scholarly journals Chamber simulation of photooxidation of dimethyl sulfide and isoprene in the presence of NO<sub>x</sub>

2012 ◽  
Vol 12 (21) ◽  
pp. 10257-10269 ◽  
Author(s):  
T. Chen ◽  
M. Jang
Keyword(s):  
Experimental Data ◽  
Kinetic Model ◽  
Rate Constants ◽  
Dimethyl Sulfide ◽  
Model Simulation ◽  
Methanesulfonic Acid ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Gaseous Products ◽  
Dms Oxidation

Abstract. To improve the model prediction for the formation of H2SO4 and methanesulfonic acid (MSA), aerosol-phase reactions of gaseous dimethyl sulfide (DMS) oxidation products [e.g., dimethyl sulfoxide (DMSO)] in aerosol have been included in the DMS kinetic model with the recently reported gas-phase reactions and their rate constants. To determine the rate constants of aerosol-phase reactions of both DMSO and its major gaseous products [e.g., dimethyl sulfone (DMSO2) and methanesulfinic acid (MSIA)], DMSO was photooxidized in the presence of NOx using a 2 m3 Teflon film chamber. The rate constants tested in the DMSO kinetic mechanisms were then incorporated into the DMS photooxidation mechanism. The model simulation using the newly constructed DMS oxidation mechanims was compared to chamber data obtained from the phototoxiation of DMS in the presence of NOx. Within 120-min simulation, the predicted concentrations of MSA increase by 200–400% and those of H2SO4, by 50–200% due to aerosol-phase chemistry. This was well substantiated with experimental data. To study the effect of coexisting volatile organic compounds, the photooxidation of DMS in the presence of isoprene and NOx has been simulated using the newly constructed DMS kinetic model integrated with the Master Chemical Mechanism (MCM) for isoprene oxidation, and compared to chamber data. With the high concentrations of DMS (250 ppb) and isoprene (560–2248 ppb), both the model simulation and experimental data showed an increase in the yields of MSA and H2SO4 as the isoprene concentration increased.

scholarly journals Chamber simulation of photooxidation of dimethyl sulfide and isoprene in the presence of NO<sub>x</sub>

2012 ◽  
Vol 12 (6) ◽  
pp. 14669-14695
Author(s):  
T. Chen ◽  
M. Jang
Keyword(s):  
Experimental Data ◽  
Kinetic Model ◽  
Dimethyl Sulfide ◽  
Model Simulation ◽  
Methanesulfonic Acid ◽  
Heterogeneous Reactions ◽  
Chemical Mechanism ◽  
Gaseous Products ◽  
Isoprene Oxidation ◽  
Master Chemical Mechanism

Abstract. In the kinetic model of this study, to advance the photooxidation of dimethyl sulfide (DMS) in the gas phase, the most recently reported reactions with their rate constants have been included. To improve the model predictability for the formation of sulfuric acid and methanesulfonic acid (MSA), heterogeneous reactions of gaseous DMS products (e.g., dimethyl sulfoxide (DMSO)) on the surface of aerosol have been included in the kinetic model. DMS was photoirradiated in the presence of NOx using a 2 m3 Teflon film chamber. The resulting chamber data was simulated using the new kinetic model. The model included in this study predicted that concentrations of both MSA and H2SO4 would significantly increase due to heterogeneous chemistry and this was well substantiated with experimental data. The model used in this study also predicted the decay of DMS, the formation of other gaseous products such as SO2, dimethyl sulfone (DMSO2), and the ozone formation linked to a NOx cycle. To study the effect of coexisting volatile organic compounds, the photooxidation of DMS in the presence of isoprene and NOx has been simulated using the new kinetic model integrated with the Master Chemical Mechanism (MCM) for isoprene oxidation, and compared to chamber data. Both the model simulation and the experimental data showed an increase in the yields of MSA and H2SO4 as the isoprene concentration increased.

scholarly journals Aromatization of light naphtha fractions on zeolites 1: Kinetic model

