Biogenic Volatile Organic Compounds (BVOCs) are massively emitted into the atmosphere by vegetation. These compounds are highly reactive towards the nitrate radical NO3, the major nocturnal oxidant. The BVOC + NO₃ chemistry is particularly effective in « mixed » atmospheres, influenced by both biogenic and anthropogenic emissions and characterized by high concentrations of both BVOCs and nitrogen oxides. These processes generate gaseous and particulate secondary pollutants, including organic nitrates which can serve as temporary NOx reservoirs and affect the NOx and ozone budgets. Additionally, these processes contribute to the formation of Secondary Organic Aerosols (SOA), which significantly impact air quality, climate, and health.

The objective of this thesis is to enhance our understanding of these processes and their impact on air quality. It comprises two main parts:

• The NO3-initiated oxidation of two BVOCs, α- and β-phellandrene, was investigated using atmospheric simulation chambers. These compounds were selected in order to study the influence of their chemical structure on their reactivity and to address experimental data gaps in the literature. The rate constants were determined using an absolute-rate determination method. Mechanisms have been proposed based on the identification of individual oxidation products in both gas and aerosol phases. Both SOA and total organic nitrates yields were also provided. The effect of mixing different VOCs on SOA yield from a single BVOC precursor was studied. Numerical simulations were performed to determine the dominant chemical regime of peroxy radicals under the experimental conditions. The obtained data contributed to a better understanding of these processes and are useful to interpret observations in the atmosphere in particular during the ACROSS field campaign.
• The role of BVOC + NO₃ nocturnal chemistry in the formation of secondary pollutants in urban plumes of « mixed » anthropogenic/biogenic atmospheres was investigated during the ACROSS field campaign. Measurements of the NO₃, N₂O₅, NO_x, and NO_y, were conducted at a top of a 40-meter tower (above the forest canopy), in the Rambouillet Forest located at the southwest of Paris. For this purpose, a part of the thesis work involved implementation and characterization of a new instrument called « NOyBox, » which integrates measurements of NO₃, N₂O₅, NO_x, and NO_y at low mixing ratios (on the order of ppt). Significant mixing ratios of NO₃ and N₂O₅ were detected for several nights when the site was under the influence of polluted air masses, with high levels of ozone and NO2 and moderate relative humidity. These measurements will allow to better assess the impact of BVOC+NO3 reactions on air quality in the Île-de-France region.

Lieu
Maison des Sciences de l’Environnement (MSE)
UPEC Campus Centre
Auditorium de la MSE
61, avenue du Général de Gaulle
94000 Créteil

En visio
https://u-pec-fr.zoom.us/j/98698479934?pwd=T0poODZEdmdsOHNHb1ZUR0dDbXUzdz09

• M. SAUVAGE Stéphane, Institut Mines-Télécom Nord Europe, rapporteur
• M. MELLOUKI Abdelwahid, Mohammed 6 Polytechnic University, rapporteur
• M. DOUSSIN Jean-François, INSU CNRS, examinateur
• Mme PERRAUDIN Emilie, UMR CNRS 5805 EPOC – OASU Université de Bordeaux, examinatrice
• M. CROWLEY John, Atmospheric Chemistry Department, Max-Planck-Institut für Chemie, examinateur
• Mme GALSOMIES Laurence, Docteur en sciences de l’environnement-ADEME, invitée
• Mme PICQUET-VARRAULT Bénédicte, LISA, directrice de thèse
• Mme CIRTOG Manuela, LISA, co-encadrante de thèse