Spelling suggestions: "subject:"atmospheric aerosol"" "subject:"tmospheric aerosol""
121 |
LINKING INFANT LOCOMOTION DYNAMICS WITH FLOOR DUST RESUSPENSION AND EXPOSURENeeraja Balasubrahmaniam (8802989) 07 May 2020 (has links)
<p>Infant exposure to the microbial and allergenic content of indoor floor dust has been shown to play a significant role in both the development of, and protection against, allergies and asthma later in life. Resuspension of floor dust during infant locomotion induces a vertical transport of particles to the breathing zone, leading to inhalation exposure to a concentrated cloud of coarse (> 1μm) and fine (≤ 1μm) particles. Resuspension, and subsequent exposure, during periods of active infant locomotion is likely influenced by gait parameters. This dependence has been little explored to date and may play a significant role in floor dust resuspension and exposure associated with forms of locomotion specific to infants. This study explores associations between infant locomotion dynamics and floor dust resuspension and exposure in the indoor environment. Infant gait parameters for walking and physiological characteristics expected to influence dust resuspension and exposure were identified, including: contact frequency (steps min<sup>-1</sup>), contact area per step (m<sup>2</sup>), locomotion speed (m s<sup>-1</sup>), breathing zone height (cm), and time-resolved locomotion profiles. Gait parameter datasets for standard gait experiments were collected for infants in three age groups: 12, 15, and 19 months-old (m/o). The gait parameters were integrated with an indoor dust resuspension model through a Monte Carlo framework to predict how age-dependent variations in locomotion affect the resuspension mass emission rate (mg h<sup>-1</sup>) for five particle size fractions from 0.3 to 10 μm. Eddy diffusivity coefficients (m<sup>2</sup> s<sup>-1</sup>) were estimated for each age group and used in a particle transport model to determine the vertical particle concentration profile above the floor.</p><p>Probability density functions of contact frequency, contact area, locomotion speed, breathing zone height, and size-resolved resuspension mass emission rates were determined for infants in each group. Infant standard gait contact frequencies were generally in the range of 100 to 300 steps min<sup>-1 </sup>and increased with age, with median values of 186 steps min<sup>-1 </sup>for 12 m/o, 207 steps min<sup>-1</sup> for 15 m/o, and 246.2 steps min<sup>-1</sup> for 19 m/o infants. Similarly, locomotion speed increased with age, from 67.3 cm s<sup>-1 </sup>at 12 m/o to 118.83 cm s<sup>-1</sup> at 19 m/o, as did the breathing zone height, which varied between 60 and 85 cm. Resuspension mass emission rates increased with both infant age and particle size. A 19 m/o infant will resuspend comparably more particles from the same indoor settled dust deposit compared to a 15 m/o or 12 m/o infant. Age-dependent variations in the resuspension mass emission rate and eddy diffusivity coefficient drove changes in the vertical particle concentration profile within the resuspended particle cloud. For all particle size fractions, there is an average of a 6% increase in the resuspended particle concentration at a height of 1 m from the floor for a 19 m/o compared to a 12 m/o infant. Time-resolved locomotion profiles were obtained for infants in natural gait during free play establish the transient nature of walking-induced particle resuspension and associated exposures for infants, with variable periods of active locomotion, no motion, and impulsive falls. This study demonstrates that floor dust resuspension and exposure can be influenced by the nature of infant locomotion patterns, which vary with age and are distinctly different from those for adults.</p> Read more
|
122 |
AIRCRAFT-BASED STUDIES OF GREENHOUSE GASES AND AEROSOLSJay M Tomlin (14221835) 06 December 2022 (has links)
