EMBARGOED UNTIL 

12:30 PM EASTERN, MONDAY, OCTOBER 31, 2011 

Cleaner Cars, Cleaner Fuel, 

Cleaner Air: 

The Need for and Benefits of 

Tier 3 Vehicle and Fuel Regulations 

National Association of Clean Air Agencies 

October 2011
About NACAA 

The National Association of Clean Air Agencies (NACAA) is the association of air quality 

agencies in 50 states and territories and over 165 metropolitan areas throughout the country. 

The members of NACAA have primary responsibility for implementing our nation’s air pollution 

control laws and regulations. The association serves to encourage the exchange of information 

and experience among air pollution control officials; enhance communication and cooperation 

among federal, state and local regulatory agencies; and facilitate air pollution control activities 

that will result in clean, healthful air across the country. 

NACAA is headquartered in Washington, DC. For further information, contact the association at 

444 North Capitol Street, NW, Suite 307, Washington, DC 20001 (telephone: 202-624-7864; 

fax: 202-624-7863; email: 4cleanair@4cleanair.org) or visit our web site at www.4cleanair.org. 

Acknowledgements 

On behalf of NACAA, we are pleased to provide Cleaner Cars, Cleaner Fuel, Cleaner Air: The 

Need for and Benefits of Tier 3 Vehicle and Fuel Regulations. Our association prepared this 

document to inform the U.S. Environmental Protection Agency’s (EPA’s) efforts to develop “Tier 

3” vehicle and fuel standards to affect emissions reductions that will lead to cleaner, more 

healthful air and better protect public health and the environment. 

The recommendations included in this report are ones previously conveyed by NACAA to EPA.1

 

Based on the analyses underlying this report, NACAA has concluded that the more rigorous 

vehicle emissions standards and 10-parts-per-million average gasoline sulfur level that we have 

recommended can be achieved at a price of around $150 per new vehicle and less than a 

penny per gallon of gasoline. In return, vehicle-related emissions of air pollutants that lead to a 

host of adverse public health and environmental consequences will be reduced substantially, 

greatly assisting states and localities in achieving their clean air goals. 

NACAA expresses gratitude to Michael P. Walsh for his expert assistance in conducting 

analyses and preparing this report. 

We believe that Cleaner Cars, Cleaner Fuel, Cleaner Air: The Need for and Benefits of Tier 3 

Vehicle and Fuel Regulations will serve as a valuable resource as our nation moves forward to 

examine and adopt air pollution control programs. 

 

David J. Shaw Bruce S. Andersen 

NACAA Co-President NACAA Co-President 

 

1

See NACAA Letter to EPA Administrator Lisa P. Jackson (June 27, 2011), available at 

http://www.4cleanair.org/Documents/Tier3NACAALettertoEPAFinal062711.pdf. 
Table of Contents 

Executive Summary 1 

 

I. Introduction: The Problem 4 

 A. Widespread Nonattainment 4 

B. The Special Problem of Ozone 5 

C. Motor Vehicles Remain the Major Contributor 8 

D. Special Concerns with Proximity to Traffic 9 

II. The Recommended Tier 3 Program: 

 Vehicle Standards 10 

A. Emissions Standards 10 

B. Technologies Needed To Comply with 12 

 Tier 3 and Associated Costs 

III. The Recommended Tier 3 Program: 12 

Fuel Standards 

A. Global Trends 12 

B. The Cost of Reducing Sulfur in Gasoline 13 

C. Relative Cost Effectiveness 15

IV. Emissions Reductions 16 

V. Conclusion 19 

Appendix A: Health Effects Associated with Vehicle- 20 

 Related Pollutants 

Appendix B: Environmental Effects Associated with 28 

 Vehicle-Related Pollutants 
Executive Summary

Ozone levels throughout the country would be reduced overnight if the U.S. Environmental 

Protection Agency (EPA) requires cleaner gasoline and low-emission passenger vehicles. The 

analysis presented by the National Association of Clean Air Agencies (NACAA) in this report 

finds that the amount of air pollution that would be immediately reduced from lowering the sulfur 

content of gasoline is equivalent to removing 33 million cars and light trucks – approximately 

one in eight – from our roads. This dramatic result would come at a price of less than a penny 

per gallon of gasoline. Cleaner gasoline would also enable improved technologies on cars and 

light trucks that could yield substantial vehicle emissions reductions at a cost of about $150 per 

car. Moreover, this highly cost-effective program would yield significant health and welfare 

benefits. 

Although motor vehicle emissions have improved dramatically since the federal mobile source 

program was introduced in 1968, they remain a primary source of the volatile organic compound 

(VOC) and nitrogen oxide (NOx) emissions that result in the formation of ozone. Accordingly, if 

we are to achieve and sustain healthful air quality across the country, we must further control 

motor vehicle emissions and fuels. 

In December 1999, EPA adopted landmark regulations to clean up light-duty motor vehicles and 

the gasoline that fuels them. This “Tier 2” program, which took effect in 2004, required lightduty vehicles, including sport utility vehicles, to be 90 to 95 percent cleaner. To enable 

automakers to meet the new standards, EPA required oil refiners to remove about 90 percent of 

the sulfur in gasoline. Sulfur poisons catalysts that control vehicle exhaust and inhibits the 

performance of catalytic converters thereby increasing vehicle emissions. 

A dozen years later, notwithstanding a substantial and sustained effort and remarkable progress, 

more must be done to reduce emissions and protect public health. Air pollution in the U.S. 

remains a serious and widespread problem. More than 125 million people still live in areas that 

exceed at least one of the health-based National Ambient Air Quality Standards (NAAQS), with 

120 million of these residing where ozone (also known as smog) levels exceed that federal 

standard. 

Fortunately, additional controls are available at very modest cost. EPA is expected to introduce, 

later this year, a “Tier 3” program of tougher light-duty vehicle emissions standards that follow 

closely the Low-Emission Vehicle (LEV) III requirements being pursued by the California Air 

Resources Board (CARB). 

A critical piece of this program, and one that will ensure cost-effective implementation of these 

stricter standards, is further improved gasoline quality, particularly a reduction in average 

gasoline sulfur levels from approximately 30 parts per million (ppm) today, enacted as part of 

the 1999 Tier 2 program, to an average of 10 ppm. Such a reduction in sulfur levels will 

immediately improve the NOx control effectiveness on all existing Tier 2 cars and will be 

equivalent to eliminating over 33 million cars from the nation’s highways. Further, overall, this 

program has the potential to yield reductions in emissions of NOx, carbon monoxide and VOCs 

on the order of 29 percent, 38 percent and 26 percent, respectively, by 2030. 

CARB has estimated the costs of its LEV III program to be about $100 per vehicle. The cost of 

the federal Tier 3 program would likely be slightly higher, approximately $150 per vehicle on 
Page | 2 

average, because under California's existing requirements new vehicles in the state are almost 

halfway to achieving the LEV III standards. 

Based upon a new study conducted by MathPro – an expert refinery consulting firm – the price 

of reducing the average gasoline sulfur content to 10-ppm would be similarly modest, likely less 

than one cent per gallon. Further, lowering sulfur in gasoline is a very cost-effective means by 

which to achieve substantial emissions reductions, at about $3,300 per ton of NOx removed. 

Reducing emissions that cause air pollution is a zero-sum game. Forgoing reductions from one 

source category means garnering reductions from another. In the absence of a federal Tier 3 

program with low-sulfur gasoline, states and localities will have no choice but to turn to other, 

more expensive, less cost-effective measures – for example, placing additional controls on 

small “mom and pop” businesses and instituting transportation control measures – to achieve 

the emissions reductions needed to attain and sustain clean air goals. Further, this could prove 

to be very difficult in areas where there may not be sufficient sources to control in order to gain 

emissions reductions on the order of those that will result from Tier 3, or where state and local 

controls on certain sources will be politically unacceptable. 

The emissions reductions to be achieved from Tier 3 vehicles and gasoline will be accompanied 

by substantial health and welfare benefits. For example, the NOx reductions anticipated to 

result from this program will lead to reduced levels of ambient particulate matter (PM) that, in 

turn, will translate into more than 400 avoided premature deaths and 52,000 avoided lost 

workdays each year. The benefits of the ozone reductions to occur from Tier 3 vehicles and 

gasoline will lead to even greater health protection. 

