What are the main types of air masses?
There are 6 based on the areas they are formed in.
Air masses are categorized as either continental or maritime based on if they form over land or water. They are also categorized based on how close to the poles they form (so based on temperature). Starting from the closest to the poles we have Continental Arctic and Maritime Arctic, then Continental Polar and Maritime Polar and finally Continental Tropical and Maritime Tropical.
Depending on what part of the world you are in you may not see all these types of air masses.