Inhomogenities of the b* surface component of the CDW wave vector, probed by LT-UHV-STM, were observed at the (-201) surface of quasi-1D blue bronze Rb0.3MoO3cleaved in-situ. Whereas on the scale of tens of nanometers, the CDW wave vector might be constant, significant changes were observed on the scale of microns in STM measurement. On the basis of first-principles DFT calculations, it is found that these inhomogenities could be due to a change in the stoichiometry of surface alkali atoms taking place after the cleavage process. It is shown that differences in the stoichiometry of surface alkali atoms change the filling of the partially filled bands of the top most layer. Consequently, in equilibrium with the bulk layers, this results in a local surface potential that changes the surface nesting vector and hence the periodicity of the CDW modulation. The DFT predictions for the changes in surface nesting vector are consistent with the observed experimental inhomogenities probed by STM. © 2007 IOP Publishing Ltd.