BMW Group  Chrysler Group LLC  Ford Motor Company  General Motors Company  Jaguar Land Rover 

Mazda  Mercedes-Benz USA  Mitsubishi Motors  Porsche  Toyota  Volkswagen  Volvo

1401 Eye Street, N.W, Suite 900, Washington, DC 20005-6562  Phone 202.326.5500  Fax 202.326.5567

www.autoalliance.org

August 24, 2011

ALLIANCE OF AUTOMOBILE MANUFACTURERS

WHITE PAPER:

WHY EPA TIER 3 MARKET GASOLINE SULFUR LIMITS 

NEED TO BE SIGNIFICANTLY LOWER, ESPECIALLY FOR 

MY 2017+ VEHICLES

Introduction

EPA is preparing to propose a new Tier 3 regulation by the end of 2011, one component of 

which would reduce the average level of sulfur in marketplace gasoline below the existing Tier 2 

sulfur standard. The members of the Alliance of Automobile Manufacturers have been engaged 

with the Agency to express their vital interest in the content of the proposal, and to underscore 

support for a meaningful reduction in retail market fuel sulfur content nationwide. 

EPA’s current Tier 2 market gasoline sulfur standard essentially imposes three limits: 

 30 ppm maximum annual average at the refinery gate; 

 80 ppm per gallon maximum/cap at the refinery gate, measured on a batch basis;

 95 ppm per gallon maximum/cap at the retail fuel pump. 

The Tier 2 gasoline sulfur regulation was promulgated in 2000. Starting in 2004, for the six

years of the implementation phase in, EPA provided a generous amount of flexibility to oil 

companies, including: corporate-wide averaging, inter-refinery trading, small refiner 

exemptions, a slower phase-in for Rocky Mountain region facilities, and a mechanism for 

hardship waivers, among others. In the aggregate, these have had the effect of “masking” some 

chronically high sulfur market gasoline supplies in certain areas, which cumulatively may have 

adversely affected vehicle catalyst performance and durability, and emissions in those markets.

The specific new Tier 3 vehicle emissions limits, and changes in fuel sulfur limits, are still in 

development. It has been suggested that EPA is considering reducing the individual refinery 

annual average maximum from 30 ppm to 10 ppm. However, EPA is also considering the 

implications of retaining the existing per gallon caps (80 ppm refinery gate; 95 ppm retail pump) 

versus lowering them (e.g., to 20 and 25 ppm, respectively). This White Paper explains why a 

proposal to keep the 80/95 ppm Tier 2 sulfur caps is adverse to Agency goals for the auto 

industry.

It is also critical that in designing Tier 3, EPA not unduly delay uniform sulfur limits at the retail 

pump, by providing another set of flexible compliance measures to refiners as were used in Tier 

2. The Alliance does not oppose flexibility for the oil industry per se, but the retail gasoline 

provided should be compatible with Tier 3 vehicle needs in order to meet both fuel 
2

economy/GHG requirements [including pending new limits for MY 20171] and pending Tier 3 

emissions reductions. The new lower sulfur fuel must be in the marketplace nationally for these 

vehicles in a timely manner to protect the vehicles, consumers, and the environment.

High sulfur cap limits and/or over-broad implementation flexibility (e.g., in calculating averages 

across refineries) that allow a wide and unpredictable range of actual sulfur content among 

different geographic areas and over time, will handicap automakers’ ability to introduce new 

advanced technology systems needed to meet the pending 2017 Fuel Economy/GHG regulations 

and maximize reductions in vehicle emissions. This approach would fail to treat the vehicle and 

the fuel as a system, and put an unfair proportion of the total regulatory burden on the auto 

industry. 

Sulfur’s Adverse Impact on Current and Future Emission Controls

Gasoline sulfur poisons all types of vehicle emission control devices and reduces their ability to 

reduce tailpipe emissions. For the three-way catalysts (TWC) used on nearly all existing 

gasoline-powered light duty vehicles in the U.S., the reduced efficiency caused by sulfur 

poisoning requires automakers to over-design their vehicles (if/when possible to do so) to meet 

emission standards. This over-design often involves the increased use of expensive and scarce 

precious metals in the catalyst, which ultimately makes the vehicle more expensive (and prone to 

catalyst theft). Furthermore, if the sulfur level is high enough, such design compromises may not 

be possible. 

In all cases, even where over-design enables a vehicle to meet its emission standards, the actual 

emissions from a vehicle with a sulfur-poisoned catalyst will be higher than they otherwise 

would be. Since chronic sulfur poisoning may be only partially reversible, the impact on catalyst 

efficiency is cumulative. Thus, all conventional emissions—including HC, CO, NOx, PM and 

toxics—will increase as a result, depending on the amount and duration of the sulfur exposure. 

Sulfur also will affect the vehicle’s fuel economy and greenhouse gas emissions adversely, due 

to the additional energy and operational steps that need to be taken to cope with the sulfur 

poisoning. 

The reversibility of the poisoning, especially over time, in a vehicle chronically exposed to 

higher sulfur retail gasoline, is an important issue. When the Tier 2 regulation was adopted, it 

was believed that the sulfur poisoning could not be reversed without physically replacing the 

catalyst.2 Over time, technology improvements did enable some reversibility, although at a cost 

of lower fuel efficiency.3 Even so, sulfur will always cause at least some permanent impairment 

of the catalyst, and this impairment causes increased concern as the vehicle accumulates mileage, 

and as emission standards become more stringent. Under Tier 2, vehicles must continue to meet 

emission standards through 120,000 miles of driving, and the Tier 3 regulation is anticipated to 

require compliance with tougher standards of driving. 

Reversing the sulfur poisoning requires very high temperature operation from time to time, but 

TWC subject to leaner exhaust hydrocarbon levels will have lower operational temperatures, 

making them easier to become and remain poisoned with sulfur. In addition, over time, repeated 

 

1 New models are introduced during the previous calendar year, i.e., MY 2017 vehicles are introduced during CY 

2016. 

2 As a compliance measure, replacing the catalyst is prohibited.

3 Removing sulfur from TWC requires increasing the fuel-air ratio and higher temperatures, among other things.
3

burn-off of the catalyst can damage the catalyst brick substrate, prematurely age it, and reduce 

catalyst durability. 

