scholarly journals Chemical ageing and transformation of diffusivity in semi-solid multi-component organic aerosol particles

2011 ◽  
Vol 11 (14) ◽  
pp. 7343-7354 ◽  
Author(s):  
C. Pfrang ◽  
M. Shiraiwa ◽  
U. Pöschl
Keyword(s):  
Atmospheric Aerosols ◽  
Particle Surface ◽  
Solid Particles ◽  
Reaction Conditions ◽  
Component Mixture ◽  
Model Treatment ◽  
Semi Solid ◽  
Organic Particles ◽  
The Impact ◽  
Chemical Ageing

Abstract. Recent experimental evidence underlines the importance of reduced diffusivity in amorphous semi-solid or glassy atmospheric aerosols. This paper investigates the impact of diffusivity on the ageing of multi-component reactive organic particles approximating atmospheric cooking aerosols. We apply and extend the recently developed KM-SUB model in a study of a 12-component mixture containing oleic and palmitoleic acids. We demonstrate that changes in the diffusivity may explain the evolution of chemical loss rates in ageing semi-solid particles, and we resolve surface and bulk processes under transient reaction conditions considering diffusivities altered by oligomerisation. This new model treatment allows prediction of the ageing of mixed organic multi-component aerosols over atmospherically relevant timescales and conditions. We illustrate the impact of changing diffusivity on the chemical half-life of reactive components in semi-solid particles, and we demonstrate how solidification and crust formation at the particle surface can affect the chemical transformation of organic aerosols.

scholarly journals Chemical ageing and transformation of diffusivity in semi-solid multi-component organic aerosol particles

2011 ◽  
Vol 11 (4) ◽  
pp. 13003-13033 ◽  
Author(s):  
C. Pfrang ◽  
M. Shiraiwa ◽  
U. Pöschl
Keyword(s):  
Atmospheric Aerosols ◽  
Particle Surface ◽  
Solid Particles ◽  
Reaction Conditions ◽  
Component Mixture ◽  
Model Treatment ◽  
Semi Solid ◽  
Organic Particles ◽  
The Impact ◽  
Chemical Ageing

Abstract. Recent experimental evidence underlines the importance of reduced diffusivity in amorphous semi-solid or glassy atmospheric aerosols. This paper investigates the impact of diffusivity on the ageing of multi-component reactive organic particles representative of atmospheric cooking aerosols. We apply and extend the recently developed KM-SUB model in a study of a 12-component mixture containing oleic and palmitoleic acids. We demonstrate that changes in the diffusivity may explain the evolution of chemical loss rates in ageing semi-solid particles, and we resolve surface and bulk processes under transient reaction conditions considering diffusivities altered by oligomerisation. This new model treatment allows prediction of the ageing of mixed organic multi-component aerosols over atmospherically relevant time scales and conditions. We illustrate the impact of changing diffusivity on the chemical half-life of reactive components in semi-solid particles, and we demonstrate how solidification and crust formation at the particle surface can affect the chemical transformation of organic aerosols.

scholarly journals Effect of Bulk Composition on the Heterogeneous Oxidation of Semi-Solid Atmospheric Aerosols

Atmosphere ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 791
Author(s):  
Hanyu Fan ◽  
Fabien Goulay
Keyword(s):  
Atmospheric Aerosols ◽  
Bulk Composition ◽  
Particle Surface ◽  
Reaction Diffusion ◽  
Solid Particles ◽  
Molar Ratio ◽  
Heterogeneous Oxidation ◽  
Reaction Diffusion Model ◽  
Semi Solid ◽  
The Impact

The OH-initiated heterogeneous oxidation of semi-solid saccharide particles with varying bulk compositions was investigated in an atmospheric pressure flow tube at 30% relative humidity. Reactive uptake coefficients were determined from the rate loss of the saccharide reactants measured by mass spectrometry at different monosaccharide (methyl-β-d-glucopyranoside, C7H14O6) and disaccharide (lactose, C12H22O11) molar ratios. The reactive uptake for the monosaccharide was found to decrease from 0.53 ± 0.10 to 0.05 ± 0.06 as the mono-to-disaccharide molar ratio changed from 8:1 to 1:1. A reaction–diffusion model was developed in order to determine the effect of chemical composition on the reactive uptake. The observed decays can be reproduced using a Vignes relationship to predict the composition dependence of the reactant diffusion coefficients. The experimental data and model results suggest that the addition of the disaccharide significantly increases the particle viscosity leading to slower mass transport phenomena from the bulk to the particle surface and to a decreased reactivity. These findings illustrate the impact of bulk composition on reactant bulk diffusivity which determines the rate-limiting step during the chemical transformation of semi-solid particles in the atmosphere.

