NSES Content Standard D  Earth and Space Science: Structure of the Earth system Grades 5-8, page 160 The atmosphere is a mixture of nitrogen, oxygen, and trace gases that include water vapor. The atmosphere has different properties at different elevations.

 
Benchmark 4B The Physical Setting: The Earth
Grades 3-5, page 68
When liquid water disappears, it turns into a gas (vapor) in the air and can reappear as a liquid when cooled, or as a solid if cooled below the freezing point of water. Clouds and fog are made of tiny droplets of water.

Benchmark 4C The Physical Setting: Processes that Shape the Earth
Grades 9-12, page 74
Plants alter the earth's atmosphere by removing carbon dioxide from it, using the carbon to make sugars and releasing oxygen. This process is responsible for the oxygen content of the air.