Preprints
https://doi.org/10.5194/acp-2021-124
https://doi.org/10.5194/acp-2021-124

  01 Apr 2021

01 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

Measurement report: Source apportionment of volatile organic compounds at the remote high-altitude Maïdo observatory

Bert Verreyken1,2,3, Crist Amelynck1,2, Niels Schoon1, Jean-François Müller1, Jérôme Brioude3, Nicolas Kumps1, Christian Hermans1, Jean-Marc Metzger4, and Trissevgeni Stavrakou1 Bert Verreyken et al.
  • 1Royal Belgian Institute for Space Aeronomy, B-1180 Brussels
  • 2Department of Chemistry, Ghent University, B-9000 Ghent, Belgium
  • 3Laboratoire de l’Atmosphère et des Cyclones, UMR 8105, CNRS, Université de La Réunion, Météo France, 97744 Saint-Denis, France
  • 4Observatoire des Sciences de l’Univers de La Réunion, UMS3365, CNRS, Université de La Réunion, Météo-France, Saint-Denis, La Réunion, France

Abstract. We present a source apportionment study of a near-continuous 2-year dataset of volatile organic compounds (VOCs), recorded between October 2017 and November 2019 with a quadrupole-based high-sensitivity proton-transfer-reaction mass-spectrometry (hs-PTR-MS) instrument deployed at the Maïdo observatory (21.1° S, 55.4° E, 2,160 m altitude). The observatory is located on La Réunion island in the south-west Indian Ocean. We discuss seasonal and diel profiles of six key VOC species unequivocally linked to specific sources – acetonitrile (CH3CN), isoprene (C5H8), isoprene oxidation products (Iox), benzene (C6H6), C8-aromatics (C8H10), and dimethyl sulfide (DMS). The data are analyzed using the positive matrix factorization (PMF) method and back-trajectory calculations based on the Lagrangian mesoscale transport model FLEXPART-AROME to identify the impact of different sources on air masses recorded at the observatory. As opposed to the biomass burning tracer CH3CN, which does not exhibit a consistent diel variability, we identify pronounced diel profiles with a daytime maximum for the biogenic (C5H8 and Iox) and anthropogenic (C6H6, C8H10) tracers. The marine tracer DMS generally displays a daytime maximum except for the austral winter when the difference between daytime and nighttime mixing ratios vanishes. Four factors were identified by the PMF: background/biomass burning, anthropogenic, primary biogenic and secondary biogenic. Despite human activity being concentrated in few coastal areas, the PMF results indicate that the anthropogenic source factor is the dominant contributor to the VOC load (38 %), followed by the background/biomass burning source factor originating in the free troposphere (33 %), and by the primary (15 %) and secondary biogenic sources (14 %). FLEXPART-AROME simulations showed that the observatory was most sensitive to anthropogenic emissions west of Maïdo while the strongest biogenic contributions coincided with airmasses passing over the north-eastern part of La Réunion. At night, the observatory is often located in the free troposphere while during the day, the measurements are influenced by mesoscale sources. Interquartile ranges of nighttime 30-minute average concentrations of methanol (CH3OH), CH3CN, acetaldehyde (CH3CHO), formic acid (HCOOH), acetone (CH3COCH3), acetic acid (CH3COOH) and methyl ethyl ketone (MEK), representative for the atmospheric composition of the free troposphere, were found to be 525–887 pptv, 79–110 pptv, 61–101 pptv, 172–335 pptv, 259–379 pptv, 64–164 and 11–21 pptv, respectively.

Bert Verreyken 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 acp-2021-124', Anonymous Referee #1, 24 May 2021
  • RC2: 'Comment on acp-2021-124', Anonymous Referee #2, 09 Jun 2021

Bert Verreyken et al.

Bert Verreyken et al.

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Short summary
We present a 2-year dataset of trace gas concentrations, specifically an array of volatile organic compounds (VOCs), recorded at the Maïdo observatory, a remote tropical high-altitude site located on a small island in the south-west Indian Ocean. We found that island-scale transport is an important driver for the daily cycle of VOC concentrations. During the day, surface emissions from the island affect the atmospheric composition at Maïdo greatly while at night, this impact is strongly reduced.
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