scholarly journals Effect of temperature, CO2 and O2 on motility and mobility of Anisakidae larvae

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Aiyan Guan ◽  
Inge Van Damme ◽  
Frank Devlieghere ◽  
Sarah Gabriël
Keyword(s):  
Enzymatic Digestion ◽  
Infected Fish ◽  
Effect Of Temperature ◽  
Video Recordings ◽  
Different Temperatures ◽  
Semi Solid ◽  
Zoonotic Parasites ◽  
The Impact ◽  
Phosphate Buffered Saline

AbstractAnisakidae, marine nematodes, are underrecognized fish-borne zoonotic parasites. Studies on factors that could trigger parasites to actively migrate out of the fish are very limited. The objective of this study was to assess the impact of different environmental conditions (temperature, CO2 and O2) on larval motility (in situ movement) and mobility (migration) in vitro. Larvae were collected by candling or enzymatic digestion from infected fish, identified morphologically and confirmed molecularly. Individual larvae were transferred to a semi-solid Phosphate Buffered Saline agar, and subjected to different temperatures (6 ℃, 12 ℃, 22 ℃, 37 ℃) at air conditions. Moreover, different combinations of CO2 and O2 with N2 as filler were tested, at both 6 °C and 12 °C. Video recordings of larvae were translated into scores for larval motility and mobility. Results showed that temperature had significant influence on larval movements, with the highest motility and mobility observed at 22 ℃ for Anisakis spp. larvae and 37 ℃ for Pseudoterranova spp. larvae. During the first 10 min, the median migration of Anisakis spp. larvae was 10 cm at 22 ℃, and the median migration of Pseudoterranova spp. larvae was 3 cm at 37 ℃. Larval mobility was not significantly different under the different CO2 or O2 conditions at 6 °C and 12 ℃. It was concluded that temperature significantly facilitated larval movement with the optimum temperature being different for Anisakis spp. and Pseudoterranova spp., while CO2 and O2 did not on the short term. This should be further validated in parasite-infected/spiked fish fillets.

scholarly journals Nitrate-dominated PM<sub>2.5</sub> and elevation of particle pH observed in urban Beijing during the winter of 2017

2020 ◽  
Vol 20 (8) ◽  
pp. 5019-5033 ◽  
Author(s):  
Yuning Xie ◽  
Gehui Wang ◽  
Xinpei Wang ◽  
Jianmin Chen ◽  
Yubao Chen ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Ammonia Concentration ◽  
Historical Record ◽  
Molar Ratio ◽  
Effective Control ◽  
Nitrate Content ◽  
Chinese Government ◽  
Low Level ◽  
The Impact ◽  
Pollution Episodes

Abstract. The Chinese government has exerted strict emission controls to mitigate air pollution since 2013, which has resulted in significant decreases in the concentrations of air pollutants such as SO2. Strict pollution control actions also reduced the average PM2.5 concentration to the low level of 39.7 µg m−3 in urban Beijing during the winter of 2017. To investigate the impact of such changes on the physiochemical properties of atmospheric aerosols in China, we conducted a comprehensive observation focusing on PM2.5 in Beijing during the winter of 2017. Compared with the historical record (2014–2017), SO2 decreased to the low level of 3.2 ppbv in the winter of 2017, but the NO2 level was still high (21.4 ppbv in the winter of 2017). Accordingly, the contribution of nitrate (23.0 µg m−3) to PM2.5 far exceeded that of sulfate (13.1 µg m−3) during the pollution episodes, resulting in a significant increase in the nitrate-to-sulfate molar ratio. The thermodynamic model (ISORROPIA II) calculation results showed that during the PM2.5 pollution episodes particle pH increased from 4.4 (moderate acidic) to 5.4 (more neutralized) when the molar ratio of nitrate to sulfate increased from 1 to 5, indicating that aerosols were more neutralized as the nitrate content elevated. Controlled variable tests showed that the pH elevation should be attributed to nitrate fraction increase other than crustal ion and ammonia concentration increases. Based on the results of sensitivity tests, future prediction for the particle acidity change was discussed. We found that nitrate-rich particles in Beijing at low and moderate humid conditions (RH: 20 %–50 %) can absorb twice the amount of water that sulfate-rich particles can, and the nitrate and ammonia with higher levels have synergetic effects, rapidly elevating particle pH to merely neutral (above 5.6). As moderate haze events might occur more frequently under abundant ammonia and nitrate-dominated PM2.5 conditions, the major chemical processes during haze events and the control target should be re-evaluated to obtain the most effective control strategy.

