Technical Abstract: Wind erosion only occurs when the friction velocity exceeds the threshold friction velocity (TFV) of the surface. The TFV of loessial soils commonly found across the Columbia Plateau region of the U.S. Pacific Northwest is virtually unknown even though these soils are highly erodible and a source of fine atmospheric particulates that reduce air quality in the region. The TFV of a sandy loam and four silt loams collected from field sites in eastern Washington was determined by systematically measuring the temporal variation in wind speed, saltation activity, and PM10 (particles with an aerodynamic diameter of less than or equal to 10 µm) and TSP (total suspended particulate matter) concentrations above the soil surface inside a wind tunnel. The erodible fraction of each soil type, obtained by drying and screening the soil, was placed in a tray inside the wind tunnel. The TFV for the sandy loam was 0.139 m s-1 whereas the TFV for the four silt loams ranged from 0.189-0.252 m s-1. The surface of the sandy loam was also aerodynamically smoother than that of two silt loams, possibly a result of a smaller size fraction of larger soil aggregates or particles on the surface of the sandy loam. The TFV’s measured in this study were lower than those previously observed in the field in the Columbia Plateau and also lower than the minimum TFV required to initiate erosion in some wind erosion models. These low TFV’s may contribute to the occasional poor performance of wind erosion models in the region.