49,791 research outputs found
Hohenpeissenberg Photochemical Experiment (HOPE 2000) : measurements and photostationary state calculations of OH and peroxy radicals
No full textMeasurements of OH, total peroxy radicals, non-methane hydrocarbons (NMHCs) and various other trace gases were made at the Meteorological Observatory Hohenpeissenberg in June 2000. The data from an intensive measurement period characterised by high solar insolation (18-21 June) are analysed. The maximum midday OH concentration ranged between 4.5x106 molecules cm-3 and 7.4x106 molecules cm-3. The maximum total ROx (ROx =OH+RO+HO2+RO2) mixing ratio increased from about 55 pptv on 18 June to nearly 70 pptv on 20 and 21 June. A total of 64 NMHCs, including isoprene and monoterpenes, were measured every 1 to 6 hours. The oxidation rate of the NMHCs by OH was calculated and reached a total of over 14x106 molecules cm-3 s-1 on two days. A simple photostationary state balance model was used to simulate the ambient OH and peroxy radical concentrations with the measured data as input. This approach was able to reproduce the main features of the diurnal profiles of both OH and peroxy radicals. The balance equations were used to test the effect of the assumptions made in this model. The results proved to be most sensitive to assumptions about the impact of unmeasured volatile organic compounds (VOC), e.g. formaldehyde (HCHO), and about the partitioning between HO2 and RO2. The measured OH concentration and peroxy radical mixing ratios were reproduced well by assuming the presence of 3 ppbv HCHO as a proxy for oxygenated hydrocarbons, and a HO2/ RO2 ratio between 1:1 and 1:2. The most important source of OH, and conversely the greatest sink for peroxy radicals, was the recycling of HO2 radicals to OH. This reaction was responsible for the recycling of more than 45x106 molecules cm-3 s-1 on two days. The most important sink for OH, and the largest source of peroxy radicals, was the oxidation of NMHCs, in particular, of isoprene and the monoterpenes
Seasonal measurements of total OH reactivity emission rates from Norway spruce in 2011
No full textNumerous reactive volatile organic compounds (VOCs) are emitted into the atmosphere by vegetation. Most biogenic VOCs are highly reactive towards the atmosphere's most important oxidant, the hydroxyl (OH) radical. One way to investigate the chemical interplay between biosphere and atmosphere is through the measurement of total OH reactivity, the total loss rate of OH radicals. This study presents the first determination of total OH reactivity emission rates (measurements via the comparative reactivity method) based on a branch cuvette enclosure system mounted on a Norway spruce (Picea abies) throughout spring, summer and autumn 2011. In parallel VOC emission rates were monitored by a second proton-transfer-reaction mass spectrometer (PTR-MS), and total ozone (O3) loss rates were obtained inside the cuvette. Total OH reactivity emission rates were in general temperature and light dependent, showing strong diel cycles with highest values during daytime. Monoterpene emissions contributed most, accounting for 56–69% of the measured total OH reactivity flux in spring and early summer. However, during late summer and autumn the monoterpene contribution decreased to 11–16%. At this time, a large missing fraction of the total OH reactivity emission rate (70–84%) was found when compared to the VOC budget measured by PTR-MS. Total OH reactivity and missing total OH reactivity emission rates reached maximum values in late summer corresponding to the period of highest temperature. Total O3 loss rates within the closed cuvette showed similar diel profiles and comparable seasonality to the total OH reactivity fluxes.
Total OH reactivity fluxes were also compared to emissions from needle storage pools predicted by a temperature-only-dependent algorithm. Deviations of total OH reactivity fluxes from the temperature-only-dependent emission algorithm were observed for occasions of mechanical and heat stress. While for mechanical stress, induced by strong wind, measured VOCs could explain total OH reactivity emissions, during heat stress they could not. The temperature-driven algorithm matched the diel variation of total OH reactivity emission rates much better in spring than in summer, indicating a different production and emission scheme for summer and early autumn. During these times, unmeasured and possibly unknown primary biogenic emissions contributed significantly to the observed total OH reactivity flux
What can 14 CO measurements tell us about OH?