Just as NACAA supported EPA’s efforts in the late 1990s to adopt the Tier 2 motor vehicle and 

fuel program, the association firmly supports the agency’s efforts to seek additional reductions 

from light-duty vehicles and fuels. An appropriately stringent Tier 3 program based on a 

systems approach that addresses both the vehicle and its fuel will yield critically needed, and 

extremely cost-effective, emissions reductions. These reductions will enable state and local air 

pollution control agencies’ efforts to achieve and maintain clean air goals and protect public 

health and welfare. 

EPA assumed a Tier 3 program with strong fuel standards in its baseline analysis for attainment 

of the ozone NAAQS (i.e., 0.075 parts per million) adopted in 2008. Now states and localities 

are also facing, or preparing to face, the challenge of meeting new NAAQS for particulate matter, 

nitrogen dioxide and sulfur dioxide. In addition, EPA has confirmed that tailpipe emissions will 

increase as a result of the federal renewable fuels standard enacted by Congress in the Energy 

Independence and Security Act of 2007, further heightening the need for the Tier 3 program. 

Moreover, EPA’s most recent National Air Toxics Assessment data show that every person in 

the U.S. has an increased cancer risk of over 10 in one million (one in one million is generally 

considered “acceptable”); and the majority of compounds that cause this risk comes from motor 

vehicles. 

In short, EPA should take full advantage of the opportunity to establish a meaningful and 

effective Tier 3 program – including vehicle and fuel standards – to ensure that states and 

localities across the nation, which face increasing air quality challenges, can meet their statutory 

obligations. 
Page | 3 

Therefore, as NACAA recommended to EPA Administrator Lisa P. Jackson in June 2011,2 EPA 

should take immediate action to propose this year and promulgate next year Tier 3 vehicle 

standards modeled after California’s LEV III program, including improved tailpipe emissions 

standards for NOx and non-methane organic gases and an average gasoline sulfur 

concentration of 10 ppm or lower. 

 

2

Id. 
Page | 4 

Cleaner Cars, Cleaner Fuel, Cleaner Air: 

The Need for and Benefits of Tier 3 Vehicle and Fuel Regulations 

I. Introduction: The Problem 

The U.S. has the proud distinction of having the strongest motor vehicle pollution control 

program in the world. As illustrated below, our nation also has the largest vehicle population on 

the planet. Although air quality in the U.S. has improved substantially, serious problems remain. 

Emissions from motor vehicles continue to be a key contributor to these problems. The good 

news is that there is still more we can do to reduce motor vehicle emissions and enhance our 

ability to protect public health and welfare. Additional cost-effective vehicle controls are 

available for passenger cars and light trucks, but availing ourselves of this opportunity will 

require reduced sulfur in gasoline. 

Source: Prepared by MP Walsh based on Data from Ward’s World’s Motor Vehicle Data (2011). 

A. Widespread Nonattainment 

In spite of a significant and sustained effort spanning more than 40 years, the air pollution 

problem in the U.S. remains serious and widespread. As illustrated below, according to the U.S. 

Environmental Protection Agency (EPA), more than 125 million people still live in areas across 

the nation where air pollutant levels exceed at least one of the health-based National Ambient 

Air Quality Standards (NAAQS). 
Page | 5 

Number of People Living in Counties with Air Quality 

Concentrations Above the Level of the Primary Health-Based NAAQS

Source: http://www.epa.gov/airtrends/2010/dl_graph.html.

B. The Special Problem of Ozone 

Health and Environmental Impacts of Ozone

Ozone, commonly referred to as smog, is the most widespread of these pollutants with almost 

120 million Americans still exposed to unhealthful levels. Exposure to ozone imperils human 

health in a host of ways and has been proven to result in premature mortality. Among the more 

immediate effects of exposure to ozone are shortness of breath, chest pain when inhaling, 

wheezing and coughing, asthma attacks and increased susceptibility to respiratory and 

pulmonary problems. In addition, ozone poses a threat to healthy ecosystems. Information 

provided in Appendices A and B elaborates on these adverse health and welfare impacts.

Ozone Levels Across the Country

As shown below, from 2001 to 2008, average ozone levels across the country decreased by 

only 10 percent, with more sites exceeding the standard than achieving it. 
Page | 6 

National 8-Hour Ozone Air Quality Trends, 2001-2008

Source: http://www.epa.gov/airtrends/2010/dl_graph.html.

In 2008, EPA revised the ozone NAAQS to 0.075 parts per million (ppm). In 2009, the agency 

announced it would undertake an initiative to reconsider that standard. In September 2011, the 

President asked the EPA Administrator to withdraw the reconsideration. Subsequently, on 

September 22, 2011, EPA issued a memorandum outlining the steps for moving forward to 

implement the 2008 0.075-ppm standard. At the same time, the agency provided the results of 

its preliminary review of ozone air quality data from 2008 through 2010 showing that 52 areas 

are initially estimated to exceed the 0.075-ppm standard, including areas such as Los Angeles, 

San Joaquin Valley, Baltimore, Dallas-Fort Worth, New York-New Jersey-Long Island, 

Philadelphia-Wilmington-Atlantic City, Charlotte-Gastonia-Rock Hill, Atlanta, Cincinnati, Boston, 

Baton Rouge, Denver, Sheboygan, Knoxville, Phoenix and St Louis.3 (The agency has noted 

that actual nonattainment areas will be determined through the designations process, which will 

include extensive input and review by the states and an opportunity for public comment.) 

In addition, EPA is currently reviewing the 2008 ozone standard, consistent with its statutory 

obligation to review and, as necessary, revise each NAAQS every five years. Upon completion 

of that review in 2013/2014, if EPA revises the standard consistent with levels recommended 

several years ago by the Clean Air Scientific Advisory Committee – EPA’s independent science 

advisors – many additional areas of the country would be in violation. EPA has estimated that 

tighter ozone standards would save as much as $100 billion in health costs and help prevent as 

many as 12,000 premature deaths.4

 

3

 See EPA’s initial estimate of areas exceeding the 2008 ozone standard (September 28, 2011), available at 

http://www.epa.gov/ozonepollution/pdfs/OzoneTable9-22-11.pdf.

4

 January 2010 Proposal to Revise the National Ambient Air Quality Standard for Ground-Level Ozone: General 

Overview, EPA Presentation (2010), available at http://www.epa.gov/air/ozonepollution/pdfs/20100106present.pdf . 
Page | 7 

The areas projected (via modeling) to violate an ozone standard in the range of 0.060 to 0.070 

ppm in 2020 are shown below. As the map illustrates, 99 counties are projected to violate a 

0.070-ppm ozone standard in 2020; 149 additional counties are projected to violate a 0.065-

ppm standard for a total of 248; and 203 additional counties on top of that are projected to 

violate 0.060 ppm for a total of 451. 

Source: http://www.epa.gov/air/ozonepollution/pdfs/20100104maps.pdf.

Clearly, additional controls on mobile sources, the largest contributor to ozone precursors, will 

be extremely helpful to states and localities as they strive to attain ozone air quality levels under 

the current standard and any potential new standard. 

The Air Quality Index

To help people determine the quality of the outdoor air on any given day, EPA has developed 

the Air Quality Index – or AQI. 5

 The AQI communicates information using six color-coded 

 

5

For further information about the AQI, see http://www.airnow.gov/index.cfm?action=aqibasics.aqi. 
Page | 8 

categories: green = good; yellow = moderate; orange = unhealthy for sensitive groups; red = 

unhealthy; purple = very unhealthy; and maroon = hazardous.6

The number of “Code Orange” and “Code Red” days experienced in the summer of 2011 bears 

out the need for tougher controls on motor vehicles and gasoline. Nationwide, through August 

2011, 39 states plus the District of Columbia declared a total of 4,275 Code Orange and Code 

Red days – days when the air quality was either unhealthy for sensitive groups or unhealthy for 

all. This number is 40 percent higher than the 3,123 Code Orange and Code Red days 

declared by 40 states during the same period in 2010. 

Ozone in National Parks

The ozone problem exists even in our national parks. This year, from April through September 

2011, there have been nearly 260 exceedances in parks with ozone monitors. Even with data 

for October 2011, the final month of this year’s ozone season, not yet in, national park ozone 

exceedances are greater than in either of the full ozone seasons in the past two years – 2010, 

when there were 223 exceedances, and 2009, when there were 196.7

 

C. Motor Vehicles Remain the Major Contributor 

Motor vehicles emit large quantities of carbon monoxide (CO), non-methane organic gases 

(NMOG), nitrogen oxides (NOx), particulate matter (PM), sulfur oxides (SOx) and such toxic 

substances as benzene, formaldehyde, acetaldehyde and 1,3-butadiene. Each of these, along 

with secondary by-products such as ozone and small particles (e.g., nitrates and sulfates), can 

cause serious adverse effects on health, as discussed in Appendix A. 

