Diverse Reactions in Highly Functionalized Organic Aerosols during Thermal Desorption

Abstract

Atmospheric organic aerosols (OA) are complex mixtures of organic molecules that are usually highly functionalized through various oxidative processes. Understanding the volatilities and chemical compositions of OA is key to elucidating their environmental impacts. Thermal desorption coupling to mass spectrometry has been used as the main approach to examine both aspects of OA. In this work, we investigated the thermal desorption-induced chemical compositional change of OA from heterogeneous oxidation of glutaric acid and α-pinene ozonolysis. Using an ion mobility spectrometry mass spectrometer, coupled with total peroxide analysis and a mass transfer evaporation model, we determined diverse reactions in the particle phase during rapid heating under moderate desorption temperatures (less than 100 °C). These reactions include irreversible oligomer (e.g., esters and organic peroxides) decomposition into monomers and new oligomer formation from decarboxylation, CO elimination, decarbonylation, and dehydration. These chemical processes may effectively modify the volatility and chemical characteristics of the residual OA particles. Further, the monomeric products from thermal desorption could interfere with quantification of the original constituents without isomer separation. These findings could help reconcile the previously observed inconsistency of OA evaporation kinetics versus volatility distribution. Further, the results from this study could help interpret and constrain thermal desorption-based measurements of OA volatility and compositions.