<p>The Earth–atmosphere energy balance is dictated by incoming solar radiation and outgoing thermal radiation with greenhouse gases (GHG) and aerosols playing a major role in this effect. The atmospheric abundance and properties of airborne particles and gases lead to the redistribution of radiative energy, resulting in a warming or cooling effect. However, the extent of this effect remains to be insufficiently constrained. Improved quantification and characterization of GHG and aerosols are important requirements to inform current climate models. High-precision instrumentation and thoughtful experimental strategies are necessary to yield various analytical measurement datasets, despite complex meteorological and environmental conditions. This dissertation focuses on the assessment of CO<sub>2 </sub>and atmospheric particles from aircraft-based measurements enabling representative and spatially sampling of local regions of interest.</p>
<p>Chapter 1 provides introductory discussion on the atmospheric implication of GHG and aerosols on the climate and related uncertainties. Chapter 2 summarizes the employed experimental techniques for quantification of GHG and characterization of atmospheric particles. We relied on an aircraft platform equipped with an air turbulence probe for 3D wind vector calculation and a high-precision cavity ring-down spectrometer for the quantification of ambient CO<sub>2</sub>, CH<sub>4</sub>, and H2O<sub><em>v</em></sub>. Furthermore, the simultaneous composition and morphological information of aerosol samples were assessed using complementary chemical imaging techniques. Chemical composition of elements with Z > 23 was determined using computer-controlled scanning electron microscopy with energy dispersive X-ray spectroscopy (CCSEM/EDX). Scanning transmission X-ray microscopy coupled with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS) was used to determined spatially resolved elemental specific molecular information present in atmospheric particles.</p>
<p>Chapter 3 presents our study focused on the characterization of mixed mineral dust and biomass burning (BB) aerosols during an intensive burning event. We identified distinct particle types based on individual elemental contribution pre-, syn-, and post-burning event including highly carbonaceous (54–83%) particles, aged mineral dust (1–6%), and sulfur-containing particles (17–41%). X-ray spectromicroscopy techniques were used to characterize the internal chemical heterogeneity of individual BB particles and the morphology of soot inclusions, as well as changes in the particle organic volume fraction (OVF). An estimation method for particle component masses (i.e., organics, elemental carbon, and inorganics) inferred from STXM measurements was used to determine quantitative mixing state metrics based on entropy-derived diversity measures for particles acquired at different periods of the BB event. In general, there was a small difference in the particle-specific diversity among the samples (<em>D</em><sub><em>α</em></sub> = 1.3–1.8). However, the disparity from the bulk population diversity observed during the intense periods was found to have high values of <em>D</em><sub><em>γ</em></sub> = 2.5–2.9, while particles collected outside of the burning event displayed lower bulk diversity of <em>D</em><sub><em>γ</em></sub> = 1.5–2.0. Quantitative methods obtained from chemical imaging measurements presented here will serve to accurately characterize the evolution of mixed BB aerosols within urban environments.</p>
<p>Chapter 4 follows the investigation of the physicochemical properties of atmospheric particles collected onboard a research aircraft flown over the Azores using offline spectromicroscopy techniques. Particles were collected within the marine boundary layer (MBL) and free troposphere (FT) comparing samples after long-range atmospheric transport episodes facilitated by dry intrusion (DI) events. The quantification of the OVF of individual particles derived from X-ray spectromicroscopy, which relates to the multi-component internal composition of individual particles, showed a factor of 2.06±0.16 and 1.11±0.04 increase in the MBL and FT, respectively, among DI samples. We show that supplying particle OVF into the <em>κ</em>-Köhler equation can be used as a good approximation of field-measured <em>in situ</em> CCN concentrations. We also report changes in the <em>κ</em> values in the MBL from <em>κ</em><sub>MBL, non-DI</sub> = 0.48 to <em>κ</em><sub>MBL, DI</sub> = 0.41, while changes in the FT result in <em>κ</em><sub>FT, non-D</sub><sub>I</sub> = 0.36 to <em>κ</em><sub>FT, DI</sub> = 0.33, which is consistent with enhancements in OVF followed by the DI episodes. Our observations suggest that the entrainment of particles from long-range continental sources alters the mixing state population and CCN properties of aerosol in the region.</p>
