Heterogeneous Reaction of OH Radicals with Terbuthylazine on Self-synthesized Silica Particles in an Aerosol Smog Chamber at Different Temperatures

2021 ◽  
Author(s):  
Lei Han ◽  
Peng Zhao ◽  
Cornelius Zetzsch
Keyword(s):  
Heterogeneous Reaction ◽  
Silica Particles ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Different Temperatures

scholarly journals Volatility and hygroscopicity of aging secondary organic aerosol in a smog chamber

2011 ◽  
Vol 11 (3) ◽  
pp. 7423-7467 ◽  
Author(s):  
T. Tritscher ◽  
J. Dommen ◽  
P. F. DeCarlo ◽  
P. B. Barmet ◽  
A. P. Praplan ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Organic Aerosol ◽  
Heterogeneous Reactions ◽  
Physical Parameters ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Chemical Aging ◽  
Aerosol Mass ◽  
Gas Phase Oxidation ◽  
Substantial Change

Abstract. The evolution of secondary organic aerosols (SOA) during (photo-)chemical aging processes was investigated in a smog chamber. SOA from 10–40 ppb α-pinene was formed during ozonolysis followed by aging with OH radicals. The particles' volatility and hygroscopicity (expressed as volume fraction remaining (VFR) and hygroscopicity parameter κ) were measured with a volatility and hygroscopicity tandem differential mobility analyzer (V/H-TDMA). These measurements were used as sensitive physical parameters to reveal the possible mechanisms responsible for the chemical changes in the SOA composition during aging: A change of VFR and/or κ during processing of atmospheric aerosol may occur either by addition of SOA mass (by condensation) or by an exchange of molecules in the SOA by other molecules with different properties. The former process increases the SOA mass by definition, while the latter keeps the SOA mass roughly constant and may occur either by heterogeneous reactions on the surface of the SOA particles, by homogeneous reactions like oligomerization or by an evaporation – gas-phase oxidation – recondensation cycle. Thus, when there is a substantial change in the aerosol mass with time, the condensation mechanism may be assumed to be dominant, while, when the mass stays roughly constant the exchange mechanism is likely to be dominant, a process termed ripening here. Depending on the phase of the experiment, an O3 mediated condensation, O3 mediated ripening, OH mediated condensation, and OH mediated ripening could be distinguished. During the O3 mediated condensation the particles volatility decreased (increasing VFR) while the hygroscopicity increased. Thereafter, in the course of O3 mediated ripening volatility continued to decrease, but hygroscopicity stayed roughly constant. After exposing the SOA to OH radicals an OH mediated condensation started with a significant increase of SOA mass. Concurrently, hygroscopicity and volatility increased. This phase was then followed by an OH mediated ripening with a decrease of volatility.

scholarly journals Volatility and hygroscopicity of aging secondary organic aerosol in a smog chamber

2011 ◽  
Vol 11 (22) ◽  
pp. 11477-11496 ◽  
Author(s):  
T. Tritscher ◽  
J. Dommen ◽  
P. F. DeCarlo ◽  
M. Gysel ◽  
P. B. Barmet ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Volume Fraction ◽  
Chemical Characterization ◽  
Mass Gain ◽  
Heterogeneous Reactions ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Chemical Aging ◽  
Aerosol Mass ◽  
Significant Mass

