A deep breath after climbing a flight of stairs…a cool breeze on a scorching-hot summer day…a warm draft from a fire on a chilly winter night…what do all of these things have in common? If you guessed "air," then you're correct!
But what exactly IS air? It's all around you, right? After all, you breathe in and out hundreds upon hundreds of times each day. Yet, you can't really see the air around you unless it interacts with something.
For example, if you open the window and the curtains flutter, you know that air is coming through the window, pushing the curtains around. Despite this evidence, you can't really see the air itself, though.
Many people assume that air is mostly made up of oxygen, since that's what our bodies need so desperately from the air we breathe. While oxygen is an important part of air, there are many other things in air other than oxygen.
Oxygen accounts for about 21% of air. However, the amount of oxygen in the air isn't the same everywhere you go. The farther you move away from sea level, the less oxygen you'll find in the air. For example, there's less oxygen in the air at the peaks of tall mountains. That's why mountain climbers often have to use oxygen tanks to ascend to the world's highest peaks, such as Mount Everest.
Around 78% of air is actually made up of another common gas called nitrogen. If you're adding up those percentages in your head, you've probably already figured out that oxygen and nitrogen only make up about 99% of air. So what's in that other 1%?
Besides oxygen and nitrogen, air also contains minute amounts of other gases, such as argon, carbon dioxide, helium, methane, and other trace gases. But that's not all! You'll also find other things in air, like dust, pollen, microbes, spores, and even water!
Water vapor in air is a natural part of the water cycle. Humans feel the water vapor in the air as moisture, especially when it's humid outside. Remember those hot summer days when it felt like the air was wet but it wasn't raining? That's humidity.
Humid days can feel so unpleasant because the amount of moisture in the air interferes with your body's natural cooling process. On a hot day, your body will sweat to cool itself down. Sweat leaves your body and evaporates on your skin, which cools your body's temperature. On humid days, sweat doesn't evaporate into the air like usual, because there's already too much water vapor in the air.
So even though you can't see all these gases and microscopic particles in the air around you, they're there and they make up a substance that your body needs. Now you can breathe easier knowing a bit more about the air you use every day!