Multiple Dust Sources Research Articles

Quantification of Contributions from Different Dust Sources to the Distribution and the Variation of Spring Dust over the Tibetan Plateau and Corresponding Mechanisms since 2000

Abstract Dust is the predominant type of aerosol over the Tibetan Plateau (TP) due to the existence of surrounding significant dust sources. However, the contributions of different dust sources to the distribution and variation of dust over the TP and corresponding mechanisms are still being explored. By separating emissions from different dust sources in a numerical model, this study detected that dust originating from East Asia, the Middle East, and North Africa are the main contributors to spring dust over the TP, accounting for 42%–68%, 13%–27%, and 9%–25% of the total dust concentration, respectively. East Asian dust primarily affects the dust over the central and northern parts of the TP, whereas Middle Eastern and North African dust mainly contributes to the dust over the western and southern parts of the TP. Additionally, the variation in dust over the TP is related to East Asian and North African dust, which contribute 58% and 35% of the total variation, respectively. The mechanism underlying this association is attributable to the SST over the northern North Atlantic and updrafts over the northern slope of the TP: the increased SST enhances westerlies from North Africa to East Asia and northwesterly winds over the northern slope of the TP and combines with the stronger westerlies to promote the transport of East Asian and North African dust to the TP. Consequently, it is necessary to focus on the impact of multiple dust sources on the dust over the TP.

A database of radiogenic Sr–Nd isotopes at the “three poles”

Abstract. The radiogenic isotope compositions of strontium (Sr) and neodymium (Nd) on the surface of the Earth are powerful tools for tracing dust sources and sinks on the Earth's surface. To differentiate between the spatial variabilities in eolian dust sources in key cryospheric regions at the three poles (the Arctic; Antarctica; and the “third pole”, covering the high mountainous area in Asia), a dataset of Sr–Nd isotopic compositions from extremely cold or arid terrestrial environments was compiled, similar to the method of Blanchet (2019). The database includes Holocene and Quaternary snow, ice, sand, soil (loess), sediment, and rock samples from the three poles based on 90 different references and our own measurement data, with a total of 1989 data points, comprising 206 data points with different grain sizes and 212 data points with fraction measurements. There are 485 data points from the third pole, 727 data points from the Arctic, and 777 data points from Antarctica. The sampling and measurement methods of these data are introduced. For each pole, geographical coordinates and other information are provided. The main scientific purpose of this dataset is to provide a Sr–Nd dataset based on collective documentation and our own measurements, which will be useful for determining the sources and transport pathways of dust in snow, ice, rivers, and oceans at or near the three poles as well as to investigate whether multiple dust sources are present at each of the poles. This dataset provides exhaustive detailed documentation of the isotopic signatures at the three poles during specific time intervals in the Quaternary period, which are useful for understanding the sources or sinks of eolian dust and sediments at the three poles. The dataset is available from the National Tibetan Plateau Data Center (https://doi.org/10.11888/Cryos.tpdc.272100, Du, 2022).

Climatology of Dust Aerosols over the Jianghan Plain Revealed with Space-Borne Instruments and MERRA-2 Reanalysis Data during 2006–2021

In recent years, climate change and the intervention of anthropogenic activities have altered the seasonal features of Asian dust storms. This may also cause seasonal variations (including dust occurrence frequency and optical/microphysical properties) in dust aerosols transported to downstream regions. The Jianghan Plain is dramatically influenced by multiple dust sources due to its geographical location in central China. In this study, we focused on the climatology of dust aerosols over the Jianghan Plain based on the 15-year (2006–2021) continuous space-borne observations of the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) as well as Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalysis data. A typical dust event that intrudes the Jianghan Plain was studied in detail. According to the statistical results, dust aerosols frequently intrude into the Jianghan Plain in spring and winter, with occurrence frequencies (under cloud free condition hereafter) exceeding 0.70 and higher altitudes of 4–6 km. The dust occurrence frequency declined to approximately 0.40 in autumn and nearly zero in summer, while the dust plumes were generally located at lower altitudes of 1–3 km. The dust plumes observed in the Jianghan Plain were simultaneously linked to the Taklimakan Desert and Gobi Desert in spring and mainly originated from the Taklimakan Desert in winter and autumn. The dust particles were mainly distributed below 4-km altitude, with the largest dust extinction coefficients and dust mass concentrations in spring. In all seasons, the particle depolarization ratios are 0.1–0.2 below 4-km altitude, suggesting a possible mix with local anthropogenic aerosols. The mean dust column mass concentrations in spring showed an evident declining trend from 210 µg m−2 in 2006 to 100 µg m−2 in 2021 in the Jianghan Plain, attributed to the reduced dust activity in the source regions of Asian dust.

