We followed over 24 hours a corrosion process in monocrystalline triangular shaped nanoparticles at a single particle level by atomic force microscopy and optical spectroscopy techniques. We observed that the corrosion starts predominantly from the tips of the particles and it creates within few hours large protrusions, which strongly suppress the plasmon character of the particles. These observations support the crystallographic model of these particles consisting of a high defect hexagonal closed packed layer. This described technique can be used to reveal kinetics of the corrosion in the nanoscale of other materials as well.