During absorptive concentration air loaded with the volatile organic compounds (VOC) is introduced to a cleaning liquid and taken by it. During multiple absorber steps the air is cleaned to a desired limit value and the liquid is loaded to a maximum with the VOC. The liquid is released from the VOC in a desorption column and can be reused again for cleaning of the air. During the regeneration (desorption) the cleaning is liquid heated and got into contact with a small air stream. The VOC moves from the liquid to the air and enrich it. By this procedure a high concentration of VOC in the desorption air can be achieved.