Dust Transport Research Articles

Optimization of ventilation and dust removal parameters in plateau extra-long tunnel inclined shaft based on orthogonal numerical simulation test method

Ventilation and dust removal system in the inclined shaft of the plateau long tunnel is an important component for ensuring safe excavation. The arrangement of wind tube and the volume of air flow have a significant impact on the movement of dust. In order to address the issues of poor ventilation and severe dust pollution in the inclined shaft of plateau long tunnels, this study establishes a dust generation and transportation model for the face of the inclined shaft based on the determination of dust source parameters and their physicochemical characteristics during the excavation process. The results indicate that the particles are predominantly spherical with an approximate diameter of 4 μm at a magnification of 500 times. The dust in high-altitude inclined shafts exhibits poor wettability, with a hydrophobic tendency during the excavation phase, making a ventilation dust removal scheme appropriate. After determining the physical parameters corresponding to the elevation of the inclined shaft, a series of orthogonal numerical simulations involving 3 factors at 5 levels were conducted. Analysis of range and variance revealed that optimal dust control is achieved when the air duct height is 5.725m, the distance from the working face is 21m, and the exit wind speed is 29.71m/s. Comparative analysis confirmed the rationality of the ventilation dust removal scheme under the optimal combination of ventilation parameters. This provides guidance for engineering and environmental management in similar construction scenarios.

Experimental Study on the Impact of Airflow Velocity and Pipeline Diameter on Dust Explosions in Vessel-Pipeline Pneumatic Conveying

To ensure the process safety of powder particles during pneumatic transport, a dust explosion experimental apparatus was designed to simulate the dust transport process. The system is supplied with a stable airflow by a high-pressure fan, capable of continuously transferring dust from the vessel to the pipeline at a controllable speed. Dust explosion experiments were meticulously executed by applying 1 kJ of ignition energy to the transported dust particles at airflow velocities of 5, 10, and 15 m/s. This study examines the effects of dust concentration, airflow velocity, and pipe diameter on explosion characteristics and delves into the mechanisms these effects through a detailed analysis of experimental results. The results demonstrate that the starch explosion flame progresses through four distinct stages within the vessel: flame development, flame stretching towards the pipe, intense combustion of starch particles, and complete combustion of the particles. As airflow velocity and pipe diameter increase, the stretching effect on the flame becomes more pronounced. At an airflow velocity of 15 m/s within a pipeline, a balance is struck between intensified particle combustion rates and unconstrained discharge, resulting in a maximum explosion pressure of 135.56 kPa for a 100 mm diameter pipe, with a maximum pressure rise rate of 7.27 MPa/s. Additionally, flame propagation velocity is higher at the pipe inlet. Different flame behaviors were observed inside the pipeline under varying airflow speeds. Compared to previous studies that utilized high-pressure gas to create dust clouds within vessels for explosion experiments, the results of this study underscore the crucial impact of airflow velocity on dust explosions. This research provides critical parameters for explosion prevention and presents a case study on the safety of dust handling processes.

Optimisation of synergistic ventilation between dust and gas in a gas tunnel.

In view of the difficult problem of gas and dust exceeding the limit during the digging process of a gas tunnel in Guizhou Province, Southwest China, the CFD numerical simulation method was applied to study the gas tunnel airflow, dust and gas transport law during the digging process. A physical simulation experimental platform was established to verify the numerical simulation results, and research was carried out in terms of gas-containing gas-carrying dust disaster prevention and control, and ventilation optimization was carried out for this gas tunnel. The results showed that the maximum gas concentration in the tunnel face under press-in ventilation could be about 1%, and the local dust concentration can be up to 900 mg/m3. The gas mass fraction in localised areas of the tunnel exceeded 0.9% under mixed ventilation pressure-extraction ratios of 9:1 and 8:2. When the pressure to pumping ratio is 6:4, the dust was concentrated on the return side of the tunnel at a distance of 40-60 m from the head of the tunnel, and the highest local dust concentration reaches 700 mg/m3. When the pressure pumping ratio was 7:3, the dust pollution problem could be controlled more effectively, and at the same time, there was no higher concentration of gas gathering in the tunnel. A comprehensive analysis of the differences between dust and gas-enriched areas in gas tunnels could provide some guidance on the synergistic control of gas and dust in gas tunnels.

