Cars, Trucks, & Air Pollution
Transportation is the largest single source of air pollution in the United States. It causes over half of the carbon monoxide, over a third of the nitrogen oxides, and almost a quarter of the hydrocarbons in our atmosphere in 2006.¹ With the number of vehicles on the road and the number of vehicle miles traveled escalating rapidly, we are on the fast lane to smoggy skies and dirty air.
The Ingredients of Air Pollution
Air pollution is associated with the full life-cycle of cars and trucks. This includes air pollution emitted during vehicle operation, refueling, manufacturing, and disposal. Additional emissions are associated with the refining and distribution of vehicle fuel. Motor vehicles cause both primary and secondary pollution. Primary pollution is emitted directly into the atmosphere; secondary pollution results from chemical reactions between pollutants in the atmosphere. The following are the major pollutants from motor vehicles:
- Particulate matter (PM). These particles of soot and metals give smog its murky color. Fine particles, PM that is less than one-tenth the diameter of a human hair, pose the most serious threat to human health as they can penetrate deep into lungs. In addition to direct emissions of fine particles, automobiles release nitrogen oxides, hydrocarbons, and sulfur dioxide, which generate additional fine particles as secondary pollution.
- Hydrocarbons (HC). These pollutants react with nitrogen oxides in the presence of sunlight to form ground level ozone, a primary ingredient in smog. Though beneficial in the upper atmosphere, at the ground level this gas irritates the respiratory system, causing coughing, choking, and reduced lung capacity.
- Nitrogen oxides (NOx). These pollutants cause lung irritation and weaken the body's defenses against respiratory infections such as pneumonia and influenza. In addition, they assist in the formation of ground level ozone and particulate matter.
- Carbon monoxide (CO). This odorless, colorless, and poisonous gas is formed by the combustion of fossil fuels such as gasoline and is emitted primarily from cars and trucks. When inhaled, CO blocks the transport of oxygen to the brain, heart, and other vital organs in the body. Fetuses, newborn children, and people with chronic illnesses are especially susceptible to the effects of CO.
- Sulfur dioxide (SO2). Power plants and motor vehicles create this pollutant by burning sulfur-containing fuels, especially diesel. Sulfur dioxide can react in the atmosphere to form fine particles and poses the largest health risk to young children and asthmatics.
- Hazardous air pollutants (toxics). These chemical compounds, which are emitted by cars, trucks, refineries, gas pumps, and related sources, have been linked to birth defects, cancer, and other serious illnesses. The Environmental Protection Agency estimates that the air toxics emitted from cars and trucks account for half of all cancers caused by air pollution. Benzene, acetaldehyde, and 1,3-butadiene are examples of toxic air pollutants associated with motor vehicle emissions.
- Greenhouse gases. Motor vehicles also emit pollutants, such as carbon dioxide, that contribute to global climate change. The transportation sector currently accounts for over a quarter of all U.S. greenhouse gas emissions.
Notes:
1. Environmental Protection Agency. 2006. National Emissions Inventory (NEI) Trends Report: Average annual emissions, all criteria pollutants. Accessed at http://www.epa.gov/ttn/chief/trends/