No full textThe possible use of 14CO measurements to constrain hydroxyl radical (OH) concentrations in the atmosphere is investigated. 14CO is mainly produced in the upper atmosphere from cosmic radiation. Measurements of 14CO at the surface show lower concentrations compared to the upper atmospheric source region, which is the result of oxidation by OH. In this paper, the sensitivity of 14CO mixing ratio surface measurements to the 3-D OH distribution is assessed with the TM5 model. Simulated 14CO mixing ratios agree within a few molecules 14CO cm¿3 (STP) with existing measurements at five locations worldwide. The simulated cosmogenic 14CO distribution appears mainly sensitive to the assumed upper atmospheric 14C source function, and to a lesser extend to model resolution. As a next step, the sensitivity of 14CO measurements to OH is calculated with the adjoint TM5 model. The results indicate that 14CO measurements taken in the tropics are sensitive to OH in a spatially confined region that varies strongly over time due to meteorological variability. Given measurements with an accuracy of 0.5 molecules 14CO cm¿3 STP, a good characterization of the cosmogenic 14CO fraction, and assuming perfect transport modeling, a single 14CO measurement may constrain OH to 0.2¿0.3×106 molecules OH cm¿3 on time scales of 6 months and spatial scales of 70×70 degrees (latitude×longitude) between the surface and 500 hPa. The sensitivity of 14CO measurements to high latitude OH is about a factor of five higher. This is in contrast with methyl chloroform (MCF) measurements, which show the highest sensitivity to tropical OH, mainly due to the temperature dependent rate constant of the MCF¿OH reaction. A logical next step will be the analysis of existing 14CO measurements in an inverse modeling framework. This paper presents the required mathematical framework for such an analysis
Characterizing the Effects of Al(OH)3 and Mg(OH)2 on Reaction Products and Drying Shrinkage Characteristics of Alkali-activated Slag
No full textThis study is undertaken to explore the relationship between the reaction products and the drying shrinkage of alkali-activated slag (AAS) with the varying hydroxide dosage. AAS pastes were firstly produced with either Al(OH)3 or Mg(OH)2 to investigate the effects of hydroxide on the composition of reaction products and the drying shrinkage of AAS. Secondly, the main reaction products formed in AAS pastes, viz. C4AH13, M4AH10, C-S-H, C-A-S-H and C-M-S-H, were synthesized individually. Synthetic products were then taken to cast the respective paste sample to examine the performance against the drying exposure. The results show that adding Mg(OH)2 indeed improved the shrinkage resistance of AAS. This is primarily connected to the increased crystalline phases, namely the hydrotalcite-like phases and the unreacted Mg(OH)2. Whereas adding Al(OH)3 did not relieve the drying shrinkage of AAS as the interlayer spacing of C-A-S-H was enlarged, which in turn allowed for more shrinkage. Further, the investigation of individual synthetic products illustrates that their drying shrinkage scales satisfied the following order: C4AH13 < M4AH10 < C-M-S-H < C-S-H < C-A-S-H. Moreover, the shrinkage scale of C-S-H was found to evolve as the Ca/Si ratio decreased.Materials and Environmen
DETECTION OF OH AND HO TOWARD ORION KL
No full textAuthor Institution: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109; Departments of Physics, Chemistry, and Astronomy, The Ohio State University, Columbus, OH 43210; Department of Astronomy, University of Michigan, Ann Arbor, MI 48109; HTTP://WWW.HEXOS.ORG/TEAM.PHPThe reactive molecular ions, OH, HO, and HO, key probes of the oxygen chemistry of the interstellar gas, have been observed toward Orion KL with the Heterodyne Instrument for Far Infrared on board the \emph{Herschel Space Observatory}. All three fine-structure transitions of OH at 909, 971, and 1033 GHz and both fine-structure components of the doublet {\it ortho}-HO transition at 1115 and 1139 GHz were detected, and an upper limit was obtained for HO. OH and HO are observed purely in absorption, showing a narrow component at the source velocity of 9~km~s, and a broad blue shifted absorption similar to that reported recently for HF and {\it para}-HO, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH and HO for the 9~km~s component of cm and cm, and those in the outflow of cm and cm. Upper limits of cm and cm were derived for the column densities of {\it ortho} and {\it para}-HO from transitions near 985 and 1657 GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. A higher gas density, despite the assumption of a large ionization rate, may explain the comparatively low column densities of OH and HO
Synthesis, characterization of some diorganotin(IV) complexes of Schiff bases derived from a non-protein amino acid. Crystal structures of {HO2CC6H4[N=C(H){C(CH3)CH(CH3)-3-OH]-p} and its di-n-butyltin(IV) complex (nBu2Sn{O2CC6H4[N=C(H){C(CH3)CH(CH3)-3-OH]-p}2)
No full textDiorganotin(IV) complexes R2Sn(LH)2 (R = Me, nBu) and {[nBu2Sn(LH)]2O}2 (LH = 4-[(2Z)-(3-hydroxy-1-methyl-2-
butenylidene)amino]benzoate and 4-[{(E)-1-(2-hydroxyphenyl)methylidene}mino]benzoate) have been reported. The complexes
were characterized by elemental analysis, IR, NMR (1H, 13C, 119Sn) and 119mSn M ̈ ossbauer spectroscopy.
