Mass transfer from air to the liquid phase is a key parameter controlling the efficiency of air cleaning biofilters. Especially the removal of sparingly soluble organic compounds such as volatile odorous sulfur compounds is mass transfer limited. When determining mass transfer rates of sparingly soluble organic compounds the approach have been to either conduct measurements using highly soluble compounds or sparingly soluble compounds with chemical removal of the compounds in the water phase to maintain maximum mass transfer. These data may, therefore, not represent the correct mass transfer rates for sparingly soluble compounds. As a consequence existing mass transfer models may not be accurate for these compounds. In addition most studies of mass transfer in granular media are based on materials consisting of uniform particles. This study investigates the impact of particle size (considering materials with multiple particle sizes), gas velocity and contaminant chemical properties on the overall volumetric mass transfer coefficient based on direct measurements (without the use of chemical reactions) of volatile, sparingly soluble, odorous organic compounds in granular media. Mass transfer was found closely related to particle size, compound solubility, particle size range, specific surface area and gas velocity. Predictive models linking mass transfer, gas velocity, contaminant solubility, media specific surface area, particle size and medium CO2 mass transfer were developed. (C) 2013 Elsevier B.V. All rights reserved.