Number fraction of dusts composed of silica gel particles coated with 0%, 20%, 30% and 40% PBDE/F-PBDE pairs 35, 47 and 99: (A) non surface modified silica gel, and (B) endcapped silica gel (100 A pore size, 3 μm average particle size). The inset electron micrograph provides a representative image of the coated dust.