Fouling of compressor blades is an important mechanism leading to performance deterioration in gas turbines over time. Experimental and simulation data are available for the impact of specified amounts of fouling on the performance as well as the amount of foulants entering the engine for defined air filtration systems and ambient conditions. This study provides experimental data on the amount of foulants in the air that actually stick to a blade surface for different conditions. Quantitative results both indicate the amount of dust as well as the distribution of dust on the airfoil, for a dry airfoil, and also the airfoils that were wet from ingested water, in addition to, different types of oil. The retention patterns are correlated with the boundary layer shear stress. The tests show the higher dust retention from wet surfaces compared to dry surfaces. They also provide information about the behavior of the particles after they impact on the blade surface, showing for a certain amount of wet film thickness, the shear forces actually wash the dust downstream and off the airfoil. Further, the effect of particle agglomeration of particles to form larger clusters was observed, which would explain the disproportional impact of very small particles on boundary layer losses.