LANDEX : An atmospheric field study in the Landes forest
Villenavea, P.-M Flauda, J. Kammera, K. Mermeta,h, E. Perraudina, E. Lamaudb, J.M. Bonnefondb, D. Garrigoub, E. Ormenoc, A. Saunierc, J. Virosc, C. Fernandezc, N. Marchandd, C. Gioriod, B. Temimed, J.L. Jaffrezoe, A. Albinetf, G. Lanzafamef, C. Schoemaeckerg, M. Al Ajamig, S. Batutg, N. Locogeh, S. Dusanterh, T. Leonardish, S. Sauvageh, C. Jamberti, C. Deloni, P. Durandi, V. Grosj, S. Bsaibesj, F. Truongj, A. Gratienk, M. Cirtogk, V. Michoudk, J.F. Doussink, J.B. Renardl, M. Staudtm, J. Byronm
a)EPOC CNRS Bordeaux, b)ISPA INRA Villenave d’Ornon, c)IMBE CNRS Marseille, d)LCE CNRS Marseille, e)IGE CNRS Grenoble, f)INERIS Verneuil en Halatte, g)PC2A CNRS Lille, h)IMT Lille Douai, i)LA CNRS Toulouse, j)LSCE CEA CNRS UVSQ, k)LISA CNRS UPEC UPD Créteil, l)LPC2E CNRS Orléans, m)CEFE CNRS Montpellier (France)
In the atmosphere, the secondary fraction constitutes an important part of organic aerosols at a global scale, and may even correspond up to 80% in specific locations (Jimenez et al., 2009). Understanding the processes governing Secondary Organic Aerosols (SOA) formation and fate is essential to assess the aerosol impacts on both air quality and climate change. Despite recent advances, chemistry-transport models representing SOA formation and evolution are not enough well-constrained. New field studies of poorly-documented ecosystems, are therefore essential to improve the understanding of atmospheric processes.
The objective of the LANDEX project is to assess the formation and the fate of SOA arising from the French Landes forest, which constitutes a suitable ecosystem to study SOA from biogenic origin. Indeed, as one of the largest forests in Europe (1 million ha), relatively homogeneous with more than 90% of maritime pines (Pinus Pinaster) and with few anthropogenic inputs, the Landes forest represents one of the best place to assess the influence of parameters such as solar radiation (with strong episodes of sunshine), relative humidity, but also inputs of sea spray (from the Atlantic ocean) on the formation of SOA. To achieve our goal, an intensive field campaign bringing together 12 French partners has been conducted in July 2017 at Bilos, consisting in measuring volatile organic compound (VOC) concentrations using both online chromatographs and PTR-TOF-MS (including monoterpenes and their by-products). Emission rates from litter, branch and trunk were also investigated thanks to dynamic enclosure chambers.
Particle size distribution was investigated using different instruments (SMPS, FIDAS, etc.) whereas a PM2.5 TEOM-FDMS was used to determine aerosol mass concentration. Particle chemical composition was followed online implementing an AMS and offline analyzing HVS and LVS daytime and nighttime filters. SO2, ozone and nitrogen oxides (NOx) were assessed by UV and chemiluminescence analysers. OH radicals were measured using the FAGE facility whereas NO3 radical concentrations were tentatively followed by BB-CEAS. Two total OH reactivity (based on CRM and FAGE techniques) were implemented on the site. Local air masses were characterized by measuring meteorological parameters (such as T, P, RH, wind and solar radiation) and modelled calculating backward trajectories using the NOAA-Hysplit facility. In addition, the quantification of heat fluxes, CO2 and water vapor fluxes (allowing to evaluate the physiological status of the tree parcel) were obtained from the ICOS network station at Bilos, and ozone and VOC fluxes (from PTR-TOF-MS measurements) were carried out simultaneously using Eddy Covariance method.
The first original results, obtained during the campaign, will be presented here, emphasizing the relevance of the Landes forest site for biogenic SOA studies.
Acknowledgements: This work was supported by the French Agency for Environment and Energy Management (ADEME), the NEEDS research program, the CNRS-INSU LEFE-CHAT program, the PEPS-IDEX Bordeaux and the COTE Bordeaux Cluster of Excellence.