Abstract. The evolution of secondary organic aerosols (SOA) during (photo-)chemical aging processes was investigated in a smog chamber. Fresh SOA from ozonolysis of 10 to 40 ppb α-pinene was formed followed by aging with OH radicals. The particles' volatility and hygroscopicity (expressed as volume fraction remaining (VFR) and hygroscopicity parameter κ) were measured in parallel with a volatility and hygroscopicity tandem differential mobility analyzer (V/H-TDMA). An aerosol mass spectrometer (AMS) was used for the chemical characterization of the aerosol. These measurements were used as sensitive parameters to reveal the mechanisms possibly responsible for the changes in the SOA composition during aging. A change of VFR and/or κ during processing of atmospheric aerosols may occur either by addition of SOA mass (by condensation) or by a change of SOA composition leading to different aerosol properties. The latter may occur either by heterogeneous reactions on the surface of the SOA particles, by condensed phase reactions like oligomerization or by an evaporation – gas-phase oxidation – recondensation cycle. The condensation mechanism showed to be dominant when there is a substantial change in the aerosol mass by addition of new molecules to the aerosol phase with time. Experiments could be divided into four periods based on the temporal evolution (qualitative changes) of VFR, κ and organic mass: O3 induced condensation, ripening, and OH induced chemical aging first with substantial mass gain and then without significant mass gain. During the O3 induced condensation the particles' volatility decreased (increasing VFR) while the hygroscopicity increased. Thereafter, in the course of ripening volatility continued to decrease, but hygroscopicity stayed roughly constant. After exposing the SOA to OH radicals an OH induced chemical aging with substantial mass gain started resulting in the production of at least 50 % more SOA mass. This new SOA mass was highly volatile and oxidized. This period was then followed by further OH induced chemical aging without significant mass gain leading to a decrease of volatility while hygroscopicity and SOA mass stayed roughly constant.

scholarly journals Secondary organic aerosol formation from smoldering and flaming combustion of biomass: a box model parametrization based on volatility basis set

2019 ◽  
Author(s):  
Giulia Stefenelli ◽  
Jianhui Jiang ◽  
Amelie Bertrand ◽  
Emily A. Bruns ◽  
Simone M. Pieber ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Secondary Organic Aerosol ◽  
Time Of Flight ◽  
Organic Aerosol ◽  
Box Model ◽  
Basis Set ◽  
Model Parameters ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Aerosol Formation

Abstract. Box model simulations based on the volatility basis set (VBS) approach were used to assess secondary organic aerosol (SOA) precursors and volatility distributions from residential wood combustion. Emissions were sampled from three different residential stoves at different combustion conditions (flaming vs. smoldering-dominated), aging temperatures (−10 °C, 2 °C and 15 °C), and emission loads, then exposed to hydroxyl (OH) radicals in a smog chamber. Primary emissions of SOA precursor compounds, organic aerosol and their evolution during aging in the smog chamber were monitored by a comprehensive suite of gas and particle instrumentation, including a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) and a high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). SOA precursors were classified according to their chemical composition and the identification of the nature of the precursors revealed useful to better constrain model parameters, in particular SOA production rates and molecular characteristics of the condensable gases formed. The general aim of the model was the determination of the parameters describing the volatility distributions of the oxidation products from the different chemical classes considered and their temperature dependence. Novel parameterization methods based on a genetic algorithm (GA) approach allowed estimation of precursor class contributions to SOA and evaluation of the effect of emission variability on SOA yield predictions. Significant differences were observed in the gas-phase composition between smoldering and flaming emissions. Smoldering phase emissions were dominated by oxidized VOCs with less than six carbon atoms family (OVOCc 

Effects of SiO2 Particles in Mechanical Properties of Iron Composite

2013 ◽  
Vol 465-466 ◽  
pp. 886-890
Author(s):  
Adibah Amir ◽  
Othman Mamat
Keyword(s):  
Mechanical Properties ◽  
Powder Metallurgy ◽  
Fine Particles ◽  
Sintering Temperature ◽  
Silica Particles ◽  
Milling Process ◽  
Powder Metallurgy Technique ◽  
Temperature Changes ◽  
Different Temperatures

Tronohs raw sand was converted into fine silica particles via a series of milling process. Addition of these fine particles into iron composite was found to modify its mechanical properties. The composite was prepared using powder metallurgy technique with varying percentage of silica particles; 5, 10, 15, 20 and 25wt%. The composites were sintered at three different temperatures; 1000° C, 1100° C and 1200° C to find the most suitable sintering temperature. Changes in density and hardness were observed. The results showed that composite consist of 20wt% silica particles and sintered at 1100° C exhibits best improvement.

