Why Is Fresh Air Fresh?

When you've been cooped up in a house or other building, there is nothing like taking a break and getting some fresh air.

So, why is fresh air fresh? What is it about the air outside that makes it seem so much better?

This video by SciShow explores the reasons why that crisp morning air is so much fresher feeling and what, if anything, you can do make the inside air a little fresher.

Do you have any tips to make the inside air feel fresher? Let us know in the comments!