What Is In The Air?
MMM, something smells good. It smells like someone’s baking
cookies!
Even though you can’t see anyone making cookies, you know
this by the familiar scent in the air. Tiny traces of molecules
that give cookies their odor are floating through the air and detected
by your nose.
 Think
of other examples of things you’ve smelled without seeing.
Hamburgers grilling on a BBQ. Freshly made popcorn. Perfume.
These odors are familiar to you, and their concentration in the
air is high enough for your nose to detect them. However, your nose
isn't sensitive enough to detect everything in the air. There are
many other things in the air in such small amounts that you would
never be able to smell them. Other molecules, such as water vapor
or carbon dioxide, are odorless. But that does not mean that they
are not present in the air. Let's learn how scientists are able
to detect all of these chemicals in the air.
How do chemicals get in the air?
 Some
chemicals are more likely to evaporate than others. This characteristic
is called volatility (VOL-ah-TIL-i-tee). A chemical
with high volatility is more likely to evaporate into a gas than
a chemical with low volatility.
What are some examples of chemicals with high volatility? Any type
of fuel is extremely volatile. So much so that you can actually
see the fumes above a fuel pump at a gas station.. You can also
readily smell acetone as soon as a fingernail polish remover container
is opened. What about other chemicals that have low volatility?
Water, oil and aluminum are just a few examples. 
As gases, some volatile (VOL-ah-til) chemicals travel very high
up into the atmosphere. When they reach high altitudes in the troposphere,
approximately 5 to 9 miles above the earth’s surface, they
can be transported very quickly over long distances. In some cases,
it can take just days for a chemical to travel over oceans to distant
continents or from one side of a continent to another.
How does this affect human health?
 Some
of the chemicals that are transported long distances in the atmosphere
can be potentially harmful to people, wildlife, and plants. For
that reason, it is extremely important to know where a chemical
may go in the environment. Depending on its chemical properties,
a chemical used in U.S. agriculture or industry could end up in
the Alps or in the Arctic. Even trace amounts of some chemicals
can cause harm in more sensitive environments.
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