Highway driving tends to produce higher exhaust temperatures than city driving, and if a vehicle 

is driven only in the city, its catalyst may not see the higher temperatures needed for sulfur burnoff, and as a result its emissions will be higher. Many, if not most, of these city vehicles will be 

located in ozone non-attainment areas. EPA should consider that many consumers may drive in 

a manner not conducive to catalyst burn off, yet are located in areas that need the emission 

reductions the most. 

New technologies are under consideration as tools to help automakers meet stringent new fuel 

economy standards, and the significantly more fuel efficient, lean burn gasoline engine 

(compared to conventional engines) is one of these. This technology requires the use of different 

emission control devices, such as the Lean NOx Trap, similar to those used in diesel engines, to 

meet NOx emission standards. Lean NOx traps also have lower operational temperatures and 

will be more easily poisoned. These devices quickly and permanently lose their ability to 

function as the fuel sulfur level rises above 10 ppm.4Some of the individual automakers have 

already provided EPA with proprietary company-specific data on this point. 

Recent Support for Reducing Sulfur: SAE 2011-01-0300, D. Ball, et al., Effects of Fuel 

Sulfur on FTP NOx Emissions from a PZEV 4 Cylinder Applications

Test data on sulfur’s impact on very low emitting vehicles (e.g., SULEV, PZEV, and Tier 2-Bin 

2) remain scarce, especially at ultra-low sulfur levels and over a 150,000 mile compliance 

lifetime. This recent SAE study provides some insight. The authors measured the impact of test 

fuels containing 3 ppm and 33 ppm sulfur on NOx emissions from a 2009 MY PZEV Malibu. 

One important aspect of the evaluation was measuring the ability of different driving cycles to 

reverse the catalyst poisoning, and the potential for “NOx creep”, i.e., the incremental permanent 

reduction in catalyst efficiency as a result of repeated sulfur exposure. As the study notes, 

catalyst efficiencies for PZEVs need to exceed 99.4% for HC and 99.3% for NOx through 

150,000 miles, and small changes in catalyst efficiency can have a large impact on tailpipe 

emissions. 

The study found that sulfur levels of 33 ppm will affect “test to test” NOx stability during FTP 

testing, and that catalyst temperatures of 600°F, common in under-floor catalysts, can allow 

sulfur poisoning that affects NOx reduction efficiency and consistency of results. Using the 

US06 test cycle (high engine flow, high load) between FTP cycles, however, can increase 

catalyst temperature enough to help reverse the poisoning and improve “test to test” stability. 

According to the study, while the US06 can help mitigate sulfur poisoning, using a 3 ppm sulfur 

gasoline would eliminate the need to use such a cycle -- also, a 3 ppm fuel would reduce NOx 

emissions by 40% compared to the 33 ppm fuel, and/or allow lower levels of precious metals in 

the catalyst. 

 

4

In 2000, the Association for Emissions Control by Catalyst (AECC) found: “The promising NOx adsorber 

technology that diesel and lean burn engines need requires sulphur levels significantly below 10 ppm. This will 

avoid compromising the lower fuel consumption and CO2 emissions by requiring frequent regeneration to remove 

the sulphur that is clogging the NOx adsorption capacity. See Response to European Commission Consultation on 

the Need to Reduce the Sulphur Content of Petrol and Diesel Fuels below 50 parts per million, July 2000, available 

at http://www.aecc.eu/en/Publications/Archive.html. 
4

Lessons from Tier 2 US Gasoline Sulfur Regulation 

Automakers found Tier 2 vehicle emission regulations much more stringent than expected, 

which in turn strengthened their call for the lowest possible gasoline sulfur levels. The Agency’s 

choice of nominal 80 ppm/95 ppm sulfur caps for Tier 2 was already a much bigger compromise 

than should have occurred. 

In addition, EPA’s Tier 2 implementation scheme allowed sulfur levels to be significantly higher 

in the marketplace than the nominal legal limits for a considerable period after the rule’s 

adoption. Besides giving most refiners two years after the 2004 effective date to phase in to the 

standard, the Agency gave an additional two years to small refiners and those in the Rocky 

Mountain region, and refiners could apply for hardship waivers that would allow an additional 

two years to comply. Thus the rule actually allowed six years to fully phase in the new fuel 

quality, with no provision to prevent local high sulfur areas during this period.

Moreover, EPA’s 30 ppm limit was reached by averaging all batches over a full year, compared 

to California’s low sulfur regulation (RFG Phase 2, implemented in 1996) which required 

averaging over a six month period. EPA imposed its 80 ppm per gallon cap at the refinery gate, 

and allowed retail gasoline to reach a 95 ppm cap at retail (and even this limit did not become 

absolute until 2011). California’s Phase 2 regulation imposed its 80 ppm per gallon cap at retail. 

In its North American Fuel Survey (NAFS) the Alliance of Automobile Manufacturers was still 

finding U.S. retail gasoline with sulfur as high as 148 ppm in the summer of 2010.5 While 

automakers would strongly welcome a significant lowering of average sulfur levels, they are 

greatly concerned about the possibility of high sulfur “hot spots” persisting at various retail 

points around the country if high caps are still allowed.

It is unclear when EPA will next revisit the issue of sulfur market fuel specifications, so the 

Agency should propose limits that will enable nationwide introduction of all emerging vehicle 

technologies for the foreseeable future. 

Implications of Retaining the Tier 2 Sulfur Caps

Even with a much-needed, much lower annual sulfur average per refinery in place by 2016 (for 

MY 2017 vehicles) (and assuming no Tier-2 type averaging flexibility), retaining the current 

Tier 2 sulfur caps (80/95 ppm) in Tier 3 would be extremely problematic for autos, given the 

challenges of the 2017-2025 Fuel Economy/GHG rule and pending Tier 3 vehicle emission 

standards. Even if EPA reduces the refinery annual average sulfur limit considerably below the 

current 30 ppm, the prospect of continuing to allow up to 95 ppm sulfur retail gasoline in the 

marketplace means consumers in some locations will be buying relatively high sulfur fuel for 

their vehicles, some of them on a regular basis. 

