scholarly journals Dust Particle Size Distributions during Spring in Yinchuan, China

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
Jiangfeng Shao ◽  
Jiandong Mao
Keyword(s):  
Particle Size ◽  
Wind Speed ◽  
Dust Particle ◽  
Dust Storm ◽  
Fine Particles ◽  
Dust Particles ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Mass Distributions ◽  
Mass Size

Dust particle size distributions in Yinchuan, China, were measured during March and April 2014, using APS-3321 sampler. The distributions were measured under different dust conditions (background, floating dust, blowing dust, and dust storm) and statistical analyses were performed. The results showed that, under different dust conditions, the instantaneous number concentrations of dust particles differed widely. For example, during blowing sand and dust storm conditions, instantaneous dust particles concentrations varied substantially, while, under floating dust conditions, concentration differences were relatively small. The average dust particles size distributions were unimodal under all dust conditions, but the average surface area and mass size distributions were all bimodal. These distributions had peaks in different locations under different dust conditions. Under different dust conditions, wind speed and humidity were very important factors for particles size distributions. With increasing wind speed and decreasing humidity, fine particles were dominant in the atmosphere and the number and mass distributions of the coarse particles were indicative of long-range transport from surrounding deserts. Different dust conditions had different influences on PM1, PM2.5, and PM10concentrations.

scholarly journals Observations of Saharan dust microphysical and optical properties from the Eastern Atlantic during NAMMA airborne field campaign

2011 ◽  
Vol 11 (2) ◽  
pp. 723-740 ◽  
Author(s):  
G. Chen ◽  
L. D. Ziemba ◽  
D. A. Chu ◽  
K. L. Thornhill ◽  
G. L. Schuster ◽  
...  
Keyword(s):  
Particle Size ◽  
Optical Properties ◽  
Dust Particle ◽  
Saharan Dust ◽  
Dust Particles ◽  
Small Range ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Field Campaign ◽  
Sahara Dust

Abstract. As part of the international project entitled "African Monsoon Multidisciplinary Analysis (AMMA)", NAMMA (NASA AMMA) aimed to gain a better understanding of the relationship between the African Easterly Waves (AEWs), the Sahara Air Layer (SAL), and tropical cyclogenesis. The NAMMA airborne field campaign was based out of the Cape Verde Islands during the peak of the hurricane season, i.e., August and September 2006. Multiple Sahara dust layers were sampled during 62 encounters in the eastern portion of the hurricane main development region, covering both the eastern North Atlantic Ocean and the western Saharan desert (i.e., 5–22° N and 10–35° W). The centers of these layers were located at altitudes between 1.5 and 3.3 km and the layer thickness ranged from 0.5 to 3 km. Detailed dust microphysical and optical properties were characterized using a suite of in-situ instruments aboard the NASA DC-8 that included a particle counter, an Ultra-High Sensitivity Aerosol Spectrometer, an Aerodynamic Particle Sizer, a nephelometer, and a Particle Soot Absorption Photometer. The NAAMA sampling inlet has a size cut (i.e., 50% transmission efficiency size) of approximately 4 μm in diameter for dust particles, which limits the representativeness of the NAMMA observational findings. The NAMMA dust observations showed relatively low particle number densities, ranging from 268 to 461 cm−3, but highly elevated volume density with an average at 45 μm3 cm−3. NAMMA dust particle size distributions can be well represented by tri-modal lognormal regressions. The estimated volume median diameter (VMD) is averaged at 2.1 μm with a small range of variation regardless of the vertical and geographical sampling locations. The Ångström Exponent assessments exhibited strong wavelength dependence for absorption but a weak one for scattering. The single scattering albedo was estimated at 0.97 ± 0.02. The imaginary part of the refractive index for Sahara dust was estimated at 0.0022, with a range from 0.0015 to 0.0044. Closure analysis showed that observed scattering coefficients are highly correlated with those calculated from spherical Mie-Theory and observed dust particle size distributions. These values are generally consistent with literature values reported from studies with similar particle sampling size range.

scholarly journals A sample formation procedure to obtain homogeneous post-erosion particle size distribution

2019 ◽  
Vol 92 ◽  
pp. 02015
Author(s):  
Shijin Li ◽  
Adrian R. Russell
Keyword(s):  
Particle Size ◽  
Fine Particles ◽  
Internal Erosion ◽  
Triaxial Tests ◽  
Experimental Investigations ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
The Matrix ◽  
Homogeneous Particle ◽  
Coarse Soil