2003 ◽  
Vol 57 (9) ◽  
pp. 399-403 ◽  
Author(s):  
Svetlana Rovenskaja ◽  
Nikolaj Ostrovski
Keyword(s):  
Experimental Data ◽  
Kinetic Model ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Scheme ◽  
Activation Energies ◽  
Modeling And Optimization ◽  
Light Naphtha ◽  
Reaction Rate Constants

On the basis of analyzing kinetic experimental data performed in laboratory integral reactors a lumping kinetic model of the "Zeoforming" process was developed. A reaction scheme of the lumped components was proposed, that was adapted to the technological requirements. The reaction rate constants and activation energies were estimated, that are valid for certain feed compositions. The model is intended for further modeling and optimization of the process.

scholarly journals DYNAMICS OF NEUROMUSCULAR TRANSMISSION REPRODUCED BY CALCIUM-DEPENDENT SERIAL TRANSITIONS IN THE VESICLE FUSION COMPLEX

2021 ◽  
Author(s):  
Alejandro Martínez-Valencia ◽  
Guillermo Ramírez-Santiago ◽  
Francisco F. De-Miguel
Keyword(s):  
Experimental Data ◽  
Kinetic Model ◽  
Electrical Activity ◽  
Rate Constant ◽  
Rate Constants ◽  
Resting State ◽  
Neuromuscular Transmission ◽  
Spontaneous Release ◽  
Calcium Dependent ◽  
Vesicle Pool

Neuromuscular transmission, from spontaneous release to facilitation and depression was accurately reproduced by a mechanistic kinetic model of sequential maturation transitions in the molecular fusion complex. The model incorporates three predictions. First, sequential calcium-dependent forward transitions take vesicles from docked to pre-primed to primed states, followed by fusion. Second, pre-priming and priming are reversible. Third, fusion and recycling are unidirectional. The model was fed with experimental data from previous studies while the backward (β) and recycling (ρ) rate constant values were fitted. Classical experiments were successfully reproduced when every forward (α) rate constant had the same value, and both backward rate constants were 50-100 times larger. Such disproportion originated an abruptly decreasing gradient of resting vesicles from docked to primed states. Simulations also predict that: i. Spontaneous release reflects primed to fusion spontaneous transitions. ii. Calcium elevations synchronize the series of forward transitions that lead to fusion. iii Facilitation reflects a transient increase of priming following calcium-dependent transitions. iv. Backward transitions and recycling restore the resting state. v. Depression reflects backward transitions and slow recycling after intense release. Such finely-tuned kinetics offers a mechanism for collective non-linear transitional adaptations of a homogeneous vesicle pool to an ever-changing pattern of electrical activity.

scholarly journals Empirical models for viscosity variation in bulk free radical polymerization

2004 ◽  
Vol 58 (9) ◽  
pp. 393-400 ◽  
Author(s):  
Silvia Curteanu ◽  
Victor Bulacovschi
Keyword(s):  
Experimental Data ◽  
Molecular Weight ◽  
Free Radical ◽  
Kinetic Model ◽  
Radical Polymerization ◽  
Model Simulation ◽  
Free Radical Polymerization ◽  
Empirical Models ◽  
Viscosity Data ◽  
Simulation Results

The validity of the Lyons-Tobolsky equation for bulk polymerization systems was verified by comparing simulation results to experimental data for different reaction conditions (temperature and initiator concentration). In this model, formerly applied for solution polymerization, the viscosity of the reaction mass was used instead of solvent viscosity. For example, the chemically initiated free radical polymerization of methyl methacrylate was considered to be achieved in a batch bulk process. In the Lyons-Tobolsky equation, the viscosity was calculated using the values of the conversion and molecular weight resulting from the kinetic model simulation. Consequently, a general discussion about the concordance between the simulation and experiment was useful, especially to emphasize the causes that generate modeling errors. It is more convenient to estimate the viscosity independently of conversion and molecular weight and, in this way, without solving the kinetic model. Empirical relations which correlate viscosity with time were elaborated using experimental viscosity data. Two kinds of models were proposed: a) two fifth order polynomials corresponding to the conversion domains before and after the gel effect; b) a model that fits the experimental data well in the whole conversion domain. Generally, these empirical models provide good simulation results and they can be easily handled.

