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We used the radicals from α-pinene ozonolysis proposed in ref.

High yields of these same HOMs have previously been reported6, 16, although our ozonolysis yields are less than half those of ref.

This results in a mean estimated uncertainty in HOM yield for either ozonolysis or hydroxyl chemistry of +100%/−60%.

The HOM yields from either ozonolysis or OH· chemistry were calculated by assuming equal production and loss rates during steady-state16:

Here, initial ozonolysis of an α-pinene molecule proceeds via a Criegee intermediate and further steps to form an RO2· radical, followed by several repeated cycles of intramolecular H abstraction and O2 addition to re-form a new RO2· radical.