28 Nov 2022
28 Nov 2022

A Combined Gas- and Particle-phase Analysis of Highly Oxygenated Organic Molecules (HOM) from α-pinene Ozonolysis

Jian Zhao1, Ella Häkkinen1, Frans Graeffe1, Jordan E. Krechmer2,a, Manjula R. Canagaratna2, Douglas R. Worsnop2, Juha Kangasluoma1, and Mikael Ehn1 Jian Zhao et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, 00014, Finland
  • 2Aerodyne Research Inc., Billerica, Massachusetts, 01821, United States
  • anow at: Bruker Daltonics Inc., Billerica, Massachusetts, 01821, United States

Abstract. Highly oxygenated organic molecules (HOM) are important for the formation of secondary organic aerosol (SOA), which poses serious health risks and exerts great influence on Earth’s climate. However, the speciation of particle-phase HOM and its relationship with gas-phase HOM formation has been limited by the lack of suitable analytical techniques. Here, combining a novel particle evaporation inlet VIA (Volatilization Inlet for Aerosols) with a nitrate chemical ionization mass spectrometer (NO3-CIMS), gas- and particle-phase HOM products of α-pinene ozonolysis were studied under different conditions. Within the 50-min residence time of our Teflon chamber, we observed enhancement of C16-C19 HOM dimers in particles compared to the HOM that were condensing. In particular, gas-phase dimer formation was considerably suppressed in experiments with the addition of CO or NO, but dimers still made up a considerable fraction of the observed SOA. In addition to the generally shorter carbon skeletons of the particle phase dimers (i.e. C16-C19) compared to the gas phase (C19-C20), average O / C ratios of the HOM (especially in the dimer range) also decreased slightly in the particle phase. C17H26Oz compounds, which have often been reported by previous offline measurements, dominate the particle-phase HOM mass spectra in α-pinene ozonolysis experiments. Our results indicate that these C17 compounds might be related to particle-phase processes within one hour after HOM condensation. However, the new VIA-NO3-CIMS system used in this work will require more detailed characterization to better understand how the thermal desorption and wall effects may modify the measured particle-phase HOM distributions. Nevertheless, for example organic nitrate measured by this novel VIA-NO3-CIMS system was consistent with the measurements of an Aerodyne Aerosol Mass Spectrometer (AMS), showing the capability of this system as a promising technique for particle-phase HOM measurements. Taken together, we believe that this system is a promising technique for combined online gas- and particle-phase HOM measurements.

Jian Zhao et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1317', Anonymous Referee #1, 20 Dec 2022
  • RC2: 'Comment on egusphere-2022-1317', Anonymous Referee #2, 25 Jan 2023

Jian Zhao et al.


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Short summary
Based on the combined measurements of gas- and particle-phase highly oxygenated organic molecules (HOM) from α-pinene ozonolysis, enhancement of C16-C19 HOM dimers in particles was observed. Especially, C17H26Oz, which has often been reported by offline measurements, dominates the particle-phase HOM. Our results indicate that these C17 compounds might be closely related to particle-phase HOM formation. These results are important for a better understanding of SOA formation in the atmosphere.