Selective catalytic reduction (SCR) is a widely popular means to reduce harmful smog-forming oxides of nitrogen (NOx) in diesel engine exhaust. NOx is formed at the high-temperature flame front commonly found in compression ignition engines. Nitrogen and oxygen are natural constituents of the engine intake air, but given sufficient heat and time will transform into unwelcome compounds (such as nitrous oxide (NO), and nitrous dioxide (NO2) the most prevalent). SCR is a well-proven technology known to reduce NOx by more than 90%. Click here to read more about SCR.