Articles de revues : « Resolved particles »

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Hameete, J., M. S. Abdallah, L. C. Thijs, T. A. M. Homan, X. C. Mi, N. J. Dam et L. P. H. de Goey. « Particle-resolved hyperspectral pyrometry of metal particles ». Combustion and Flame 264 (juin 2024) : 113435. http://dx.doi.org/10.1016/j.combustflame.2024.113435.

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Kannosto, J., M. Lemmetty, A. Virtanen, J. M. Mäkelä, J. Keskinen, H. Junninen, T. Hussein, P. Aalto et M. Kulmala. « Mode resolved density of atmospheric aerosol particles ». Atmospheric Chemistry and Physics Discussions 8, n^o 2 (15 avril 2008) : 7263–88. http://dx.doi.org/10.5194/acpd-8-7263-2008.

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Abstract. In this study, we investigate the mode resolved density of ultrafine atmospheric particles measured in boreal forest environment. The method used here enables us to find the distinct density information for each mode in atmospheric fine particle population: the density values for nucleation, Aitken, and accumulation mode particles are presented. The experimental data was gained during 2 May 2005–19 May 2005 at the boreal forest measurement station "SMEAR II" in Hyytiälä, southern Finland. The density values for accumulation mode varied from 1.1 to 2 g/cm3 (average 1.5 g/cm3) and for Aitken mode from 0.4 to 2 g/cm3 (average 0.97 g/cm3. As an overall trend during the two weeks campaign, the density value of Aitken mode was seen to gradually increase. With the present method, the time dependent behaviour of the particle density can be investigated in time scale of 10 min. This allows us the follow the density evolution of the nucleation mode particles during the particle growth process following the nucleation burst. The density of nucleation mode particles decreased during the growth process. The density values for 15 nm particles were 1.2–1.5 g/cm3 and for grown 30 nm particles 0.5–1 g/cm3. These values are consistent with the present knowledge that the condensing species are semi volatile organics, emitted from the Boreal forest.

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Kannosto, J., A. Virtanen, M. Lemmetty, J. M. Mäkelä, J. Keskinen, H. Junninen, T. Hussein, P. Aalto et M. Kulmala. « Mode resolved density of atmospheric aerosol particles ». Atmospheric Chemistry and Physics 8, n^o 17 (8 septembre 2008) : 5327–37. http://dx.doi.org/10.5194/acp-8-5327-2008.

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Abstract. In this study, we investigate the mode resolved density of ultrafine atmospheric particles measured in boreal forest environment. The method used here enables us to find the distinct density information for each mode in atmospheric fine particle population: the density values for nucleation, Aitken, and accumulation mode particles are presented. The experimental data was gained during 2 May 2005–19 May 2005 at the boreal forest measurement station "SMEAR II" in Hyytiälä, Southern Finland. The density values for accumulation mode varied from 1.1 to 2 g/cm3 (average 1.5 g/cm3) and for Aitken mode from 0.4 to 2 g/cm3 (average 0.97 g/cm3). As an overall trend during the two weeks campaign, the density value of Aitken mode was seen to gradually increase. With the present method, the time dependent behaviour of the particle density can be investigated in the time scale of 10 min. This allows us to follow the density evolution of the nucleation mode particles during the particle growth process following the nucleation burst. The density of nucleation mode particles decreased during the growth process. The density values for 15 nm particles were 1.2–1.5 g/cm3 and for grown 30 nm particles 0.5–1 g/cm3. These values are consistent with the present knowledge that the condensing species are semi-volatile organics, emitted from the boreal forest.

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Kakavas, Stylianos, David Patoulias, Maria Zakoura, Athanasios Nenes et Spyros N. Pandis. « Size-resolved aerosol pH over Europe during summer ». Atmospheric Chemistry and Physics 21, n^o 2 (20 janvier 2021) : 799–811. http://dx.doi.org/10.5194/acp-21-799-2021.

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Abstract. The dependence of aerosol acidity on particle size, location, and altitude over Europe during a summertime period is investigated using the hybrid version of aerosol dynamics in the chemical transport model PMCAMx. The pH changes more with particle size in northern and southern Europe owing to the enhanced presence of non-volatile cations (Na, Ca, K, Mg) in the larger particles. Differences of up to 1–4 pH units are predicted between sub- and supermicron particles, while the average pH of PM1−2.5 can be as much as 1 unit higher than that of PM1. Most aerosol water over continental Europe is associated with PM1, while coarse particles dominate the water content in the marine and coastal areas due to the relatively higher levels of hygroscopic sea salt. Particles of all sizes become increasingly acidic with altitude (0.5–2.5 units pH decrease over 2.5 km) primarily because of the decrease in aerosol liquid water content (driven by humidity changes) with height. Inorganic nitrate is strongly affected by aerosol pH with the highest average nitrate levels predicted for the PM1−5 range and over locations where the pH exceeds 3. Dust tends to increase aerosol pH for all particle sizes and nitrate concentrations for supermicron range particles. This effect of dust is quite sensitive to its calcium content. The size-dependent pH differences carry important implications for pH-sensitive processes in the aerosol.

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Tien, Wei Hsin, et Zi-Ling Lin. « Single-Frame Lagrangian Tracking Of 3-D Acoustic Streaming Flows Using Digital Defocusing Micro Particle Streak Velocimetry ». Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (8 juillet 2024) : 1–12. http://dx.doi.org/10.55037/lxlaser.21st.191.

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In this study, a single-frame particle streak velocimetry technique is applied to the classic DDPIV(Digital Defocusing Particle Image Velocimetry) concept to achieve a single-frame 3-D Lagrangian tracking of particles in microscopic flows. The shortcoming of images suffering low signal to noise ratio due to pinholes can be avoided. With the streak resolving algorithm, it allows extended exposure time when streak images are taken, and the single-frame approach also eliminates the need for high-cost and complicated synchronization hardware for double-pulse frame-straddling light sources. For each long-exposure, color-coded images received from each pinhole equipped with red, green or blue color filters, the streak-resolving algorithm is applied first to find each streak on the separate color channel, followed by an one-time triplet-matching process to group the red, green and blue streak projections. From the streak triplets, 3-D reconstruction can be done on all the resolved points on the streak, and trajectory fitting can then be applied to resolve the tracer particle trajectories in the field of view with temporal history. This procedure was applied for visualizing a microscale 3-D acoustic streaming flow pattern induced by a longitudinal spine-shaped fin oscillating at 12kHz. The height of the channel is 1mm with the spine of 0.3mm height and a 30 。 tip angle. Resolved flow fields show that the particle streak images can be resolved with the same level of accuracy to the particle tracking method, while the throughput of velocity vectors can be significantly higher due to multiple velocity vectors can be resolved from each streak triplet. The methodology has the potential to be applied to various applications that can capture long-exposure images and possible to resolve higher-order information such as acceleration and forces applied on the particles or the flow.

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Kontkanen, Jenni, Chenjuan Deng, Yueyun Fu, Lubna Dada, Ying Zhou, Jing Cai, Kaspar R. Daellenbach et al. « Size-resolved particle number emissions in Beijing determined from measured particle size distributions ». Atmospheric Chemistry and Physics 20, n^o 19 (5 octobre 2020) : 11329–48. http://dx.doi.org/10.5194/acp-20-11329-2020.

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Abstract. The climate and air quality effects of aerosol particles depend on the number and size of the particles. In urban environments, a large fraction of aerosol particles originates from anthropogenic emissions. To evaluate the effects of different pollution sources on air quality, knowledge of size distributions of particle number emissions is needed. Here we introduce a novel method for determining size-resolved particle number emissions, based on measured particle size distributions. We apply our method to data measured in Beijing, China, to determine the number size distribution of emitted particles in a diameter range from 2 to 1000 nm. The observed particle number emissions are dominated by emissions of particles smaller than 30 nm. Our results suggest that traffic is the major source of particle number emissions with the highest emissions observed for particles around 10 nm during rush hours. At sizes below 6 nm, clustering of atmospheric vapors contributes to calculated emissions. The comparison between our calculated emissions and those estimated with an integrated assessment model GAINS (Greenhouse Gas and Air Pollution Interactions and Synergies) shows that our method yields clearly higher particle emissions at sizes below 60 nm, but at sizes above that the two methods agree well. Overall, our method is proven to be a useful tool for gaining new knowledge of the size distributions of particle number emissions in urban environments and for validating emission inventories and models. In the future, the method will be developed by modeling the transport of particles from different sources to obtain more accurate estimates of particle number emissions.

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Yu, X. Y., J. P. Cowin, M. J. Iedema et H. Ali. « Fast time-resolved aerosol collector : proof of concept ». Atmospheric Measurement Techniques Discussions 3, n^o 3 (1 juin 2010) : 2515–34. http://dx.doi.org/10.5194/amtd-3-2515-2010.

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Abstract. Atmospheric particles can be collected in the field on substrates for subsequent laboratory analysis via chemically sensitive single particle methods such as scanning electron microscopy with energy dispersive x-ray analysis. With moving substrates time resolution of seconds to minutes can be achieved. In this paper, we demonstrate how to increase the time resolution when collecting particles on a substrate to a few milliseconds to provide real-time information. Our fast time-resolved aerosol collector ("Fast-TRAC") microscopically observes the particle collection on a substrate and records an on-line video. Particle arrivals are resolved to within a single frame (4–17 ms in this setup), and the spatial locations are matched to the subsequent single particle analysis. This approach also provides in-situ information on particle size and number concentration. Applications are expected in airborne studies of cloud microstructure, pollution plumes, and surface long-term monitoring.

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Yu, X. Y., J. P. Cowin, M. J. Iedema et H. Ali. « Fast time-resolved aerosol collector : proof of concept ». Atmospheric Measurement Techniques 3, n^o 5 (12 octobre 2010) : 1377–84. http://dx.doi.org/10.5194/amt-3-1377-2010.

