Suspended Samples Research Articles

Pedo-geochemical background and sediment contamination of metal(loid)s in the old mining-district of Salsigne (Orbiel valley, France)

The mining district of Salsigne in the Orbiel valley (Aude, France) was at one time the first gold mine in Europe and the first arsenic mine in the world. However, no scientific studies have evaluated the magnitude of its environmental impact. In this study, the pedo-geochemical background (PGB) was determined for 14 metal (loid) elements, including As. It appears that the PGB values for As and Sb are relatively high with 44±12 and 0.9±1.2 mg kg−1, respectively, because of the geological particularities of this area. In a second step, these PGB values (normalized with Ti concentrations) were used as local references to determine enrichment factors (EFs) of bed river sediments for the Orbiel River and two of its major tributaries (Gresillou and Russec rivers) collected between November 2018 and July 2020. Results showed that riverine sediments are contaminated by past mining activity and/or current storage areas. If we except the major elements (Fe, Ti and at a lesser extent Mn), we observed that As, Cu, Sb, Pb present the highest concentrations relative to the remaining elements (Cd, Co, V, Ni and Cr). In the case of As, EFs can reach 74 in the Orbiel River, 1000 in the Gresillou River and 27 in the Russec River. These calculations were also performed for sediments transported by the extreme flood of October 14, 2018, that killed 15 people and potentially remobilized contamination in the valley. We observed that the As concentrations of suspended samples from Grésillou and Russec rivers have reached 870 mg kg−1. Finally, the As concentrations measured in the river sediments of this valley are of the same order of magnitude than those published in the literature for environments strongly impacted by mining or mineral processing activities.

Stable Mercury Isotopes Revealing Photochemical Processes in the Marine Boundary Layer

AbstractThe marine boundary layer (MBL) is an important transportation and reaction zone of atmospheric mercury on Earth. However, the transformation mechanisms of Hg in the MBL remain unclear. In this study, total suspended particle samples were collected in the MBL during two cruises, and the levels of particulate bound mercury (PBM) and mercury isotopes were analyzed. The results showed that (a) continental anthropogenic emissions have limited contribution to PBM in the MBL; (b) PBM likely experienced the oxidation of Hg0 by Br radicals and subsequent adsorption of Hg2+ on to particulate surfaces, as inferred from the significant negative δ202Hg; (c) the Δ199Hg/Δ201Hg ratio of ∼1.0 suggests that PBM underwent photoreduction, which was influenced by organic compounds, and the contribution of photoreduction to the extent of odd‐number mass‐independent fractionation in PBM in the MBL was more significant than that of oxidation triggered by Br atoms. This study provides insights into the photochemical processes influencing mercury in the MBL.

Isotopic compositions and geological significance of sediments from the Heihe River, North Qilian Orogen, NW China

Strontium (Sr), neodymium (Nd), and hafnium (Hf) isotopic analyses of different size-fractions of sediments collected from the Heihe River in the North Qilian Orogen (NQO) were carried out to trace the sediment sources and to determine the relationships between the Sr–Nd–Hf isotopic behaviors, and the grain-size and hydraulic sorting effects during fluvial transport. Our results demonstrate that the sand and suspended load samples collected from the same site have different Nd isotopic compositions, while their 87Sr/86Sr ratios are only slightly different. These features indicate that contributions to the sediments from different sources with different grain sizes vary greatly. Coarse-grained sand may more intuitively reflect the variations in local sources than the suspended load. The suspended load samples are distributed along the Clay Array on the ԐHf vs. ԐNd diagram due to zircon sorting. A similar NdHf decoupling phenomenon is widespread in the global oceans and large river systems, indicating that the NdHf isotopic behavior depends on the hydrodynamic sorting of minerals during fluvial transport. Moreover, the crustal accretion of the NQO from the depleted mantle occurred in the Proterozoic based on the constraints provided by the TDM values of the river sediments. The Nd isotopic compositional characteristics of the river sediments indicate that the NQO has an affinity with the Yangtze Craton. The determination of the basement tectonic affinity of the NQO significantly contributes to our understanding of the Neoproterozoic evolution of the Gondwana continental margin.

