Ventilation of air in a vehicle is one of the important characteristics to maintain the indoor air quality, and the ventilation performance changes depending on the driving and other conditions. The present study evaluated the ventilation performance through the continuous measurements of airborne particulate matters in a moving vehicle under various conditions including driving speed, flow rate of air from an air-conditioner, window opening, and particle emitting. Cigarettes were used as a source of particles. One cigarette was smoked at 7 puffs/min in a vehicle. Light scattering photometers were used for measuring the aerosol concentration at 10 s interval. Driving speed was kept constant at zero (stopping), low (20 km/h), medium (40 km/h) and high (100 km/h). The ventilation performance was evaluated by using the apparent air change rate and the decay rate of aerosol concentration in the vehicle. The aerosol concentration decay rate was the ratio of the concentration just after smoking (2.5 minute average) and the concentration during smoking (6.5 minute average). As a result, we found that the ventilation performance during the moving is much better than that during stopping, and the apparent air change rates changed 28.2-93.5 h-1 during moving and 9.5 h-1 during stopping and air-conditioner-off condition.
