- Combustion of fossil fuels: When fossil fuels such as coal, oil, and natural gas are burned, they produce nitrogen oxides as a byproduct. This is a major source of NOx emissions, particularly from power plants, industrial facilities, and vehicles.
- Industrial processes: Certain industrial processes, such as the production of nitric acid and adipic acid, also emit nitrogen oxides.
- Natural sources: Nitrogen oxides can also be produced naturally, such as during thunderstorms and from microbial processes in the soil. However, these natural sources are relatively small compared to human-made emissions.
The primary nitrogen oxides emitted from these sources are nitric oxide (NO) and nitrogen dioxide (NO2). These gases can react with other pollutants in the atmosphere to form secondary pollutants, such as ozone, smog, and acid rain.
