Abstract:β-ray continuous ambient particulate monitor and aethalometer were employed to investigate the pollution characteristics of PM25 and the black carbon aerosol (BC)at a northwest suburban site of Beijing from July 21 to August 6, 2010.The results indicated that the mass concentration of PM25 and BC were (13316±8164)μg/m3 and (289±162)μg/m3, respectively. Affected by the obvious mountain-valley wind, the mass concentration of PM25 and BC increased when the contaminated air came from Beijing urban areas, which located in southeast of the observation place, and decreased when the relatively sanitary airflow came from mountain areas, which located in northwest of the observation place. The mass concentrations of PM25 and BC displayed obvious diurnal variation characteristics and significantly increased during forenoon, nightfall and night due to local emissions, regional transportation and meteorological conditions.