Formaldehyde is also used extensively in wood finish, glue, fabric coating, insulation, etc. In mobile homes, concentrations have been measured in excess of 5,000 micrograms per cubic meter. In 'non-sick' buildings, the typical level is 50 micrograms per cubic meter. Benzene and toluene are mentioned as potential ETS carcinogens. In humans they are associated with leukemia.
Gasoline is the primary source of benzene, toluene and related aromatics in the air.
Also copy machines, glue, paint and the like. When filling your gas tank, you're exposed to concentrations 50-100 times that high. Everyone is exposed to potentially toxic or carcinogenic chemicals every day. 20 cigarettes produce about 1 gram. Thus, if you smoke a half pack a day for 40 years, you'll produce about the same amount of CO as one full day of driving.