Air Naturally

Air… we know it’s there. It envelops the earth and makes life possible. We must expose delicate lung tissue to about 35 pounds of it everyday! Scientists divide this mass of air, or atmosphere, into layers. The layer closest to the earth is called the troposphere, and it is in this layer that we go about our daily routines. It is also in this layer that the mostly invisible chemical cycling of essential elements and compounds occurs, as well as the uneven heating of earth’s surfaces that creates our weather.

The air of the troposphere is made up of gases and has several other natural ingredients. See the chart on clean air components on page 26. Some of air’s gases remain fairly constant. Nitrogen, oxygen and argon make up the chief of these gases at approximately 78, 21, and 1 percent by volume respectively. Several rare gases round out the mathematical picture of air’s consistency.

Small amounts of other naturally occurring gases are found in varying amounts and play an important role in regulating and sustaining life on earth. These varying gases are water vapor, carbon dioxide, methane, nitrogen dioxide and sulfur dioxide. These gases and their natural occurrence in the troposphere are explained below. Also occurring naturally are particles, light enough to be suspended in the air. These particles are bits of the earth blown into the air by wind, or which result from natural fires and volcanoes, sea salts, pollen and tiny microbes. More of these natural particles are found at lower altitudes, while in the higher elevations concentrations drop, simply because some of the particles are too heavy to get up that high. The lightest of particles are transported very far distances. All of these bits of matter play an important role in our weather by providing surfaces for condensation and eventually, precipitation, allowing water that evaporates from the ocean and land to rejoin us on the earth’s surface. Additionally, rain and other forms of precipitation wash some of these particles down to the earth’s surface, or they may settle to earth as dry dust.

Nitrogen (N₂) is one of the most common elements that makes up our air and earth. Almost ten pounds of molecular nitrogen occurs over every square inch of the earth’s surface, and yet this is still only 2 percent of all nitrogen on, in or above the earth. The remaining 98 percent occurs in the rocks of the earth’s crust and mantle, or is tied up, so to speak, in tissue. This element’s biological importance ranks with that of carbon, oxygen and hydrogen, because of its commonness in living structures and metabolic processes. Elemental nitrogen’s abundance, however, is tempered by its limited availability to most living things which need it, because most living things can only take up and use this nitrogen in its relatively scarce, reduced form of ammonia (NH₃+). Converting N₂ to NH₃+, known as nitrogen fixing, can be accomplished by certain microbes and by lightning. Nitrogen does not remain available in this form indefinitely, however, but is continually being "unfixed" during natural processes. Additionally, some nitrogen dioxide is released into the atmosphere during an additional bacteria-mediated process called denitrification.

Oxygen (O₂) is important to most living organisms, for it allows food to be "burned" for energy on a cellular level (respiration). When this burning occurs, the oxygen combines with carbon to form carbon dioxide(CO₂) which rejoins the atmosphere. An additional use of oxygen is for any extra cellular burning, whether it is during a forest fire, under the hood of your car or at the local power plant on your behalf!

Green plants, in addition to respiring, photosynthesize when exposed to sunlight. Photosynthesis involves taking CO₂ out of the air and converting it to a carbon-based sugar, releasing O₂ in the process. An additional source of oxygen is found in rocks, where it has been trapped for millennia and released slowly during the weathering process.

Whether the plant sugar made during photosynthesis remains as sugar, is converted to another plant part or passed to an animal as food during the playing out of the food chain, the bacteria that eventually cause it to decay consume large amounts of oxygen in their task, while effecting the release of methane, carbon dioxide and other compounds.

It is difficult to refer to nitrogen and oxygen, the constant gases of the atmosphere, without talking about the varying gases as well, so we have combined them in the paragraphs above.

Water molecules are a varying but ubiquitous presence which play an active role in much of air’s chemistry. The air picture is not quite complete, however, without mentioning two more components, argon and sulfur oxides. Argon is a colorless, odorless, tasteless gas that is relatively inert, and so it is not a player in the complex cycling that we see with other chemicals. Sulfur oxides, a group of compounds which vary naturally, enter the atmosphere from sea spray and from volcanic action. Additionally, sulfur oxides enter the atmosphere as a result of biological decay.

So air is more than just air. It is a media, rich in natural chemical reactions, which links and supports all life forms.