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It probably seems like there is an unlimited supply of air. The Earth is surrounded by what seems like a huge ocean of air. Actually, a huge band of air stretches from the ground upwards to about 500 miles. This band of air is called the atmosphere (at-mo-sfear).
Air is a mixture. It contains many things – mostly gases we can’t see. Gases are neither solid nor liquid. They move around and do not have shape. Adults breathe in about 35 pounds of air a day. One fifth of this is oxygen (21%) and the rest is nitrogen (78%) and small amounts of argon, carbon dioxide and other gases and water vapor (1%).
 The most important gas in air that people and animals use is oxygen. Oxygen has no color or smell. People and animals need to breathe oxygen in order to live. Here on Earth, plants help us breathe by giving off oxygen. As people and animals exhale, they give off carbon dioxide. This is what plants “breathe”. It is a very unique relationship we share with plants. Plants take in what we exhale (carbon dioxide) and we inhale what plants give off (oxygen). Plants and people and animals need each other to survive!
Is Our Air Clean?
On a clear breezy day, the air smells fresh and clean. Clean air is air that has no harmful levels of pollutants (dirt and chemicals) in it. Clean air is good for people to breathe.
On a hot day with no wind, the air can feel heavy and have a bad smell. Once in a while, the air can even make your chest feel tight, or make you cough. When too much dirt and chemicals get into the air, the air is dirty or polluted. Dirty air is not good for people to breathe.
Much of our air pollution comes from burning. For example, when we burn gasoline to operate motor vehicles the contaminant, carbon monoxide, is released into the air. Carbon monoxide is an odorless and colorless gas, but it can be very harmful to our health when there is enough of it in the air we breathe.
In the winter,we have a special problem with pollution caused by woodstoves. Tiny smoke particles are released into the air, and inhaled by people and other living things. Toxic or poisonous gases, such as carbon monoxide, and particles make it difficult for people and other living things to breathe.
The Earth can tolerate small amounts of pollution, but when large amounts of pollution are being poured into our air, including carbon monoxide,we exceed the atmosphere’s ability to disperse the pollutants. The result is that we are forced to breathe the pollutants along with the oxygen we need.
Here’s your chance to show what you know about the air around us. Answer these questions in complete sentences.
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What is atmosphere?
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What is air made up of?
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How much of the air is oxygen?
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What do plants give off?
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What do people and animals exhale?
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How can our air get dirty?
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Is dirty air healthy to breathe? 
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