Criegee intermediates and their impacts on the troposphere

Area of Science:

• Atmospheric Chemistry
• Tropospheric Oxidation
• Aerosol Science

Background:

• Criegee intermediates (CIs), or carbonyl oxides, are formed during alkene ozonolysis and significantly impact tropospheric chemistry.
• CI decomposition is a key source of hydroxyl (OH) radicals, particularly during nighttime and winter.
• Estimated surface concentrations of stabilized Criegee intermediates (sCIs) range from 1 x 10^4 to 1 x 10^5 cm^-3, contributing to the terrestrial boundary layer's oxidative capacity.

Purpose of the Study:

• To elucidate the role of Criegee intermediates in atmospheric oxidation cycles.
• To highlight the significance of sCI reactions with water and sulfur dioxide.
• To explore the formation pathways of secondary organic aerosols (SOA) and new particle formation initiated by sCIs.

Main Methods:

• Model-measurement studies were used to estimate sCI concentrations.
• Analysis of reaction kinetics and product formation from sCI interactions.
• Investigation of sCI oxidation of SO2 and subsequent sulfuric acid formation.

Main Results:

• The reactions of sCIs with water (monomer and dimer) are the primary bimolecular loss pathways for smaller carbonyl oxides.
• sCI oxidation of SO2 leads to significant H2SO4 production, a key species for atmospheric nucleation.
• Reactions with various compounds (carboxylic acids, alcohols, etc.) yield highly oxygenated products, promoting nucleation and SOA formation.

Conclusions:

• Stabilized Criegee intermediates play a critical role in tropospheric oxidation and new particle formation.
• Understanding sCI reaction mechanisms is essential for accurate atmospheric modeling.
• sCI chemistry directly influences air quality and climate through aerosol formation and oxidative capacity.