Team Challenge: Composition of Atmosphere
1. What do we do with the nitrogen we breathe from the air around us?
2. What is the percent of each of the two most abundant gases in the atmosphere?
3. What is the most abundant gas in the remaining 1%? What are some of the other gases
present?
4. Why is carbon dioxide important even though there is so little of it in the atmosphere?
5. How does oxygen get into the atmosphere?
6. What happens to the oxygen that is taken up in cellular respiration?
Did life evolve to match the atmosphere or is the fit just coincidence?
Life as we know it would not survive if there were no ozone layer to protect it from high energy
ultraviolet radiation. Most life needs oxygen to survive. Nitrogen is also needed, albeit in a
different form from that found in the atmosphere. Greenhouse gases keep the temperature
moderate so that organisms can live around the planet. Life evolved to match the conditions that
were available and to some extent changed the atmosphere to suit its needs.
Composition of Air
Several properties of the atmosphere change with altitude, but the composition of the natural
gases does not. The proportions of gases in the atmosphere are everywhere the same, with one
exception. At 20 km to 40 km above the surface, there is a greater concentration of ozone
molecules ; ozone layer.
Nitrogen and Oxygen
Nitrogen and oxygen together make up 99% of the planet’s atmosphere. Nitrogen makes up the
bulk of the atmosphere, but is not involved in geological or biological processes in its gaseous
form. Nitrogen fixing is described in the chapter Life on Earth. Oxygen is extremely important
because it is needed by animals for respiration. The rest of the gases are minor components but
sometimes are very important.
Water Vapor
Humidity is the amount of water vapor in the air. Humidity varies from place to place and
season to season. This fact is obvious if you compare a summer day in Atlanta, Georgia, where
humidity is high, with a winter day in Phoenix, Arizona, where humidity is low. When the air is
very humid, it feels heavy or sticky. Dry air usually feels more comfortable. When humidity is
high, water vapor makes up about 4% of atmosphere.
Where around the globe is mean atmospheric water vapor higher and where is it lower.
Higher humidity is found around the equatorial regions because air temperatures are higher and
warm air can hold more moisture than cooler air. Of course, humidity is lower near the polar
regions because air temperature is lower.
Greenhouse Gases
Remember that greenhouse gases trap heat in the atmosphere. Important natural greenhouse
gases include carbon dioxide, methane, water vapor, and ozone. CFCs and some other man-made
compounds are also greenhouse gases.
Particulates
Some of what is in the atmosphere is not gas. Particles of dust, soil, fecal matter, metals, salt,
smoke, ash, and other solids make up a small percentage of the atmosphere and are called
particulates. Particles provide starting points (or nuclei) for water vapor to condense on and
form raindrops. Some particles are pollutants.
Summary
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The major atmospheric gases are nitrogen and oxygen. The atmosphere also contains minor
amounts of other gases, including carbon dioxide.
Greenhouse gases trap heat in the atmosphere. These gases include carbon dioxide, methane,
water vapor, and ozone.
Not everything in the atmosphere is gas. Particulates are particles that are important as the
nucleus of raindrops and snowflakes.