A ventilation system for a mobile structure, in particular a motor vehicle, includes: a variably adjustable filter device including at least one controllable, variable filter characteristic with regard to a pollutant class; means for collecting information about the air quality in the surroundings of the mobile structure and in particular information about the air quality in an interior of the mobile structure; and a control unit for varying filter characteristics of the filter device in a variable, in particular continuous, manner, on the basis of the information about the air quality.