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Abstract. Atmospheric particles can be collected in the field on substrates for subsequent laboratory analysis via chemically sensitive single particle methods such as scanning electron microscopy with energy dispersive x-ray analysis. With moving substrates time resolution of seconds to minutes can be achieved. In this paper, we demonstrate how to increase the time resolution when collecting particles on a substrate to a few milliseconds to provide real-time information. Our fast time-resolved aerosol collector ("Fast-TRAC") microscopically observes the particle collection on a substrate and records an on-line video. Particle arrivals are resolved to within a single frame (4–17 ms in this setup), and the spatial locations are matched to the subsequent single particle analysis. This approach also provides in-situ information on particle size and number concentration. Applications are expected in airborne studies of cloud microstructure, pollution plumes, and surface long-term monitoring.

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Guo, S., M. Hu, Z. B. Wang, J. Slanina et Y. L. Zhao. « Size-resolved aerosol water-soluble ionic compositions in the summer of Beijing : implication of regional secondary formation ». Atmospheric Chemistry and Physics 10, n^o 3 (1 février 2010) : 947–59. http://dx.doi.org/10.5194/acp-10-947-2010.

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Abstract. To characterize aerosol pollution in Beijing, size-resolved aerosols were collected by MOUDIs during CAREBEIJING-2006 field campaign at Peking University (urban site) and Yufa (upwind rural site). Fine particle concentrations (PM1.8 by MOUDI) were 99.8±77.4 μg/m3 and 78.2±58.4 μg/m3, with PM1.8/PM10 ratios of 0.64±0.08 and 0.76±0.08 at PKU and Yufa, respectively, and secondary compounds accounted for more than 50% in fine particles. PMF model analysis was used to resolve the particle modes. Three modes were resolved at Yufa, representing condensation, droplet and coarse mode. However, one more droplet mode with bigger size was resolved, which was considered probably from regional transport. Condensation mode accounted for 10%–60% of the total mass at both sites, indicating that the gas-to-particle condensation process was important in summer. The formation of sulfate was mainly attributed to in-cloud or aerosol droplet process (PKU 80%, Yufa 70%) and gas condensation process (PKU 14%, Yufa 22%). According to the thermodynamic instability of NH4NO3, size distributions of nitrate were classified as three categories by RH. The existence of Ca(NO3)2 in droplet mode indicated the reaction of HNO3 with crustal particles was also important in fine particles. A rough estimation was given that 69% of the PM10 and 87% of the PM1.8 in Beijing urban were regional contributions. Sulfate, ammonium and oxalate were formed regionally, with the regional contributions of 90%, 87% and 95% to PM1.8. Nitrate formation was local dominant. In summary regional secondary formation led to aerosol pollution in the summer of Beijing.

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Lu, Senlin, Teng Ma, Lu Zhang, Yule Feng, Shumin Zhou, Wei Zhang, Shinichi Yonemochi et al. « Relationships between Mass Level of Allergenic Platanus acerifolia Protein 3 (Pla a3) and Redox Trace Elements in the Size-Resolved Particles in Shanghai Atmosphere ». Atmosphere 13, n^o 10 (21 septembre 2022) : 1541. http://dx.doi.org/10.3390/atmos13101541.

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Allergenic pollen protein can be released from pollen grains and suspended in the air to cause allergenic reactions. However, the allergenic protein and its relationship with redox trace elements in ambient size-resolved particles has not been reported. Ambient size-resolved particles in Shanghai’s atmosphere were sampled during the Platanus pollen season in the spring season of 2017. Planatus pollen protein 3 (Pla a3) and redox trace elements in the ambient particles were investigated and their relationship was analyzed. Our data demonstrated that the mass level of the Pla a3 in the size-resolved particles ranged from 0.41 ± 0.28 to 7.46 ± 2.23 pg/m3, and decreased with the size range. Mass concentrations (ppb) of crustal elements (Fe, Al, Ca, Mg, Na) in the size-resolved particles ranged from 20.11 ± 9.87 to 1126.22 ± 659.51, while trace elements (V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Cd, Cs, Ba, Pb) varied from 0.05 ± 0.03 to 57.53 ± 19.7. Mass levels of these trace elements decreased according to particle size. The Abundance of redox trace elements, including Fe (R2 = 0.82), Mn (R2 = 0.54), Cu (R2 = 0.61), Ba (R2 = 0.82), and Pb (R2 = 0.82) in the size-resolved particles was significantly related to that of Pla a3, and our data implied redox trace elements might take syngenetic effects on the allergenicity induced by Pla a3 protein.

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Vowinckel, B., J. Withers, Paolo Luzzatto-Fegiz et E. Meiburg. « Settling of cohesive sediment : particle-resolved simulations ». Journal of Fluid Mechanics 858 (31 octobre 2018) : 5–44. http://dx.doi.org/10.1017/jfm.2018.757.

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We develop a physical and computational model for performing fully coupled, grain-resolved direct numerical simulations of cohesive sediment, based on the immersed boundary method. The model distributes the cohesive forces over a thin shell surrounding each particle, thereby allowing for the spatial and temporal resolution of the cohesive forces during particle–particle interactions. The influence of the cohesive forces is captured by a single dimensionless parameter in the form of a cohesion number, which represents the ratio of cohesive and gravitational forces acting on a particle. We test and validate the cohesive force model for binary particle interactions in the drafting–kissing–tumbling (DKT) configuration. Cohesive sediment grains can remain attached to each other during the tumbling phase following the initial collision, thereby giving rise to the formation of flocs. The DKT simulations demonstrate that cohesive particle pairs settle in a preferred orientation, with particles of very different sizes preferentially aligning themselves in the vertical direction, so that the smaller particle is drafted in the wake of the larger one. This preferred orientation of cohesive particle pairs is found to remain influential for systems of higher complexity. To this end, we perform large simulations of 1261 polydisperse settling particles starting from rest. These simulations reproduce several earlier experimental observations by other authors, such as the accelerated settling of sand and silt particles due to particle bonding, the stratification of cohesive sediment deposits, and the consolidation process of the deposit. They identify three characteristic phases of the polydisperse settling process, viz. (i) initial stir-up phase with limited flocculation, (ii) enhanced settling phase characterized by increased flocculation, and (iii) consolidation phase. The simulations demonstrate that cohesive forces accelerate the overall settling process primarily because smaller grains attach to larger ones and settle in their wakes. For the present cohesive number values, we observe that settling can be accelerated by up to 29 %. We propose physically based parametrization of classical hindered settling functions introduced by earlier authors, in order to account for cohesive forces. An investigation of the energy budget shows that, even though the work of the collision forces is much smaller than that of the hydrodynamic drag forces, it can substantially modify the relevant energy conversion processes.

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Vreman, A. W. « Particle-resolved direct numerical simulation of homogeneous isotropic turbulence modified by small fixed spheres ». Journal of Fluid Mechanics 796 (28 avril 2016) : 40–85. http://dx.doi.org/10.1017/jfm.2016.228.

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A statistically stationary homogeneous isotropic turbulent flow modified by 64 small fixed non-Stokesian spherical particles is considered. The particle diameter is approximately twice the Kolmogorov length scale, while the particle volume fraction is 0.001. The Taylor Reynolds number of the corresponding unladen flow is 32. The particle-laden flow has been obtained by a direct numerical simulation based on a discretization of the incompressible Navier–Stokes equations on 64 spherical grids overset on a Cartesian grid. The global (space- and time-averaged) turbulence kinetic energy is attenuated by approximately 9 %, which is less than expected. The turbulence dissipation rate on the surfaces of the particles is enhanced by two orders of magnitude. More than 5 % of the total dissipation occurs in only 0.1 % of the flow domain. The budget of the turbulence kinetic energy has been computed, as a function of the distance to the nearest particle centre. The budget illustrates how energy relatively far away from particles is transported towards the surfaces of the particles, where it is dissipated by the (locally enhanced) turbulence dissipation rate. The energy flux towards the particles is dominated by turbulent transport relatively far away from particles, by viscous diffusion very close to the particles, and by pressure diffusion in a significant region in between. The skewness and flatness factors of the pressure, velocity and velocity gradient have also been computed. The global flatness factor of the longitudinal velocity gradient, which characterizes the intermittency of small scales, is enhanced by a factor of six. In addition, several point-particle simulations based on the Schiller–Naumann drag correlation have been performed. A posteriori tests of the point-particle simulations, comparisons in which the particle-resolved results are regarded as the standard, show that, in this case, the point-particle model captures both the turbulence attenuation and the fraction of the turbulence dissipation rate due to particles reasonably well, provided the (arbitrary) size of the fluid volume over which each particle force is distributed is suitably chosen.

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Chen, Jingchuan, Zhijun Wu, Jie Chen, Naama Reicher, Xin Fang, Yinon Rudich et Min Hu. « Size-resolved atmospheric ice-nucleating particles during East Asian dust events ». Atmospheric Chemistry and Physics 21, n^o 5 (8 mars 2021) : 3491–506. http://dx.doi.org/10.5194/acp-21-3491-2021.

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Abstract. Asian dust is an important source of atmospheric ice-nucleating particles (INPs). However, the freezing activity of airborne Asian dust, especially its sensitivity to particle size, is poorly understood. In this study we report the first INP measurement of size-resolved airborne mineral dust collected during East Asian dust events. The measured total INP concentrations in the immersion mode ranged from 10−2 to 102 L−1 in dust events at temperatures between −25 and −5 ∘C. The average contributions of heat-sensitive INPs at three temperatures, −10, −15, and −20 ∘C, were 81±12 %, 70±15 %, and 38±21 %, respectively, suggesting that proteinaceous biological materials have a substantial effect on the ice nucleation properties of Asian airborne mineral dust at high temperatures. The dust particles which originated from China's northwest deserts are more efficient INPs compared to those from northern regions. In general, there was no significant difference in the ice nucleation properties between East Asian dust particles and other regions in the world. An explicit size dependence of both INP concentration and surface ice-active-site density was observed. The nucleation efficiency of dust particles increased with increasing particle size, while the INP concentration first increased rapidly and then leveled, due to the significant decrease in the number concentration of larger particles. A new set of parameterizations for INP activity based on size-resolved nucleation properties of Asian mineral dust particles were developed over an extended temperature range (−35 to −6 ∘C). These size-dependent parameterizations require only particle size distribution as input and can be easily applied in models.