Where is the Dust Source of 2023 Several Severe Dust Events in China?

Abstract Northern China was hit by 13 unprecedented mega dust events in spring 2023. However, a comprehensive understanding of the relative contributions of potential dust sources to dust concentrations in China remains elusive, threatening air quality, damaging ecosystems, and further complicating dust forecasting and warning efforts. The impact of five major Asian dust sources on China and its downstream regions has been accurately quantified using the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem). Notably, dust particles originating from Mongolia play a crucial role in downstream air pollution. Approximately 56% (82.7 μg m−3) of the dust in North China originated from Mongolia, while Mongolia contributed nearly 51% (15.9 μg m−3) of the dust in the Korean Peninsula and surroundings. In southwest China, the prevalence of dust was predominantly attributable to sources within Inner Mongolia, China (46%). Due to geographical constraints, dust in the Tibetan Plateau mainly originated from dust sources in Xinjiang, China. Topographic blocking by the Tibetan Plateau and limitations on local dust emissions are further unfavorable to the long-distance transport of dust from South Asia to downstream regions. We also highlight the importance of variation in surface soil parameters in driving frequent dust events in spring 2023. Our findings emphasize the urgent need for collaborative research and policymaking to effectively address international dust disaster mitigation.

Global characterization of the early-season dust storm of Mars year 36

Dust storms are one of the most important dust transport mechanisms on Mars with significant impacts on temperatures and atmospheric dynamics. Regional storms generally occur during the spring and summer of the southern hemisphere, but some of them have been observed earlier in the year. While these early-season storms have been little studied over the years, their occurrence produces important dust liftings. Their study, both vertically and horizontally, allows us to understand the mechanism of dust distribution that initiates them and the areas in which their onset takes place. In this study we compare the dust patterns of the early storms of MY 29 and 36. In addition, we analyzed globally, in each longitude, the early storm that occurred in MY 36 which was the most intense detected in such an early time. It presents maximum values of column dust optical depth (CDOD) of 0.5 and temperatures of 197 K. We use dust and temperature measurements provided by the Mars Climate Sounder (MCS) instrument and images by the Mars Color Imager (MARCI), both on board Mars Reconnaissance Orbiter (MRO).

Long-range transport of coarse mineral dust: an evaluation of the Met Office Unified Model against aircraft observations

Abstract. Coarse mineral dust particles have been observed much further from the Sahara than expected based on theory. They have impacts different to finer particles on Earth's radiative budget, as well as carbon and hydrological cycles, though they tend to be under-represented in climate models. We use measurements of the full dust size distribution from aircraft campaigns over the Sahara, Canaries, Cabo Verde and Caribbean. We assess the observed and modelled dust size distribution over long-range transport at high vertical resolution using the Met Office Unified Model, which represents dust up to 63.2 µm diameter, greater than most climate models. We show that the model generally replicates the vertical distribution of the total dust mass but transports larger dust particles too low in the atmosphere. Importantly, coarse particles in the model are deposited too quickly, resulting in an underestimation of dust mass that is exacerbated with westwards transport; the 20–63 µm dust mass contribution between 2 and 3.7 km altitude is underestimated by factors of up to 11 in the Sahara, 140 in the Canaries and 240 in Cabo Verde. In the Caribbean, there is negligible modelled contribution of d > 20 µm particles to total mass, compared to 10 % in the observations. This work adds to the growing body of research that demonstrates the need for a process-based evaluation of climate model dust simulations to identify where improvements could be implemented.

