Air Masses and Weather â¢ An air mass is a large body of air in the lower troposphere that has similar characteristics throughout. â Can be several kilometers in diameter and several kilometers high. â The temperature and humidity for the air mass depends on where it originates and when it moves it takes the characteristics from its origin with it. â As air masses travel, there characteristics can change based where it has traveled to and how long it sits in the new location. â Earthâs topography can also contribute to changes in the temperature and humidity of an air mass as it travels.