The Jeep emission system has a lot of parts.  From input sensors to PVC (Positive Crankcase Ventilation) valves, to carbon canisters and catalytic converts, each part has it's job and does due diligence to help keep the pollution out of the air.

Some quick definitions of most common parts that make up the Jeep emissions system:

EGR valve: Exhaust Gas Recirculation valve sites between the exhaust and intake manifold and it's only job is to allow a specific amount of exhaust gas back into the air/fuel mixture to lower the peak combustion temperatures. 

Catalytic Converters: Also called the "cat", this part is placed inline with your exhaust before the muffler usually just after the downturn pipe of the manifold or headers on your Jeep.  The catalytic converter converts various emissions into less harmfull ones using a combination of platinum, palladium and/or rhodium.

Carbon Canisters: To help reduce fumes from your Jeep, the vapors from the fuel tank are channeled through the carbon canister, which has excellent vapor absorbing properties.