Numerical Insights Into Gobi Wind‐Blown Sand: Deriving a Saltation Flux Scheme

AbstractDust emissions from land‐air interaction in arid and semi‐arid regions are crucial for predicting the global dust cycle. However, a comprehensive understanding of the complex physical mechanisms contributing to dust emissions from Gobi surfaces remains elusive. The expansive Gobi Desert, spanning northern China and Mongolia, significantly intensifies sandstorms in East Asia. Although researchers use models to study global dust transport, current models primarily depend on the aerodynamic roughness of the Gobi Desert. They often overlook the particle‐bed collision processes unique to the Gobi bed surface, which differ significantly from those of desert surfaces, thus compromising the accuracy of global dust cycle simulations. In this article, we establish a numerical model for drift sand in the Gobi based on existing theoretical and experimental studies. The model accurately simulates the wind‐blown sand in the Gobi and been used to investigate the saltation structure of sand transport. Simulations reveal an exponential decay of mass concentration with height, with an average attenuation rate of 0.00385 in the Gobi compared to 0.00806 in sandy deserts. The horizontal velocity of saltating particles increases with height following a power law. Through quantitative analysis of this structure, we present a saltation flux formula suitable for the Gobi.

Combined Impacts of Temperature, Sea Ice Coverage, and Mixing Ratios of Sea Spray and Dust on Cloud Phase Over the Arctic and Southern Oceans

AbstractWe analyze the importance of cloud top temperature, dust aerosol, sea salt aerosol, and sea ice cover for the thermodynamic phase of low‐level, mid‐level, and mid to low‐level clouds observed by CloudSat/CALIPSO over the Arctic and the Southern Ocean using an explainable machine learning technique. As expected, the cloud top temperature is found to be the most important parameter for determining cloud phase. The results show also a predictive power of sea salt and sea ice on the phase of low‐level clouds, while in mid‐level clouds dust shows predictive power. Over the Southern Ocean, strong zonal winds coincide with the aerosol distribution. While they can produce high mixing ratios of sea spray at lower levels, the strong zonal winds may prevent the pole‐ward transport of dust. Sea ice may prevent the release of sea salt aerosols and marine organic aerosols leading to higher liquid fractions in clouds over sea ice.

Sensitivity of Dust Deposition for Parabolic Trough Collector Mirrors to Different Meteorological Drivers

This abstract presents a soiling forecasting tool (SFT) for assessing the deposition of dust on parabolic trough collector (PTC) mirrors and its cumulative impact on their reflectivity. The SFT was developed by the University of Patras in the frame of the Smart Solar System (S3) project (Horizon 2020 Solar-Era.net). An initial version of the model was presented at the SolarPACES 2022 conference, where the adaptation of the model to dust transport phenomena was demonstrated. The subsequent step in the evolution of the algorithm concerned the calibration of the SFT under different atmospheric conditions. In addition, the model was modified to incorporate meteorological and aerosol forecast data as inputs. The atmospheric predictions of dust and aerosol optical depth are from the global atmospheric forecasts of the Copernicus Atmosphere Monitoring Service. Regarding the meteorological data, three independent sources are used. Those are the Norwegian Meteorological Institute's meteorological forecasts (YR), the METAR meteorological observations from the closest airport, and lastly, the data from the automatic weather station at the location of the PTC system at the KEAN Soft Drinks Ltd factory in Limassol, Cyprus. The aim of this paper is to assess the impact of the three distinct meteorological input sources on the modelled reflectivity and its comparison to measurements taken during the experimental campaign.

Origin of transition disk cavities: Pebble-accreting protoplanets vs super-Jupiters

Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of gas-giant-hosting systems. Therefore, we investigate whether a sequence of low-mass planets can create the appearance of cavities in the dust disk. We evolve the disks with low-mass growing embryos in combination with 1D dust transport and 3D pebble accretion, to investigate the reduction of the pebble flux at the embryos' orbits. We vary the planet and disk properties to understand the resulting dust profile. We find that multiple pebble-accreting planets can efficiently decrease the dust surface density, resulting in dust cavities consistent with transition disks. The number of low-mass planets necessary to sweep up all pebbles decreases with decreasing turbulent strength and is preferred when the dust Stokes number is $10^ $. Compared to dust rings caused by pressure bumps, those by efficient pebble accretion exhibit more extended outer edges. We also highlight the observational reflections: the transition disks with rings featuring extended outer edges tend to have a large gas content in the dust cavities and rather high stellar accretion rates. We propose that planet-hosting transition disks consist of two groups. In Group A disks, planets have evolved into gas giants, opening deep gaps in the gas disk. Pebbles concentrate in pressure maxima, forming dust rings. In Group B, multiple Neptunes (unable to open deep gas gaps) accrete incoming pebbles, causing the appearance of inner dust cavities and distinct ring-like structures near planet orbits. The morphological discrepancy of these rings may aid in distinguishing between the two groups using high-resolution ALMA observations.

