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.

Isolating α-Pinene Ozonolysis Pathways Reveals New Insights into Peroxy Radical Chemistry and Secondary Organic Aerosol Formation

“…Thus, different drift times usually suggest different structures. In our previous studies, we have demonstrated that the IMS-TOF is able to clearly separate structural isomers. ,,, Using the ESI in both the positive (+) and negative (−) ion modes allows for detections of the majority of the SOA constituents. An overview of the SOA molecular compositions is shown in Figures S10, S11 …”

“…The SOA samples were then characterized offline by the IMS-TOF with electrospray ionization (ESI) (Tofwerk Inc. and Aerodyne Research Inc., t/Δt ∼ 100) through direct infusion or analyzed by the GC-EI-MS (Agilent Inc., 7890 GC and 5975 MSD) after derivatization (by additions of 25 μL N,O-Bis­(trimethylsilyl)­trifluoroacetamide (BSTFA) and 25 μL pyridine, both reagents from Sigma-Aldrich). Both analytical methods have been described in detail in our prior studies. ,− …”

Site-Specific Mechanisms in OH-Initiated Organic Aerosol Heterogeneous Oxidation Revealed by Isomer-Resolved Molecular Characterization

“…The IMS separation could resolve isomeric products beyond the typical mass spectra shown in Figure . The major isomers for each chemical formula in individual OA heterogeneous oxidation experiments could be obtained and the CID fragmentation mass spectra for individual isomers could help differentiate and possibly elucidate the chemical structures between them. ,,, Two generations of functionalization products were observed in the studied systems. Figure presents the isomer-resolved drift time spectra (i.e., “driftgrams”) of these functionalization product formulas for all of the studied OA proxies.…”

Development and application of a low-cost vaporizer for rapid, quantitative, in situ addition of organic gases and particles to an environmental chamber

“…In addition, it is well established that monofunctional ethers and esters are also stable and unreactive at temperatures above 400 C (Steacie 1933;Hurd and Blunck 1938). Conversely, organic peroxides decompose in the neighborhood of 100 C (Benson and Shaw 1970) and multifunctional compounds containing various combinations of hydroxyl, carboxyl, and carbonyl groups may be susceptible to thermal decomposition at temperatures <100 C (Zhao et al 2020). As such, when using the vaporizer it is recommended that particleand gas-phase composition be monitored to identify the occurrence of thermal decomposition.…”