The scanning Kelvin probe (SKP) and FT-IR microscope have been applied for investigations of atmospheric corrosion of carbon steel, zinc and aluminum. From surface distributions of Volta (corrosion) potential and of corrosion products in presence of local NaCl contamination the areas of cathodic and anodic reactions have been identified. The passive metal surface around a local deposition is shown to participate in the corrosion process. The galvanic current created between these areas was measured with sensors. From the ratio of cathodic to anodic areas the ratio of partial current densities and the rate-determining reaction for the atmospheric corrosion process have been determined. The non-equal efficiency of partial reactions in the chloride-contaminated zone is the moving force for spreading out the cathodic or anodic front to the surrounding passive surface. For Fe and Zn a decreased efficiency of the cathodic reaction (as compared to the anodic) inside the contaminated zone involves the surrounding surface in a cathodic process. For Al an increased efficiency of the cathodic process (as compared to the anodic) produces an anodic polarization and dissolution of the surrounding surface. (C) 2004 Elsevier Ltd. All rights reserved.