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Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy for NO3 Radical and Aerosol Measurements : Application to Field and Chamber Studies

Abstract : Particulate matter in the atmosphere is also one of the main components of air pollution. The inclusion of aerosols in global climate models is still at its infancy due to large uncertainties in particle properties, especially regarding organic aerosol of secondary origin. Therefore, studies are needed to improve our knowledge of aerosol physicochemical and optical properties that may help understand their impacts on both air quality and climate. In this work, one of the aims is to develop a developed custom-designed incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) instrument, and to apply it to the in situ measurement of aerosol extinction near the ground surface in effort to address the issue of missing data in the light detection and ranging (Lidar) blind zone in the first hundreds of meters of the observation range. Combined measurements of aerosol extinction at the same location using Lidar remote sensing at 355 nm and in situ IBBCEAS operating in the UV spectral region around 370 nm showed results with a good correlation (R2 = 0.90) between the two measurement techniques, which provides a new strategy for near-end Lidar calibration, using a ground-based compact and robust IBBCEAS located at the Lidar measurement site to determine the vertical profile of the aerosol extinction coefficient with a higher accuracy. The nitrate radical is one of the important nitrogen inorganic species in the atmosphere, and has been recognized for decades to play a key role in nocturnal chemistry. Its low concentrations in the troposphere and its rapid photolysis in sunlight make it challenging to detect. Kinetics and mechanistic studies on NO3-initiated oxidation of VOCs are also much less abundant in the literature compared to OH radical chemistry, thus limiting the understanding of NO3 impact in atmospheric chemistry. This thesis aims to develop an IBBCEAS instrument for detecting the NO3 on the simulation chamber CHARME, aiming at investigating NO3 chemistry with biogenic VOCs. Chamber studies were performed to validate the IBBCEAS instrument by following nitrate radical concentrations during its production by reaction of NO2 with O3 in the simulation chamber. Furthermore, the reaction of guaiacol (2-methoxyphenol, a VOC emitted by biomass burning) with nitrate radicals was investigated in both LPCA simulation chambers (CHARME and LPCA-ONE). The SOAs yield and products of NO3 + guaiacol have been studied. The rate coefficient determined using the relative rate method ((3.77 ± 0.39) × 10-11 cm3 molecule-1 s-1) leads to an atmospheric lifetime of about 53 s with respect to the oxidation of NO3 with guaiacol. The formation of secondary organic aerosols from the reaction of guaiacol with nitrate radicals was also observed. The SOAs yields were shown to be influenced by the initial guaiacol concentration, leading to aerosol yields ranging from 0.01 to 0.21. A very good agreement was observed between the experiments performed in both chambers which gives confidence in the data obtained in this study.
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Lingshuo Meng. Incoherent Broadband Cavity-Enhanced Absorption Spectroscopy for NO3 Radical and Aerosol Measurements : Application to Field and Chamber Studies. Earth Sciences. Université du Littoral Côte d'Opale, 2020. English. ⟨NNT : 2020DUNK0576⟩. ⟨tel-03399390⟩

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