1. Introduction
2. Layers of the Atmosphere
3. Air Pressure
4. The Transfer of Heat Energy
5. Energy Balance
6. Hydrologic Cycle
7. Review Questions

• Additional Info:
• Lesson Plan Overview
• Topic Matrix
• JetStream News

Introduction

Gas	Symbol	Content
Nitrogen	N2	78.084%		99.998%
Oxygen	O2	20.947%
Argon	Ar	0.934%
Carbon dioxide	CO2	0.033%
Neon	Ne	18.20 parts per million
Helium	He	5.20 parts per million
Krypton	Kr	1.10 parts per million
Sulfur dioxide	SO2	1.00 parts per million
Methane	CH4	2.00 parts per million
Hydrogen	H2	0.50 parts per million
Nitrous oxide	N2O	0.50 parts per million
Xenon	Xe	0.09 parts per million
Ozone	O3	0.07 parts per million
Nitrogen dioxide	NO2	0.02 parts per million
Iodine	I2	0.01 parts per million
Carbon monoxide	CO	trace
Ammonia	NH3	trace

The atmosphere is a cloud of gas and suspended solids extending from the Earth's surface out many thousands of miles, becoming increasingly thinner with distance but always held by the Earth's gravitational pull.

The atmosphere is made up of layers. it surrounds the Earth and holds the air we breathe; it protects us from outer space; and holds moisture (clouds), gases, and tiny particles. In short, the atmosphere is the protective bubble we live in.

This protective bubble consists of several gases (listed in the table to the right) with the top four making up 99.998% of all gases. Of the dry composition of the atmosphere nitrogen, by far, is the most common. Nitrogen dilutes oxygen and prevents rapid burning at the Earth's surface. Living things need it to make proteins. Oxygen is used by all living things and is essential for respiration.

It is also necessary for combustion or burning.

Argon is used in light bulbs, in double-pane windows, and to preserve the original Declaration of Independence and the Constitution. Plants use carbon dioxide to make oxygen. Carbon dioxide also acts as a blanket that prevents the escape of heat into outer space.

These percentages of atmospheric gases are for a completely dry atmosphere. The atmosphere is rarely, if ever, dry. Water vapor (water in a 'gas' state) is nearly always present up to about 4% of the total volume. In the Earth's desert regions (30°N/S) when dry winds are blowing, the water vapor contribution to the composition of the atmosphere will be near zero.

Water vapor contribution climbs to near 3% on extremely hot/humid days. The upper limit, approaching 4%, is found in tropical climates. The table below shows the changes in atmospheric composition with the inclusion of different amounts of water vapor.

Next: Layers of the Atmosphere