Which factor generally has the least effect on evaporation rates?

Chemical concentration in water generally has the least effect on evaporation rates compared to other factors. This is primarily because evaporation is primarily influenced by the physical properties of water, not by the solutes dissolved in it. While the presence of certain chemicals can affect the vapor pressure of water, in most typical circumstances, such as evaporation from a body of water, the impact of temperature, wind speed, and relative humidity plays a more significant role.

Temperature directly affects the kinetic energy of water molecules; higher temperatures increase evaporation rates. Wind speed enhances evaporation by removing vapor-laden air from the surface of the liquid, allowing more molecules to escape. Relative humidity affects the rate of evaporation since higher humidity levels reduce the concentration gradient between the water surface and the air, which can slow down the process.

While chemical concentration can alter the physical characteristics of water—such as its boiling point or surface tension—the fundamental process of evaporation is predominantly governed by temperature, wind speed, and humidity. Therefore, while chemical concentration may have a role, it is typically much less pronounced than the other factors listed.