Abstract:The mass concentration, size distribution and mixing state of black carbon (BC) were characterized during Beijing Paralympics using a newly developed single-particle soot photometer (SP2). The measurement showed that the average BC mass concentration was 1.65μg/m3, which was lower than the same period of former years. The average mass size distribution had one mode peaking at a BC volume-equivalent diameter of 207nm. About 56.1% of the BC particles were internally mixed, higher than other cities, suggesting local emission was relatively less. With the variation of boundary layer height and local emissions, the BC concentrations exhibited a diurnal pattern of “two peaks” peaking at 8 a.m. and 0 a.m. While the diurnal pattern of internally mixed BC percentage exhibited an opposite manner. Wind direction analysis showed that BC in urban was effected significantly by traffic emission from vehicles outside the limit area during the Paralympic Games.