The influence of O-3 in combination with SO2 in the ppb range on the atmospheric corrosion of copper was investigated using on-line gas analysis and gravimetry. Corrosion products were characterized qualitatively by x-ray diffraction and quantitatively by gravimetry and ion-chromatography of leaching solutions. Mechanisms are suggested for the interaction of O-3 with the copper surface and for the sulfation process. The accelerating effect of O-3 added to SO2 is considerable at 70% relative humidity resulting in the formation of large amounts of cuprite and sulfates. At 90% relative humidity the effect of O-3 is moat marked at high SO2 concentrations that otherwise tend to inhibit copper corrosion. In combination with SO2, O-3 is a more powerful corrosion accelerator than NO2. The influence of the two oxidizers on the corrosion process is basically different. O-3 favors the formation of massive amounts of cuprite, while only small amounts are formed in the presence of NO2.