When it comes to auto repair, a mechanic has to know more than which way to twist a wrench. They also must know the parts of the car that few of us ever think about—starting with one of the most important elements, the catalytic converter.

A car’s engine is a dirty place, and it produces even dirtier exhaust. But in the last few decades, cars have gotten cleaner thanks in large part to the catalytic converter. Put simply, exhaust follows a simple path through the car:

1. Vapors exit the combustion chamber carrying a nasty trio of smog promoters: nitrogen oxides, hydrocarbons, and carbon monoxide.
   
2. These pollutants barrel through the exhaust manifold—the set of tubes that feeds exhaust from each cylinder into the exhaust pipe.
   
3. Just before they reach the muffler, the pollutants often meet their end at their largest obstacle: the three-way catalytic converter.
   

How the Catalytic Converter Makes Cleaner Air

At its heart, a catalytic converter is a set of honeycombed ceramic cores coated with some combination of platinum, rhodium, and palladium—three rare metals that interact with the main components of the pollutants. When exhaust enters, the metals trigger chemical reactions that heat the gases and rearrange their molecules: nitrogen oxides splinter into pure oxygen and nitrogen, while hydrocarbons and carbon monoxide are oxidized into less harmful carbon dioxide and simple water.

Bonus Points

Since their introduction during the 1975 model year, catalytic converters have made air more breathable and much tastier. The EPA estimates that cars built today are 98% cleaner than their counterparts from the 1960s.