Motor vehicle-related pollutants also endanger the environment. Ozone has detrimental effects 

on vegetation and ecosystems and makes sensitive plants more susceptible to diseases and 

damage. Ozone also inhibits plant growth and crop yields, and may impair biodiversity. Beyond 

their contribution to ozone, motor vehicle NOx emissions contribute to a variety of other adverse

health and environmental effects including NO2 and secondary PM levels, visibility impairment, 

acid rain, eutrophication and nitrification of water bodies and soiled materials, as discussed in 

Appendix B. 

Many sources contribute to air pollution levels but, despite great progress, motor vehicles 

remain key, as the chart below illustrates. This is especially true with regard to NOx and VOCs, 

which are precursors to ozone. Therefore, further control of vehicle emissions is necessary if 

healthy air quality levels are ever to be attained and maintained.

 

6 When AQI values are between 101 and 150, a Code Orange alert is issued. Members of sensitive groups may 

experience adverse health effects at this time. For example, people with lung disease are at greater risk from 

exposure to ozone. When AQI values are between 151 and 200, a Code Red alert is issued. Everyone may begin to 

experience adverse health effects and members of sensitive groups may experience more serious health effects. 

7

See table of 2011 ozone standard exceedances at national parks, National Parks Service (accessed October 25, 

2011), available at http://www.nature.nps.gov/air/monitoring/exceed.cfm.
Page | 9 

Distribution of National Total Emissions Estimates 

by Source Category for Specific Pollutants 

Source: http://www.epa.gov/airtrends/2010/dl_graph.html.

It is important to note, in particular, that EPA assumed more stringent mobile source controls 

(characterized as “additional technology changes in the onroad transportation sector”) in its 

primary analysis baseline for attainment of the ozone NAAQS adopted in 2008.8

 The additional 

technology changes contemplated by EPA in its Regulatory Impact Analysis of the 2008 ozone 

standard equate to the Tier 3 program. Therefore, the ability of states and localities to attain the 

2008 ozone standard is tied directly to timely promulgation and implementation of Tier 3 vehicle 

and gasoline standards. 

 

D. Special Concerns with Proximity to Traffic 

Children, older adults and people with existing respiratory problems are at even greater risk if 

they live, work or go to school near major roadways. Several studies estimate the national 

population, including children, residing near major roads and other transportation sources. For 

example, the American Housing Study (AHS)9 – conducted by the U.S. Census Bureau every 

other year in odd-numbered years – surveys over 50,000 housing units nationwide. One 

question asked is whether the house is located within "half a block" or 300 feet of a railroad, 

airport or highway with four or more lanes. In the most recent AHS, for 2009, the estimated 

number of homes that met that description was 22,064,000, which is approximately 17 percent 

of all U.S. housing units.10 Assuming that housing units are distributed fairly evenly among the 

308 million residents of the U.S., approximately 52 million people live in those homes. Further, 

 

8

See Final Ozone NAAQS Regulatory Impact Analysis, Appendix 7a, EPA (March 2008), available at 

http://www.epa.gov/ttn/ecas/regdata/RIAs/452_R_08_003.pdf. 

9

See American Housing Survey, U.S. Census Bureau (2009), available at 

http://www.census.gov/hhes/www/housing/ahs/ahs.html.

10 See American Housing Survey, Table 1-6, U.S. Census Bureau (2009), available at 

http://www.census.gov/hhes/www/housing/ahs/ahs09/ahs09.html. 
Page | 10 

a review of historical surveys shows that the fraction of homes within 300 feet of a railroad, 

airport or four-plus-lane highway has been increasing since about the late 1990s. 

In another study, 11 researchers examined the number of public schools and students near 

interstate, U.S. and state highways. The metropolitan areas studied contained about 25 percent 

of the national population residing in Metropolitan Statistical Areas (MSAs) with population over 

1,000,000. In total, among the surveyed schools and students, over 30 percent fell within 400 

meters of a major roadway and over 10 percent were within 100 meters. For some MSAs, 

almost half of the student population attended schools near (within 400 meters) major roadways, 

resulting in a potentially increased risk for asthma and other chronic respiratory problems. 

Most recently, the Health Effects Institute (HEI) investigated proximity of the general population 

to roadways. HEI summarizes the literature as follows: "Estimates of the percentage of the 

population exposed to pollution from traffic range from 30% to about 45%, depending on the 

distance chosen to represent near-source effects. Traffic-related pollution, in short, affects a 

large percentage of the urban population." 12

II. The Recommended Tier 3 Program: Vehicle Standards 

To address our continuing air pollution problems it is necessary to take advantage of the 

improved vehicle emissions control technologies that have already entered the marketplace and 

to require nationwide the same low-sulfur gasoline that is already available in California. 

EPA is expected soon to propose so-called Tier 3 requirements. Based on plans already 

announced by the California Air Resources Board (CARB) to tighten California’s vehicle 

emissions standards, this NACAA study estimates what requirements would be feasible for EPA 

to adopt at the national level. 

Fortunately, additional control technologies are already available and at very modest cost. EPA 

should capitalize on this and introduce a Tier 3 program of more rigorous light-duty vehicle 

emissions standards that harmonize with the Low-Emission Vehicle (LEV) III requirements 

being pursued by the California Air Resources Board. 

A. Emissions Standards 

The figure below charts the declining NMOG+NOx standards anticipated to occur if EPA 

harmonizes federal Tier 3 standards with California’s LEV III standards beginning with Model 

Year (MY) 2017 for cars and MY 2018 for light trucks. 

 

11 Appatova, A.S.; Ryan, P.H.; LeMasters, G.K., et al. Proximal Exposure of Public Schools and Students to Major 

Roadways: A Nationwide U.S. Survey, Journal of Environmental Planning and Management 51: 631-646 (2008). 

12 Traffic-Related Air Pollution: A Critical Review of the Literature on Emissions, Exposure, and Health Effects, Health 

Effects Institute Special Report 17, Health Effects Institute (January 12, 2010), available at 

http://pubs.healtheffects.org/view.php?id=334. 
Page | 11 

Source: MP Walsh (2011). 

Not only should EPA harmonize as much as possible with CARB’s LEV III program, matching 

the LEV III fleet average in 2017, the agency should also match its vehicle “bin” structure13 with 

CARB’s LEV vehicle categories and standards (see table below). 

 

 

13 EPA’s “bin” structure is a set of ranked vehicle emission standards to which manufacturers can certify their 

vehicles. Bin 1 represents the cleanest standards.
Page | 12 

EPA and California Federal Test Procedure 

Exhaust Emission Standard Categories for Cars and Light Trucks 

Source: MP Walsh (2011). 

B. Technologies Needed To Comply with Tier 3 and Associated Costs 

The technologies needed to comply with such a Tier 3 program are almost entirely the same as 

those already on California’s Partial Zero-Emissions Vehicle (PZEV)/Super Ultra-Low-Emissions 

Vehicle (SULEV) (i.e., EPA Tier 2 bin 2) models of today: 1) increased precious metal 

(platinum/palladium/rhodium) catalyst loading, 2) optimized close-coupled catalysts, 3) 

secondary air injection pumps and 4) evaporative control systems. The only advanced 

technology that may be needed is an active hydrocarbon (HC) adsorber, but this would most 

likely be limited to just a few, if any, larger V8 engines. 

Light-duty diesel vehicles need urea-selective catalytic reduction (SCR) for NOx, diesel oxidation 

catalysts for HC, CO and PM and diesel particulate filters for PM – essentially the same 

technologies used to comply with Tier 2, although only the German automakers (which 

represent less than 10 percent of U.S. sales) are bringing diesels into the U.S. in significant 

numbers. 

CARB has estimated the costs of its LEV III program to be about $100 per vehicle. The cost of 

the federal Tier 3 program would likely be slightly higher, approximately $150 per vehicle on 

average, because under California's existing requirements new vehicles in the state are almost 

halfway to achieving the LEV III standards (2008 sales in California were about 22 percent 

SULEV, 55 percent ULEV and 23 percent LEV). 