In addition, automakers are very concerned about repeated exposure of such vehicles to high 

sulfur levels, because the accumulation of sulfur on their catalysts over time and miles will put 

them at an unfair (and unpredictable) disadvantage for in-use compliance testing. Under Tier 2 

 

5 The Alliance of Automobile Manufacturers North American Fuel Survey (NAFS) conducted in the summer of 

2010 found regular gasoline in Kansas City containing 148 ppm sulfur. However, the first NAFS survey for 2011 

(conducted in January 2011) showed all gasoline samples apparently compliant with the 95ppm sulfur retail 

standard.
5

standards, vehicles must comply with emission standards for 120,000 miles of driving (and many 

vehicles are in Sec. 177 states requiring California emissions limit compliance for 150,000 

miles, but which are exposed to federal fuels rather than the benefit of California fuels). Under 

the Tier 3 rule, automakers anticipate that all vehicles will be required to comply with tighter 

emissions standards. Many will need to comply with the longer California useful life criterion. 

In addition, long-term usage patterns (e.g., predominantly urban driving versus high-load 

highway driving) will differently affect catalyst performance and durability. Adding the element 

of unpredictable levels of market fuel sulfur (geographically and over time) could affect future 

in-use testing results, especially if no sulfur preconditioning steps are applied. 

Vehicles have reduced catalyst efficiencies during and after chronic higher sulfur exposures, and 

this can cause significantly higher emissions. Poor or incomplete reversibility will cause ongoing 

higher emissions wherever the vehicle travels, including ozone non-attainment areas. 

Furthermore, future gasoline is likely to contain more ethanol, which contributes to higher NOx 

emissions, so higher sulfur gasoline will exacerbate the likelihood of an emissions increase. 

These combined effects would set back state efforts to meet stringent ozone ambient air quality 

standards. Importantly for the states and the general public, even occasional vehicle exposures to 

sulfur levels as high as 95 ppm will cause significantly higher HC, NOx, PM and toxic emissions 

than the design capability of vehicles. As a result, EPA will risk failing to prevent air quality 

backsliding, which Congress required EPA to study specifically out of concern about ethanol’s 

impact on emissions.6

Allowing retail sulfur levels as high as 95 ppm also will inhibit the introduction of new fuel 

efficient, lean burn gasoline engine technology, as already publicly noted by some automakers. 

These engines are capable of providing significantly improved fuel economy and greenhouse gas 

benefits compared to conventional engines, but they require emission control devices that are 

quickly poisoned as the fuel sulfur level rises above 10 ppm. 

Countries and regions that have capped gasoline sulfur at 10 ppm (for example, Europe and 

Japan) have been able to enjoy the benefits of lean burn technology over the past decade. If EPA 

retains the 95 ppm retail cap, U.S. consumers will continue to be deprived of this fuel efficient 

option, and they will continue to wonder why other countries seem to have more advanced and a 

greater diversity of fuel efficient technologies than the United States. 

Maintaining a 95 ppm retail sulfur cap would be damaging to the U.S. reputation as a leader in 

air pollution control because so many other countries and some cities have already achieved 

ultra-low sulfur levels in their gasoline.7 In Canada, for example, according to the Alliance’s 

North American Fuel Survey, the highest sulfur level recorded last summer (2010) was 32 ppm 

for regular grade and 20 ppm for premium, and since 2007, the levels there have been 

consistently below 40 ppm. In Mexico all premium grade samples in the Alliance surveys have 

had less than 52 ppm sulfur since 2007. In half of the cities sampled, regular grade samples have 

had less than 80 ppm sulfur since 2009.

 

6. See 42 USC 7545(q). Though due in draft form by 2009, this analysis has not yet been published. EPA expects 

to work on this analysis in parallel with drafting the Tier 3 Proposed Rule.

7According to Hart’s International Fuel Quality Center, as of May 2010, Japan, South Korea, Iceland, Greenland, 

and the countries of the European Union require less than 10 ppm sulfur gasoline. The U. S. ranks 44th in a ranking 

of the top 100 countries by gasoline sulfur standard stringency. See PR Newswire, “IFQC Ranks Top 100 Countries 

by Gasoline Sulfur Standards: Europeans’ Major Progress Bumps U.S. to 44th Place,” May 5, 2011, and IFQC, 

http://www.ifqc.org/NM_Top 5.aspx.
6

Automakers that engineer vehicles for the U. S. have waited a long time for lower fuel sulfur 

levels that harmonize with foreign standards, enable lean-burn technology, and make full use of 

advanced technologies. Maintaining existing U.S. high sulfur caps would inhibit needed 

technology and international harmonization of fuels and vehicle design, and waste scarce 

economic and commodity resources on over-sophisticated emission control systems. 

Flaws in the Purported Reasons for Retaining the Tier 2 Sulfur Caps 

The main argument against more stringent sulfur limits boils down to concern that a few, perhaps 

older or small refineries that supply U. S. retail gasoline might be unable to consistently produce 

a lower sulfur product. 

This argument seems weak, given how long refiners have known about sulfur’s effects and have 

been producing lower sulfur gasoline. As noted, California began requiring a low sulfur gasoline 

in 1996. In 1998 EPA imposed Federal RFG Phase 2 requirements—affecting about one third of 

the country’s gasoline market. To comply with federal RFG2’s required NOx reductions, 

refiners needed to substantially reduce sulfur. As a result, by 2000, refiners were well on their 

way to producing Tier 2 compliant gasoline, as shown in EPA’s Fuel Trends Report 2008, which 

studied retail sulfur levels from 1995 to 2005. By 2005, several years after Federal RG2 

implementation and one year after Tier 2 implementation, the Federal RFG summer retail 

average had already dropped to about 70 ppm from about 200 ppm in 1998. The annual average 

for all gasoline in 2005 was 92 ppm. It is very difficult to conclude that a lower sulfur retail 

limit would not be feasible in the U.S. A few stressed refineries should not drive the universally 

applicable prospective federal limits. 

A second argument is that contamination during distribution through the finished product 

pipeline infrastructure contributes to retail gasoline sulfur levels and that this contamination 

cannot be further controlled. The Alliance would appreciate the opportunity to see what current 

data EPA or other stakeholders have, including any comparisons of past versus current samples 

showing the relative magnitude of sulfur contamination levels, or that support the need for a 95 

ppm sulfur retail cap. 

