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 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 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 Influence of NO<sub>2</sub> on secondary organic aerosol formation from ozonolysis of limonene

2017 ◽  
Author(s):  
Changjin Hu ◽  
Qiao Ma ◽  
Zhi Liu ◽  
Yue Cheng ◽  
Liqing Hao ◽  
...  
Keyword(s):  
Experimental Data ◽  
Secondary Organic Aerosols ◽  
Secondary Organic Aerosol ◽  
Organic Aerosols ◽  
Organic Aerosol ◽  
Chemical Mechanism ◽  
Aerosol Formation ◽  
Model Simulations ◽  
Negative Effect ◽  
Master Chemical Mechanism

Abstract. Limonene has a strong tendency to undergo ozonolysis to form semi-volatile and low-volatility compounds that contribute to secondary organic aerosols (SOAs) both outdoors and indoors. The influence of NO2 on SOA formation from ozonolysis of limonene has been evaluated using chamber experiments and the Master Chemical Mechanism (MCM) coupled with a gas-particle partitioning model in this work. A series of 21 indoor chamber experiments were carried out with or without NO2 under different [O3]0 / [VOC]0 ratios, and these experimental data were compared with the model simulations. Agreement in SOA yields was observed between the experimental observations and model simulations under varying conditions. Generally, SOA mass yields are positively dependent on [O3]0 / [VOC]0 without the presence of NO2. However, the introduction of NO2 leads to a more complicated change in SOA yield, which is shown to be related to initial [O3] / [VOC] ratios. When [O3]0 / [VOC]0 > 2, the introduction of NO2 results in an increase of SOA yield in the range of NO2 studied in this work; whereas a weak negative effect was found for SOA formation according to the introduction of ~ 250 ppbv NO2 under [O3]0 / [VOC]0 

scholarly journals Technical Note: Conversion of Isoprene Hydroxy Hydroperoxides (ISOPOOH) on Metal Environmental Simulation Chamber Walls

2016 ◽  
Author(s):  
Anne-Kathrin Bernhammer ◽  
Martin Breitenlechner ◽  
Frank N. Keutsch ◽  
Armin Hansel ◽  
Keyword(s):  
Gas Phase ◽  
Technical Note ◽  
Heterogeneous Reactions ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Stainless Steel Surface ◽  
Sources And Sinks ◽  
Environmental Surfaces ◽  
Isoprene Oxidation

Abstract. Sources and sinks of isoprene oxidation products from low NOx isoprene chemistry have been studied at the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber with a custom-built selective reagent ion time of flight mass spectrometer (SRI-ToF-MS), which allows quantitative measurement of isoprene hydroxy hydroperoxides (ISOPOOH). The measured concentrations of the main oxidation products were compared to chemical box model simulations based on the Leeds Master Chemical Mechanism (MCM) v3.3. The modelled ISOPOOH concentrations are by a factor of 20 higher than the observed and methyl vinyl ketone (MVK) and methacrolein (MACR) concentrations are by a factor of up to 2 lower compared to observations, despite the artifact-free detection method. Addition of catalytic conversion of 1,2-ISOPOOH and 4,3-ISOPOOH to MVK and MACR on the stainless steel surface of the chamber to the chemical mechanism resolves the discrepancy between model predictions and observation. This suggests that isoprene chemistry in a metal chamber under low NOx conditions cannot be described by a pure gas phase model alone. Biases in the measurement of ISOPOOH, MVK and MACR can not only be caused intra-instrumentally but also by the general experimental setup. The work described here extends the role of heterogeneous reactions affection gas phase composition and properties from instrumental surfaces, described previously, to general experimental setups. The role of such conversion reactions on real environmental surfaces is yet to be explored.

scholarly journals OH reactivity in a South East Asian Tropical rainforest during the Oxidant and Particle Photochemical Processes (OP3) project

2013 ◽  
Vol 13 (2) ◽  
pp. 5233-5278 ◽  
Author(s):  
P. M. Edwards ◽  
M. J. Evans ◽  
K. L. Furneaux ◽  
J. Hopkins ◽  
T. Ingham ◽  
...  
Keyword(s):  
Tropical Rainforest ◽  
Primary Source ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Large Variability ◽  
Reactive Carbon ◽  
Carbon Compounds ◽  
Isoprene Oxidation ◽  
Master Chemical Mechanism ◽  
Physical And Chemical

