Thèses

Jeudi 16 Décembre 2021 à 14h30.

Laboratory experiments on polarized light scattering by pollen bioaerosols

''This work is dedicated to the interaction of light with complex-shaped pollens grains, which are incriminated for their impact on the Earth’s climate and on public health with socio-economical costs reaching 150 billion euros per year in Europe. Still, the detection and identification of the involved pollens taxa remains challenging, mainly due to the complexity in size and shape of these grains. Also, existing methodologies are limited by their time duration (several days) and by their inherent volumetric sampling. In this context, the goal of this thesis is to achieve, in partnership with TERA Sensor, a laboratory demonstrator to detect pollens grains embedded in ambient air, in real time and without sampling, with a special focus on ragweed pollen, one of the major allergens in Europe and North America. In complement, ash, birch and pine pollen are also studied. All these pollen grains exhibit a large size and complex small-scale morphological structures, beyond the reach of numerically exact light-scattering models. Therefore, the approach followed in this thesis is to perform a controlled laboratory experiment that takes benefit from light polarimetry to address the complex shape of pollens grains, based on the robust scattering matrix formalism. Moreover, the laboratory experiment is extended to the VIS and NIR spectral ranges (Cholleton et al., JQSRT, 2020). Interestingly, our laboratory experimental error bars are precise enough to show that the considered set of four pollens, when embedded in ambient air, exhibit different spectral and polarimetric light scattering characteristics, in the form of ten scattering matrix elements (five per wavelength), which allow identifying each separately (Cholleton et al., AMT Discussion, 2021). Finally, this laboratory methodology is adapted to the detection of airborne ragweed pollen grains, in real-time and without sampling, using modified light source and detector as part of the industrial cooperation. Hence, the precision achieved in the laboratory experiment opens new insights on the atmospheric detection of complex-shaped pollen grains.

Directeur de thèse / thesis director:
Dr. Alain MIFFRE

Membres du jury / members of the jury:
Prof. Matthew BERG (Kansas State University, Reviewer)
Prof. Jérôme KASPARIAN (Geneva University, Reviewer)
Prof. Anne PILLONNET (iLM, Examiner)
Prof. Evelyne GÉHIN (Université Paris-Est Créteil, Examiner)
Dr. Émilie BIALIC (TERA Sensor, Examiner)
Dr. Alain MIFFRE (iLM, PhD supervisor)

''