<p>Chapter 5 discusses the identification and characterization of fine-mode primary biogenic atmospheric particles (PBAP) from the harvesting of crops. Particle samples were analyzed using complementary chemical imaging techniques to apportion the particle-type population based on their size, morphology, and composition. The contribution of PBAP in the size range of 0.15−1.25 μm is estimated to be 10−12% of ∼39,000 analyzed particles. In addition, particle viscosity and phase state were inferred with X-ray spectromicroscopic analysis has shown that the fine-mode organic particles collected are viscous/semisolid (10<sup>2</sup>−10<sup>12</sup> Pa s) while the majority of PBAP fragments are solid (>10<sup>12 </sup>Pa s). The observation of submicrometer, solid carbonaceous fragments of biogenic origin have implications for the regional CCN and ice nuclei budget. Therefore, the seasonal harvesting of crops may play an important, yet unrecognized, role in regional cloud formation and climate.</p>
<p>Chapter 6 explores the measurements and quantification of latent heat, sensible heat, and CO<sub>2</sub> fluxes among different land covers in the surrounding area of urban regions using airborne flux techniques. Cities account for the majority of the global CO<sub>2</sub> emissions due to the consumption of energy, resources, infrastructure, and transportation demands. Accordingly, the accurate quantification of these emissions, with exceptional precision, is necessary so that progress towards emission reduction can be monitored. However, a major challenge in quantifying urban emission estimates arises from accurate background emission definitions and apportionment of emission sources in complex urban environments. Airborne eddy covariance measurements were performed to quantify the bidirectional exchange of latent heat, sensible heat, and CO<sub>2</sub> fluxes in the upwind region of Indianapolis within an active biosphere. Here, we observed differences in fluxes across different days and land covers (e.g., corn, soybean, and forests) allowing us to understand the impact of seasonal variability in urban emissions during the full growing season. These experiments illustrate the capability of a research aircraft to perform technically challenging near-direct measurements of atmosphere–surface exchange over local and regional scales.</p>
<p>Chapter 7 presents a new method to spatially allocate airborne mass balance CO<sub>2</sub> emissions. We performed seven aircraft measurements downwind of New York City (NYC) quantifying CO<sub>2</sub> emissions during the non-growing seasons of 2018–2020. A series of prior inventories and footprint transport models were used to account for flux contribution outside the area of interest and attribute emission sources within policy-relevant boundaries of the five boroughs encompassing NYC and then employ the modeled enhancement fraction (Φ) to the bulk emission observations from the mass balance approach. Here, we calculated a campaign-averaged source apportioned mass balance CO<sub>2</sub> emission rate of 56±24 kmol/s. The performance and accuracy of this approach were evaluated against other published works including inventory scaling and inverse modeling, yielding a difference of 5.1% with respect to the average emission rate reported by the two complementary approaches. Utilizing the ensemble of emissions inventories and transport models, we also evaluated the overall sources of variability induced by the prior (1.7%), the transport (4.2%), and the daily variability (42.0%). This approach provides a solution to interpreting aircraft-based mass balance results in complex emission environments.</p>
