Which gas is primarily produced from vehicle emissions and contributes to urban smog?

The primary gas produced from vehicle emissions that significantly contributes to urban smog is nitrogen oxide. This gas is a byproduct of combustion engines, particularly in vehicles, and plays a crucial role in the formation of ground-level ozone, a major component of urban smog. Nitrogen oxides react with volatile organic compounds (VOCs) in the presence of sunlight to create ozone, leading to smog formation, which can have detrimental effects on human health, ecosystems, and visibility.

While carbon monoxide is indeed emitted from vehicle exhaust, its contribution to urban smog is not as significant as that of nitrogen oxides. Carbon dioxide is primarily a greenhouse gas with less direct impact on smog formation, and sulfur dioxide, although a pollutant produced by various means, including vehicular emissions, is more associated with acid rain than with urban smog. Overall, understanding the role of nitrogen oxide in urban environments is vital for effective environmental health management.