The organic colorant curcumin (1, 7-bis(4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3,5-dione) was exposed to ozone in purified air in the dark, and the exposed samples were analyzed by mass spectrometry. The major reaction products included vanillin (4-hydroxy-3-methoxybenzaldehyde) and vannillic acid (4-hydroxy-3-methoxybenzoic acid). These products and the corresponding loss chromophore (i.e., fading of curcumin) are consistent with a reaction mechanism involving electrophilic addition of ozone onto the olefinic bonds of curcumin. Vanillin and vanillic acid did not react with ozone under the conditions of this study. -- CAL