Biomass Burning is an Important Source of Organic Aerosols in Interior Alaska

AbstractBiomass burning (BB) affects air quality, the global cycling of carbon, climate, and human health. Intensive BB activities occur throughout the year due to wildfires and domestic wood burning in Fairbanks. We collected total suspended particle samples from the air in Fairbanks from June 2008 to June 2009. Here, we report seasonal variations in the molecular composition of organic aerosols and its BB contributions in Fairbanks. Levoglucosan is the dominant BB tracer (annual mean 67 ± 77 ng m−3), showing a winter maximum (145 ± 47 ng m−3) and spring minimum (12 ± 12 ng m−3). Levoglucosan showed significant correlations (p < 0.001) with organic carbon (OC), water‐soluble organic carbon (WSOC), and PM2.5, indicating a significant contribution of BB to hazes in Fairbanks. However, no correlation exists between levoglucosan and non‐sea salt potassium (nss‐K+), which has been proposed as a BB tracer. We hypothesize that nss‐K+ is removed by deposition on the inner surfaces of woodstove chimneys. Levoglucosan contributes 3.6% to OC and 6.3% to WSOC in winter, indicating that BB significantly affects carbonaceous aerosols in central Alaska. Moreover, positive matrix factorization analysis demonstrates that BB is an important source (47.5%) of Fairbanks year‐round aerosols. We conclude that domestic wood burning is an important source of atmospheric particles that impact the air quality of Fairbanks, especially in winter. We presumed that Fairbanks BB products might be transported to the remote Arctic, potentially affecting the chemical composition of Arctic aerosols. These findings will be useful to better understand the seasonal influence of BB on the Arctic and subarctic aerosols.

Exploring the effect of ultrasonic power, frequency, and load toward remediation of oil-contaminated beach and oilfield sands using ANOVA

Despite the potential shown by previous investigations on the use of ultrasound for the remediation of oil-contaminated sand, the influence and interactions among ultrasonic parameters and oily sand are unclear, leading to possible ineffective treatment and high-power consumption. In order to improve the process efficiency, this work analyzes the effects of ultrasonic power, frequency, and load toward the cleaning of crude oil-contaminated sand, using two different sample positions and sand types. Crude oil-contaminated beach sand and produced sand from offshore oil well were used as samples. They were cleaned in custom-made ultrasonic bath reactor for 10 min with power from 30 to 120 W, frequency covering 25-60 kHz, and sand load of 10-100 g. With experimental design consisting multiple factors and levels, the interactions between factors in all possible combinations were determined using ANOVA (n = 210). From p-value based at 95% confidence interval and extensive F test, the three most significant factors were the sand type, the ultrasonic frequency, and the interaction between sand type and frequency. The best setting for suspended samples involved high frequency of 60 kHz, whereas bottom samples preferred low frequency at 28 kHz. This finding was justified when the acoustic pressure attenuation, standing wave pattern, and surface pitting/cracking were found in correlation with the cleaning results. Overall, the maximum treatment under ultrasonic bath solely gained around 60%, improvable by hybrid cleaning with other techniques such as chemical, biological, mechanical, and thermal.

Distribution characteristics and correlation of heavy metals in soil and total suspended particles of Urumqi City

In this study, soil and total suspended particles samples (TSP) were collected from different soil layers in four functional areas of Urumqi City, Northwest China, and electric heating plate digestion and inductively coupled plasma-optical emission spectrometry (ICP-OES) were used to determine the mass fractions and spatial distribution of six heavy metals. The aim was to determine the effects of human activities on the urban soil and atmosphere and provide a theoretical basis for environmental protection and management in Urumqi. The results showed that: (1) The average mass fractions of Cr, Cu, Mn, Ni, Pb, and Zn were 129.24, 42.445, 691.70, 48.705, 31.36, and 126.5 mg kg−1, respectively; the average mass fractions of Cr, Zn, Ni, and Cu exceeded the limit of the national soil standard; the pollution indexes were 1.44, 1.27, 1.22, and 1.21, respectively. (2) The heavy metal contents of surface soils are higher in the industrial, traffic, and cultural and educational areas than in the clean park area; in the vertical section, the heavy metals in the industrial, traffic, and culture and education areas show a weak epimerism, and the soil in the park area shows a good primitivity. (3) The ratios of the highest to lowest concentration of heavy metals in TSP can be ranked as follows: Pb (9.75) > Mn (2) > Ni (1.48) > Cr (1.36) > Cu (1.32) > Zn (1.17). (4) The correlations of heavy metals between the soil and TSP are significant, indicating that dry and wet deposition significantly affect the heavy metal content of the soil.

