Application of the Junge- and Pankow-equation for estimating indoor gas/particle distribution and exposure to SVOCs

In the indoor environment, distribution and dynamics of an organic compound between gas phase, particle phase and settled dust must be known for estimating human exposure. This, however, requires a detailed understanding of the environmentally important compound parameters, their interrelation and of the algorithms for calculating partitioning coefficients. The parameters of major concern are: (I) saturation vapor pressure (P_S) (of the subcooled liquid); (II) Henry's law constant (H); (III) octanol/water partition coefficient (K_OW); (IV) octanol/air partition coefficient (K_OA); (V) air/water partition coefficient (K_AW) and (VI) settled dust properties like density and organic content. For most of the relevant compounds reliable experimental data are not available and calculated gas/particle distributions can widely differ due to the uncertainty in predicted Ps and K_OA values. This is not a big problem if the target compound is of low (<10 ^{- 6} Pa) or high (>10 ^{- 2} Pa) volatility, but in the intermediate region even small changes in Ps or K_OA will have a strong impact on the result. Moreover, the related physical processes might bear large uncertainties. The K_OA value can only be used for particle absorption from the gas phase if the organic portion of the particle or dust is high. The Junge- and Pankow-equation for calculating the gas/particle distribution coefficient K_P do not consider the physical and chemical properties of the particle surface area. It is demonstrated by error propagation theory and Monte-Carlo simulations that parameter uncertainties from estimation methods for molecular properties and variations of indoor conditions might strongly influence the calculated distribution behavior of compounds in the indoor environment