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Guo, S., M. Hu, Z. B. Wang, J. Slanina et Y. L. Zhao. « Size-resolved aerosol water-soluble ionic compositions in the summer of Beijing : implication of regional secondary formation ». Atmospheric Chemistry and Physics Discussions 9, n^o 6 (11 novembre 2009) : 23955–86. http://dx.doi.org/10.5194/acpd-9-23955-2009.

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Abstract. To characterize aerosol pollution in Beijing, size-resolved aerosols were collected by MOUDIs during CAREBEIJING-2006 field campaign at Peking University (urban site) and Yufa (upwind rural site). Fine particle concentrations (PM1.8 by MOUDI) were 99.8±77.4 μg/m3 and 78.2±58.4 μg/m3, with PM1.8/PM10 ratios of 0.64±0.08 and 0.76±0.08 at PKU and Yufa, respectively, and secondary compounds accounted for more than 50% in fine particles. PMF model was used to resolve the particle modes. Three modes were resolved at Yufa, representing condensation, droplet and coarse mode. However, one more droplet mode with bigger size was resolved, which was considered probably from regional transport. Condensation mode accounted for 10%–60% of the total mass at both sites, indicating it must be taken into account in summer. The formation of sulfate was mainly attributed to in-cloud or aerosol droplet process (PKU 80%, Yufa 70%) and gas condensation process (PKU 14%, Yufa 22%). According to the thermodynamic instability of NH4NO3, size distributions of nitrate were classified as three categories by RH. The existence of Ca(NO3)2 in droplet mode indicated the reaction of HNO3 with crustal particles was also important in fine particles. Linear regression gave a rough estimation that 69% of the PM10 and 87% of the PM1.8 at PKU were regional contributions. Sulfate, ammonium and oxalate were formed regionally, with the regional contributions of 90%, 87% and 95% to PM1.8. Nitrate formation was local dominant. In summary regional secondary formation led to aerosol pollution in the summer of Beijing.

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Rademacher, Markus, Jonathan Gosling, Antonio Pontin, Marko Toroš, Jence T. Mulder, Arjan J. Houtepen et P. F. Barker. « Measurement of single nanoparticle anisotropy by laser induced optical alignment and Rayleigh scattering for determining particle morphology ». Applied Physics Letters 121, n^o 22 (28 novembre 2022) : 221102. http://dx.doi.org/10.1063/5.0128606.

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We demonstrate the measurement of nanoparticle anisotropy by angularly resolved Rayleigh scattering of single optical levitated particles that are oriented in space via the trapping light in vacuum. This technique is applied to a range of particle geometries from perfect spherical nanodroplets to octahedral nanocrystals. We show that this method can resolve shape differences down to a few nanometers and be applied in both low-damping environments, as demonstrated here, and in traditional overdamped fluids used in optical tweezers.

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Wu, Z. J., J. Zheng, D. J. Shang, Z. F. Du, Y. S. Wu, L. M. Zeng, A. Wiedensohler et M. Hu. « Particle hygroscopicity and its link to chemical composition in the urban atmosphere of Beijing, China during summertime ». Atmospheric Chemistry and Physics Discussions 15, n^o 8 (20 avril 2015) : 11495–524. http://dx.doi.org/10.5194/acpd-15-11495-2015.

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Abstract. Simultaneous measurements of particle number size distribution, particle hygroscopic properties, and size-resolved chemical composition were made during the summer of 2014 in Beijing, China. During the measurement period, the median hygroscopicity parameters (κ) of 50, 100, 150, 200, and 250 nm particles are respectively 0.15, 0.19, 0.22, 0.27, and 0.29, showing an increasing trend with increasing particle size. When PM2.5 mass concentration is greater than 50 μg m−3, the fractions of the hydrophilic mode for 150, 250, 350 nm particles increased towards 1 as PM2.5 mass concentration increased. This indicates that aged particles dominated during severe pollution periods in the atmosphere of Beijing. Particle hygroscopic growth can be well predicted using high time-resolution size-resolved chemical composition derived from AMS measurement on a basis of ZSR mixing rule. An empirical relationship between κ of organic fraction (κorg) and oxygen to carbon ratio (O : C) (κorg= 0.08·O : C+0.02) is obtained. During new particle formation event associating with strongly active photochemistry, the hygroscopic growth factor or κ of newly formed particles is greater than for particle with the same sizes during non-NPF periods. A quick transformation from external mixture to internal mixture for pre-existing particles (for example 250 nm particle) was observed. Such transformations can modify the state of mixture of pre-exiting particles and thus modify properties such as the light absorption coefficient and cloud condensation nuclei activation.

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Willis, M. D., R. M. Healy, N. Riemer, M. West, J. M. Wang, C. H. Jeong, J. C. Wenger, G. J. Evans, J. P. D. Abbatt et A. K. Y. Lee. « Quantification of black carbon mixing state from traffic : implications for aerosol optical properties ». Atmospheric Chemistry and Physics Discussions 15, n^o 22 (27 novembre 2015) : 33555–82. http://dx.doi.org/10.5194/acpd-15-33555-2015.

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Abstract. The climatic impacts of black carbon (BC) aerosol, an important absorber of solar radiation in the atmosphere, remain poorly constrained and are intimately related to its particle-scale physical and chemical properties. Using particle-resolved modelling informed by quantitative measurements from a soot-particle aerosol mass spectrometer, we confirm that the mixing state (the distribution of co-emitted aerosol amongst fresh BC-containing particles) at the time of emission significantly affects BC-aerosol optical properties even after a day of atmospheric processing. Both single particle and ensemble aerosol mass spectrometry observations indicate that BC near the point of emission co-exists with hydrocarbon-like organic aerosol in two distinct particle types: HOA-rich and BC-rich particles. The average mass fraction of black carbon in HOA-rich and BC-rich particles was 0.02–0.08 and 0.72–0.93, respectively. Notably, approximately 90 % of BC mass resides in BC-rich particles. This new measurement capability provides quantitative insight into the physical and chemical nature of BC-containing particles and is used to drive a particle-resolved aerosol box model. Significant differences in calculated single scattering albedo (an increase of 0.1) arise from accurate treatment of initial particle mixing state as compared to the assumption of uniform aerosol composition at the point of BC injection into the atmosphere.

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Frank, G. P., U. Dusek et M. O. Andreae. « Technical note : A method for measuring size-resolved CCN in the atmosphere ». Atmospheric Chemistry and Physics Discussions 6, n^o 3 (19 juin 2006) : 4879–95. http://dx.doi.org/10.5194/acpd-6-4879-2006.

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Abstract. We present a method to investigate cloud condensation nuclei (CCN) concentrations and activation efficiencies as a function of two independent variables, aerosol particle size and water vapor supersaturation. To date, most ambient CCN measurements have been made as the integral (total) CCN concentration as a function of water vapor supersaturation only. However, since CCN properties of aerosol particles are strongly dependent on particle size, as well as on chemical composition, which commonly varies with particle size, more detailed measurements can provide additional important information about the CCN activation. With size-resolved measurements, the effect of particle size on CCN activity can be kept constant, which makes it possible to directly assess the influence of particle chemistry. The instrumental set-up consists of a differential mobility analyzer (DMA) to select particles of a known size, within a narrow size range. A condensation nuclei (CN) counter (condensation particle counter, CPC) is used to count the total number of particles in that size range, and a CCN counter is used to count the number of CCN as a function of supersaturation, in that same size range. The activation efficiency, expressed as CCN/CN ratios, can thus directly be calculated as a function of particle size and supersaturation. We present examples of the application of this technique, using salt and smoke aerosols produced in the laboratory as well as ambient aerosols.

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Zhang, F., Y. Li, Z. Li, L. Sun, R. Li, C. Zhao, P. Wang et al. « Aerosol hygroscopicity and cloud condensation nuclei activity during the AC<sup>3</sup>Exp campaign : implications for cloud condensation nuclei parameterization ». Atmospheric Chemistry and Physics 14, n^o 24 (16 décembre 2014) : 13423–37. http://dx.doi.org/10.5194/acp-14-13423-2014.

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Abstract. Aerosol hygroscopicity and cloud condensation nuclei (CCN) activity under background conditions and during pollution events are investigated during the Aerosol-CCN-Cloud Closure Experiment (AC3Exp) campaign conducted at Xianghe, China in summer 2013. A gradual increase in size-resolved activation ratio (AR) with particle diameter (Dp) suggests that aerosol particles have different hygroscopicities. During pollution events, the activation diameter (Da) measured at low supersaturation (SS) was significantly increased compared to background conditions. An increase was not observed when SS was > 0.4%. The hygroscopicity parameter (κ) was ~ 0.31–0.38 for particles in accumulation mode under background conditions. This range in magnitude of κ was ~ 20%, higher than κ derived under polluted conditions. For particles in nucleation or Aitken mode, κ ranged from 0.20–0.34 for background and polluted cases. Larger particles were on average more hygroscopic than smaller particles. The situation was more complex for heavy pollution particles because of the diversity in particle composition and mixing state. A non-parallel observation CCN closure test showed that uncertainties in CCN number concentration estimates ranged from 30–40%, which are associated with changes in particle composition as well as measurement uncertainties associated with bulk and size-resolved CCN methods. A case study showed that bulk CCN activation ratios increased as total condensation nuclei (CN) number concentrations (NCN) increased on background days. The background case also showed that bulk AR correlated well with the hygroscopicity parameter calculated from chemical volume fractions. On the contrary, bulk AR decreased with increasing total NCN during pollution events, but was closely related to the fraction of the total organic mass signal at m/z 44 (f44), which is usually associated with the particle's organic oxidation level. Our study highlights the importance of chemical composition in determining particle activation properties and underlines the significance of long-term observations of CCN under different atmospheric environments, especially regions with heavy pollution.