Internal erosion (suffusion) is caused by water seeping through the matrix of coarse soil and progressively transporting out fine particles. The mechanical strength of soils within water retaining structures may be affected after internal erosion occurs. However, most experimental investigations on the mechanical consequences of internal erosion have used triaxial tests on samples having nonhomogeneous particle size distributions along their lengths. Such nonhomogeneities arise from the most commonly used sample formation procedure, in which seeping water enters one end of a sample and washes fine particles out the other. In this paper a new soil sample formation procedure is presented which results in homogeneous particle size distributions along the direction of seepage, that is at all locations along a sample's length.

scholarly journals Observations of Saharan dust microphysical and optical properties from the Eastern Atlantic during NAMMA airborne field campaign

2010 ◽  
Vol 10 (5) ◽  
pp. 13445-13493 ◽  
Author(s):  
G. Chen ◽  
L. D. Ziemba ◽  
D. A. Chu ◽  
K. L. Thornhill ◽  
G. L. Schuster ◽  
...  
Keyword(s):  
Particle Size ◽  
Optical Properties ◽  
Dust Particle ◽  
North Atlantic Ocean ◽  
Saharan Dust ◽  
Small Range ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Field Campaign ◽  
Sahara Dust

Abstract. As part of the international project entitled "African Monsoon Multidisciplinary Analysis (AMMA)", NAMMA (NASA AMMA) aimed to gain a better understanding of the relationship between the African Easterly Waves (AEWs), the Sahara Air Layer (SAL), and tropical cyclogenesis. The NAMMA airborne field campaign was based out of the Cape Verde Islands during the peak of the hurricane season, i.e., August and September 2006. Multiple Sahara dust layers were sampled during 62 encounters in the eastern portion of the hurricane main development region, covering both the eastern North Atlantic Ocean and the western Saharan desert (i.e., 5–22° N and 10–35° W). The centers of these layers were located at altitudes between 1.5 and 3.3 km and the layer thickness ranged from 0.5 to 3 km. Detailed dust microphysical and optical properties were characterized using a suite of in situ instruments aboard the NASA DC-8 that included a particle counter, an Ultra-High Sensitivity Aerosol Spectrometer, an Aerodynamic Particle Sizer, nephelometer, and Particle Soot Absorption Photometer. The NAMMA dust observations showed relatively low particle number densities, ranging from 268 to 461 cm−3, but highly elevated volume density with an average at 45 μm3 cm−3. NAMMA dust particle size distributions were well represented by tri-modal lognormal regressions. The estimated volume median diameter (VMD) is averaged at 2.1 μm with a small range of variation regardless of the vertical and geographical sampling locations. The absorption coefficient measurements exhibited a strong wavelength dependence for absorption but a weak one for scattering. The single scattering albedo was estimated at 0.97±0.02. Closure analyses showed that observed scattering and absorption coefficients are highly correlated with those calculated from spherical Mie-Theory and observed dust particle size distributions. The imaginary part of the refractive index for Sahara dust was estimated at 0.0022, with a range from 0.0015 to 0.0044. These values are generally consistent with literature values.

Influence of particle-size distribution homogeneity on shearing of soils subjected to internal erosion

2020 ◽  
Vol 57 (11) ◽  
pp. 1684-1694
Author(s):  
Shijin Li ◽  
Adrian R. Russell ◽  
David Muir Wood
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Soil Sample ◽  
Size Distribution ◽  
Fine Particles ◽  
Internal Erosion ◽  
Triaxial Tests ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Homogeneous Particle

Internal erosion (suffusion) is caused by water seeping through the matrix of coarse soil and progressively transporting out fine particles. The mechanical strength and stress–strain behavior of soils within water-retaining structures may be affected by internal erosion. Some researchers have set out to conduct triaxial erosion tests to study the mechanical consequences of erosion. Prior to conducting a triaxial test they subject a soil sample, which has an initially homogeneous particle-size distribution and density throughout, to erosion by causing water to enter one end of a sample and wash fine particles out the other. The erosion and movement of particles causes heterogeneous particle-size distributions to develop along the sample length. In this paper, a new soil sample formation procedure is presented that results in homogeneous particle-size distributions along the length of an eroded sample. Triaxial tests are conducted on homogeneous samples formed using the new procedure as well as heterogeneous samples created by the more commonly used approach. Results show that samples with homogeneous post-erosion particle-size distributions exhibit slightly higher peak deviator stresses than those that were heterogeneous. The results highlight the importance of ensuring homogeneity of post-erosion particle-size distributions when assessing the mechanical consequences of erosion. Forming samples using the new procedure enables the sample’s response to triaxial loading to be interpreted against a measure of its initially homogenous state.

scholarly journals Size-segregated particle number and mass concentrations from different emission sources in urban Beijing

