scholarly journals Detailed characterizations of a Comparative Reactivity Method (CRM) instrument: experiments vs. modelling

2015 ◽  
Vol 8 (4) ◽  
pp. 3803-3850 ◽  
Author(s):  
V. Michoud ◽  
R. F. Hansen ◽  
N. Locoge ◽  
P. S. Stevens ◽  
S. Dusanter
Keyword(s):  
Reaction Rate ◽  
Trace Gases ◽  
Ambient Air ◽  
Bimolecular Reaction ◽  
Chemical Mechanism ◽  
First Order ◽  
Reaction Rate Constants ◽  
First Order Kinetics ◽  
Comparative Reactivity

Abstract. The Hydroxyl radical (OH) is an important oxidant in the daytime troposphere that controls the lifetime of most trace gases, whose oxidation leads to the formation of harmful secondary pollutants such as ozone (O3) and Secondary Organic Aerosols (SOA). In spite of the importance of OH, uncertainties remain concerning its atmospheric budget and integrated measurements of the total sink of OH can help reducing these uncertainties. In this context, several methods have been developed to measure the first-order loss rate of ambient OH, called total OH reactivity. Among these techniques, the Comparative Reactivity Method (CRM) is promising and has already been widely used in the field and in atmospheric simulation chambers. This technique relies on monitoring competitive OH reactions between a reference molecule (pyrrole) and compounds present in ambient air inside a sampling reactor. However, artefacts and interferences exist for this method and a thorough characterization of the CRM technique is needed. In this study, we present a detailed characterization of a CRM instrument, assessing the corrections that need to be applied on ambient measurements. The main corrections are, in the order of their integration in the data processing: (1) a correction for a change in relative humidity between zero air and ambient air, (2) a correction for the formation of spurious OH when artificially produced HO2 react with NO in the sampling reactor, and (3) a correction for a deviation from pseudo first-order kinetics. The dependences of these artefacts to various measurable parameters, such as the pyrrole-to-OH ratio or the bimolecular reaction rate constants of ambient trace gases with OH are also studied. From these dependences, parameterizations are proposed to correct the OH reactivity measurements from the abovementioned artefacts. A comparison of experimental and simulation results is then discussed. The simulations were performed using a 0-D box model including either (1) a simple chemical mechanism, taking into account the inorganic chemistry from IUPAC 2001 and a simple organic chemistry scheme including only a generic RO2 compounds for all oxidized organic trace gases; and (2) a more exhaustive chemical mechanism, based on the Master Chemical Mechanism (MCM), including the chemistry of the different trace gases used during laboratory experiments. Both mechanisms take into account self- and cross-reactions of radical species. The simulations using these mechanisms allow reproducing the magnitude of the corrections needed to account for NO interferences and a deviation from pseudo first-order kinetics, as well as their dependence on the Pyrrole-to-OH ratio and on bimolecular reaction rate constants of trace gases. The reasonable agreement found between laboratory experiments and model simulations gives confidence in the parameterizations proposed to correct the Total OH reactivity measured by CRM. However, it must be noted that the parameterizations presented in this paper are suitable for the CRM instrument used during the laboratory characterization and may be not appropriate for other CRM instruments, even if similar behaviours should be observed. It is therefore recommended that each group characterizes its own instrument following the recommendations given in this study. Finally, the assessment of the limit of detection and total uncertainties is discussed and an example of field deployment of this CRM instrument is presented.

scholarly journals Detailed characterizations of the new Mines Douai comparative reactivity method instrument via laboratory experiments and modeling

2015 ◽  
Vol 8 (8) ◽  
pp. 3537-3553 ◽  
Author(s):  
V. Michoud ◽  
R. F. Hansen ◽  
N. Locoge ◽  
P. S. Stevens ◽  
S. Dusanter
Keyword(s):  
Rate Constants ◽  
Laboratory Experiments ◽  
Reaction Rate ◽  
Limit Of Detection ◽  
Trace Gases ◽  
Ambient Air ◽  
Bimolecular Reaction ◽  
Reaction Rate Constants ◽  
Measurement Artifacts ◽  
Comparative Reactivity