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Zhang, G., X. Bi, L. Li, L. Y. Chan, M. Li, X. Wang, G. Sheng, J. Fu et Z. Zhou. « Mixing state of individual submicron carbon-containing particles and their seasonal variation in urban Guangzhou, China ». Atmospheric Chemistry and Physics Discussions 12, n^o 12 (19 décembre 2012) : 32707–39. http://dx.doi.org/10.5194/acpd-12-32707-2012.

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Abstract. Growing evidence suggests that size-resolved mixing state of carbon-containing particles is very critical in determining their optical properties, atmospheric lifetime, and impact on the environment. However, still little is known about the mixing state of particles in urban area of Pearl River Delta (PRD) region, China. To investigate the mixing state of submicron carbon-containing particles, measurements were carried out during spring and fall periods of 2010 using a single particle aerosol mass spectrometer (SPAMS). Approximate 700 000 particles for each period were detected. This is the first report on the size-resolved mixing state of carbon-containing particles by direct observations in PRD region. Cluster analysis of single particle mass spectra was applied to identify carbon-containing particle classes. These classes represented ~80% and ~90% of all the detected particles for spring and fall periods, respectively. Carbon-containing particle classes mainly consisted of biomass/biofuel burning particles (Biomass), organic carbon (OC), fresh elemental carbon (EC-fresh), internally mixed OC and EC (ECOC), internally mixed EC with sulfate (EC-Sulfate), vanadium-containing ECOC (V-ECOC), and amines-containing particles (Amine). In spring, the top three ranked carbon-containing particle classes were ECOC (26.1%), Biomass (23.6%) and OC (10%), respectively. However, the fraction of Biomass particles increased remarkably and predominated (61.0%), while the fraction of ECOC (3.0%) and V-ECOC (0.1%) significantly decreased in fall. To highlight the influence of monsoon on the properties of carbon-containing particles in urban Guangzhou, their size distribution, mixing state, and aerosol acidity were compared between spring and fall seasons. In addition, a case study was also performed to investigate how the formation of fog and haze influenced the mixing state of carbon-containing particles. These results are of importance in understanding atmospheric chemistry and modeling direct and indirect forcing of carbon-containing particles.

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Peng, Long, Lei Li, Guohua Zhang, Xubing Du, Xinming Wang, Ping'an Peng, Guoying Sheng et Xinhui Bi. « Technical note : Measurement of chemically resolved volume equivalent diameter and effective density of particles by AAC-SPAMS ». Atmospheric Chemistry and Physics 21, n^o 7 (12 avril 2021) : 5605–13. http://dx.doi.org/10.5194/acp-21-5605-2021.

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Abstract. Size and effective density (ρe) are important properties of aerosol particles and are related to their influences on human health and the global climate. The volume equivalent diameter (Dve) is an intrinsic property that is used to evaluate particle size. Three definitions of ρe are generally used to characterize the physical property of a particle as an alternative to particle density, in which only the ρeII, defined as the ratio of particle density (ρp) to a dynamic shape factor (χ), has the characteristic of being independent of particle size. However, it is still challenging to simultaneously characterize the Dve and ρeII of aspherical particles. Here, we present a novel system that classifies particles with their aerodynamic diameter (Da) by aerodynamic aerosol classifier (AAC) and determines their vacuum aerodynamic diameter (Dva) by single-particle aerosol mass spectrometry (SPAMS) to achieve a measurement of Dve and ρeII. The reliability of the AAC-SPAMS system for accurately obtaining Dve and ρeII is verified based on the result that the deviation between the measured and theoretical values is less than 6 % for the size-resolved spherical polystyrene latex (PSL). The AAC-SPAMS system was applied to characterize the Dve and ρeII of (NH4)2SO4 and NaNO3 particles, suggesting that these particles are aspherical and their ρeII is independent of particle size. Finally, the AAC-SPAMS system was deployed in a field measurement, showing that it is a powerful technique to characterize the chemically resolved Dve and ρeII of particles in real time.

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Healy, R. M., J. Sciare, L. Poulain, K. Kamili, M. Merkel, T. Müller, A. Wiedensohler et al. « Sources and mixing state of size-resolved elemental carbon particles in a European megacity : Paris ». Atmospheric Chemistry and Physics Discussions 11, n^o 11 (9 novembre 2011) : 30333–80. http://dx.doi.org/10.5194/acpd-11-30333-2011.

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Abstract. An Aerosol Time-Of-Flight Mass Spectrometer (ATOFMS) was deployed to investigate the size-resolved chemical composition of single particles at an urban background site in Paris, France, as part of the MEGAPOLI winter campaign in January/February 2010. ATOFMS particle counts were scaled to match coincident Twin Differential Mobility Particle Sizer (TDMPS) data in order to generate hourly size-resolved mass concentrations for the single particle classes observed. The total scaled ATOFMS particle mass concentration in the size range 150–1067 nm was found to agree very well with the sum of concurrent High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and Multi-Angle Absorption Photometer (MAAP) mass concentration measurements of organic carbon (OC), inorganic ions and black carbon (BC) (R2 = 0.91). Clustering analysis of the ATOFMS single particle mass spectra allowed the separation of elemental carbon (EC) particles into four classes: (i) EC attributed to biomass burning (ECbiomass), (ii) EC attributed to traffic (ECtraffic), (iii) EC internally mixed with OC and ammonium sulfate (ECOCSOx), and (iv) EC internally mixed with OC and ammonium nitrate (ECOCNOx). Average hourly mass concentrations for EC-containing particles detected by the ATOFMS were found to agree reasonably well with semi-continuous quantitative thermal/optical EC and optical BC measurements (r2 = 0.61 and 0.65–0.68, respectively, n = 552). The EC particle mass assigned to fossil fuel and biomass burning sources also agreed reasonably well with BC mass fractions assigned to the same sources using seven-wavelength aethalometer data (r2 = 0.60 and 0.48, respectively, n = 568). Agreement between the ATOFMS and other instrumentation improved noticeably when a period influenced by significantly aged, internally mixed EC particles was removed from the intercomparison. 88 % and 12 % of EC particle mass was apportioned to fossil fuel and biomass burning respectively using the ATOFMS data compared with 85 % and 15 % respectively for BC estimated from the aethalometer model. On average, the mass size distribution for EC particles is bimodal; the smaller mode is attributed to locally emitted, mostly externally mixed EC particles, while the larger mode is dominated by aged, internally mixed ECOCNOx particles associated with continental transport events. Periods of continental influence were identified using the Lagrangian Particle Dispersion Model (LPDM) "FLEXPART". A consistent minimum between the two EC mass size modes was observed at approximately 400 nm for the measurement period. EC particles below this size are attributed to local emissions using chemical mixing state information and contribute 79 % of the scaled ATOFMS EC particle mass, while particles above this size are attributed to continental transport events and contribute 21 % of the EC particle mass. These results clearly demonstrate the potential benefit of monitoring size-resolved mass concentrations for the separation of local and continental EC emissions. Knowledge of the relative input of these emissions is essential for assessing the effectiveness of local abatement strategies.

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Healy, R. M., J. Sciare, L. Poulain, K. Kamili, M. Merkel, T. Müller, A. Wiedensohler et al. « Sources and mixing state of size-resolved elemental carbon particles in a European megacity : Paris ». Atmospheric Chemistry and Physics 12, n^o 4 (15 février 2012) : 1681–700. http://dx.doi.org/10.5194/acp-12-1681-2012.

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Abstract. An Aerosol Time-Of-Flight Mass Spectrometer (ATOFMS) was deployed to investigate the size-resolved chemical composition of single particles at an urban background site in Paris, France, as part of the MEGAPOLI winter campaign in January/February 2010. ATOFMS particle counts were scaled to match coincident Twin Differential Mobility Particle Sizer (TDMPS) data in order to generate hourly size-resolved mass concentrations for the single particle classes observed. The total scaled ATOFMS particle mass concentration in the size range 150–1067 nm was found to agree very well with the sum of concurrent High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and Multi-Angle Absorption Photometer (MAAP) mass concentration measurements of organic carbon (OC), inorganic ions and black carbon (BC) (R2 = 0.91). Clustering analysis of the ATOFMS single particle mass spectra allowed the separation of elemental carbon (EC) particles into four classes: (i) EC attributed to biomass burning (ECbiomass), (ii) EC attributed to traffic (ECtraffic), (iii) EC internally mixed with OC and ammonium sulfate (ECOCSOx), and (iv) EC internally mixed with OC and ammonium nitrate (ECOCNOx). Average hourly mass concentrations for EC-containing particles detected by the ATOFMS were found to agree reasonably well with semi-continuous quantitative thermal/optical EC and optical BC measurements (r2 = 0.61 and 0.65–0.68 respectively, n = 552). The EC particle mass assigned to fossil fuel and biomass burning sources also agreed reasonably well with BC mass fractions assigned to the same sources using seven-wavelength aethalometer data (r2 = 0.60 and 0.48, respectively, n = 568). Agreement between the ATOFMS and other instrumentation improved noticeably when a period influenced by significantly aged, internally mixed EC particles was removed from the intercomparison. 88% and 12% of EC particle mass was apportioned to fossil fuel and biomass burning respectively using the ATOFMS data compared with 85% and 15% respectively for BC estimated from the aethalometer model. On average, the mass size distribution for EC particles is bimodal; the smaller mode is attributed to locally emitted, mostly externally mixed EC particles, while the larger mode is dominated by aged, internally mixed ECOCNOx particles associated with continental transport events. Periods of continental influence were identified using the Lagrangian Particle Dispersion Model (LPDM) "FLEXPART". A consistent minimum between the two EC mass size modes was observed at approximately 400 nm for the measurement period. EC particles below this size are attributed to local emissions using chemical mixing state information and contribute 79% of the scaled ATOFMS EC particle mass, while particles above this size are attributed to continental transport events and contribute 21% of the EC particle mass. These results clearly demonstrate the potential benefit of monitoring size-resolved mass concentrations for the separation of local and continental EC emissions. Knowledge of the relative input of these emissions is essential for assessing the effectiveness of local abatement strategies.

