Dark Ozonolysis of cis-Cycloalkenes (C5-C8): Investigating SOA Formation, Transition Temperatures, and Temperature Cycling Effects in the UCR Atmospheric Chamber

DANIEL GONZALEZ, Sunandan Mahant, Yanyu Zhang, Markus Petters, David R. Cocker III, University of California, Riverside

     Abstract Number: 598
     Working Group: Aerosol Chemistry

Abstract
Cis-cycloalkenes provide a structurally constrained and chemically relevant model system for studying secondary organic aerosol (SOA) formation, offering unique opportunities to isolate the effects of molecular ring size and configuration on aerosol properties. Despite their relevance to both biogenic and anthropogenic emissions, the mechanistic drivers of SOA evolution from these compounds remain underexplored.

This study investigates the dark ozonolysis of a homologous series of cis-cycloalkenes (C5-C8) using the UCR Environmental Chamber, focusing on how ring size influences SOA formation, volatility, density, and phase behavior under temperature cycling. Multiday experiments were conducted to capture both the initial particle formation and its subsequent evolution through controlled thermocycling.

A comprehensive suite of instruments was used to characterize particle size, volatility profiles, effective density, and phase transition temperatures. The extended duration of the experiments allowed for assessment of thermal hysteresis in SOA produced from cycloalkene ozonolysis. Two distinct aerosol modes were observed in experiments with initial seed aerosol at temperatures of 5 °C, conversely in experiments with initial temperatures of 35 °C only a unimodal aerosol peak was observed. Additionally, non-equilibrium thermodynamic behavior was observed with respect to thermocycles (5-35-5 °C).

This work provides insight into how molecular structure and thermal history interact to influence SOA formation. The results underscore the need to incorporate precursor-specific behavior and temperature dependent processing into atmospheric models.