[First flush analysis of PAHs in roof runoff in Beijing]

Roof runoff samples of six storm events were collected at three different sites in the urban area of Beijing during the rainy season of 2008. The samples were analyzed for PAHs in both particle and dissolved phases. On the basis of the field measured data, the first flush phenomenon of PAHs was quantitatively analyzed using a newly defined FF(n-Max), and the influences of the storm event characteristics were discussed. In roof runoff, the first flush phenomena of total PAHs and PAHs in particle phase were noted, and PAHs in dissolved phase was not observed with first flush. The ranges of the first flush values for FF25 and FF30 were 0.6-2.4 and 0.6-2.1, respectively. For different types of roof materials, the strength of the first flush followed the order of: tile roof, cement roof > asphaltic felt roof. There is no significant difference between the tile roof and cement roof. No significant correlation was observed between the occurrence of first flush and the rainfall characteristics.