How does nitrogen dioxide (NO2) contribute to air pollution?

Nitrogen dioxide (NO2) significantly contributes to air pollution by participating in complex atmospheric reactions. One of the most critical ways it affects air quality is through its involvement in the formation of ground-level ozone. When NO2 is released into the atmosphere—primarily from vehicle emissions and industrial processes—it reacts with volatile organic compounds (VOCs) in the presence of sunlight, resulting in the formation of ozone at ground level. This type of ozone is a harmful air pollutant that can cause respiratory issues and other health problems.

Moreover, NO2 is a precursor to acid rain. It reacts with water, oxygen, and other chemicals in the atmosphere to form nitric acid. When this nitric acid falls to the ground as precipitation, it can harm ecosystems, damage infrastructure, and adversely affect water quality.

In contrast, while nitrogen dioxide can contribute to haze, its primary role in forming ground-level ozone and contributing to acid rain makes the latter the more comprehensive and accurate statement regarding its impact on air pollution. The incorrect options misrepresent the effects of NO2 or attribute effects that are not directly associated with nitrogen dioxide.