The capacity of atmospheric air to hold water vapor as vapor depends primarily on its temperature. As the temperature of the air increases, the air becomes more capable of holding water vapor. This is because higher temperatures increase the kinetic energy of the air molecules, allowing them to move faster and hold more water vapor.

Option 1: Pressure is not the fundamental factor that determines the capacity of air to retain water vapor. While changes in pressure can affect the dew point and condensation, it is the temperature that primarily determines the capacity of air to hold water vapor.

Option 3: Density, or the mass per unit volume of air, is not the fundamental factor that determines the capacity of air to hold water vapor. While changes in density can affect the amount of water vapor that air can hold, it is the temperature that primarily determines the capacity of air to hold water vapor.

Option 4: The velocity of the winds does not fundamentally affect the capacity of air to hold water vapor. While high winds can accelerate evaporation and increase the mixing of air, it is the temperature that primarily determines the capacity of air to hold water vapor.

In conclusion, the capacity of atmospheric air to hold water vapor primarily depends on its temperature.