<p>Chapter 8 concludes with a brief discussion of technological advances and research outlooks for X-ray spectromicroscopy analysis on atmospheric particles and the quantification of GHG. Opportunities for future applications and novel development of CCSEM/EDX and STXM/NEXAFS to substantially extend the instrument capabilities and improve our understanding of the physicochemical properties of individual atmospheric particles. Chapter 8 also discusses recent developments in satellite-based CO<sub>2</sub> monitoring to complement direct airborne observations. In recent years, significant progress has been made in satellite-based measurements of CO<sub>2</sub> to reveal the spatio-temporal variation in atmospheric CO<sub>2</sub> concentration. The column-averaged dry air CO<sub>2</sub> mole have reached an accuracy of ~1 ppm with a spatial resolution of less than 4 km. Furthermore, column-averaged retrievals can be used to detect and estimate the surface CO<sub>2</sub> fluxes in an active biosphere, quantify anthropogenic emissions over megacities, and monitor the transport of fossil fuel plumes across different continents and seasons.</p> Read more
|
123 |
MOLECULAR & STRUCTURAL CHARACTERIZATION OF COMPLEX ATMOSPHERIC AND ENVIRONMENTAL MIXTURES USING MULTI MODAL SEPARATIONS & HIGH RESOLUTION MASS SPECTROMETRYChristopher P West (7542944) 06 December 2022 (has links)
<p> </p>
<p>Atmospheric aerosols formed through primary emissions, secondary gas-particle formations, and multi-phase chemical processes are composed of solid, semi-solid, or liquid-like particles suspended in the air that have direct implications towards the global radiative balance and human health as air pollutants. Direct emissions of primary organic aerosols (POA; e.g. soot, BrC) and multi-phase formation of secondary organic aerosols (SOA) from the oxidation of biogenic monoterpene isomers represent two important sources/classes of particulate matter in the atmosphere. Multi-phase chemical processes driving the atmospheric and environmental aging through the photochemistry of iron(III), FeIII in organic aerosol particles and aqueous media drives the multiphase chemistry leading to systematic aging of their chemical composition and modifications to resulting light-absorption properties. The molecular composition, organic structures, physical properties, and sources of emissions are complex requiring development of powerful multi-modal analytical metrology, such as high-resolution mass spectrometry (HRMS) hyphenated with liquid chromatography (LC), photodiode array optical detection, drift tube ion mobility (IM) spectrometry, and desorption and ambient ionization of multi-components mixtures in atmospheric particles using temperature programmed desorption Direct analysis in real time (TPD-DART). Disseminating the molecular-specific composition, chemical and physical properties of complex mixtures in atmospheric organic particles and mixed inorganic/organic systems will help improve our understanding of their formation mechanisms, transformative chemical ageing processes, as well as improved detection of individual components in complex mixtures. </p>
<p> </p>
<p>Chapter 1 and 2 of dissertation introduces complexity of atmospheric organic, carbonaceous aerosols, and complex environmental mixtures and discusses analytical metrology, experiments, and data analysis procedures used for detailed molecular-level characterization of mixtures. Chapter 3 the development of a robust analytical method for untargeted screening and determination of the physical and chemical properties (e.g. vapor pressures, enthalpies of sublimation, and saturation mass concentrations) of single components out of complex SOA particles using temperature programmed desorption Direct analysis in real time ionization – high resolution mass spectrometry (TPD-DART-HRMS). Chapter 4 introduces the use of ion mobility - mass spectrometry (IM-MS) separation and multidimensional characterization of structural isomers in complex SOA mixtures. The chapter discusses the advanced usage of IM-MS to