Hydroxysulfinyl radical (HOSO) is important due to its involvement in climate geoengineering upon SO2 injection and generation of the highly hygroscopic H2SO4. Its photochemical behavior in the upper atmosphere is however uncertain. Here we present the ultraviolet-visible photochemistry and photodynamics of this species simulating the atmospheric conditions with highlevel quantum chemistry methods. Photocleavage to HO + SO arises as the major solar-induced channel with a minor contribution of H + SO2 photoproducts. The efficient generation of SO is relevant due to its reactivity with O3 and the consequent depletion of ozone in the stratosphere
