The reactions of SO3 with HO2 radical and H2O⋯HO2 radical complex. Theoretical study on the atmospheric formation of HSO5 and H2SO4

Abstract

The influence of a single water molecule on the gas-phase reactivity of the HO(2) radical has been investigated by studying the reactions of SO(3) with the HO(2) radical and with the H(2)O...HO(2) radical complex. The naked reaction leads to the formation of the HSO(5) radical, with a computed binding energy of 13.81 kcal mol(-1). The reaction with the H(2)O...HO(2) radical complex can give two different products, namely (a) HSO(5) + H(2)O, which has a binding energy that is computed to be 4.76 kcal mol(-1) more stable than the SO(3) + H(2)O...HO(2) reactants (Delta(E + ZPE) at 0K) and an estimated branching ratio of about 34% at 298K and (b) sulfuric acid and the hydroperoxyl radical, which is computed to be 10.51 kcal mol(-1) below the energy of the reactants (Delta(E + ZPE) at 0K), with an estimated branching ratio of about 66% at 298K. The fact that one of the products is H(2)SO(4) may have relevance in the chemistry of the atmosphere. Interestingly, the water molecule acts as a catalyst, [as it occurs in (a)] or as a reactant [as it occurs in (b)]. For a sake of completeness we have also calculated the anharmonic vibrational frequencies for HO(2), HSO(5), the HSO(5)...H(2)O hydrogen bonded complex, H(2)SO(4), and two H(2)SO(4)...H(2)O complexes, in order to help with the possible experimental identification of some of these species.

Parameterisation and impact of aerosol uptake of HO<sub>2</sub> on a global tropospheric model

“…However, the majority of aerosol surface area in the troposphere is not dry sea salt. For other aerosol types (such as sulfate) the observed kinetics suggest other reactions may occur (Cooper and Abbatt, 1996;Gonzalez et al, 2010). Reaction with sulfur-compounds in the aerosol (forming water and sulfate) have also been suggested as alternative reaction products (Mao et al, 2010).…”

“…The dot-dash line indicates the temperature dependence of the parameterisation in this work (assuming 50% relative humidity). The black dotted line indicates a value of 0.2, as recommended by , and the dashed black line indicates the parameterisation of Thornton et al (2008) (Cooper and Abbatt, 1996;Gonzalez et al, 2010) which would not lead to H 2 O 2 production. Only one laboratory study indicates that H 2 O 2 is the product of the reaction (Loukhovitskaya et al, 2009).…”

Perspective: Water cluster mediated atmospheric chemistry

“…40 The influence of water on the gas phase reactivity of OH and HO 2 with other molecules such as SO 3 , CH 4 and DMS has been investigated with varying conclusions about the potential for water catalysis. 35,101,102 The unstable radical HOOO can form water complexes with longer atmospheric lifetimes than the HOOO radical, allowing for the possibility of reaction with other species. However, the atmospheric importance of this radical water complex depends on its stability, which is currently under investigation.…”

Understanding the catalytic role of oxalic acid in the SO<sub>3</sub> hydration to form H<sub>2</sub>SO<sub>4</sub> in the atmosphere

“…These atmospheric HAT reactions have a main feature that two-point hydrogen bond can occur and can facilitate hydrogen atom transfer (Kumar et al, 2016). The presence of water, acid and 5 other catalysts, as the hydrogen donors and acceptors, contributes to the formation of two-point hydrogen bond (Vöhringer-Martinez et al, 2007;da Silva, 2010;Gonzalez et al, 2010;Bandyopadhyay et al, 2017). Thus, the effect of catalysts on promoting atmospheric HAT reactions has attracted more attention of atmospheric scientists.…”