“…Several recent studies have revealed the formation of OSs from photooxidation of anthropogenic precursors, such as polycyclic aromatic hydrocarbons (Riva et al, 2015) or long‐chain alkanes (Riva, Barbosa, et al, 2016), on sulfate seed particles. Moreover, direct formation of OSs from uptake of gaseous SO 2 by unsaturated fatty acids (Passananti et al, 2016; Shang et al, 2016) and organic peroxides (Wang, Zhou, et al, 2019) and OS formation from reaction of hydrogen sulfite with unsaturated carbonyl compounds in the presence of Fe 3+ (Huang, Cochran, et al, 2018) have been reported. However, the atmospheric relevance of these processes has yet to be elucidated.…”