Abstract. The hydroxyl (OH) radical is an important oxidant in the troposphere, which controls the lifetime of most air quality- and climate-related trace gases. However, there are still uncertainties concerning its atmospheric budget, and integrated measurements of OH sinks have been valuable to improve this aspect. Among the analytical tools used for measuring total OH reactivity in ambient air, the comparative reactivity method (CRM) is spreading rapidly in the atmospheric community. However, measurement artifacts have been highlighted for this technique, and additional work is needed to fully characterize them. In this study, we present the new Mines Douai CRM instrument, with an emphasis on the corrections that need to be applied to ambient measurements of total OH reactivity. Measurement artifacts identified in the literature have been investigated, including (1) a correction for a change in relative humidity between the measurement steps leading to different OH levels, (2) the formation of spurious OH in the sampling reactor when hydroperoxy radicals (HO2) react with nitrogen monoxide (NO), (3) not operating the CRM under pseudo-first-order kinetics, and (4) the dilution of ambient air inside the reactor. The dependences of these artifacts on various measurable parameters, such as the pyrrole-to-OH ratio and the bimolecular reaction rate constants of ambient trace gases with OH, have also been studied. Based on these observations, parameterizations are proposed to correct ambient OH reactivity measurements. On average, corrections of 5.2 ± 3.2, 9.2 ± 15.7, and 8.5 ± 5.8 s−1 were respectively observed for (1), (2) and (3) during a field campaign performed in Dunkirk, France (summer 2014). Numerical simulations have been performed using a box model to check whether experimental observations mentioned above are consistent with our understanding of the chemistry occurring in the CRM reactor. Two different chemical mechanisms have been shown to reproduce the magnitude of corrections (2) and (3). In addition, these simulations reproduce their dependences on the pyrrole-to-OH ratio and on bimolecular reaction rate constants of gases reacting with OH. The good agreement found between laboratory experiments and model simulations gives us confidence in the proposed parameterizations. However, it is worth noting that the numerical values given in this study are suitable for the Mines Douai instrument and may not be appropriate for other CRM instruments. It is recommended that each group characterize its own instrument following the recommendations given in this study. An assessment of performances for the Mines Douai instrument, including a propagation of errors from the different corrections, indicates a limit of detection of 3.0 s−1 and total uncertainties of 17–25 % for OH reactivity values higher than 15 s−1 and NOx mixing ratios lower than 30 ppbv.

scholarly journals Studies of Degradation Kinetics of a 5-HT3 Antagonist, Ramosetron Hydrochloride: Effects of Temperature

2018 ◽  
Vol 17 (2) ◽  
pp. 167-173
Author(s):  
Md Mokaram Hossain ◽  
Reza Ul Jalil ◽  
Mohammad A Rashid
Keyword(s):  
Reaction Rate ◽  
Arrhenius Equation ◽  
Degradation Kinetics ◽  
First Order ◽  
Reaction Rate Constants ◽  
First Order Kinetics ◽  
Antiemetic Activity ◽  
Effects Of Temperature ◽  
Kinetics Of ◽  
Subtype 3

Ramosetron hydrochloride is the hydrochloride salt of ramosetron, a selective serotonin (5-HT3) receptor antagonist with potential antiemetic activity. Upon administration, ramosetron selectively binds to and blocks the activity of 5-HT subtype 3 (5-HT3) receptors located in the vagus nerve terminal and the vomiting center of central nervous system (CNS), suppressing chemotherapy-induced nausea and vomiting. Degradation of Ramosetron HCl was conducted with 0.1N NaOH at 60°C, 70°C and 80°C to study the reaction kinetics. The reaction rate constants (k) for degradation at 60°C, 70°C and 80°C were -2.2680 molL-1s-1 , -3.3714 molL-1s-1 and -5.3686 molL-1s-1 for zero order and -1.05 x 10-2s-1, -1.60 x 10-2s-1 and -2.70 x 10-2s-1 for first order kinetics, respectively. The activation energy of Ramosetron HCl was found as 10.05 kcalmol-1 by using Arrhenius equation. Dhaka Univ. J. Pharm. Sci. 17(2): 167-173, 2018 (December)

