Emissions components consist of parts of an engine that their only function is to clean the amount of emissions that are expelled from the engine. The catalytic converter has the job of trying to clean up the unburned gas from the exhaust. Air pumps would also help out with this job by injecting air into the engine’s exhaust manifold. The hot unburned fuel would immediately ignite in the presence of fresh oxygen. The unburned fuel is called HC or hydrocarbons. This is usually the hardest pollutant to keep low and is why all cars run fuel injection. The CO or carbon monoxide is controlled by keeping the air to fuel ratio correct and getting a clean burn in the chamber. NOX or oxides of nitrogen are caused by the high pressures and temperatures of combustion in the chamber. The EGR or exhaust gas re circulation valve lowers the NOX by injecting a small amount of exhaust into the intake air. The exhaust has low oxygen and CO in it. These make the combustion pressures and temperatures lower, lowering NOX. The O2 or oxygen sensor tells the computer if the AFR or air to fuel ratio is correct. If the ratio is wrong in the exhaust it will adjust the fuel injection until it’s correct.