Catalytic Converters and Diesel Particulate Filters.
A catalytic converter "cat" is a device used to reduce the toxicity of emissions from an internal combustion engine. A catalytic converter works by using a catalyst to stimulate a chemical reaction in which toxic by-products of combustion are converted to less-toxic substances. This typically results in 90% conversion of carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful gases.
Diesel Particulate Filter
A diesel particulate filter, sometimes called a DPF, is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine. Wall-flow diesel particulate filters usually remove 85% or more of the soot, and can at times (heavily loaded condition) attain soot removal efficiencies of close to 100%. A diesel-powered vehicle equipped with a functioning filter will emit no visible smoke from its exhaust pipe.