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Deventer, Malte Julian, Frank Griessbaum et Otto Klemm. « Size-resolved flux measurement of sub-micrometer particles over an urban area ». Meteorologische Zeitschrift 22, n^o 6 (1 décembre 2013) : 729–37. http://dx.doi.org/10.1127/0941-2948/2013/0441.

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Wang, X., L. Zhang et M. D. Moran. « On the discrepancies between theoretical and measured below-cloud particle scavenging coefficients for rain – a numerical investigation using a detailed one-dimensional cloud microphysics model ». Atmospheric Chemistry and Physics 11, n^o 22 (29 novembre 2011) : 11859–66. http://dx.doi.org/10.5194/acp-11-11859-2011.

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Abstract. Existing theoretical formulations for the size-resolved scavenging coefficient Λ(d) for atmospheric aerosol particles scavenged by rain predict values lower by one to two orders of magnitude than those estimated from field measurements of particle-concentration changes for particles smaller than 3 μm in diameter. Vertical turbulence is not accounted for in the theoretical formulations of Λ(d) but does contribute to the field-derived estimates of Λ(d) due to its influence on the overall concentration changes of aerosol particles in the layers undergoing impaction scavenging. A detailed one-dimensional cloud microphysics model has been used to simulate rain production and below-cloud particle scavenging, and to quantify the contribution of turbulent diffusion to the overall Λ(d) values calculated from particle concentration changes. The relative contribution of vertical diffusion to below-cloud scavenging is found to be largest for submicron particles under weak precipitation conditions. The discrepancies between theoretical and field-derived Λ(d) values can largely be explained by the contribution of vertical diffusion to below-cloud particle scavenging for all particles larger than 0.01 μm in diameter for which field data are available. The results presented here suggest that the current theoretical framework for Λ(d) can provide a reasonable approximation of below-cloud aerosol particle scavenging by rain in size-resolved aerosol transport models if vertical diffusion is also considered by the models.

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Wu, Z. J., J. Zheng, D. J. Shang, Z. F. Du, Y. S. Wu, L. M. Zeng, A. Wiedensohler et M. Hu. « Particle hygroscopicity and its link to chemical composition in the urban atmosphere of Beijing, China, during summertime ». Atmospheric Chemistry and Physics 16, n^o 2 (1 février 2016) : 1123–38. http://dx.doi.org/10.5194/acp-16-1123-2016.

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Abstract. Simultaneous measurements of particle number size distribution, particle hygroscopic properties, and size-resolved chemical composition were made during the summer of 2014 in Beijing, China. During the measurement period, the mean hygroscopicity parameters (κs) of 50, 100, 150, 200, and 250 nm particles were respectively 0.16 &pm; 0.07, 0.19 &pm; 0.06, 0.22 &pm; 0.06, 0.26 &pm; 0.07, and 0.28 &pm; 0.10, showing an increasing trend with increasing particle size. Such size dependency of particle hygroscopicity was similar to that of the inorganic mass fraction in PM1. The hydrophilic mode (hygroscopic growth factor, HGF > 1.2) was more prominent in growth factor probability density distributions and its dominance of hydrophilic mode became more pronounced with increasing particle size. When PM2.5 mass concentration was greater than 50 μg m−3, the fractions of the hydrophilic mode for 150, 250, and 350 nm particles increased towards 1 as PM2.5 mass concentration increased. This indicates that aged particles dominated during severe pollution periods in the atmosphere of Beijing. Particle hygroscopic growth can be well predicted using high-time-resolution size-resolved chemical composition derived from aerosol mass spectrometer (AMS) measurements using the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. The organic hygroscopicity parameter (κorg) showed a positive correlation with the oxygen to carbon ratio. During the new particle formation event associated with strongly active photochemistry, the hygroscopic growth factor or κ of newly formed particles is greater than for particles with the same sizes not during new particle formation (NPF) periods. A quick transformation from external mixture to internal mixture for pre-existing particles (for example, 250 nm particles) was observed. Such transformations may modify the state of the mixture of pre-existing particles and thus modify properties such as the light absorption coefficient and cloud condensation nuclei activation.

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Zhang Xiao-Jie, Zhao Qian-Qian et Huang Rong-Zong. « Investigation of the drafting-kissing-tumbling movement of two particles with conjugate heat transfer ». Acta Physica Sinica 74, n^o 4 (2025) : 0. https://doi.org/10.7498/aps.74.20241453.

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The conjugate heat transfer at the particle-fluid interface and the collision between particles play a crucial role in the sedimentation process of particles. In this work, the recent volumetric lattice Boltzmann method for thermal particulate flows with conjugate heat transfer is adopted to investigate the drafting-kissing-tumbling movement in the sedimentation process of two particles in a closed channel. This volumetric lattice Boltzmann method is based on double distribution functions, with the density distribution function for the velocity field and the internal energy distribution function for the temperature field. It is a single-domain approach, and the nonslip velocity condition within the solid domain can be strictly ensured. The difference in thermophysical properties between the solid and fluid can be correctly handled, and the conjugate heat transfer condition can be automatically achieved without any additional treatments. Based on this particle-resolved simulation, the influences of the solid-to-fluid specific heat ratio, the Grashof number, and the particle’s initial temperature on the drafting-kissing-tumbling movement are discussed in detail. It is found that the fluid cooled by the particle and thus subjected to the downward buoyancy force can promote particle sedimentation. As the specific heat ratio increases, the particle’s temperature rises relatively slowly. In the sedimentation of two cold particles, the drafting and tumbling durations of the drafting-kissing-tumbling movement decrease when the heat capacity ratio increases. In contrast, the kissing duration increases as the heat capacity ratio increases. When the Grashof number increases, the heat transfer between the particle and fluid is enhanced, and the drafting duration significantly decreases while the kissing and tumbling durations remain almost unchanged in the sedimentation of two cold particles. The particle’s initial temperature significantly influences the occurrence moment of the drafting-kissing-tumbling movement. To be specific, the drafting-kissing-tumbling movement occurs at the earliest moment for the sedimentation of two cold particles, followed by the sedimentation of one cold and one hot particle, and the latest for the sedimentation of two hot particles. The promoting effect of the low particle’s initial temperature on the drafting-kissing-tumbling movement mainly takes place in the dragging and kissing stages. The particle’s initial temperature has almost no influence on the tumbling duration.

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Willis, Megan D., Robert M. Healy, Nicole Riemer, Matthew West, Jon M. Wang, Cheol-Heon Jeong, John C. Wenger, Greg J. Evans, Jonathan P. D. Abbatt et Alex K. Y. Lee. « Quantification of black carbon mixing state from traffic : implications for aerosol optical properties ». Atmospheric Chemistry and Physics 16, n^o 7 (14 avril 2016) : 4693–706. http://dx.doi.org/10.5194/acp-16-4693-2016.

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Abstract. The climatic impacts of black carbon (BC) aerosol, an important absorber of solar radiation in the atmosphere, remain poorly constrained and are intimately related to its particle-scale physical and chemical properties. Using particle-resolved modelling informed by quantitative measurements from a soot-particle aerosol mass spectrometer, we confirm that the mixing state (the distribution of co-emitted aerosol amongst fresh BC-containing particles) at the time of emission significantly affects BC-aerosol optical properties even after a day of atmospheric processing. Both single particle and ensemble aerosol mass spectrometry observations indicate that BC near the point of emission co-exists with hydrocarbon-like organic aerosol (HOA) in two distinct particle types: HOA-rich and BC-rich particles. The average mass fraction of black carbon in HOA-rich and BC-rich particle classes was < 0.1 and 0.8, respectively. Notably, approximately 90 % of BC mass resides in BC-rich particles. This new measurement capability provides quantitative insight into the physical and chemical nature of BC-containing particles and is used to drive a particle-resolved aerosol box model. Significant differences in calculated single scattering albedo (an increase of 0.1) arise from accurate treatment of initial particle mixing state as compared to the assumption of uniform aerosol composition at the point of BC injection into the atmosphere.

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Puderbach, Vanessa, Kilian Schmidt et Sergiy Antonyuk. « A Coupled CFD-DEM Model for Resolved Simulation of Filter Cake Formation during Solid-Liquid Separation ». Processes 9, n^o 5 (9 mai 2021) : 826. http://dx.doi.org/10.3390/pr9050826.

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In cake filtration processes, where particles in a suspension are separated by forming a filter cake on the filter medium, the resistances of filter cake and filter medium cause a specific pressure drop which consequently defines the process energy effort. The micromechanics of the filter cake formation (interactions between particles, fluid, other particles and filter medium) must be considered to describe pore clogging, filter cake growth and consolidation correctly. A precise 3D modeling approach to describe these effects is the resolved coupling of the Computational Fluid Dynamics with the Discrete Element Method (CFD-DEM). This work focuses on the development and validation of a CFD-DEM model, which is capable to predict the filter cake formation during solid-liquid separation accurately. The model uses the Lattice-Boltzmann Method (LBM) to directly solve the flow equations in the CFD part of the coupling and the DEM for the calculation of particle interactions. The developed model enables the 4-way coupling to consider particle-fluid and particle-particle interactions. The results of this work are presented in two steps. First, the developed model is validated with an empirical model of the single particle settling velocity in the transition regime of the fluid-particle flow. The model is also enhanced with additional particles to determine the particle-particle influence. Second, the separation of silica glass particles from water in a pressurized housing at constant pressure is experimentally investigated. The measured filter cake, filter medium and interference resistances are in a good agreement with the results of the 3D simulations, demonstrating the applicability of the resolved CFD-DEM coupling for analyzing and optimizing cake filtration processes.

