Transportation is the largest single source of air pollution in
the United States.
It causes nearly two-thirds of the carbon monoxide, a third of the nitrogen
oxides, and a quarter of the hydrocarbons in our atmosphere. 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 ai 242f59c r.
The Ingredients of Air Pollution
Cars and trucks pollute the air during manufacturing, oil refining
and distribution, refueling and, most of all, vehicle
use. 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:
- Ozone (O . The
primary ingredient in the smog, ozone is created when hydrocarbons and
nitrous oxides from automobile combustion react with sunlight. Though
beneficial in the upper atmosphere, at the ground level this gas irritates
the respiratory system, causing coughing, choking, and reduced lung
capacity.
- Particulate matter
(PM). These particles of soot, metals, and pollen 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, penetrating deep into the 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.
- 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 the formation of ozone and particulate matter. In
many cities, NOx accounts
for one third of the fine particulate pollution.
- Carbon monoxide
(CO). This odorless, colorless 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
(SO . Power plants and
motor vehicles create this pollutant by burning sulfur-containing
fuels, especially diesel. It 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.