Dust transport behaviour in the Nanwenhe extra-large stepped underground metal mine stope

This paper is aimed at studying the dust behaviour of a super-large stepped stope, which is essential in reducing the dust hazards and setting up effective dust control facilities. In this paper, a three-dimensional model is established for the super-large stepped stope of Nanwenhe. Based on the theory of gas-solid two-phase flow, the Fluent software was applied to carry out a numerical simulation of the air flow distribution in the stope and the dust concentration distribution from multiple dust sources. The simulation results reveal that air flow is affected by the roof fault, resulting in it being diverted to the connecting roadway of the return air roadway, the roof of the lower stope and the interior of the stope. A part of the air flow flows back to the upper stope operation area at a speed of 0.3–0.6 m/s. The dust produced by the shovelling and dumping operations forms a high concentration dust belt with a length of 41 m, a width of 3.6 m and an average concentration of over 260 mg/m³. A portion of the dust flows back to the operation area by bypassing the ore pillar, with a concentration of 60–80 mg/m³. The reliability of our simulation method was verified by field measurements of the air flow velocity and dust concentration. Finally, a new intelligent wind-fog combined dust removal system was designed according to the dust concentration distribution, which achieved an overall dust removal efficiency of 76.9%. These research results provide certain references for the study of dust migration law in underground metal mines and the development of dust removal equipments.

Air Pollution Associated with Total Suspended Particulate and Particulate Matter in Cement Grinding Plant in Vietnam

Air pollution associated with suspended particles has become a significant concern in Vietnam recently. The study aimed to (1) investigate dust sources; (2) measure concentration levels of Total Suspended Particulate (TSP), Particulate Matter (PM) fractions; (3) identify silica levels and the correlation with respirable particles at a cement grinding plant in Vietnam. A total of 312 samples (52 TSP, 160 PMs) at 13 processes were measured using the direct-reading dust meter. The silica composition was analyzed in a certified laboratory using the X-ray fluorescence (XRF) technique. SPSS version 26 for Window was used to analyze the data. The operations of the cement grinding plant created multiple dust sources from the jetty to the cement dispatch process. The TSP levels ranged 0.06–38.24 mg m−3, and 40.38% (n = 21) TSP samples exceeded the Permissible Exposure Limit (PEL) for an 8-h working shift. Besides that, there was a wide range and significant concentration levels of PMs in the cement processes. The levels of PMs were PM1 (0.00–0.06 mg m−3), PM2.5 (0.01–0.83 mg m−3), PM4 (0.02–4.59 mg m−3), PM7 (0.03–16.94 mg m−3), and PM10 (0.04–26.85 mg m−3). The highest mean levels of PMs factions were measured at the pre-grinding process. The inefficient operation of the dust collector contributed a significant factor to the dust dispersion in this process. The silica’s mean (SD) composition in respirable dust was 20.4% (0.86) and was not significantly different amongst the processes. There was a significant correlation between the levels of respirable dust and silica exposure in the cement grinding plant (r = 0.99). The improvement of indoor air quality is needed to prevent health effects on cement workers.

