We have previously shown with X-ray photoelectron spectroscopy that acetone remaining on the surface of a copper strip after degreasing, can react slowly with water vapor under ambient light to form acetic acid and cause severe corrosion. The reaction was completely inhibited in darkness. This suggested that copper reacted photochemically with acetone and water. This paper shows that acetone degreasing of the AA2024-T3, as per ASTM E1078-97 cleaning protocol, has a similar effect on constituent copper-rich intermetallic particles. When an acetone-degreased alloy was exposed to a mist of sodium chloride solution under ambient light, the formation of acetic acid together with a layer of chloride solution resulted in severe pitting. Fitting was inhibited under conditions of darkness. The slow reaction of surface-absorbed acetone with water leading to the formation of acetic acid appeared to be prevented. There was also evidence for the redeposition of dissolved copper onto the alloy matrix under conditions that induced pitting.