Impact of Asian Dust on Cirrus Formation Over the Central Pacific: CALIOP‐ and CloudSat‐Observation‐Based Case Studies

AbstractCirrus clouds are of great importance to the global climate, with their net radiative forcing strongly dependent on the microphysical properties that are related to the ice‐nucleating regime. However, the influence of long‐range transport of dust on primary ice formation in cirrus clouds is limitedly understood, specifically over the clean remote ocean regions. Here, two case studies show that transpacific Asian dust can impact the ice formation of cirrus clouds over the central Pacific based on Cloud‐Aerosol Lidar with Orthogonal Polarization and Cloud Profiling Radar (CPR, CloudSat) observations. One case shows a well‐developed horizontally extended cirrus embedded in a pure dust layer, with an average dust‐related ice‐nucleating particle concentration (INPC) of 7 L−1 and 96 L−1 for an ice saturation ratio Si of 1.15 and 1.25, respectively; ice crystal number concentration (ICNC) with diameters >25 and 100 μm (denoted as nice,25 μm and nice,100 μm) are 64 L−1 and 7 L−1, respectively. Another case shows that cirrus clouds with a much smaller horizontal extent appeared in the vicinity of polluted dust, with an average INPC of 42–310 L−1 for the typical higher Si of 1.25–1.35 by considering a tenfold reduction of the ice nucleation efficiency of ice crystals; nice,25 μm and nice,100 μm are 168 L−1 and 20 L−1, respectively. The estimated INPC and ICNC values suggest the dominance of ice formation by dust‐induced heterogeneous nucleation, proving that the long‐range transport of dust toward the upper troposphere and the potential influence on cirrus formation over the central Pacific should be well considered in atmospheric models.

Long-Range Atmospheric Transport of Dust from the Caspian Sea Region to the Arctic Zone of the European Part of Russia in December 2023

Long-Range Atmospheric Transport of Dust from the Caspian Sea Region to the Arctic Zone of the European Part of Russia in December 2023

A Quick Look at the Atmospheric Circulation Leading to Extreme Weather Phenomena on a Continental Scale

The study delves into the primary large-scale atmospheric features contributing to extreme weather events across Europe during early September 2023. The period was examined using a dataset composed by the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and satellite imagery. In early September 2023, an omega blocking pattern led to the development of a low-pressure system over the Iberian Peninsula producing heavy precipitation and flooding over Spain and acting as a mechanism for a mineral dust outbreak. A second low-pressure system developed over Greece. Extreme precipitation was recorded across Greece, Turkey, and Bulgaria as the system gradually shifted southward over the Mediterranean. The system earned the name “Storm Daniel” as it acquired subtropical characteristics. It caused floods over Libya and its associated circulation favoured the transport of mineral dust over Northern Egypt as it moved eastward. Meanwhile, the high-pressure blocking system associated with the omega pattern induced heatwave temperatures in countries further north. This period was compared with the large-scale circulation observed in mid-September 2020, when severe weather also affected the Mediterranean region. However, the weather systems were not directly connected by the large-scale circulation, as shown in September 2023. Although mesoscale conditions are relevant to formation and intensification of some atmospheric phenomena, the establishment of an omega blocking pattern in early September 2023 showed how large-scale atmospheric dynamics can produce abnormal weather conditions on a continental scale over several days.

