| 10 Apr 2026
Isomer-resolved online analysis of organic aerosols using ion mobility mass spectrometry
Abstract. Secondary organic aerosol (SOA) makes up much of the particulate matter in the troposphere and impacts global climate and human health, though uncertainties regarding the sources and properties of SOA limit our understanding of these effects. New analytical techniques are required to better characterize the molecular composition of SOA, including methods that can identify isomeric compounds that may have different contributions to SOA properties such as hygroscopicity or volatility. We present a method for isomer-resolved analysis of SOA using a commercially available chemical ionization ion-mobility time-of-flight mass spectrometer (CI-IMS-TOF) and a Vaporization Inlet for Aerosols (VIA). The compatibility of the VIA and the CI-IMS-TOF was assessed through the analysis of 10 carboxylic acid standards across a large temperature range (30 - 170 °C). Ion drift times were found to be stable to within 0.075% of their initial values after drift time calibration. The VIA-CI-IMS-TOF was also used to collect real-time ion mobility and mass spectra of SOA constituents during an α-pinene ozonolysis chamber experiment. Several reaction products were identified in the SOA using synthetic standards, including structural isomers of C8H12O4 and C9H14O4. Temporal evolution of reaction products was used to assess formation timescales and determine the generation of oxidation for individual isomers. Both iodide and bromide reagent ions were used in the VIA-CI-IMS-TOF to achieve a more comprehensive analysis of SOA. This study demonstrates the performance of the VIA-CI-IMS-TOF for online, isomer-resolved analysis of organic aerosol and its potential for improving the current understanding of SOA composition.
Competing interests: MRC and HS are employees of Aerodyne Research Inc., which sells the VIA and CI-IMS-TOF
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