Research in the application of nonthermal plasma technology to remove NOx from combustion flue gas is dominated by the oxidation of NO to NO2 and HNO3 (nitric acid), undesirable end products for mobile engine applications. An alternative approach is to react the NO with atomic nitrogen injected into the gas stream to reduce the NO into nitrogen and oxygen. The atomic nitrogen is generated by flowing nitrogen through multiple electrically excited, high-speed jet nozzles. The technology functions well in the sooty and wet conditions characteristic of diesel engines. A prototype system has been built and successfully demonstrated on a diesel engine exhaust slipstream at Caterpillar Inc.