Why does air humidity affect evaporation rate?

The process of evaporation is that the kinetic energy of molecular thermal motion in liquid reaches a certain level, leaves the liquid surface and flies into the air; But at the same time, molecules in the air fly into the liquid, which is a reciprocating process. So the two processes are balanced, so it won't evaporate macroscopically. Therefore, evaporation is related to temperature (the intensity of molecular thermal motion) and water vapor saturation pressure (exposure or air flow will reduce the molecular density on the liquid surface, the saturated vapor pressure will be lower, and the probability of returning to the liquid will be low). Of course, the larger the surface area, the more molecules are discarded.

Generally speaking, the drier the weather, the faster the evaporation.

For example, there is a saying in summer called "sauna days". It means that the temperature is high and evaporation is slow, and people can't evaporate quickly after sweating, resulting in less heat absorbed from the human body and people will feel stuffy.