The tip of a scanning probe microscope was used to detach nanometer-scale, single crystal NaCl particles grown on soda lime glass substrates. After imaging a particle at low contact forces, a single line scan at high contact Force was used to detach the particle From the substrate. The peak lateral Force at detachment is a strong function of particle contact area and humidity. As the relative humidity is raised from low to high values, the strength of the particle-substrate bond decreases dramatically. We interpret these results in terms of detachment by chemically-assisted crack growth along the NaCl-glass interface. Numerical estimates of the electrostatic and dispersive contributions to the work of adhesion are also discussed.