Abstract: An air-conditioning system for a vehicle includes at least one sensor unit which senses an air-quality-relevant variable of the air of the passenger compartment of a vehicle, an evaluation and control unit which evaluates the air-quality-relevant variable and an air-purification device which purifies the air of the passenger compartment in a circulation mode or in a fresh air mode or in a mixed air mode. The evaluation and control unit activates the air-purification device if the air quality of the passenger compartment satisfies at least one predefined criterion. A starting signal in the state of rest of the vehicle activates the air-conditioning system which then determines the current air quality in the passenger compartment and activates the air-purification device as a function of the current air quality in the passenger compartment. The air-purification device purifies the air of the passenger compartment before a time of departure.