary and off-road portable diesel-fueled engines. The

proposed implementation dates listed in Table 11 are tentative. The actual

implementation dates may vary based on engine type or service and on the availability

of very low-sulfur fuel. The measures identified in this section are discussed in more

detail in Appendix II. For new engines, the recommended control measures presented

in Table 11 require the application of catalyst-based DPFs or a similar technology that

will reduce diesel PM emissions by at least 90 percent from uncontrolled levels. For

existing vehicles, ARB staff is proposing diesel PM emissions be reduced, for almost all

(90 percent) engines, by at least 85 percent. This equates to an overall diesel PM

emission reduction of 75 percent from existing vehicles. This reduction will be achieved

through the addition of after-treatment technology, replacement of older technology

engines with new technology or alternatively fueled engines, or restrictions placed on

the operation of existing equipment. The details of each of the recommended measures

will be addressed during the development of each of the air toxic control measures and

regulations. Because of the variety of existing engines, as well as the multitude of

applications, staff expects that no single control technology will be universally applicable

to all retrofit applications.

Tables 9a and 9b presented information on the costs associated with applying

catalyst-based DPFs on both new and retrofit stationary and portable engines. The

preliminary cost-effectiveness for the control measures identified in Table 11 ranges

from 5 to 200 dollars per pound of diesel PM reduced. The cost per pound of diesel PM

reduced reflects the predicted costs associated with purchasing, installing, and

maintaining a catalyst-based DPF on each of the diesel-fueled engines addressed by

the recommended measures. We believe these cost-effectiveness estimates similar to

the cost-effectiveness estimates for regulations developed to reduce other particulate

compounds that have been identified as toxic air contaminants (e.g., hexavalent

chromium and lead).
28

Table 11: Recommended Measures to Reduce Diesel PM from Stationary and

Off-Road Portable Sources

Control Measure Proposed Board

Adoption Date

Proposed

Implementation

Date

Estimated PM

Reduction

2010 (TPY)

Estimated PM

Reduction

2020 (TPY)

Stationary Engine

New Engines 2002 2002 33 21

Prime Engine Retrofit 2002 2003 70 66

Emergency Standby

Retrofit 2002 2003 105 105

Off-Road Portable Engine

Retrofit 2002 2003-2005 712 252

Agricultural Engine

Retrofit 2002 2003-2005 297 197

Stationary

The recommended measures for stationary diesel-fueled engines listed in

Table 11 address both new and existing engines. For new engines, the ARB staff

recommends an ATCM be developed based on the requirements of the ARB’s

permitting guidance document, Risk Management Guidance for the Permitting of New

Stationary Diesel-fueled Engines, (September 2000). (See Appendix II for a more

detailed description of Guidance requirements.) Diesel PM emission reductions from

new stationary diesel-fueled engines will be accomplished by requiring these engines to

meet either specific technology requirements (i.e., stringent diesel PM engine

certification levels, usage of low-sulfur diesel fuel, and application of catalyst-based

DPFs); or an equally stringent performance standard.

For existing prime (non-emergency) engines and emergency standby engines,

ARB staff recommends the development of ATCMs that define retrofit control

requirements. As shown in Table 11, ARB staff predicts the implementation of the

prime engine and emergency standby engine ATCMs by 2003 will result in diesel PM

reductions of up to 70 tons and 105 tons in 2010, respectively. To achieve this

reduction, ARB staff is proposing diesel PM emissions be reduced, for almost all

(90 percent) engines, by at least 85 percent. This represents a 75 percent reduction in

diesel PM emissions from engines in these categories. The details of each of the

recommended measures will be addressed during the development of the regulations.

Although catalyst-based DPFs are available, for these sources, this technology may not

prove to be cost-effective for all engines especially smaller engines with limited hours of

operation. During the ATCM development process, the ARB staff will conduct a more

detailed cost-effectiveness analysis to help in determining the appropriateness of these

controls. It is anticipated that both of these ATCMs would be fully implemented prior to

2010.
29

There are over 6,000 agricultural irrigation pump engines in California,

representing about 11 percent of the total stationary and portable engine inventory.