Formation Mechanism of Thixotropic Microstructure of AM60 Alloy during Solidification

2014 ◽  
Vol 1030-1032 ◽  
pp. 86-89
Author(s):  
Bo Xing
Keyword(s):  
Formation Mechanism ◽  
Solid Substrate ◽  
Research Field ◽  
Primary Phase ◽  
Solid Particles ◽  
Metallographic Analysis ◽  
Semisolid Slurry ◽  
Dendritic Microstructure ◽  
Quenching Method ◽  
Semi Solid

A research field on semi-solid metal processing is the preparation of semi-solid slurry with non-dendritic microstructure. Nowadays, with the technological innovation of semi-solid slurry preparation, people turn to produce the non-dendritic semisolid microstructure by locally cooling of the alloy melt during solidification. Therefore, it is necessary to investigate the formation mechanism of the non-dendritic microstructure formation because the primary phase undergoes a specially controlled nucleation and growth which distinctly different from the commom solidification. In this paper, the semisolid slurry of AM60 alloy was produced by Self-Inoculation Method (SIM), and the microstructure evolution of primary α-Mg was investigated by water quenching method and metallographic analysis. The results indicate that the semisolid microstructure of AM60 alloy produced by SIM composed of small and globular α-Mg particles, and these grains undergone a coarsing process during quiescent holding. The solid substrate caused by the fusion of solid particles and the dendritic fragments caused by melt flow caused the grain multiplication, and then the grain undergone a steadily growth because of the uniform temperature distribution, resulting in the increase of grains density and a small grain size of the AM60 semisolid slurry.

scholarly journals Impact of vehicular emissions on the formation of fine particles in the Sao Paulo Metropolitan Area: a numerical study with the WRF-Chem model

2016 ◽  
Vol 16 (2) ◽  
pp. 777-797 ◽  
Author(s):  
A Vara-Vela ◽  
M. F. Andrade ◽  
P. Kumar ◽  
R. Y. Ynoue ◽  
A. G. Muñoz
Keyword(s):  
Size Distribution ◽  
Metropolitan Area ◽  
Atmospheric Aerosols ◽  
Fine Particles ◽  
Sao Paulo ◽  
Vehicular Emissions ◽  
São Paulo ◽  
Mass Size Distribution ◽  
Mass Size ◽  
The Impact

Abstract. The objective of this work is to evaluate the impact of vehicular emissions on the formation of fine particles (PM2.5;  ≤  2.5 µm in diameter) in the Sao Paulo Metropolitan Area (SPMA) in Brazil, where ethanol is used intensively as a fuel in road vehicles. The Weather Research and Forecasting with Chemistry (WRF-Chem) model, which simulates feedbacks between meteorological variables and chemical species, is used as a photochemical modelling tool to describe the physico-chemical processes leading to the evolution of number and mass size distribution of particles through gas-to-particle conversion. A vehicular emission model based on statistical information of vehicular activity is applied to simulate vehicular emissions over the studied area. The simulation has been performed for a 1-month period (7 August–6 September 2012) to cover the availability of experimental data from the NUANCE-SPS (Narrowing the Uncertainties on Aerosol and Climate Changes in Sao Paulo State) project that aims to characterize emissions of atmospheric aerosols in the SPMA. The availability of experimental measurements of atmospheric aerosols and the application of the WRF-Chem model made it possible to represent some of the most important properties of fine particles in the SPMA such as the mass size distribution and chemical composition, besides allowing us to evaluate its formation potential through the gas-to-particle conversion processes. Results show that the emission of primary gases, mostly from vehicles, led to a production of secondary particles between 20 and 30 % in relation to the total mass concentration of PM2.5 in the downtown SPMA. Each of PM2.5 and primary natural aerosol (dust and sea salt) contributed with 40–50 % of the total PM10 (i.e. those  ≤  10 µm in diameter) concentration. Over 40 % of the formation of fine particles, by mass, was due to the emission of hydrocarbons, mainly aromatics. Furthermore, an increase in the number of small particles impaired the ultraviolet radiation and induced a decrease in ozone formation. The ground-level O3 concentration decreased by about 2 % when the aerosol-radiation feedback is taken into account.

