This is a very precious world we live in and it's in our best interest to not fill it up with toxic gases our engines produce. Thankfully, there is a system in place that works from the beginning to end of the engine with the purpose of using up all that toxic gas before it can pollute our breathable air.
Exhaust system:
-Pipes
-Catalytic converters
-Sensors
-mufflers
-Emission valve & filter