MATERIAL AND METHODS This study was conducted on a road simulator, which consists of four electrically driven wheels running on a circular track. The simulator was fitted with studded tires of a type which is commonly used on Light Duty Vehicles (LDV) in the Scandinavian countries during the winter season and the pavement is typical for city streets. The particles were measured with an Aerodynamic Particle Sizer (APS, model 3021, TSI Inc., USA) equipped with a PM10-inlet. After the road simulator is started and accelerated to 70 km/h the particle concentration builds up and reaches a steady state. The measured change in concentration of each APS-channel over time can be described by assuming a box model.