scholarly journals An advanced modeling study on the impacts and atmospheric implications of multiphase dimethyl sulfide chemistry

2016 ◽  
Vol 113 (42) ◽  
pp. 11776-11781 ◽  
Author(s):  
Erik Hans Hoffmann ◽  
Andreas Tilgner ◽  
Roland Schrödner ◽  
Peter Bräuer ◽  
Ralf Wolke ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Dimethyl Sulfide ◽  
Oxidation Products ◽  
Radical Mechanism ◽  
Sulfur Source ◽  
Aerosol Formation ◽  
Detailed Model ◽  
Model Studies ◽  
Dms Oxidation ◽  
Phase Chemistry

Oceans dominate emissions of dimethyl sulfide (DMS), the major natural sulfur source. DMS is important for the formation of non-sea salt sulfate (nss-SO42−) aerosols and secondary particulate matter over oceans and thus, significantly influence global climate. The mechanism of DMS oxidation has accordingly been investigated in several different model studies in the past. However, these studies had restricted oxidation mechanisms that mostly underrepresented important aqueous-phase chemical processes. These neglected but highly effective processes strongly impact direct product yields of DMS oxidation, thereby affecting the climatic influence of aerosols. To address these shortfalls, an extensive multiphase DMS chemistry mechanism, the Chemical Aqueous Phase Radical Mechanism DMS Module 1.0, was developed and used in detailed model investigations of multiphase DMS chemistry in the marine boundary layer. The performed model studies confirmed the importance of aqueous-phase chemistry for the fate of DMS and its oxidation products. Aqueous-phase processes significantly reduce the yield of sulfur dioxide and increase that of methyl sulfonic acid (MSA), which is needed to close the gap between modeled and measured MSA concentrations. Finally, the simulations imply that multiphase DMS oxidation produces equal amounts of MSA and sulfate, a result that has significant implications for nss-SO42− aerosol formation, cloud condensation nuclei concentration, and cloud albedo over oceans. Our findings show the deficiencies of parameterizations currently used in higher-scale models, which only treat gas-phase chemistry. Overall, this study shows that treatment of DMS chemistry in both gas and aqueous phases is essential to improve the accuracy of model predictions.

scholarly journals Exploring DMS oxidation and implications for global aerosol radiative forcing

2021 ◽  
Author(s):  
Ka Ming Fung ◽  
Colette L. Heald ◽  
Jesse H. Kroll ◽  
Siyuan Wang ◽  
Duseong S. Jo ◽  
...  
Keyword(s):  
Gas Phase ◽  
Radiative Forcing ◽  
Dimethyl Sulfide ◽  
Methanesulfonic Acid ◽  
Atmospheric Model ◽  
Cloud Formation ◽  
Aerosol Formation ◽  
Gas Phase Chemistry ◽  
Dms Oxidation ◽  
Phase Chemistry

