What's the difference among DOC, DPF and SCR?

To reduce the amount of diesel emissions, trucks built since 2007 are equipped with an aftertreatment system composed of a diesel particulate filter (DPF) and a diesel oxidation catalyst (DOC) that trap pollutants and remove them from a truck's exhaust

Diesel Oxidation Catalysts (DOC) are catalytic converters designed specifically for diesel engines and equipment to reduce Carbon Monoxide (CO), Hydrocarbons (HC) and Particulate Matter (PM) emissions.

Diesel Particulate Filter (DPF) is a filter that captures and stores exhaust soot (some refer to them as soot traps) in order to reduce harmful emissions from diesel cars. But because they only have a finite capacity, this trapped soot periodically has to be emptied or 'burned off' to regenerate the DPF.

Selective Catalytic Reduction (SCR) is a technology used in diesel engines to reduce nitrogen oxide (NOx) emissions.

SCR systems inject diesel exhaust fluid (DEF) into the exhaust stream of a diesel engine, where it mixes with the exhaust and passes through a catalyst. The DEF is a non-toxic fluid made of 32% automotive grade urea and purified water. The chemical reaction between the DEF and exhaust converts NOx into nitrogen, water, and small amounts of carbon dioxide.