III. The Recommended Tier 3 Program: Fuel Standards 

A. Global Trends 

As indicated above, in order to achieve the stricter emissions standards at minimal cost, and to 

take advantage of technologies already in the market place, EPA will need to lower sulfur levels 

in gasoline from the current average of about 30 parts per million (ppm) to approximately 10 

ppm. Such a reduction in national sulfur levels will immediately improve the NOx control 
Page | 13 

effectiveness on all existing Tier 2 cars and will be equivalent to eliminating over 33 million cars 

from the nation’s highways in 2017. California’s gasoline already achieves this level and, and 

as illustrated by the chart below, there is a global movement toward lower-sulfur gasoline. In 

fact, it is expected that the city of Beijing, China will introduce a 10-ppm sulfur limit for its 

gasoline next year. 

 

Source: MP Walsh (2011).

B. The Cost of Reducing Sulfur in Gasoline 

To independently determine the cost implications of lower sulfur gasoline, the International 

Council on Clean Transportation (ICCT) contracted with an expert refinery consulting company, 

MathPro, to update and slightly modify an earlier study MathPro carried out in 2009. In this new 

study,14 MathPro estimates the cost of reducing sulfur in gasoline to 10 ppm under differing sets 

of assumptions. As detailed below, based on conservative assumptions, producing 10-ppmsulfur fuel could be accomplished for less than a penny a gallon. 

In its study, MathPro found the following: 

“All U.S. refineries currently produce gasoline with an average sulfur content of 30 ppm (the Tier 

2 standard). In a typical U.S. conversion or coking refinery, FCC [fluidized catalytically cracked] 

naphtha is the primary source of sulfur in the gasoline pool. It constitutes approximately 35% of 

 

14 Refinery Economics of a National Low Sulfur, Low RVP Gasoline Standard, MathPro, Inc. (October 25, 2011), 

available at http://www.theicct.org. 
Page | 14 

the gasoline pool, and by virtue of its volume and its sulfur content accounts for about 95% of 

the sulfur content of untreated gasoline. Consequently, the primary task in meeting a tighter 

gasoline sulfur standard is reducing the sulfur content of FCC naphtha. Meeting the current 30-

ppm standard requires that the FCC naphtha have an average sulfur content of ≈ 50 ppm. 

“U.S. refineries achieve this level of sulfur control by one of three means: 

• FCC feed hydrotreating (“pre-treating”) to reduce the sulfur content of FCC feed to a 

level sufficiently low that the FCC naphtha produced by the FCC unit has a sulfur 

content of around 50 ppm. (This requires a suitable crude slate and severe FCC feed 

hydrotreating.) 

• FCC naphtha hydrotreating (“post-treating”) to reduce the sulfur content of the FCC 

naphtha to about 50 ppm. 

• A combination of pre-treating and post-treating. 

“Producing gasoline with average sulfur content of 10 ppm (the proposed standard) requires 

reducing the average sulfur content of FCC naphtha to ≈ 10 ppm. In general, there are three 

prospective routes for doing so, all of which are represented in the regional refining models. 

• Revamp an existing FCC feed hydrotreater (“pre-treater”) to reduce the sulfur content of 

FCC feed to a level sufficiently low that the FCC naphtha produced by the FCC unit has 

sulfur content of around 10 ppm. 

• Revamp an existing FCC naphtha hydrotreater (“post-treater”) to reduce the sulfur 

content of the FCC naphtha to about 10 ppm. 

• Install a new, grassroots FCC naphtha hydrotreater to reduce the sulfur content of the 

FCC naphtha to about 10 ppm. 

“Each of these requires additions to hydrogen supply, refinery energy supply, sulfur recovery 

facilities and off-sites [e.g., terminal management systems, flare systems, utilities, 

environmental treatment units]. 

“The refineries that now meet the Tier 2 sulfur standard with post-treating (with or without pretreating) would most likely follow the second route: revamp the existing post-treater. [MathPro] 

understand[s] that many of the FCC naphtha hydrotreaters installed to meet the Tier 2 sulfur 

standard are already capable of producing treated FCC naphtha with sulfur content < 10 ppm. 

Only those units that do not have this capability would require revamping. However, to be 

conservative, [MathPro] assumed that all existing FCC naphtha hydrotreating capacity would 

require revamping to meet the 10 ppm standard. 

“The refineries that now meet the Tier 2 sulfur standard solely with pre-treating (i.e., no posttreating) could adopt either the first or the third route: revamp the existing pre-treater to further 

reduce the sulfur content of the FCC feed or install a grassroots post-treater. [MathPro] 

assumed that refineries now meeting the Tier 2 sulfur standard solely with pre-treating would 

adopt the third route: install a grassroots post-treater. If the refinery’s sole focus is on gasoline

sulfur control, then installing a grassroots post-treater is likely to be the less costly route, in 

terms of both investment and operating cost.”15

 

15 Id. at 14-15. 
Page | 15 

Based on the MathPro study, it appears the most reasonable, but still conservative, 

assumptions would be: 

• All existing FCC post-treaters would require revamping to meet the 10-ppm sulfur 

standard; 

• The average capital expenditure for revamping the fleet of FCC post-treaters is 30 

percent of the expenditure for grassroots post-treaters (even though some of the existing 

units may require no revamping); and 

• The target rate of return on refinery investments is 7 percent before tax. 

Using these conservative assumptions, MathPro concluded that the per-gallon price of 10-ppmsulfur fuel would be just $0.008 – eight-tenths of a penny. 

C. Relative Cost Effectiveness 

Not only is cleaner gasoline modest in price, it is also highly cost effective at about $3,300 per 

ton of NOx reduced. This cost effectiveness makes low-sulfur gasoline especially appealing 

given that other NOx control measures being considered by states and localities are far less 

cost-effective, as shown in the chart below, which depicts NOx control measures being pursued 

by states in the Ozone Transport Region. 

Cost Effectiveness of Tier 3 Low-Sulfur Gasoline 

Relative to Other NOx Reduction Measures 

NOx Reduction Measure Cost Per Ton of NOx

Reduced 

Tier 3 Low-Sulfur Gasoline $3,300 

Oil/Gas Boilers Serving EGUs $1,100 - 8,700 

New Small Gas Boilers $3,300 - 16,000 

Municipal Waste Incinerators $2,140 (SNCR) 

HEDD EGUs $45,000 - $300,000 

per unit 

Stationary Generators $39,700 - 79,700 

Minor New Source Review $600 - $18,000 

Source: Senate Staff Briefing on the Need for Strong NOx Caps in the Eastern U.S – OTC, ICAC, NACAA 

and Maryland (July 2010). 

Reducing emissions that cause air pollution is a zero-sum game. Forgoing reductions from one 

source category means garnering reductions from another. In the absence of a federal Tier 3 

program with low-sulfur gasoline, states and localities will have no choice but to turn to other, 

more expensive, less cost-effective measures – for example, placing additional controls on 

small “mom and pop” businesses and instituting transportation control measures – to achieve 

the emissions reductions they need to attain and sustain clean air goals. Further, this could 

prove to be very difficult in areas where there may not be sufficient sources to control in order to 

gain emissions reductions on the order of those that will result from Tier 3, or where state and 

local controls on certain sources will be politically unacceptable. 
Page | 16 

IV. Emissions Reductions 

A systems-based Tier 3 program as described above has the potential to yield truly meaningful 

emissions reductions. As shown in the figure below, by 2030, overall emissions of NOx, CO and 

VOCs would be expected to decline by 29 percent, 38 percent and 26 percent, respectively. 

Source: MP Walsh (2011). 

Sulfur in gasoline is a poison that reduces the efficiency and performance of catalysts designed 

to limit vehicle emissions and adversely affects heated exhaust-gas oxygen sensors. 

Laboratory testing of catalysts has demonstrated reductions in efficiency resulting from higher 

sulfur levels across a full range of air/fuel ratios. The effect is greater in percentage for lowemission vehicles than for traditional vehicles. Studies have also shown that sulfur adversely 

affects heated exhaust-gas oxygen sensors; slows the lean-to-rich transition, thereby 

introducing an unintended rich bias into the emission calibration; and may affect the durability of 

advanced on-board diagnostic systems. 

The combustion of sulfur produces SO2, an acidic irritant that also leads to acid rain and the 

formation of sulfate particulate matter. 
Page | 17 

A more recent study indicates especially significant NOx reductions with the cleanest existing 

Tier 2/SULEV vehicles from lowering sulfur levels down almost to zero.16 Thus it is clear that 

reducing sulfur levels in gasoline will not only enable the introduction of tighter emissions 

standards for new vehicles but will also immediately reduce emissions from the existing fleet, 

particularly the large proportion of Tier 2 vehicles already on the nation’s highways. 

