Second Derivative UV Spectroscopy Study of the Thermal and Photochemical Reaction of NO 2 with SO 2 and SO 3

The rate constants for the thermal reaction of NO 2 with SO 2 ( k 9 = (1.4 ± 0.1) · 10 −5 l/mol · s) and SO 3 ( k 10 = 88 ± 8 l/mol · s) have been determined employing second derivative UV spectroscopy. This technique was shown to be adequate to solve the problem of light scattering by aerosols always present in these systems. NOHSO 4 and H 2 O were found to strongly catalyze the NO 2 – SO 2 reaction. – The quantum yields of O 2 production and NO 2 depletion as well as the NO yield from the photolysis of NO 2 in the presence of SO 2 and/or CO 2 were determined at 366 nm as a function of SO 2 and CO 2 partial pressure at room temperature. The results were satisfactorily correlated with a reaction mechanism. – The relevance of the above reactions in urban aerosol formation are briefly commented.