2 research outputs found
Synthesis and Characterization of Organic Peroxides from Monoterpene-Derived Criegee Intermediates in Secondary Organic Aerosol
Ozonolysis
of alkenes is known to produce reactive intermediatesstabilized
Criegee intermediates (SCIs), and their subsequent bimolecular reactions
with various carboxylic acids can form α-acyloxyalkyl hydroperoxides
(AAHPs), which is considered a major class of organic peroxides in
secondary organic aerosol (SOA). Despite their atmospheric and health
importance, the molecular-level identification of organic peroxides
in atmospheric aerosols is highly challenging, preventing further
assessment of their environmental fate. Here, we synthesize 20 atmospherically
relevant AAHPs through liquid-phase ozonolysis, in which two types
of monoterpene-derived SCIs from either α-pinene or 3-carene
are scavenged by 10 different carboxylic acids to form AAHPs with
diverse structures. These AAHPs are identified individually by liquid
chromatography coupled with high-resolution mass spectrometry. AAHPs
were previously thought to decompose quickly in an aqueous environment
such as cloud droplets, but we demonstrate here that AAHPs hydrolysis
rates are highly compound-dependent with rate constants differing
by 2 orders of magnitude. In contrast, the aqueous-phase formation
rate constants between SCI and various carboxylic acids vary only
within a factor of 2–3. Finally, we identified two of the 20
synthesized AAHPs in α-pinene SOA and two in 3-carene SOA, contributing
∼0.3% to the total SOA mass. Our results improve the current
molecular-level understanding of organic peroxides and are useful
for a more accurate assessment of their environmental fate and health
impact
Spontaneous Iodide Activation at the Air–Water Interface of Aqueous Droplets
We present experimental evidence that atomic and molecular
iodine,
I and I2, are produced spontaneously in the dark at the
air–water interface of iodide-containing droplets without any
added catalysts, oxidants, or irradiation. Specifically, we observe
I3– formation within droplets, and I2 emission into the gas phase from NaI-containing droplets
over a range of droplet sizes. The formation of both products is enhanced
in the presence of electron scavengers, either in the gas phase or
in solution, and it clearly follows a Langmuir–Hinshelwood
mechanism, suggesting an interfacial process. These observations are
consistent with iodide oxidation at the interface, possibly initiated
by the strong intrinsic electric field present there, followed by
well-known solution-phase reactions of the iodine atom. This interfacial
chemistry could be important in many contexts, including atmospheric
aerosols