2020 ◽  
Vol 20 (21) ◽  
pp. 12721-12740
Author(s):  
Jing Cai ◽  
Biwu Chu ◽  
Lei Yao ◽  
Chao Yan ◽  
Liine M. Heikkinen ◽  
...  
Keyword(s):  
Particle Size ◽  
Particulate Matter ◽  
Source Apportionment ◽  
Particle Number ◽  
Fine Particles ◽  
Size Distributions ◽  
Vehicular Emissions ◽  
Particle Size Distributions ◽  
Chemical Fingerprints ◽  
Mass Concentrations

Abstract. Although secondary particulate matter is reported to be the main contributor of PM2.5 during haze in Chinese megacities, primary particle emissions also affect particle concentrations. In order to improve estimates of the contribution of primary sources to the particle number and mass concentrations, we performed source apportionment analyses using both chemical fingerprints and particle size distributions measured at the same site in urban Beijing from April to July 2018. Both methods resolved factors related to primary emissions, including vehicular emissions and cooking emissions, which together make up 76 % and 24 % of total particle number and organic aerosol (OA) mass, respectively. Similar source types, including particles related to vehicular emissions (1.6±1.1 µg m−3; 2.4±1.8×103 cm−3 and 5.5±2.8×103 cm−3 for two traffic-related components), cooking emissions (2.6±1.9 µg m−3 and 5.5±3.3×103 cm−3) and secondary aerosols (51±41 µg m−3 and 4.2±3.0×103 cm−3), were resolved by both methods. Converted mass concentrations from particle size distributions components were comparable with those from chemical fingerprints. Size distribution source apportionment separated vehicular emissions into a component with a mode diameter of 20 nm (“traffic-ultrafine”) and a component with a mode diameter of 100 nm (“traffic-fine”). Consistent with similar day- and nighttime diesel vehicle PM2.5 emissions estimated for the Beijing area, traffic-fine particles, hydrocarbon-like OA (HOA, traffic-related factor resulting from source apportionment using chemical fingerprints) and black carbon (BC) showed similar diurnal patterns, with higher concentrations during the night and morning than during the afternoon when the boundary layer is higher. Traffic-ultrafine particles showed the highest concentrations during the rush-hour period, suggesting a prominent role of local gasoline vehicle emissions. In the absence of new particle formation, our results show that vehicular-related emissions (14 % and 30 % for ultrafine and fine particles, respectively) and cooking-activity-related emissions (32 %) dominate the particle number concentration, while secondary particulate matter (over 80 %) governs PM2.5 mass during the non-heating season in Beijing.

scholarly journals Effect of Particle Size Distributions and Shapes on the Failure Behavior of Dry Coke Aggregates

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5558
Author(s):  
Alireza Sadeghi-Chahardeh ◽  
Roozbeh Mollaabbasi ◽  
Donald Picard ◽  
Seyed Mohammad Taghavi ◽  
Houshang Alamdari
Keyword(s):  
Particle Size ◽  
Fine Particles ◽  
Rolling Resistance ◽  
Structural Defects ◽  
Failure Behavior ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Resistance Model ◽  
The Stability ◽  
Carbon Anodes

Carbon anodes participate in chemical reactions to reduce alumina in the Hall–Héroult process, of which coke aggregates make up a major part. The failure analysis of coke aggregates not only leads to a better understanding of the deformation mechanisms of anode paste under compressive loading but also can identify potential causes of structural defects in carbon anodes, such as horizontal cracks. The coke aggregates are composed of particles with different size distributions and shapes, which may strongly affect the failure behavior of the anode during compaction. In this paper, the effects of particle size distributions and shapes on the mechanical behavior and the failure of coke aggregates are investigated using the discrete element method modeling technique. The numerical results reveal that, although the mechanical behavior of coke mixtures is generally dependent on larger particles, the presence of fine particles in the coke aggregates reduces fluctuations in the stress–strain diagram. In addition, the rolling resistance model is employed as a parameter representing the effect of particle shape. It is shown that the rolling resistance model can be an alternative to the overlapped spheres model, which has a higher computational cost than the rolling resistance model. The second-order work criterion is used to evaluate the stability of the coke aggregates, the results of which indicate that the addition of fine particles as well as increasing the rolling resistance between the particles increases the stability range of the coke aggregates. Moreover, by using the analysis of micro-strain contour evaluations during the compaction process, it is shown that, both by adding fine particles to the coke mixture and by increasing the rolling resistance between the particles, the possibility of creating a compression band in the coke aggregates is reduced. Since the presence of the compaction bands in the anode paste creates an area prone to horizontal crack generations, the results of this study could lead to the production of carbon anodes with fewer structural defects.

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