The same contamination concerns were voiced when EPA was developing the ultra-low sulfur 

diesel (ULSD) fuel standard in 2002. Yet the country has successfully converted to retail 15 

ppm sulfur diesel fuel nationwide, using the same pipelines to distribute the fuel as used for 

gasoline. Further, since the 2002 ULSD rule, EPA has greatly reduced the sulfur levels in other 

petroleum products that move through the pipelines. Non-highway diesel fuel and fuel used for 

locomotive and marine applications will have to meet the same 15 ppm sulfur limit by 2014, 

before Tier 3 is implemented. Thus, it should be much easier to move ultra-low sulfur gasoline 

in pipelines in 2016-17 than it was in 2006, when ULSD began its phase-in. In addition, since 

most gasoline today contains 10% ethanol, the sulfur levels are further reduced (diluted) during 

blending after the fuel leaves the pipeline, which also provides refiners with some flexibility. 

EPA Opportunity to Promote International Harmonization Regarding Sulfur Levels

The 2000 edition of global automakers’ Worldwide Fuel Charter stressed the need for sulfur-free 

gasoline. Shortly afterward, Europe and Japan started moving toward a 10 ppm maximum sulfur 

standard. Both of these markets have now had ultra-low sulfur gasoline for several years. Other 

countries, including Canada and Mexico, also are moving to well below 80 ppm8consistent with 

 

8 Based on retail sulfur levels measured through the Alliance North American Fuel Survey, 2007-2011. 
7

the goals of the UNEP-managed Partnership for Clean Fuels and Vehicles, in which both EPA 

and the oil industry participate.9 In 2005, the PCFV conservatively recommended a 50 ppm 

sulfur limit for all countries, even those in Africa, while recognizing the benefits of further 

reduction, but keeping in mind the challenge presented for developing countries. 

Conclusion 

EPA should use its opportunity in Tier 3 to provide a strategy toward achieving a 5-10 ppm cap 

on sulfur in U.S. retail gasoline. Any issues relating to particular refinery capability, pipeline, or 

other sulfur contributions should be addressed individually, as part of the larger strategy to 

achieve this goal, but should not be used to change the goal itself. Allowing sulfur caps as high 

as 80 ppm at the refinery gate and 95 ppm at retail pumps to continue indefinitely in the US 

marketplace is unwarranted, would handicap maximizing vehicle emission reductions and 

achieving fuel economy and GHG standards, and would inhibit development and use of cleaner, 

more efficient combustion technologies.

The Alliance looks forward to additional opportunities to work with EPA and other stakeholders 

on the gasoline sulfur reduction challenge. 

***

For additional information, please contact:

Valerie Ughetta, Director, Automotive Fuels

Alliance of Automobile Manufacturers

vughetta@autoalliance.org

 

9

See Partnership for Clean Fuels and Vehicles,

http://www.unep.org/transport/pcfv/partners/partners.asp); and Low Sulphur Campaign, 

http://www.unep.org/transport/pcfv/corecampaigns/campaigns.asp#sulphur). In 2005, the Partnership recommended 

that countries aim “To reduce sulphur in vehicle fuels to 50 ppm or below worldwide, concurrent with clean 

vehicles and clean vehicle technologies, with roadmaps and timelines developed regionally and nationally”. See 

Summary of the Fourth Meeting of the Global Partnership for Clean Fuels and Vehicles, UNEP Headquarters, 

Nairobi, Kenya, 14-15 December, 2005, available at http://www.unep.org/transport/pcfv/PDF/4GPM-reportfinal.pdf.
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

1

APPENDIX 1: Overview of Pertinent Studies on Sulfur’s Impact on Vehicle Emissions

1. According to EPA staff, a new EPA-designed and managed sulfur test program has been 

conducted. Results not yet publicly available.

2. SAE 2011-01-0300, D. Ball, et al., Effects of Fuel Sulfur on FTP NOx Emissions from a 

PZEV 4 Cylinder Application.

The authors measured the impacts of test fuels containing 3 ppm and 33 ppm sulfur on NOx 

emissions from a 2009MY PZEV Malibu. An important aspect was the evaluation of the 

ability of different driving cycles to reverse the catalyst poisoning and the potential for ―NOx 

creep,” i.e., the incremental permanent reduction in catalyst efficiency as a result of repeated 

sulfur exposure. Test data on sulfur’s impact on very low emitting vehicles (e.g., SULEV, 

PZEV, Tier 2 Bin 2) are scarce, especially at ultra-low sulfur levels and over a 150,000 mile 

compliance lifetime, so these data begin to fill an important gap. As the study notes, catalyst 

efficiencies for PZEVs need to exceed 99.4% for HC and 99.3% for NOx through 150,000 

miles, and small changes in catalyst efficiency can have a large impact on tailpipe emissions. 

The study found that sulfur levels of 33 ppm will affect test to test NOx stability during FTP 

testing, and that catalyst temperatures of 600°F, common in under-floor catalysts, can allow 

sulfur poisoning that affects NOx reduction efficiency and consistency of results. Using the

US06 test cycle (high engine flow, high load) between FTP cycles, however, can increase 

catalyst temperature enough to help reverse the poisoning and improve test to test stability. 

According to the study, while the US06 can help mitigate sulfur poisoning, using a 3 ppm 

sulfur gasoline would eliminate the need to use such a cycle –also, a 3 ppm fuel also would 

reduce NOx emissions by 40% compared to the 33 ppm fuel, and/or allow lower levels of 

precious group metals in the catalyst. 

3. Pembina Institute, Fuel Quality in Canada, prepared for the Association of International 

Automobile Manufacturers of Canada, November 26, 2008.

This report concluded that reducing gasoline sulfur would lead to a direct reduction in SOx 

emissions. Additionally, it discussed other studies that found sulfur reduces the performance 

of three-way catalysts (TWC) and other after-treatment devices. By reducing sulfur content, 

these devices can work more effectively, leading to reductions in the emissions of VOCs, 

NOx and CO. 

4. SAE 2008-01-0628. Y. Shen et al., Effects of Gasoline Fuel Properties on Engine 

Performance.