The Extraterrestrial Dust Flux: Size Distribution and Mass Contribution Estimates Inferred From the Transantarctic Mountains (TAM) Micrometeorite Collection

AbstractThis study explores the long‐duration (0.8–2.3 Ma), time‐averaged micrometeorite flux (mass and size distribution) reaching Earth, as recorded by the Transantarctic Mountains (TAM) micrometeorite collection. We investigate a single sediment trap (TAM65), performing an exhaustive recovery and characterization effort and identifying 1,643 micrometeorites (between 100 and 2,000 μm). Approximately 7% of particles are unmelted or scoriaceous, of which 75% are fine‐grained. Among cosmic spherules, 95.6% are silicate‐dominated S‐types, and further subdivided into porphyritic (16.9%), barred olivine (19.9%), cryptocrystalline (51.6%), and vitreous (7.5%). Our (rank)‐size distribution is fit against a power law with a slope of −3.9 (R2 = 0.98) over the size range 200–700 μm. However, the distribution is also bimodal, with peaks centered at ~145 and ~250 μm. Remarkably similar peak positions are observed in the Larkman Nunatak data. These observations suggest that the micrometeorite flux is composed of multiple dust sources with distinct size distributions. In terms of mass, the TAM65 trap contains 1.77 g of extraterrestrial dust in 15 kg of sediment (<5 mm). Upscaling to a global annual estimate gives 1,555 (±753) t/year—consistent with previous micrometeorite abundance estimates and almost identical to the South Pole Water Well estimate (~1,600 t/year), potentially indicating minimal variation in the background cosmic dust flux over the Quaternary. The greatest uncertainty in our mass flux calculation is the accumulation window. A minimum age (0.8 Ma) is robustly inferred from the presence of Australasian microtektites, while the upper age (~2.3 Ma) is loosely constrained based on 10Be exposure dating of glacial surfaces at Roberts Butte (6 km from our sample site).

Numerical simulation study on dust pollution characteristics and optimal dust control air flow rates during coal mine production

Ventilation and dust removal is the most basic means of dust prevention in mines. In the paper, a highly simulated physical model of the goaf and multiple dust sources were established in order to obtain the optimal dust-removal air flow rate in the roadway. In addition, by combining the numerical simulation method, the influence of the flow rate on dust diffusion rules of the dust sources was analyzed. The research results showed that the mass concentration of the dust in the fully-mechanized working face was gradually decreased with the increase of the air flow rate at a certain range of 700–1600 m3/min. However, high air flow rate can cause the re-entrainment of the dust, contaminating the working environment again. It was confirmed that the optimal dust-removal air flow rate of the inlet air was within a range of 1500–1600 m3/min, which generated the lowest average mass of the dust in the working area suitable for normal operations. This range of air flow rate might be used as a reference in the mine ventilation design in order to provide the coal mine workers with a clean and safe production environment. In addition, the research method and results are of great significance to the formulation and development of effective dust control and dust removal cleaner production technology, and can be used as a reference for the ventilation design in underground projects such as non-coal mines and tunnels.

Mineralogical evidence for multiple dust sources in an early Triassic loessite

AbstractLoessite present in a borehole into the Smith Bank Formation (early Triassic age, Central North Sea) differentiates five coeval source terranes for aerosol dust, three long‐distance sources and two local sources. All were active immediately following the end Permian mass extinction. Long‐distance sources are sedimentary, basic magmatic and acid–intermediate volcanic. Although predominantly silt‐sized and dominated by quartz with subordinate feldspars, muscovite and illite, evidence of basic and acid–intermediate magmatic/volcanic sources are pervasive. Baddeleyite is diagnostic of basic magmatism, an origin supported by enrichment of plagioclase relative to potassium feldspar. Deduction of acid–intermediate volcanism comes from the collective occurrence of irregular geometry quartz, volcanic shards, Ti‐mineralization, euhedral biotite, sanidine, the co‐occurrence of apatite and zircon, and the common occurrence of a tosuditic clay mineral. The tosuditic phase occurs as an unusual diagenetic dioctahedral chlorite/smectite formed at low temperature (<45°C), during very shallow burial by the decomposition of unstable rhyo‐dacitic and andesitic grains in alkaline pore water from an adjacent lake that yielded pore fluids with a high Al : Si ratio. The Siberian Traps large igneous province is the likely source terrane for the magmatic and volcanic silt. Locally sourced clay pellets and kaolinite booklets formed from aeolian erosion of an adjacent, periodically desiccated lake‐floor and a kaolinitic regolith, respectively. Inference of a prolonged harsh, arid climate leaves no evidence of any periods of sustained humidity or climatic fluctuation, such as pedogenesis. The association between the end Permian mass extinction, emplacement and aeolian erosion of the Siberian Traps large igneous province, and location of the Smith Bank Formation in a large lacustrine endorheic basin, combine to preserve a record of prolonged harsh climate in the early Triassic.

