The Moon is not like planet Earth. Earth has an atmosphere full of oxygen for living creatures to breathe in, on the Moon you'd be gasping for air. On the moon, there's no air to breathe, no summer breezes, no movement of air because there is no oxygen. However, there is a very thin layer of gases on the lunar surface that some might mistakenly call this an atmosphere. Technically, it's considered an exosphere.

In an exosphere, the gases are so spread out that they rarely collide with one another. They are rather like microscopic cannon balls flying unimpeded on curved, ballistic trajectories and bouncing across the lunar surface. In the moon's atmosphere, there are only 100 molecules per cubic centimeter. In comparison, Earth's atmosphere at sea level has about 100 billion billion molecules per cubic centimeter. The total mass of these gases is about 55,000 pounds (25,000 kilograms), about the same weight as a loaded dump truck.”

One of the sources for the moon's atmosphere is outgassing, the release of gases from the lunar interior, usually due to radioactive decay. Outgassing events may also occur during moonquakes. After being released, lighter gases escape into space almost immediately. Outgassing replenishes the tenuous atmosphere.

 

[via Space.com