Criegee intermediates are involved in the formation of secondary organic aerosols. How? Recent works show that they contribute to the oxidation of SO2
. We have found that the studied ozonolysis reactions only led to nucleation in the presence of SO2
, which behaved as a catalyst. So the role of SO2
to form SOA depends on the structure of the alkene. For these reactions, the formation of low-volatility organic acid is expected to be responsible for nucleation, since SO3
was not released.