The First Validation of Aerosol Optical Parameters Retrieved from the Terrestrial Ecosystem Carbon Inventory Satellite (TECIS) and Its Application

In August 2022, China successfully launched the Terrestrial Ecosystem Carbon Inventory Satellite (TECIS). The primary payload of this satellite is an onboard multi-beam lidar system, which is capable of observing aerosol optical parameters on a global scale. This pioneering study used the Fernald forward integration method to retrieve aerosol optical parameters based on the Level 2 data of the TECIS, including the aerosol depolarization ratio, aerosol backscatter coefficient, aerosol extinction coefficient, and aerosol optical depth (AOD). The validation of the TECIS-retrieved aerosol optical parameters was conducted using CALIPSO Level 1 and Level 2 data, with relative errors within 30%. A comparison of the AOD retrieved from the TECIS with the AERONET and MODIS AOD products yielded correlation coefficients greater than 0.7 and 0.6, respectively. The relative error of aerosol optical parameter profiles compared with ground-based measurements for CALIPSO was within 40%. Additionally, the correlation coefficients R2 with MODIS and AERONET AOD were approximately between 0.5 and 0.7, indicating the high accuracy of TECIS retrievals. Utilizing the TECIS retrieval results, combined with ground air quality monitoring data and HYSPLIT outcomes, a typical dust transport event was analyzed from 2 to 7 April 2023. The results indicate that dust was transported from the Taklamakan Desert in Xinjiang, China, to Henan and Anhui provinces, with a gradual decrease in the aerosol depolarization ratio and backscatter coefficient during the transport process, causing varying degrees of pollution in the downstream regions. This research verifies the accuracy of the retrieval algorithm through multi-source data comparison and demonstrates the potential application of the TECIS in the field of aerosol science for the first time. It enables the fine-scale regional monitoring of atmospheric aerosols and provides reliable data support for the three-dimensional distribution of global aerosols and related scientific applications.

An OSL-dated, stacked Holocene dust mass accumulation rate record on the Chinese Loess Plateau and its implications for Northern Hemisphere dust activity

Accurate reconstruction of geological dust activity is crucial for understanding past climate change and its interaction with dust cycle. Loess on the Chinese Loess Plateau (CLP) is an ideal and sensitive material for revisiting past dust activity. Previously, the changes in the dust mass accumulation rate (MAR) over various time scales were widely established on the CLP. However, few absolutely dated dust records have been obtained and synthesized for the Holocene. This study addresses this gap by compiling 23 optically stimulated luminescence-dated Holocene loess sections across the CLP. We developed a high-quality chronology via Bayesian age-depth modeling and derived a MAR record for each section. Then, we obtained a mean MAR record for the CLP by stacking individual records. We propose that, in contrast to site-specific MARs, stacked MARs represent the mean dust accumulation conditions for the entire CLP and can be used to track relatively large-scale dust activity and climate change. The stacked MAR record suggests a moderate weakening trend of dust accumulation from ∼11.5 to 7.5 thousand years ago (ka BP), followed by a pronounced strengthening trend from ∼7.5 to 3.0 ka BP. A comparison with other regional dust records reveals a shift in dust activity at ∼8–6 ka BP in northern China and western Mongolia. We argue that the East Asian winter and summer monsoons jointly contributed to Holocene mean dust MAR variations on the CLP by changing dust transport wind energy and dust source aridity, respectively. A comparison of Holocene dust records in Asia with those in the northwestern Pacific Ocean and Greenland suggests asynchronous variations in dust activity between proximal and distal Asia-sourced dust deposition. This is because, unlike proximal deposition, distal deposition can be controlled not only by the dust source conditions but also by the intensity and the position of the Westerlies.

