Rapid quenching of O-2(a(1)Delta) in O(P-3)/O-2/O-3 mixtures has been observed. Oxygen atoms and singlet oxygen O2( a) molecules were produced by 248 nm laser photolysis of ozone. Fast collisional removal of O2( a) was found to be correlated with the presence of O atoms. Attempts to model the fast decay using the three-body quenching process O-2(a(1 Delta)) + O + O-2 -> 2O(2) + O yielded a rate constant of (1.1 +/- 0.1) x 10 (31) cm(6)/s, which is inconsistent with data obtained from. owing afterglow experiments. This result indicates that additional quenching species are generated by the secondary photochemistry. (C) 2009 Elsevier B. V. All rights reserved.