This study aimed to provide technical support for automotive gasoline fuel quality standards 

to match new vehicle emission standards in Beijing, China. While the study found sulfur had 

little impact on the conversion efficiency of fresh catalysts, it did have an influence on the 

conversion efficiency of aged catalysts. Catalysts aged up to 100 hours with 50 ppm or 150 

ppm sulfur gasoline increased the catalyst light-off temperatures, and when operated at high 

temperature, catalyst performance recovered only partly. 
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

2

5. Joint EPA-Automobile Industry Tier 2 Vehicle Fuel Effects Test Program (―MSAT Study‖), 

2006; results presented as a Poster at the 17th CRC On-Road Vehicle Emissions Workshop, 

March 31-April 2, 2007.

EPA and several automobile manufacturers cooperatively undertook the so-called MSAT 

Study to assess the emissions sensitivity of lower emission vehicles (Tier 2 or LEVII) to 

various fuel properties, primarily RVP, benzene and sulfur. The study tested five gasoline 

blends on nine Tier 2 vehicles with a fleet average emissions level below the Tier 2 Bin 5 

standard (0.07 g/mi of NOx and 0.09 g/mi of NMOG). Four of the test fuels contained ultralow sulfur levels (6 ppm for the base fuel and base fuel adjusted for RVP and benzene, and 5 

ppm for the non-oxygenated commercial California fuel). The fifth test fuel was a 50th 

percentile commercial federal fuel containing 32 ppm sulfur. 

The study found the California test fuel was the best overall performer, significantly lowering 

benzene, NMHC and NOx emissions, and this was the only test fuel that caused a significant 

drop in tailpipe NMHC emissions. Sulfur could not have been the deciding factor in the 

NMHC results, however, because most of the test fuels had similar sulfur levels. Sulfur was 

the key factor in the NOx emission results, however, since the federal commercial fuel (with 

32 ppm sulfur) had significantly higher average composite NOx emissions than all the other 

fuels tested (which contained either 5 or 6 ppm sulfur). The emission differences were quite 

large, representing emission decreases of 30% to 38% from the federal fuel’s high mean of 

0.056 g NOx/mi. Looked at another way, increasing the sulfur from 5 or 6 ppm to 32 ppm 

resulted in emission increases of 43% to 63%.

6. Worldwide Fuel Charter, 2006 Edition, available at www.autoalliance.org (click on

Environment and Energy, to Clean Fuels).

This document, produced by ACEA, the Alliance of Automobile Manufacturers, EMA and 

JAMA, and endorsed by automobile manufacturers from around the world, summarized 

several sulfur impact studies available at the time of publication. 

7. CRC Project E-60, The Effect of Fuel Sulfur on NH3 and Other Emissions from 2000-2001 

Model Year Vehicles, May 2003.

This study, which was designed to measure NH3 production at the catalyst under the US06 

and FTP test cycles using gasoline with 5, 30 and 150 ppm sulfur gasoline, also examined 

other emissions and found significant reductions of common criteria pollutants as well as 

N2O as the sulfur was reduced. The impact of lower sulfur on aged catalysts (from in-use 

vehicles), especially for NOx and NHMC, was even bigger than on fresh catalysts. 

8. Alliance of Automobile Manufacturers/Association of International Automobile 

Manufacturers, Gasoline Sulfur/Oxygen Impacts Study, conducted for the California Air 

Resources Board, 2001, available at www.autoalliance.org.

This study examined the impact of sulfur levels at 1 ppm, 30 ppm and 100 ppm on LEV and 

SULEV technology vehicles. While the reductions for 1 ppm sulfur were less than predicted, 

the study did indicate greater sulfur sensitivity as the sulfur decreased below 30 ppm, and it 

provided support for modifying CARB’s Predictive Model for newer vehicle technologies. 
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

3

9. Association for Emissions Control by Catalyst (AECC), Response to European Commission 

Consultation on the need to reduce the Sulphur Content of Petrol and Diesel Fuels below 50 

parts per million, July 2000, available at http://www.aecc.eu/en/Publications/Archive.html.

This report by manufacturers of emission control equipment summarized the findings of 

several studies into the impact of sulfur on catalyst performance. The report included these 

comments on various studies relating to sulfur’s impact on lean-burn gasoline engines and on 

three-way catalysts (as excerpted from the report):

 Quissek et al. (ADA) showed DaimlerChrysler data showing >80% NOx conversion 

[with a lean NOx trap] on a DI petrol engine for 10 000 km on the EU III hot test on 8 

ppm sulphur fuel but falling to <30% with 50 ppm sulphur fuel.

 Hachisuka et al. (Toyota Motor Corp.) describe a new NOx storage-reduction (NSR) 

system for lean burn petrol engines being introduced into the Japanese market where 

sulphur levels in petrol are much lower. The first generation of NSR catalyst 

introduced by Toyota gave (after 100 hours of aging on fuel containing 500 ppm 

sulphur) NOx conversion one-eighth of the level obtained with a fuel sulphur of 30 

ppm - but even at this level NOx conversion efficiency gradually decreases. 

Improvements of NOx conversion of 50% in the new catalyst still give limited 

application in Europe because of fuel sulphur levels. Toyota says ―it is critical that 

sulphur content in fuels be reduced‖.

 Johnson (Corning Inc.) published a comprehensive review of 1999 SAE papers on 

―Gasoline Vehicle Emissions‖. He cites the conclusion of Asunama et al (Toyota) 

that increased sulphate grain size results from higher petrol sulphur levels and this 

makes NOx trap desulphation more difficult. After aging for 16 000 km at various 

sulphur levels they showed that at 8 ppm fuel NOx conversion efficiency could be 

instantly returned to >90% by regeneration at 620°C whereas at 500 ppm sulphur 30 

minutes regeneration restored conversion from <20% to only 50%. At 30 ppm 

sulphur 30 minutes regeneration restored NOx conversion from 75% to <90%. 

Regarding sulfur and three way catalyst research generally: 

 Most of the studies compare the tailpipe emissions using fuels with different sulphur 

levels and all conclude that the lower the sulphur level the lower the emissions on 

fresh or aged catalysts. There is however some evidence of a non-reversible 

interaction between the washcoat components and sulphur.

