Air is mostly gasAir is all around us, but we can’t see it. So what is air, exactly? It’s a mixture of different gases. The air in Earth’s atmosphere is made up of approximately 78 percent nitrogen and 21 percent oxygen. Air also has small amounts of lots of other gases, too, such as carbon dioxide, neon, and hydrogen.
Carbon dioxide in the air can be both good and bad
When humans and animals breathe, we give off an odorless gas called carbon dioxide, or CO2. Plants use this gas, along with sunlight, to make food—a process called photosynthesis. In this process, plants give off oxygen, too! However, large amounts of CO2 are also produced when cars and power plants burn coal, oil, and gasoline. CO2 is also the most important contributor to human-caused global warming.
Air changes as you go up, up, up
Air seems light, but there is a lot of it pushing down on Earth’s surface. This is called air pressure. You experience high air pressure at sea level because the whole atmosphere is pushing down on you. When you’re on top of a mountain, there is less air pushing on you and the pressure is low. That change in pressure can cause your ears to pop when you’re taking off in an airplane or driving up a hill.
Air can move fast and far
Even on a very still day, the air around us is always moving. But when a big wind comes, that air can really go! The fastest gust of wind ever recorded on Earth clocked in at 253 miles per hour. And as the wind picks up seeds and dust and other particles, it can carry them miles away from their original home!
Air also holds water
When it’s a hot, muggy summer day, you’ve probably heard the word “humid.” But what does that mean, exactly? Relative humidity is the amount of water that the air can hold before it rains. Humidity is usually measured in percentages, so the highest level of relative humidity—right before it rains—is 100%. Humidity in the air is measured with an instrument called a psychrometer.
source:Nasa
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