Thermal Relaxation in Metal Films Limited by Diffuson Lattice Excitations of Amorphous Substrates

Here we examine the role of the amorphous insulating substrate in the thermal relaxation in thin NbN, InO$_x$, and Au/Ni films at temperatures above 5 K. The studied samples are made up of metal bridges on an amorphous insulating layer lying on or suspended above a crystalline substrate. Noise thermometry was used to measure the electron temperature $T_e$ of the films as a function of Joule power per unit of area $P_{2D}$. In all samples, we observe the dependence $P_{2D}\propto T_e^n$ with the exponent $n\simeq 2$, which is inconsistent with both electron-phonon coupling and Kapitza thermal resistance. In suspended samples, the functional dependence of $P_{2D}(T_e)$ on the length of the amorphous insulating layer is consistent with the linear $T$-dependence of the thermal conductivity, which is related to lattice excitations (diffusons) for the phonon mean free path smaller than the dominant phonon wavelength. Our findings are important for understanding the operation of devices embedded in amorphous dielectrics.

Ice-nucleating particles in precipitation samples from the Texas Panhandle

Abstract. Ice-nucleating particles (INPs) influence the formation of ice crystals in clouds and many types of precipitation. This study reports unique properties of INPs collected from 42 precipitation samples in the Texas Panhandle region from June 2018 to July 2019. We used a cold stage instrument called the West Texas Cryogenic Refrigerator Applied to Freezing Test system to estimate INP concentrations per unit volume of air (nINP) through immersion freezing in our precipitation samples with our detection capability of > 0.006 INP L−1. A disdrometer was used for two purposes: (1) to characterize the ground-level precipitation type and (2) to measure the precipitation intensity as well as size of precipitating particles at the ground level during each precipitation event. While no clear seasonal variations of nINP values were apparent, the analysis of yearlong ground-level precipitation observation as well as INPs in the precipitation samples showed some INP variations, e.g., the highest and lowest nINP values at −25 ∘C both in the summer for hail-involved severe thunderstorm samples (3.0 to 1130 INP L−1), followed by the second lowest at the same temperature from one of our snow samples collected during the winter (3.2 INP L−1). Furthermore, we conducted bacteria community analyses using a subset of our precipitation samples to examine the presence of known biological INPs. In parallel, we also performed metagenomics characterization of the bacterial microbiome in suspended ambient dust samples collected at commercial open-lot livestock facilities (cattle feedyards hereafter) in the Texas Panhandle (i.e., the northernmost counties of Texas, also known as “West Texas”) to ascertain whether local cattle feedyards can act as a source of bioaerosol particles and/or INPs found in the precipitation samples. Some key bacterial phyla present in cattle feedyard samples appeared in precipitation samples. However, no known ice nucleation active species were detected in our samples. Overall, our results showed that cumulative nINP in our precipitation samples below −20 ∘C could be high in the samples collected while observing > 10 mm h−1 precipitation with notably large hydrometeor sizes and an implication of cattle feedyard bacteria inclusion.

Effect of easy axis alignment on dynamic magnetization of immobilized and suspended magnetic nanoparticles

Magnetic nanoparticles (MNPs) have been widely studied for use in biomedical applications such as magnetic particle imaging and magnetic hyperthermia. We studied the effect of easy axis alignment on dynamic magnetization of both immobilized and suspended MNPs. For immobilized samples, easy axes of magnetization were aligned by applying a dc field during immobilization. For suspended samples, the applied ac field was set so that the alignment of the easy axes was caused by the ac field. Magnetization (M–H) curves of MNPs with different degrees of easy axis alignment were measured with an applied ac field. We found that the easy axis alignment of MNPs considerably affects their M–H curve and harmonic spectra, which indicates the importance of this alignment for their biomedical applications. The experimental results were quantitatively explained with numerical simulation that took account of easy axis alignment and core size distribution in the sample. We can express the degree of easy axis alignment using a distribution function of the easy axis angle for both immobilized and suspended cases. The distribution function will be useful for quantitatively evaluating MNP performance in biomedical applications.