The fuel quality changes, especially lowering the sulfur content of gasoline, have significant 

benefits for the existing pre-Tier 3 fleet. The NOx-reduction benefits from introducing low-sulfur 

gasoline to the existing fleet in 2017 has an immediate benefit equivalent to removing 33 million 

Tier 2 cars from the nation’s highways. The three figures below illustrate the emissions 

reduction benefits of Tier 3 vehicles and gasoline. Over time, and especially by 2030 when a 

substantial fraction of the light-duty fleet will have turned over to Tier 3 vehicles, the emissions 

reduction for the Tier 3 vehicles will dominate for each pollutant shown (NOx, CO and VOC). 

Source: MP Walsh (2011). 

 

16 Douglas Ball et al., Effects of Fuel Sulfur on FTP NOx Emissions from a PZEV 4 Cylinder Application, SAE Paper 

2011-01-0300 (April 12, 2011). 
Page | 18 

Source: MP Walsh (2011). 

Source: MP Walsh (2011). 
Page | 19 

Of course, reducing emissions in and of itself is not the ultimate goal. Rather, the goal is to 

better protect public health and the environment. The emissions reductions to be achieved from 

the Tier 3 vehicles and gasoline will lead to tremendous strides in this regard. As an example, 

the NOx reductions anticipated to result from this program will lead to reduced levels of ambient 

particulate matter that, in turn, would translate into more than 400 avoided premature deaths 

and 52,000 avoided lost workdays each year. Again, these are based only on reductions in 

ambient PM. The benefits of the ozone reductions to occur from Tier 3 vehicles and gasoline 

will lead to even greater health protection. 

V. Conclusion 

Promulgation and implementation of a systems-based Tier 3 program, with vehicle standards 

modeled after CARB’s LEV III program and an average fuel sulfur level of about 10 ppm, would 

result in dramatically reduced ozone levels across the U.S. Such a program has the potential to 

reduce emissions of NOx, CO and VOCs by 29 percent, 38 percent and 26 percent, respectively, 

by 2030. In addition, the introduction of 10-ppm-sulfur gasoline would bring about overnightreductions from the existing Tier 2 fleet, equivalent to removing 33 million cars and trucks from 

the roads in 2017. Moreover, the price of this highly effective and much-needed program is 

modest, at less than a penny per gallon for 10-ppm-sulfur fuel and about $150 per vehicle. 

Further, this highly cost-effective program would yield substantial health and welfare benefits. 
Page | 20 

Appendix A: Health Effects Associated with Vehicle-Related 

 Pollutants17

Exposure to air pollution has been associated with a variety of adverse health effects. Based on 

available information, the World Health Organization (WHO) sets and periodically updates air 

quality guidelines. The following summary is based on the guidelines adopted by WHO18 and 

standards adopted by EPA. 

1. Ozone 

Ground-level ozone pollution is formed by the reaction of volatile organic compounds (VOCs) 

and nitrogen oxides (NOx) in the atmosphere in the presence of heat and sunlight. The science of 

ozone formation, transport and accumulation is complex. Ground-level ozone is produced and 

destroyed in a cyclical set of chemical reactions, many of which are sensitive to temperature and 

sunlight. When ambient temperatures and sunlight levels remain high for several days and the air is 

relatively stagnant, ozone and its precursors can build up and result in more ozone than typically would 

occur on a single high-temperature day. Ozone also can be transported from pollution sources 

into areas hundreds of miles downwind, resulting in elevated ozone levels even in areas with low 

local VOC or NOx emissions. 

The health and welfare effects of ozone are well documented.19 Ozone can irritate the respiratory 

system, causing coughing, throat irritation and/or an uncomfortable sensation in the chest. It can 

reduce lung function and make it more difficult to breathe deeply, and breathing may become more 

rapid and shallow than normal, thereby limiting a person’s activity. Ozone can also aggravate 

asthma, leading to more asthma attacks that require a doctor’s attention and/or the use of 

additional medication. Animal toxicological evidence indicates that with repeated exposure, 

ozone can inflame and damage the lining of the lungs, which may lead to permanent changes in 

lung tissue and irreversible reductions in lung function. People who are more susceptible to 

effects associated with exposure to ozone include children, the elderly and individuals with 

respiratory disease such as asthma. There is suggestive evidence that certain people may 

have greater genetic susceptibility. Those with greater exposures to ozone, for instance due to 

time spent outdoors (e.g., children and outdoor workers), are also of concern. 

Short-term exposure to current levels of ozone in many areas is likely to contribute to premature 

death, according to the National Research Council (NRC).20 Evidence of a relationship between 

short-term – less than 24 hours – exposure to ozone and mortality has been mounting, but 

interpretations of the evidence have differed, prompting EPA to request the NRC report. Based 

on a review of recent research, the NRC committee found that deaths related to ozone 

exposure are more likely among individuals with pre-existing diseases and other factors that 

 

17 Derived from Walsh, MP, Mobile Source-Related Air Pollution: Effects on Health and the Environment, 

Encyclopedia of Environmental Health, Volume 3, pp. 803-809; Nriago J (ed.), Burlington: Elsevier (2011). 

18 Air Quality Guidelines for Particulate Matter, Ozone, Nitrogen Dioxide and Sulfur Dioxide: Global Update 2005, 

Summary of Risk Assessment, World Health Organization (2006), available at 

www.who.int/phe/health_topics/outdoorair_aqg/en/. 

19 See Air Quality Criteria for Ozone and Related Photochemical Oxidants (Final). U.S. Environmental Protection Agency, EPA 

600/R–05/004aF–cF (2006); Review of the National Ambient Air Quality Standards for Ozone, Policy Assessment of Scientific 

and Technical Information, OAQPS Staff Paper Second Draft, U.S. Environmental Protection Agency, EPA– 452/D–05–002 (2006). 

20 See Committee on Reducing Mortality Risk Reduction Benefits from Decreasing Tropospheric Ozone Exposure, 

National Research Council, Estimating Mortality Risk Reduction and Economic Benefits from Controlling Ozone Air 

Pollution, National Academies Press (2008). 
Page | 21 

could increase their susceptibility. However, premature deaths are not limited to people who 

are already within a few days of dying. 

In addition, the committee examined research based on large population groups to find how 

changes in ozone air concentration could affect mortality, specifically to determine the existence 

of a threshold – a concentration of ozone below which exposure poses no risk of death. The 

committee concluded that if a threshold exists, it is probably at a concentration below the 

current public health standard. As people have individual susceptibilities to ozone exposure, not 

everyone may experience an altered risk of death if ozone air concentration also changes. The 

research on short-term exposure does not account for all ozone-related mortality, and the 

estimated risk of death may be greater than if based solely on these studies, the committee 

noted. 

Since the mid-1990s, there has been no major addition to the evidence from chamber studies or 

field studies. There has, however, been a marked increase in health effects evidence from 

epidemiological time-series studies. Combined evidence from those studies shows convincing, 

though small, positive associations between daily mortality and ozone levels, independent of the 

effects of particulate matter. Similar associations have been observed in North America and 

Europe. These time-series studies have shown effects at ozone concentrations below the 

previous WHO guideline of 120 micrograms per cubic meter (μg/m3

) without clear evidence of a 

threshold. Evidence from both chamber and field studies also indicates that there is 

considerable individual variation in response to ozone.

2. Nitrogen Dioxide 

Evidence from animal toxicological studies indicates that long-term exposure to nitrogen dioxide 

(NO2) at concentrations above current ambient concentrations has adverse effects. In 

population studies, NO2 has been associated with adverse health effects even when the annual 

average NO2 concentration complied with the WHO-2000 annual guideline value of 40 μg/m3. 

Also, some indoor studies suggest effects on respiratory symptoms among infants at 

concentrations below 40 μg/m3. Together these results support a lowering of the annual NO2

guideline value. However, NO2 is an important constituent of combustion-generated air pollution 

and is highly correlated with other primary and secondary combustion products; it is unclear to 

what extent the health effects observed in epidemiological studies are attributable to NO2 itself 

or to other correlated pollutants. 

Many short-term experimental human toxicology studies show acute health effects at levels 

higher than 500 μg/m3, and one meta-analysis has indicated effects at levels exceeding 200 

μg/m3. 