investigate the molecular and structural properties of isomers of alpha-pinene and limonene derived SOA, use of advanced data analysis procedures to resolved complex conformational and structural isomers, and investigate single-molecule structural changes from atmospheric-like ageing in SOA particles using IM-MS. Chapter 5 discusses the chemical characterization and analysis of individual brown carbon (BrC) chromophores out of mixture of colorless organic carbon constituents and insoluble soot particles generated from controlled flame combustion of ethane fuel, a surrogate system representing gasoline combustion of motor vehicles. The chapter focuses on the quantitative method development and use of state-of-the-art liquid chromatography coupled to photodiode array followed by dopant assisted atmospheric pressure photoionization and HRMS (LC-PDA-HRMS) analysis, followed by conversion to quantitative optical information for comparisons with retrieved literature reports. Chapter 6 examines the complex multiphase photochemical cycling of Fe(III)-citrate, a relevant proxy for [FeIII-carboxylate]2+ complexes in atmospheric water using complementary analytical metrology of optical spectroscopy, LC-PDA-HRMS, oil immersion flow microscopy. Multi-modal datasets from these complementary techniques provide a unique experimental description of various stages of FeIII-citrate photochemistry, elucidate individual components of this reacting system, determine mechanistic insights, and quantify environmental parameters affecting the photochemistry. </p> Read more
|
124 |
Usage of aerosol mass spectrometry for the measurement of the physical and chemical properties of the atmospheric nanoparticles / Χρήση της φασματομετρίας μάζας αεροζόλ για τη μέτρηση των φυσικών και χημικών ιδιοτήτων των ατμοσφαιρικών νανοσωματιδίωνΚωστενίδου, Ευαγγελία 13 July 2010 (has links)
The Aerosol Mass Spectroscopy (AMS) is a recently developed method that provides on-line measurements of the chemical composition, mass spectrum and mass distributions of the atmospheric aerosol. Using the AMS with a thermodenuder in smog chamber experiments of ozonolysis of α-pinene, β-pinene and limonene, the mass spectrum of the secondary organic aerosols (SOA) is deconvoluted in low, medium and high volatility mass spectra. The spectrum of the surrogate component with the lower volatility for α-pinene and β-pinene is quite similar to that of ambient oxygenated organic aerosol (OOA). This could explain part of the difference between the AMS mass spectrum in the lab and the field. Combining an AMS and a Scanning Mobility Particle Sizer (SMPS) in smog chamber experiments of α-pinene, β-pinene and limonene ozonolysis, the density of the SOA is calculated and estimated between 1.4 and 1.65 g cm-3. This high density implies that the SOA is likely in a solid or a waxy state. The method is applied on field measurements at Finokalia, Crete during the FAME. For the summer campaign (FAME-08) the organic density is in the range of 0.8 and 1.8 g cm-3 with a mean value of 1.35±0.22 g cm-3¬, while for the winter (FAME-09) the average organic density is 1.14±0.36 g cm-3. This technique can also calculate the Collection Efficiency (CE) of the AMS, since AMS does not measure all the particles that enter the instrument. Applying the estimated CE, the AMS is in a good agreement with other instrumentation. The CE and the organic density of the thermodenuded samples are calculated as well. The CE and the organic density both for the ambient and the themodenuded samples are used as post corrections in the volatility estimation. For FAME-08 the organic aerosol is one order of magnitude less volatile than laboratory-generated α-pinene SOA. Furthermore they are highly oxidized due to the photochemistry conditions (especially in the summer) and the station location (away from detectable sources of pollution). Finally, modifying the steam-jet aerosol collector (SJAC) method both particulate and gas phase of the main inorganic species can be measured. Testing the approach at ambient conditions at the ICE-FORTH Institute, we were able to measure together with the inorganic