From the report’s conclusions:

 For the existing fleet of vehicles lowering sulphur levels in petrol to below 10 ppm 

would give a reduction in emissions from all three-way catalyst equipped vehicles of 

up to 20%. US data indicates an enhanced effect on emissions at 30 ppm sulphur and 

it is known that sulphur affects catalyst performance all the way down to 0 ppm.

 The promising NOx adsorber technology that diesel and lean burn engines need 

requires sulphur levels significantly below 10 ppm. This will avoid compromising the 
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

4

lower fuel consumption and CO2 emissions by requiring frequent regeneration to 

remove the sulphur that is ―clogging‖ the NOx adsorption capacity.

 The best option to allow the unconstrained development and introduction of new 

emission control technologies is to set a specification for sulphur levels at below 10 

ppm for introduction as soon as possible. This will allow Member States to introduce 

tax incentives and for market forces to bring the ultra-low sulphur fuels to the market 

to allow the early introduction of the new technologies. 

 Ultra low sulphur fuels are shown to reduce greenhouse gas emissions by: 

o Reducing CO2 emissions by allowing low fuel consumption vehicles, e.g. 

diesel and lean burn/petrol fuel injection, to flourish 

o Reducing emissions of greenhouse gases such as methane (CH4) and nitrous 

oxide (N2O) by allowing catalysts to more efficiently remove them.
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

5

APPENDIX 2: Additional Background on the History of Market Sulfur Regulation

In the early 1990s, the auto and oil industries produced significant new research documenting the 

adverse impact of gasoline sulfur on the effectiveness of three way catalysts.1 The State of 

California acted on these findings by adopting the ―Phase 2 Reformulated Gasoline‖ (California 

RFG2) regulation, which reduced gasoline sulfur levels across the state.2 The California RFG2 

sulfur standard, which was implemented in 1996, allowed refiners to meet either a flat limit of 40 

ppm sulfur per batch or a 180-day average limit of 30 ppm sulfur.3 In no case could the gasoline 

exceed an absolute per gallon cap of 80 ppm sulfur. California RFG2 proved highly effective 

not only at reducing vehicle emissions but also causing measurable reductions in ambient ozone 

levels.4 Soon after, other states became interested in this achievement, leading the Ozone 

Transport Assessment Group to recommend that EPA adopt a regulation to reduce sulfur across 

the country.5 

EPA agreed that reducing sulfur below the then current retail average of about 330 ppm sulfur 

and maximum retail level of 1000 ppm6 would yield significant air quality benefits. Sulfur, in 

fact, was one of the key tools that was already being used in the late 1990s to improve the NOx 

performance of Federal RFG Phase 2.7 As a result, in 1999 the Agency adopted nationwide 

gasoline sulfur controls in conjunction with Tier 2 vehicle emission standards, to be phased-in 

between 2004 and 2006.8 EPA further modified the rule in connection with the 2002 ultra-low 

sulfur diesel fuel regulation (phased-in between 2006 and 2010), whereby it offered refiners 

additional flexibility in implementing the gasoline sulfur rule as an inducement to reduce sulfur 

in diesel fuel more quickly.9 The specific sulfur limits adopted by EPA were somewhat more 

relaxed than in California RFG2, however, and by the time the federal limits were adopted in 

1999, California already was well on the way to tightening sulfur further to a 30 ppm cap. 

Actual sulfur levels in that state have been driven even lower through the use of the Predictive 

Model.

 

1

See Coordinating Research Council, ―Auto-Oil Emissions Program,‖ found at http://www.crcao.com/reports/autooil/default.htm.

2

For background on California’s ―Phase 2‖ gasoline rulemaking, see 

http://www.arb.ca.gov/fuels/gasoline/carfg2/carfg2.htm. 

3 Refiners also could meet alternative limits if they could show the fuel would produce at least the same amount of 

emission benefits. See http://www.arb.ca.gov/fuels/gasoline/pub/pub.htm.

4

For one analysis of the rule’s impact on air quality, see, e.g., Larson, ―An assessment of the impact of California's 

Phase 2 Reformulated Gasoline on ozone air quality,‖ J Air Waste Management Assoc. 2001, Jan;51(1):37-48.

5

See OTAG’s source specific recommendation for gasoline at

http://earth1.epa.gov/ttn/naaqs/ozone/rto/otag/finalrpt/chp6/final.htm.

6 These commercial levels might have been higher but for various constraints imposed through pipeline contract 

limits and ASTM D4814 gasoline specifications, which are adopted by many states.

7 EPA requires states to use Federal RFG2 in certain ozone non-attainment areas; much of the fuel sold on the east 

coast, west coast, Chicago and certain other limited areas is federal RFG2. 

8 EPA finalized the rule on December 21, 1999 and published it in the Federal Register on February 20, 2000 (see

http://www.epa.gov/tier2/finalrule.htm). It was further corrected and amended several times between 2001 and 2006 

(see http://www.epa.gov/tier2/amendments.htm). In 2000, California reduced sulfur levels further to a 30 ppm per 

gallon cap; while this limit fell short of the 10 ppm cap advocated by automakers, the state’s regulatory approach 

(using a Predictive Model) in combination with increased ethanol levels has driven the maximum sulfur found in the 

Alliance surveys to well below 16 ppm since 2009 and below 12 ppm since 2010, with the averages approaching 

zero in some cases.

9

Ibid.
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

6

APPENDIX 3: Executive Summary National Clean Gasoline: An Investigation of Costs 

and Benefits, Alliance of Automobile Manufacturers, June 2009

Introduction

The Alliance of Automobile Manufacturers (Alliance)10 recently commissioned two studies 

examining the costs and benefits of introducing a cleaner national gasoline, defined as a Clean 

Air Act regulatory standard, into the U.S. market. The first study, conducted by MathPro, Inc., 

investigated the refining costs of producing the proposed fuel standard, and the second study, 

conducted by Air Improvement Resources, Inc., investigated the standard’s impacts on emissions 

from on-road gasoline-powered vehicles (excluding motorcycles). The Alliance designed the 

gasoline standard to reduce vehicle emissions and, importantly, to enable lean burn gasoline 

engines, which are a new, fuel efficient vehicle technology. The Alliance also sought to create a 

standard that could be used as a single national gasoline, eventually replacing the so-called 

boutique gasolines being sold in parts of the U.S. to reduce emissions. For study purposes, the 

Alliance named its proposed fuel ―National Clean Gasoline‖ (NCG). 