Abstract. Aerosol indirect radiative forcing (IRF), which characterizes how aerosols alter cloud formation and properties, is very sensitive to the preindustrial (PI) aerosol burden. Dimethyl sulfide (DMS), emitted from the ocean, is a dominant natural precursor of non-sea-salt sulfate in the PI and pristine present-day (PD) atmospheres. Here we revisit the atmospheric oxidation chemistry of DMS, particularly under pristine conditions, and its impact on aerosol IRF. Based on previous laboratory studies, we expand the simplified DMS oxidation scheme used in the Community Atmospheric Model version 6 with chemistry (CAM6-chem) to capture the OH-addition pathway as well as the H-abstraction pathway and the associated isomerization branch. These additional oxidation channels of DMS produce several stable intermediate compounds, e.g., methanesulfonic acid (MSA) and hydroperoxymethyl thioformate (HPMTF), delay the formation of sulfate, and hence, alter the spatial distribution of sulfate aerosol and radiative impacts. The expanded scheme improves the agreement between modeled and observed concentrations of DMS, MSA, HPMTF, and sulfate over most marine regions based on the NASA Atmospheric Tomography (ATom), the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA), and the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) measurements. We find that the global HPMTF burden, as well as the burden of sulfate produced from DMS oxidation are relatively insensitive to the assumed isomerization rate, but the burden of HPMTF is very sensitive to a potential additional cloud loss. We find that global sulfate burden under PI and PD emissions increase to 412 Gg-S (+29 %) and 582 Gg-S (+8.8 %), respectively, compared to the standard simplified DMS oxidation scheme. The resulting annual mean global PD direct radiative effect of DMS-derived sulfate alone is −0.11  W m−2. The enhanced PI sulfate produced via the gas-phase chemistry updates alone dampens the aerosol IRF as anticipated (−2.2 W m−2 in standard versus −1.7 W m−2 with updated gas-phase chemistry). However, high clouds in the tropics and low clouds in the Southern Ocean appear particularly sensitive to the additional aqueous-phase pathways, counteracting this change (−2.3 W m−2). This study confirms the sensitivity of aerosol IRF to the PI aerosol loading, as well as the need to better understand the processes controlling aerosol formation in the PI atmosphere and the cloud response to these changes.

Achieving Procedure of a Kinetic Model to Predict the Influence of the Process Global Temperature on a Technological Alcoholic Fermentation II. An Arrhenius type Kinetic Model

2008 ◽  
Vol 59 (4) ◽  
Author(s):  
Neculai Catalin Lungu ◽  
Maria Alexandroaei
Keyword(s):  
Experimental Data ◽  
Saccharomyces Cerevisiae ◽  
Kinetic Model ◽  
Economic Efficiency ◽  
Fermentation Process ◽  
Alcoholic Fermentation ◽  
Global Temperature ◽  
Medium Temperature ◽  
Biotechnological Process

The aim of the present work is to offer a practical methodology to realise an Arrhenius type kinetic model for a biotechnological process of alcoholic fermentation based on the Saccharomyces cerevisiae yeast. Using the experimental data we can correlate the medium temperature of fermentation with the time needed for a fermentation process under imposed conditions of economic efficiency.

Comparative TG/DTG/DTA+FTIR Studies Concerning the Stability of Some Mineral and Vegetable Electro-Insulating Fluids

2018 ◽  
Vol 69 (9) ◽  
pp. 2366-2371
Author(s):  
Andrei Cucos ◽  
Petru Budrugeac ◽  
Iosif Lingvay ◽  
Adriana Mariana Bors ◽  
Andreea Voina
Keyword(s):  
Vegetable Oils ◽  
Electrical Equipment ◽  
Inert Atmosphere ◽  
Oxidation Products ◽  
Gaseous Products ◽  
Mineral Oils ◽  
Ftir Studies ◽  
Dta Analysis ◽  
Anti Oxidant ◽  
The Stability

Thermal TG/DTG/DTA analysis coupled with FTIR spectroscopy was applied to some sorts of mineral and vegetable oils used in electrical equipment. On heating in inert atmosphere, it was observed that the mineral oils vaporize, while the vegetable oils undergo hydrolysis, yielding fatty acids as main volatiles, as indicated by FTIR. In synthetic air, the FTIR spectra of gaseous products confirm the presence of similar oxidation products, both for mineral and vegetable oils. The TG results indicated that the vegetable-based oils exhibit a substantially higher thermal stability than the mineral oils. The presence or absence of anti-oxidant inhibitors in these oils greatly influences the onset of the oxidation process in air environment factor, as results from the DTA results.

Diffusion model for deposition of epitaxial GaAs layers prepared by the MOCVD method

1991 ◽  
Vol 56 (10) ◽  
pp. 2020-2029
Author(s):  
Jindřich Leitner ◽  
Petr Voňka ◽  
Josef Stejskal ◽  
Přemysl Klíma ◽  
Rudolf Hladina
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Kinetic Model ◽  
Gas Phase ◽  
Substrate Surface ◽  
Deposition Process ◽  
Hydrogen Atmosphere ◽  
Epitaxial Gaas ◽  
Kinetics Of ◽  
Good Agreement

The authors proposed and treated quantitatively a kinetic model for deposition of epitaxial GaAs layers prepared by reaction of trimethylgallium with arsine in hydrogen atmosphere. The transport of gallium to the surface of the substrate is considered as the controlling process. The influence of the rate of chemical reactions in the gas phase and on the substrate surface on the kinetics of the deposition process is neglected. The calculated dependence of the growth rate of the layers on the conditions of the deposition is in a good agreement with experimental data in the temperature range from 600 to 800°C.