aerosol composition the gas-phase concentrations of NH3, HONO and very low HNO¬3. The results are consistent with the predictions of the thermodynamic model ISORROPIA. / Τα αεροζόλ είναι σωματίδια που αιωρούνται στην ατμόσφαιρα. Η Φασματομετρία Μάζας Αεροζόλ (AMS) είναι μία νέα μέθοδος που μπορεί να δώσει ταυτόχρονα και σε πραγματικό χρόνο τη χημική σύσταση, το φάσμα μάζας και τις κατανομές μάζας των ατμοσφαιρικών σωματιδίων. Χρησιμοποιώντας το AMS με έναν θερμικό απογυμνωτή σε πειράματα οζονόλυσης α-πινενίου, β-πινενίου και λεμονενίου σε περιβαλλοντικό θάλαμο, το φάσμα μάζας των δευτερογενών οργανικών σωματιδίων (SOΑ) αναλύεται σε 3 επιμέρους φάσματα, ανάλογα με την πτητικότητα των οργανικών σωματιδίων. Το φάσμα που αντιστοιχεί στις ενώσεις με τη χαμηλότερη πτητικότητα για το α- και β-πινένιο είναι αρκετά όμοιο με αυτό των οξυγονωμένων οργανικών σωματιδίων (ΟΟΑ) από το περιβάλλον. Αυτό εξηγεί και μέρος της διαφοράς του φάσματος μάζας AMS μεταξύ εργαστηρίου και πεδίου. Συνδυάζοντας το AMS με ένα σαρωτή μεγέθους κινούμενων σωματιδίων (SMPS) υπολογίζεται η πυκνότητα των SOA από οζονόλυση α-πινενίου, β-πινενίου και λεμονενίου μεταξύ 1.4 και 1.65 g cm-3. Η σχετικά υψηλή τιμή της πυκνότητας μάλλον σημαίνει ότι τα παραγόμενα σωματίδια είναι στερεά ή κερώδη.Η παραπάνω μέθοδος εφαρμόζεται σε μετρήσεις πεδίου στη Φινοκαλιά, στην Κρήτη (FAME). Για το FAME-08 (καλοκαίρι) η πυκνότητα των οργανικών σωματιδίων είναι μεταξύ 0.8 και 1.8 g cm-3 με μέση τιμή 1.35±0.22 g cm-3, ενώ για το FAME-09 (χειμώνας) η μέση τιμή είναι 1.14±0.36 g cm-3. Η τεχνική αυτή υπολογίζει και το ποσοστό συλλογής (CE) σωματιδίων του AMS, καθώς το AMS μετράει ένα ποσοστό αυτών. Εφαρμόζοντας την CE που υπολογίζεται, η συμφωνία μεταξύ του AMS και άλλων οργάνων είναι αρκετά καλή. Υπολογίζεται επίσης η CE και η πυκνότητα των οργανικών για τα δείγματα που έχουν θερμανθεί στον θερμικό απογυμνωτή. Οι CE και οι οργανικές πυκνότητες χρησιμοποιούνται ως διορθώσεις για την αποφυγή υποεκτίμησης της πτητικότητας του οργανικού αεροζόλ. Για το FAME-08 οι οργανικές ενώσεις είναι περισσότερο από μία τάξη μεγέθους λιγότερο πτητικές από τα SOA που δημιουργούνται σε συνθήκες εργαστηρίου. Επίσης είναι υψηλά οξειδωμένες λόγω της φωτοχημείας (καλοκαίρι) και της τοποθεσίας της δειγματοληψίας (μακριά από πρωτογενείς ρύπους). Τέλος τροποποιώντας τη μέθοδο δειγματοληψίας υγροποιημένων σωματιδίων (SJAC) είναι δυνατό να μετρηθεί και η σωματιδιακή αλλά και η αέρια φάση των κυρίως ανόργανων ενώσεων. Πειράματα που έγιναν από δειγματοληψία στο ΕΙΧΗΜΥΘ δείχνουν την ύπαρξη ΝΗ3 αλλά σχεδόν μηδενικού ΗΝΟ3. Τα αποτελέσματα συγκρίνονται με ένα θερμοδυναμικό μοντέλο (ISΟRROPIA) και η συμφωνία είναι καλή. Read more
|
125 |
Composition, propriétés et comportement des aérosols atmosphériques, des brouillards, des rosées et des pluies en région bruxelloiseFally, Sophie 13 December 2001 (has links)
La pollution atmosphérique en milieu urbain est un problème préoccupant car une fraction croissante de la population mondiale vit dans les villes. Les effets de la pollution se manifestent également sur la végétation urbaine et sur notre patrimoine architectural, de sorte que c'est la qualité de la vie de l'ensemble des habitants des métropoles de la planète qui est en jeu. Il est indispensable de connaître la composition des atmosphères urbaines et de comprendre les mécanismes qui régissent cette composition pour évaluer les conséquences de la pollution, définir les exigences de réduction des émissions et établir des scénarios des tendances futures.<p><p>L'objectif du présent travail est de déterminer la composition chimique, les propriétés et le comportement des particules et des dépôts humides en Région bruxelloise. On a distingué les aérosols atmosphériques, les brouillards, les rosées (ou givres) récoltés à la fois sur les végétaux et sur un collecteur inerte, les pluies et les dépôts totaux (formés des pluies et des dépôts secs accumulés dans l'entonnoir de collecte en l'absence de pluie). Ce vaste objectif a été réalisé grâce à la collecte de nombreux échantillons sur une échelle de temps suffisante en différents endroits de la capitale, et à l'analyse de ces échantillons par des techniques variées et complémentaires (techniques classiques d'analyse d'échantillons liquides telles que spectrométrie d'absorption et d'émission atomique, chromatographie liquide, colorimétrie, ainsi que microscopie électronique et fluorescence des rayons-X). Trois collecteurs (pour le brouillard, la pluie et la rosée) ont été entièrement conçus et réalisés au laboratoire dans le cadre de ce travail. Les éléments suivants sont analysés: NO3, SO4, NH4, Na, Mg, Al, Si, P, S, CI, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Pb.