50 research outputs found

    Photolysis of CH3CHO at 248 nm: Evidence of triple fragmentation from primary quantum yield of CH3 and HCO radicals and H atoms

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    Radical quantum yields have been measured following the 248 nm photolysis of acetaldehyde, CH3CHO. HCO radical and H atom yields have been quantified by time resolved continuous wave Cavity Ring Down Spectroscopy in the near infrared following their conversion to HO2 radicals by reaction with O2. The CH3 radical yield has been determined using the same technique following their conversion into CH3O2. Absolute yields have been deduced for HCO radicals and H atoms through fitting of time resolved HO2 profiles, obtained under various O2 concentrations, to a complex model, while the CH3 yield has been determined relative to the CH3 yield from 248 nm photolysis of CH3I. Time resolved HO2 profiles under very low O 2 concentrations suggest that another unknown HO2 forming reaction path exists in this reaction system besides the conversion of HCO radicals and H atoms by reaction with O2. HO2 profiles can be well reproduced under a large range of experimental conditions with the following quantum yields: CH3CHO+hÎœ248nm → CH 3CHO*, CH3CHO* → CH3+HCO φ1a = 0.125±0.03, CH3CHO* → CH 3+H+CO φ1e = 0.205±0.04, CH 3CHO* o2→ CH3CO+HO2 φ1f = 0.07±0.01. The CH3O2 quantum yield has been determined in separate experiments as φCH3 = 0.33 ± 0.03 and is in excellent agreement with the CH3 yields derived from the HO2 measurements considering that the triple fragmentation (R1e) is an important reaction path in the 248 nm photolysis of CH3CHO. From arithmetic considerations taking into account the HO2 and CH3 measurements we deduce a remaining quantum yield for the molecular pathway: CH3CHO* → CH 4+CO φ1b = 0.6. All experiments can be consistently explained with absence of the formerly considered pathway: CH 3CHO* → CH3CO+H φ1c = 0. © 2014 AIP Publishing LLC.Fil: Pranay Morajkar. University Of Lille.; FranciaFil: Bossolasco, Adriana Gabriela. University Of Lille.; Francia. Consejo Nacional de Investigaciones CientĂ­ficas y TĂ©cnicas. Centro CientĂ­fico TecnolĂłgico Conicet - CĂłrdoba. Instituto de Investigaciones en FĂ­sico-quĂ­mica de CĂłrdoba. Universidad Nacional de CĂłrdoba. Facultad de Ciencias QuĂ­micas. Instituto de Investigaciones en FĂ­sico-quĂ­mica de CĂłrdoba; ArgentinaFil: Schoemaecker, Coralie. University Of Lille.; FranciaFil: Fittschen, Christa. University Of Lille.; Franci

    A modelling study of the impact of photolysis on indoor air quality

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    The importance of photolysis as an initiator of air chemistry outdoors is widely recognized, but its role in chemical processing indoors is often ignored. This paper uses recent experimental data to modify a detailed chemical model, using it to investigate the impacts of glass type, artificial indoor lighting, cloudiness, time of year and latitude on indoor photolysis rates and hence indoor air chemistry. Switching from an LED to an uncovered fluorescent tube light increased predicted indoor hydroxyl radical concentrations by ~13%. However, moving from glass that transmitted outdoor light at wavelengths above 380 nm to one that transmitted sunlight above 315 nm led to an increase in predicted hydroxyl radicals of more than 400%. For our studied species, including ozone, nitrogen oxides, nitrous acid, formaldehyde, and hydroxyl radicals, the latter were most sensitive to changes in indoor photolysis rates. Concentrations of nitrogen dioxide and formaldehyde were largely invariant, with exchange with outdoors and internal deposition controlling their indoor concentrations. Modern lights such as LEDs, together with low transmission glasses, will likely reduce the effects of photolysis indoors and the production of potentially harmful species. Research is needed on the health effects of different indoor air mixtures to confirm this conclusion

    The past, present and future of indoor air chemistry

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    This is the peer reviewed version of the following article: Bekö, G. et al. (2020). The past, present and future of indoor air chemistry. Indoor Air, 30(3), 373-376. , which has been published in final form at https://doi.org/10.1111/ina.12634. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.This is an editorial contribution to the Journal Indoor Air on the future direction of indoor air chemistry research

    Diagnostics laser dans une flamme de diffusion (imagerie quantitative de nanoparticules de suies et d'espĂšces majoritaires et minoritaires)

