Final answer:
Humidifier performance is primarily affected by temperature, surface area, and time of contact with the air. Altitude can also impact the efficiency due to changes in air pressure and saturation vapor densities.
Step-by-step explanation:
Three variables that affect the quality of a humidifier's performance include temperature, surface area, and time of contact. Firstly, the temperature of the environment can significantly affect evaporation rates, as higher temperatures increase the water vapor pressure, facilitating more efficient humidification. Secondly, the surface area of the water exposed to air within the humidifier influences performance; larger surface areas allow for more evaporation and thus better humidification. Lastly, the time of contact between the air and the water surface within the humidifier is crucial; longer contact times result in more effective humidity adjustment because there is more opportunity for the air to absorb moisture.
Understand that variables like altitude also play a role, as they can affect both air pressure and saturation vapor densities, thereby influencing the humidifier's efficiency. In higher altitudes, the reduced air pressure may lower the humidifier's performance because lower air pressure can lead to faster evaporation but lesser water holding capacity of the air.