The rate constant and product ion distribution of the reactions of H 3 O + , NO + and O 2 •+ with methyl vinyl ketone (MVK), methacrolein (MaCR), pivaldehyde, 2-methyl-butanal, glyoxal, o-, m-and p-tolualdehyde have been investigated at 150 Pa and 297 K using a selected ion flow tube (SIFT). All reactions, except the NO + /glyoxal reaction, proceed at a rate close to the collisional rate, calculated with the Su and Chesnavich model, using the polarizability and electric dipole moment of the compounds derived from quantum chemical calculations. All H 3 O + reactions proceed by proton transfer, non-dissociative for all compounds, except for 2-methyl-butanal, where two minor channels resulting from fragmentation after protonation are observed. Association is the only pathway in the NO + /MVK and NO + /glyoxal reaction. Hydride ion transfer is the major process occurring in all the other NO + reactions. Elimination of CHO for pivaldehyde and association for MaCR are also non-negligible channels in their reaction with NO +. All O 2 •+ reactions result in the parent cation by charge transfer and in at least one fragment ion. Hydration of the product ions has been investigated by adding water vapor in the reaction zone. A method is proposed to derive the three-body association rate constants of the product ions with water and to estimate the rate constants of the reactions of the hydrated precursor ions H 3 O + ·H 2 O and NO + ·H 2 O with the reactants.