Abstract. OH reactivity, the reciprocal of its lifetime from reaction with its sinks, was measured for 12 days in April 2008 within a tropical rainforest on Borneo as part of the OP3 project. The maximum observed value was 83.8 &amp;pm; 26.0 s−1 with the campaign averaged noon-time maximum being 29.1 &amp;pm; 8.5 s−1. The maximum OH reactivity calculated using the campaign averaged noon-time concentrations of observed sinks was ~18 s−1, significantly less than the observations, consistent with other studies in similar environments. OH reactivity was dominated by reaction with isoprene. Numerical simulations of isoprene oxidation using the Master Chemical Mechanism (v3.2) in a highly simplified physical and chemical environment show that the steady state OH reactivity is a linear function of the OH reactivity due to isoprene alone, with a maximum multiplier being equal to the number of isoprene OH attackable bonds (10). Thus the emission of isoprene constitutes a significantly larger emission of reactivity than is offered by the primary reaction with isoprene alone, with significant scope for the secondary oxidation products of isoprene to constitute the missing reactivity. A physically and chemically more sophisticated simulation (including physical loss, photolysis, and other oxidants) showed that the calculated OH reactivity is reduced by the removal of the OH attackable bonds by other oxidants and photolysis, and by physical loss (mixing and deposition). The calculated OH reactivity is increased by peroxide cycling, and by the OH concentration itself. Notable in these calculations is that the lifetime of OH reactivity is significantly longer than the lifetime of isoprene and critically depends on the chemical and physical lifetime of intermediate species. When constrained to the observed campaign averaged diurnal concentrations of primary volatile organic compounds (VOCs), O3, nitrogen oxides (NOx) and other parameters, the model underestimated the observed mean OH reactivity by 30%. However, it was found that: (1) the short lifetimes of isoprene and OH lead to a large variability in their concentrations and so significant variation in the calculated OH reactivity, (2) uncertainties in the OH chemistry in these high isoprene environments can lead to an underestimate of the OH reactivity, and (3) the physical loss of species that react with OH plays a significant role in the calculated OH reactivity, (4) a missing primary source of reactive carbon would have to be emitted at a rate equivalent to 50% that of isoprene to account for the missing OH sink. A clear argument for a significant missing flux of primary emitted VOC compounds to account for the unmeasured reactivity is not found and the development of techniques for the measurement of secondary multifunctional carbon compounds is needed to close the OH reactivity budget.

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.

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;

scholarly journals Nitrate formation from heterogeneous uptake of dinitrogen pentoxide during a severe winter haze in southern China

2018 ◽  
Author(s):  
Hui Yun ◽  
Weihao Wang ◽  
Tao Wang ◽  
Men Xia ◽  
Chuan Yu ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Time Resolution ◽  
Southern China ◽  
Fine Particulate Matter ◽  
Measurement Data ◽  
Heterogeneous Reactions ◽  
Chemical Mechanism ◽  
Rural Site ◽  
Phase Reaction ◽  
Dinitrogen Pentoxide

Abstract. Nitrate (NO3−) has become a major component of fine particulate matter (PM2.5) during hazy days in China. However, the role of the heterogeneous reactions of dinitrogen pentoxide (N2O5) in nitrate formation is not well constrained. In January 2017, a severe haze event occurred in the Pearl River Delta (PRD) of southern China during which high levels of PM2.5 (~ 400 μg m−3) and O3 (~ 160 ppbv) were observed at a semi-rural site (Heshan) in the western PRD. Nitrate concentrations were up to 108 μg m−3 (1 h time resolution), and the contribution of nitrate to PM2.5 reached nearly 40 %. Concurrent increases in NO3− and ClNO2 (with a maximum value of 8.3 ppbv in 1 min time resolution) were observed in the first several hours after sunset, indicating an intense N2O5 heterogeneous uptake on aerosols. The formation potential of NO3− via N2O5 heterogeneous reactions was estimated to be 39.7 to 77.3 μg m−3 in the early hours (3 to 6 h) after sunset based on the measurement data, which could completely explain the measured increase in the NO3− concentration during the same time period. Daytime production of nitric acid from the gas-phase reaction of OH + NO2 was calculated with a chemical box model built using the Master Chemical Mechanism (MCM v3.3.1) and constrained by the measurement data. The integrated nocturnal nitrate formed via N2O5 chemistry was comparable to or even higher than the nitric acid formed during the daytime. This study confirms that N2O5 heterogeneous chemistry was a significant source of aerosol nitrate during hazy days in southern China.

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