Converting the masses

• By Mel Zimmerman, PhD
• Jun 01, 1999

Automotive technology has made incredible leaps in the past few months. Just recently, DaimlerChrysler introduced its NECAR 4, a zero-emission fuel cell car, to the United States. Powered by cryogenically-stored liquid hydrogen, the only emission from fuel cell cars is water. Compared to the prospect of zero emission vehicles zipping down the smog-free highways of the future, today's catalytic converter technology seems primitive. But 30 years ago, the catalytic converter revolutionized the auto industry's, and America's, emission standard capabilities.

In 1970, clean air was quickly becoming a political platform. Maine's Senator Edmund Muskie was, at the time, chairman of the water pollution subcommittee of the Senate Public Works Committee. Muskie had sponsored the Clean Air Act of 1967, but he needed more support from America's rapidly growing constituency of environmentalists if he was to make a successful bid in the 1972 presidential campaign. As an outspoken proponent for tougher air pollution laws, Muskie helped clear the way for the Clean Air Act of 1970. This legislation made the U.S. Environmental Protection Agency (EPA) responsible for establishing and enforcing air pollutant limits. For more resources on the history of environmental legislation and technology, please click here.

Auto emissions had long been recognized as a source of smog; research in the early '50s had placed the blame for Los Angeles' soupy skies squarely on cars. In 1966, Congress had required minimal emission controls on all 1968 and later model cars. But with the passage of 1970's Clean Air Act, minimal was no longer adequate. Emission standards of 0.41 grams per mile for hydrocarbons (HC) and 3.4 grams per mile for carbon monoxide (CO) were to be met by all autos by 1975. Further, nitrogen oxide (NO_x) emission limits were to be 0.4 grams per mile by 1976. These new standards represented a 90 percent reduction in automotive emissions, and left auto manufacturers scrambling to produce technology capable of compliance.

"There was a lot of fear, because we didn't know how to do it," said John Hrinevich, who at the time was part of the research and development metallurgical laboratory for the AC Sparkplugs division of General Motors (GM). "It was almost like going to war. There was a feeling of we had to do this to survive."

What followed was a massive effort to find technology that would meet the new requirements. "There were literally thousands of people who worked on this," Hrinevich said. "We really felt like we had to get everybody mobilized and everybody aligned." A number of innovations began appearing on American cars, including charcoal canisters to trap gasoline vapors and exhaust gas recirculation valves to reduce NO_x. It was not until 1975, however, that the catalytic converter made its debut on American cars. A form of catalytic converters, called catalytic crackers, had already been in use in the petrochemical and pharmaceutical fields, said Hrinevich. From there, automakers scaled down and refined the device for application in vehicles.

Catalytic converters are located in the exhaust line of a vehicle. Gases generated from the burning of fuel must pass through the converter before they exit the exhaust pipe. The converter is lined with chemicals and metals such as platinum, palladium, rhodium and aluminum oxide. As the gas passes through the converter, chemicals in the gas react with the converter's lining, producing a chemical change. NO_x, CO and HC are destroyed or converted into less harmful byproducts, such as carbon dioxide. Although not all of the gas is converted, a significant amount of the car's emissions is cleaned before it is released to the atmosphere. Over 98 percent of HC and CO is typically destroyed by the catalytic converter.

The components of auto emissions are also those which make up smog. The advent of the catalytic converter brought health, as well as environmental, benefits, since a reduction in smog typically brings a reduction in respiratory infections. The catalytic converter also had the unforeseen benefit of lead reduction.

EPA had known for years that lead in gasoline, and the resulting lead emissions, presented a serious health threat. Elevated lead levels in humans can result in everything from behavioral disorders to permanent nerve damage. In 1973, EPA called for a reduction in lead levels in gasoline from two to three grams per gallon (200,000 tons of lead per year) to one-tenth of a gram per gallon by 1986. But with the introduction of the catalytic converter, leaded gasoline quickly became obsolete for passenger cars.

Lead interferes with the operation of the catalytic converter by coating the chemicals present there. Because the chemical lining does not then come in contact with the pollutants, no reaction can take place, and the converter is rendered ineffective.

"We had been interested for years in making our products environmentally friendly," said Hrinevich, but the incompatibility of leaded gasoline and emission reduction technology had always been a concern. Hrinevich credits GM's then-president Ed Cole as being a major force in convincing the petrochemical industry to begin producing unleaded gas for mass market. Cole, said Hrinevich, was at heart an engineer, who was known for having models made of new research developments, and then improving on them. He understood, said Hrinevich, the fundamental changes in production that the converter would require.

Unleaded gasoline became the norm as new cars equipped with catalytic converters replaced older models on America's highways. "The elimination of lead from gas is one of the great environmental achievements of all time," said Carol M. Browner, EPA administrator. "Thousands of tons of lead have been removed from the air, and blood levels of lead in our children are down 70 percent as of 1996. This means that millions of children will be spared the painful consequences of lead poisoning," she said. Today, lead levels in the air have been reduced by 98 percent.

By 1981, technology had advanced to the point that further emission reductions were achieved by three-point catalysts, which convert CO and HC to CO2 and water, and breaks down NO_x into nitrogen and oxygen. Computer and oxygen sensors further improved the catalytic converter's efficiency.

While the catalytic converter has indisputably contributed to pollution prevention in America, the end results have been mixed. Today's emission standards are considerably stricter than they were just a few decades ago, before the passage of the Clean Air Act of 1970: 0.25 grams per mile HC, 0.4 grams per mile NO_x and 3.4 grams per mile CO. But while today's vehicles are 97 percent cleaner than in 1970, the number of miles the average American drives has doubled. An increase in traffic and large heavy-duty trucks and vans has also largely offset the benefits of decreased emissions.

Many scientists are now concerned with nitrous oxide, a byproduct of the catalytic converter process. This greenhouse gas is 300 times more powerful than carbon dioxide (also an automotive emission), the most common greenhouse gas. An EPA report published last year estimates about 7.2 percent of greenhouse gases contributing to global warming is nitrous oxide. Half of that is created by vehicle emissions.

The future of the catalytic converter is unclear. A reconstructed, better performing catalytic converter may be the answer to today's pollution problems, as could be low-sulfur gasoline and alternative fuel source powered vehicles. Regardless, the catalytic converter's contribution to emission reduction remains a milestone in U.S. environmental history.

---

E-sources For more information, please see the following Web sites: GM Research & Development Center www.gm.com/about/info/overview/index.html EPA Environmental Milestones www.epa.gov/ngispgm3/nrmp/history Milestones in Auto Emission Control www.epa.gov/r10earth/offices/air/emission.html

Photo courtesy of General Motors/Delphi Automotive Systems

This article originally appeared in the 06/01/1999 issue of Environmental Protection.