What major pollutants are primarily released from vehicles that worsen urban air quality?

Vehicles are a significant source of pollutants that contribute to urban air quality degradation. Nitrogen oxides (NOx) and particulate matter (PM) are particularly problematic in this context. NOx compounds are generated during the combustion of fuel in engines and can lead to the formation of ground-level ozone, which is a key component of smog. Furthermore, nitrogen oxides can contribute to respiratory issues and other health problems in urban populations.

Particulate matter, which includes tiny particles and droplets in the air, can originate from vehicle exhaust as well as from the wear of brakes, tires, and road surfaces. These particles can be inhaled and may cause various health effects, including cardiovascular and respiratory issues, particularly in densely populated urban areas where vehicle traffic is heavy.

Other pollutant options listed have different roles and sources; for instance, carbon dioxide and methane are greenhouse gases primarily linked to climate change but are not directly responsible for worsening urban air quality in the same way NOx and PM are. Similarly, ozone is a secondary pollutant resulting from reactions involving NOx and VOCs rather than being directly emitted from vehicles, and sulfur dioxide mainly comes from industrial sources and the burning of fossil fuels, not directly from vehicles. Lastly, volatile organic compounds (V