Flexi Says: Nitrogen and oxygen together make up 99% of air. Argon and carbon dioxide make up much of the rest. These percentages are the same just about everywhere in the atmosphere. Air also includes water vapor. The amount of water vapor varies from place to place. It can make up as much as 4% of the air. Ozone is a molecule made of three oxygen atoms. Ozone collects in a layer in the stratosphere.