A portable air quality monitoring system was developedto monitor the indoor air quality (IAQ) in a truck cabin that wasused for in-city transportation. Temperature, relative humidity,and the levels of various airborne contaminants (CO, CO2,NO2, and particles) were measured in the truck cabin betweenAugust 16 and September 20, 2005. Temperature and relativehumidity were found to be outside the comfort level recommendedby ASHRAE. The concentrations of CO, CO2, and NO2were acceptable, although the levels of CO and NO2 wereoccasionally greater than the recommended standards. Theparticle number was higher than those in a typical office.Further analyses showed that the temperature and relativehumidity in the truck cabin changed with the time of the day,while other IAQ parameters did not show obvious variation.Comparison with the field data in motorcars and airplanesshowed that the concentrations of CO and NO2 were higher inthe truck cabin than in other transportation cabins.