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Discussion papers
https://doi.org/10.5194/acp-2019-741
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-741
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Sep 2019

Submitted as: research article | 04 Sep 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Terpenes and their oxidation products in the French Landes forest: insight from Vocus PTR-TOF measurements

Haiyan Li1, Matthieu Riva2, Pekka Rantala1, Liine Heikkinen1, Kaspar Daellenbach1, Jordan E. Krechmer3, Pierre-Marie Flaud4,5, Douglas Worsnop3, Markku Kulmala1, Eric Villenave4,5, Emilie Perraudin4,5, Mikael Ehn1, and Federico Bianchi1 Haiyan Li et al.
  • 1Institute for Atmospheric and Earth System Research / Physics, Faculty of Science, University of Helsinki, Finland
  • 2Univ. Lyon, Université Claude Bernard Lyon 1, CNRS, IRCELYON, 69626, Villeurbanne, France
  • 3Aerodyne Research Inc., Billerica, Massachusetts 01821, USA
  • 4Univ. Bordeaux, EPOC, UMR 5805, 33405 Talence Cedex, France
  • 5CNRS, EPOC, UMR 5805, 33405 Talence Cedex, France

Abstract. The capabilities of the recently developed Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF) are reported for the first time based on ambient measurements. With the deployment of the Vocus PTR-TOF, we present an overview of the observed gas-phase (oxygenated) molecules in the French Landes forest during summertime 2018 and gain insights into the atmospheric oxidation of terpenes, which are emitted in large quantities in the atmosphere and play important roles in secondary organic aerosol production. Due to the greatly improved detection efficiency compared to traditional PTR instruments, the Vocus PTR-TOF identifies a large amount of gas-phase signals with elemental composition categories including CH, CHO, CHN, CHS, CHON, CHOS, and others. Multiple hydrocarbons are detected, with carbon numbers up to 20. Particularly, we report the first direct observations of low-volatility diterpenes in the ambient air. The diurnal cycle of diterpenes is similar to that of monoterpenes and sesquiterpenes, but contrary to that of isoprene. Various types of terpene reaction products and intermediates are also characterized. Generally, the more oxidized products from terpene oxidations show a broad peak in the day due to the strong photochemical effects, while the less oxygenated products peak in the early morning and/or in the evening. To evaluate the importance of different formation pathways in terpene chemistry, the reaction rates of terpenes with main oxidants (i.e., hydroxyl radical, OH; ozone, O3; and nitrate radical, NO3) are calculated. For the less oxidized non-nitrate monoterpene oxidation products, their morning peaks likely have contributions from both O3- and OH-initiated monoterpene oxidation. Due to the decreased OH concentration at night, monoterpene ozonolysis becomes more important in the evening. For the monoterpene-derived organic nitrates, oxidations by O3, OH, and NO3 radicals all contribute to their formation, with their relative roles varying considerably over the course of the day. Through a detailed analysis of terpene chemistry, this study demonstrates the capability of the Vocus PTR-TOF in the detection of a wide range of oxidized reaction products in ambient and remote conditions, which highlights its importance in investigating atmospheric oxidation processes.

Haiyan Li et al.
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Short summary
We deploy the recently developed Vocus PTR-TOF in the French Landes forest during summertime to gain insights into terpene chemistry. In addition to isoprene, monoterpenes, sesquiterpenes, and the low-volatility diterpenes, various terpene reaction products are characterized. Through the analysis of terpene chemistry, this work demonstrates the capability of Vocus PTR-TOF in the detection of oxidized reaction products, highlighting its importance in investigating atmospheric oxidation processes.
We deploy the recently developed Vocus PTR-TOF in the French Landes forest during summertime to...
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