Nitrate ions, which are known as efficient inhibitors for the corrosion of aluminum, have been shown to become very aggressive in pitting of 2024 aluminum alloy in specific conditions. Plotting potentiokinetic curves and immersion tests revealed strong dissolution of 2024 alloy in nitrate solutions with or without chloride ions. Scanning electron microscopy observations showed that pitting of 2024 alloy mainly occurred on the intermetallic particles. Nitrate ions caused the dissolution of intermetallic particles whereas they acted as very good inhibitors for the aluminum matrix. However, local dissolution of the matrix has been found to occur around the Cu- and Mg-rich particles and has been quantified by using atomic force microscopy. Secondary ion mass spectroscopy and ultraviolet spectroscopy helped elucidate the mechanism of dissolution of the intermetallics. Reduction of nitrate ions to nitrite ions and then to ammonia on intermetallics induced pitting nucleation on these particles. Copper redeposition occurred and dissolution of the surrounding matrix was observed. (C) 2003 The Electrochemical Society.