The kinetics of the glyoxal + HO2 reaction have been investigated using computational chemistry and statistical reaction rate theory techniques, with consideration of a novel pathway that results in the conversion of HO2 to OH. Glyoxal is shown to react with HO2 to form an a-hydroxyperoxy radical with additional alpha-carbonyl functionality. Intramolecular H atom abstraction from the carbonyl moiety proceeds with a relatively low barrier, facilitating decomposition to OH + CO + HC(O)OH (formic acid). Time-dependent master equation simulations demonstrate that direct reaction to form OH is relatively slow at ambient temperature. The major reaction product is predicted to be collisionally deactivated HC(OH)(OO)CHO, which predominantly dissociates to reform the reactants under low-NOx conditions. The mechanism described here for the conversion of OH to HO2 is available to a diverse range of carbonyls, including methylglyoxal, glycolaldehyde, hydroxyacetone, and glyoxylic acid, and energy surfaces are reported for the reaction of these species with HO2.