As part of the PRIDE-PRD2006 intensive cam paign, atmospheric boundary layer (ABL) measurements were performed in Qingyuan, Panyu, and Xinken over the Pearl River Delta (PRD) on 1-30 July 2006.During the sum mer, the surface winds over the PRD are generally controlled by the south, usually with vertical wind shear at a height of approximately 800 m.Subsidence and precipitation from a tropical cyclone affects the air quality of the PRD.Under subsidence, wind speed in the ABL and the height of the ABL decrease and result in high-level concentrations.When the background wind speed is small or calm, the wind pro file in Panyu and Xinken changes dramatically with height,which is perhaps caused by local circulation, such as sea land breezes.To better understand the ABL of the PRD,simulations that used the Weather Research and Forecast ing (WRF) mesoscale model were utilized to analyze the ABL characteristics over the PRD.Based on three types of weather condition simulations (i.e., subsidence days, miny days, and sunny days), the WRF model revealed that the sim ulated temperature and wind fields in these three cases were moderately consistent with the measurements.The results showed that diurnal variations of the ABL height on subsi dence days and sunny days were obvious, but diurnal vari ations of the ABL heist on rainy days were not apparent.The ABL is obviously affected by local circulation, and the ABL features are different at various stations.A simulation focused on a high pollution episode during the subsidence days on 12-15 July 2006, occurred under high-pressure con ditions, accompanied by the tropical cyclone "Bilis".A com parison of the simulated vertical wind fields and temperature structure with the ABL measurements at Xinken, Panyu, and Qingyuan stations found that the modeled and measured at mospheric fields revealed two different types of ABL char acteristics over the PRD.When the surface winds over the PRD were light or nearly calm, the local circulation domi nated, such as the sea-land breeze at Xinken station and the mountain-valley circulation at Qingyuan station.When the surface winds were strong, the stations were under the same background weather system, and the wind directions were almost the sume.Furthermore, the modeled results also sug gest that the subsidence by the typhoon "Bilis" had a great impact on the high Air Pollution Index (API).