Probing Criegee intermediate reactions with methanol by FTMW spectroscopy

Area of Science:

• Atmospheric Chemistry
• Spectroscopy
• Aerosol Science

Background:

• Criegee intermediates (CIs) are reactive atmospheric species formed from unsaturated hydrocarbon ozonolysis.
• CIs can react with other atmospheric compounds, influencing aerosol formation and tropospheric budgets.
• Reactions of CIs with alcohols produce α-alkoxyalkyl hydroperoxides, contributing to secondary organic aerosols (SOAs).

Purpose of the Study:

• To directly detect and identify hydroperoxide products from Criegee intermediate reactions with methanol.
• To investigate the reactivity of Criegee intermediates (CH2OO and CH3CHOO) with methanol.
• To characterize the conformers of the resulting hydroperoxides using high-resolution microwave spectroscopy.

Main Methods:

• High-resolution Fourier transform microwave spectroscopy was employed for direct detection.
• Analysis of reaction products between CIs (CH2OO, CH3CHOO) and methanol.
• Identification of specific hydroperoxides: methoxymethyl hydroperoxide (MMHP) and methoxyethyl hydroperoxide (MEHP).

Main Results:

• Direct detection of MMHP and MEHP from the reactions of CH2OO and CH3CHOO with methanol, respectively.
• Identification of one conformer of MMHP and two conformers of MEHP.
• The pre-reactive complex CH2OO-CH3OH was not observed, suggesting different CI reactivity compared to water.
• MEHP was produced in similar ratios from both syn- and anti-CH3CHOO isomers reacting with methanol.

Conclusions:

• The study provides direct evidence for the formation of MMHP and MEHP from CI-methanol reactions.
• The findings highlight the role of these hydroperoxides in SOA formation.
• The observed reactivity differences between CH2OO and water versus methanol are significant for atmospheric modeling.