Airflow-Dust Migration Law and Control Technology Under the Simultaneous Operations of Shotcreting and Drilling in Roadways

The simultaneous operations of drilling (cutting rock) and shotcreting are occasionally carried out in order to advance the tunneling speed in underground roadways. Under these circumstances, the dust pollution from multiple dust sources is serious, especially threatening worker health. In this paper, the main dust sources were divided; a new ventilation system under the simultaneous operations was proposed by adding one turbulator (T) and the second exhaust air outlet (SEAO). The airflow-dust migration law after improving ventilation system was analyzed to determine the optimum combination and corresponding working parameters of T and SEAO based on computational fluid dynamics. Results showed that the combinatorial arrangements of A-3 pattern, T installed upstream while SEAO laid downstream of shotcreting area, were the best ventilation pattern in terms of dust suppression. The more air volume from SEAO is, the smaller the diffusion distance of high concentration dust is. The dust concentration at the interface between cutting rock and shotcrete declined and then increased with increasing total forced air volume. The bigger the forced-exhaust air ratio is, the larger the dust concentration at interface is. According to the on-site test, the new method prevented the high concentration dust from diffusing at tunneling district and reduces the dust concentration at shotcreting district.

Aeolian dust chemistry and bacterial communities in snow are unique to airshed locations across northern Utah, USA

Wind-blown dust is an important source of trace metals, nutrients, and biological material to montane ecosystems. Mountain ranges in northern Utah are located downwind of multiple dust sources including the Great Basin Desert and the Wasatch Front urban area, providing an opportunity to investigate regional-scale differences in dust deposition chemistry and bacterial composition. We sampled discrete dust layers from snowpack across multiple locations in the Wasatch and Uinta Mountains (Utah) and the Snake Range (Nevada) during spring 2014 and 2015. Dust chemistry was unique in each airshed, suggesting that spatial variability and local sources were more important than temporal variability for the sampling period. The central Wasatch dust contained the highest concentrations of playa-associated elements (U, Mg, Li, Ca, Sr, As) and anthropogenic elements (Sb, Cu, Pb, Se) compared with lowest concentrations of these elements in the northern Wasatch, which is further from playa and anthropogenic sources. Sequential extractions indicate that the majority of Ca, Sr, and Cd is potentially available for transport during snowmelt while other elements are relatively immobile. Central Wasatch dust was more reactive to acetic acid than northern Wasatch dust for most elements, including REE + Y. Sr isotopes (87Sr/86Sr ratios) were also unique to each sampling area, with the most radiogenic values in the central Wasatch. Similar to dust chemistry, bacterial communities in dusty snow reflected geographically localized dust events. In the central Wasatch, 69% of bacterial species were unique, suggesting that the airshed received the most diverse dust inputs from a combination of playa and anthropogenic sources. Gram-positive Actinobacteria and Firmicutes were common in snow but specific bacterial families distinguished airsheds (e.g., Bacillaceae, Geodermatophilaceae, Nakamurellaceae). Our results demonstrate that evaluating dust chemistry and bacteria in snow on a regional scale may more clearly link dust sources to the entrainment of pollutants and seeding of bacteria species to montane systems.

