Formation of highly-oxygenated organic molecules from α-pinene ozonolysis: chemical characteristics, mechanism and kinetic model development

Terpenes are emitted by vegetation and their oxidation in the atmosphere is an important source of secondary organic aerosol (SOA). A part of this oxidation can proceed through an autoxidation process yielding highly-oxygenated organic molecules (HOM) with low saturation vapour pressure. They can therefore contribute, even in the absence of sulphuric acid, to new-particle formation (NPF). The understanding of the autoxidation mechanism and its kinetics is still far from complete. Here we present a mechanistic and kinetic analysis of mass spectrometry data from α-pinene (AP) ozonolysis experiments performed during the CLOUD 8 campaign at CERN. We grouped HOM in classes according to their identified chemical composition and investigated the relative changes of these groups and their components as a function of the reagent concentration. We determined reaction rate constants for the different HOM peroxy radical reaction pathways. The accretion reaction between HOM peroxy radicals was found to be extremely fa...