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Chemical Differences between Phenolic Secondary Organic Aerosol Formed through Gas-Phase and Aqueous-Phase Reactions
Wenqing Jiang1,2, Lu Yu1,2, Lindsay Yee3
1Department of Environmental Toxicology, University of California, Davis, California 95616, United States.
ACS Earth & Space Chemistry
|November 27, 2024
Summary
Biomass burning releases phenolic compounds that form secondary organic aerosol (SOA) through gas-phase and aqueous-phase reactions. Aqueous reactions yield more SOA, forming distinct chemical compositions like oligomers and carboxylic acids compared to gas-phase reactions.
Area of Science:
- Atmospheric Chemistry
- Biomass Burning Emissions
- Secondary Organic Aerosol Formation
Background:
- Phenolic compounds are key emissions from biomass burning (BB).
- These compounds react in both gas and aqueous phases to form secondary organic aerosol (SOA).
- Gas-phase SOA (gasSOA) and aqueous-phase SOA (aqSOA) formation involve different mechanisms and yield distinct products.
Purpose of the Study:
- To investigate the gaseous and aqueous reactions of guaiacol, a representative BB phenol.
- To elucidate the compositional differences between phenolic aqSOA and gasSOA.
- To compare SOA yields and evolution pathways in both phases.
Main Methods:
- Studied gaseous and aqueous reactions of guaiacol.
- Analyzed SOA yields and chemical composition (oxidation state, molecular weight, functional groups).
- Identified characteristic spectral signatures and tracer ions for gasSOA and aqSOA.
Main Results:
- Aqueous-phase reactions of guaiacol produced higher SOA yields (approx. 60%) than gas-phase reactions (approx. 30%).
- Initially, gasSOA had higher oxidation levels (O/C > 0.82) than aqSOA (0.55-0.75), but prolonged aqueous reactions increased aqSOA oxidation.
- Aqueous reactions generated more oligomers, high-molecular-weight compounds, and sustained carboxylic acid production.
Conclusions:
- Phenolic gasSOA and aqSOA exhibit significant chemical differences.
- Aqueous reactions are more complex and lead to more gradual SOA evolution.
- Accurate representation of both gas and aqueous pathways is crucial for atmospheric models predicting aerosol properties and impacts from biomass burning.
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