Yield of the Four-Carbon Stabilized Criegee Intermediates from Isoprene Ozonolysis
Résumé
Isoprene is the single most abundant nonmethane hydrocarbon emitted into the atmosphere. Despite this, uncertainties in the oxidation chemistry remain. Here, we investigate the yields of Criegee intermediates that are produced from the ozonolysis reaction, where we conduct a series of atmospheric simulation chamber experiments in which the transient stabilized Criegee intermediates (sCIs) are titrated in the gas phase using either biacetyl or acetylpropionyl. This reaction yields a stable ketone-substituted secondary ozonide (SOZ), which was observed directly in the gas phase using a proton-transfer-reaction time-of-flight mass spectrometer operated in NH4+ mode. Both C1 and C4 sCIs were observed in this way, with the mass of the NH4+ adduct shifting according to the mass of the sCI and its diketone titrant. The relative abundance of the C4 sCI was constrained against C1 assuming a similar sensitivity for the two SOZ derivatives. This was supported by quantum chemical calculations that demonstrated very similar binding energies between NH4+ and the C1 and C4 SOZ adducts. Our results demonstrate an overall yield of ∼11% for the long-lived C4 sCIs, which may survive long enough to participate in various bimolecular reactions in the atmosphere.
