Criegee Chemistry on Aqueous Organic Surfaces

Area of Science:

• Atmospheric Chemistry
• Chemical Kinetics
• Aerosol Science

Background:

• Gas-phase Criegee intermediates (CIs) are key oxidants in the troposphere.
• Their atmospheric fate is primarily attributed to reactions with water molecules.
• However, their behavior in heterogeneous environments like aerosol surfaces is less understood.

Purpose of the Study:

• To investigate the reaction pathways of Criegee intermediates (CIs) on aqueous organic aerosol surfaces.
• To determine if CIs react with species other than water in these environments.
• To quantify the competition between water and carboxylic acids for CI reactions.

Main Methods:

• Online electrospray mass spectrometry was used to probe CI chemistry.
• Experiments were conducted on water/acetonitrile microjets containing α-humulene and β-caryophyllene.
• Criegee intermediates were generated in situ via ozone exposure (<10 μs).
• Reactions with H2O, D2O, H218O, and n-alkyl-COOH (n=1-7) were studied.

Main Results:

• Criegee intermediates (CIs) react competitively with millimolar carboxylic acids on aerosol surfaces.
• The competition with n-alkyl-carboxylic acids increases with alkyl chain length (n).
• Interfacial water is not the sole reactant for CIs on these surfaces.

Conclusions:

• Criegee intermediates (CIs) can react with carboxylic acids on aqueous organic aerosol surfaces.
• This reaction pathway is significant due to low water concentrations in interfacial layers.
• The findings highlight alternative CI reaction channels in atmospheric aerosols.