Since 1904, the American Lung Association has been fighting lung disease through education, community service, advocacy and research. Gasoline and diesel fuels contain toxic substances that can enter the environment and cause adverse health effects in people. Some of these substances, such as benzene, toluene and xylenes, are found in crude oil and occur naturally in fuels and their vapors. Other substances, such as 1,3-butadiene and formaldehyde, are formed in engines during combustion and are only present in exhaust. Ozone, the major component of urban smog, is formed when nitrogen oxides react in sunlight with hydrocarbons.
Diesel exhaust is a particular health concern.
There are 1.25 million diesel-fueled engines and vehicles operating in California. These diesel vehicles account for only 2 percent of on-road motor vehicles in the state, but they produce 30 percent of the nitrogen oxides and 60 percent of the particulate matter directly emitted from California motor vehicles. The particulate matter in diesel exhaust has been identified as a toxic air contaminant by ARB, and it has been linked to lung cancer. The harmful substances in fuels can enter the environment in a number of ways throughout the entire cycle of fuel production, manufacturing, transportation, storage, distribution and usage. Most commonly, they come out the tailpipes of vehicles as exhaust or unburned fuel.