Response to Comment on “Modeling Maximum Adsorption Capacities of Soot and Soot-like Materials for PAHs and PCBs”

A comment by John C. Fetzer on modeling maximum adsorption capacities of soot and soot-like materials for PAH and PCB and the adsorption behavior of PAH on soots and on other adsorptive materials is presented. The authors (van Noort et al.) base their model on van der Waal's forces only. This may be a valid assumption for bioavailable PAH. These weak forces allow extraction by rain or surface water, and the equilibria are solubility limited. The PAH adsorb more strongly than just due to van der Waal's forces through the interactions of the ¿ electrons with those of the partially graphitic structures in soots and other solid combustion products. In the paper by Fetzer and Rechsteiner, they looked at soots, carbon blacks, and diesel particulate. Fetzer later work on fullerene-rich soots and other materials. There is no absolute definable level of total PAH. The solvent sequence used was dichloromethane, chlorobenzene, and 1,2,4-trichlorobenzene, with hexane as a starting solvent for some types of samples. The defined PAH in many materials, including standard reference materials, is defined by desorption conditions. A response to the comment by van Noort et al. is also presented. They doubt the theory of Fetzer that "PAH adsorb more strongly than just due to van der Waal's forces through the interactions of the ¿ electrons with those of the partially graphitic structures in soots and other solid combustion products". In fact this may not be the case as it has been shown that adsorption of aromatic compounds onto carbon surfaces can be quantitatively described on the basis of van der Waals interactions only. The comments illustrate that further work is needed on both the molecular characterization of adsorption on carbon surfaces and on the morphological characteristics of carbon sorbents influencing this sorption.