Crystal structures of a ligand {HO2CC6H4[N C(H)}{C(CH3)CH(CH3)-3-OH]-p} and one of its di-n-butyltin(IV) complexes
(nBu2Sn{O2CC6H4[N C(H)}{C(CH3)CH(CH3)-3-OH]-p}2) were determined. The spectroscopic data suggest that R2Sn(LH)2
complexes have skew-trapezoidal bipyramidal structure while {[nBu2Sn(LH)]2O}2 complexes adopt a dimeric tetraorganodistannoxane
structure in the solid state and undergo complex exchange processes in deuterochloroform solution, as
revealed by 119Sn NMR spectroscopy
THE VIBRATIONAL STRUCTURE OF OH RADICAL AND OH-HO COMPLEX: A MATRIX ISOLATION STUDY
No full textAuthor Institution: Universite Pierre et Marie Curie-Paris 6; CNRS; Laboratoire; de Dynamique, Interactions et Reactivite (LADIR), UMR 7075, Case Courrier; 49, 4 Place Jussieu, 75252 Paris Cedex 05, FranceHydroxyl radical, 'the detergent of atmosphere', the title is acquired due to capability of transformation of trace component present in atmosphere mainly troposphere into water soluble forms and also plays vital role in chemistry of the interstellar medium. The infrared spectra of OH radical isolated in solid neon have been investigated by Fourier Transform infrared spectroscopy (FTIR). OH monomer was prepared by microwave discharge of a mixture of water and neon gas at different concentrations prior to deposition on the cold mirror at 5 K. The microwave discharge of HO/Ne system is remarkable due to its propensity to form OH radical and other species like H, HO, OH-HO, OH-HO and (OH)-HO and IR spectroscopy reveals a variety of phenomena far from being fully understood. OH concentration studies, D/H isotopic substitution, and subsequent annealing leads to the characterization of the different species trapped in the neon matrix. All vibrationnal mode of OH-HO complex have been detected. The presence of species such as H and HO after matrix deposition led us to carry subsequent UV photolysis of our samples where the complex OH-HO may also be formed by following reaction: HO-H + h OH-H
Laser-induced fluorescence study of OH in flat flames of 1–10 bar compared with resonance CARS experiments
No full textKohse-Höinghaus K, Meier U, Attal-Trétout B. Laser-induced fluorescence study of OH in flat flames of 1–10 bar compared with resonance CARS experiments. Applied Optics. 1990;29(10):1560-1569.Laser-induced fluorescence (LIF) measurements of OH were performed in flat stoichiometric CH4/air flames burning at 1, 3, 5, 7, and 9.6 bar, which had previously been investigated using OH resonance CARS. In the LIF study, line shape information and temperatures were extracted from excitation spectra; in addition, OH profiles as a function of height above the burner surface and an estimate of the OH concentration for the different flames were obtained. The perspectives and feasibility of quantitative fluorescence measurements in high pressure flames are discussed, particularly in comparison with the application of resonance CARS
The nanostructure and degradation of C-S-H in Portland and blended cements
No full textThe microstructure and composition of water and KOH activated hardened pastes of commercial neat white Portland cement (WPC) and blends with 30% fly ash (PFA) have been characterised using a multi-technique approach, With particular emphasis on the nature of the C-S-H phase. The neat and fly ash blended pastes were activated with water or a 5M KOH solution and cured for one year at 25'C, one month at 55'C and one month at 85'C. The mean length of the aluminosilicate anion structure of C-S-H (29 Si MAS NMR) increased with age and it was higher in the fly ash blended systems. Formulae were presented for the average structural units in the C-S-H present in the systems analysed by TEM-EDX. SEM micrographs showed that as hydration occurred,
the microstructure became denser because outer product C-S-H was formed in the water filled spaces and additional C-S-H resulted from the pozzolanic reaction. The chemical
composition of C-S-H could not be determined by SEM-EDX because of intermixing with other phases; TEM-EDX was necessary. Inner product C-S-H morphology was fine and homogeneous and that of outer product C-S-H was fibrillar in the water activated systems and foil-like with alkali activation. Fly ash replacement did not change the morphology of lp and Op C-S-H. Small fully hydrated cement and PFA particles were filled with a less dense lp C-S-H with morphology very similar to the foil-like one. TEM-EDX showed that, in general, the mean Ca/(AI+Si) atomic ratio was lower in the water activated blends than that in the neat cement pastes due to the fly ash reaction. The composition- structure data were discussed in terms of models for the nanostructure of C-S-H.
Higher curing temperature accelerated the rate of the cement hydration. The mean length of the aluminosilicate of the C-S-H anions was much higher than that of C-S-H formed at lower temperatures, and it was also higher in the blended pastes than with neat cement. Backscattered electron images showed that the grey level of C-S-H in the
systems cured at 55T and 85T was in places quite similar to that of the calcium hydroxide: that is, it was brighter than in pastes cured at lower temperature. SEM also showed that the microstructure of the systems cured at higher temperature exhibited non uniform porosity. Inner product C-S-H with a fine scale, homogeneous morphology,
was abundant in all systems cured at 55'C and 85'C. Op C-S-H was generally fibrillar with Nvater, and foil-like with alkali. However, the higher temperature curing did result
in coarser fibrillar morphology (water activated systems) than that formed at lower temperatures.
The C-S-H gel formed in the commercial WPC-30% PFA blended paste hydrated for one year at 25'C and water leached for twelve weeks was also characterised in this work. A matrix effect was clearly observed by 29 Si MAS NMR. Cross-linking of the aluminosilicate anion structure of C-S-H occurred after leaching the sample for four weeks. Formulae were also presented for the average structural units in the C-S-H
present in the unleached and four weeks water leached systems analysed by TEM-EDX. lp C-S-H morphology was fine and homogeneous and Op C-S-H had fibrillar morphology. There were many areas in the microstructure of the leached sample where Op C-S-H with foil-like morphology coexisted with fibrillar Op C-S-H
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