[1] Total removal rate constants of OH(u = 9) by O atoms, O 2 , O 3 , N 2 , and CO 2 were measured at room temperature. Ozone photodissociation at 248 nm in a mixture containing H 2 generates O atoms and OH(u = 9) by the secondary reaction of H atoms with excess O 3 . Steady state OH(u = 9) population measurements using laser-induced fluorescence (LIF) determine the relative rate constants for OH(u = 9) removal by other species present in the gas mixture. Using available measurements of the absolute removal rate constants by O 3 and CO 2 , we extract a value of (4 ± 1) × 10 −10 cm 3 s −1 (2s) for the OH(u = 9) + O rate constant. Collisional removal by O 2 and N 2 is approximately 20 and 600 times slower, respectively. The result for OH(u = 9) + O indicates that fast O-atom processes play an important role in determining the OH emission and chemical heating rates in the middle terrestrial atmosphere.Citation: Kalogerakis, K. S., G. P. Smith, and R. A. Copeland (2011), Collisional removal of OH(X 2 P, u = 9) by O, O 2 , O 3 , N 2 , and CO 2 ,