The atmosphere is the protective air envelope around the earth. IAir contains oxygen that we breathe and protects us from the harmful UV rays of the sun. Air is a mixture of different gases and is all around us. We cannot see it but it is essential for all living organisms. Atmosphere consists mainly of nitrogen (78%), oxygen (21%), argon (0.93%), carbon dioxide (0.03%) and other gases like helium, ozone, argon and hydrogen (0.04%). Air in the atmosphere has several critical functions that help in the sustenance of life.
Air and the Water Cycle: The water cycle ensures that life around the planet receives the water it needs by replenishing lakes, rivers and other waterways and helping in irrigating parched lands.
Air and the Carbon Cycle: Air is important for recycling of carbon that comes into the biosphere from fossil fuel combustion, the decay of dead animals and eruption of volcanoes. Most of the living organisms exhale carbon dioxide into the air during respiration. Plants utilize the exhaled carbon dioxide present in the air for photosynthesis, which produces oxygen.
Air Makes the Earth's Cosy: Air contains carbon dioxide and other greenhouse gases that absorb infrared radiation released from the earth. This phenomenon, called greenhouse effect, keeps the earth's surface warm which would not have been possible otherwise.
Air Protects us: Air helps protect us from the harmful radiations and celestial particles like the x-rays, cosmic rays, meteors, asteroids can be too destructive. Air also reduces the possibility of destruction by meteorites and asteroids.
Figure 1: Water Cycle
Air Helps to Hear: People can hear sound only because air carries sound waves from one point to another.
Air Helps to See the Sky Blue: Due to air molecules causing violet and blue wavelengths of sunlight to scatter, the sky appears blue.
Air Causes Change in Weather: Climatic phenomena like rain, snow and sea storms are all the attributes of air.
Air has oxygen as one of its key elements. It is vital for the sustenance of life on earth as all living organisms and plants depend on oxygen in the air for breathing in oxygen. There are many uses of air in daily life. In living organisms, oxygen is supplied to all the cells in the body through blood. In a similar way, plant cells also utilize carbon dioxide in air to produce food that we eat to get energy.
Pollination: Pollination is the process where pollen grains from the male flower reach the female flower. Air is also an important medium for transportation of these pollen grains without which flowers could not bloom and fruits could not be produced.
Land and Sea Breezes: During conditions of extreme heat, the land surface becomes hotter compared to oceans or sea surfaces. The hot air on the land rises rapidly and the place is filled by the cool air coming from the ocean . This cycle of rapid movement of air is useful in maintaining temperature over land.
Monsoon: Monsoon is of critical importance as it provides for irrigation and thus, production of crops. This monsoon is aided by the winds which carry the clouds from above the oceans of the world. Thus, Air plays an important role in the movement of clouds and its absence can cause drought-like conditions in some regions.
Aerodynamics: Parachutes and hot air balloons use air for mobility. Parachutes land safely using the function of buoyancy and hot air balloons travel up in the air using hot air as a medium. Air also enables airplanes to fly and travel from one place to another.
Land transportation: Air-filled tires, commonly used for land-based transport, reduce the friction between the tire and the solid surface, thus enabling automobiles to move faster.
Transportation in airplanes: Air makes transportation easier as it facilitates the smooth movement of airplanes. It is a common mode of transport globally across long distances. One can avoid obstacles through air travel. Several other living beings like birds and insects depend on air for mobility. Air also has several tiny living organisms called bioaerosols. They cannot fly on their own and depend on air for transportation.
Minimizing pollution: Major cities are getting choked with pollutants, dust, smog, and chemicals preventing visibility and causing several health hazards. Air is useful in minimizing air pollution by spreading it across vast areas instead of clogging it at a specific place.
Wind power energy: Air is a good source of wind energy. In recent times there is a significant increase in the usage of wind energy to generate electricity by using wind turbines. Turbines rotate with the wind flow and thus generate electricity.
Figure 2: Generating Electricity Using Wind Energy
Combustion is a chemical reaction between oxygen in the air and fuel accompanied by the production of heat energy. In simple terms, it is called burning which is a chemical reaction. It is similar to photosynthesis but in reverse.
Generating heat by burning coal or wood
Utilizing petrol or diesel as sources for transportation (car)
Utilizing natural gas as fuel for cooking
Utilizing fuel as an energy source in thermal power plants
Fireworks during festivals or events
The combustion process is also called oxidation. Combustion needs an ignition. Matchstick is a common ignition device that uses friction to create sufficient heat to ignite the phosphorus at the end of the match which causes a flame. The combustion process is used in car motors, rocket engines, and industrial machinery.
Rapid Combustion: Burning of a substance rapidly is known as rapid combustion. Example is the burning of an LPG stove. Heat and light are produced.
Complete Combustion: It happens in the availability of an unlimited supply of oxygen and leaves only water and carbon dioxide as byproducts. An example of this is when a candle burns and in an ideal situation all the wax burns up.
Incomplete Combustion: Burning of a substance in a limited supply of air is called incomplete combustion. It is also called dirty combustion. Due to lack of oxygen(air), this combustion will produce soot and carbon monoxide.
Spontaneous Combustion: It occurs spontaneously and requires no external energy for initiation. This happens in forest wildfires in summer when the ambient temperature becomes higher than the ignition point of dry wood and the wood bursts into flames.
Explosive Combustion: This happens when the reaction occurs very rapidly producing large amounts of light, heat and sound energy. Some examples are fireworks or explosions with dynamite.