Impacts of salinity on the dynamics of fine particles and their associated metals during stormwater management

Abstract Elevated salinity in stormwater runoff may adversely impact the efficacy of stormwater management practices (SMPs) in intercepting contaminants via changing the stability of suspended particles as well as the fate and transport of their associated contaminants. Field-collected soil samples were employed to characterize the impacts of salinity on suspended particles. Varying concentrations (10 mM to 1000 mM) of chloride salts (NaCl, KCl, MgCl2, and CaCl2) were applied to suspended particle samples to assess the changes in particle size distribution (PSD) and metal desorption from particles. The concentration of fine particles (d

Properties of single- and multi-core magnetic nanoparticles assessed by magnetic susceptibility measurements

Characterization of structural and magnetic properties of MNP ensembles is crucial in tailoring their performance for biomedical applications. In this work, we evaluate the size distribution of magnetic cores in single- and multi-core nanoparticles in water suspension using transmission electron microscopy (TEM) and static magnetization curve, with the geometrical core size ranges from 8.3 to 40.2 nm. A reasonable core size derived from the magnetization curve is obtained in comparison to the geometrical size from TEM image. The magnetic moment distribution possibly reveals that the reduction of effective magnetic core size is due to the magnetization degradation in cores. The hydrodynamic size and average anisotropy energy ratio obtained from the AC susceptibility response of MNPs from 5 Hz to 100 kHz are also evaluated. The complex distribution of relaxation time is constructed by applying a non-negative least square method to an AC susceptibility model that incorporates the inter- and intra-potential-well contributions. It is found that a log-normal distribution might not be adequate to represent the hydrodynamic size distribution reconstructed from the AC susceptibility responses of the suspended samples. It is demonstrated that the AC susceptibility model used in this study can be used to fairly estimate the average anisotropy energy ratio for MNP ensembles dominated by thermally blocked particles. Moreover, it can be suggested that besides the geometrical core size, the degree of core aggregation also plays an important role in determining the anisotropy energy ratio and effective magnetic moment.

PCBs, HCB and PAHs in the seawater of Arctic fjords – Distribution, sources and risk assessment

In the present study, we examine contamination with PCBs, HCB and PAHs in the seawater of Arctic fjords (Hornsund, Kongsfjorden and Adventfjorden) which differ in environmental conditions and are particularly sensitive to climate change. We also investigate how the melting glaciers and ocean currents may affect the distribution and fate of target compounds in the seawater column in the fjords. The ∑7 PCB, HCB and ∑12 PAH concentrations in seawater ranged from, respectively: 0.002 to 41.2 ng/L; from LOQ to 233 ng/L; and from 0.196 to 311 ng/L. The research indicates that the concentrations of contaminants detected in Arctic fjords depend on the physicochemical properties of these compounds, local human activity and occurrence of glacier meltwaters. Detected HCB and PAH concentrations in most of the seawater samples were at levels classified as harmless, however in 30 out of 80 analysed suspended particulate matter samples some compounds were present at toxic levels.

Effect of Carcass Electrical Stimulation and Suspension Methods on Meat Quality Characteristics of Longissimus lumborum of Young Buffalo (Bubalus bubalis) Bulls.

Buffalo animals are slaughtered at their early age and carcasses are chilled rapidly which deteriorates its meat quality and decreases the consumer likeliness of buffalo meat. This study investigated the appropriate methods to prevent the quality deterioration of buffalo meat during chilling. Twenty four 18-mon-old buffalo bulls were slaughtered, electrically stimulated and suspended either by hip or achilles tendon. After 24 h postmortem, meat quality characteristics were recorded. Results showed that electrical stimulation (ES) led to rapid decline of carcass pH compared to non-ES method (p<0.05). Furthermore, electrically stimulated meat presented lower shear force accompanied with the higher CIE L*, a*, and b* values (p<0.05). Suspension methods only affect the meat shear values and were lowered in hip suspended samples. It can be concluded that ES combined with hip suspension can be adopted to prevent the meat quality deterioration of young buffalo bulls during postmortem storage.

Algal nutrient limitation and metal uptake experiment in the Åkerberg pit lake, northern Sweden

A microcosm nutrient limitation experiment was conducted in the Åkerberg pit lake, located in Västerbotten, northern Sweden, in the summer of 2018. The microcosms were fertilized with N, P and N and P in combination. Chlorophyll-a concentrations were used to estimate algal growth. Filtered and suspended metal concentrations of the microcosms were compared to see if an increase in algal growth would lead to higher metal uptake. The results show that the microcosms fertilized with N and P had the highest chlorophyll-a concentrations (3–3.4 μg/l). This corresponds to an increase of 9.5–11 times compared to the initial chlorophyll-a concentrations, suggesting that the lake is nutrient poor with regards to both N and P. An increase of the metal concentration in the suspended particulate samples (>0.2 μm) of the microcosms fertilized with both N and P could be observed particularly for the mining-related metals Cd, Co, Ni, and Zn. The uptake of these metals amounted to 2.5–20% (Cd), 2.6–14% (Co), 0.87–1.8% (Ni), and 19–64% (Zn) of their filtered concentrations (<0.2 μm).

