The Influence of Oxidation Catalysts on NO2 in Diesel Exhaust

In underground noncoal mines the emission of nitrogen dioxide (NO₂) in the exhaust of a diesel engine is more important than the emission of nitrogen oxide (NO) because of the much lower permissible exposure limit for NO₂. Consequently, the tendency of aftertreatment devices such as oxidation catalytic converters (OCCs) to oxidize NO to NO₂ is counterproductive.

The U.S. Bureau of Mines (USBM) is investigating the effects of OCCs upon NO₂ emission by using a Fourier Transform Infrared (FTIR) exhaust gas analyzer to compare the concentration of NO₂ in diesel exhaust upstream and downstream of the OCC. We find that some OCCs increase the concentration of NO₂ much more than others, and that over some temperature ranges the aftertreatment results in an apparent decrease in NO₂ concentration.