The California Air Resources Board approved staff recommendations to amend its NO2

standard on February 22, 2007. The recommendations were based on a review of the scientific 

literature on the health effects of NO2 that was conducted by staff from the Air Resources Board 

and the Office of Environmental Health Hazard Assessment. On January 5, 2007, staff 

recommended lowering the existing 1-hour-average standard for NO2 of 0.25 ppm to 0.18 ppm, 

not to be exceeded, and established a new annual-average standard of 0.030 ppm, not to be 

exceeded. 

An EPA final risk assessment finds evidence from recent studies is "sufficient to infer a likely 

causal relationship" between short-term exposure to NO2 and adverse effects on the respiratory 
Page | 22 

system.21 According to the report, a 30-minute exposure to NO2 concentrations between 0.2 

ppm and 0.3 ppm has been shown to irritate airways in asthmatics. Children, whose lung 

function continues to develop into adolescence, and adults over the age of 65, are also 

particularly susceptible to NO2 exposure. The risk assessment also identified as an at-risk 

group those whose jobs require significant periods of driving. Mean NO2 levels inside vehicles 

are often two to three times the outdoor concentrations. 

3. Carbon Monoxide 

Carbon monoxide – an odorless, invisible gas created when fuels containing carbon are burned 

incompletely – also poses a serious threat to human health. Persons afflicted with heart 

disease and fetuses are especially at risk. Because the affinity of hemoglobin in the blood is 

200 times greater for carbon monoxide than for oxygen, carbon monoxide hinders oxygen 

transport from blood into tissues. Therefore, more blood must be pumped to deliver the same 

amount of oxygen. Numerous studies in humans and animals have demonstrated that those 

individuals with weak hearts are placed under additional strain by the presence of excess CO in 

the blood. In particular, clinical health studies have shown a decrease in time to onset of angina 

pain in those individuals suffering from angina pectoris and exposed to elevated levels of 

ambient CO.22 Some recent epidemiologic studies have found relationships between increased 

CO levels and increases in mortality and morbidity.23

Healthy individuals also are affected, but only at higher levels. Exposure to elevated CO levels 

is associated with impairment of visual perception, work capacity, manual dexterity, learning 

ability and performance of complex tasks. 

4. Particulate Matter 

Particulate matter (PM) represents a broad class of chemically and physically diverse substances. It 

can be principally characterized as discrete particles that exist in the condensed (liquid or solid) 

phase spanning several orders of magnitude in size. PM10 refers to particles generally less than 

or equal to 10 micrometers (μm). PM2.5 refers to fine particles, generally less than or equal to 2.5 

μm in diameter. Inhalable (or ‘‘thoracic’’) coarse particles refer to those particles generally greater than 

2.5 μm but less than or equal to 10 μm in diameter. Ultrafine PM refers to particles less than 100 

nanometers (0.1 μm). Larger particles tend to be removed by the respiratory clearance mechanisms 

(e.g., coughing), whereas smaller particles are deposited deeper in the lungs. 

Fine particles are produced primarily by combustion processes and by transformations of gaseous 

emissions (e.g., SOx, NOx and VOCs) in the atmosphere. Thus, PM2.5 may include a complex 

mixture of different pollutants including sulfates, nitrates, organic compounds, elemental carbon 

and metal compounds. These particles can remain in the atmosphere for days to weeks and travel 

through the atmosphere hundreds to thousands of kilometers. 

The evidence on airborne PM and public health is consistent in showing adverse health effects 

at exposures experienced by urban populations in cities throughout the world, in both developed 

and developing countries. The range of effects is broad, affecting the respiratory and 

 

21 Risk and Exposure Assessment to Support the Review of the NO2 Primary National Ambient Air Quality Standard 

(Final), U.S. Environmental Protection Agency, EPA-452/R-08-008a (November 2008). 

22 See Aronow, et. al., Effect of Carbon Monoxide on Exercise Performance in Chronic Obstructive Pulmonary 

Disease, Am. J. Med., (1977); Ferris, Health Effects of Exposure to Low Levels of Regulated Air Pollutants, A Critical 

Review, Journal of the Air Pollution Control Association, (May 1978). 

23 See Air Quality Criteria for Carbon Monoxide, EPA Office of Research and Development (June 2000). 
Page | 23 

cardiovascular systems and extending to children and adults and to a number of large, 

susceptible groups within the general population. The risk for various outcomes has been 

shown to increase with exposure and there is little evidence to suggest a threshold below which 

no adverse health effects would be anticipated. In fact, the lower range of concentrations at 

which adverse health effects have been demonstrated is not greatly above the background 

concentration that has been estimated at 3-5 μg/m3 in the U.S. and Western Europe for particles 

smaller than PM2.5. The epidemiological evidence shows adverse effects of particles after both 

short-term and long-term exposures. 

Health effects associated with short-term exposures (hours to days) to ambient PM include 

premature mortality, increased hospital admissions, heart and lung diseases, increased cough, 

adverse lower-respiratory symptoms, decrements in lung function and changes in heart rate rhythm 

and other cardiac effects. Studies examining populations exposed to different levels of air 

pollution over a number of years, including the Harvard Six-Cities Study24 and the American 

Cancer Society (ACS) Study,25 show associations between long-term exposure to ambient PM2.5 

and both total and cardiovascular and respiratory mortality. In addition, a reanalysis of the ACS 

Study shows an association between fine particle and sulfate concentrations and lung cancer 

mortality.26 

The health effects of PM2.5 have been further documented in local impact studies that have focused 

on health effects due to PM2.5 exposures measured on or near roadways. Taking account of all air 

pollution sources, including both spark-ignition (gasoline) and diesel-powered vehicles, these latter 

studies indicate that exposure to PM2.5 emissions near roadways, dominated by mobile sources, are 

associated with potentially serious health effects. For instance, a recent study found associations 

between concentrations of cardiac risk factors in the blood of healthy young police officers and PM2.5

concentrations measured in vehicles.27 Also, a number of studies have shown associations between 

residential or school outdoor concentrations of some constituents of fine particles found in motor 

vehicle exhaust and adverse respiratory outcomes, including asthma prevalence in children who 

live near major roadways.28,29,30

The WHO annual average guideline value of 10 μg/m3 for PM2.5 was chosen to represent the 

lower end of the range over which significant effects on survival have been observed in the ACS 

Study. 31 Adoption of a guideline at this level places significant weight on the long-term 

exposure studies using the ACS and Harvard Six-Cities data. In these studies, robust 

associations were reported between long-term exposure to PM2.5 and mortality. Thresholds 

were not apparent in either of these studies. 

 

24 Dockery, DW; Pope, CA III: Xu, X; et al., An Association between Air Pollution and Mortality in Six U.S. Cities, N Engl J 

Med..329:1753–1759 (1993). 

25 Pope CA, III; Thun, MJ; Namboodiri, MM; Dockery, DW; Evans, JS; Speizer, FE; Heath, CW, Particulate Air Pollution as a 

Predictor of Mortality in a Prospective Study of U.S. Adults, Am J Respir Crit Care Med 151:669–674 (1995). 

26 Krewski D et al., Reanalysis of the Harvard Six Cities Study and the American Cancer Society Study of Particulate 

Air Pollution and Mortality, Health Effects Institute Special Report (July 2000).

27 Riekider, M; Cascio, WE; Griggs, TR; Herbst, MC; Bromberg, PA; Neas, L; Williams, RW; Devlin, RB, Particulate Matter 

Exposures in Cars Is Associated with Cardiovascular Effects in Healthy Young Men, Am. J. Respir. Crit. Care Med 169:934–940 

(2003). 

28 Van Vliet, P; Knape, M; de Hartog, J; Janssen, N; Harssema, H; Brunekreef, B, Motor Vehicle Exhaust and Chronic 

Respiratory Symptoms in Children Living Near Freeways, Env. Research 74:122–132 (1997). 

29 Brunekreef, B, Janssen, NAH; de Hartog, J; Harssema, H; Knape, M; van Vliet, P, Air Pollution from Truck Traffic and Lung 

Function in Children Living Near Roadways, Epidemiology 8:298–303 (1997). 

30 Kim, JJ; Smorodinsky, S; Lipsett, M; Singer, BC; Hodgson, AT; Ostro, B, Traffic-Related Air Pollution Near Busy Roads: The 

East Bay Children’s Respiratory Health Study, Am. J. Respir. Crit. Care Med 170: 520–526 (2004). 

