A constituent of the exhaust gases of motor vehicles which causes serious air pollution is

The constituent of the exhaust gases of motor vehicles that causes serious air pollution is carbon monoxide. Carbon monoxide (CO) is a colorless, odorless gas that is produced when fuel is burned. Incomplete combustion of gasoline, diesel, or other fossil fuels in vehicles' engines releases CO into the air. CO is dangerous because it binds to hemoglobin in the blood and reduces the amount of oxygen that can be carried, causing dizziness, headaches, and even death in high concentrations. It is also a significant contributor to the formation of smog and can worsen respiratory problems like asthma. Therefore, reducing CO emissions from motor vehicles is essential to improving air quality and public health.