National Weather Service
JetStream - Online School for Weather
The Atmosphere
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 surrounding the earth that 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 (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. N2 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. Plants use carbon dioxide to make oxygen. Carbon dioxide also acts as a blanket and prevents the escape of heat into outer space.
The atmosphere is rarely, if ever, dry. Water Vapor is nearly always present up to about 4% of the total volume. In the deserts regions (30°N/S) when dry winds are blowing, the water vapor content will be near zero. This climbs to near 3% on extremely hot/humid days. The upper limit, approaching 4%, is for tropical climates. The table below shows the change in atmospheric composition with inclusion of water vapor.
| Gas | Symbol | Content | ||||
|---|---|---|---|---|---|---|
| Nitrogen | N2 | 78.084% | 77.30% | 76.52% | 75.74% | 74.96% |
| Oxygen | O2 | 20.947% | 20.74% | 20.53% | 20.32% | 20.11% |
| Water Vapor | H2O | 0% | 1% | 2% | 3% | 4% |
| Argon | Ar | 0.934% | 0.92% | 0.91% | 0.90% | 0.89% |