Fuel quality plays a critical role in vehicle operation and emissions because it affects the 

combustion process and can interact with vehicle components, including, but not limited to, 

emission control systems. Certain gasoline compounds—especially those containing sulfur—

reduce the effectiveness of emission control systems, thereby causing vehicle emissions to 

increase.11 As another example, gasoline’s distillation characteristics affect combustion 

efficiency and smoothness, and its vapor pressure affects evaporative emissions. Depending on 

the property or contaminant, effects may occur immediately, build up gradually over time or be 

irreversible. Most importantly for policymakers, fuel quality may affect a vehicle’s ability to 

comply with emission standards, deliver planned fuel economy, use certain technologies or 

satisfy customers. This is why vehicles and fuels must be viewed as a system. 

Quality of National Clean Gasoline

In specifying NCG, the Alliance capped sulfur at 10 parts per million (ppm), which is 

significantly lower than current federal limits.12 As noted, sulfur reduces the effectiveness of 

catalytic converters used to meet stringent U.S. and California vehicle emission standards. 

Manufacturers have been able to build compliant vehicles despite the sulfur levels found in 

federal gasoline, but vehicle emissions would be much lower if the sulfur levels were lower. As 

EPA seeks to reduce smog-forming emissions further, reducing gasoline sulfur levels would be a 

helpful control strategy. It would also help reduce emissions in California where sulfur levels 

 

10 The Alliance is a trade association of eleven car and light truck manufacturers—BMW Group, Chrysler, Ford 

Motor Company, General Motors, Jaguar Land Rover, Mazda, Mercedes-Benz, Mitsubishi Motors, Porsche, Toyota 

and Volkswagen. 

11 Metallic additives also reduce the effectiveness of emission controls, but the federal government and California 

prohibit their use in federal and California reformulated gasolines, respectively, and virtually all U.S. refiners refrain 

from using such additives in conventional gasolines. 

12 EPA regulations require gasoline produced for sale outside of California to have an annual average of no more 

than 30 ppm sulfur at retail with a per gallon cap of 80 ppm, but the EPA test tolerance limit allows an individual 

gasoline sample sold at retail to contain as much as 95 ppm sulfur. California rules require sulfur to be no more than 

30 ppm, and the average today is about 9 ppm, which is better than the federal limit but still not as clean as gasoline 

standards in Europe and Japan, which allow a maximum of 10 ppm sulfur. Under its ―Phase 3‖ gasoline regulation, 

California is scheduled to reduce its maximum per gallon sulfur limit to 20 ppm on December 31, 2011, and the 

average is expected to decline further. 
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

7

are relatively low, even if the state did not adopt NCG, because vehicles coming into the state 

would be cleaner than they are now.

Sulfur is also important because certain new technologies require different emission control 

systems that are more sensitive to sulfur. Like diesel engines, lean-burn gasoline engines are 

very efficient at burning hydrocarbons, which improves the vehicle’s fuel economy compared 

with similar vehicles using conventional spark ignition engines. Lean burn gasoline engines, 

however, are optimized for fuel economy, which can lead to higher engine-out NOx emissions, 

also like diesel. The higher NOx emissions require new, advanced emission control systems 

similar to those used in diesel vehicles to enable compliance with stringent U.S. and California 

emission standards, but the systems are quickly poisoned by sulfur. Lean burn gasoline 

technology can work acceptably only with gasoline containing less than 10 ppm sulfur (also 

called ultra-low sulfur gasoline or ULSG). 

The Alliance constrained additional gasoline properties either to match existing federal or 

voluntary ASTM standards (e.g., benzene, driveability index), the lowest level acceptable for 

vehicle operation across the U.S. (e.g., vapor pressure) or to comply with EPA’s Complex Model 

constraints (e.g., aromatics, olefins). Ethanol content was set at 10% by volume (the limit under 

existing federal regulations) to reflect the national ethanol mandate volumes required under the 

Renewable Fuel Standard in the Energy Independence and Security Act of 2007. 

Table 1: Proposed National Clean Gasoline Specifications 

Property Units Limit Comments

Sulfur ppm 10 max

Reduces emissions from the 

existing fleet and enables fuel 

efficient lean burn technologies. 

Regulated by EPA and California.

RVP psi 7 max

Selected to match the lowest 

emitting value while maintaining 

acceptable vehicle operation. 

Regulated by EPA and some states.

Benzene % v/v 0.62 avg New EPA national toxics standard 

(―MSAT2‖).

Ethanol % v/v 10 max Current federal maximum.

Octane

Regular

Premium

(R+M)/2 87 min

93 min

Based on industry practice. Limits 

apply at all altitudes.13

 

13 In general, refiners select octane levels to meet consumer demand. The Alliance believes it is acceptable for 

Premium gasoline to be defined as having a minimum 91 octane ((R+M)/2).
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

8

Property Units Limit Comments

ASTM Driveability 

Index14 * 1250 max

The ASTM voluntary standard, 

which is enforceable in some states. 

DI is important for engine 

calibration, engine performance 

and emissions.

Alliance Distillation 

Index5 * 1200 max For sensitivity analysis (preferred Alliance DI limit).

Aromatics, Olefins, 

E200, E300

*

Unconstrained for NCG but 

indirectly regulated through EPA’s 

Complex Model, which is used to 

certify gasoline compliance.

*No units apply but, in this context, temperatures are measured in degrees Fahrenheit.

Approach

The studies targeted 2010 as the earliest possible year for implementing the NCG specifications. 

The refining economics study was completed first, to provide baseline data for the emissions 

analysis. The study modeled NCG costs to reflect a phased rollout: first, it introduced NCG in 

current federal RFG areas; second, it replaced all low RVP gasolines with NCG; and third, it 

replaced all conventional gasoline with NCG. This sequence begins with the least-cost fuel 

replacement and moves on to progressively more costly fuel replacements. The study area 

covered most of the U.S. (PADDs15 1-3) and its gasoline pool but excluded the Rockies and 

West Coast states (PADDs 4 and 5) for reasons explained in the study. 