31 Pope, CA et al., Lung Cancer, Cardiopulmonary Mortality, and Long-Term Exposure to Fine Particulate Air 

Pollution, Journal of the American Medical Association 287:1132–1141 (2002). 
Page | 24 

In addition to PM2.5 and PM10, ultra-fine (UF) particles have recently attracted significant scientific 

and medical attention. These are particles smaller than 0.1 μm and are measured as a number 

concentration. While there is considerable toxicological evidence of potential detrimental effects 

of UF particles on human health, the existing body of epidemiological evidence is insufficient in 

the view of WHO to reach a conclusion on the exposure/response relationship to UF particles. 

Therefore, no recommendations have been provided by WHO as to guideline concentrations of 

UF particles at this point. 

A study led by UCLA researchers has revealed that the smallest particles from vehicle 

emissions may be the most damaging components of air pollution in triggering plaque buildup in 

the arteries, which can lead to heart attack and stroke.32 In the study, researchers exposed 

mice with high cholesterol to one of two sizes of air pollutant particles from downtown Los 

Angeles freeway emissions and compared them with mice that received filtered air that 

contained very few particles. Researchers found that mice exposed to UF particles exhibited 55 

percent greater atherosclerotic-plaque development than animals breathing filtered air and 25 

percent greater plaque development than mice exposed to fine-sized particles. 

Another study, published in the New England Journal of Medicine, linked exposure to diesel 

exhaust with asthma.33 The researchers recruited 60 adults with either mild or moderate asthma 

to participate in a randomized, crossover study. Each participant walked for 2 hours along a 

London street (Oxford Street) and, on a separate occasion, through a nearby park (Hyde Park). 

Detailed real-time exposure, physiological and immunologic measurements were taken. 

Participants had significantly higher exposures to fine particles (less than 2.5 μm in aerodynamic 

diameter), UF particles, elemental carbon and NO2 on Oxford Street than in Hyde Park. Walking 

for 2 hours on Oxford Street induced asymptomatic but consistent reductions in the forced 

expiratory volume in 1 second (FEV1) (up to 6.1%) and forced vital capacity (FVC) (up to 5.4%) that 

were significantly larger than the reductions in FEV1 and FVC after exposure in Hyde Park (P = 

0.04 and P = 0.01, respectively, for the overall effect of exposure, and P<0.005 at some time 

points). The effects were greater in subjects with moderate asthma than in those with mild 

asthma. These changes were accompanied by increases in biomarkers of neutrophilic 

inflammation (sputum myeloperoxidase, 4.24 ng per milliliter after exposure in Hyde Park versus 

24.5 ng per milliliter after exposure on Oxford Street; P = 0.05) and airway acidification (maximum 

decrease in pH, 0.04% after exposure in Hyde Park and 1.9% after exposure on Oxford Street; P 

= 0.003). The changes were associated most consistently with exposures to UF particles and 

elemental carbon. 

5. Air Toxics 

People experience elevated risk of cancer and other noncancerous health effects from exposure to 

air toxics. Mobile sources are a major source of this exposure. According to the most recent 

U.S. National Air Toxic Assessment (NATA), for 2005,

34 mobile sources were responsible for 43 

 

32 Araujo, JA; Barajas, B; Kleinman, M; Wang, X; Bennett, BJ; Gong KW; Navab, M; Harkema, J; Sioutas, C; Lusis; 

AJ; and Nel AE, Ambient Particulate Pollutants in the Ultrafine Range Promote Early Atherosclerosis and Systemic 

Oxidative Stress, Circulation Research (January 17, 2008). 

33 James McCreanor, M.R.C.P., Paul Cullinan, M.D., Mark J. Nieuwenhuijsen, Ph.D., James Stewart-Evans, M.Sc., 

Eleni Malliarou, M.Sc., Lars Jarup, Ph.D., Robert Harrington, M.S., Magnus Svartengren, M.D., In-Kyu Han, M.P.H., 

Pamela Ohman-Strickland, Ph.D., Kian Fan Chung, M.D., and Junfeng Zhang, Ph.D., Respiratory Effects of

Exposure to Diesel Traffic in Persons with Asthma, N Engl J Med 357:2348-2358 (December 6, 2007).

34 See EPA’s 2005 National-Scale Air Toxics Assessment, available at 

http://www.epa.gov/ttn/atw/nata2005/index.html.
Page | 25 

percent of outdoor toxic emissions and almost 21 percent of the cancer risk among the 139 pollutants 

quantitatively assessed. Formaldehyde was the largest contributor to cancer risk of all the assessed

pollutants, contributing 44 percent of the total risk, and mobile sources were responsible for about 46 

percent of all formaldehyde emissions in 2005. Benzene contributed 15 percent of the total risk with 

mobile sources responsible for about 60 percent of all benzene emissions in 2005. 

According to the 2005 NATA, nearly the entire U.S. population was exposed to an average level of air 

toxics that has the potential for adverse respiratory noncancerous health effects. Mobile sources were 

responsible for 33 percent of the potential noncancerous hazard from outdoor air toxics. It is 

important to note that NATA estimates of noncancerous hazard do not include the adverse health 

effects associated with particulate matter. 

The following section provides a brief overview of the air toxics associated with vehicles, and 

includes a discussion of the health risks associated with each. 

a. Diesel Exhaust 

Diesel exhaust is a complex mixture comprised of 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 of fine particles (less than 2.5 μm), including a subgroup with a large 

number of UF particles (less than 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 and able to reach the deep lung. Many of the organic compounds present on 

the particles and in the gases 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, 

accelerate, decelerate) and fuel formulations (high-sulfur, low-sulfur). After being emitted, 

diesel exhaust undergoes chemical and physical changes in the atmosphere. 

Diesel Exhaust: Potential Cancer Effects 

In EPA’s 2002 Diesel Health Assessment Document (Diesel HAD),35 diesel exhaust was classified as 

likely to be carcinogenic to humans by inhalation at environmental exposures, in accordance with the 

revised draft 1996/1999 EPA cancer guidelines. A number of other agencies (National Institute for 

Occupational Safety and Health, the International Agency for Research on Cancer, the World Health 

Organization, California EPA and the U.S. Department of Health and Human Services) have 

made similar classifications. 

For the Diesel HAD, EPA reviewed 22 epidemiologic studies on the subject of the 

carcinogenicity of workers exposed to diesel exhaust in various occupations, finding increased 

lung cancer risk, although not always statistically significant, in eight out of 10 cohort studies 

and 10 out of 12 case-control studies within several industries, including railroad workers. 

Relative risk for lung cancer associated with exposure ranged from 1.2 to 1.5, although a few 

studies show relative risks as high as 2.6. Additionally, the Diesel HAD also relied on two 

independent meta-analyses, which examined 23 and 30 occupational studies, respectively, and 

found statistically significant increases in smoking-adjusted relative lung cancer risk associated 

 

35 Health Assessment Document for Diesel Engine Exhaust, EPA Office of Research and Development, EPA/600/8–

90/057F (2002). 
Page | 26 

with diesel exhaust, of 1.33 to 1.47. These meta-analyses demonstrate the effect of pooling 

many studies and in this case show the positive relationship between diesel exhaust exposure 

and lung cancer across a variety of diesel exhaust-exposed occupations. 36, 37

The EPA Diesel HAD concluded that environmental risks from diesel exhaust exposure could 

range from a low of 10-4 to 10-5 to as high as 10-3, reflecting the range of occupational 

exposures that could be associated with the relative and absolute risk levels observed in the 

occupational studies. 

 

Retrospective health studies of railroad workers have played an important part in determining 

that diesel exhaust is a likely human carcinogen. Key evidence of the diesel exhaust exposure 

linkage to lung cancer comes from two retrospective case-control studies of railroad workers. 

Diesel Exhaust: Other Health Effects 

Noncancerous health effects of acute and chronic exposure to diesel exhaust emissions are also 

of concern. EPA derived a Reference Concentration (RfC) from consideration of four wellconducted chronic rat inhalation studies showing adverse pulmonary effects.38,39,40,41 The RfC is 5 

μ/m3 for diesel exhaust as measured by diesel PM. This RfC does not consider allergenic effects 

such as those associated with asthma or immunologic effects even though there is growing 

evidence that exposure to diesel exhaust can exacerbate these effects. 

b. Other Air Toxics 

Vehicles contribute to ambient levels of other air toxics known or suspected as human or animal 

carcinogens, or that have non-cancer health effects. These other compounds include benzene, 

1,3-butadiene, formaldehyde, acetaldehyde, acrolein, polycyclic organic matter and naphthalene. 

