FEATURE

Putting the Brakes on Clean Cars

Researchers agree that conventional high-sulfur

gasoline can poison a catalyst. But is the effect reversible?

CATHERINE M. COONEY

The White House announcement in February of this year launching a national low-emissions vehicle (NLEV) program was heralded by Vice President Al Gore as a demonstration that "government and industry, working in part­

nership, can achieve cost-effective environmental gains." Establishing a program to put clean cars on the road five years ahead of a Clean Air Act man­date, the "Big Three" auto­makers agreed to voluntar­ily begin producing low-emission automobiles by the end of this year for sale in northeastern states. These low-emission vehicles (LEVs) would achieve emission re­ductions of 50% for NO and 70% for hydrocarbons*

Even while the NLEV concept was being unveiled, however, major studies in­volving EPA and the automobile and oil industries were showing that the high-technology, low-emission vehicles planned for sale would not cut hy­drocarbon and nitrogen oxide emissions if the cars were fueled with high-sulfur gasoline commonly sold in the United States.

The same researchers found that the sulfur con­tent of gasoline sold in many parts of the country is high enough to impair function of the advanced cat­alytic converter used in the LEVs to reduce pollu­tion. Although the petroleum and refining indus­tries maintain that the damage done to an LEVs catalytic converter from sulfur can be easily re­versed, automobile makers and state regulators dis­agree. EPA is moving toward resolution of this issue and plans to propose by the end of 1998 a require­ment that either vehicles meet stricter tailpipe stan­dards that go beyond the LEV or refiners pro­

duce lower-sulfur fuel, or both. The automakers plan to have LEVs for sale in all states by 2001.

Most gasoline sold in the United States has fairly high sulfur levels. The national average is 350 parts per mil­lion (ppm); as much as one-fourth of gasoline has a sul­fur level of 500 ppm or higher, according to petro­leum industry figures. On the otiier hand, California, the nation's smoggiest state, now has a statewide sul­

fur standard of 30-40 ppm. California's standard allows refiners to produce gasoline in batches that meet a sulfur content average of 30 ppm so that in some cases sulfur lev­els in gasoline can be as high

the state's sulfur C3.p of 80 ppm. Most northeastern states also suffering from high ozone levels sell refor­mulated gasoline with sulfur levels of 150 ppm

StnHip<i rnndnr tpH hv EPA and industry groups show that sulfur can affect the LEVs advanced cat­alytic converter rendering useless its abilitv to con­trol emissions As earlv as 1992 the Societv of Au­tomotive Fneinpprs nnhlisherl'spvpral lahoratorv studi i h h ar inmfi ipl tvnp>5 wpre fpri throiigh an advanced technology catalyst. The studies dem-onstrated that sulfur affects emission controls by poi-somng the catalyst, according to Allen Zengle, exec-

J- , A l _ ^ J - j.- n i f / - . -1 utive director of the Coordinating Research Council , „ _ , „ . . . - , , ° j - j j i i

(CRC), an Auanta-based research group funded largely by the automobile and oil industries.

The studies showed that sulfur atoms can bond with and block reactive sites on the catalyst sur­face, preventing the occurrence of the catalyzed re­actions that break down NO^ and hydrocarbons. The research also indicated that high sulfur levels can cause a vehicle's on-board diagnostic equipment to

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malfunction, leaving drivers unaware that the pol­lution control equipment is not working.

The concern over sulfur in fuel picked up speed in late 1997, when a CRC study involving EPA was released, said John Kowalczyk, a member of EPA's Mo­bile Source Advisory Committee and who is retired from Oregon's Department of Environmental Qual­ity. "This effect was known for several years," Kow­alczyk said about the poisoning phenomenon. CRC's "Sulfur/LEV Program" studies, released last Decem­ber, were conducted using catalytic converters lo­cated in vehicles, and thus were closer to simulat­ing conditions in the real world, said Kowalczyk. Because tticy were done usin&f 3, vehicle, "they be-c3IHG the best studies around."

Call for low-sulfur fuel The public debate over sulfur levels in gasoline was ignited by a January announcement from the na­tion's fourth-largest petroleum refiner, Tosco Corp., that it would support a government requirement for a major reduction in sulfur content of U.S. gaso­line. Tosco committed to produce gasoline with 75% less sulfur and called for a national sulfur cap of 80 ppm by 2000, similar to California's program.

Shortly after announcing its members' commit­ment to produce NLEVs, the American Automobile Manufacturers Association asked EPA to imple­ment California's sulfur requirement nationwide. The automakers argued that their companies have done as much as they can to improve air quality. "No­body knows how to make a catalyst that can meet today's low-emission vehicle standards and still do all of the things that are needed for today's cars," said Ellen Shapiro, spokesperson for the American Au­tomobile Manufacturers Association. "The catalyst manufacturers are doing research on this, and they have said that the state of the art is not here."

Although the automakers and gas producers usu­ally work together on federal regulations, the auto in­dustry's support for a nationwide, low-sulfur gaso­line sparked an unusual public disagreement between the two industries. "We don't believe that the mo­toring public [in other states] wants to pay for Cal­ifornia prices," said William E O'Keefe, vice presi­dent of the American Petroleum Institute (API), a lobbying organization. In March, the petroleum pro­ducers and refiners joined forces and asked EPA to set a regional low-sulfur gas requirement by 2004. Un­der this proposal, only dealers in the 22 eastern states composing the Ozone Transport Assessment Group (OTAG), would sell conventional fijcisoline with 3. sul­fur content of 150 DDOI in the summer months while the western states (except California) would sell gas with a 300-DDm level

In the view of state and local air pollution regu­lators, API's proposal will not improve air quality. Cit­ing studies showing that high-sulfur gasoline can poi­son a car's catalyst, the State and Territorial Air Pollution Program Administrators and the Associa­tion of Local Air Pollution Control Officials (STAPPA/ ALAPCO) last October announced support for the California fuel program, said Kowalczyk, who is also a consultant for STAPPA/ALAPCO.

