See Figures 1 through 6
There are basically three sources of automotive pollutants; crankcase fumes, exhaust gases, and gasoline evaporation. The pollutants formed from these sources fall into three categories: unburnt hydrocarbons (HC), carbon monoxide (C), and oxides of nitrogen (NOx). The equipment used to limit these pollutants is called Emissions control equipment.
Due to varying state, federal, and provincial regulations, specific Emissions control equipment will vary. The U.S. Emissions equipment is divided into two categories: California and Federal. Some equipment installed on trucks designed to meet California Emissions standards is generally not shared with equipment installed on trucks built to be sold in other states (Federal). Though, changes in legislation may lead to California Emissions equipped vehicles in other states with standards which are tighter than the Federal Emissions requirement. In any case, the improvements which have been made over the years with Emissions equipment has led to a closing of the gap between the two standards and vehicles built to meet the two standards are often quite similar to one another.