| Pollutant |
Sources |
Effects |
| Ozone. A gas that can be found
in two places. Near the ground (the troposphere), it is a major part
of smog. The harmful ozone in the lower atmosphere should not be
confused with the protective layer of ozone in the upper atmosphere
(stratosphere), which screens out harmful ultraviolet rays. |
Ozone is not created directly, but is
formed when nitrogen oxides and volatile organic compounds mix in
sunlight. That is why ozone is mostly found in the summer. Nitrogen
oxides come from burning gasoline, coal, or other fossil fuels.
There are many types of volatile organic compounds, and they come
from sources ranging from factories to trees. |
Ozone near the ground can cause a
number of health problems. Ozone can lead to more frequent asthma
attacks in people who have asthma and can cause sore throats,
coughs, and breathing difficulty. It may even lead to premature
death. Ozone can also hurt plants and crops. |
| Carbon monoxide. A gas that
comes from the burning of fossil fuels, mostly in cars. It cannot be
seen or smelled. |
Carbon monoxide is released when
engines burn fossil fuels. Emissions are higher when engines are not
tuned properly, and when fuel is not completely burned. Cars emit a
lot of the carbon monoxide found outdoors. Furnaces and heaters in
the home can emit high concentrations of carbon monoxide, too, if
they are not properly maintained. |
Carbon monoxide makes it hard for body
parts to get the oxygen they need to run correctly. Exposure to
carbon monoxide makes people feel dizzy and tired and gives them
headaches. In high concentrations it is fatal. Elderly people with
heart disease are hospitalized more often when they are exposed to
higher amounts of carbon monoxide. |
| Nitrogen dioxide. A
reddish-brown gas that comes from the burning of fossil fuels. It
has a strong smell at high levels. |
Nitrogen dioxide mostly comes from
power plants and cars. Nitrogen dioxide is formed in two ways—when
nitrogen in the fuel is burned, or when nitrogen in the air reacts
with oxygen at very high temperatures. Nitrogen dioxide can also
react in the atmosphere to form ozone, acid rain, and
particles. |
High levels of nitrogen dioxide
exposure can give people coughs and can make them feel short of
breath. People who are exposed to nitrogen dioxide for a long time
have a higher chance of getting respiratory infections. Nitrogen
dioxide reacts in the atmosphere to form acid rain, which can harm
plants and animals. |
| Particulate matter. Solid or
liquid matter that is suspended in the air. To remain in the air,
particles usually must be less than 0.1-mm wide and can be as small
as 0.00005 mm. |
Particulate matter can be divided into
two types—coarse particles and fine particles. Coarse particles are
formed from sources like road dust, sea spray, and construction.
Fine particles are formed when fuel is burned in automobiles and
power plants. |
Particulate matter that is small
enough can enter the lungs and cause health problems. Some of these
problems include more frequent asthma attacks, respiratory problems,
and premature death. |
| Sulfur dioxide. A corrosive gas
that cannot be seen or smelled at low levels but can have a “rotten
egg” smell at high levels. |
Sulfur dioxide mostly comes from the
burning of coal or oil in power plants. It also comes from factories
that make chemicals, paper, or fuel. Like nitrogen dioxide, sulfur
dioxide reacts in the atmosphere to form acid rain and
particles. |
Sulfur dioxide exposure can affect
people who have asthma or emphysema by making it more difficult for
them to breathe. It can also irritate people's eyes, noses, and
throats. Sulfur dioxide can harm trees and crops, damage buildings,
and make it harder for people to see long distances. |
| Lead. A blue-gray metal that is
very toxic and is found in a number of forms and locations. |
Outside, lead comes from cars in areas
where unleaded gasoline is not used. Lead can also come from power
plants and other industrial sources. Inside, lead paint is an
important source of lead, especially in houses where paint is
peeling. Lead in old pipes can also be a source of lead in drinking
water. |
High amounts of lead can be dangerous
for small children and can lead to lower IQs and kidney problems.
For adults, exposure to lead can increase the chance of having heart
attacks or strokes. |
| Toxic air pollutants. A large
number of chemicals that are known or suspected to cause cancer.
Some important pollutants in this category include arsenic,
asbestos, benzene, and dioxin. |
Each toxic air pollutant comes from a
slightly different source, but many are created in chemical plants
or are emitted when fossil fuels are burned. Some toxic air
pollutants, like asbestos and formaldehyde, can be found in building
materials and can lead to indoor air problems. Many toxic air
pollutants can also enter the food and water supplies. |
Toxic air pollutants can cause cancer.
Some toxic air pollutants can also cause birth defects. Other
effects depend on the pollutant, but can include skin and eye
irritation and breathing problems. |
| Stratospheric ozone depleters.
Chemicals that can destroy the ozone in the stratosphere. These
chemicals include chlorofluorocarbons (CFCs), halons, and other
compounds that include chlorine or bromine. |
CFCs are used in air conditioners and
refrigerators, since they work well as coolants. They can also be
found in aerosol cans and fire extinguishers. Other stratospheric
ozone depleters are used as solvents in industry. |
If the ozone in the stratosphere is
destroyed, people are exposed to more radiation from the sun
(ultraviolet radiation). This can lead to skin cancer and eye
problems. Higher ultraviolet radiation can also harm plants and
animals. |
| Greenhouse gases. Gases that
stay in the air for a long time and warm up the planet by trapping
sunlight. This is called the “greenhouse effect” because the gases
act like the glass in a greenhouse. Some of the important greenhouse
gases are carbon dioxide, methane, and nitrous oxide. |
Carbon dioxide is the most important
greenhouse gas. It comes from the burning of fossil fuels in cars,
power plants, houses, and industry. Methane is released during the
processing of fossil fuels, and also comes from natural sources like
cows and rice paddies. Nitrous oxide comes from industrial sources
and decaying plants. |
The greenhouse effect can lead to
changes in the climate of the planet. Some of these changes might
include more temperature extremes, higher sea levels, changes in
forest composition, and damage to land near the coast. Human health
might be affected by diseases that are related to temperature or by
damage to land and water. |
