Today, we don't go up in smoke. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

The year 1970 was a landmark for environmentalists. On January 1, then President Richard Nixon signed into law an act that not only led to the birth of the EPA, but to a flurry of environmental legislation. That same year the Clean Air Act passed the Senate without a single no vote. And it cleared a path for an amazingly simple technology that would revolutionize the automotive industry.

Richard Nixon signing the Clean Air Act Missouri Department of Natural Resources

By 1970 smog in big cities was out of control. For a long time it wasn't clear that car exhaust was a culprit. It's invisible, so how could it cause smog? In point of fact, the bulk of car exhaust is remarkably clean, with well over 99 percent posing no direct threat to humans. But what we find in the remaining fraction of a percent is a different story. When released into the atmosphere, chemical reactions ensue that create smog. In places like Los Angeles, where conditions were perfect for brewing an unhealthy elixir, dark skies and watery eyes became the norm. Something had to be done. And that something came in the form of the catalytic converter.

Catalytic Converter Photo Credit:Right Image Wikimedia Commons, Left Image Wikimedia Commons

The catalytic converter is part of a car's exhaust system. It's typically situated about halfway between the engine at the front and the muffler at the rear, and is roughly the shape and size of a muffler. Its purpose is to convert most of the nasty remnants of exhaust into oxygen and other human-friendly gases. And it achieves this by exposing the exhaust to catalysts — substances that promote chemical reactions but don't themselves get consumed. That means you can place catalysts in a catalytic converter and they'll stay there, happily doing their job without the need of replenishment. And that's a good thing, because the preferred catalysts are expensive; expensive enough that in some regions catalytic converters are stolen just for the value of the materials inside. These handy devices don't consume additional energy since they rely on the heat of the exhaust to do their job.

Five years after the Clean Air Act of 1970 was passed, catalytic converters became the law of the land. And in doing so, they not only cleaned the air, they changed how we buy gas. Catalytic converters don't like lead. So gas companies had to get the lead out — a common gas additive at the time. For twenty years, leaded and unleaded gas were sold side by side in gas stations. That ended in 1995 by government mandate. Interestingly, the negative health effects of lead weren't fully established when the lead phase-out began. Lead removal was largely an effort to protect catalytic converters, not people.

We've now reaped the benefits of catalytic converters for many years. Smog is still a problem. But for those who remember what it was like before these uncomplicated devices arrived, the difference is, well, night and day.

I'm Andy Boyd at the University of Houston, where we're interested in the way inventive minds work.

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Around 15 percent of exhaust consists of carbon dioxide which, while a greenhouse gas, is not directly harmful to human life.

G. Hill and J. Holman. Chemistry in Context. 5th ed. Cheltenham, U.K.: Nelson Thornes Ltd, 2000.

S. Gardner. LA Smog: The Battle Against Air Pollution. From the Marketplace website: http://www.marketplace.org/topics/sustainability/we-used-be-china/la-smog-battle-against-air-pollution. Accessed December 8, 2014. 

R. Newell and K. Rogers. The U.S. Experience in the Phasedown of Lead in Gasoline. Discussion Paper, Resources for the Future, 2003. See also the MIT website: http://web.mit.edu/ckolstad/www/Newell.pdf. Accessed December 8, 2014.

This episode first aired on December 10, 2014.