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Wang, X., L. Zhang et M. D. Moran. « On the discrepancies between theoretical and measured below-cloud particle scavenging coefficients for rain – a numerical study ». Atmospheric Chemistry and Physics Discussions 11, n^o 7 (18 juillet 2011) : 20375–87. http://dx.doi.org/10.5194/acpd-11-20375-2011.

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Abstract. Existing theoretical formulations for size-resolved scavenging coefficient Λ (r) for atmospheric aerosol particles scavenged by rain predict values lower by one to two orders of magnitude than those estimated from field measurements of particle-concentration changes for particles smaller than 3 μm in diameter. Vertical turbulence does not influence the theoretical formulation of Λ (r), but contributed to the field-generated Λ (r) due to its influence on the overall concentration changes of aerosol particles in the layers undergoing impaction scavenging. A detailed one-dimensional cloud microphysics model is used to simulate rain production and below-cloud particle scavenging, and to quantify the contribution of turbulent diffusion to the overall Λ (r) generated from concentration changes. The relative contribution of vertical diffusion to below-cloud scavenging is found to be largest for submicron particles under weak precipitation conditions. The discrepancies between theoretical and field Λ (r) values can largely be explained by the contribution of vertical diffusion for all particles larger than 0.01 μm in diameter for which field data were available. The results presented here suggest that the current theoretical framework for Λ (r) can provide a reasonable approximation of below-cloud aerosol particle scavenging by rain in size-resolved aerosol transport models if vertical diffusion is also considered.

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Tegze, György, Frigyes Podmaniczky, Ellák Somfai, Tamás Börzsönyi et László Gránásy. « Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime ». Soft Matter 16, n^o 38 (2020) : 8925–32. http://dx.doi.org/10.1039/d0sm00370k.

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Shao, Xueming, Tenghu Wu et Zhaosheng Yu. « Fully resolved numerical simulation of particle-laden turbulent flow in a horizontal channel at a low Reynolds number ». Journal of Fluid Mechanics 693 (17 janvier 2012) : 319–44. http://dx.doi.org/10.1017/jfm.2011.533.

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AbstractA fictitious domain method is used to perform fully resolved numerical simulations of particle-laden turbulent flow in a horizontal channel. The effects of large particles of diameter 0.05 and 0.1 times the channel height on the turbulence statistics and structures are investigated for different settling coefficients and volume fractions (0.79 %–7.08 %) for the channel Reynolds number being 5000. The results indicate the following. (a) When the particle sedimentation effect is negligible (i.e. neutrally buoyant), the presence of particles decreases the maximum r.m.s. of streamwise velocity fluctuation near the wall by weakening the intensity of the large-scale streamwise vortices, while increasing the r.m.s. of the streamwise fluctuating velocity in the region very close to the wall and in the centre region. On the other hand, the particles increase the r.m.s. of transverse and spanwise fluctuating velocities in the near-wall region by inducing the small-scale vortices. (b) When the particle settling effect is so substantial that most particles settle onto the bottom wall and form a particle sediment layer (SL), the SL plays the role of a rough wall and parts of the vortex structures shedding from the SL ascend into the core region and substantially increase the turbulence intensity there. (c) When the particle settling effect is moderate, the effects of particles on the turbulence are a combination of the former two situations, and the Shields number is a good parameter for measuring the particle settling effects (i.e. the particle concentration distribution in the transverse direction). The average velocities of the particle are smaller in the lower half-channel and larger in the upper half-channel compared to the local fluid velocities in the presence of gravity effects. The effects of the smaller particles on the turbulence are found to be stronger at the same particle volume fractions.

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Hong, J., S. A. K. Häkkinen, M. Paramonov, M. Äijälä, J. Hakala, T. Nieminen, J. Mikkilä et al. « Hygroscopicity, CCN and volatility properties of submicron atmospheric aerosol in a boreal forest environment during the summer of 2010 ». Atmospheric Chemistry and Physics 14, n^o 9 (13 mai 2014) : 4733–48. http://dx.doi.org/10.5194/acp-14-4733-2014.

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Abstract. A Volatility-Hygroscopicity Tandem Differential Mobility Analyzer (VH-TDMA) was applied to study the hygroscopicity and volatility properties of submicron atmospheric aerosol particles in a boreal forest environment in Hyytiälä, Finland during the summer of 2010. Aitken and accumulation mode internally mixed particles (50 nm, 75 nm and 110 nm in diameter) were investigated. Hygroscopicity was found to increase with particle size. The relative mass fraction of organics and SO42- is probably the major contributor to the fluctuation of the hygroscopicity for all particle sizes. The Cloud Condensation Nuclei Counter (CCNC)-derived hygroscopicity parameter κ was observed to be slightly higher than κ calculated from VH-TDMA data under sub-saturated conditions, potential reasons for this behavior are discussed shortly. Also, the size-resolved volatility properties of particles were investigated. Upon heating, more small particles evaporated compared to large particles. There was a significant amount of aerosol volume (non-volatile material) left, even at heating temperatures of 280 °C. Using size resolved volatility-hygroscopicity analysis, we concluded that there was always hygroscopic material remaining in the particles at different heating temperatures, even at 280 °C. This indicates that the observed non-volatile aerosol material did not consist solely of black carbon.

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Waza, Andebo, Kilian Schneiders, Johannes Heuser et Konrad Kandler. « Analysis of Size Distribution, Chemical Composition, and Optical Properties of Mineral Dust Particles from Dry Deposition Measurement in Tenerife : Determined by Single-Particle Characterization ». Atmosphere 14, n^o 4 (10 avril 2023) : 700. http://dx.doi.org/10.3390/atmos14040700.

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In this paper, individual particle analysis by automated scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) was used to assess the size-resolved information of composition, size distribution, complex refractive index, and mixing state of mineral dust aerosol particles collected using different passive and active samplers. In the study, over 120,000 particles from 53 samples were analyzed. Results show that dust particles are the dominating mineral particle type during this campaign, comprising different classes of silicates, Si-rich (quartz-like), Ca-rich (calcite-like), CaMg-rich (dolomite-like), and CaS-rich (gypsum-like). The results also show that there is no significant difference in composition between suspended and deposited dust particles. By using the particle composition, the size-resolved complex refractive index of dust particles was calculated. The real part of the refractive index varied between 1.71 and 1.53 for wavelengths in the range of 370 to 950 nm. The imaginary part of the refractive index, determined mostly by iron oxide, varied between 3.28×10−4 and 7.11×10−5 for wavelengths ranging from 250 nm to 1640 nm. In addition, the refractive index values showed a slight decrease with increasing particle size. We also analyzed the potential for buffering of the acid mobilization of iron by other dust compounds. For particles which contain both iron (Fe) and (unprocessed) calcium (Ca), acids that are able to dissolve insoluble Fe particles can react with the Ca particles before reacting with Fe, but eventually, with longer processing time, the Fe particles could be processed. By analyzing the ratio of sulfate mass to the total aerosol mass of individual particles, the mixing state of sulfate particles to the total dust particles was investigated. The analysis showed that the finer dust particles were associated with higher content of sulfate, while the coarse dust particles correspond to lower sulfate contents, revealing that only fine mode sulfate is more internally mixed with mineral dust aerosol particles.

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Guo, Xiaoman, Sina Alavi, Elham Dalir, Jingmin Dai et Javad Mostaghimi. « Time-resolved particle image velocimetry and 3D simulations of single particles in the new conical ICP torch ». Journal of Analytical Atomic Spectrometry 34, n^o 3 (2019) : 469–79. http://dx.doi.org/10.1039/c8ja00407b.

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Ghosal, Sutapa, Peter K. Weber et Alexander Laskin. « Spatially resolved chemical imaging of individual atmospheric particles using nanoscale imaging mass spectrometry : insight into particle origin and chemistry ». Anal. Methods 6, n^o 8 (2014) : 2444–51. http://dx.doi.org/10.1039/c3ay42012d.

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Knowledge of the spatially resolved composition of atmospheric particles is essential for differentiating between their surface versus bulk chemistry and understanding particle reactivity and the potential environmental impact.

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Zhang, G., X. Bi, L. Li, L. Y. Chan, M. Li, X. Wang, G. Sheng, J. Fu et Z. Zhou. « Mixing state of individual submicron carbon-containing particles during spring and fall seasons in urban Guangzhou, China : a case study ». Atmospheric Chemistry and Physics 13, n^o 9 (7 mai 2013) : 4723–35. http://dx.doi.org/10.5194/acp-13-4723-2013.

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Abstract. Growing evidence suggests that the size-resolved mixing state of carbon-containing particles is very critical in determining their optical properties, atmospheric lifetime, and impact on the environment. However, still little is known about the mixing state of particles in the urban area of the Pearl River Delta (PRD) region, China. To investigate the mixing state of submicron carbon-containing particles, measurements were carried out during spring and fall periods of 2010 using a single-particle aerosol mass spectrometer (SPAMS). Approximately 700 000 particles for each period were detected. This is the first report on the size-resolved mixing state of carbon-containing particles by direct observations in the PRD region. Cluster analysis of single-particle mass spectra was applied to identify carbon-containing particle classes. These classes represented ~80% and ~90% of all the detected particles for spring and fall periods, respectively. Carbon-containing particle classes mainly consisted of biomass/biofuel burning particles (Biomass), organic carbon (OC), fresh elemental carbon (EC-fresh), internally mixed OC and EC (ECOC), internally mixed EC with sulfate (EC-Sulfate), vanadium-containing ECOC (V-ECOC), and amines-containing particles (Amine). In spring, the top three ranked carbon-containing particle classes were ECOC (26.1%), Biomass (23.6%) and OC (10%), respectively. However, the fraction of Biomass particles increased remarkably and predominated (61.0%), while the fraction of ECOC (3.0%) and V-ECOC (0.1%) significantly decreased in fall. To highlight the influence of monsoon on the properties of carbon-containing particles in urban Guangzhou, their size distributions, mixing state, and aerosol acidity were compared between spring and fall seasons. In addition, a case study was also performed to investigate how the formation of fog and haze influenced the mixing state of carbon-containing particles. These results could improve our understanding of the mixing state of carbon-containing particles, and may also be helpful in modeling the climate forcing of aerosol in the PRD region.

