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

## TL;DR

This study measures the yield of a specific type of chemical intermediate formed when isoprene reacts with ozone in the atmosphere.

## Contribution

The study experimentally determines the yield of long-lived four-carbon Criegee intermediates from isoprene ozonolysis.

## Key findings

- The yield of long-lived C4 stabilized Criegee intermediates is approximately 11%.
- Gas-phase detection of sCIs was achieved using proton-transfer-reaction mass spectrometry.
- Quantum calculations confirmed similar detection sensitivities for C1 and C4 intermediates.

## Abstract

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.