Isomer-Resolved Mobility-Mass Analysis of α-Pinene Ozonolysis Products

Abstract

Highly oxygenated organic molecules (HOMs) are important sources of atmospheric aerosols. Resolving the molecular-level formation mechanisms of these HOMs from freshly emitted hydrocarbons improves the understanding of aerosol properties and their influence on the climate. In this study, we measure the electrical mobility and mass-to-charge ratio of α-pinene oxidation products using a secondary electrospray-differential mobility analyzer-mass spectrometer (SESI-DMA-MS). The mass-mobility spectrum of the oxidation products is measured with seven different reagent ions generated by the electrospray. We analyzed the mobility-mass spectra of the oxidation products C 9–10 H 14–18 O 2–6 . Our results show that acetate and chloride yield the highest charging efficiencies. Analysis of the mobility spectra suggests that the clusters have 1–5 isomeric structures (i.e., ion-molecule cluster structures with distinct mobilities), and the number is affected by the reagent ion. Most of the isomers are likely cluster isomers originating from binding of the reagent ion to different sites of the molecule. By comparing the number of observed isomers and measured mobilities and collision cross sections between standard pinanediol and pinonic acid to the values observed for C 10 H 18 O 2 and C 10 H 16 O 3 produced from oxidation of α-pinene, we confirm that pinanediol and pinonic acid are the only isomers for these elemental compositions in our experimental conditions. Our study shows that the SESI-DMA-MS produces new information from the first steps of oxidation of α-pinene.

Molecular and Structural Characterization of Isomeric Compounds in Atmospheric Organic Aerosol Using Ion Mobility-Mass Spectrometry

“…The broad DT distribution indicates the presence of multiple isomers of C 10 H 16 O 3 in the PSOA mixture. Previous study investigating isomers of C 10 H 16 O 3 generated in the ozonolysis of α-pinene reported the presence of up to three individual peaks for C 10 H 16 O 3 species ionized as Na + adducts . Therefore, the two small shoulder peaks on both the compact and extended sides of DT distribution may be related to isomers or conformers of pinonic acid + Na + , while the abundant peak centered at 21.66 ms most likely corresponds to pinonic acid.…”

“…Previous study investigating isomers of C 10 H 16 O 3 generated in the ozonolysis of α-pinene reported the presence of up to three individual peaks for C 10 H 16 O 3 species ionized as Na + adducts. 84 Therefore, the two small shoulder peaks on both the compact and extended sides of DT distribution may be related to isomers or conformers of pinonic acid + Na + , while the abundant peak centered at 21.66 ms most likely corresponds to pinonic acid. On the other hand, we observe two distinct features (19.5 and 20.3 ms) in the DT distributions of C 10 H 16 O 3 in PSOA (Figure 3d) in negative mode.…”

“…The DT distributions for LSOA monomers appear to be similar in positive and negative modes (Figure 3c,d S1. The larger cross section of [M + Na] + may be attributed to the size of the sodium cation coordinated to the analytes observed as positive ions, 84,112 which increases the surface area of the ions. These observations are consistent with the results of a previous study, 84 in which an increase in the CCS with the mass of inorganic reagent ions (e.g., Na + , Li + , and K + ) was observed for the ozonolysis products of α-pinene.…”

“…Meanwhile, a differential mobility analyzer has been used to measure CCS and ion mobility of a few monomeric isomers of PSOA . Although the initial works ,,− reported on the use of IM-MS for SOA characterization, a comprehensive, untargeted characterization of structural isomers in biogenic SOA has not been reported. Drift tube IM-MS instruments are ideally suited for the accurate determination of CCS values of compounds ( DT CCS) in complex mixtures. , The development of DT CCS library databases for atmospheric SOA systems will facilitate rapid and accurate isomer detection, which, in turn, will aid in the predictive understanding of their chemical and physical properties.…”

“…75 Meanwhile, a differential mobility analyzer has been used to measure CCS and ion mobility of a few monomeric isomers of PSOA. 84 Although the initial works 26,57,82−86 reported on the use of IM-MS for SOA characterization, a comprehensive, untargeted characterization of structural isomers in biogenic SOA has not been reported. Drift tube IM-MS instruments are ideally suited for the accurate determination of CCS values of compounds ( DT CCS) in complex mixtures.…”