Abstract: This invention relates to a method and apparatus for purifying gases such as air of unwanted gaseous compounds, in which method the gas to be purified is brought into contact with a solution (2) that binds the unwanted gaseous compounds, and in which method the gas to be purified is caused to flow through a reactor filler (3) in a space filled with the solution that binds the unwanted gaseous compounds. At least the saturation level of the solution (2) and the surface level of the solution (2) are monitored in essence continuously, and on the basis of monitoring data the solution's saturation level and surface level are maintained essentially within predetermined limit values.