BROMINATION OF NR WITH N-BROMOSUCCINIMIDE

2021 ◽  
Author(s):  
Nuorn Choothong ◽  
Seiichi Kawahara
Keyword(s):  
Activation Energy ◽  
1H Nmr Spectroscopy ◽  
Reaction Rate ◽  
Bromine Atom ◽  
Reaction Times ◽  
Nitrogen Atmosphere ◽  
Methylene Proton ◽  
First Order ◽  
Reaction Rate Constants ◽  
First Order Kinetics

ABSTRACT The mechanism of bromination of NR was studied by solution-state 1H-NMR spectroscopy. The bromination of NR was carried out at 20–50 °C with N-bromosuccinimide as the brominating agent, and the kinetic study of bromination was conducted under nitrogen atmosphere at 30–50 °C for various reaction times. The influence of bromine atom substituent on the bromination rate constant (k) also was investigated. Bromine atom content was found to be dependent upon the reaction time, indicating first-order kinetics. The activation energy of bromination of NR, calculated from the reaction rate constants, was 19.3, 5.5, and 5.8 kJ mol−1 for bromine atom linked to carbon atom with methylene proton and methylene protons, respectively.

scholarly journals Modeling of Carbonyl/Ammonium Sulfate Aqueous Brown Carbon Chemistry via UV/Vis Spectral Decomposition

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 358 ◽  
Author(s):  
Mengjie Fan ◽  
Shiqing Ma ◽  
Nahin Ferdousi ◽  
Ziwei Dai ◽  
Joseph L. Woo
Keyword(s):  
Climate Forcing ◽  
Reaction Products ◽  
Brown Carbon ◽  
Reaction Systems ◽  
Reaction Rate Constants ◽  
Kinetic Information ◽  
First Order Kinetics ◽  
Aggregate Effect ◽  
Light Absorbance

The proper characterization of aqueous brown carbon (BrC) species, their formation, and their light absorbance properties is critical to understanding the aggregate effect that they have on overall atmospheric aerosol climate forcing. The contribution of dark chemistry secondary organic aerosol (SOA) products from carbonyl-containing organic compounds (CVOCs) to overall aqueous aerosol optical properties is expected to be significant. However, the multiple, parallel pathways that take place within CVOC reaction systems and the differing chromophoricity of individual products complicates the ability to reliably model the chemical kinetics taking place. Here, we proposed an alternative method of representing UV-visible absorbance spectra as a composite of Gaussian lineshape functions to infer kinetic information. Multiple numbers of curves and different CVOC/ammonium reaction systems were compared. A model using three fitted Gaussian curves with magnitudes following first-order kinetics achieved an accuracy within 65.5% in the 205–300-nm range across multiple organic types and solution aging times. Asymmetrical peaks that occurred in low-200-nm wavelengths were decomposed into two overlapping Gaussian curves, which may have been attributable to different functional groups or families of reaction products. Component curves within overall spectra exhibited different dynamics, implying that the utilization of absorbance at a single reference wavelength to infer reaction rate constants may result in misrepresentative kinetics for these systems.

Modified ferron assay for speciation characterization of hydrolyzed Al(III): a precise k value based judgment

2009 ◽  
Vol 59 (4) ◽  
pp. 823-832 ◽  
Author(s):  
Ye Changqing ◽  
Wang Dongsheng ◽  
Wu Xiaohong ◽  
Qu Jiuhui ◽  
John Gregory
Keyword(s):  
Kinetic Constant ◽  
Nonlinear Least Squares ◽  
Precise Determination ◽  
K Value ◽  
First Order ◽  
First Order Kinetics ◽  
Parallel Reactions

