Hydrolysis of Sulfur Dioxide in Small Clusters of Sulfuric Acid: Mechanistic and Kinetic Study

Abstract

The deposition and hydrolysis reaction of SO2 + H2O in small clusters of sulfuric acid and water are studied by theoretical calculations of the molecular clusters SO2-(H2SO4)n-(H2O)m (m = 1,2; n = 1,2). Sulfuric acid exhibits a dramatic catalytic effect on the hydrolysis reaction of SO2 as it lowers the energy barrier by over 20 kcal/mol. The reaction with monohydrated sulfuric acid (SO2 + H2O + H2SO4 - H2O) has the lowest energy barrier of 3.83 kcal/mol, in which the cluster H2SO4-(H2O)2 forms initially at the entrance channel. The energy barriers for the three hydrolysis reactions are in the order SO2 + (H2SO4)-H2O > SO2 + (H2SO4)2-H2O > SO2 + H2SO4-H2O. Furthermore, sulfurous acid is more strongly bonded to the hydrated sulfuric acid (or dimer) clusters than the corresponding reactant (monohydrated SO2). Consequently, sulfuric acid promotes the hydrolysis of SO2 both kinetically and thermodynamically. Kinetics simulations have been performed to study the importance of these reactions in the reduction of atmospheric SO2. The results will give a new insight on how the pre-existing aerosols catalyze the hydrolysis of SO2, leading to the formation and growth of new particles.

Gas-phase degradation of 2-butanethiol initiated by OH radicals and Cl atoms: kinetics, product yields and mechanism at 298 K and atmospheric pressure

“…3,4,14 2-Butanethiol was detected in samples of air from sewerage treatment tanks of chemical petroleum, geothermal areas, muddy beach water and wastewater treatment plants. 2,[15][16][17][18] There are several experimental and theoretical studies of the reactions of alkyl thiols with Cl atoms and OH radicals. [19][20][21][22][23][24][25][26][27] In all cases the rates coefficients for Cl-atoms were an order of magnitude faster than the corresponding reaction with OH radical.…”

Theoretical study of the oxidation reactions of sulfurous acid/sulfite with ozone to produce sulfuric acid/sulfate with atmospheric implications

“…New models have been recently proposed for the formation of sulfate in the troposphere, clouds, aerosols, acid rain, and fog to bridge the gap between the modeled and observed sulfate. 20,[32][33][34][35] SO 2 can be quickly taken into fog and rain droplets, 36 which is followed by its liquid phase oxidation by O 3 and H 2 O 2 . 20,24,28,29,37,38 Model studies suggest that the oxidation of SO 2 in the aqueous phase results in more than 80% of the global sulfate production.…”

“…47 Recent studies have shown that SO 2 can hydrolyze to produce sulfurous acid (H 2 SO 3 ) or HSO 3 À in the gas phase in the presence of acid molecules or clusters such as water, hydrated ammonia, and hydrated sulfuric acid clusters. 33,34 In addition, sulfurous acid and bisulte were thought to be potential precursors for the formation of atmospheric aerosols. However, to the best of our knowledge, no studies have been reported on the atmospheric oxidation of H 2 SO 3 /HSO 3 À to produce H 2 SO 4 /HSO 4 À .…”

Nanoparticles grown from methanesulfonic acid and methylamine: microscopic structures and formation mechanism

“…The second method is quantum chemical calculations which can be used to obtain equilibrium structures, energies and thermochemical parameters, and for which results for a number of small clusters in the atmosphere have been reported. These theoretical studies include equilibrium structures, [35][36][37][38][39][40][41] transition states, 44,45 formation energies 36,37,[46][47][48][49][50][51] and nucleation rates. 58,59 However, quantum chemical calculations on nanosize clusters have been somewhat limited.…”