Spatiotemporal spreading characteristics of dust aerosols by coal mining machine cutting and "partition/multi-level composite field" atomization dust purification technology

To locally atomize the spatial confinement of primary dust generated by the shearer cut-off, the CFD-DPM mathematical model was used to simulate and analyze the wind-borne dust transport law, which resulted in the heavily polluted area of primary dust. A multi-level and multi-dimensional coal machine spray system was developed for the polluted area, its atomization effect was verified by using the TAB breakup model. The results show that the heavily polluted area of primary dust is mainly concentrated in the position of fully mechanized mining face Z=24–39 m area of shearer, and the average concentration is 738.2 mg/m³. The average concentration of droplets generated by the multi-level and multi-dimensional shearer spray system at the shearer drum is 0.66 kg/m³, with a percentage of droplets with particle size between 40 and 160 μm exceeding 85 %. The coverage rate of the shearer drum is 95 %. The relationship between droplet concentration and time is consistent with the Boltzmann function fitting model. Following the implementation of the multi-level and multi-dimensional coal machine spray system in the field, it was observed that the average reduction in dust levels was 90.9 % for total dust and 85.7 % for exhaled dust in the synthesized mining face.

Evaluating and comparison of WRF-chem model configurations for wind field impact on the April 2022 dust episode in western Iran

Accurate estimation of wind direction and speed is essential for enhancing the simulation and prediction of dust storms. Being highly susceptible to dust storms, Western Iran necessitates a detailed evaluation of dust concentration and wind fields. This study employs the WRF-Chem model to simulate these parameters over the period from April 7 to 26, 2022. Four different model configurations were tested, involving the Yonsei University (YSU) and Mellor-Yamada-Janjic (MYJ) boundary layer schemes, as well as the Lin and WRF Single-Moment 6-Class (WSM6) microphysics schemes. The results indicate that during the selected period, different synoptic systems led to the release of dust from Iraq and Saudi Arabia and its transport to western Iran. The mid-level southerly and southwesterly wind directions have a significant impact on dust transport to the northwestern regions of Iran by high and complex mountainous terrain. The horizontal and vertical distribution of simulated dust demonstrates good agreement with TERRA satellite imagery, MERRA-2 dust surface concentration, and CALIPSO, respectively. The daily dust concentration of the WRF-Chem model has a correlation of −0.32 to −0.96 with visibility and 0.68 to 0.86 with MERRA-2 data in Western Iran. The simulated dust concentration relation with visibility and AERONET AOD (Aerosol Optical Depth at 500 nm) was calculated at −0.78 and 0.29, respectively in Zanjan station. The horizontal and vertical distribution, temporal series, and statistical indices of the wind field show that the WRF-Chem model performs well in the Iran West boundary, especially in the west and northwest, where the 10-m wind speed increased to 14 m s−1. The boundary layer scheme in the WRF-Chem model has a more significant impact than the microphysics scheme in simulated 10-m wind speed and dust concentration. The final result shows that the combination of the YSU boundary layer and WSM6 microphysics schemes performs very well in simulating wind fields and dust in western Iran under various weather conditions.

The source, transport, deposition and direct radiative effect of mineral dust over western China: A modeling study of July 2022 with focus on the Tibetan Plateau

A Regional Air Quality Model System (RAQMS) driven by WRF was applied to explore the emission, transport, deposition, and direct radiative effect of mineral dust over western China in July 2022, with focus on the Tibetan Plateau (TP). Model validation against ground and satellite observations demonstrated the model reproduced meteorological variables, PM10 concentration, aerosol optical depth (AOD), and extinction coefficients in the vertical reasonably well. There was a dust event during 3–7 July 2022, which was originated from the Taklimakan Desert (TKD) and affected eastern and central TP under anticyclonic flows, resulting in the maximum hourly PM10 concentration exceeding 50 μg m−3 in Lhasa. Shortwave radiation was reduced considerably by dust aerosols over eastern TP, with the maximum decrease in daytime mean shortwave radiation reaching 30 W m−2 around Nyingchi on 5 July. Anthropogenic aerosols dominated PM10 mass in the capital cities of western China (54–67 %), while dust aerosols were dominant in the cities near the deserts. During this dust event, dust aerosols from TKD and Qaidam Desert (QDD) significantly influenced eastern TP, with dust contributions to PM10 mass concentration of 52 %, 76 % and 69 %, respectively, in Chamdo, Lhasa and Nyingzhi, respectively. The total dust emission in western China was about 10.6 Tg in July 2022, with the largest contribution from TKD (63.5 %), followed by Gobi Desert (GB) (26 %). The total deposition of dust was estimated to be 6.2 Tg, in which TKD and GB contributed 66 % and 22 %, respectively. During the study period, about 418 Gg dust aerosols were deposited on TP, 49 % of which was from TKD and 25 % from QDD. Foreign dust sources contributed approximately 7 % and 9 % to dust concentration and total deposition over TP, respectively. Over southern TP, the source contribution to dust deposition was estimated to be 42 %, 24 % and 21 % from TKD, foreign sources and QDD, respectively, suggesting potentially important impact of long-range transboundary dust transport on deposition, surface albedo and climate over TP.

