Air

Air is a mixture, a physical combination of two or more substances present in variable substances and is the layers of gases in the earth's atmosphere, which is used for breathing and photosynthesis. It was given the name because of breathing and the photosynthesis process. Air is nothing but a mixture of a variety of gases that are odorless. It is comprised of five gases: 78.1% nitrogen, 20.9% oxygen, 0.9% argon, about 0.035% __carbon dioxide__, as well as other small amounts of trace gases that are present such as: water vapor, carbon dioxide, methane, and nitrous gases. Nitrogen and oxygen are life-sustaining substances that are essential for humans, animals and plants. The amount of water in the air greatly varies. Depending on how much water vapor is in the air determines the amount of the other gases. For example if there are large amounts of water vapor in the air the other elements present in lower amounts. The amount of water in the air can rise up to 4% and it can decrease to 0.5% as well. It is the way humans live and many animals need it too. The way that it helps us breathe is very unique as we breathe out carbon dioxide after inhaling all the nitrogen, oxygen, argon, carbon, and other materials from the air.

The most reactant part of the atmosphere is oxygen; its tendency to react contributes to it being far less common than nitrogen in the air. The least reactant is argon, which is a noble gas and inert. The air we breathe is in the inner most layer of earths atmosphere, the troposphere. While air content and atmospheric pressure varies at different layers, air suitable for the survival of terrestrial plants and animals is currently only known to be found in Earth's troposphere and artificial atmospheres.

__**Human Respiration**__ Air is a precious resource that we take for granted. It supplies us with oxygen, and without oxygen we would die within minutes. Adults breath in about 10-20 cubic meters of air everyday, which is approximately 20,000 breaths. Children breath in roughly twice that amount because their respiratory system is still maturing. The air that leaves a person's lungs when exhaled contains 14% oxygen and 4.4% carbon dioxide. Atmospheres with oxygen concentrations below 19.5% can have adverse physiological effects, and atmospheres with less than 16% oxygen is life threatening. Human's respiratory system allows a person to obtain oxygen and eliminate carbon dioxide. The medulla sends signals to adjust the levels of oxygen presented in our body by breathing rate. Without the presence of oxygen, sugars cannot be broken down by the human metabolic system past the glycolysis stage, creating only 2 ATP for the same amount of glucose which can (in the presence of O2) create up to 36 ATP. Basically without the O2 found in air we would have no source of energy.






 * Air quality** is defined as a measure of the condition of air relative to the requirements of one or more biotic species or to any human need or purpose. Air quality indices (AQI) are numbers used by government agencies to characterize the quality of the air at a given location. As the AQI increases, an increasingly large percentage of the population is likely to experience increasingly severe adverse health effects. To compute the AQI requires an air pollutant concentration from a monitor or model. The function used to convert from air pollutant concentration to AQI varies by pollutant, and is different in different countries. Air quality index values are divided into ranges, and each range is assigned a descriptor and a color code. Standardized public health advisories are associated with each AQI range. An agency might also encourage members of the public to take public transportation or work from home when AQI levels are high.

HISTORY: The ancient Greeks regarded air as one of the four elements, but the first scientific studies of atmospheric composition began in the 18th century. In the late 19th and early 20th centuries interest shifted towards trace constituents with very small concentrations. One particularly important discovery for atmospheric chemistry was the discovery of ozone by Christian Friedrich Schönbeinin 1840. In the 20th century atmospheric science moved on from studying the composition of air to a consideration of how the concentrations of trace gases in the atmosphere have changed over time and the chemical processes, which create and destroy compounds in the air. Two particularly important examples of this were the explanation by Sydney Chapman and Gordon Dobson of how the ozone layer is created and maintained, and the explanation of photochemical smog by Arie Jan Haagen-Smit. Further studies on ozone issues led to the 1995 Nobel Prize in Chemistry award shared between Paul Crutzen, Mario Molina and Frank Sherwood Rowland. In the 21st century the focus is now shifting again. Atmospheric chemistry is increasingly studied as one part of the Earth system. Instead of concentrating on atmospheric chemistry in isolation the focus is now on seeing it as one part of a single system with the rest of the atmosphere, biosphere and geosphere. An especially important driver for this is the links between chemistry and climate such as the effects of changing climate on the recovery of the ozone hole and vice versa but also interaction of the composition of the atmosphere with the oceans and terrestrial ecosystems.

Airplane Air: All of us who have been on an airplane have to make the tough choice of dying of heat stroke or having that foul air blown in our face. And, when we get off the plane we feel sick or need a shower. However, experts say that there is nothing wrong with the air in airplanes. The filters in planes filter out almost 100% of the germs. More bacteria is in normal air. Now while the air that is coming out of the vents is clean, it can't do much about the sick old man, or sneezing lady next to you. To prevent contracting an illness form this you should wear a face mask.

Air Pollution Impacts on Health: Fun Facts about Your Lungs

 * The right lung is slightly larger than the left.
 * Hairs in your nose help to clean the air we breathe as well as warm it.
 * The highest recorded "sneeze speed" is 99 miles per hour!
 * The surface area of the lungs is roughly the same size as a tennis court.
 * If placed end to end, capillaries would extend 960 miles.
 * We lose half a liter of water every day through breathing.
 * A person at rest breathes between 12-15 times a minute.
 * The breathing rate is faster in children and women than it is in men.

Air is needed by almost all the living things living on Earth. Most plants and animals take in air, use the oxygen in it and give out another gas, carbon dioxide. This process is called respiration. Air also protects life on Earth by absorbing harmful ultraviolet solar radiation and reducing temperature extremes between day and night.
 * Why is air so important? **



Beyond the atmosphere of the Earth, air does not exist. Therefore humans would not survive in space without protection.

= Circulation =

//Atmospheric circulation// is the large-scale movement of air through the troposphere, and the means (with ocean circulation ) by which heat is distributed around the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant as it is determined by the Earth's rotation rate and the difference in solar radiation between the equator and poles.