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

Abstract

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.

Recent advances in mass spectrometry techniques for atmospheric chemistry research on molecular‐level

“…The CHARON‐PTR‐MS has been successfully used for detection of organic compounds and ammonium constituents in aerosol particles (Eichler et al, 2015; Leglise et al, 2019; Piel et al, 2021). The second example is the Vocus inlet for aerosols (VIA), recently introduced by Häkkinen et al for measurements of particle‐phase HOMs by coupling to NO 3 − ‐CIMS (Häkkinen et al, 2022; Zhao, Häkkinen, et al, 2022). Similar to the CHARON inlet, the VIA first passes aerosols samples through an activated charcoal gas denuder to remove gas‐phase constituents (Zhao, Häkkinen, et al, 2022).…”

“…The second example is the Vocus inlet for aerosols (VIA), recently introduced by Häkkinen et al for measurements of particle‐phase HOMs by coupling to NO 3 − ‐CIMS (Häkkinen et al, 2022; Zhao, Häkkinen, et al, 2022). Similar to the CHARON inlet, the VIA first passes aerosols samples through an activated charcoal gas denuder to remove gas‐phase constituents (Zhao, Häkkinen, et al, 2022). Then the remaining aerosol species are evaporated at a chosen temperature between 25°C and 300°C by a Sulfinert‐coated stainless‐steel thermal desorption tube under ambient pressure (Avery et al, 2023; Häkkinen et al, 2022).…”

Explaining apparent particle shrinkage related to new particle formation events in western Saudi Arabia does not require evaporation

“…There are several possible candidates for this mismatch, including undetected condensable species and heterogeneous/particle phase formation of organic salts and oligomers, which reduce the volatilities of the sorbed compounds. Simultaneous measurements of the gas and particle phase compounds point towards lower-volatility products in the particle phase than expected directly from the gas-phase measurements (Baltensperger et al, 2005;Häkkinen et al, 2022;Zhao et al, 2022). These observations suggest that the hypothetically reversible condensation-evaporation dynamics governing aerosol growth might have a preferential direction towards accumulating more mass into the aerosols.…”