Impact of Temperature on Gas-Particle Phase Transitions and Secondary Organic Aerosol Formation in α-Pinene and Cyclohexene Ozonolysis Systems

DANIEL GONZALEZ, Yanyu Zhang, Thomas Eckel, David R. Cocker III, University of California, Riverside

     Abstract Number: 20
     Working Group: Aerosol Chemistry

Abstract
This work probes the deviations from gas-particle phase transition theories via temperature cycle experiments in α-pinene and cyclohexene dark ozonolysis systems. In these theories, it is assumed that the transition between gas and particle phases is entirely reversible throughout temperature cycles. However, recent studies have shown that aerosol particles can transition from liquid to solid when they reach a specific temperature threshold, significantly impacting partitioning behaviors. The findings from this study unveil the considerable influence of temperature on SOA formation and emphasize the necessity for additional research to explore the role of temperature and particle viscosity in gas-particle phase theories and SOA behaviors.

In the α-pinene system, gas-particle phase transitions demonstrated consistent reversibility throughout repeated temperature cycling (5 – 35°C) over 48 hours. However, in the cyclohexene system, there was an irreversible mass loss after the initial temperature cycle, though consistent reversibility was observed during subsequent cycles. The findings suggest that α-pinene SOA does not undergo a phase change within this temperature range, whereas cyclohexene SOA might become more viscous, impeding partitioning. This is bolstered by compositional (e.g., H:C, O:C) and physical evaluations (e.g., size, density, volatility, viscosity, hygroscopicity). This study highlights the importance of understanding the influence of temperature on SOA, which is essential for accurate modeling of atmospheric processes and air quality management strategies.