Atmospheric particulate matter characterization by Fourier transform infrared spectroscopy: a review of statistical calibration strategies for carbonaceous aerosol quantification in US measurement networks

Atmospheric particulate matter (PM) is a complex mixture of many different substances and requires a suite of instruments for chemical characterization. Fourier transform infrared (FT-IR) spectroscopy is a technique that can provide quantification of multiple species provided that accurate calibration models can be constructed to interpret the acquired spectra. In this capacity, FT-IR spectroscopy has enjoyed a long history in monitoring gas-phase constituents in the atmosphere and in stack emissions. However, application to PM poses a different set of challenges as the condensed-phase spectrum has broad, overlapping absorption peaks and contributions of scattering to the mid-infrared spectrum. Past approaches have used laboratory standards to build calibration models for prediction of inorganic substances or organic functional groups and predict their concentration in atmospheric PM mixtures by extrapolation. In this work, we review recent studies pursuing an alternate strategy, which is to build statistical calibration models for mid-IR spectra of PM using collocated ambient measurements. Focusing on calibrations with organic carbon (OC) and elemental carbon (EC) reported from thermal-optical reflectance (TOR), this synthesis serves to consolidate our knowledge for extending FT-IR spectroscopy to provide TOR-equivalent OC and EC measurements to new PM samples when TOR measurements are not available. We summarize methods for model specification, calibration sample selection, and model evaluation for these substances at several sites in two US national monitoring networks: seven sites in the Interagency Monitoring of Protected Visual Environments (IMPROVE) network for the year 2011 and 10 sites in the Chemical Speciation Network (CSN) for the year 2013. We then describe application of the model in an operational context for the IMPROVE network for samples collected in 2013 at six of the same sites as in 2011 and 11 additional sites. In addition to extending the evaluation to samples from a different year and different sites, we describe strategies for error anticipation due to precision and biases from the calibration model to assess model applicability for new spectra a priori. We conclude with a discussion regarding past work and future strategies for recalibration. In addition to targeting numerical accuracy, we encourage model interpretation to facilitate understanding of the underlying structural composition related to operationally defined quantities of TOR OC and EC from the vibrational modes in mid-IR deemed most informative for calibration. The paper is structured such that the life cycle of a statistical calibration model for FT-IR spectroscopy can be envisioned for any substance with IR-active vibrational modes, and more generally for instruments requiring ambient calibrations

The SuperCam Instrument Suite on the Mars 2020 Rover: Science Objectives and Mast-Unit Description

On the NASA 2020 rover mission to Jezero crater, the remote determination of the texture, mineralogy and chemistry of rocks is essential to quickly and thoroughly characterize an area and to optimize the selection of samples for return to Earth. As part of the Perseverance payload, SuperCam is a suite of five techniques that provide critical and complementary observations via Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), visible and near-infrared spectroscopy (VISIR), high-resolution color imaging (RMI), and acoustic recording (MIC). SuperCam operates at remote distances, primarily 2-7 m, while providing data at sub-mm to mm scales. We report on SuperCam's science objectives in the context of the Mars 2020 mission goals and ways the different techniques can address these questions. The instrument is made up of three separate subsystems: the Mast Unit is designed and built in France; the Body Unit is provided by the United States; the calibration target holder is contributed by Spain, and the targets themselves by the entire science team. This publication focuses on the design, development, and tests of the Mast Unit; companion papers describe the other units. The goal of this work is to provide an understanding of the technical choices made, the constraints that were imposed, and ultimately the validated performance of the flight model as it leaves Earth, and it will serve as the foundation for Mars operations and future processing of the data.In France was provided by the Centre National d'Etudes Spatiales (CNES). Human resources were provided in part by the Centre National de la Recherche Scientifique (CNRS) and universities. Funding was provided in the US by NASA's Mars Exploration Program. Some funding of data analyses at Los Alamos National Laboratory (LANL) was provided by laboratory-directed research and development funds

Organic nanoparticles based on Hexaarylbiimidazoles : characterization and photochromic properties