The speciation of Al-OH complexes in terms of Ala, Alb and Alc could be achieved by traditional ferron assay and Alb is generally considered as Al13, however, the inherent correlation between them remains an enigma. This paper presents a modified ferron assay to get precise determination of Al13 using nonlinear least squares analysis, and to clarify the correlation between Alb and Al13. Two parallel reactions conforming to pseudo-first-order kinetics can simulate the complicate reactions between polynuclear complexes and ferron successfully. Four types of experimental kinetic constant (k value) of Al-OH complexes can be observed by this method when investigating three typical aluminium solutions. Comparing with the results of 27Al NMR, the species with moderate kinetics around 0.001 s−1 can be confirmed to resemble to Al13 polycation. The other types of kinetics are also well-regulated in partially neutralized aluminium solutions with various OH/Al ratios (b values) in the range 0 ∼ 2.5. It would provide potential means to trace the in-situ formation of Al13 in dilute solutions such as coagulation with Al-based coagulants

Kinetics of the Ozonation of Tetrabromobisphenol-A in Wastewater

2011 ◽  
Vol 383-390 ◽  
pp. 2945-2950 ◽  
Author(s):  
Jie Zhang ◽  
Shi Long He ◽  
Mei Feng Hou ◽  
Li Ping Wang ◽  
Li Jiang Tian
Keyword(s):  
Rate Constants ◽  
Apparent Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Kinetic Studies ◽  
Tetrabromobisphenol A ◽  
First Order ◽  
Reaction Rate Constants ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of TBBPA degradation by ozonation in semi-batch reactor was studied. The reaction rate constants of TBBPA with O3 and •OH were measured by means of direct ozone attack and competition kinetics, and the values of which were 6.10 l/(mol•s), 4.8×109 l/(mol•s), respectively. Results of kinetic studies showed that TBBPA degradation by ozonation under the different conditions tested followed the pseudo-first-order. The values of apparent rate constant of TBBPA degradation increased with the increase of ozone dosage and pH, but decreased with the increase of initial TBBPA concentration.

Kinetics and mechanism of the osmium-tetroxide-catalysed oxidation of mandelate ion by hexacyanoferrate(III) ion

1968 ◽  
Vol 21 (12) ◽  
pp. 2913 ◽  
Author(s):  
NP Singh ◽  
VN Singh ◽  
MP Singh
Keyword(s):  
Benzoic Acid ◽  
Oxidation Product ◽  
Osmium Tetroxide ◽  
Reaction Rate ◽  
Zero Order ◽  
Ion Concentration ◽  
First Order ◽  
First Order Kinetics ◽  
Catalysed Oxidation ◽  
Hydroxyl Ion

The osmium-tetroxide-catalysed oxidation of mandelate ion by hexacyanoferrate(111) ion has been studied kinetically. The reaction rate has been found to be independent of hexacyanoferrate(111) ion while the order with respect to both osmium tetroxide and mandelate ion comes out to be unity. The reaction rate follows first-order kinetics at low hydroxyl ion concentration and becomes zero order at higher concentrations. The course of the reaction has been considered to proceed through the formation of an activated mandelate-OsO4, complex which decomposes in alkaline medium giving reduced osmium(V1) followed by a fast oxidation by hexacyanoferrate(111) ion. The probable course of the reactions is also described with the help of its oxidation product, benzoic acid.

scholarly journals Kinetic analysis of myoglobin autoxidation by isoelectric-focusing electrophoresis

1981 ◽  
Vol 193 (1) ◽  
pp. 181-185 ◽  
Author(s):  
A Tomoda ◽  
T Takizawa ◽  
A Tsuji ◽  
Y Yoneyama
Keyword(s):  
Isoelectric Focusing ◽  
Superoxide Anion ◽  
Reaction Rate ◽  
Ph Dependence ◽  
Acid Base ◽  
First Order ◽  
Reaction Rate Constants ◽  
Ph Values ◽  
Ph Dependent ◽  
Three State Model