Successful start-up of anammox process from activated sludge and anaerobic sludge in a sequencing batch reactor using an unconventional strategy

In this study, the start-up of anammox in a sequencing batch reactor (SBR) using conventional activated and anaerobic sludge in 1:1 ratio (v/v) as inoculum was achieved using an unconventional strategy. The ratio of NH4+-N to NO2−–N in the influent was not maintained as per the stoichiometry (1:1.32) of anammox and rather varied depending on the effluent characteristics. Nitrite was omitted during its accumulation period to avoid its toxicity during the start-up phase. The SBR having polyurethane foam impregnated with activated carbon (Levapor® carriers) was operated for 212 d (temperature, 37 °C; influent pH, 8). Anammox process was started up in ~95 d with 85% average total nitrogen (TN) removal. Thereafter, the reactor showed average TN removal efficiency of 85% and exhibited an average NH4+-N and NO2−–N removals of 99.9% each at maximum influent NH4+-N and NO2−–N concentrations of 200 mg L−1 and 264 mg L−1, respectively. The 16S rRNA gene amplicon sequencing analysis of suspended sludge samples (100 d, 150 d, and 186 d) from the reactor revealed the dominance of infrequently occurring anammox bacterial genus Candidatus Jettenia in the reactor. The phyla Chloroflexi, Proteobacteria, and Bacteriodetes were also detected in the reactor.

Temperature- and power-dependent phonon properties of suspended few layers of tungsten diselenide

In this study we report the temperature- and laser power-dependence of the out-of-plane A1g Raman mode of mechanically exfoliated few-layered WSe2 suspended on Si3N4 holes. The A1g phonon frequency is red-shifted for a temperature in the range 77–548 K, with first-order temperature coefficients estimated to be −0.0083 and −0.0079 cm−1/K for suspended four- and six-layer WSe2, respectively. The laser power-dependence of suspended four-layer WSe2 sample is estimated to be −0.0079 cm−1/μW and no shift is observed for six-layer WSe2. By using the laser power-dependence of the suspended four layers WSe2 and the 1D Balandin's approach, we calculate the in-plane thermal conductivity of WSe2 at room temperature to be ∼57.7 W/m K.

Integrating Suspended Sediment Flux in Large Alluvial River Channels: Application of a Synoptic Rouse‐Based Model to the Irrawaddy and Salween Rivers

AbstractA large portion of freshwater and sediment is exported to the ocean by a small number of major rivers. Many of these megarivers are subject to substantial anthropogenic pressures, which are having a major impact on water and sediment delivery to deltaic ecosystems. Due to hydrodynamic sorting, sediment grain size and composition vary strongly with depth and across the channel in large rivers, complicating flux quantification. To account for this, we modified a semi‐empirical Rouse model, synoptically predicting sediment concentration, grain‐size distribution, and organic carbon (%OC) concentration with depth and across the river channel. Using suspended sediment depth samples and flow velocity data, we applied this model to calculate sediment fluxes of the Irrawaddy (Ayeyarwady) and the Salween (Thanlwin), the last two free‐flowing megarivers in Southeast Asia. Deriving sediment‐discharge rating curves, we calculated an annual sediment flux of Mt/year for the Irrawaddy and Mt/year for the Salween, together exporting 46% as much sediment as the Ganges‐Brahmaputra system. The mean flux‐weighted sediment exported by the Irrawaddy is significantly coarser (D84 = 193 ± 13 μm) and OC‐poorer (0.29 ± 0.08 wt%) compared to the Salween (112 ± 27 μm and 0.59 ± 0.16 wt%, respectively). Both rivers export similar amounts of particulate organic carbon, with a total of Mt C/year, 53% as much as the Ganges‐Brahmaputra. These results underline the global significance of the Irrawaddy and Salween rivers and warrant continued monitoring of their sediment flux, given the increasing anthropogenic pressures on these river basins.