Numerical Simulation of a Mini-Channel Three-Way Catalytic Converter

2010 ◽  
Author(s):  
M. H. Akbari ◽  
R. Roohi ◽  
S. A. Asaee
Keyword(s):  
Conversion Efficiency ◽  
Single Channel ◽  
Heterogeneous Reaction ◽  
Catalytic Converter ◽  
Three Dimensional ◽  
Space Velocity ◽  
Kinetic Mechanism ◽  
Operating Conditions ◽  
Three Dimensional Model ◽  
Different Temperatures

A three-dimensional model is developed to simulate the behavior of a single-channel three-way catalytic converter. The flow regime is assumed to be steady and laminar, and the channel walls are considered as isothermal. A multi-step, global heterogeneous reaction mechanism with 16 reactions and 11 species is used in this investigation to enhance the accuracy of the results. The chemical reactions are assumed to occur only on the reactor walls. The developed model is validated against available experimental data for stoichiometric operating conditions. The effect of the feed temperature on the conversion efficiency of the main pollutant components is studied. The light-off temperature for the stoichiometric A/F is found to be about 530 K for CO, NO and UHC, and 425 K for H2 conversion. The model is also applied to predict the effect of reactor length and inlet mixture space velocity on the conversion efficiency at two different temperatures. By using the same kinetics a well-stirred, unsteady model is also developed to identify the sensitivity of the multi-step kinetic mechanism to the mixture composition. The effect of mole fraction variation of each species on the conversion of other mixture components is investigated.

scholarly journals Consecutive reactions of aromatic–OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

2006 ◽  
Vol 6 (4) ◽  
pp. 7623-7656 ◽  
Author(s):  
R. Koch ◽  
R. Knispel ◽  
M. Elend ◽  
M. Siese ◽  
C. Zetzsch
Keyword(s):  
Reaction Mechanism ◽  
Flash Photolysis ◽  
Effective Rate Constant ◽  
Effective Rate ◽  
Atmospheric Composition ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Resonance Fluorescence ◽  
Consecutive Reactions ◽  
Benzene Toluene

Abstract. Consecutive reactions of adducts, resulting from OH radicals and aromatics, with the tropospheric scavenger molecules O2, NO and NO2 have been studied for benzene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline by observing decays of OH at temperatures where the thermal back-decomposition to OH is faster than 3 s−1, typically between 300 and 340 K. The experimental technique was resonance fluorescence with flash photolysis of water as source of OH. Biexponential decays were observed in the presence of either O2 or NO, and triexponential decays were obtained in the presence of NO2. The kinetic analysis was performed by fitting the relevant rate constants of the reaction mechanism to whole sets of decays obtained at various concentrations of aromatic and scavenger. In the case of hexamethylbenzene, the biexponential decays suggest the existence of the ipso-adduct, and the slightly higher necessary temperatures show that it is even more stable. In addition, smog chamber experiments at O2 concentrations from atmospheric composition down to well below 100 ppm have been carried out for benzene, toluene and p-xylene. The drop of the effective rate constant of removal by OH occurs at reasonable O2 levels, given the FP/RF results. Comparison of the adduct reactivities shows for all aromatics of this study that the reaction with O2 predominates over that with NO2 under all tropospheric conditions, and that a reaction with NO may only occur after the reaction with O2.

