Using pulse radiolysis combined with UV absorption spectroscopy, upper limits for the rate constants of the reaction of the FO2 radical with O-3, CH4, and CO were determined to be < 3.4 x 10(-16), < 4.1 x 10(-15), and < 5.1 X 10(-16) cm(3) molecule(-1) s(-1), respectively. The rate constants for the reactions of FO2 radicals with NO and NO2 were measured : FO2 + NO --> FNO + O-2 (10a); FO2 + NO2 --> products (11). The rate constants for reactions 10 and 11 were determined to be (1.47 +/- 0.08) x 10(-12) and (1.05 +/- 0.15) x 10(-13) cm(3) molecule(-1) s(-1), respectively. Reaction 10a was found to give FNO in a yield of 100 +/- 14%. As a part of this work, an upper limit of the reaction of FO radicals with O-3 was determined to be < 1.2 x 10(-12) cm(3) molecule(-1) s(-1). Results are discussed in the context of the atmospheric chemistry of the FO2 radical and hydrofluorocarbons.