What are NOx emissions primarily composed of?

The correct answer focuses on the nature of NOx emissions, which are primarily made up of nitrogen oxides released during combustion processes. When fuels burn, particularly in high-temperature environments such as engines or power plants, nitrogen in the air combines with oxygen to form nitrogen oxides (NO and NO2). This reaction is a key component of the process that leads to the formation of pollutants known as NOx.

Understanding NOx emissions is vital because they play a significant role in air pollution and contribute to problems like smog and acid rain, as well as health-related issues. The other options refer to different types of emissions or pollutants; for instance, carbon dioxide is a greenhouse gas resulting from incomplete combustion of fossil fuels, while volatile organic compounds (VOCs) are emitted from products like paints and solvents, and particulate matter is comprised of tiny particles found in exhaust. None of those correctly describe the composition of NOx emissions, which specifically pertains to nitrogen oxides formed from combustion.