An air mass if a distinct body that creates a homogeneous mixture of temperature, humidity, and stability that extends through the lower half of the atmosphere.
m --> maritime (wet)
c --> continental (dry)
A --> Arctic
P --> Polar
T --> Tropical
E --> Equatorial
AA --> Antarctic
The CONTINENTAL POLAR air mass only forms in the Northern Hemisphere. An area covered by this air mass (cP) in winter experiences cold, stable air, clear skies, high pressure, and antcyclonic wind flow.
The MARITIME POLAR air mass in the Northern Hemisphere sits over the Northern Oceans and are cool, moist, unstable, and prevail throughout the year.
There are two MARITIME TROPICAL air masses --> the mT Gulf/Atlantic + the mT Pacific
Hope that helps!