Nanomaterials are being produced and used in increasingly significant amounts. Although they can enter the environment in a number of ways, little is known about their fate or environmental implications as emerging contaminants. To understand the transport of nanomaterials in the unsaturated zone, the dynamic adsorption of nanomaterials to the air-water interface during primary drainage was studied in laboratory experiments using two different sizes of glass beads. Three similarly-sized nanomaterials were selected for this work: polystyrene latex nanospheres, and tin oxide (SnO2) and titanium dioxide (TiO2) nanopowders. Measurements involved tracking the concentration decrease of nanomaterials in the pore solution due to adsorption to air-water interfaces created during drainage, and simultaneous tracking of capillary pressure and saturation in the porous medium. A continuous mass balance was used to calculate the mass of nanomaterials adsorbed at air-water interfaces. Results indicate that total mass adsorbed to air-water interfaces increases with decreasing saturation, as more interfacial area is formed. However, normalization to measured interfacial areas indicates that for most systems, the adsorbed nanomaterial mass per unit area is approximately the same for both sizes of glass beads over a wide range of saturations. Experiments with three different concentrations of SnO2 showed increased adsorption at the air-water interface with increasing concentration. Differences between the adsorption behavior of the three nanomaterials will be discussed.