An analysis has been carried out of the different approaches used to describe partitioning between the gas and aerosol particulate phases. The equation of Junge ( Fate of Pollutants in the Air and Water Environments, edited by I.H. Suffet, Part I, pp. 7–26, Wiley, New York, 1977) has been shown to be based on a linear Langmuir isotherm, and as such has been shown to be equivalent to the equation of Yamasaki et al. ( Environ. Sci. Technol. 16, 189–194, 1982). Prior to this work, Bidleman and Foreman ( The Chemistry of Aquatic Pollutants, edited by R.A. Hites and S.J. Eisenreich, ACS Advances in Chemistry Series, 1987) developed a parameterization describing an equivalence between these two equations that is applicable when the enthalpy of desorption ( Q 1) from the paniculate matter surface is similar to the enthalpy of vaporization ( Q v ) of the pure liquid compound. That parameterization is valid when ¦ Q 1- Q v ¦ is significantly less than 1 kcal mole −1. A fundamental consideration of the process of gas/solid partitioning is used in this work to develop predictive equations for the value of the equilibrium constant K Y = c g (TSP Y) c p where c g and c p are the gas phase and paniculate phase-associated concentrations (ng m −3), respectively, and TSP Y is the concentration of suspended paniculate matter (ng m −3). In particular, it is derived that for a given compound, log K Y = −Q 1 (2.303 RT) + log [ 2.53 × 10 5 (M T) 1 2 /A tsp t O ] where R = gas constant, T = temperature, M = mol. wt, A tsp = specific surface area for the paniculate matter and t 0 is a characteristic molecular vibration time. In terms of the vapor pressure p o (torr) of a compound or series of compounds, K Y = 1.6 × 10 4p o N sA tspTexp [ (Q 1- Q v) RT ] where N s is the number of moles of sorption sites per cm 2 of particulate matter surface area. When sorption to the surface is liquid-like (i.e. ¦Q 1- Q v¦∼-0 ), then K y = 1.6 × 10 4p o N sA tspT