Greenland ice cores constrain glacial atmospheric fluxes of phosphorus

Phosphorus is a limiting nutrient for primary productivity, but little is known about past atmospheric fluxes to the open ocean. In this study, phosphate and phosphorus concentrations have been determined in the North Greenland Eemian Ice Drilling Project ice core for selected periods during the last glacial. Phosphate was determined continuously by using a molybdenum blue spectroscopic absorption method and discretely using an ion chromatograph. Total P was determined discretely using an inductively coupled plasma sector field mass spectrometer. For the last glacial period, we found concentrations of between 3 and 62 nM PO43− and 7 and 929 nM P. We find glacial atmospheric fluxes of phosphorus to Greenland were 4 to 11 times higher than in the past century, with the highest input during the cold glacial stadials (GS). Changes in P and PO43− fluxes between mild glacial interstadials (GI) and GS correlate positively with dust variability. The soluble fraction of P is larger in the mild GIs as compared to the dust-rich GSs. For the very high phosphate and phosphorus loads during the Last Glacial Maximum, the relationship between phosphate and dust is weaker than in GIs and milder GSs, suggesting either secondary phosphate sources or multiple dust sources. Based on crustal abundances, we find that dust inputs are sufficient to account for all P deposited during all periods investigated except the Last Glacial Maximum. During the glacial, sea salts contributed 10−3 nM P, while land biogenic emissions were a minor source of P.

Magnetic properties and particle-size analysis of dust-storm samples collected in Lanzhou and Sydney

Measurements of magnetic properties and particle size were carried out for dust-storm samples collected from Sydney (Australia) on 23 September 2009 and from Lanzhou (China) on April 2010. The results show that the magnetic mineral content of the Lanzhou sample is much higher than that of the Sydney sample. Magnetite, maghemite and possibly hematite occur in the Lanzhou sample. In addition to these minerals, there is also goethite in the Sydney sample. The magnetic grainsize of the Sydney sample is finer than that of the Lanzhou sample. These magnetic property differences are probably related to the source materials and anthropogenic particles. As to particle-size distribution, the Sydney sample shows a wide and flat curve with four peaks, while the Lanzhou sample displays a narrow curve with three peaks. The multi-peak particle-size distribution curves for the dust-storm samples indicate that there are multiple dust sources. Furthermore, a comparison of particle size between the Lanzhou storm sample and Jiuzhoutai loess/paleosol samples was also carried out. The results show that an increase in the 1–10 µm component and decrease in the 10–20 µm component of the loess/paleosol samples are mainly caused by pedogenic process (i.e. physical and chemical weathering of unstable minerals), while the increase in the 0.02–1 µm component is principally attributed to the formation of new minerals and the weathering of unstable minerals. The similarity of particle-size distribution curves between dust-storm and loess/paleosol samples implies that modern storm events are a good analogue for eolian processes operating in the Quaternary Period when loess/paleosol layers formed.

Multiple dust sources in the Sahara Desert: The importance of sand dunes

We determine the current sources of dust in the Sahara Desert using quantitative correlation between the number of days with dust storms (NDS), derived from remote‐sensing data of high temporal resolution, with the distribution of the soil types and geomorphic units. During 2006–8 the source of over 90% of the NDS was found to be sand dunes, leptosols, calcisols, arenosols, and rock debris. In contrast to previous studies, only few dust storms originated from playas and dry lake beds. Land erodibility was estimated by regressing the NDS to the number of days with high‐speed wind events, and was found to be high for sand dunes. Clay and fine‐silt grains and aggregates are scarce in sand dunes, which most likely produce dust particles through aeolian abrasion of sand grains. Thus, saltating sand grains impacting clay aggregates on playa surfaces cannot be the sole process for generating dust in the Sahara.