Cette thèse s’intéresse à la synthèse et à l’étude des propriétés de nanoparticules organiques photochromes d’Hexaarylbiimidazoles (HABIs) pontés. Deux voies de synthèse ont été envisagées. La photofragmentation laser (I), pour laquelle la réaction photochrome a lieu conjointement à la fragmentation de la matière, et la méthode de reprecipitation (II) qui ne nécessite pas d’irradiation lumineuse. La photodynamique des HABIs pontés a été pour la première fois déterminée à l’aide des techniques de spectroscopies électronique (UV-visible) et vibrationnelle (IR) d’absorption transitoire aux échelles femtoseconde et nanoseconde. Les espèces transitoires impliquées ont été caractérisées par une approche chimiométrique de résolution de courbes multivariées. Celle-ci a été adaptée afin de prendre en compte la spécificité des signaux transitoire tels que les processus de relaxation vibrationnelle. Pour les nanoparticules synthétisées par (I), nous avons observé : i) une photodissociation et une augmentation de la distance entre les groupes imidazoles en 210 fs, ii) une rotation partielle des groupes imidazoles en 5 ps, iii) une relaxation lente en environ 200 ps et iv) un retour thermique rapide (≈ 800 µs contre 300 ms en solution). Par contre, pour les nanoparticules formées par (II), le temps de retour thermique est comparable à celui observé en solution. Cela suggère que la photofragmentation induit un réarrangement des molécules au sein des nanoparticules avec une géométrie spécifique de type monocristal. Cette hypothèse est discutée sur la base de calculs de chimie théorique et par comparaison des propriétés des HABIs en solution et à l’état de solide polycristallin.This work deals with the study of photochromic organic nanoparticles of bridged-Hexaarylbiimidazoles (HABIs) molecules. Two synthesis paths were proposed. On the one hand, laser photofragmentation (I) for which photochromic reaction and matter fragmentation occur simultaneously. On the other hand, the reprecipitation method (II) does not involve light excitation. The photodynamics of bridged-HABIs has been characterized for the first time using electronic (UV – visible) and vibrational (IR) transient absorption spectroscopy in femtosecond and nanosecond time scale. Transient spectra were analyzed by a chemometric approach based on multivariate curve resolution. The algorithm was adapted to deal with specific signals such as vibrational relaxation processes. For nanoparticles synthesized with (I), we report: i) a photo-dissociation and an increase of the distance between imidazole groups within 210 fs, ii) a partial rotation of the former in 5 ps, iii) a slow relaxation in about 200 ps and iv) a fast thermal back reaction (≈ 800 µs compare to 300 ms in solution). However, for nanoparticles synthesized by (II), the thermal back reaction is similar to the one reported in solution. This suggests that photofragmentation induces a molecular rearrangement with a specific geometry as observed in single crystal. This hypothesis is discussed on the basis of theoretical chemistry calculation and by comparing HABI’s properties in solution and in polycrystalline powder

Nanoparticules organiques à base d‟Hexaarylbiimidazoles : caractérisation et propriétés photochromes