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    Les principales sources d'Ă©nergies actuelles sont basĂ©es sur la combustion d'hydrocarbures qui peut ĂȘtre le siĂšge de la formation de particules de suies. L'Ă©mission de suies entraĂźne une baisse du rendement Ă©nergĂ©tique des installations mais surtout ces particules carbonĂ©es ont un effet nĂ©faste sur la santĂ©. En effet, les suies de petites tailles (quelques nanomĂštres) sont assimilĂ©es par l'organisme. Leur prĂ©sence est associĂ©e Ă  celle des Hydrocarbures Aromatiques Polycycliques (HAP) qui sont reconnus comme cancĂ©rigĂšnes. Il apparaĂźt primordial de dĂ©velopper de nouvelles techniques quantitatives de dĂ©tection dans des systĂšmes en combustion afin de doser les nanoparticules de suies ainsi que la phase gaz. AppliquĂ©s Ă  des flammes, les diagnostics laser offrent des mĂ©thodes de dosage non intrusives et produisent une mesure instantanĂ©e avec une bonne sensibilitĂ© et sĂ©lectivitĂ©. Ce travail de thĂšse a permis d'Ă©tendre le potentiel des diagnostics laser utilisĂ©s au laboratoire Ă  l'Ă©tude de flammes produisant des suies avec la mise en Ɠuvre notamment de techniques d'imagerie laser. Ces Ă©tudes ont Ă©tĂ© rĂ©alisĂ©es dans une flamme de diffusion laminaire stabilisĂ©e sur un brĂ»leur Wolfhard-Parker contenant des suies en teneurs variables. Les espĂšces majoritaires ont Ă©tĂ© mesurĂ©es par diffusion Raman et la tempĂ©rature par diffusion Raman/Rayleigh. Des stratĂ©gies de dĂ©tections originales par Fluorescence Induite par Laser des radicaux CH et OH ont Ă©tĂ© mises en Ɠuvre en prĂ©sence de suies. Un effort important a Ă©tĂ© consacrĂ© au dĂ©veloppement d'une technique novatrice appelĂ©e Incandescence Induite par Laser qui permet la dĂ©tection de nanoparticules prĂ©sentant des fractions volumiques de quelques ppb. Cette technique a Ă©tĂ© couplĂ©e Ă  la Cavity-Ring-Down-Spectroscopy afin d'obtenir des cartographies quantitatives de nanoparticules [...]LILLE1-BU (590092102) / SudocSudocFranceF

    Experimental and theoretical investigation of the reaction of RO 2 radicals with OH radicals: Dependence of the HO 2 yield on the size of the alkyl group

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    The HO2 yield in the reaction of peroxy radicals with OH radicals has been determined experimentally at 50 Torr helium by measuring simultaneously OH and HO2 concentration time profiles, following the photolysis of XeF2 in the presence of different hydrocarbons and O2. The following yields have been obtained: urn:x-wiley:05388066:media:kin21191:kin21191-math-0001 = (0.90 ± 0.1), urn:x-wiley:05388066:media:kin21191:kin21191-math-0002 = (0.75 ± 0.15), urn:x-wiley:05388066:media:kin21191:kin21191-math-0003 = (0.41 ± 0.08), and urn:x-wiley:05388066:media:kin21191:kin21191-math-0004 = (0.15 ± 0.03). The clear decrease in HO2 yield with increasing size of the alkyl moiety can be explained by an increased stabilization of the trioxide adduct, ROOOH. This has been confirmed by ab initio and Rice–Ramsperger–Kassel–Marcus master equation calculations. Extrapolation of the experimental results to atmospheric conditions shows that the stabilized adduct, ROOOH, is the nearly exclusive product of the reaction between OH radicals and peroxy radicals containing more than three C‐atoms. The fate and possible impact of these species is completely unexplored so far

    The reaction of fluorine atoms with methanol: yield of CH 3 O/CH 2 OH and rate constant of the reactions CH 3 O + CH 3 O and CH 3 O + HO 2

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    Xenondifluoride, XeF2, has been photolysed in the presence of methanol, CH3OH. Two reaction pathways are possible: F + CH3OH → CH2OH + HF and F + CH3OH → CH3O + HF. Both products, CH2OH and CH3O, will be converted to HO2 in the presence of O2. The rate constants for the reaction of both radicals with O2 differ by more than 3 orders of magnitude, which allows an unequivocal distinction between the two reactions when measuring HO2 concentrations in the presence of different O2 concentrations. The following yields have then been determined from time-resolved HO2 profiles: ϕCH2OH = (0.497 ± 0.013) and ϕCH3O = (0.503 ± 0.013). Experiments under low O2 concentrations lead to reaction mixtures containing nearly equal amounts of HO2 (converted from the first reaction) and CH3O (from the second reaction). The subsequent HO2 decays are very sensitive to the rate constants of the reaction between these two radicals and the following rate constants have been obtained: k(CH3O + CH3O) = (7.0 ± 1.4) × 10−11 cm3 s−1 and k(CH3O + HO2) = (1.1 ± 0.2) × 10−10 cm3 s−1. The latter reaction has also been theoretically investigated on the CCSD(T)//M06-2X/aug-cc-pVTZ level of theory and CH3OH + O2 have been identified as the main products. Using ÎŒVTST, a virtually pressure independent rate constant of k(CH3O + HO2) = 4.7 × 10−11 cm3 s−1 has been obtained, in good agreement with the experiment

    Rate Constant of the Reaction between CH 3 O 2 Radicals and OH Radicals Revisited

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