An air purifier allows the air to pass through a series of filters. These filters remove contaminants and dust particles from the air.
A humidifier adds moisture to the air. Hence, it is useful and soothing for those suffering from sinus and respiratory tract irritation due to dry air.
An air purifier is a better option for purifying contaminated air and removing lousy odor while a humidifier works well in dry climates for increasing the humidity level in the room.