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- Title
Variability of OH reactivity in the Landes maritime Pine forest: Results from the LANDEX campaign 2017.
- Authors
Bsaibes, Sandy; Ajami, Mohamad Al; Mermet, Kenneth; Truong, François; Batut, Sébastien; Hecquet, Christophe; Dusanter, Sébastien; Léornadis, Thierry; Sauvage, Stéphane; Kammer, Julien; Flaud, Pierre-Marie; Perraudin, Emilie; Villenave, Eric; Locoge, Nadine; Gros, Valérie; Schoemaecker, Coralie
- Abstract
Total OH reactivity measurements were conducted during the LANDEX intensive field campaign in a coniferous temperate forest located in the Landes area, south-western France, during July 2017. In order to investigate inter-canopy and intra-canopy variability, measurements were performed inside (6 m) and above the canopy level (12 m), as well as at two different locations within the canopy, using a Comparative Reactivity Method (CRM) and a Laser Photolysis-Laser Induced Fluorescence (LP-LIF) instrument. The two techniques were intercompared at the end of the campaign by performing measurements at the same location. Volatile organic compounds were also monitored at both levels with a proton transfer-time of flight mass spectrometer and online gas Chromatography instruments to evaluate their contribution to total OH reactivity, with monoterpenes being the main reactive species emitted in this Pinus pinaster Aiton dominated forest. Total OH reactivity varied diurnally, following the trend of BVOCs of which emissions and concentrations were dependent on meteorological parameters. Highest levels of total OH reactivity were observed during nights with a low turbulence (u* ≤ 0.2 m/s) leading to lower mixing of emitted species within the canopy and thus an important vertical stratification, characterized by a strong concentration gradient. By comparing the calculated OH reactivity from contributions of individually measured compounds to the measured OH reactivity, a discrepancy was seen at both heights mainly related to ambient temperature during day-time. It highlights that missing OH sinks could be due to temperature-dependent missing primary emissions or secondary products linked to a temperature-enhanced photochemistry. During night-time hours, atmospheric stability and relative humidity played a key role in the missing reactivity. Lower turbulence showed to be favourable for night-time chemistry, inducing a higher missing OH reactivity. Humid surfaces may have represented an additional sink for oxygenated compounds, escaping de facto total OH reactivity, and leading to lower or no missing OH reactivity.
- Subjects
FRANCE; LASER-induced fluorescence; TEMPERATE forests; CLUSTER pine; CONIFEROUS forests; VOLATILE organic compounds; DISPERSION (Atmospheric chemistry)
- Publication
Atmospheric Chemistry & Physics Discussions, 2019, p1
- ISSN
1680-7367
- Publication type
Article
- DOI
10.5194/acp-2019-548