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Aria, Arash Imani, Bjørn Holmedal, Tomas Mánik et Knut Marthinsen. « A Full-Field Crystal Plasticity Study on the Bauschinger Effect Caused by Non-Shearable Particles and Voids in Aluminium Single Crystals ». Metals 14, n^o 4 (3 avril 2024) : 424. http://dx.doi.org/10.3390/met14040424.

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In the present work, the goal is to use two-scale simulations to be incorporated into the full-field open software DAMASK crystal plasticity framework, in relation to the Bauschinger effect caused by the composite effect of the presence of second-phase particles with surrounding deformation zones. The idea is to achieve this by including a back stress of the critical resolved shear stress in a single-phase simulation, as an alternative to explicitly resolving the second-phase particles in the system. The back stress model is calibrated to the volume-averaged behaviour of detailed crystal plasticity simulations with the presence of hard, non-shearable spherical particles or voids. A simplified particle-scale model with a periodic box containing only one of the spherical particles in the crystal is considered. Applying periodic boundary conditions corresponds to a uniform regular distribution of particles or voids in the crystal. This serves as an idealised approximation of a particle distribution with the given mean size and particle volume fraction. The Bauschinger effect is investigated by simulating tensile–compression tests with 5% and 10% volume fractions of particles and with 1%, 2%, and 5% pre-strain. It is observed that an increasing volume fraction increases the Bauschinger effect, both for the cases with particles and with voids. However, increasing the pre-strain only increases the Bauschinger effect for the case with particles and not for the case with voids. The model with back stress of the critical resolved shear stress, but without the detailed particle simulation, can be fitted to provide reasonably close results for the volume-averaged response of the detailed simulations.

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Saitoh, Katsumi, Masayuki Shima, Yoshiko Yoda, Ryouhei Nakatsubo, Takatoshi Hiraki, Daisuke Tsunetomo et Koichiro Sera. « Physicochemical characterization and size-resolved source apportionment of airborne particles in Himeji City, Japan ». International Journal of PIXE 24, n^o 01n02 (janvier 2014) : 1–15. http://dx.doi.org/10.1142/s0129083514500016.

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As a part of epidemiological study on the effects of the chemical composition of airborne particulate matter (PM) and ozone on asthma attacks, we carried out size-resolved sampling of PM in Himeji City, Japan and elemental and ionic composition analyses of the PM samples. Size-resolved PM was collected using a 3-stage NLAS impactor (Tokyo Dylec Co., Ltd.; particle cut size at sampling stages was 10, 2.5 and 1.0 [Formula: see text]m for a flow rate of 3 L/min) with a 1-week sampling interval from November 2009 to May 2012. Concentrations of several elemental and ionic species in the PM samples were determined by PIXE and ion chromatography analysis, respectively. In addition, source apportionment analysis of the PM was performed by positive matrix factorization (PMF) model using the analytical data of size-resolved particles. The research results are important for the physicochemical characterization of PM in the atmosphere, enabling evaluation of various PM emission sources and atmospheric processes. Of particular note is that the PM10 consisted mainly of [Formula: see text] and [Formula: see text], and PM2.5 consisted only of [Formula: see text]. This is believed to suggest the different formation processes of [Formula: see text] and [Formula: see text]. Based on the results from the PMF model analysis, the particles larger then PM2.5 were estimated to have been from soil and sea salt particles. On the other hand, the particles smaller than PM2.5 were estimated to have been from soot, smoke and secondary particles. In particular, the majority of particle smaller than PM1.0 were estimated to be secondary sulfate particles.

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Stevens, R. G., et J. R. Pierce. « The contribution of plume-scale nucleation to global and regional aerosol and CCN concentrations : evaluation and sensitivity to emissions changes ». Atmospheric Chemistry and Physics Discussions 14, n^o 15 (21 août 2014) : 21473–521. http://dx.doi.org/10.5194/acpd-14-21473-2014.

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Abstract. We implement the Predicting Particles Produced in Power-Plant Plumes (P6) sub-grid sulphate parameterization for the first time into a global chemical-transport model with online aerosol microphysics, the GEOS-Chem-TOMAS model. Compared to simulations using two other previous treatments of sub-grid sulphate, simulations using P6 sub-grid sulphate predicted similar or smaller increases (depending on other model assumptions) in globally, annually averaged concentrations of particles larger than 80 nm (N80). We test the sensitivity of particle number concentrations in simulations using P6 sub-grid sulphate to changes in SO2 or NOx emissions to represent recent emissions control changes. For global increases in emissions of SO2, NOx, or both SO2 and NOx by 50%, we find increases in globally, annually averaged N80 of 9.00%, 1.47%, or 10.24%, respectively; however, these changes include changes to both sub-grid and grid-resolved processes. Finally, we compare the model results against observations of particle number concentrations. Compared with previous treatments of sub-grid sulphate, use of the P6 parameterization generally improves correlation with observed particle number concentrations. The P6 parameterization is able to resolve spatial heterogeneity in new-particle formation and growth that cannot be resolved by any constant assumptions about sub-grid sulphate. However, the differences in annually averaged aerosol size distributions due to the treatment of sub-grid sulphate at the measurement sites examined here are too small to unambiguously establish P6 as providing better agreement with observations.

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Stevens, R. G., et J. R. Pierce. « The contribution of plume-scale nucleation to global and regional aerosol and CCN concentrations : evaluation and sensitivity to emissions changes ». Atmospheric Chemistry and Physics 14, n^o 24 (20 décembre 2014) : 13661–79. http://dx.doi.org/10.5194/acp-14-13661-2014.

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Abstract. We implement the Predicting Particles Produced in Power-Plant Plumes (P6) sub-grid sulphate parameterization for the first time into a global chemical-transport model with online aerosol microphysics, the GEOS-Chem-TOMAS model. Compared to simulations using two other previous treatments of sub-grid sulphate, simulations using P6 sub-grid sulphate predicted similar or smaller increases (depending on other model assumptions) in globally, annually averaged concentrations of particles larger than 80 nm (N80). We test in simulations using P6 sub-grid sulphate the sensitivity of particle number concentrations to changes in SO2 or NOx emissions to represent recent emissions control changes. For global increases of 50% in emissions of either SO2 or NOx, or both SO2 and NOx, we find that globally, annually averaged N80 increase by 9.00, 1.47, or 10.24% respectively. However, both sub-grid and grid-resolved processes contribute to these changes. Finally, we compare the model results against observations of particle number concentrations. Compared with previous treatments of sub-grid sulphate, use of the P6 parameterization generally improves correlation with observed particle number concentrations. The P6 parameterization is able to resolve spatial heterogeneity in new-particle formation and growth that cannot be resolved by any constant assumptions about sub-grid sulphate. However, the differences in annually averaged aerosol size distributions due to the treatment of sub-grid sulphate at the measurement sites examined here are too small to unambiguously establish P6 as providing better agreement with observations.

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Dietzel, M., M. Ernst et M. Sommerfeld. « Application of the Lattice-Boltzmann Method for Particle-laden Flows : Point-particles and Fully Resolved Particles ». Flow, Turbulence and Combustion 97, n^o 2 (20 janvier 2016) : 539–70. http://dx.doi.org/10.1007/s10494-015-9698-x.

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Zhai, Jinghao, Xiaohui Lu, Ling Li, Qi Zhang, Ci Zhang, Hong Chen, Xin Yang et Jianmin Chen. « Size-resolved chemical composition, effective density, and optical properties of biomass burning particles ». Atmospheric Chemistry and Physics 17, n^o 12 (21 juin 2017) : 7481–93. http://dx.doi.org/10.5194/acp-17-7481-2017.

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Abstract. Biomass burning aerosol has an important impact on the global radiative budget. A better understanding of the correlations between the mixing states of biomass burning particles and their optical properties is the goal of a number of current studies. In this work, the effective density, chemical composition, and optical properties of rice straw burning particles in the size range of 50–400 nm were measured using a suite of online methods. We found that the major components of particles produced by burning rice straw included black carbon (BC), organic carbon (OC), and potassium salts, but the mixing states of particles were strongly size dependent. Particles of 50 nm had the smallest effective density (1.16 g cm−3) due to a relatively large proportion of aggregate BC. The average effective densities of 100–400 nm particles ranged from 1.35 to 1.51 g cm−3 with OC and inorganic salts as dominant components. Both density distribution and single-particle mass spectrometry showed more complex mixing states in larger particles. Upon heating, the separation of the effective density distribution modes confirmed the external mixing state of less-volatile BC or soot and potassium salts. The size-resolved optical properties of biomass burning particles were investigated at two wavelengths (λ = 450 and 530 nm). The single-scattering albedo (SSA) showed the lowest value for 50 nm particles (0.741 ± 0.007 and 0.889 ± 0.006) because of the larger proportion of BC content. Brown carbon played an important role for the SSA of 100–400 nm particles. The Ångström absorption exponent (AAE) values for all particles were above 1.6, indicating the significant presence of brown carbon in all sizes. Concurrent measurements in our work provide a basis for discussing the physicochemical properties of biomass burning aerosol and its effects on the global climate and atmospheric environment.

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Straaten, Agnes, et Stephan Weber. « Measurement report : Three years of size-resolved eddy-covariance particle number flux measurements in an urban environment ». Atmospheric Chemistry and Physics 21, n^o 24 (23 décembre 2021) : 18707–26. http://dx.doi.org/10.5194/acp-21-18707-2021.

