Development and validation of a new experimental set-up to study reactions between peroxy RO2 + HOx radicals

International audienc

Development and validation of a new experimental set-up to study reactions between peroxy RO2 + HOx radicals

National audienc

Experimental study of premixed ozone-seeded DME/O2 cool flames on a stagnation plate burner

International audienc

Development and validation of a new experimental set-up to study reactions between peroxy RO2 + HOx radicals

National audienc

Legislative Documents

Also, variously referred to as: Senate bills; Senate documents; Senate legislative documents; legislative documents; and General Court documents

A new method to analyze the hygroscopic properties of soot particles from their aging process

National audienceSoot particles are considered as important aerosols in the atmosphere due to their potential role as cloud condensation nuclei (CCNs). Freshly released soot is generally considered as hydrophobic. However, the so-called aging process in the atmosphere can modify morphology and surface composition of soot particles and turn them into efficient CCNs. The hygroscopic properties of soot are commonly measured from their activated fraction F_a that is the ratio of the number of nucleated droples on the number of CCNs. For spherical and monodisperse aerosols, the κ-Köhler theory is generally used to obtain the parameter κ which quantifies the hygroscopic properties of aerosol. In this work, a model to obtain κ is proposed by taking into account the size distribution and the morphology of the aerosol particles. The model is first tested on dry ammonium sulfate that is well known to produce quasi-spherical particles. The results of the activation experiments are in good agreement with the predictions of the model. Then, the model is applied to soot particles that are characterized by complex morphology. Soot particles had to be activated by aging with ozone before activation experiments to increase their k into the validity range of the model (i.e. to turn fresh soot to hydrophilic aggregates). The parameters of the determination of κ are soot particle mobility diameter Dm, fractal dimension Df, the primary particle diameter Dpp and the geometric standard deviation of volume equivalent particles of soot.Les particules de suie sont considérées comme des aérosols importants dans l'atmosphère en raison de leur rôle dans la formation du nuage en tant que potentiels noyaux de condensation (CCNs). Les suies fraîches sont généralement considérées comme hydrophobes. Néanmoins, les processus de vieillissement dans l'atmosphère peuvent modifier leur morphologie et composition chimique de surface, et les rendre hydrophiles. Les propriétées hygroscopiques des particules de suie sont généralement estimées par la mesure de la fraction activée F_a qui est donnée par le rapport du nombre des goutelettes formées sur le nombre de CCNs. En supposant que les CCNs sont monodispersés et de forme sphérique, la théorie de κ-Köhler est généralement utilisée pour obtenir un « paramètre d’hygroscopicité » κ qui exprime quantitativement les propriétés hygroscopiques de l'aérosol. Dans ce travail, un modèle pour obtenir κ est proposé en prenant en compte la distribution de taille et la morphologie des CCNs. Le modèle est testé avec des CCNs générés à partir de sulfate d'ammonium qui produit des particules quasi-sphériques et qui possèdent des distributions log-normale. Les résultats expérimentaux de l'hygroscopie des particules sèches de sulfate d'ammonium concordent très bien avec la simulation par le modèle. Ensuite, le modèle est utilisé pour obtenir κ des particules de suie vieillies en presence de radicaux OH. Les paramètres pris en compte sont le diamètre de mobilité Dm, la dimension fractale Df, le diamètre des particules primaires Dpp et l'écart type géométrique des volumes équivalents des particules de suie

Quantitative IBBCEAS measurements of I2 in the presence of aerosols

International audienceAn instrument implementing Incoherent BroadBand Cavity-Enhanced Absorption Spectroscopy (IBBCEAS) for quantitative measurements of molecular iodine (I2) at ambient pressure and in the presence of aerosols is presented. The instrument is based on a LED emitting in the green spectral region around 500–550 nm, exciting a multitude of rovibronic transitions in the I2 B ← X electronic absorption spectrum. I2 was generated using a permeation device and was mixed with a dilution flow of Ar and another flow containing NaCl aerosols. Retrieval of the mirror reflectivity, necessary for quantitative IBBCEAS measurements, was not pursued in this study. Instead, calibrated I2 flows were used, and a differential optical absorption spectroscopy type of algorithm was implemented for the data analysis. This approach has several benefits, in particular when light extinction due to aerosols is substantial. Estimated detection limits are roughly 0.04 nmol/l without aerosols and 0.4 nmol/l in the presence of aerosols (1010 particles/l with 60–70 nm mean diameter, leading to I 0/I aerosols ≈ 5.4). A drop in measured I2 concentration in relation to the expected mixing ratio was observed when using the highest aerosol concentration, likely due to adsorption of I2 onto aerosols

Atmospheric Chemistry linked to HO x radicals of a Suburban Forest during the ACROSS summer Field Campaign

International audienceParis, one of the largest European megacities, transports pollution to different surrounding areas depending on the variation of the wind direction associated with specific meteorological conditions. The relatively unique situation of this isolated megacity from other urban areas make it a suitable location to study the impact of urban emissions on the chemistry of close biogenic environments such as forests and vice versa. In order to investigate this influence, the ACROSS (Atmospheric ChemistRy Of the Suburban foreSt) field campaign was performed during summer 2022, with a measurement site located in the Rambouillet forest. The combination of the data provided during this field campaign from different research groups (such as measurements of VOCs, inorganic species, particle concentration and composition, …) will allow a better understanding of the influence of mixing anthropogenic urban or oceanic air masses, leading to different NO concentrations, with biogenic forestry emissions on the oxidation of tropospheric VOCs. This will ultimately help improving this chemistry within atmospheric models. The UL-FAGE instrument was deployed during the ACROSS campaign, where different types of measurements were performed: OH, HO2, ROx radical quantification at the ground level and OH reactivity. The OH reactivity was alternatively measured at two different levels: below (ground level) and above the forest canopy (top of a 40 m tower). Clear stratification was observed during the night with a higher OH reactivity at the ground level than above the canopy. Comparison between the measured and the calculated OH reactivity allows to identify the diurnal missing reactivity at both levels. Preliminary results of the OH reactivity and the radical quantification will be presented