<p><p>Afin de comprendre les causes de la variabilité spatio-temporelle des concentrations, l'influence de paramètres tels que la saison, la direction du vent, et le lieu de prélèvement a été examinée. De plus, dans le cas des pluies et des brouillards, l'étude de l'évolution des concentrations au cours d'un même épisode a permis d'investiguer les processus physico-chimiques qui contrôlent le dépôt humide. Elle a permis d'acquérir une meilleure connaissance des mécanismes d'incorporation des aérosols dans la phase aqueuse et du phénomène de lessivage de l'atmosphère. Tout au long de ce travail, les interactions entre la phase particulaire (aérosols) et les phases liquides (brouillards, rosées, pluies) ont été examinées. Une relation entre les concentrations en éléments dissous et le volume d'eau de l'échantillon a été établie dans le cas des pluies, des rosées et des brouillards. Cette relation traduit un effet de dilution et démontre l'importance du mécanisme de condensation-évaporation des gouttes d'eau. L'importance du phénomène de nucléation des sulfates, nitrates et chlorures d'ammonium constitutifs de la fraction fine de l'aérosol soluble a été démontrée. Ces sels d'ammonium sont formés secondairement par des réactions de conversion gaz-particules. L'abondance des ions ammonium, et l'importance de leur action de neutralisation de l'acidité, constituent une particularité de l'atmosphère bruxelloise.<p>L'identification des sources de particules et d'éléments en relation avec leurs propriétés chimiques et granulométriques a été réalisée en utilisant divers outils statistiques (corrélations entre éléments, analyse factorielle) et géochimiques (rapports de concentration, facteurs d'enrichissement, granulométrie). Les apports d'origine marine, continentale, biologique et anthropique (trafic, incinération des déchets, processus de combustion) ont ainsi été clairement mis en évidence dans l'aérosol et le brouillard bruxellois.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished Read more
|
126 |
<b>Molecular investigation of the multi-phase photochemistry of environmental aquatic systems</b>Maria V Misovich (17553087) 08 December 2023 (has links)
<p dir="ltr">The chemical constituents of terrestrial and atmospheric waters originate from biomass burning, fertilizer runoff, and anthropogenic activity, among other sources, and their multi-phase chemistry is complex. Sunlight plays an essential role in aquatic chemistry. Photosensitizers in terrestrial and atmospheric waters absorb light to form highly reactive species such as triplet excited carbon (<sup>3</sup>C*), hydroxyl radical (•OH), and singlet oxygen (<sup>1</sup>O<sub>2</sub>), driving the photochemical transformations of dissolved organic matter (DOM) in the aqueous phase. Of note, these reactive species transform DOM compounds that do not undergo direct photolysis. DOM frequently undergoes a change in optical properties following photochemical processing, with implications for air quality, water quality, and human and animal health. The presence of inorganic minerals, such as the fertilizer compound struvite, in terrestrial or atmospheric waters introduces further complexity and impacts the photochemical processes that occur. Simplified proxy systems are created in the laboratory to simulate aquatic photochemical processes and evaluate the formation and/or photodegradation of photoproducts. These mixtures typically consist of a representative organic carbon (OC) compound and a photosensitizer, along with struvite or another inorganic mineral.</p> Read more
|
Page generated in 0.1083 seconds