Low-sulfur gasoline: A regional approach

The petroleum industry has proposed a regional strategy rather than a national sulfur standard. The Ozone Transport Assessment Group and state air pollution regulators believe a national sulfur standard is needed. (Courtesy American Petroleum Institute, Washington, D.C.)

"The vehicles in the NLEV program are not go­ing to provide the emission reduction that is being portrayed," said Kowalczyk. "In most areas of the country, people will pay for a more costly vehicle, but they won't get all the benefits because of high-sulfur fuel." Sulfur also contributes to particulate mat­ter, and states are scrambling now to devise ways to meet the new PM2 5 standard. "Reducing sulfur in gas­oline will help states meet a number of different air pollution requirements. We are looking at a na­tional attainment strategy here," added Nancy Kruger, STAPPA/ALAPCO's deputy director.

The high cost of change Most petroleum makers who say it will cost 2 to 3 cents per gallon to manufacture 150-ppm fuel ar­gue that a national sulfur cap of 80 ppm would cost the gasoline industry $15 billion. Producing Califor­nia's standard of fuel nationwide would add 7 to 10 cents to a gallon of gas for consumers and put some of the smaller refiners out of business, asserted David O'Reilly, vice president of Chevron Corp.

However, because state air quality regulators, most members of OTAG, and EPA's Mobile Source Advi­sory Committee all recommend that EPA consider adopting standards similar to California's, the gaso­line makers' position faces tough odds.

To combat this, API has launched research projects to show that the effect of sulfur on catalysts is not per­manent. "There are questions that concern us [as to] whether the sulfur effect on catalysts is reversible," said O'Keefe. A key component of that research is a $1.5 mil­lion, fast-track study under way at CRC—launched the same day that API unveiled its plan. Studies already show that under certain conditions, the sulfur can be driven off the catalyst, said CRC's Zengle. But left open

JUNE 1, 1998/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS » 2 7 3 A

is whether those test conditions are replicated by a typ­ical driver in the real world. "The issue is not can it be done; die issue is will you see these conditions and will you see them often enough," said Zengle. Data from this study should be available this summer. The stud­ies done to date mat corroborate Zengle's assertion show that a vehicle must be running at full throttle for at least 30 seconds, through 10 cycles, witii accelerations from 30 to 70 mph before the sulfur at 600 ppm can be purged from the catalyst, said Kowalczyk. "They had to get the catalyst extremely hot, and most people would say that these conditions don't exist in the real world. But there haven't been any real-world studies to prove that. And nobody has done studies to see if they oc~

and how frequently they occur in the real world "

EPA's tailpipe standard proposal, due at the end of the year, will be influenced by the findings of its Tier 2 study. The 1990 Clean Air Act called on the agency to assess the technical feasibility, cost, and health need for stricter tailpipe emission standards that would go into effect in 2004. The CAA spells out a proposed emission limit, known as the Tier 2 stan­dard, for light-duty vehicles, of 0.2 gram per mile for NOx and 1.7 g/mi for C02 .

But under the CAA, EPA may either set tighter standards or establish none. With this flexibility, the agency could decide that the automakers ' pro­posed reductions in NO,,. and hydrocarbon emis­sions, spurred forward by the NLEV program, have pushed the automakers far enough.

"The only potential downside from the NLEV [pro­gram] is that it might be more difficult to argue for tighter standards," said one EPA staffer familiar with the NLEV discussions between EPA and the auto­makers. "We may be portrayed as trying to squeeze more and more and more."

In a draft of the Tier 2 study released in April, EPA wrote that engine technology exists to reduce tailpipe emissions beyond current standards, and the tech­nology appears to be cost-effective relative to other emission-control strategies. But these findings are not enough to require a new standard, said Sue Willis, manager of die fuels study and standards at EPA's Na­tional Vehicle and Fuel Emission Laboratory. EPA has considered a regional low-sulfur fuel approach, sim­ilar to API's plan, but that is only viable if the ongo­ing studies show that LEVs can drive off the poison­ing effect of sulfur Willis said. A regional solution would also be difficult for EPA to enforce foec<iuse 23-S can change direction midpipeline

Without a national sulfur cap, engine technolo­gies that can reduce emissions further are not likely to be pursued by U.S. automakers, nor embraced by the public, adds Kowalczyk. Japan manufacturers are producing an engine that increases fuel economy by 20 to 30%. If the country does choose to require low-sulfur fuel nationwide, "it can break the barriers for a lot of new technologies."

Catherine M. Cooney is an associate editor of ES&T.

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Introduction: Combinatorial Chemistry

Approaches the Next Millenium Walter H. Moos

Using Combinatorial Tools to Analyze Molecular Diversity ...Peter Willett

Solid-Phase Strategies

The Context of Solid-Phase Synthesis George Barany and Maria Kempe

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Michael C. Griffith, and Yazhong Pei

On-Resin Analysis in

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Deconvolution Tools for Solid-Phase Synthesis John J. Baldwin and

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Solution-Phase Strategies

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Deconvolution Tools in Solution-Phase Synthesis Xavier Williard and

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Application of Automated Parallel Synthesis Adnan M. M. Mjalli

Information Managemenl and Biological Approaches

Information Management Steven M. Muskal

Screening of Combinatorial Libraries ,.F. F. Craig

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2 7 4 A • J U N E 1 , 1998 / E N V I R O N M E N T A L SCIENCE & T E C H N O L O G Y / N E W S