There are multiple different forms of air pollution in smog. The two biggest one is Nitrogen oxide and Sulfur oxide, with personal and commercial vehicles being

There are multiple different forms of air pollution in smog. The two biggest one is Nitrogen oxide and Sulfur oxide, with personal and commercial vehicles being responsible for around 50% of the nitrogen oxide. Sulfur oxide comes from homes being heated by oil, coal plants burning coal, chemical industries, and boat traffic. After those two main components there are secondary pollutants like ozone, smoke (primarily from burning wood) and other particulates. So simplified one can say that cars and trucks are responsible for half of slightly less then half the picture, but naturally ratios can differ depending on the exact environment.