Abstract: Dailyaverage PM₁₀ mass concentrations in Beijing and adjacent areas in August and September 2008 were significantly lower than those in 2006 and 2007. In thispaper, the reasons for the low PM₁₀ mass concentrations in Beijing duringthe Olympic Games and Paralympic Games period are studied by employing influence factor data and statistics, and using typical case diagnostic analysis with air pollution and meteorological data. Comparative analysis of wind speeds from 2006 to 2008 indicates that in Beijing from July to October 2008, the monthly average wind speed was lower than that in previous years, and the frequency of wind speeds stronger than 2 m/s was lower than in previous years. The wind speed conditions were not conducive to air pollution diffusion. The rainfall in Beijing inAugust 2008 was close to that in August 2005. However, PM₁₀ mass concentrations in August 2008 were significantly lower than that in August 2005, suggesting that precipitation was not the reason for lower monthly average PM₁₀ mass concentration. PM₁₀ daily average mass concentration evolution processes under typical similar accumulative synoptic type backgrounds in Beijing during August and September from 2006 to 2008 were compared. PM₁₀ daily mass concentration values and evolution curves in Beijing in 2008 were lower than those in previous years. Considering the above influence factors and the strict emission abatement measures, it is concluded that synoptic types and accompanying meteorological factors are the main causes of the daily average PM₁₀ mass concentration fluctuations, while synchronous emission abatement of six provinces and cities of North China is the main factor that ensured the excellent air quality during the Olympic Games and Paralympic Games.