Studies have been done in the U.S., Japan, and England comparing the pollution caused in cities by automobile emissions as opposed to other types of pollutants. It was discovered that virtually 100 % of carbon monoxide is produced by motor vehicle emissions; such emissions are also the source of 60 % of the nitrous oxide and CH compounds, 50 % of the dust and particulates, and 10 % of the sulfur dioxide.
美、日、英等國家曾就市區內汽車排氣汙染物，與其他汙源所造成之汙染作過研究比較，發現近百分之百的一氧化碳系由機動車輛排氣造成，其他如百分之六十的氮氧化物、碳氫化物、百分之五十的塵粒，以及百分之十的二氧化硫之汙染來源都是來自機動車輛。