Yield of the Four-Carbon Stabilized Criegee Intermediates from Isoprene Ozonolysis

High Resolution Image Download MS PowerPoint Slide 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 NH 4 + mode. Both C 1 and C 4 sCIs were observed in this way, with the mass of the NH 4 + adduct shifting according to the mass of the sCI and its diketone titrant. The relative abundance of the C 4 sCI was constrained against C 1 assuming a similar sensitivity for the two SOZ derivatives. This was supported by quantum chemical calculations that demonstrated very similar binding energies between NH 4 + and the C 1 and C 4 SOZ adducts. Our results demonstrate an overall yield of ∼11% for the long-lived C 4 sCIs, which may survive long enough to participate in various bimolecular reactions in the atmosphere.