If gasoline produces only carbon dioxide and water when it burns completely, why is automobile exhaust a source of air pollution even before it begins to react with other chemicals in the air?

Automobiles release hydrocarbons that react to form pollutants in dry air.

Explanation:

As carbon from the gasoline mixes with the air it reacts and starts to burn and this burning of hydrocarbon in the air produces heat, smoke, and gases, as well as chemical byproduct like water and carbon particulate matter. 22.38% of CO2 is produced by burning one gallon of petroleum. So, for the hydrocarbon to get successfully converted into carbon dioxide and produce carbon monoxide in the air it needs to react and burn, and CO is the result of not a sufficient amount of O2 in the air. Various automobiles release the nitrogen sulfur into the air and soil and give sooty dust and particle sizes that can change the composition of the further atmospheric cycle. As earth air is composed of 78% nitrogen, 21% oxygen, 0.9% argon, and 0.03% carbon dioxide. The more gases that are released more spread the pollutant content of the air.