A laboratory study of the effect of CO2 and NaCl on the atmospheric corrosion of aluminum is reported. The samples were exposed to pure air with 95% relative humidity and the concentration of CO2 was <1 and 350 ppm, respectively. Sodium chloride was added before exposure (0, 14, and 70 g/cm(2)). The main result is that the NaCl-induced atmospheric corrosion of aluminum is about 10 to 20 times faster in CO2-free humid air compared to air containing ambient levels of CO2. It is suggested that the rapid corrosion of aluminum coated with NaCl in humid CO2-free air is connected to high-pH areas in the surface electrolyte that develop due to the cathodic reduction of oxygen. The anodic dissolution of aluminum is known to be enhanced by high pH. The unexpected corrosion-inhibitive effect of CO2 is explained by the neutralization of the surface electrolyte. In the absence of CO2, bayerite, Al(OH)(3), forms. Only minute amounts of carbonate were found on the surface after exposure to CO2-containing air.