Distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans in various sizes of airborne particles

We investigated the particle size distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in atmospheric samples collected at four sites. The largest amounts of particle-bound PCDD/F were found on small particles with aerodynamic diameters (dae) of less than 1.1μm that accounted for over 50% of the total PCDD/F, contributing mostly to the toxicity and providing over 47% of the total TEQs (Toxicity Equivalents) loading. PCDF showed about twice the concentration of the PCDD in the total TEQs. The total PCDD/F concentration for accumulation mode particles (dae<1.114m) ranged from 8.2 to 16 pg/m3 and that on coarse particles (daeal.l1μm) from 3.5 to 8.6 pg/m3. Five to eight percent of the total PCDD/F was found on large particles of dae>71μm. It was observed that the PCDD/F homologue profiles on large particles were different from the small particles and the fraction of less chlorinated PCDD/F in the homologue groups increased with increasing particle size. The reentrainment of soil particles including PCDD/F did not significantly influence the PCDD/F on the large particles. Two plausible mechanisms, the mass transfer of the gas phase PCDD/F on the particle surface and the contribution of the large size fly ash emitted from incinerators are proposed to explain the observed PCDD/F homologues partitioning among particle size fractions.