Abstract. It was formerly demonstrated that O2SOO− forms at collisions
rate in the gas phase as a result of SO2 reaction with
O2-. Here, we present a theoretical investigation of the
chemical fate of O2SOO− by reaction with O3 in the
gas phase, based on ab initio calculations. Two main mechanisms were found
for the title reaction, with fundamentally different products: (i) formation
of a van der Waals complex followed by electron transfer and further
decomposition to O2 + SO2 + O3- and
(ii) formation of a molecular complex from O2 switching by
O3, followed by SO2 oxidation to SO3- within
the complex. Both reactions are exergonic, but separated by relatively low
energy barriers. The products in the former mechanism would likely initiate
other SO2 oxidations as shown in previous studies, whereas the
latter mechanism closes a path wherein SO2 is oxidized to
SO3-. The latter reaction is atmospherically relevant since it
forms the SO3- ion, hereby closing the SO2 oxidation
path initiated by O2-. The main atmospheric fate of
SO3- is nothing but sulfate formation. Exploration of the
reactions kinetics indicates that the path of reaction (ii) is highly
facilitated by humidity. For this path, we found an overall rate constant of
4.0×10-11 cm3 molecule−1 s−1 at 298 K and 50 %
relative humidity. The title reaction provides a new mechanism for sulfate
formation from ion-induced SO2 oxidation in the gas phase and
highlights the importance of including such a mechanism in modeling
sulfate-based aerosol formation rates.