The autoxidation of horse myoglobin was studied in the presence or absence of catalase (EC 1.11.1.6) and/or superoxide dismutase (EC 1.15.1.1) at various pH values (6.6-7.8). Changes in the percentages of oxymyoglobin and metmyoglobin during the reaction were analysed by means of isoelectric focusing on Ampholine gel plates. Oxymyoglobin was decreased in a first-order manner, with an accompanying increase in metmyoglobin, under the various conditions studied. The observed reaction rate constants obtained under these conditions were pH-dependent; however, they were also greatly affected by the presence of the enzymes. The pH-dependence of the overall reaction was explained by the acid-base three-state model of myoglobin proposed by Shikama & Sugawara [(1978) Eur. J. Biochem. 91, 407-413]. The reaction process of myoglobin autoxidation was explained by the model suggested by Winterbourn, McGrath & Carrell [(1976) Biochem. J. 155, 493-502], indicating that superoxide anion and hydrogen peroxide are involved in the reaction mechanism.

scholarly journals Kinetics study the decomposition of the cellulose into cellulose nanocrystals by hydrothermal with hydrochloric acid catalyst

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Zulnazri Zulnazri ◽  
Rozanna Dewi ◽  
Sulhatun Sulhatun ◽  
Nasrun Nasrun
Keyword(s):  
Hydrochloric Acid ◽  
Cellulose Nanocrystals ◽  
Reaction Rate ◽  
Acid Catalyst ◽  
Reaction Rate Constant ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
Reaction Rate Constants ◽  
Ft Ir

The aim of this study was to hydrolyzed cellulose nanocrystals as cellulose-based biomass residues from oil palm by using hydrochloric acid under hydrothermal conditions. The characterization of cellulose nanocrystals was determined by FT-IR spectroscopy and X- ray diffraction. The infrared spectroscopy showed there has been a removal of lignin and hemicellulose in the spectrum. Crystallinity which reaches 78.59% was obtained by hydrolysis using hydrochloric acid catalyst 3 mol/L with a reaction time of 1 hour. Based on the graph of -ln CA/CA0 vs. time obtained that Cellulose nanocrystals forming reaction is of first order. The reaction rate constants to the formation of glucose (k2) is greater than the reaction rate constant to the formation of Cellulose nanocrystals (k1), which indicates that the phase of slow reaction is the reaction of the most influential on the overall reaction rate, the reaction of the formation of Cellulose nanocrystals.

PENGARUH KONSENTRASI KATALIS ASAM DAN KECEPATAN PENGADUKAN PADA HIDROLISIS SELULOSA DARI AMPAS BATANG SORGUM MANIS

EKUILIBIUM ◽  
2013 ◽  
Vol 12 (1) ◽  
Author(s):  
Enny Kriswiyanti
Keyword(s):  
Hydrochloric Acid ◽  
Sweet Sorghum ◽  
Reaction Rate ◽  
Acid Catalyst ◽  
Agitation Speed ◽  
First Order ◽  
Reaction Rate Constants ◽  
Glucose Levels ◽  
Hydrolysis Of Cellulose ◽  
Hydrolysis Of

<p>Abstract : Sweet sorghum stem residues contains high enough cellulose (36.92%)so it can be<br />hydrolyzed to glucose. In this research, hydrolysis of cellulose is carried out using hydrochloric<br />acid catalyst. This research aims to determine the effect of acid catalyst concentration and<br />agitation speed on the resulting reduction of glucose levels and determine the reaction rate<br />constant of hydrolysis of sweet sorghum stem residues. The observed variables were the<br />concentration of hydrochloric acid catalyst (0.5 N, 1 N, 1.5 N, 2 N) and the agitation speed (150<br />rpm, 200 rpm, 250 rpm, 300 rpm). Glucose samples were analyzed by using the Lane-Eynon<br />method. Data analysis showed the higher concentration of hydrochloric acid (HCl) and the<br />agitation speed, the levels of reduced glucose that is formed is also higher. In this study by<br />assuming a first order reaction, the reaction rate constants obtained at variable concentrations of<br />hydrochloric acid catalyst ranged from 0.0010 to 0.0033 / minute and at agitation speeds variable<br />ranged from 0.0023 to 0.0030 / minute.<br />Keywords : sweet sorghum stem residues, hydrochloric acid, hydrolysis, cellulose</p>

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