Here's a breakdown:

* Temperature: Air masses take on the temperature of their source region. A cold air mass from the Arctic will bring cold temperatures, while a warm air mass from the tropics will bring warm temperatures.

* Humidity: The amount of moisture in the air mass is determined by its source region. Air masses forming over oceans will be very humid, while air masses forming over deserts will be very dry.

* Atmospheric pressure: Air masses also carry their own atmospheric pressure, which is the weight of the air above a given location. High pressure air masses are associated with clear skies and calm weather, while low pressure air masses are associated with clouds and precipitation.

The interaction of different air masses is a major factor in creating weather patterns.