Because of the high use of these engines, they are a significant source of diesel PM

and contribute about half of the diesel PM emissions from the entire stationary engine

category. In addition, agricultural irrigation pumps tend to be concentrated in specific

regions of the State, contributing proportionally higher emissions within these regions.

H&SC section 42310(e) prohibits districts from requiring a permit for most

equipment used in agricultural operations. However, the State and districts may

establish emission control requirements for stationary agricultural equipment.

Therefore, ARB staff recommends working with the agricultural community to develop a

comprehensive program to reduce emissions from engines used in agricultural

operations. This program should evaluate both the substitution of diesel engines with

electrically driven equipment and a comprehensive retrofit element.

ARB staff predicts a reduction of diesel PM from agricultural irrigation pumps of

up to 297 tons per year by 2010 and 197 tons per year by 2020. To achieve this

reduction, ARB staff is proposing diesel PM emissions be reduced, for almost all

(90 percent) engines, by at least 85 percent. This represents a 75 percent reduction in

diesel PM emissions from the engines in this category. This reduction will be achieved

through the addition of after-treatment technology, replacement of older technology

engines with new technology engines, use of alternative-fueled engines, or

electrification. The details of each of the recommended measures will be addressed

during the development of each of the regulations.

Off-Road Portable

Staff recommends that the ARB develop regulations to reduce diesel PM

emissions from existing off-road portable diesel engines. New engines for off-road

portable equipment will be regulated by the off-road rules discussed above. The ARB

currently administers the Statewide Portable Equipment Registration Program

(Statewide Registration Program) Regulation (Title 13 California Code of Regulation

§2450 - 2466), which is a voluntary program for the statewide registration and regulation

of off-road portable engines. To date, approximately 12,000 off-road portable engines

have been registered. The staff recommends that the Statewide Registration Program

Regulation be amended to include requirements for reducing diesel PM emissions from

portable diesel engines through the application of catalyst-based DPFs, electrification

where feasible, and consideration of alternate fuels. In addition, staff recommends the

development of an ATCM, for implementation by local districts, consistent with

amendments to the PERP regulation. Staff predicts compliance with the ATCM would

reduce diesel PM emissions up to 712 tons per year in 2010 and up to 252 tons per

year by 2020. To achieve this reduction, ARB staff is proposing diesel PM emissions be

reduced, for almost all (90 percent) engines, by at least 85 percent. This represents a

75 percent reduction in diesel PM emissions the engines in this category. This

reduction will be achieved through the addition of after-treatment technology,

replacement of existing engines with new technology or alternatively fueled engines, or
30

restrictions placed on the operation of existing equipment. The details of each of the

recommended measures will be addressed during the development of the regulations.

C. What measures does ARB recommend regarding diesel fuel reformulation?

Table 12 summarizes the recommended measures regarding diesel fuel

reformulation. The measures identified in this section are discussed in more detail in

Appendix IV.

Table 12: Summary of Recommendations

Emission

Reduction (%)

Recommendation Diesel PM

Incremental

Cost ($/gal)

Implementation

or Issue Date

Very low-sulfur CARB diesel

(< 15 ppmw S) > 90 * < 0.05 2005-2006

Guidance on alternative “diesel”

fuels 20 ** < 0.18 ** 2001

* Emission reductions with after-treatment.

** Estimated for emulsions of water in CARB diesel.

ARB staff recommends that a regulation be adopted in 2001 that requires very

low-sulfur CARB diesel for all diesel-fueled engines statewide, effective in 2006. ARB

also recommends that programs be developed to ensure the adequate supply of very

low-sulfur diesel fuel for vehicle fleets and stationary engines that are required through

state or local rules to install catalytic add-on controls prior to 2006. The U.S. EPA has

published proposed regulations which would require that all diesel fuel sold for use in

on-road vehicles have a sulfur content no greater than 15 ppmw, beginning June 1,

2006. It is envisioned that the ARB regulation would apply to on-road and off-road

sources but would otherwise be consistent with the U.S. EPA’s efforts and enable the

retrofit of off-road and stationary diesel engines with catalyst-based after-treatment

control technologies.

