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Selective Deuteration Reveals the Importance of Multiple Branching Pathways in α-Pinene Autoxidation
Melissa Meder1, Frans Graeffe1, Yuanyuan Luo1
1Institute for atmospheric and earth system research (INAR/physics), University of Helsinki, Helsinki 00014, Finland.
Journal of the American Chemical Society
|April 15, 2025
Summary
Understanding monoterpene oxidation, a major source of atmospheric aerosols, is key for climate and air quality. This study reveals surprising autoxidation pathways for alpha-pinene, challenging existing models.
Area of Science:
- Atmospheric Chemistry
- Environmental Science
- Organic Chemistry
Background:
- Monoterpene oxidation significantly contributes to atmospheric secondary organic aerosol (SOA) formation, impacting climate and air quality.
- The detailed autoxidation mechanisms of abundant monoterpenes like alpha-pinene remain poorly understood.
- Accurate modeling of these processes is crucial for predicting atmospheric changes.
Purpose of the Study:
- To elucidate the molecular-level autoxidation mechanisms of alpha-pinene during ozonolysis.
- To identify the specific carbon atoms involved in the formation of oxygenated products.
- To reassess the significance of proposed intermediate species and reaction pathways.
Main Methods:
- Utilized advanced isotopic labeling with eight selectively deuterated alpha-pinene analogues.
- Employed state-of-the-art chemical ionization mass spectrometry for sensitive detection.
- Supported experimental findings with quantum chemical calculations.
Main Results:
- Identified that a limited number of carbon atoms are involved in the autoxidation of alpha-pinene to highly oxygenated products.
- Demonstrated that prompt pinonic acid formation is likely overestimated.
- Found that alpha-pinene-derived dioxirane is more stable than previously assumed.
- Revealed the importance of multiple branching pathways over linear progression in autoxidation.
Conclusions:
- The autoxidation of alpha-pinene involves surprisingly few carbon atoms and complex branching pathways.
- Current atmospheric oxidation models require revision to incorporate these newly identified mechanisms.
- Accurate modeling of alpha-pinene oxidation is essential for reliable climate and air quality predictions.
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