Air
We cannot see the air around us. We tend to take it for granted. There seems to be an inexhaustible supply. What is air anyway; just a mix of something that blows our hair out of place or dries the perspiration from our bodies on a hot day? Air must consist of something; otherwise we would feel nothing against our skins as we move. Wave your hands in front of your eyelids. Molecules!
[Author's Request: Two illustrations: 1. The molecular states of solid, liquid, and gas. 2. Gas molecules: three types, a) single atom molecule (Argon, Helium, etc.), b) two-atom molecule (same element, ex. N2, O2, H2), c) compound molecule (methane CH4). With descriptions.]
We know that air is not a solid. The molecules that make up a solid are closely bound together in an ordered structure called a lattice. The electrons in a solid's atoms permit only microscopic shifts unless heated to very high temperatures. We couldn't move through it if air were a solid. Air fells like it moves fluidly and randomly. It behaves more like a liquid than a solid.
Is air a liquid then? It can become a liquid if the temperatures are low enough and the molecules are pressed tightly enough together. However, in its normal state air is not a liquid, either. The molecules of a liquid are packed tightly together like those of a solid. However, the atomic bonds between the outer electrons of a liquid's molecules permit the molecules to slide around each other. As heat is added to a liquid's molecules, they separate and move individually out into the surrounding gas.
A gas expands to fill whatever volume it is in. At the atomic level of distances, a surprisingly large percentage of this volume is taken up by empty space through which the molecules travel and bounce into one another. Air must be a gas [Standard 2.2], a mix of gases to be precise. In order to discover what gases are in a given sample of air, scientists take the sample mix of gases and place it in a container. Then they refrigerate the container to hundreds of degrees below zero. At extremely cold temperatures gases liquefy. When all of the gases reach the liquid stage, the scientists reverse the process. Gradually, as they raise the temperature-which still extremely cold, by the way-each gas boils off, evaporates, and is collected and measured. Since every liquid-gas has a different boiling temperature, a different liquid-gas boils and evaporates as the temperature rises. In this way, scientists can identify which gases are in a given volume of "air."
The Pressure's On!
Our Earth's atmosphere is composed of a mix of gases for a reason. Over the past millions of years, gases have spewed from volcanoes and arisen from dying plants and the death of billions of tons of microscopic creatures. All of these natural processes formed, and continue to replenish, the Earth's atmosphere. This thick layer of gasses presses down on the Earth's surface and creates what we call atmospheric pressure. If we go up into the air, the air's pressure changes because the "stack" of air's gas molecules above us gets shorter the higher we go. Air pressure also changes with weather and temperature changes. Throughout all of these changes in weather or altitude, however, the air's mix of gases remains the same, unless, of course it is changed by man. From the beginning of man's existence on Earth, our lungs, brains, blood, and other vital organs have acclimated to a very specific mix of gases. If this gaseous mixture changes significantly, the gases we depend upon for sustaining life would be unable to penetrate the lining of our lungs.
Along with the natural cycles of carbon and water that constantly modify and change our atmosphere, we are constantly challenging our atmosphere as we seek to advance ourselves scientifically and technologically. The mixture of gases in the atmosphere changes as the result of our actions. When we "advance our civilization" by creating more carbon-based sources of energy, more powerful automobiles, more factories, and new ways to grow food, we sometimes fail to take into account the effects our advances may have on the gases in the atmosphere. Evidence suggests that we tend to forget that we live within a bubble (a bubble a lot larger than Space Station Alpha, but a bubble nonetheless), so our decisions directly influence all of us. Consequently, we have affected the composition of the ozone layer and have added strange and foreign gases to the air we breathe. If the air's gas mixture changes too drastically, we may endanger ourselves. Think about it. Over time we adapted to the air we now breathe. The air did not adapt to us. What are the chances that we can adjust quickly enough to the changes in the new mixes of gas we are creating in the name of improvements?
Space Station Alpha: A "Bubble" in Space
Two hundred and fifty miles up in space, the atmospheric conditions in the Space Station are even more precarious. The astronauts' minds and bodies continue to function as they did on Earth. In the almost perfect gasless vacuum of space, the astronauts require earth-like conditions-a continuous supply of enough oxygen to keep their minds and bodies functioning and healthy. They need nitrogen in the air to dilute the highly flammable oxygen and thus avoid an explosion. Meanwhile they are changing their own atmosphere as they breathe and emit carbon dioxide and other naturally created gases. Monitoring the changes in the atmospheric pressure and the mixture of gases inside the space station is the only way to ensure that the astronauts can continue working and thinking clearly.
Like a submarine at the bottom of the ocean, Space Station Alpha is a "bubble" full of air completely surrounded by danger. The only difference is that the astronauts cannot come up for air. So what can the astronauts do if they need a little fresh air? They can't open a window or a hatch; otherwise the air inside the space station would rush out into the vacuum of space. The astronauts would suffocate almost instantly.
Scientists, engineers, and technicians have used what they know about the interaction between atmospheric gases and the human body to create a safe environment for the astronauts. The space station's Environmental Control and Life Support System (ECLS System) [Science Standard: Science and Technnology 1.1] creates, cleans, stores, and expels atmospheric gases. [Ed. Note: link to ECLS System image map] This system is an ingenious web of technology that supports the life-needs of the astronauts. The station's air must be monitored at all times.
