TA6 Atmospheric Transport and Fate
202 Oregon Ballroom
8:00 AM - 12:00 PM, Tuesday
() A dual two-dimensional adsorbed gas model for adsorption onto black carbon.
van Noort, P.C.M.1, 1 RIZA, Lelystad, The Netherlands
ABSTRACT- Low-polarity organic compounds adsorb onto black carbon (BC) as a result of van der Waals forces. Literature data suggest that the difference in enthalpy between the BC adsorbed state and the pure solid state is negligible. Therefore, the equilibrium constant for BC adsorption from the pure solid can be expected to be determined by the entropy only. Adsorbed organic compounds can be considered to be in a two-dimensional gas state. It will be proposed that there are two types of BC adsorption sites. On one type of site, adsorbed compounds are translationally unrestricted in the two-dimensional plane, leading to an entropy of adsorption of about 82 J/mol.K for rigid aromatic compounds such as chlorobenzenes, PAHs, and PCBs. On the other type of site, translationally restrictions result in an entropy of adsorption of about 31 J/mol.K. In many cases, the number of sites imposing translational restrictions is about equal to the number of translationally unrestricted sites. Consequently, at low concentrations in air or water, translationally unrestricted BC adsorption can be expected to dominate.
Key words: thermodynamics