Volatility of Secondary Organic Aerosol from β-Caryophyllene Ozonolysis over a Wide Tropospheric Temperature Range

We investigated secondary organic aerosol (SOA) from beta-caryophyllene oxidation generated over a wide tropospheric temperature range (213-313 K) from ozonolysis. Positive matrix factorization (PMF) was used to deconvolute the desorption data (thermograms) of SOA products detected by a chemical ionization mass spectrometer (FIGAERO-CIMS). A nonmonotonic dependence of particle volatility (saturation concentration at 298 K, C-298K(*)) on formation temperature (213-313 K) was observed, primarily due to temperature-dependent formation pathways of beta-caryophyllene oxidation products. The PMF analysis grouped detected ions into 11 compound groups (factors) with characteristic volatility. These compound groups act as indicators for the underlying SOA formation mechanisms. Their different temperature responses revealed that the relevant chemical pathways (e.g., autoxidation, oligomer formation, and isomer formation) had distinct optimal temperatures between 213 and 313 K, significantly beyond the effect of temperature-dependent partitioning. Furthermore, PMF-resolved volatility groups were compared with volatility basis set (VBS) distributions based on different vapor pressure estimation methods. The variation of the volatilities predicted by different methods is affected by highly oxygenated molecules, isomers, and thermal decomposition of oligomers with long carbon chains. This work distinguishes multiple isomers and identifies compound groups of varying volatilities, providing new insights into the temperature-dependent formation mechanisms of beta-caryophyllene-derived SOA particles.

Automated summary

"We investigated the secondary organic aerosol (SOA) formed from the oxidation of beta-caryophyllene at different tropospheric temperatures. Positive matrix factorization (PMF) analysis was used to separate the SOA products detected by a chemical ionization mass spectrometer (FIGAERO-CIMS). We observed a nonmonotonic dependence of particle volatility on formation temperature due to temperature-dependent formation pathways. The PMF analysis grouped the detected ions into 11 compound groups that act as indicators for the underlying formation mechanisms."