Numerical model simulation of the Saharan dust event of 6–11 March 2006 using the Regional Climate Model version 3 (RegCM3)

The Sahara desert is the world's primary source of mineral dust aerosols and is known to be an important but poorly understood component of the climate system. Climate models which incorporate dust modules have the potential to improve our understanding of the climate impacts of dust. In this study, the performance of the Regional Climate Model version 3 (RegCM3) with an active dust scheme is evaluated, using a major dust event of 6–11 March 2006 as a test case. To account for the distribution of preferential dust source regions, soil texture characteristics were modified in dust source regions identified from long‐term SEVIRI satellite data. The dust event was associated with a pronounced cold outbreak of midlatitude air over the northern Sahara which produced anomalously strong northerly winds, which propagated from west to east over the Sahara during the study period. This resulted in dust mobilization from multiple dust sources across the domain. RegCM3 represents the space/time structure of near‐surface meteorology well, although surface winds are underestimated in absolute terms. The experiment in which soils are modified provides a better representation of local dust sources and emission and resulting atmospheric optical thickness (AOT). In this experiment, model simulated dust flux exported from the Sahara to the Sahel and the tropical east Atlantic is estimated as 1.9 Tg d−1. The dust event had a profound impact on the surface solar radiation budget of ∼−140 W m−2 per unit AOT (domain average). The shortwave radiative effect at the top of the atmosphere is ∼−10 W m−2 per unit AOT over the study domain. However, this is strongly dependent on surface albedo. The results also highlight how errors in model simulated circulation lead to errors in the position of the dust plume.

Dust source identification using MODIS: A comparison of techniques applied to the Lake Eyre Basin, Australia

The impact of mineral aerosol (dust) in the Earth's system depends on particle characteristics which are initially determined by the terrestrial sources from which the sediments are entrained. Remote sensing is an established method for the detection and mapping of dust events, and has recently been used to identify dust source locations with varying degrees of success. This paper compares and evaluates five principal methods, using MODIS Level 1B and MODIS Level 2 aerosol data, to: (a) differentiate dust (mineral aerosol) from non-dust, and (2) determine the extent to which they enable the source of the dust to be discerned. The five MODIS L1B methods used here are: (1) un-processed false colour composite (FCC), (2) brightness temperature difference, (3) Ackerman's (1997: J.Geophys. Res., 102, 17069–17080) procedure, (4) Miller's (2003:Geophys. Res. Lett. 30, 20, art.no.2071) dust enhancement algorithm and (5) Roskovensky and Liou's (2005: Geophys. Res. Lett. 32, L12809) dust differentiation algorithm; the aerosol product is MODIS Deep Blue (Hsu et al., 2004: IEEE Trans. Geosci. Rem. Sensing, 42, 557–569), which is optimised for use over bright surfaces (i.e. deserts). These are applied to four significant dust events from the Lake Eyre Basin, Australia. OMI AI was also examined for each event to provide an independent assessment of dust presence and plume location. All of the techniques were successful in detecting dust when compared to FCCs, but the most effective technique for source determination varied from event to event depending on factors such as cloud cover, dust plume mineralogy and surface reflectance. Significantly, to optimise dust detection using the MODIS L1B approaches, the recommended dust/non-dust thresholds had to be considerably adjusted on an event by event basis. MODIS L2 aerosol data retrievals were also found to vary in quality significantly between events; being affected in particular by cloud masking difficulties. In general, we find that OMI AI and MODIS AQUA L1B and L2 data are complementary; the former are ideal for initial dust detection, the latter can be used to both identify plumes and sources at high spatial resolution. Overall, approaches using brightness temperature difference (BT10–11) are the most consistently reliable technique for dust source identification in the Lake Eyre Basin. One reason for this is that this enclosed basin contains multiple dust sources with contrasting geochemical signatures. In this instance, BTD data are not affected significantly by perturbations in dust mineralogy. However, the other algorithms tested (including MODIS Deep Blue) were all influenced by ground surface reflectance or dust mineralogy; making it impossible to use one single MODIS L1B or L2 data type for all events (or even for a single multiple-plume event). There is, however, considerable potential to exploit this anomaly, and to use dust detection algorithms to obtain information about dust mineralogy.

