LABORATORY STUDIES OF ATMOSPHERIC AQUEOUS-PHASE FREE-RADICAL CHEMISTRY - KINETIC AND SPECTROSCOPIC STUDIES OF REACTIONS OF NO3 AND SO4- RADICALS WITH AROMATIC-COMPOUNDS

Recent results from kinetic and spectroscopic laboratory studies of re actions of free radicals such as NO3 and SO4- with aromatic compounds in aqueous solution at T = 298 K are presented. Three different experi mental approaches, (i) laser photolysis-visible long-path laser absorp tion, (ii) laser photolysis-UV long-path laser absorption and (iii) ti me-resolved broadband diode-array spectroscopy, have been used to inve stigate the kinetics of reactions of NO3 and SO4- with aromatics, as w ell as the formation of oxidation intermediates. For the reactions of NO3 with benzene (1), anisole (2), p-xylene (3), p-cresol (4), toluene (5), mesitylene (6) and 1,4-dimethoxybenzene (7), rate coefficients o f k(1) = (4.0 +/- 0.6) x 10(8) 1 mol(-1) s(-1), k(2) = (1.0 +/- 0.4) x 10(9) 1 mol(-1) s(-1), k(3) (1.6 +/- 0.1) x 10(9) 1 mol s(-1), k(2) = (1.0 +/- 0.4) x 10(9) mol(-1) 1 s(-1), k(3) = (1.6 +/- 0.1) x 10(9) 1 mol(-1) s(-1), k(4) = (8.4 +/- 2.3) x 10(8) 1 mol s(-1) k(5) = (1.2 /- 0.3) x 10(9) 1 mol(-1) s(-1), k(6) = (1.3 +/- 0.3) x 10(9) 1 mol(-1 ) s(-1) and k(7) = (1.0 +/- 0.3) x 10(9) 1 mol(-1) s(-1) were obtained . For the corresponding reactions of SO4- with benzene (8), toluene (9 ), p-xylene (10), p-cresol (11) and mesitylene (12), rate coefficients of k(8) = (6.4 +/- 2.5) x 10(8) 1 mol(-1) s(-1), k(9) = (1.3 +/- 0.6) x 10(9) 1 mol(-1) s(-1), k(10) = (2.7 +/- 0.9) x 10(9) 1 mol(-1) s(-1 )k(11) = (2.8 +/- 0.8) x 10(9) 1 mol(-1) s(-1) and k(12) = (1.3 +/- 0. 4) x 10(9) 1 mol(-1) s(-1) were determined. Reactivity correlations fo r both radical species with the aromatic compounds are presented and p otential applications of such correlations are discussed. In addition, the effect of ionic strength in the reactions of NO3 with benzene and toluene has been investigated. Transient intermediates have been spec troscopically identified in the reactions of the sulfate radical anion in aerated as well as in oxygen-free solutions. The nature of these i ntermediates is discussed in view of the existing literature. Finally, possible impacts of free-radical reactions with aromatic compounds on the current understanding of chemical conversion processes within tro pospheric multiphase systems are considered.