The refining economics study estimated the refining costs of producing the specified new fuel in 

volumes consistent with the three implementation phases. This analysis was limited to 

examining refining costs; it did not include analyzing NCG’s possible impacts on fuel 

distribution, price (which is determined by market forces) or other non-refinery factors. The 

primary analysis assumed a crude oil price of $51.20/barrel, which was the reference case 

projection derived by the Energy Information Administration for its 2007 Annual Energy 

Outlook (AOE2007).16 The unprecedented rise in crude oil prices during 2008, however, led the 

Alliance to conduct a sensitivity analysis using a crude oil price of $125/barrel. 

The emissions study used fuel quality estimates from the refining economics study as inputs to 

well-accepted and publicly available emissions modeling tools. For public policy purposes, it is 

insufficient to know how emissions change for one vehicle; models must be used to estimate the 

fleet-wide emission impacts, to accommodate variations in vehicle type, age, usage and other 

 

14 The Alliance used the ASTM Driveability Index limit, which applies at the refinery gate, as the basis for the study 

instead of its preferred Distillation Index, which applies at the retail pump, because recent changes have brought the 

ASTM limit much closer to the Alliance recommendation and because refiners are using the ASTM limit in the 

market. To determine the impact of imposing the Alliance Distillation Index with a tighter limit, a sensitivity 

analysis was conducted.

15 ―PADD‖ means Petroleum Administration Defense District; see www.eia.doe.gov for a map. Roughly, PADD 1 

corresponds to the east coast, PADD 2 corresponds to the Midwest and PADD 3 corresponds to the gulf coast states.

16 Energy Information Administration, ―Annual Energy Outlook 2007 with Projections to 2030,‖ Report 

#:DOE/EIA-0383(2007), February 2007, available at http://www.eia.doe.gov/oiaf/archive/aeo07/index.html (May 

21, 2009). 
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

9

factors, including fuel quality. Emissions also change year to year; this study looked at the 

emission changes between 2010 and 2020 for the same geographic area covered by the cost 

study. Recent results from an EPA study of toxic emissions from Tier 2 vehicles were included 

as part of a sensitivity analysis. 

Findings

Refining Economics. The estimated average cost of producing the full volume of NCG, using the 

AEO2007 crude oil reference price estimate, is 2.75¢/gallon; the estimates are slightly lower for 

PADDs 1 and 2. The estimated marginal cost of introducing the last increment of NCG is about 

3.9¢/gallon and slightly higher in PADDs 1 and 3. Improving the distillation index by using the 

Alliance’s preferred Distillation Index equation and limit of 1200—i.e., tightening the distillation 

constraints further—would increase average refining cost by about 1¢/gallon in PADD 1 only; 

other regions would see no impact on average refining costs because their gasoline already meets 

this limit. The estimated marginal cost for the last increment of NCG is about 5¢/gallon, also 

only in PADD 1. These estimates pertain to average refining costs, and as such, they do not 

indicate costs that would be incurred by any individual refineries. 

The sensitivity analysis using a higher crude oil price indicates that large increases in crude oil 

prices lead to moderately higher refining costs for producing NCG. With crude oil at 

$125/barrel, the estimated average cost of producing the full volume of NCG is about 

4.5¢/gallon, an increase of 1.75¢/gallon compared with the estimates based on crude oil priced at 

$51/barrel. The corresponding estimated marginal cost of producing the last increment of NCG 

is about 6.5¢/gallon, which is an increase of about 2.5¢/gallon. Assuming no change in 

electricity and natural gas prices, each $10 change in the price of crude oil would lead to a 

change of about 0.24¢/gallon in the average cost of producing NCG.

Table 2. Estimated Refining Cost Changes

Estimated Average Refining Cost, 

at Two Crude Oil Prices

Cost Impact of 

Higher Crude 

Refining Cost of NCG units $51/bbl $125/bbl Price

Average cost ¢/gal 2.75 4.5 1.75

Average cost 

(Alliance DI sensitivity case) ¢/gal 3.75(PADD 1 only)

* *

Incremental cost ¢/gal 4 6.5 2.5

Incremental cost 

(Alliance DI sensitivity case) ¢/gal 8.75(PADD 1 only)

* *

*Not estimated. 

Emissions. The emissions investigation found that NCG would have significant impacts on 

evaporative hydrocarbon (HC) and exhaust nitrogen oxides (NOx) emissions. Between the study 

years of 2010 and 2020 and on a per-PADD basis, evaporative HC reductions ranged from 12% 

to 19%, and exhaust NOx reductions ranged from 10% to 14%. Exhaust HC emissions also 

declined, ranging from 1% to almost 4% from their already very low baseline. The sensitivity 

analysis using newer Tier 2 emission impacts suggests these vehicles are more sensitive to fuel 

sulfur effects than the existing models indicate. Compared to the national on-road HC and NOx 

emissions inventory, these reductions are significant, especially if the estimates are conservative 
Alliance of Automobile Manufacturers, Appendices to White Paper on Tier 3 Sulfur 8/24/11

10

as the sensitivity analysis suggests. This finding could be very important to states trying to meet 

more stringent ozone ambient air quality standards. 

Table 3. Summary of Emission Reductions due to NCG

2010 2015 2020

Exhaust HC 1 – 3% 1.5 – 3.5% 1.75 – 3.75%

Evaporative HC 12 – 19.5% 11.5 – 18.5% 11 – 18.5%

NOx 10 – 11% 12 – 13% 13 – 14%

Conclusion

These studies highlight the potential benefits and costs of improving national gasoline quality. 

The estimated costs are reasonable, even when crude oil prices are high. The emission benefits 

would be substantial. Additional benefits to gasoline supply accrue simply by eliminating the 

many boutique gasolines introduced over the years for air pollution control purposes. 

Introducing an ultra-low sulfur gasoline nationwide would enable automakers to introduce a new 

fuel efficient vehicle technology—lean burn gasoline engines—increasing the options for 

improving fuel economy for both automakers and consumers. All of these factors support 

improving fuel quality on a national basis as a feasible emissions control strategy that will also 

help the country meet other important national objectives.