All of these compounds, except acetaldehyde, were identified as national or regional risk drivers in 

the 2005 NATA. For a substantial segment of the population, these compounds pose a significant 

portion of the total cancer and noncancerous risk from breathing outdoor air toxics. 

Noncancerous health effects resulting from inhalation exposures include neurological, 

cardiovascular, liver, kidney and respiratory effects as well as effects on the immune and 

reproductive systems. 

 

36 Bhatia, R; Lopipero, P; Smith, A., Diesel Exposure and Lung Cancer, Epidemiology 9(1):84– 91 (1998). 

37 Lipsett, M: Campleman, S, Occupational Exposure to Diesel Exhaust and Lung Cancer: A Meta-Analysis, Am J Public Health

80(7): 1009–1017 (1999). 

38 Ishinishi, N; Kuwabara, N; Takaki, Y; et al., Long-Term Inhalation Experiments on Diesel Exhaust, Results of the HERP 

Studies, Ibaraki, Japan: Research Committee for HERP Studies (1988) pp. 11–84. 

39 Heinrich, U; Fuhst, R; Rittinghausen, S; et al., Chronic Inhalation Exposure of Wistar Rats and Two Different Strains of 

Mice to Diesel Engine Exhaust, Carbon Black, and Titanium Dioxide, Inhal. Toxicol. 7:553–556 (1995). 

40 Mauderly, JL; Jones, RK; Griffith, WC; et al., Diesel Exhaust Is a Pulmonary Carcinogen in Rats Exposed Chronically by 

Inhalation, Fundam. Appl. Toxicol. 9:208–221 (1987). 

41 Nikula, KJ; Snipes, MB; Barr, EB; et al., Comparative Pulmonary Toxicities and Carcinogenicities of Chronically Inhaled 

Diesel Exhaust and Carbon Black in F344 Rats, Fundam. Appl. Toxicol. 25:80–94 (1995). 
Page | 27 

Appendix B: Environmental Effects Associated with Vehicle-Related 

 Pollutants 

1. Visibility 

Visibility can be defined as the degree to which the atmosphere is transparent to visible light. 

Visibility impairment manifests in two principal ways: as local visibility impairment and as 

regional haze.42 Local visibility impairment may take the form of a localized plume, a band or 

layer of discoloration appearing well above the terrain as a result of complex local meteorological 

conditions. Alternatively, local visibility impairment may manifest as an urban haze, sometimes 

referred to as a ‘‘brown cloud.’’ This urban haze is largely caused by emissions from multiple 

sources in the urban areas and is not typically attributable to only one nearby source or to long-range 

transport. The second type of visibility impairment, regional haze, usually results from multiple 

pollution sources spread over a large geographic region. Regional haze can impair visibility in large

regions and across states. 

Visibility is important because it has direct significance to people’s enjoyment of daily activities. 

Individuals value good visibility for the well being it provides them directly, where they live and 

work and in places where they enjoy recreational opportunities. Visibility is also highly valued in 

significant natural areas such as national parks and wilderness areas and special emphasis is 

given to protecting visibility in these areas.43, 44

2. Plant and Ecosystem Effects of Ozone 

Ozone can produce both acute and chronic injury in sensitive species depending on the 

concentration level and the duration of the exposure.45 Ozone effects also tend to accumulate 

over the growing season of the plant, so that even lower concentrations experienced for a 

longer duration have the potential to create chronic stress on vegetation. Ozone damage to 

plants includes visible injury to leaves and a reduction in food production through impaired 

photosynthesis, both of which can lead to reduced crop yields, forestry production and use of 

sensitive ornamentals in landscaping. In addition, the reduced food production in plants and 

subsequent reduced root growth and storage below ground, can result in other, more subtle 

plant and ecosystems impacts. These include increased susceptibility of plants to insect attack, 

disease, harsh weather, interspecies competition and overall decreased plant vigor. The 

adverse effects of ozone on forest and other natural vegetation can potentially lead to species 

shifts and loss from the affected ecosystems, resulting in a loss or reduction in associated 

ecosystem goods and services. Lastly, visible ozone injury to leaves can result in a loss of 

aesthetic value in areas of special scenic significance like national parks and wilderness areas. 

 

42 See discussion in National Ambient Air Quality Standards for Particulate Matter; Proposed Rule, 71 Federal Register 2676 

(January 17, 2006). 

43 See Air Quality Criteria for Particulate Matter, U.S. Environmental Protection Agency, EPA600/P–99/002aF and EPA600/P–

99/002bF (October 2004). 

44 See Review of the National Ambient Air Quality Standard for Particulate Matter: Policy Assessment of Scientific and 

Technical Information, EPA OAQPS Staff Paper. EPA-452/R–05–005 (2005). 

45 See Air Quality Criteria for Ozone and Related Photochemical Oxidants (Final). U.S. Environmental Protection Agency, 

EPA 600/R–05/004aF–cF (2006). 
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3. Acid Deposition 

Acid deposition, or acid rain as it is commonly known, occurs when NOx and SO2 react in the 

atmosphere with water, oxygen and oxidants to form various acidic compounds that later fall to earth 

in the form of precipitation or dry deposition of acidic particles. It contributes to damage of trees

at high elevations and in extreme cases may cause lakes and streams to become so acidic that they 

cannot support aquatic life. In addition, acid deposition accelerates the decay of building 

materials and paints, including irreplaceable buildings, statues and sculptures that are part of a 

nation’s cultural heritage. 

Nitrogen oxides have also been found to contribute to ocean acidification, thereby amplifying 

one of the many deleterious impacts of climate change. 46 Approximately one third of all 

nitrogen oxide emissions end up in the oceans. The impact of these emissions on 

acidification is intensely felt in specific, vulnerable areas; in some areas it can be as high as 10 

to 50 percent of the impact of carbon dioxide. The hardest hit areas are likely to be those 

directly around the release site, so these emissions are especially significant in and around 

coastal waters.

4. Eutrophication and Nitrification 

Eutrophication is the accelerated production of organic matter, particularly algae, in a water body. 

Nitrogen deposition contributes to eutrophication of watersheds, particularly in aquatic systems 

where atmospheric deposition of nitrogen represents a significant portion of total nitrogen 

loadings. This increased growth can cause numerous adverse ecological effects and economic 

impacts, including nuisance algal blooms, dieback of underwater plants due to reduced light 

penetration and toxic plankton blooms. Algal and plankton blooms can also reduce the level of 

dissolved oxygen, which can adversely affect fish and shellfish populations. In recent decades, 

human activities have greatly accelerated nutrient impacts, such as nitrogen and phosphorus, 

causing excessive growth of algae and leading to degraded water quality and associated impairment 

of freshwater and estuarine resources for human uses.47

Severe and persistent eutrophication often directly impacts human activities. For example, losses 

in the nation’s fishery resources may be directly caused by fish kills associated with low 

dissolved oxygen and toxic blooms. Declines in tourism occur when low dissolved oxygen 

causes noxious smells and floating mats of algal blooms create unfavorable aesthetic conditions. 

Risks to human health increase when the toxins from algal blooms accumulate in edible fish and 

shellfish, and when toxins become airborne, causing respiratory problems due to inhalation. 

5. Materials Damage and Soiling 

The deposition of airborne particles can reduce the aesthetic appeal of buildings and culturally 

important structures through soiling, and can contribute directly (or in conjunction with other 

pollutants) to structural damage by means of corrosion or erosion.48 Particles affect materials 

principally by promoting and accelerating the corrosion of metals, by degrading paints and by 

deteriorating building materials such as concrete and limestone. Particles contribute to these effects 

because of their electrolytic, hygroscopic and acidic properties, and their ability to adsorb corrosive 

 

46 See Doney, Scott C., et al., Impact of Anthropogenic Atmospheric Nitrogen and Sulfur Deposition on Ocean 

Acidification and the Inorganic Carbon System, PNAS 104:14580-14585, at 14580 (2007). 

47 See Deposition of Air Pollutants to the Great Waters, Third Report to Congress, EPA– 453/R–00–005 (June 2000). 

48 See Review of the National Ambient Air Quality Standards for Particulate Matter: Policy Assessment of Scientific and 

Technical Information, EPA OAQPS Staff Paper (2005). 
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gases (principally sulfur dioxide). The rate of metal corrosion depends on a number of factors, 

including the deposition rate and nature of the pollutant; the influence of the metal protective 

corrosion film; the amount of moisture present; variability in the electrochemical reactions; the 

presence and concentration of other surface electrolytes; and the orientation of the metal surface.