Is Air Made of Matter?

Woman and child flying a red kite

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Is air made of matter? To fit into the standard definition of matter in science, air must have mass and it must take up space. You can't see or smell the air, so you may be wondering about its status. Matter is physical material, and it is the fundamental element in all of us, all of life, and all of the universe. But...air?

Yes, air does have mass and does take up physical space, so, yes, air is made of matter.

Proving Air Is Matter

One way to prove that air is made of matter is to blow up a balloon. Before you add air into the balloon, it is empty and shapeless. When you puff air into it, the balloon expands, so you know it is filled with something—air is taking up the space. You'll also notice that a balloon filled with air sinks to the ground. That's because compressed air is heavier than its surroundings, so the air has mass or weight.

Consider the ways you experience air. You can feel the wind and see that it exerts a force on the leaves on trees or a kite. Pressure is mass per unit volume, so if there is pressure, you know the air must have mass.

If you have access to the equipment, you can weigh air. You need a vacuum pump and either a large volume of air or a sensitive scale. Weigh a container filled with air, then use the pump to remove the air. Weigh the container again and note the decrease in weight. That proves something that had mass was removed from the container. Also, you know the air you removed was taking up space. Therefore, air fits the definition of matter.

Air is quite important matter, in fact. The matter in the air is what supports the enormous weight of a plane. It also holds clouds aloft. The average cloud weighs about a million pounds. If there were nothing between a cloud and the ground, it would fall.

What Type of Matter Is Air?

Air is an example of the type of matter known as gas. Other common forms of matter are solids and liquids. Gas is a form of matter that can change its shape and volume. Considering the air-filled balloon, you know you can squeeze the balloon to change its shape. You can compress a balloon to force the air into a smaller volume, and when you pop the balloon, the air expands to fill a larger volume.

If you analyze air, it consists mostly of nitrogen and oxygen, with smaller amounts of several other gases, including argon, carbon dioxide, and neon. Water vapor is another important component of air.

The Amount of Matter in Air Isn't Constant

The amount of matter in a sample of air isn't constant from one place to another. The density of air depends on temperature and altitude. A liter of air from sea level contains many more gas particles than a liter of air from a mountaintop, which in turn would contain much more matter than a liter of air from the stratosphere. Air is most dense close to the surface of the Earth. At sea level, there is a large column of air pushing down on the surface, compressing the gas at the bottom and giving it a higher density and pressure. It's like diving into a pool and feeling the pressure increase as you go deeper into the water, except liquid water doesn't compress nearly as readily as gaseous air.

While you can't see or taste the air, that is because as a gas, its particles are very far apart. When air is condensed into its liquid form, it becomes visible. It still doesn't have a flavor (not that you could taste liquid air without getting frostbite).

Using human senses isn't a definitive test for whether something is matter or not. For example, you can see light, yet it's energy and not matter. Unlike light, air has mass and takes up space.

Resources and Further Reading

  • Butcher, Samuel and Robert J. Charlson. "An Introduction to Air Chemistry." New York: Academic Press, 1972
  • Jacob, Daniel J. "Introduction to Atmospheric Chemistry." Princeton NJ: Princeton University Press, 1999.