ARB staff is also proposing to develop guidance on synthetic or alternative diesel

fuel options. Synthetic or alternative diesel fuels may cost more than reformulated very

low-sulfur CARB diesel, but should be considered if shown to be cost-effective for

reducing diesel PM. These alternatives may result in significant benefits for

higher-emitting categories, such as off-road engines. Synthetic or alternative diesel

fuels may also prove to be part of the preferred control strategy for diesel-fueled

engines or vehicles that result in relatively high risk, or where control retrofit options are

very expensive or difficult to implement.

The guidance will identify alternative diesel fuels and provide information on

associated emission reductions and cost. The guidance would assist local districts in

their permitting of fleets and equipment, and may be especially useful in cases where

control equipment retrofits are impractical.
31

D. What impact will the recommended measures have on diesel PM emissions

and risk?

As illustrated in Figures 3 and 4, ARB staff estimates the full implementation of

the recommended measures, including retrofit of locomotives and commercial marine

vessels, will result in an overall 75 percent reduction in the diesel PM inventory and the

associated potential cancer risk for 2010, and an 85 percent reduction for 2020, when

compared to today’s diesel PM inventory and risk. These reductions will occur through

the combined actions of both California and the U.S. EPA to adopt and implement rules

that reduce diesel PM.

From 2000 to 2010, ARB staff predicts diesel PM emissions and risk would

decrease by only about 20 percent if the recommended measures are not implemented.

This reduction would result from the implementation of existing federal and state

regulations and the attrition of older diesel-fueled passenger cars and light-duty trucks

from the on-road fleet. The U.S. EPA has proposed new, lower emission standards for

heavy-duty trucks for 2007 and lower sulfur limits for diesel fuel (on-road vehicles only)

in 2006. The benefits of these proposed rules are not included as existing measures

because they have not been adopted as of the date of this Plan.

The recommended measures can be grouped as follows: measures addressing

on-road vehicles; measures addressing off-road equipment and vehicles, and measures

addressing stationary and portable engines. These measures include the U.S. EPA

proposed 2007 new heavy-duty truck standards and the proposed 2006 low-sulfur fuel

limits. Figure 4 illustrates the impact of each of these groups of measures on projected

diesel PM emission levels for 2010 and 2020. As shown, off-road recommended

measures have the largest impact. Of the off-road recommended measures, the retrofit

measures (see Table 10) result in over 90 percent of the diesel PM reductions

associated with all of the off-road measures.
32

Figure 3: Projected Percent Reduction in Diesel PM Cancer Risk from year 2000 Levels With and Without 

ARB Risk Reduction Plan (RRP) Implemented

0

10

20

30

40

50

60

70

80

90

100

2000 2010(w/o RRP) 2010(w RRP) 2020(w RRP)

Year

Percent of Year 2000 Cancer Risk

Figure 4: Projected Diesel PM Emission Levels With and Without ARB Risk Reduction Plan 

(RRP) Implemented

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

2000 2010 (w/o RRP) 2010 (w/ RRP) 2020 (w/o RRP) 2020 (w/ RRP)

Year

Diesel PM Emissions (Tons/Year)

Off-Road On-Road Stationary & Portable
33

E. What other expected benefits are associated with implementing the

recommended measures?

As discussed in the previous two sections, full implementation of the measures in

this plan will result in significant reductions in diesel PM emissions and the associated

risk. There are additional benefits associated with reducing diesel PM emissions.

These include:

♦ Increased visibility;

♦ Less material damage due to “soiling” of surfaces with diesel PM;

♦ Decreased noncancer health effects associated with diesel PM; and

♦ Decreased deposits of diesel PM and toxic chemicals on to surface water.

