Nitrogen oxides emissions in the U.S. 1970-2021

Approximately 7.6 million tons of nitrogen oxide (NOx) were emitted in the United States in 2021. This was a decrease of roughly 4.3 percent compared with the previous year. Emissions of nitrogen oxides (NOx) in the U.S. have been cut by almost 70 percent since 1990.

What are nitrogen oxides?

Nitrogen oxides are a group of highly reactive gases consisting of nitrogen dioxide, nitric oxides, and other oxides containing nitrogen. These gases are produced naturally or from fuel combustion processes. NOx is responsible for smog, as well as particle pollution when they react with ammonia and other compounds. Ozone is also formed when NOx gases react with volatile organic compounds (VOC).

Sources of NOx

NOx pollution is produced by several sources, including power plants, domestic combustion, and manufacturing processes. However, transportation is the main source of NOx pollution. In 2020, the transportation sector accounted for more than half of U.S. NOx emissions, with road vehicles a significant contributor.