Sulfuric Acid Formation via H₂SO₃ Oxidation by H₂O₂ in the Atmosphere

Abstract

With the help of quantum mechanical methods, the formation of H2SO4 by the oxidation of H2SO3 with H2O2 was studied theoretically. Both stepwise and concerted mechanisms were calculated. It was found that the direct oxidation of H2SO3 by H2O2 alone requires prohibitive activation energies of >38.6 kcal/mol. However, the addition of one water molecule exhibits a strong catalytic effect that dramatically reduces the overall reaction barrier to 6.2 (2.3 with PCM) kcal/mol. The deprotonated HSO3 – species also reduces the overall reaction barrier to 5.6 (−5.8 with PCM) kcal/mol. Both of these proceed via concerted pathways. On the other hand, the stepwise mechanisms generally produce intermediates with a hydroperoxy group (−O–O–H), which is a result of a nucleophilic attack by the oxygens of H2O2. While studying the catalytic effect of water, a previously unknown hydroperoxy intermediate (HOO)­S­(OH)3, where sulfur is coordinated with three OH groups, was found. This work also reveals a rearrangement step of another hydroperoxy intermediate (HOO)­SO2 – to HSO4 – that was found in earlier experimental studies. For all of the mechanisms calculated, the final H2SO4 is formed with a significant exothermicity of >60 kcal/mol. In general, even without sunlight, it was found that the formation of sulfuric acid by hydrogen peroxide can occur in a heterogeneous moisturized environment.

Reaction of Criegee Intermediates with SO2─A Possible Route for Sulfurous Acid Formation in the Atmosphere

“…The above studies clearly show that the CIs contribute significantly to the oxidation of SO 2 and the formation of sulfur-containing species in the atmosphere. As reported in an earlier study, one of the sources for H 2 SO 4 in the atmosphere is the oxidation reaction of sulfurous acid (H 2 SO 3 ) which was detected in the atmosphere . Therefore, it is important to explore the possibility of the formation of H 2 SO 3 and other acids from the reaction of CIs with SO 2 in the atmosphere.…”

“…It has been shown in earlier studies that the oxidation of CIs by SO 2 results in the formation of sulfuric acid and sulfate aerosol. ,− Mauldin et al reported that in the lower region of the troposphere, the oxidation of SO 2 by CIs is more significant than the oxidation of SO 2 by OH radicals. Welz et al studied the reaction of CH 2 OO with SO 2 at 298 K by using photoionization mass spectrometry and reported a rate constant of (3.9 ± 0.7) × 10 –11 cm 3 molecule –1 s –1 .…”

“…As reported in an earlier study, one of the sources for H 2 SO 4 in the atmosphere is the oxidation reaction of sulfurous acid (H 2 SO 3 ) which was detected in the atmosphere. 33 Therefore, it is important to explore the possibility of the formation of H 2 SO 3 and other acids from the reaction of CIs with SO 2 in the atmosphere. To the best of our knowledge, the reaction on CIs with SO 2 that results in the formation of H 2 SO 3 without any catalyst has not been studied theoretically.…”

Modelling SO2 conversion into sulfates in the mid-troposphere with a 3D chemistry transport model: the case of Mount Etna's eruption on 12 April 2012

“…One pathway for oxidation of S(+IV) to S(+VI) in the aqueous phase is the reaction of HSO − 3 with hydrogen peroxide H 2 O 2 (e.g. Shostak et al, 2019).…”

Modelling SO<sub>2</sub> conversion into sulphates in the mid-troposphere with a 3D chemistry-transport model: the case of Mount Etna's eruption on April 12, 2012

“…One pathway for oxidation of S(+IV) to S(+VI) in aqueous phase is reaction of HSO − 3 with hydrogen peroxyde H 2 O 2 (e.g. Shostak et al (2019)):…”