Photolysis and Heterogeneous Reaction of Coniferyl Aldehyde Adsorbed on Silica Particles with Ozone

ChemPhysChem ◽  
2010 ◽  
Vol 11 (18) ◽  
pp. 4019-4027 ◽  
Author(s):  
Sopheak Net ◽  
Elena Gomez Alvarez ◽  
Natalja Balzer ◽  
Henri Wortham ◽  
Cornelius Zetzsch ◽  
...  
Keyword(s):  
Heterogeneous Reaction ◽  
Silica Particles

scholarly journals Oil absorption in mesoporous silica particles

2010 ◽  
Vol 4 (4) ◽  
pp. 265-269 ◽  
Author(s):  
Radislav Filipovic ◽  
Dragica Lazic ◽  
Mitar Perusic ◽  
Ivan Stijepovic
Keyword(s):  
Mesoporous Silica ◽  
Sodium Silicate ◽  
Sodium Silicate Solution ◽  
Silicate Solution ◽  
Processing Parameters ◽  
Synthesis Temperature ◽  
Silica Particles ◽  
Clear Correlation ◽  
Oil Absorption ◽  
Different Temperatures

Mesoporous silica particles were prepared from highly basic sodium silicate solutions, having different silica modulus and SiO2 concentrations, by adding sulphuric acid at different temperatures. Pore structure of prepared silica particles (aggregates) is strongly influenced by processing conditions and easy controllable in broad range of the specific surface area, pore size, pore volume and size distribution. It is shown that there is a clear correlation between volume of absorbed oil and processing parameters used in preparation of silica aggregates. Thus, oil absorption is higher in the samples prepared from sodium silicate solution with higher SiO2 concentration and at higher synthesis temperature.

scholarly journals Application of positive matrix factor analysis in heterogeneous kinetics studies: an improvement to the mixed-phase relative rates technique

2014 ◽  
Vol 14 (6) ◽  
pp. 8695-8722 ◽  
Author(s):  
Y. Liu ◽  
S.-M. Li ◽  
J. Liggio
Keyword(s):  
Citric Acid ◽  
Heterogeneous Reaction ◽  
Organic Aerosol ◽  
Mixed Phase ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Positive Matrix ◽  
Heterogeneous Kinetics ◽  
Aerosol Mass ◽  
Uptake Coefficients

Abstract. The mixed-phase relative rate approach for determining aerosol particle organic component heterogeneous reaction kinetics and OH uptake coefficients to particles is often performed utilizing mass spectral tracers as a proxy for particle phase reactant concentration. However, this approach may be influenced by signal contaminations from oxidation products during the experiment. In the current study, the mixed-phase relative rates technique has been improved by combining a Positive Matrix Factor (PMF) analysis with electron ionization Aerosol Mass Spectrometry, thereby removing the influence of m / z fragments from reaction products on the reactant signals. To demonstrate the advantages of this approach, the heterogeneous reaction between OH radicals and citric acid (CA) was investigated using a photochemical flow tube coupled to a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS). The measured heterogeneous rate constant (k2) of citric acid toward OH was (3.31 ± 0.29) × 10−12 cm3 molecule−1 s−1 at 298 K and (30 ± 3)% RH and was ∼7.7 times greater than previously reported results utilizing individual m / z fragments. This phenomenon was further confirmed for particulate-phase organophosphates (TPhP, TDCPP, and TEHP), leading to k2 values significantly larger than previously reported. The results suggest that heterogeneous kinetics can be significantly underestimated when a non-molecular ion peak is used as the tracer. Finally, the results suggest that the heterogeneous lifetime of organic aerosol in models can be overestimated due to underestimated OH uptake coefficients, and that it may be necessary to revisit the heterogeneous kinetic data of organic aerosol components which were derived in the context of the relative rates technique.

A Simulated Heterogeneous Reaction of SO2 on the Surface of Hematite at Different Temperatures

2008 ◽  
Vol 24 (12) ◽  
pp. 2331-2336 ◽  
Author(s):  
CUI Hu-Xiong ◽  
◽  
◽  
CHENG Tian-Tao ◽  
CHEN Jian-Min ◽  
...  
Keyword(s):  
Heterogeneous Reaction ◽  
Different Temperatures
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