scholarly journals Development of A Flexible Cell Targeting System Based on Silica Nanoparticles

1998 ◽  
Vol 530 ◽  
Author(s):  
T. Schiimstel ◽  
H. Schirra ◽  
J. Gerwann ◽  
C. Lesniak ◽  
A. Kalaghi-Nafchi ◽  
...  
Keyword(s):  
Silica Nanoparticles ◽  
Electrostatic Interactions ◽  
Particle Concentration ◽  
Biological Function ◽  
Particle Surface ◽  
Cell Types ◽  
Silica Particles ◽  
Hydrodynamic Diameter ◽  
Reaction Conditions ◽  
Physiological Conditions

AbstractCommercially available and synthesized silica particles were fluorescently labeled with FITC and modified to get a wide variety of particle systems with defined size and surface charge. By a variation of reaction conditions particles with diameters of 10 and 80 nm determined with TEM and with zetapotentials between -50 to +30 mV under physiological conditions (pH: 7.4, PBS-buffer) were available.A further molecular shell consisiting of avidin was obtained by binding the molecules to negatively charged particle surfaces through electrostatic interactions. The amount of avidin coupled to the silica particles was 1.7 μg per mg particle. Starting with particles with an hydrodynamic diameter determined with PCS of 260 nm, the size increased to 500 nm, while the zeta potential was altered to -8 mV under physiological conditions.Biotinylated wheat germ agglutinin (bio-WGA) can be bonded to such particles through avidin / biotin complex formation. Up to 2.8 μg lectin per mg particles could be coupled to the particle surface. This leads to a further increase of hydrodynamic diameter to 650 nm. It could be shown by hemagglutination test, that the bonded lectin is still active. No toxic effects of the silica particles were found at 1 wt.-% particle concentration with various cell types (Caco-2, L132). The binding of lectin-particle complexes to cells was increased by a factor of 4.4 in comparison to uncoated particles.In addition it was found that WGA can directly be coupled to the particle surface. An amount of 1.8 μg Lectin per mg particle was determined. The hydrodynamic diameter increases from 260 nm to 432 rm, while a zetapotential of-28 mV was found under physiological conditions.It could be shown, that negatively charged silica nanoparticles are suitable systems to couple various biomolecules retaining their biological function.

scholarly journals The influence of physical parameters on the in-situ metal carbonyl complex formation studied with the Fast On-line Reaction Apparatus (FORA)

2021 ◽  
Vol 109 (4) ◽  
pp. 261-281
Author(s):  
Yves Wittwer ◽  
Robert Eichler ◽  
Dominik Herrmann ◽  
Andreas Türler
Keyword(s):  
Gas Flow ◽  
Metal Carbonyl ◽  
Fission Products ◽  
Reaction Chamber ◽  
Single Atom ◽  
Physical Parameters ◽  
Carbonyl Complex ◽  
Reaction Conditions ◽  
On Line ◽  
The Impact

