Exploring autoxidation pathways in α-pinene oxidation through particulate measurements

Area of Science:

• Atmospheric Chemistry
• Aerosol Science
• Organic Chemistry

Background:

• Alpha-pinene is a key volatile organic compound contributing to secondary organic aerosol (SOA) formation.
• Understanding oxidation pathways is vital for accurate atmospheric modeling of aerosol impacts.

Purpose of the Study:

• To investigate the influence of different α-pinene oxidation pathways on highly oxygenated organic molecule (HOM) and SOA formation.
• To evaluate the contribution of various autoxidation-initiation routes to SOA mass and size distributions.

Main Methods:

• Utilized chamber-based particulate measurements from MAC20120215 and AIDA20081127 datasets.
• Employed COSIMA-SOA and PyCHAM box-model simulations to test O3 and OH radical attack pathways, and later-generation oxidation.
• Compared model simulations with experimental data on particle mass and size distributions.

Main Results:

• Simulations underestimating SOA mass were improved by including HOM formation pathways.
• Both first-generation and later-generation HOM chemistry were necessary for accurate model-measurement agreement.
• Later-generation HOM chemistry is essential for reproducing second-stage SOA growth.

Conclusions:

• No single α-pinene oxidation pathway is sufficient to explain observed SOA formation under the studied conditions.
• A combined approach of particulate measurements and modeling provides constraints for refining organic oxidation and aerosol formation mechanisms.
• Further research may benefit from direct HOM measurements to validate model improvements.