The main components of air are nitrogen (78%), oxygen (2 1%), rare gas (0.94%), carbon dioxide (0.03%) and other impurities (0.03%).
Nitrogen is a very stable gas at room temperature, which can be used as a protective gas, for example, it can be filled into a light bulb to prolong the service life of a filament, and it can be filled into a food packaging bag to prolong the shelf life of food. Nitrogen can also react with other substances under special conditions. For example, in the chemical industry, nitrogen is an important raw material for making fertilizers, nitric acid, explosives and other products. When the temperature drops to-196℃, nitrogen will become a liquid that can flow like water. Pour liquid nitrogen into pure milk with white sugar and honey, and the milk will soon become cool and delicious ice cream.
Animals and plants on the earth can't breathe without oxygen in the air. In addition to breathing for life, oxygen can also support combustion, because oxygen at high temperature is very active and can combine with many substances to form new oxides. Therefore, the important principle of fire fighting is to isolate oxygen, block the contact between combustion products and air, splash water, bury soil, spray dry powder, foam, carbon dioxide and so on. Use a fire extinguisher to isolate the air and put out the flame.
Rare gases in the air mainly include argon, neon, helium, krypton, xenon and so on. They are very stable, also known as inert gases, so they can be used as protective gases for metal welding, and can also be filled into light bulbs to protect filaments like nitrogen and prolong their service life. Rare gases can emit different colors of light when electrified, and people use this characteristic to make beautiful and colorful neon lights. Helium is less dense than air and can be used to fill balloons instead of combustible hydrogen, thus avoiding the danger of explosion and combustion of hydrogen balloons and making children safer when playing.
Carbon dioxide in the air is also very stable. Like nitrogen, it does not support burning and breathing of animals and plants. Carbon dioxide can be slightly dissolved in water to form carbonic acid. The carbonated drinks we often drink are made by filling carbon dioxide gas into the drinks under certain pressure. Although carbon dioxide does not support the breathing of life, it is an important raw material for plant photosynthesis. Photosynthesis is a process in which green plants absorb carbon dioxide in the air, combine the water absorbed by roots from the soil, use chloroplasts to make nutrients and release oxygen at the same time.
Since carbon dioxide is an essential raw material for plant photosynthesis, wouldn't it be better to have more carbon dioxide? The answer is no, because carbon dioxide is a greenhouse gas, which can absorb a lot of infrared radiation from sunlight, prevent heat from being lost into space, and keep the earth warm just like a greenhouse. Too much carbon dioxide in the atmosphere will lead to global warming. Global warming is one of the main environmental problems facing mankind at present. There are two main reasons for this problem. On the one hand, humans release a lot of carbon dioxide into the atmosphere by burning fossil fuels such as coal and oil. On the other hand, a large number of forests have been destroyed, reducing the consumption of carbon dioxide by photosynthesis. Global warming causes glaciers to melt and sea levels to rise, which poses a great threat to animals living near the polar regions and humans in coastal areas. Tuvalu, a small island country in the Pacific Ocean, moved to New Zealand because it could not resist the threat of rising sea level. The Maldives, a resort in the Indian Ocean, will also disappear below sea level in a few decades. The land on which human beings depend is being eroded by the ocean.
In addition to these gas components, there are a small amount of water vapor and solid impurities in the air, which are necessary conditions for cloud formation and rainfall.
In recent years, with the development of industry, there are many things that people don't want to see in the air around us, such as sulfur dioxide, nitrogen oxides and inhalable particles. These impurities are mixed with small water droplets in the air, forming a gray smog that hangs over the city. The smog mixed with bacteria, viruses, toxic gases and dust seriously affects people's physical and mental health and is one of the main environmental problems we are facing in the near future. These harmful components mainly come from the combustion of coal and oil, such as smoke and dust generated by coal-fired power generation and heating in winter, and tail gas emitted by automobiles. In daily life, we save electricity, drive less, walk or ride bicycles more, which will help reduce smog.
The composition of the air is constantly changing. Billions of years ago, there was only a small amount of oxygen and a large amount of acid gas in the earth's atmosphere, and human beings could not survive at all. Nowadays, the earth has evolved an environment suitable for human survival, and we must take good care of it. From the human point of view, in the long geological history, the natural environment of the earth is much worse than it is now, but the earth itself has not been harmed. It is countless biological species that have been extinct because they can't adapt to the great changes in the environment. All our efforts to protect the environment are not for the earth, but for ourselves.