On the left is a view of the Phoenix skyline through a layer of its infamous smog due to increasing vehicle emissions. On the right is a view of the same skyline on a particularly clear day.
Vehicle emissions come out of the tailpipe of a running automobile. Under ideal conditions, gasoline and oxygen are burnt to produce carbon dioxide and water. In reality, this rarely happens and many toxic pollutants are also formed. Study the pictures below to get an idea of the type of pollutants produced and under what conditions they form.
Below is a list of pollutants which come directly from automobiles or form from auto exhaust. Follow the links to learn more about them.
Carbon monoxide is an
odorless, colorless, potentially fatal gas formed when carbon doesn’t completely
oxidize during combustion due to lack of oxygen. In the human body,
carbon monoxide replaces the oxygen in the blood. At a level of 100 parts per
million (ppm), carbon monoxide causes headaches and shortness of breath. This
level can be reached in enclosed areas such as tunnels and parking garages.
At high temperatures and
pressure the nitrogen and oxygen molecules from the air react to form various oxides
of nitrogen. At levels as low as 3 parts per million (ppm), they can cause lung
irritation and lowered lung function. In addition, they combine with hydrocarbons to form a harmful pollutant called ozone. They are also responsible for the brown haze you might see around the city.
There are three different reactions to produce each of the three
oxides but they are all quite similar.
For example,
NO2
(Nitrogen Dioxide) is produced through the following reaction: N2 + 2O2
→2NO2
Hydrocarbons are produced by an automobile when gasoline is not completely burnt during
combustion. Long term exposure is linked to cancer. In
addition, they combine with nitrogen oxides to form ozone.
Particulate matter is the name given to tiny
airborne particles in the atmosphere. They can be made up of many substances. In
automobile exhaust a major portion of the particulate matter is soot. Soot
particles are tiny bits of carbon resulting from the combustion of fuel. In the
picture above, the truck is emitting a cloud of soot formed from its diesel fuel.
Particulate matter is very unhealthy to inhale. It lodges deep in the lungs and
causes both lung and heart problems. It has been linked to asthma, bronchitis,
irregular heart beat, and heart attacks.
If you have ever heard someone complain about a
hole in the ozone layer, you might think that ozone is a good thing. In fact,
an ozone layer exists many miles above us and protects us from the sun.
However, when ozone exists at ground level it is quite harmful to people.
At levels as low as 100 parts per billion (ppb), ozone causes eye irritation and
respiratory problems. Ozone does not come directly out of an automobile's exhaust
pipe but it is formed when hydrocarbons and nitrogen oxides react with each other and the sun's rays.
