Oxidation of Heterocycles in the Atmosphere: Kinetic Study of Their Reactions with NO3 Radical

The fast-flow-discharge technique has been used to determine the absolute rate coefficients for the gas-phase reactions of the NO 3 radical with a series of five-membered heterocycles (furan, pyrrole, tetrahydrofuran, and tetrahydrothiophene). The experiments involved monitoring the NO 3 radical by laser-induced fluorescence. The influence of temperature was studied in the range 260−345 K for the reactions of NO 3 with furan, tetrahydrofuran, and tetrahydrothiophene, and the proposed Arrhenius expressions are respectively k = (1.3 ± 0.8) × 10 -13 exp[(700 ± 200)/ T ] (cm 3 molecule -1 s -1 ), k = (2 ± 2) × 10 -9 exp[−(3800 ± 400)/ T ] (cm 3 molecule -1 s -1 ), and k = (1 ± 1) × 10 -13 exp[(1000 ± 200)/ T ] (cm 3 molecule -1 s -1 ). For the reaction of NO 3 with pyrrole, only an upper limit value (<1.8 × 10 -10 cm 3 molecule -1 s -1 ) of the rate constant at 298 K is given due to decomposition processes observed in the flow tube. The rate coefficients obtained were compared with those from previous studies carried out using different techniques. The differences in the rate constants and the activation energies suggest different reaction mechanisms for the studied reactions. Mean atmospheric lifetimes for these compounds have been calculated in relation to their reactions with NO 3 and OH radicals.