If I can remember back to high school physics... temperature is an an average of the energy in any substance. Some molecules have more, some have less. Some of the water molecules are closer to a temp where they will move into a gaseous state, but are held in check by other close by molecules that are not. Only molecules on the surface can change state easily and evaporate. If you atomize the water, there is more surface area so more high energy molecules can vaporize thus lowering the average energy/temperature.
Now, I am not 100% sure if this is correct because High school was about 30 years ago... so take it with a grain of salt.