This work deals with the study of photochromic organic nanoparticles of bridged-Hexaarylbiimidazoles (HABIs) molecules. Two synthesis paths were proposed. On the one hand, laser photofragmentation (I) for which photochromic reaction and matter fragmentation occur simultaneously. On the other hand, the reprecipitation method (II) does not involve light excitation. The photodynamics of bridged-HABIs has been characterized for the first time using electronic (UV – visible) and vibrational (IR) transient absorption spectroscopy in femtosecond and nanosecond time scale. Transient spectra were analyzed by a chemometric approach based on multivariate curve resolution. The algorithm was adapted to deal with specific signals such as vibrational relaxation processes. For nanoparticles synthesized with (I), we report: i) a photo-dissociation and an increase of the distance between imidazole groups within 210 fs, ii) a partial rotation of the former in 5 ps, iii) a slow relaxation in about 200 ps and iv) a fast thermal back reaction (≈ 800 µs compare to 300 ms in solution). However, for nanoparticles synthesized by (II), the thermal back reaction is similar to the one reported in solution. This suggests that photofragmentation induces a molecular rearrangement with a specific geometry as observed in single crystal. This hypothesis is discussed on the basis of theoretical chemistry calculation and by comparing HABI’s properties in solution and in polycrystalline powder.Cette thèse s’intéresse à la synthèse et à l’étude des propriétés de nanoparticules organiques photochromes d’Hexaarylbiimidazoles (HABIs) pontés. Deux voies de synthèse ont été envisagées. La photofragmentation laser (I), pour laquelle la réaction photochrome a lieu conjointement à la fragmentation de la matière, et la méthode de reprecipitation (II) qui ne nécessite pas d’irradiation lumineuse. La photodynamique des HABIs pontés a été pour la première fois déterminée à l’aide des techniques de spectroscopies électronique (UV-visible) et vibrationnelle (IR) d’absorption transitoire aux échelles femtoseconde et nanoseconde. Les espèces transitoires impliquées ont été caractérisées par une approche chimiométrique de résolution de courbes multivariées. Celle-ci a été adaptée afin de prendre en compte la spécificité des signaux transitoire tels que les processus de relaxation vibrationnelle. Pour les nanoparticules synthétisées par (I), nous avons observé : i) une photodissociation et une augmentation de la distance entre les groupes imidazoles en 210 fs, ii) une rotation partielle des groupes imidazoles en 5 ps, iii) une relaxation lente en environ 200 ps et iv) un retour thermique rapide (≈ 800 µs contre 300 ms en solution). Par contre, pour les nanoparticules formées par (II), le temps de retour thermique est comparable à celui observé en solution. Cela suggère que la photofragmentation induit un réarrangement des molécules au sein des nanoparticules avec une géométrie spécifique de type monocristal. Cette hypothèse est discutée sur la base de calculs de chimie théorique et par comparaison des propriétés des HABIs en solution et à l’état de solide polycristallin

Nanoparticules organiques à base d Hexaarylbiimidazoles (caractérisation et propriétés photochromes)

Cette thèse s intéresse à la synthèse et à l étude des propriétés de nanoparticules organiques photochromes d Hexaarylbiimidazoles (HABIs) pontés. Deux voies de synthèse ont été envisagées. La photofragmentation laser (I), pour laquelle la réaction photochrome a lieu conjointement à la fragmentation de la matière, et la méthode de reprecipitation (II) qui ne nécessite pas d irradiation lumineuse. La photodynamique des HABIs pontés a été pour la première fois déterminée à l aide des techniques de spectroscopies électronique (UV-visible) et vibrationnelle (IR) d absorption transitoire aux échelles femtoseconde et nanoseconde. Les espèces transitoires impliquées ont été caractérisées par une approche chimiométrique de résolution de courbes multivariées. Celle-ci a été adaptée afin de prendre en compte la spécificité des signaux transitoire tels que les processus de relaxation vibrationnelle. Pour les nanoparticules synthétisées par (I), nous avons observé : i) une photodissociation et une augmentation de la distance entre les groupes imidazoles en 210 fs, ii) une rotation partielle des groupes imidazoles en 5 ps, iii) une relaxation lente en environ 200 ps et iv) un retour thermique rapide ( 800 s contre 300 ms en solution). Par contre, pour les nanoparticules formées par (II), le temps de retour thermique est comparable à celui observé en solution. Cela suggère que la photofragmentation induit un réarrangement des molécules au sein des nanoparticules avec une géométrie spécifique de type monocristal. Cette hypothèse est discutée sur la base de calculs de chimie théorique et par comparaison des propriétés des HABIs en solution et à l état de solide polycristallin.This work deals with the study of photochromic organic nanoparticles of bridged-Hexaarylbiimidazoles (HABIs) molecules. Two synthesis paths were proposed. On the one hand, laser photofragmentation (I) for which photochromic reaction and matter fragmentation occur simultaneously. On the other hand, the reprecipitation method (II) does not involve light excitation. The photodynamics of bridged-HABIs has been characterized for the first time using electronic (UV visible) and vibrational (IR) transient absorption spectroscopy in femtosecond and nanosecond time scale. Transient spectra were analyzed by a chemometric approach based on multivariate curve resolution. The algorithm was adapted to deal with specific signals such as vibrational relaxation processes. For nanoparticles synthesized with (I), we report: i) a photo-dissociation and an increase of the distance between imidazole groups within 210 fs, ii) a partial rotation of the former in 5 ps, iii) a slow relaxation in about 200 ps and iv) a fast thermal back reaction ( 800 s compare to 300 ms in solution). However, for nanoparticles synthesized by (II), the thermal back reaction is similar to the one reported in solution. This suggests that photofragmentation induces a molecular rearrangement with a specific geometry as observed in single crystal. This hypothesis is discussed on the basis of theoretical chemistry calculation and by comparing HABI s properties in solution and in polycrystalline powder.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

