Nitrogen Oxides
Nitrogen oxides (NOx) are amongst the primary pollutants emitted into the atmosphere during the combustion process. The term NOx refers to the cu- mulative emissions of NO, NO2, and trace amounts of other species (Oland, 2002).
The majority of NOx is initially formed as NO and is then oxidized fur- ther to form NO2, either immediately within the combustion chamber or as the flue gases are discharged into the atmosphere. When NOx reacts with volatile organic compounds in the presence of sunlight they form ground- level ozone (O3), which is a major ingredient of smog. When NOx reacts with water and air it forms very dilute nitric acid (HNO3), causing acid rain. The formation of NOx is generally controlled by three routes, thermal NOx, fuel NOx and prompt NOx (Oland, 2002).