Influence of temperature on the molecular composition of ions and charged clusters during pure biogenic nucleation

Carla Frege, Ismael Ortega, Matti Rissanen, Arnaud Praplan, Gerhard Steiner, Martin Heinritzi, Lauri Ahonen, Antonio Amorim, Anne-Kathrin Bernhammer, Federico Bianchi, Sophia Brilke, Martin Breitenlechner, Lubna Dada, Antonio Aroso Dias, Jonathan Duplissy, sebastian Ehrhart, Imad El-hadad, Lukas Fischer, Claudia Fuchs, Olga GarmashMarc Gonin, Armin Hansel, Christopher Hoyle, Tuija Jokinen, Heikki Junninen, Jasper Kirkby, Andreas Kurten, Katrianne Lehtipalo, Markus Leiminger, Roy Lee Mauldin, Ugo Molteni, Leonid Nichman, Tuuka Petaja, Nina Sarnela, Siegfried Schobesberger, Mario Simon, Mikko Sipila, Dominik Stolzenburg, Antonio Tome, Alexander Vogel, Andrea Wagner, Robert Wagner, Mao Xiao, Chao Yan, Penglin Ye, Joachim Curtius, Neil Donahue, Rick Flagan, Markku Kulmala, Douglas Worsnop, Paul Winkler, Josef Dommen, Urs Baltensperger

    Research output: Working paperDiscussion paper

    Abstract

    It was recently shown by the CERN CLOUD experiment that biogenic highly oxygenated molecules (HOMs) form particles under atmospheric conditions in the absence of sulfuric acid where ions enhance the nucleation rate by one to two orders of magnitude. The biogenic HOMs were produced from ozonolysis of α-pinene at 5 °C. Here we extend this study to compare the molecular composition of positive and negative HOM clusters measured with atmospheric pressure interface time-of-flight mass spectrometers (APi-TOFs), at three different temperatures (25 °C, 5 °C and −25 °C). Most negative HOM clusters include a nitrate (NO3−) ion and the spectra are similar to those seen in the nighttime boreal forest. On the other hand, most positive HOM clusters include an ammonium (NH4+) ion and the spectra are characterized by mass bands that differ in their molecular weight by ~ 20 C atoms, corresponding to HOM dimers. At lower temperatures the average oxygen to carbon (O : C) ratio of the HOM clusters decreases for both polarities, reflecting an overall reduction of HOM formation with decreasing temperature. This indicates a decrease in the rate of autoxidation with temperature due to a rather high activation energy as has previously been determined by quantum chemical calculations. Furthermore, at the lowest temperature (−25 °C) the presence of C30 clusters show that HOM monomers start to contribute to the nucleation of positive clusters. These experimental findings are supported by quantum chemical calculations of the binding energies of representative neutral and charged clusters.
    Original languageEnglish
    DOIs
    Publication statusPublished - 2017

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