Definition: Abbreviation for Oxides of Nitrogen. The "N" stands for Nitrogen, the "O" for Oxygen, and the "X" is scientific notation for all the various combinations of the two. NOX is formed inside an engine when combustion temperatures exceed 2500 degrees Fahrenheit. NOX is considered to be a serious air pollutant because it is so irritating. NOX emissions are minimized by the EGR valve, and by the catalytic converter in 1981 and newer model cars.

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