Nitrogen oxides are a group of highly reactive gases composed of nitrogen and oxygen, primarily nitric oxide (NO) and nitrogen dioxide (NO2). They are formed through combustion processes, such as vehicle emissions, power plants, and industrial activities. Nitrogen oxides are major pollutants that contribute to air quality issues, including smog formation and acid rain. They also play a role in the formation of ground-level ozone and can have harmful effects on human health, such as respiratory problems and aggravating existing conditions like asthma. Research in this area focuses on understanding the sources, impacts, and control of nitrogen oxides to mitigate their environmental and health effects.