27 Oct 2022
27 Oct 2022
Status: this preprint is currently under review for the journal ACP.

Simulation of organic aerosol, its precursors and related oxidants in the Landes pine forest in south-western France: Need to account for domain specific land-use and physical conditions

Arineh Cholakian1,2,4, Matthias Beekmann2, Guillaume Siour3, Isabelle Coll3, Manuela Cirtog3, Elena Ormeno5, Pierre-Marie Flaud1, Emilie Perraudin1, and Eric Villenave1 Arineh Cholakian et al.
  • 1Univ. Bordeaux, CNRS, EPOC, EPHE, UMR 5805, F-33405 Talence Cedex, France
  • 2Université de Paris Cité and Univ Paris Est Créteil, CNRS, LISA, F-75013, Paris, France
  • 3Univ Paris Est Créteil and Université de Paris Cité, CNRS, LISA, F-94010, Créteil, France
  • 4LMD UMR CNRS 8539, ENS, Ecole Polytechnique, Institut Pierre Simon Laplace (IPSL), Palaiseau, France
  • 5CNRS, Aix Marseille Univ, IRD, Avignon Univ, IMBE, 13397 Marseille, France

Abstract. Organic aerosol (OA) still remains one of the most difficult components of the atmospheric aerosols to simulate, given the multitude of its precursors, the uncertainty of its formation pathways and the lack of measurements of its detailed composition. The LANDEX project (The LANDes Experiment), during its intensive field campaign in summer 2017, gives us not only the opportunity to compare biogenic secondary OA (BSOA), but also its precursors and oxidants obtained within and above the Landes forest canopy, to simulations performed with CHIMERE, a state of the art regional Chemistry-Transport Model. The Landes forest is situated in the south-western part of France, and is one of the largest anthropized forests in Europe (1 million ha), composed by a majority of maritime pine trees, strong terpenoid emitters, providing a large potential for biogenic SOA formation. In order to simulate OA build-up in this area, a specific model configuration set-up, adapted to the local peculiarities was necessary. As the forest is inhomogeneous, with interstitial agricultural fields, high-resolution 1 km simulations over the forest area were performed. BVOC emissions were predicted by MEGAN, but specific land cover information needed to be used, chosen from the comparison of several high-resolution land cover databases. Moreover, the tree species distribution needed to be updated for the specific conditions of the Landes forest. In order to understand the canopy effect in the forest, canopy effects on vertical diffusivity, winds and radiation were implemented in the model in a simplified way. The refined simulations show a redistribution of BVOCs with a decrease in isoprene and an increase in terpenoid emissions with respect to the standard case, in line with observations. Corresponding changes on simulated BSOA sources are tracked. Very low night-time ozone, sometimes near zero, remains overestimated in all simulations. This has implications to the night-time oxidant budget, including NO3. Despite careful treatment of physical conditions, simulated BSOA is overestimated in the most refined simulation. Simulations are also compared to air quality sites surrounding the Landes forest, reporting a more realistic simulation in these stations in the most refined test case. Finally the importance of the see breeze system which also impacts species concentrations inside the forest is made evident.

Arineh Cholakian et al.

Status: open (until 28 Dec 2022)

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Arineh Cholakian et al.

Arineh Cholakian et al.


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Short summary
This article revolves around the simulation of biogenic secondary organic aerosols in the Landes forest (south-west France). In order to do so, several sensitivity cases involving biogenic emission factors, landcover data, anthropogenic emissions and physical parameters were performed and each compared to measurements both in the forest canopy and around the forest. The chemistry behind the formation of these aerosols and their production and transport in the forest canopy are discussed.