Mobile Source Related Air Pollution: Effects on Health and the Environment

Motor vehicles emit large quantities of carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and such toxic substances as benzene, formaldehyde, acetylaldehyde, 1,3-butadiene, and fine particles (particulate matter, PM). Depending on fuel composition, they can also emit significant amounts of sulfur oxides (SOx) and lead. Each of these, along with secondary by-products such as ozone (O3), can cause serious adverse effects on health and the environment. Greenhouse gases (GHGs) responsible for climate change are also increasingly emitted by the transportation sector. Vehicle emissions most closely identified with this sector include carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). However, it is important to note that other vehicle-related pollutants also contribute to global warming, although their quantification has been more difficult; these include CO, nonmethane hydrocarbons (NMHCs) and nitrogen dioxides, black carbon, and water vapor. It is generally agreed, for example, that the CO that is emitted from vehicles is eventually converted to carbon dioxide in the atmosphere and in the process consumes hydroxyl radicals, which might otherwise reduce methane concentrations. Similarly NMHCs and NOx contribute to global background tropospheric ozone, a very potent GHG. Pollutants of concern from mobile sources that can cause or contribute to a variety of adverse impacts on health and the environment are described briefly in this article.