F. What possible adverse impacts may be associated with the recommended

measures?

Most recommended measures require the use of add-on control devices, engine

modifications, catalysts, low-sulfur diesel fuel and/or alternative fuel formulations. ARB

staff has identified possible adverse environmental and safety impacts associated with

the recommended measures. Each of these impacts will be fully investigated and

addressed during the rulemaking process. Possible adverse impacts are identified

below.

♦ Potential for decrease in fuel economy;

♦ Potential for increases in emissions of hydrocarbons (HC), oxides of nitrogen

(NOx), and carbon monoxide (CO);

♦ Potential for changes in composition of diesel exhaust that could result in an

increase in emissions of other toxic air pollutants.

♦ Potential for contamination of ground and surface waters;

♦ Potential safety issues due to use and handling of gaseous-fuels; and

♦ Potential increase in hazardous waste from the disposal of spent catalyst

material.

G. What actions should the U.S. EPA pursue to support the ARB staff’s

recommended measures?

ARB staff recommends that the U.S. EPA adopt standards and regulations

applicable to all 50 states that are similar in both scope and stringency to the measures

in this plan. Further, ARB staff recommends the U.S. EPA take the following actions to

support the measures in this plan and to reduce diesel PM emissions nationwide.

♦ The U.S. EPA should implement more stringent emission standards for diesel

PM in the Tier 3 rulemaking than are currently envisioned in the Off-Road

Statement of Principles.
34

Currently, the federal Clean Air Act preempts California from regulating new

construction and farm equipment below 175 horsepower, new locomotives

and locomotive engines, and commercial marine engines. Preempted

off-road vehicles and equipment generate approximately 60 percent of the

diesel PM emissions from off-road sources, thus limiting California’s ability to

achieve significant emission reductions on its own. Recent developments

suggest that off-road engine control can move directly to after-treatment

technology-based standards with higher emission reductions, on a

cost-effective per engine basis. The U.S. EPA should, therefore, consider

accelerating the implementation of emission standards based on

after-treatment technologies with the goal of reducing diesel PM emissions by

90 percent from engines in these categories.

♦ Require all diesel-fueled on-road and off-road engines and vehicles to use

very low-sulfur diesel fuel (<15 ppm).

The U.S. EPA has proposed regulations that would require all very low-sulfur

diesel fuel to be sold for use in on-road vehicles beginning June 1, 2006, but

has not proposed to extend this requirement to off-road sources. ARB staff’s

recommended measures for off-road engines are based on the use of very

low-sulfur diesel fuel and the use of exhaust after-treatment devices which

would require low-sulfur fuel. It is critical that very low-sulfur diesel fuel be

required to be sold nationwide for use in both on-road and off-road engines

and vehicles. If not, California-only off-road regulations should be developed,

but issues concerning the cost-effectiveness of developing California-only

engine/after treatment systems and the compatibility of those systems with a

higher sulfur national off-road diesel fuel need to be explored.

♦ The U.S. EPA should require more stringent control of PM emissions from

commercial marine vessels through retrofit of existing engines.

Emissions from commercial marine vessels, which include ocean-going

vessels, tugboats, fishing boats, cruise ships, and other large ships, are a

major source of diesel PM which is expected to grow from 2000 to 2010. A

program to retrofit existing engines could provide significant benefits over the

adopted controls for new engines recently adopted by the U.S. EPA. The

U.S. EPA should, therefore, develop standards to reduce diesel PM

emissions from these engines.

♦ The U.S. EPA should require the implementation of a retrofit program to

reduce diesel PM from locomotives.

The current national rule only affects particulate matter emissions from model

year 2005 and later locomotives and does not significantly reduce PM

emissions from older locomotives. Recent developments in diesel particulate

filter technology suggest that a locomotive retrofit program may be feasible

and cost-effective. The U.S. EPA should, therefore, develop retrofit standards

to reduce diesel PM emissions from engines in these categories.