Investigating the NO-dependent photooxidation of limonene by OH and O3 using the atmosphere simulation chamber SAPHIR

2021 ◽  
Author(s):  
Yat Sing Pang ◽  
Martin Kaminski ◽  
Anna Novelli ◽  
Philip Carlsson ◽  
Ismail-Hakki Acir ◽  
...  
Keyword(s):  
Organic Aerosol ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Reaction Pathways ◽  
Oh Radicals ◽  
Oh Radical ◽  
Simulation Experiments ◽  
Master Chemical Mechanism ◽  
Simulation Results ◽  
Atmosphere Simulation Chamber

&lt;p&gt;Limonene is the fourth-most abundant monoterpene in the atmosphere, which upon oxidation leads to the formation of secondary organic aerosol (SOA) and thereby influences climate and air quality.&lt;/p&gt;&lt;p&gt;In this study, the oxidation of limonene by OH at different atmospherically relevant NO and HO&lt;sub&gt;2&lt;/sub&gt; levels (NO: 0.1 &amp;#8211; 10 ppb; HO&lt;sub&gt;2&lt;/sub&gt;: 20 ppt) was investigated in simulation experiments in the SAPHIR chamber at Forschungszentrum J&amp;#252;lich. The analysis focuses on comparing measured radical concentrations (RO&lt;sub&gt;2&lt;/sub&gt;, HO&lt;sub&gt;2&lt;/sub&gt;, OH) and OH reactivity (k&lt;sub&gt;OH&lt;/sub&gt;) with modeled values calculated using the Master Chemical Mechanism (MCM) version 3.3.1.&lt;/p&gt;&lt;p&gt;At high and medium NO concentrations, RO&lt;sub&gt;2&lt;/sub&gt; is expected to quickly react with NO. An HO&lt;sub&gt;2&lt;/sub&gt; radical is produced during the process that can be converted back to an OH radical by another reaction with NO. Consistently, for experiments conducted at medium NO levels (~0.5 ppb, RO&lt;sub&gt;2&lt;/sub&gt; lifetime ~10 s), simulated RO&lt;sub&gt;2&lt;/sub&gt;, HO&lt;sub&gt;2&lt;/sub&gt;, and OH agree with observations within the measurement uncertainties, if the OH reactivity of oxidation products is correctly described.&lt;/p&gt;&lt;p&gt;At lower NO concentrations, the regeneration of HO&lt;sub&gt;2&lt;/sub&gt; in the RO&lt;sub&gt;2&lt;/sub&gt; + NO reaction is slow and the reaction of RO&lt;sub&gt;2&lt;/sub&gt; with HO&lt;sub&gt;2&lt;/sub&gt; gains importance in forming peroxides. However, simulation results show a large discrepancy between calculated radical concentrations and measurements at low NO levels (&lt;0.1 ppb, RO&lt;sub&gt;2&lt;/sub&gt; lifetime ~ 100 s). Simulated RO&lt;sub&gt;2&lt;/sub&gt; concentrations are found to be overestimated by a factor of three; simulated HO&lt;sub&gt;2&lt;/sub&gt; concentrations are underestimated by 50 %; simulated OH concentrations are underestimated by about 35%, even if k&lt;sub&gt;OH&lt;/sub&gt; is correctly described. This suggests that there could be additional RO&lt;sub&gt;2&lt;/sub&gt; reaction pathways that regenerate HO&lt;sub&gt;2&lt;/sub&gt; and OH radicals become important, but they are not taken into account in the MCM model.&lt;/p&gt;

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