Characterization of two photon excited fragment spectroscopy (TPEFS) for HNO3 detection in gas-phase kinetic experiments

We have developed and tested two-photon excited fragment spectroscopy (TPEFS) for detecting HNO3 in pulsed laser photolysis kinetic experiments. Dispersed (220–330 nm) and time-dependent emission at (310 ± 5) nm following the 193 nm excitation of HNO3 in N2, air and He was recorded and analysed to characterise the OH(A2Σ) and NO(A2Σ+) electronic excited states involved. The limit of detection for HNO3 using TPEFS was ∼5 × 109 molecule cm−3 (at 60 torr N2 and 180 μs integration time). Detection of HNO3 using the emission at (310 ± 5 nm) was orders of magnitude more sensitive than detection of NO and NO2, especially in the presence of O2 which quenches NO(A2Σ+) more efficiently than OH(A2Σ). While H2O2 (and possibly HO2) could also be detected by 193 nm TPEFS, the relative sensitivity (compared to HNO3) was very low. The viability of real-time TPEFS detection of HNO3 using emission at (310 ± 5) nm was demonstrated by monitoring HNO3 formation in the reaction of OH + NO2 and deriving the rate coefficient, k2. The value of k2 obtained at 293 K and pressures of 50–200 torr is entirely consistent with that obtained by simultaneously measuring the OH decay and is in very good agreement with the most recent literature values

Mesure des radicaux OH et HO2 dans l atmosphère en utilisant la technique FAGE (Développement et mesures de terrain)

Les radicaux HOx (=OH+HO2) jouent un rôle central dans la dégradation des hydrocarbures dans la troposphère. La réaction d OH avec les hydrocarbures mène en présence de NOx à la formation de polluants secondaires comme l ozone. Du fait de sa réactivité élevée, la concentration en OH (<1 ppt) ainsi que son temps de vie (<1 s) sont faibles. Pour valider les modèles de chimie atmosphérique, le développement d appareils capable de mesurer ces très faibles concentrations est nécessaire. Un appareil basé sur la technique FAGE (Fluorescence Assay by Gas Expansion) a été développé à l Université de Lille pour la mesure simultanée des radicaux HOx. La limite de détection atteinte est de 4 . 10[puissance 5] cm-3 pour OH and et 5 . 10[puissance 6] cm-3 pour HO2 pour un temps de mesure de 1 min. L appareil a été utilisé dans 4 campagnes de mesure dans différents environnements : en chambre de simulation, en milieu rural, en milieu urbain et à l intérieur d une classe. Le FAGE de Lille a été validé grâce à 2 intercomparaisons en chambre de simulation et en air ambiant. En parallèle, le FAGE a été adapté pour la mesure de la réactivité d OH. La réactivité d OH est l inverse du temps de vie. L air ambiant est échantillonné au travers d une cellule de photolyse dans laquelle OH est produit. La décroissance d OH mesurée est due à la réaction de OH avec les réactifs présents dans l air ambiant. L appareil de mesure de la réactivité d OH a participé à une campagne de mesure où il a été intercomparé. De plus, la réaction entre NO2* et H2O comme nouvelle source potentielle d OH a été étudiée.HOx(=OH+HO2) radicals play a central role in the degradation of hydrocarbons in the troposphere. Reaction of OH with hydrocarbons leads in the presence of NOx to the formation of secondary pollutants such as O3. Due to its high reactivity, the concentration of OH radicals (<1ppt) and its lifetime are very low (<1s). In order to validate atmospheric chemistry models, the development of highly sensitive instruments for the measurement of OH and HO2 is needed. An instrument based on the FAGE technique (Fluorescence Assay by Gas Expansion) was developed at the University of Lille for the simultaneous measurement of HOx radicals. The limit of detection for OH and HO2 is of 4 . 10[power 5] cm-3 and 5 . 10[power 6] cm-3 respectively for 1 min integration time, appropriate for ambient measurements. The instrument was deployed in 4 field campaigns in different environments: simulation chamber, rural, suburban and indoor. The Lille FAGE was validated during 2 intercomparative measurements in an atmospheric chamber and in ambient air. In parallel, the FAGE set-up was adapted for the measurement of the OH reactivity. OH reactivity is the measure of the total loss of OH radicals that includes the reaction of all chemical species with OH. Ambient air is sampled through a photolysis cell where OH is artificially produced and it decays from the reaction with reactants present in ambient air is recorded by LIF in the FAGE. The OH reactivity system was deployed during an intercomparative measurement and used for the study of the reaction between NO2* and H2O as a source of OH.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Reaction between CH₃C(O)OOH (peracetic acid) and OH in the gas phase: a combined experimental and theoretical study of the kinetics and mechanism

Peracetic acid (CH3C(O)OOH) is one of the mostabundant organic peroxides in the atmosphere; yet the kinetics of itsreaction with OH, believed to be the major sink, have only been studied onceexperimentally. In this work we combine a pulsed-laser photolysis kineticstudy of the title reaction with theoretical calculations of the ratecoefficient and mechanism. We demonstrate that the rate coefficient isorders of magnitude lower than previously determined, with an experimentallyderived upper limit of 4×10-14 cm3 molec.−1 s−1. The relatively low rate coefficient is in good agreement withthe theoretical result of 3×10-14 cm3 molec.−1 s−1 at 298 K, increasing to ∼6×10-14 cm3 molec.−1 s−1 in the cold uppertroposphere but with associated uncertainty of a factor of 2. The reactionproceeds mainly via abstraction of the peroxidic hydrogen via a relativelyweakly bonded and short-lived prereaction complex, in which H abstractionoccurs only slowly due to a high barrier and low tunnelling probabilities.Our results imply that the lifetime of CH3C(O)OOH with respect toOH-initiated degradation in the atmosphere is of the order of 1 year (notdays as previously believed) and that its major sink in the free and uppertroposphere is likely to be photolysis, with deposition important in theboundary layer

