PhD thesis defense by Joris Léglise
Study of secondary organic aerosol formation by mass spectrometry during ozonolysis of unsaturated volatile organic compounds
February 26, 2019 at 13:30 at the ICARE Laboratory (CNRS)
The understanding of the formation of secondary organic aerosols (OSA) remains deficient. One of the objectives of this thesis work was the installation and use of a system for sampling and measuring the chemical composition of the aerosol by chemical ionization mass spectrometry (FIGAERO-CI-ToF-MS) . This instrument has been used in the ozonolysis of unsaturated VOCs in the atmospheric simulation chamber HELIOS and has evaluated the conditions for the formation of carboxylic acids and organosulfur compounds. The specific formation pathways of organosulfates (OS) have been studied. This study confirmed the low efficiency of the esterification of hydroxyl groups. Conversely, OS formation by epoxide ring opening is more efficient at pH more acidic. Moreover, the increase in relative humidity has a positive impact on the generation of carboxylic acids in the particulate phase. A second objective was the characterization of a system for aerosol collection and measurement of its chemical composition, coupled with a proton transfer mass spectrometer (CHARON-PTR-ToF-MS). The measurement of the fragmentation of 26 pure compounds in the particulate phase allowed the development of a corrective procedure taking into account the phenomenon of fragmentation. This procedure was applied to the measurement of SOAs generated by the ozonolysis of biogenic VOCs in a flow reactor. The volatility of the product aerosol has been estimated by the installation of a thermo-stripper tube. Taking account of fragmentation greatly improved the agreement between the measurement of volatility and its calculation by several parametric equations.
To know more :