The present application relates to an apparatus for purifying and/or humidifying air, and a related method for purifying and/or humidifying air. The apparatus comprises a rotary filter (1), a fan (9, 10) for passing air through the rotary filter (1), and a reservoir (4, 5), and wherein the rotation speed of the rotary filter (1) and the settings of the fan (9, 10) depend on the ambient relative humidity and ambient gas pollutant concentration. The apparatus combines the feature of chemisorption with the use of a rotary filter (1), thereby providing an apparatus which is able to purify air and/or regulate the ambient humidity based on humidity levels and levels of a target gas pollutant in the air. The invention removes the need for a pump for liquid transport, removes the need for frequent and expensive filter changes by the user, and instead only requires the user to periodically refresh the filtration solution in the reservoir (4, 5).