Air pressure has a few effects on evaporation. If the air pressure is high on the surface of a body of water, the water will not evaporate quickly. The pressure on the water makes it very difficult for the water to disperse as a vapor into the atmosphere. Air pressure is the force of the surrounding air that is acting on the surface of the water. Greater air pressure means greater force per unit area. This pressure is forced on evaporating water molecules, so greater air pressure means that the water molecules will exert more energy to evaporate. That being said, you could say the air particles are heavier and weighing down on the water. I hope this helps! Have a great day. :)