275,966 research outputs found
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
Regularity for multi-phase variational problems
No full textDe Filippis C, Oh J. Regularity for multi-phase variational problems. JOURNAL OF DIFFERENTIAL EQUATIONS. 2019;267(3):1631-1670.We prove C-1,C-nu -regularity for local minimizers of the multi-phase energy: w bar right arrow integral(Omega)vertical bar Dw vertical bar(p)+a(x)vertical bar Dw vertical bar(q)+b(x)vertical bar Dw vertical bar(s)dx, under sharp assumptions relating the couples (p, q) and (p, s) to the Holder exponents of the modulating coefficients a(.) and b(.), respectively. (C) 2019 Elsevier Inc. All rights reserved
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
Hydrodynamic size distribution of fullerene particles in nC and C(OH) preparations
No full textShown are the volume distributions (each line is the average of at least twelve measurements per sample) of the nC water suspension (), and C(OH) in 10mM Nacl ().<p><b>Copyright information:</b></p><p>Taken from "Adverse effects of fullerenes on endothelial cells: Fullerenol C(OH) induced tissue factor and ICAM-1 membrane expression and apoptosis in vitro"</p><p></p><p>International Journal of Nanomedicine 2008;3(1):59-68.</p><p>Published online Jan 2008</p><p>PMCID:PMC2527653.</p><p>© 2008 Dove Medical Press Limited. All rights reserved</p
Entwicklung der cw-Laser-Frequenzmodulations-Spektroskopie zu einer Methode zur Messung von OH im troposphärischen Konzentrationsbereich
No full textS.105-113Obwohl das OH-Radikal eine der wichtigsten reaktiven Substanzen der Atmosphäre ist, existieren bislang nur sehr wenige Meßaufbauten, die mit ausreichender Genauigkeit troposphärischer OH-Konzentrationen bestimmen können. Es wird ein uv-cw-Laser-Absorptionsexperiment vorgestellt, das eine Nachweisempfindlichkeit von 10 E6 OH/cbcm bei 1 km Absorptionsweg haben wird. Eine Untersuchung des Laserrauschen legt die Verwendung einer Frequenzmodulationsmethode nahe. Erste Labormessungen mit Modulationsfrequenzen im Tonfrequenzbereich in einer Vielfachreflexionszelle ergeben eine minimal nachweisbare Absorption von 5.10 E-5, das entspricht bei dem verwendeten Absorptionsweg von 100m einer OH-Konzentration von 7.10 E6 cm E-3. (ITA
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
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
New platinum hydrido acetylides. Crystal and molecular structure of [PtHC≡C-C(OH)MeEt(PPh3)2]
No full textThe complex trans-[PtClH(PPh3)2] reacts with monosubstituted acetylenes HC≡CR (R = CH2OH, CH(OH)Me, C(OH)Me2, C(OH)MeEt, CH(OH)Ph, C6H10OH, Ph, or CMe=CH2) in the presence of NEt2H to give trans-[PtH(C≡CR)(PPh3)2], which have been characterized by i.r., u.v., and n.m.r. spectroscopy. An X-ray diffraction analysis was carried out on [PtH{C≡C-C(OH) MeEt}(PPh3)2]. Crystals are monoclinic, space group P21/n, with unit cell dimensions a = 15.560(3), b = 26.696(5), c = 9.038(2) Å, β = 98.51(2)°, Z = 4. A total of 3 855 observed reflections have been measured by single-crystal diffractometry and refined by blocked full-matrix least squares to R = 0.067. Co-ordination around platinum is distorted square planar and involves the acetylide ligand trans to hydrogen which was directly located. In some reaction conditions cationic intermediates have been demonstrated by conductivity measurements
Entwicklung der cw-Laser-Frequenzmodulations-Spektroskopie an einer Methode zur Messung von OH im troposphärischen Konzentrationsbereich
No full textS.105-113Eine Methode zur Messung schwacher Absorptionen durch Frequenzmodulation eines Ringlasers im kHz-Bereich wird vorgestellt. Mit 1 mW Laserleistung bei 308 nm wurde eine Nachweisgrenze der Absorption von 5x10 E-5 erreicht. Fuer OH-Radikale ergibt dies bei einem Absorptionsweg von 100 m in einer Vielflachreflexionszelle eine Nachweisgrenze von 7x10 E6 Radikalen pro cbm. (ITA
Vibrational spectroscopic study of poldervaartite CaCa[SiO3(OH)(OH)]
No full textWe have studied the mineral poldervaartite CaCa[SiO<sub>3</sub>(OH)(OH)] which forms a series with its manganese analogue olmiite <i>CaMn</i><i>[SiO<sub>3</sub>(OH)]</i>(OH) using a range of techniques including scanning electron microscopy, thermogravimetric analysis, Raman and infrared spectroscopy. Chemical analysis shows the mineral is reasonably pure and contains only calcium and manganese with low amounts of Al and F. Thermogravimetric analysis proves the mineral decomposes at 485 <sup>o</sup>C with a mass loss of 7.6% compared with the theoretical mass loss of 7.7%. A strong Raman band at 852 cm<sup>-1</sup> is assigned to the SiO stretching vibration of the SiO<sub>3</sub>(OH) units. Two Raman bands at 914 and 953 cm<sup>-1</sup> are attributed to the antisymmetric vibrations. Intense prominent peaks observed at 3487, 3502, 3509, 3521 and 3547 cm<sup>-1</sup> are assigned to the OH stretching vibration of the SiO<sub>3</sub>(OH) units. The observation of multiple OH bands supports the concept of the non-equivalence of the OH units. Vibrational spectroscopy enables a detailed assessment of the molecular structure of poldervaartite
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