What is a major source of nitrogen oxides (NOx)?

Auto exhaust is a major source of nitrogen oxides (NOx) because vehicles, especially those with internal combustion engines, produce these gases as a byproduct of fuel combustion. When fossil fuels are burned at high temperatures, nitrogen in the atmosphere reacts with oxygen, resulting in the formation of NOx. This emission is significant in urban areas where traffic congestion can lead to elevated levels of nitrogen oxides.

While industrial processes, natural sources like forests, and volcanic eruptions can also contribute to nitrogen oxides, the scale and regularity of emissions from auto exhaust make it a predominant factor in overall NOx pollution, particularly in populated regions. Understanding this impact is crucial for urban planning and environmental policy aimed at improving air quality and public health.