What is smog, and how does it form?

Smog is defined as a type of air pollution that results from the interaction of various pollutants, primarily nitrogen oxides and volatile organic compounds (VOCs), which come from vehicle emissions, industrial discharges, and other sources. When these pollutants are exposed to sunlight, they undergo photochemical reactions that produce ground-level ozone and other secondary pollutants, contributing to the formation of smog.

This process is particularly prevalent in urban areas with high traffic and sunlight, leading to the characteristic brown haze often associated with smog. The heat from the sun facilitates these chemical reactions, resulting in a mixture of pollutants that can significantly impact air quality and public health.

The other choices do not accurately reflect the nature or formation of smog. For instance, while fog is indeed related to water vapor, it does not involve the chemical reactions or various pollutants that smog does. Similarly, volcanic ash can impact air quality but is not a component of smog as understood in urban pollution contexts. Natural photosynthesis actually involves the uptake of carbon dioxide and release of oxygen, which does not align with the formation of air pollution.