It is made up of a mixture of gases that we cannot see. Water in the form of vapor is mixed with the gases. Air also carries tiny particles of solid material such as dust, but the water and the solid particles are not considered part of the air.
Air also contains very small amounts of several other gases.
They include neon, helium, krypton, xenon, hydrogen, azone, carbon dioxide, nitrous oxide, and methane. Air often contains many solid particles which are usually invisible except when present in great numbers. Some of these are salt from the oceans, pollen from plants, and tiny living things called microbes. Characteristics of air are pressure and resistance, movement, and air compression. Air pressure is caused by the weight of air from the top of the atmosphere as it presses down upon the layers of air below.