Quantification of OH and HO2 radicals during the low-temperature oxidation of hydrocarbons by Fluorescence Assay by Gas Expansion technique

International audienceOH and *HO2 radicals are known to be the key species in the development of ignition. A direct measurement of these radicals under low-temperature oxidation conditions (T = 550 - 1000 K) has been achieved by coupling a technique named fluorescence assay by gas expansion, an experimental technique designed for the quantification of these radicals in the free atmosphere, to a jet-stirred reactor, an experimental device designed for the study of low-temperature combustion chemistry. Calibration allows conversion of relative fluorescence signals to absolute mole fractions. Such radical mole fraction profiles will serve as a benchmark for testing chemical models developed to improve the understanding of combustion processes

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

Article on gas phase kinetics and equilibrium of allyl radical reactions with NO and NO₂

Quality of life of children born with a congenital heart defect

International audienceObjectives: To identify subgroups with a congenital heart defect (CHD) at risk of health-related quality of life (QoL) impairment at 8 years of age according to their medical and surgical management.Study design: From a prospective population-based cohort study, 598 patients with CHD were subdivided according to their medical and surgical management: (1) CHD followed-up in an outpatient clinic, (2) complete repair before age 3 years, (3) complete repair after age 3 years, (4) palliative repair, or (5) CHD with spontaneous resolution (reference subgroup). Self-reported QoL and parent-reported QoL were measured using the Pediatric Quality of Life Inventory version 4.0 (score range, 0-100) at age 8 years. Multivariable regression analysis and Cohen effect size were used to compare outcomes across the CHD groups.Results: Self-reported and parent-reported QoL scores for the palliative repair subgroup were lower (β = −2.1 [95% CI, −3.9 to −0.2] and β = −16.0 [95% CI, −22.4 to −9.5], respectively), with a large effect size (δ = −0.9 [95% CI, −1.4 to −0.4] and δ = −1.3 [95% CI, −1.8 to −0.7], respectively). Parent-reported QoL scores for the complete repair after age 3 years subgroup were lower (β = −9.2; 95% CI, −15.0 to −3.5), with a large effect size (δ = −0.9; 95% CI, −1.4 to −0.5). Self-reported QoL scores for the complete repair before age 3 years subgroup was lower (β = −1.3; 95% CI, −1.9 to −0.6), with a small effect size (δ = −0.4; 95% CI, −0.6 to −0.2).Conclusions: The QoL of children with CHD who experienced a hospital intervention is reduced at age 8 years. Patient age at the last cardiac intervention might influence QoL at 8 years

Gas Phase Kinetics and Equilibrium of Allyl Radical Reactions with NO and NO₂

Allyl radical reactions with NO and NO₂ were studied in direct, time-resolved experiments in a temperature controlled tubular flow reactor connected to a laser photolysis/photoionization mass spectrometer (LP-PIMS). In the C₃H₅ + NO reaction , a dependence on the bath gas density was observed in the determined rate coefficients and pressure falloff parametrizations were performed. The obtained rate coefficients vary between 0.30–14.2 × 10^–12 cm³ s^–1 (<i>T</i> = 188–363 K, <i>p</i> = 0.39–23.78 Torr He) and possess a negative temperature dependence. The rate coefficients of the C₃H₅ + NO₂ reaction did not show a dependence on the bath gas density in the range used (<i>p</i> = 0.47–3.38 Torr, <i>T</i> = 201–363 K), and they can be expressed as a function of temperature with <i>k</i>(C₃H₅ + NO₂) = (3.97 ± 0.84) × 10^–11 × (<i>T</i>/300 K) ^{–1.55±0.05} cm³ s^–1. In the C₃H₅ + NO reaction, above 410 K the observed C₃H₅ radical signal did not decay to the signal background, indicating equilibrium between C₃H₅ + NO and C₃H₅NO. This allowed the C₃H₅ + NO ⇄ C₃H₅NO equilibrium to be studied and the equilibrium constants of the reaction between 414 and 500 K to be determined. With the standard second- and third-law analysis, the enthalpy and entropy of the C₃H₅ + NO ⇄ C₃H₅NO reaction were obtained. Combined with the calculated standard entropy of reaction (Δ<i>S</i>°₂₉₈ = 137.2 J mol^–1K^–1), the third-law analysis resulted in Δ<i>H</i>°₂₉₈ = 102.4 ± 3.2 kJ mol^–1 for the C₃H₅–NO bond dissociation enthalpy

Quality of life in children participating in a non-selective INR self-monitoring VKA-education programme

International audienceThe quality of life (QoL) of children receiving vitamin K antagonist (VKA) treatment has been scarcely studied

Health-related quality of life of patients with pulmonary arterial hypertension associated with CHD: the multicentre cross-sectional ACHILLE study

International audienceThe aim of this study was to assess health-related quality of life in patients with pulmonary arterial hypertension associated with CHD and correlations with clinical status