Interfacial coupling effects on the thermal conductivity of few-layer graphene

The thermal conductivities of both suspended and supported few-layer graphene (FLG) were investigated via molecular dynamics simulations. The results indicate that the thermal conductivity of a suspended FLG sample decreases by 3.9% from 511.2 W m−1 K−1 upon an increase in the number of layers from 1 to 20 layers, whereas it increases by 5.5% to 486.8 W m−1 K−1 in the case of supported FLG specimens on a smooth crystalline silicon surface. Both trends converge when the number of layers is higher than five. The effects of the substrate roughness on the supported FLG samples were also investigated. The results show that their thermal conductivity on a rough silicon surface is lower than that on a smooth silicon surface. In order to demonstrate the importance of interfacial coupling on the phonon transport properties, the coupling strength parameter was enhanced by a factor of 3 or 10 to see the influence on the thermal conductivity. The simulations show that the thermal conductivity decreases with an increasing coupling strength. Lastly, the phonon dispersion of a two-layer graphene specimen was calculated by varying the interlayer coupling strength. The calculations show that the coupling strength is mainly influenced by the out-of-plane phonon dispersion relation. The frequency of flexural acoustic (ZA’) phonons around the center of the first Brillouin zone increases significantly from 2.14 to 6.78 THz when the interlayer coupling strength is enhanced by a factor of 10. This may decrease the phonon group velocity and provide more scattering channels, and thus reduce the thermal conductivity.

Constraining barium isotope fractionation in the upper water column of the South China Sea

Enabled by the success in the determination of stable barium (Ba) isotopic compositions in seawater, Ba isotopes have been suggested as a novel tool to study physical and biogeochemical processes in the present and past ocean. However, a better understanding of the fractionation of Ba isotopes during particle-seawater interactions is a prerequisite for such applications. In this study, we use an extensive data set of concentrations and isotopic compositions of dissolved Ba (DBa and δ138BaDBa) and bulk particulate Ba (pBabulk and δ138BapBabulk) collected in the northern South China Sea (NSCS) to constrain Ba isotope fractionation in the upper ocean. Seawater and suspended particle samples for Ba isotope measurements were collected in January 2010 along a transect from the outer shelf to the lower slope. The water column profiles reaching depths of 1000 m are characterized by a general decrease of δ138BaDBa and an increase of DBa with depth. However, δ138BaDBa signatures are essentially constant at +0.6‰ in the upper 150 m of the entire study area. The corresponding δ138BapBabulk, which primarily represents the isotopic compositions of oceanic or excess particulate Ba (pBaxs), is consistently lower than δ138BaDBa but also constant at values of +0.1 to +0.2‰. This suggests that the same Ba isotope fractionation process prevails above 150 m on the NSCS outer shelf and slope resulting in a constant in situ fractionation factor of −0.5‰. This value is consistent with previously reported values of −0.4 to −0.5‰ in the upper 200 m of the open ocean and a lake. Moreover, we observe significant differences of pBaxs distributions from those of particulate calcium, particulate organic carbon and nitrogen, and biogenic silica indicating that passive adsorption onto particles rather than active biological utilization is most likely the primary process inducing Ba isotope fractionation in the upper NSCS. The constant δ138BapBabulk signatures suggest that particulate Ba isotopes integrate reliable information during transformation of DBa to pBaxs and are thus a more robust proxy for total particle fluxes than pBaxs concentrations, which show variable values potentially affected by other processes (e.g., particle sinking and/or zooplankton grazing) and thus reflects “snapshot” processes in the water column. We contend that biological productivity plays only a subordinate role in regulating the surface Ba isotopic composition of bulk suspended particles. The extent to which Ba isotopes may nevertheless be a reliable proxy for present and past export productivity requires further analyses of the δ138Ba signature of specific Ba carriers such as barite throughout the water column and in the sediments.

Atomic Resolution Imaging of CrBr3 Using Adhesion-Enhanced Grids.

Suspended specimens of 2D crystals and their heterostructures are required for a range of studies including transmission electron microscopy (TEM), optical transmission experiments, and nanomechanical testing. However, investigating the properties of laterally small 2D crystal specimens, including twisted bilayers and air-sensitive materials, has been held back by the difficulty of fabricating the necessary clean suspended samples. Here we present a scalable solution that allows clean free-standing specimens to be realized with 100% yield by dry-stamping atomically thin 2D stacks onto a specially developed adhesion-enhanced support grid. Using this new capability, we demonstrate atomic resolution imaging of defect structures in atomically thin CrBr3, a novel magnetic material that degrades in ambient conditions.