SAFIR-I: first NEMA NU 4-2008-based performance characterization

Background: Small Animal Fast Insert for MRI detector I (SAFIR-I) is a novel Positron Emission Tomography insert for a 7T Bruker BioSpec 70/30 Ultra Shield Refrigerated Magnetic Resonance Imaging (MRI) system. It facilitates truly simultaneous quantitative imaging in mice and rats at injected activities as high as 500MBq . Exploitation of the resulting high count rates enables quick image formation at few seconds per frame. In this investigation, key performance parameters of SAFIR-I have been determined according to the evaluations outlined in the National Electrical Manufacturers Association (NEMA) Standards Publication NU 4-2008 (NEMA-NU4) protocol. Results: Using an energy window of 391 to 601keV and a Coincidence Timing Window of 500ps , the following performance was observed: The average spatial resolution at 5mm radial offset (Full Width at Half Maximum) is 2.54mm when using Filtered Backprojection, 3D Reprojection reconstruction. For the mouse- and rat-like phantoms, the maximal Noise-Equivalent Count Rates (NECRs) are 1368kcps at the highest tested average effective concentration of 14.7MBqcc-1 , and 713kcps at the highest tested average effective concentration of 1.72MBqcc-1 , respectively. The NECR peak is not yet reached for either of these cases. The peak sensitivity is 1.46% . The Image Quality phantom uniformity standard deviation is 4.8% . The Recovery Coefficient for the 5mm rod is (1.08 ± 0.10) . The Spill-Over Ratios are (0.22 ± 0.03) and (0.22 ± 0.02) , for the water- and air-filled cylinder, respectively. An accuracy of 4.3% was achieved for the quantitative calibration of reconstructed voxel values. Conclusions: The measured performance parameters indicate that the various design goals have been achieved. SAFIR-I offers excellent performance, especially at the high activities it was designed for. This facilitates planned experiments with fast tracer kinetics in small animals. Ways to potentially improve performance can still be explored. Simultaneously, further performance gains can be expected for a forthcoming insert featuring 2.7 times longer axial coverage named Small Animal Fast Insert for MRI detector II (SAFIR-II)

Fusion of ultraviolet-visible and infrared transient absorption spectroscopy data to model ultrafast photoisomerization

International audienceUltrafast photoisomerization reactions generally start at a higher excited state with excess of internal vibrational energy and occur via conical intersections. This leads to ultrafast dynamics which are difficult to investigate with a single transient absorption spectroscopy technique, be it in the ultraviolet-visible (UV-vis) or infrared (IR) domain. On one hand, the information available in the UV-vis domain is limited as only slight spectral changes are observed for different isomers. On the other hand, the interpretation of vibrational spectra is strongly hindered by intramolecular relaxation and vibrational cooling. These limitations can be circumvented by fusing UV-vis and IR transient absorption spectroscopy data in a multiset multivariate curve resolution analysis. We apply this approach to describe the spectrodynamics of the ultrafast cis-trans photoisomerization around the C-N double bond observed for aromatic Schiff bases. Twisted intermediate states could be elucidated, and isomerization was shown to occur through a continuous complete rotation. More broadly, data fusion can be used to rationalize a vast range of ultrafast photoisomerization processes of interest in photochemistry