Mohamad Al Ajami
Docteur en physico-chimie
Thèse soutenue le 26 octobre 2018
Laboratoire de Physicochimie des Processus de Combustion et de l’Atmosphérique – PC2A
Titre et résumé de thèse
Publications scientifiques
Présentations orales et posters
Perspectives
Titre et résumé de thèse
Characterization and deployment of a FAGE instrument for studying the atmospheric oxidation processes
The hydroxyl radical, OH, the hydroperoxyl radical HO2 (known collectively as HOx) and peroxy radicals RO2, play a key role in the tropospheric chemistry and are intricately related to the chemical cycles that control the concentration of greenhouse gases such as methane and have important implications for air quality through VOC oxidation and ozone formation. Accurate quantification of these three important radicals and investigations on the chemical mechanisms that control their formation and removal through comparisons between measured and modeled concentrations are needed to develop a better understanding of the atmospheric chemistry mechanisms.
Different types of instruments have been developed and deployed to quantify HOx radicals in the field. One has been developed over the last few years in our group based on the most deployed technique: the FAGE (Fluorescence Assay by Gas Expansion). This technique represents direct measurement of OH and indirect measurement of HO2 radicals by chemical conversion to OH after addition of NO. However, some RO2 radicals can also be converted to OH by a similar radical reaction sequence as HO2, so that they are potential interferences for HO2 measurements.
For UL-FAGE, the conversion efficiency of various RO2 species to HO2 has been investigated and it has been shown that variation of NO allows to selectively detect HO2 and double bound RO2. With similar FAGE instruments, field campaigns have been carried out in remote biogenic environments (dominated by isoprene emission) in the last decade. They have highlighted unidentified interferences in these measurements. In our laboratory, we used our FAGE instrument in controlled conditions to investigate the origin of the interference and we have shown that ROOOH (trioxides), product of radical-radical reactions in the atmosphere may be responsible.
PC2A calibration cell was intercompared to other calibrators (IMT-Douai and LPC2E) of similar design over wide range of conditions. One goal of the intercomparison was to evaluate each other’s calibration and to make sure that they had no significant biases. The results showed a good agreement between the three calibration cells for HOx and RO2 radicals. Finally, the UL-FAGE in both configurations (quantification and reactivity) was deployed to a field measurement (LANDEX) in forest environment.
Part of the campaign was conducted to an intercomparison between LP-FAGE and LSCE-CRM instruments. Measured reactivity showed very good agreement between both techniques.
Directrices de thèse: Christa FITTSCHEN, Coralie SCHOEMAECKER
Rapporteurs: Yoshizumi KAJII, Valérie GROS
Examinateurs: Sébastien DUSANTER, Alexandre KUKUI
Laboratoire: PC2A
Financement: Labex CaPPA / Ecole doctorale SMRE
Publications scientifiques
Christa Fittschen, Mohamad Al Ajami, Sebastien Batut, Valerio Ferracci, Scott Archer-Nicholls, Alexander T. Archibald, Coralie Schoemaecker « ROOOH: The Missing Piece of the Puzzle for OH measurements in low NO Environments » Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-441
Sandy Bsaibes, Mohamad Al Ajami, François Truong, Sébastien Batut, Christophe Hecquet, Sébastien Dusanter, Thierry Léonardis, Nadine Locoge, Valérie Gros, Coralie Schoemaecker « OH Reactivity measurement in a pinus fores » submitted
+ 2 publications manuscripts in preparation
Présentations orales et poster
Mohamad al Ajami, Sébastien Batut, Coralie Schoemaecker, and Christa Fittschen’’ OH quantification in the atmosphere by FAGE: Identification of the source of interferences’’ accepted for oral presentation at IREPS conference, Lille, France « award for best presentation ».
Mohamad Al Ajami, Sebastien Batutt, Valerio Ferraccib, Scott Archer-Nicholls, Alexander T. Archibald, Coralie Schoemaecker and Christa Fittschen « ROOOH: a missing piece of puzzle in the understanding of OH in remote environments?’’ accepted for oral presentation at the 16th Workshop on Atmospheric Chemistry and Air Quality, Leipzig, Germany.
Sébastien Dusanter, Coralie Schoemaecker, Mohamad Al Ajami, Marius Duncianu, Sébastien Batut, Asma Grira, Alexandre Tomas, and Christa Fittschen ’’Impact of the reactions of peroxy radicals (RO2) with hydroxyl radical (OH) in the atmospheric chemistry understanding’’, accepted for oral presentation at 4 Journee scientifique, Villeneuve d’Ascq, France.
M. Al Ajami, C. Schoemaecker, S. Batut, V. Ferracci, S. Archer-Nicholls, A. Archibald, C. Fittschen ’’ roooh: the missing piece of the puzzle for oh measurements in low no environments » accepted for oral presentation at 25th International Symposium on Gas Kinetics & Related Phenomena, Lille, France.
Mohamad Al Ajami, Marion Blocquet, Sébastien Dusanter, Nadine Locoge, Benjamin Hanoune, Christa Fittschen, Coralie Schoemaecker « Study of oxidation processes in the atmosphere by OH reactivity measurements », poster at Cappa 3 Journee scientifique, Villeneuve d’Ascq, France.
E. Villenave, M. Al Ajami, C. Schoemacker, et al., « LANDEX: An atmospheric field study in the Landes forest’’, accepted for oral presentation at the 16th Workshop on Atmospheric Chemistry and Air Quality, Leipzig, Germany.
Christa Fittschen, Mohamad Al Ajami, Sebastien Batut, Valerio Ferracci, Scott Archer-Nicholls, Alexander T. Archibald, Coralie Schoemaecker1 « ROOOH: the missing Piece of the Puzzle for OH measurements in low NO Environments’’, accepted for oral presentation at 15th IGAC science conference 2018, Takamatsu kagawa, Japan.
E. Villenave, M. Al Ajami, C. Schoemacker, et al., « LANDEX: An atmospheric field study in the Landes forest’’, accepted for oral presentation at 6th Sino-French Workshop, 2018 at Orleans, France.
Perspectives
Looking for a postdoctoral opportunity in the environmental chemistry domain.