Abstract The Fast On-line Reaction Apparatus (FORA) was used to investigate the influence of various reaction parameters onto the formation and transport of metal carbonyl complexes (MCCs) under single-atom chemistry conditions. FORA is based on a 252Cf-source producing short-lived Mo, Tc, Ru and Rh isotopes. Those are recoiling from the spontaneous fission source into a reaction chamber flushed with a gas-mixture containing CO. Upon contact with CO, fission products form volatile MCCs which are further transported by the gas stream to the detection setup, consisting of a charcoal trap mounted in front of a HPGe γ-detector. Depending on the reaction conditions, MCCs are formed and transported with different efficiencies. Using this setup, the impact of varying physical parameters like gas flow, gas pressure, kinetic energy of fission products upon entering the reaction chamber and temperature of the reaction chamber on the formation and transport yields of MCCs was investigated. Using a setup similar to FORA called Miss Piggy, various gas mixtures of CO with a selection of noble gases, as well as N2 and H2, were investigated with respect to their effect onto MCC formation and transport. Based on this measurements, optimized reaction conditions to maximize the synthesis and transport of MCCs are suggested. Explanations for the observed results supported by simulations are suggested as well.

Determination of the viscosity of levitated droplets at atmospheric temperatures in an electrodynamic trap

2021 ◽  
Author(s):  
Stephanie Jones ◽  
Mohit Singh ◽  
Denis Duft ◽  
Alexei Kiselev ◽  
Thomas Leisner
Keyword(s):  
Amorphous Solid ◽  
Organic Aerosol ◽  
Photochemical Reactions ◽  
Temperature Range ◽  
Ability To Act ◽  
Levitated Droplets ◽  
Semi Solid ◽  
Future Work ◽  
The Impact

&lt;p&gt;The impact of atmospheric aerosol on the climate remains poorly understood. Organic aerosol makes up a significant fraction of total aerosol and is prevalent throughout the atmosphere. It can exist as a liquid, semi-solid or amorphous solid. The viscosity of organic aerosol will have an impact on transformations that organic aerosol will undergo during its lifetime such as evaporation and growth, heterogeneous and photochemical reactions as well as the ability to act as an ice nucleating particle.&amp;#160; Therefore, it is of key importance to be able to determine aerosol viscosity over a range of atmospherically relevant conditions in order to better understand the impact of organic aerosol on the climate.&lt;/p&gt; &lt;p&gt;Here we report proof of concept viscosity measurements of water droplets levitated in an electrodynamic balance over a range of temperatures. Charged droplets are levitated in a temperature and relative humidity-controlled environment allowing properties over a temperature range of 300 to 220 K to be studied. As the droplets evaporate they reach a point where Coulomb instabilities are induced resulting in droplet oscillations. The relaxation of these oscillations can then be probed to determine the droplet viscosity. Future work will involve determination of the viscosity of different types of organic aerosol over a broad temperature range.&lt;/p&gt;

Bending Strength and Fracture Behaviour of Metal-Ceramic Interpenetrating Phase Composites Manufactured by Using Semi-Solid Forming Technology

2022 ◽  
Vol 327 ◽  
pp. 111-116
Author(s):  
Laura Schomer ◽  
Kim Rouven Riedmüller ◽  
Mathias Liewald
Keyword(s):  
Bending Strength ◽  
Fracture Behaviour ◽  
Structural Characteristics ◽  
Process Window ◽  
Metallic Material ◽  
Forming Technology ◽  
Metal Ceramic ◽  
Semi Solid ◽  
The Impact ◽  
Interpenetrating Phase Composites

Interpenetrating Phase Composites (IPC) belong to a special category of composite materials, offering great potential in terms of material properties due to the continuous volume structure of both composite components. While manufacturing of metal-ceramic IPC via existing casting and infiltration processes leads to structural deficits, semi-solid forming represents a promising technology for producing IPC components without such defects. Thereby, a solid open pore body made of ceramic is infiltrated with a metallic material in the semi-solid state. Good structural characteristics of the microstructure as the integrity of the open-pore bodies after infiltration and an almost none residual porosity within the composites have already been proven for this manufacturing route within a certain process window. On this basis, the following paper focuses on the mechanical properties such as bending strength of metal-ceramic IPC produced by using semi-solid forming technology. Thereby, the impact of the significant process parameters on these properties is analysed within a suitable process window. Furthermore, a fractographic analysis is carried out by observing and interpreting the fracture behaviour during these tests and the fracture surface thereafter.

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