Characteristics of the Aeolian Sediments Transported Above a Gobi Surface

AbstractGobi’s (gravel deserts) are one of the largest dust sources in northern China. Previous studies indicated that sand transport processes above the surface differed between Gobi and sand surfaces. However, the sand transport rate and related dust emission processes above Gobi (gravel) surfaces are still poorly understood. In this field study, we quantified this transport to provide important support for parameterizing Aeolian sediment transport models and clarifying the relationship between dust emission and transport. Threshold wind velocity can reach 0.38 ± 0.04 (mean ± SD) m s−1 above Gobi surfaces. Compared to the most commonly used sand‐transport models, we found that the Lettau and Lettau sediment transport model can be used to calculate horizontal sediment transport above a Gobi surface. The relationship between the vertical sediment transport (Fs) and shear velocity could be expressed using a power function. Although the horizontal sand transport and vertical flux (Q and Fs, respectively) above Gobi surfaces can be expressed similarly to previous results (i.e., using similar equation forms), the equation coefficients were much larger for the Gobi surface than for a shifting sand surface; that is, sediment transport was higher above the Gobi surface. This difference resulted from the larger sand transport rate and saltation height above the Gobi surface, and the larger transport and higher saltation height were related to the larger sand transport height and higher content of coarse sand transported above the Gobi surface.

Controls on the stable Mo isotopic composition of inner-continental precipitation

The molybdenum (Mo) isotope budget of the surface environment has been well characterized in recent decades, facilitating accurate mass balance modeling of the ancient redox-driven Mo cycle. One yet unresolved component is the range of possible processes and sources that result in isotopically heavy river waters relative to continental sources. Following a recent hypothesis that isotopically heavy δ98Mo of precipitation may control the final δ98Mo of river water relative to its continental source bedrock, we investigated the δ98Mo composition of 19 snow samples from three locations in Central Europe: the Swiss Alps (“Alpine” samples) from the Hochalpine Forschungsstation Jungfraujoch (HFSJ) in both summer and winter, the Swiss Jura Mountains in winter and the French Vosges Mountains in winter. Stream waters from two snowmelt-fed streams were additionally collected from the Alpine site. Snow sample δ98Mo compositions were highly variable, ranging from −0.03 to +1.93 ‰, with no clear mixing trends indicating complex sources, source pathways, or post-depositional processing. Only the winter snow samples from the high-altitude HFSJ site had δ98Mo values consistently heavier than typical continental crust. The δ98Mo results were coupled with radiogenic Sr isotopic, major ion, and trace element compositions as tracers for three major sources of airborne ion inputs: sea salt, mineral dust, and anthropogenic aerosols. We found that the most likely source of Mo to precipitation in the lower elevation Vosges and Jura Mountains samples was isotopically light soil mineral dust, which reflected the underlying bedrock sources, with a likely additional anthropogenic component. The isotopically heavy winter snow samples at the elevated HFSJ site were attributed to a higher input of carbonate mineral dust from long-distance transport of carbonate-rich Saharan dust, which was overwritten in the summer by an influx of low elevation sources transported upwards during higher vertical thermal mixing. Finally, we concluded that precipitation has a negligible direct effect on the overall Mo content and isotopic composition of inner continental European streams and rivers relative to other sources, such as bedrock weathering. Future time-series studies may augment these conclusions to show possible heterogeneity of precipitation as well as the addition of sample sites closer to marine sources, where a larger flux of isotopically heavy marine aerosols to streams might be expected.