An air mass is a concentrated volume of air that adapts to the same weather attributes of the region below it.
Air masses can be small and cover hundreds of square miles, or they can be large and cover thousands of square miles.
Air masses are categorized by their temperature, cold or warm, and their water vapor conditions.
Air mass classifications are dependent on the environment of their origin. That is why they are referred to as an arctic air mass, polar air mass or tropical air mass.
Air masses can originate over land or water. Air masses that form over water are called maritime air masses. Air masses that form over land are called continental air masses.
Air masses create fronts, and move the characteristics of a given region across a new region for a couple of days. That is why an arctic air mass creates cold weather fronts.