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Abstract. Size-resolved particle number fluxes in the size range of 10 nm < particle diameter (Dp) < 200 nm were measured over a 3-year period (April 2017–March 2020) using the eddy-covariance technique at an urban site in Berlin, Germany. The observations indicated the site as a net source of particles with a median total particle number flux of FTNC=0.86 × 108 m−2 s−1. The turbulent surface–atmosphere exchange of particles was clearly dominated by ultrafine particles (Dp < 100 nm) with a share of 96 % of total particle number flux (FUFP=0.83 × 108 m−2 s−1). Annual estimates of median FTNC and FUFP slightly decreased by −9.6 % (−8.9 % for FUFP) from the first to the second observation year and a further −5.9 % (−6.1 % for FUFP) from the second to the third year. The annual variation might be due to different reasons such as the variation of flux footprints in the individual years, a slight reduction of traffic intensity in the third year, or a progressive transition of the vehicle fleet towards a higher share of low-emission standards or electric drive. Size-resolved measurements illustrated events of bidirectional fluxes, i.e. simultaneous emission and deposition fluxes within the size spectrum, which occurred more often in spring, late summer, and autumn than in winter. Multi-year observations of size-resolved particle fluxes proved to be important for a deeper understanding of particle exchange processes with the urban surface and the pronounced influence of traffic at this urban site.

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Wang, Zekun, Khuram Walayat et Moubin Liu. « A velocity corrected unresolved CFD-DEM coupled method to reproduce wake effects at moderate Reynolds number ». Engineering Computations 36, n^o 8 (7 octobre 2019) : 2612–33. http://dx.doi.org/10.1108/ec-10-2018-0454.

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Purpose The purpose of this paper is to develop a corrected unresolved CFD-DEM method that can reproduce the wake effects in modeling particulate flows at moderate Reynolds number. Design/methodology/approach First, the velocity field in the wake behind a settling particle is numerically investigated by a resolved method, in which the finite volume method (FVM) is applied to model the fluid flow, discrete element method (DEM) is applied to simulate the motion of particles and immersed boundary method (IBM) is used to tackle fluid solid interaction. Second, an analytical scaling law is given, which can effectively describe the velocity field in the wake behind the settling particle at low and middle Reynolds numbers. Third, this analytical expression is incorporated into unresolved modeling to correct the relative velocity between the particle and its surrounding fluid and enable the influence of the wake of the particle on its neighboring particles. Findings Two numerical examples, the sedimentation of dual particles, a list of particles and even more particles are provided to show the effectiveness of the presented velocity corrected unresolved method (VCUM). It is found that, in both examples simulated with VCUM, the relative positions of the particles changed, and drafting & kissing phenomenon and particle clustering phenomenon were clearly observed. Practical implications The developed VCUM can be highly beneficial for modeling industrial particulate flows with DKT and particle clustering phenomena. Originality/value VCUM innovatively incorporates the wake effects into unresolved CFD-DEM method. It improves the computational accuracy of conventional unresolved methods with comparable results from resolved modeling, while the computational cost is greatly reduced.

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Payne, Lukas M., Wiebke Albrecht, Wolfgang Langbein et Paola Borri. « The optical nanosizer – quantitative size and shape analysis of individual nanoparticles by high-throughput widefield extinction microscopy ». Nanoscale 12, n^o 30 (2020) : 16215–28. http://dx.doi.org/10.1039/d0nr03504a.

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We demonstrate rapid and quantitative nanoparticle analysis by measuring the polarisation-resolved optical extinction cross-section of hundreds of particles in wide-field microscopy, determining particle size and shape via modelling.

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Owolabi, Bayode Emmanuel, Robert Jäckel, Luca Moriconi et Juliana Braga Rodrigues Loureiro. « Turbulence Modulation By Large Heavy Particles In Wall-Bounded Turbulence ». Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (8 juillet 2024) : 1–10. http://dx.doi.org/10.55037/lxlaser.21st.172.

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"Most studies on particle laden flows have focused either on small heavy particles or large neutrally buoyant particles. We present, for the first time (to the best of our knowledge), results in the regime of large and heavy particles, investigating the particle-turbulence dynamics over a parameter space covering a wide range of particle-volume fractions, Stokes and Froude numbers. We consider a flow in a pipe aligned with the gravitational vector, thus allowing for the investigation of the two-way coupling between particles and carrier phase turbulence, while excluding the effect of gravity on the wall-normal migration of particles. Time-resolved images of both tracers (10 micrometers particles) and the dispersed particles (700 micrometers in diameter) were taken in the streamwise-wall-normal pipe plane using a planar particle image velocimetry (PIV) system consisting of a high speed camera (Phantom VEO 440), and an Nd:YLF Laser as light source. Using Voronoi tessellations to analyze the inertial particle dynamics, we show a strong deviation from Poisson behaviour for cases with and without turbophoresis. From the time-resolved PIV measurements, we also show that the carrier phase turbulence is modulated even at particle concentrations as low as 0.3% indicating that particle-induced stresses due to distortion of fluid streamlines cannot be neglected. An increase or decrease in the peak streamwise velocity fluctuation in the particle laden flow was observed, depending on the Stokes number, while the radial velocity fluctuation was found either to be the same as in the single phase flow case or higher. Furthermore, pressure drop measurements indicate a linear increase in the skin friction coefficient with volume fraction of particles. This was true for all Stokes and Froude numbers considered. The growth rate (β) of the skin friction coefficient was however observed to be only a function of the Froude number. A power-law fit to the data shows that β scales inversely with the Froude number indicating that for Froude numbers less than 1, the influence of gravity cannot be neglected. "

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Bergmann, Stephan, Oliver Wrede, Thomas Huser et Thomas Hellweg. « Super-resolution optical microscopy resolves network morphology of smart colloidal microgels ». Physical Chemistry Chemical Physics 20, n^o 7 (2018) : 5074–83. http://dx.doi.org/10.1039/c7cp07648g.

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We present a new method to resolve the network morphology of colloidal particles in an aqueous environment via super-resolution microscopy. The 3D structure of thermoresponsive microgels with different cross-linker content is resolved and compared to established models.

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Schneiders, Lennart, Konstantin Fröhlich, Matthias Meinke et Wolfgang Schröder. « The decay of isotropic turbulence carrying non-spherical finite-size particles ». Journal of Fluid Mechanics 875 (22 juillet 2019) : 520–42. http://dx.doi.org/10.1017/jfm.2019.516.

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Direct particle–fluid simulations of heavy spheres and ellipsoids interacting with decaying isotropic turbulence are conducted. This is the rigorous extension of the spherical particle analysis in Schneiders et al. (J. Fluid Mech., vol. 819, 2017, pp. 188–227) to $O(10^{4})$ non-spherical particles. To the best of the authors’ knowledge, this represents the first particle-resolved study on turbulence modulation by non-spherical particles of near-Kolmogorov-scale size. The modulation of the turbulent flow is precisely captured by explicitly resolving the stresses acting on the fluid–particle interfaces. The decay rates of the fluid and particle kinetic energy are found to increase with the particle aspect ratio. This is due to the particle-induced dissipation rate and the direct transfer of kinetic energy, both of which can be substantially larger than for spherical particles depending on the particle orientation. The extra dissipation rate resulting from the translational and rotational particle motion is quantified to detail the impact of the particles on the fluid kinetic energy budget and the influence of the particle shape. It is demonstrated that the previously derived analytical model for the particle-induced dissipation rate of smaller particles is valid for the present cases albeit these involve significant finite-size effects. This generic expression allows us to assess the impact of individual inertial particles on the local energy balance independent of the particle shape and to quantify the share of the rotational particle motion in the kinetic energy budget. To enable the examination of this mechanistic model in particle-resolved simulations, a method is proposed to reconstruct the so-called undisturbed fluid velocity and fluid rotation rate close to a particle. The accuracy and robustness of the scheme are corroborated via a parameter study. The subsequent discussion emphasizes the necessity to account for the orientation-dependent drag and torque in Lagrangian point-particle models, including corrections for finite particle Reynolds numbers, to reproduce the local and global energy balance of the multiphase system.

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Wang, X., L. Zhang et M. D. Moran. « Uncertainty assessment of current size-resolved parameterizations for below-cloud particle scavenging by rain ». Atmospheric Chemistry and Physics Discussions 10, n^o 2 (2 février 2010) : 2503–48. http://dx.doi.org/10.5194/acpd-10-2503-2010.

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Abstract. A detailed review has been conducted of current size-resolved parameterizations of below-cloud scavenging by rain, including their formulation in terms of scavenging coefficient (Λ), their associated input parameters and comparisons with size-resolved Λ values obtained from field measurements. The three dominant factors in the theoretical formulations of Λ – raindrop-particle collection efficiency, raindrop number size distribution and raindrop terminal fall velocity – are investigated through numerical sensitivity tests. It is found that the use of different formulations for raindrop-particle collection efficiency can cause uncertainties in the Λ values of nearly one order of magnitude for particles smaller than 3 μm. The use of different formulations of raindrop number size distribution can cause the Λ values to vary by a factor of 3 to 5 for all particle sizes. The uncertainty in Λ, caused by the use of different droplet terminal velocity formulations, is generally smaller than a factor of 2. All of the current theoretical Λ parameterizations, however, underpredict the Λ values by one to two orders of magnitude for particles smaller than 3 μm, compared with most available field measurements or with empirical formulas generated from field observations. The combined uncertainties from known sources are, thus, not enough to explain the large discrepancies between the theoretical and experimental studies, suggesting a need for further investigations of the collection mechanisms through field, laboratory and numerical studies. The differences in the predicted particle concentrations, due to the use of different Λ parameterizations, can be larger than a factor of 10 for ultrafine and coarse particles even after a small amount of rain (e.g., 2–5 mm). The differences for submicron-sized particles can also be larger than a factor of 2 if sufficient rainfall occurs. Lastly, predicted bulk concentrations (integrated over the particle size distribution) from using different theoretical and empirical Λ parameterizations can differ by up to 50% for particle number and by up to 25% for particle mass after just 2–5 mm of rain.

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