From the eight nitrogen oxides that can be formed, all but dinitrogen monoxide (N2O), nitrogen monoxide (NO) and nitrogen dioxide (NO2) are unstable. However, emission levels of these three stable gases are too high in big cities.
Due to the serious consequences nitrogen oxides have on the environment and people’s health (NO reacts with hemoglobin and causes cyanosis; NO2 causes pulmonary conditions and gastrointestinal disorders; and N2O may cause polyneuropathy and myelopathy), anthropogenic emissions of these gases, which are mostly related to combustion for energy production and transportation, must be controlled.
First of all, production of nitrogen oxides must be minimized as much as possible (decreasing combustion temperature, decreasing residence time and adjusting the oxigen/carbon relationship). Once produced, these may be eliminated using the folowing methods: