OH reactivity and concentrations of biogenic volatile organic compounds in a Mediterranean forest of downy oak trees
- 1LSCE, Laboratoire des Sciences du Climat et de l'Environnement, CNRS-CEA-UVSQ, Orme des Merisiers, 91191 Gif sur Yvette, France
- 2Ionicon Analytik GmbH, Eduard-Bodem-Gasse 3, 6020 Innsbruck, Austria
- 3CNRS, Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), 38000 Grenoble, France
- 4Univ. Grenoble Alpes, LGGE, 38000 Grenoble, France
- 5Laboratoire d'Aerologie, Université de Toulouse-CNRS, 14 Avenue Edouard Belin, 31400 Toulouse, France
- anow at: Institute of Nuclear Technology and Radiation Protection, Environmental Radioactivity Laboratory, National Centre of Scientific Research “Demokritos”, 15310 Ag. Paraskevi, Attiki, Greece
Abstract. Total OH reactivity, defined as the total loss frequency of the hydroxyl radical in the atmosphere, has proved to be an excellent tool to identify the total loading of reactive species in ambient air. High levels of unknown reactivity were found in several forests worldwide and were often higher than at urban sites.
Our study presents atmospheric mixing ratios of biogenic compounds and total OH reactivity measured during late spring 2014 at the forest of downy oak trees of the Observatoire de Haute Provence (OHP), France. Air masses were sampled at two heights: 2 m, i.e., inside the canopy, and 10 m, i.e., above the canopy, where the mean canopy height is 5 m.
We found that the OH reactivity at the site mainly depended on the main primary biogenic species emitted by the forest, which was isoprene and to a lesser extent by its degradation products and long-lived atmospheric compounds (up to 26 % during daytime). During daytime, no significant missing OH reactivity was reported at the site, either inside or above the canopy. However, during two nights we determined a missing fraction of OH reactivity up to 50 %, possibly due to unmeasured oxidation products. We confirmed that no significant oxidation of the primary species occurred within the canopy; primary compounds emitted by the forest were fast transported to the atmosphere. Finally, the OH reactivity at this site was maximum 69 s−1, which is a high value for a forest characterized by a temperate climate. Observations in various and diverse forests in the Mediterranean region are therefore needed to better constrain the impact of reactive gases over this area.