The air treatment unit 1 comprises a housing 3 provided with a stale air inlet opening 5 and a stale air outlet opening 7 for exhausting stale air to the environment 6. A stale air duct 8 extends between the stale air inlet opening and the stale air outlet opening. In the stale air duct a plurality of air ducts 11 extend via which the outside air flows into the cattle shed. Ventilation means 13 and 15 ensure the intake of fresh outside air and the sucking of stale air from the cattle shed to the environment 6. Spraying means 17 and atomizing means 19 are located in the stale air duct 8. The spraying means 17 serve to cool the air ducts 11 in summer, to regulate the temperature in the cattle shed and furthermore to free the outside of the air ducts from pollution caused by the stale air flowing past them. The atomizing means 19 are used for purifying the stale air that flows through the stale air duct to the environment 6.