Calibration of modelled mixing patterns in loess grain‐size distributions: an example from the north‐eastern margin of the Tibetan Plateau, China

AbstractGenetically meaningful decomposition (unmixing) of sediment grain‐size distributions is accomplished with the end‐member modelling algorithm. Unmixing of the loess grain‐size distributions of a Late Quaternary loess–palaeosol succession from the north‐eastern Tibetan Plateau indicates that the loess is a mixture of three end‐members representing very fine sandy, coarse silty and medium silty loess. The unmixing approach potentially enables the unravelling of sediment fluxes from multiple dust sources, opening the way to significant advances in palaeoclimatic reconstructions from loess grain‐size distribution data. However, as laser‐diffraction size analysis is a volume‐based technique, the proportional contributions of the modelled end‐members might deviate (significantly) from weight proportions. Hence, calibration of the end‐member volume proportions to weight proportions must be established before one can calculate the source‐specific dust fluxes. This paper reports the findings of a sediment‐mixing experiment which enables calibration of the modelled mixing patterns established for the Tibetan loess–palaeosol succession.

Major element, rare earth element, and sulfur isotopic composition of a high‐elevation firn core: Sources and transport of mineral dust in central Asia

The arid region extending from the Caspian Sea into China contains some of the most extensive dust aerosol production areas in the world. Major element (Al, Fe, Ca, and S), rare earth element (REE), and isotopic (δ34S and δ18O) data from a 14.4‐m‐long firn core recovered on the Inilchek Glacier (Tien Shan Mountains, Kyrgyzstan; 5100‐m elevation) are presented and used to investigate the composition, sources, and transport of mineral dust to this central Asian site. The combination of geochemical compositions points to three distinct types of mineral deposits (loess, calcium carbonate, and gypsum), which do not covary in a linear fashion during the period recorded in the firn core, (1992–1998). Loess, identified by its REE composition, is characterized by distinct large‐scale deposition events and by ubiquitous background deposition at other times. Significant interannual‐scale variability is evident, with the two largest loess events occurring within a single accumulation year, (1997) and background conditions prevailing during 1994–1996. REE compositions, specifically Nd/Yb ratios, point to multiple sources and transport directions of loess to Inilchek Glacier. Nonloess sources provide a significant fraction of the total Ca and S deposited at the Inilchek Glacier. Hence the downcore profiles of Ca and S reflect variability in the deposition of calcium carbonate and gypsum. Differences in the sulfur isotopic composition (δ34S) of high dust period (+15.0‰) and low (background) dust period (+5.4‰) samples provide strong evidence for two sources of sulfate. The former isotopic composition reflects a marine evaporite source of which there are many to the west of the Tien Shan Mountains. The latter composition indicates that a major portion of the atmospheric SO42− was derived from anthropogenic emissions. While the deposition of non‐loess Ca (calcite) and non‐loess S (gypsum) is also high during the periods of high loess deposition, there is pronounced Ca and S variability during background loess periods, (1994–1996). We suggest that the observed geochemical variability in the firn core can be explained by changes in local‐ to regional‐scale atmospheric circulation and associated transport from multiple dust sources (western Kyrgyzstan/Kazakhstan versus the Taklimakan Desert, China).

Respirable dust concentration distribution model on longwall faces — multiple dust source approach

A mathematical model is developed for description of the dust concentration distribution on the longwall faces of coal mines involving multiple dust sources of various particle sizes. Longwall mining is an efficient and productive coal-mining method. However, it generates a large quantity of respirable dust in the working area during the shearing and transportation of coal. Multiple dust sources on the longwall face make dust distribution prediction very difficult. In this paper, the primary sources of respirable dust and transportation of dust particles on a longwall face are determined. The dust particle size distributions at various locations of the longwall face are analyzed, classified and incorporated into the dust distribution model. General trends of dust concentration obtained at different working positions on a longwall face are discussed. The mathematical model takes into account the characteristics of airflow, the effect of particle size, various dust sources, and the mechanisms of dust transport along a longwall face. It predicts the dust behaviors and dust distribution in the longwall mining atmosphere under various operating conditions. Computer programs based on the respirable dust distribution model are also developed. The predicted results are compared with the field data from several longwall faces.