In addition, we obtained ambient air pollution data provided by the Taiwan Environmental Protection Adminis-tration (TEPA) from one fixed-site monitoring station (Guting station) in downtown Taipei. Guting station is located in the center of our study area. The station was placed on the roof of a three-story building, which is 14 m above the ground level and 40 m away from main traffic roads. The fixed-site air monitoring data of PM10 and PM2.5 were used to compare with personal monitoring of commuter exposures of the same sampling periods. PM1.0 was not measured at the fixed-site station.