This writing looks at several important gases that make up the atmosphere and information about each gas.


Oxygen comprises about 21% of the atmosphere. Without the presence of Oxygen emitting plants, there will be very little Oxygen in the air. The early atmosphere had very little Oxygen but this value rose upon the development of photosynthesis where Carbon Dioxide, water and energy are converted into sugar and Oxygen. The generation of Oxygen allowed Oxygen breathing life to take hold on the planet.

Oxygen is element number 8 on the Periodic Table with an average atomic mass of 16.00 amu. The atomic mass of 16 comes from the presence of 8 protons and typically 8 neutrons in the nucleus of the atom. Both Carbon Dioxide (CO2) and water (H2O) contain Oxygen as one of the elements in the compound. Thus breaking these compounds will produce Carbon, Oxygen and Hydrogen. Oxygen is found naturally as a diatomic molecule. Oxygen is highly reactive. Thus, single Oxygen atoms will quickly combine with other elements or with each other instead of existing as free floating individual Oxygen atoms. A diatomic molecule is denoted as O2.

Besides being critical for Oxygen breathing organisms (respiration), the presence of Oxygen allows fires to burn more aggressively. Without photosynthesis to continually recharge Oxygen levels, the Oxygen level in the atmosphere would decrease over time. Oxygen is also the constituent within Ozone (O3). Ozone is responsible for shielding a large amount of harmful UV (Ultraviolet) radiation from reaching the Earth’s surface. This ozone forms high aloft in the stratosphere and is called the Ozone Layer. This shielding makes it easier for life to inhabit the land surface without being quickly damaged from excessive UV radiation.


Water vapor is known as a variable gas which means its percent abundance in the air at any one place in the troposphere is not constant. This variation results due to influences from temperature, altitude, and availability of water to evaporate into the air. As temperature increases, then an increasing amount of liquid or solid water can vaporize into the air. This is limited though by the availability of water to evaporate. The warmest places on earth may or may not have abundant moisture in the air depending on availability. Hot temperatures and warm ocean waters are the best combination for high amounts of moisture. Even at these locations the maximum amount of water vapor as a percentage of the air is a few percent. Very cold and very dry locations will have a water vapor percentage of close to 0%. The amount of water vapor is the air tends to decrease with altitude. This is because temperatures decrease with height and the availability of a moisture source is farther away.

Although water vapor is typically just a small percentage of the total air, it is the critical component to producing the Earth’s weather such as clouds and thunderstorms. This variable gas has vast influences on latent heat release and absorption as well as distributing water over the Earth. Water has the unique property that it can exist as a liquid, solid and gas within the temperatures experienced on Earth. This allows it to be readily distributable by wind currents, ocean currents, groundwater, rivers/streams, and glaciers. Water is in all three phases within a thunderstorm (water vapor advected into the storm, water vapor condensed to liquid as in rain formation, and ice such as in the formation of hail). The unique properties of water are a reason for the magnificence of Earth’s weather.


Argon is element 18 on the Periodic Table and it has an average atomic mass of 39.95 g/mol. Argon is a Noble gas. Noble gases are not very reactive since they have a very stable electron configuration. It is only about 1% of the air in the atmosphere but it is more abundant than any other element on the Periodic Table behind Nitrogen and Oxygen. There are three reasons why this gas is found in the atmosphere. One reason is because it is non-reactive. Like other noble gases, it is stable and resists combining with other elements. Once it gets in the atmosphere it is difficult to get rid of. Another reason it is found in the atmosphere is because it is relatively heavy. Argon is heavy enough that it tends to not be lost to space like for example Helium is lost. Helium is also a noble gas but it is very light and can over time travel to the upper atmosphere and escape into space. Third, there is a relative abundance of Argon that is emitted from the Earth as compared to other gases. This resupply with very little escaping the atmosphere or reacting with other elements helps maintain a high level of Argon as compared to most other gases.


Nitrogen is the most abundant gas in the atmosphere. About 78% of the atmosphere is Nitrogen. Nitrogen is element 7 on the Periodic Table and has an atomic mass of 14.01 g/mol. Nitrogen in the natural state exists as N2 molecules. This gives diatomic Nitrogen an atomic mass of around 28 g/mol. There are several reasons why Nitrogen is abundant in the atmosphere. First, there is an abundance of Nitrogen available to be emitted into the atmosphere. It is a very common element in the universe and the Earth is no exception. Second, the diatomic bonding of Nitrogen is very strong (a triple bound). This makes it relatively difficult to break Nitrogen apart. It is a very stable diatomic molecule. Third, it is heavy enough so that little is lost from the atmosphere. Unlike, Hydrogen and Helium, Nitrogen is heavy enough that it resists floating off into space easily. Nitrogen gas gives the atmosphere much of its mass and is a very important gas in many ways.


Carbon Dioxide composes about 0.04% of the atmosphere. It is not famous for being a large component of the atmosphere by volume (it's not) but rather by being a very effective greenhouse gas and being part of the Carbon cycle. Carbon Dioxide is composed of a Carbon atom and two Oxygen atoms (CO2). Plants use this gas in the photosynthesis process and animals use its components that become part of sugar molecules. Animals breathe out this gas in the respiration process. As Carbon based life forms, Carbon Dioxide is a critical component for life. The Carbon in Carbon Dioxide is used in sugar molecules and this sugar is used for energy and other functions in living organisms.

Carbon Dioxide is a greenhouse gas. It is effective at absorbing and emitted longwave radiation. This helps traps extra energy in the lower atmosphere and causes the Earth’s atmosphere to be warmer than it otherwise would be. As Carbon Dioxide increases, then more energy can be trapped and surface temperature will warm. This is the concern involved in the global warming debate. The emissions of CO2 in the atmosphere contribute to increased greenhouse warming. Even with the small amount of CO2 in the atmosphere, significant greenhouse warning occurs. The concern is that even small increases in CO2 can cause significant global temperature increases.