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At least 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Hairy nanoparticles by atom transfer radical polymerization in miniemulsion

Polymer nanoparticles with various architectures and functionalities are promising materials in numerous fields. Miniemulsion polymerization is one of the suitable pathways to prepare polymer nanoparticles since each droplet could act as a “nanoreactor”. A “smart” atom transfer radical polymerization (ATRP) catalytic system comprising Cu-TPMA/DS – (TPMA = tris(2-pyridylmethyl)amine, DS – = dodecyl sulfate anion) ion pair catalyst was efficiently applied in miniemulsion ATRP at low catalyst concentrations. Herein, hairy nanoparticles consisting of hydrophobic poly(n-butyl methacrylate) (P(BMA/EGDMA), EGDMA = ethylene glycol dimethacrylate) network “core” and hydrophilic oligo(ethylene oxide) methyl ether methacrylate (OEOMA) chains as “hair” were prepared by miniemulsion ATRP and a successive chain extension by aqueous ATRP from the particle surface. The addition of an inimer, 2-(α-bromoisobutyryloxy)ethyl methacrylate (HEMA-iBBr) to the P(BMA/EGDMA) network introduced more ATRP initiation sites for ATRP of OEOMA, enabling adjustment of the particle size from >400 nm to <150 nm. The miniemulsion system remained stable after the one pot synthesis of P(BMA/EGDMA)-g-POEOMA and P(BMA/EGDMA/HEMA-iBBr)-g-POEOMA, and the resulting polymer nanoparticles were re-dispersed in water for further modification. A zwitterionic monomer, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA), was grafted from P(BMA/EGDMA/HEMA-iBBr)-g-POEOMA. The resulting hairy nanoparticles provide an avenue for the design and preparation of novel nanostructured materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Improved signal stability in inductively coupled plasma–atomic emission spectrometry through use of tandem spray chambers and surfactant addition

A search for causes of intermittent mid-term (about two hours) instability in emission signals from an inductively coupled plasma led to adoption of a tandem spray-chamber arrangement and subsequently to use of a surfactant (Triton X-100) to mitigate the remaining and newly found instabilities. Through a series of investigations, abrupt signal excursions in the tandem setup were traced to droplet coagulation and drainage inside the glass tube that connected the two spray chambers. However, the signal shifts were not the result of sample-solution release directly but rather to the influence of the underlying factors on plasma behavior. Experiments tailored to the study included not only examination of temporal signal behavior but also collection of long-term videos and measurement of radiofrequency characteristics of the plasma. The addition of a surfactant, Triton X-100, for signal-stability improvement is applicable not only to systems that employ tandem spray chambers but also to conventional single Scott-type chamber arrangements. Further, use of the surfactant was unsuccessful in overcoming “acid effects”, either of the steady-state or transient nature, and did not alter plasma background or analyte signals significantly.

Inductively coupled plasma–atomic emission spectro↗
DOE OSTI2023

Characterization of the aerosol vertical distributions and their impacts on warm clouds based on multi-year ARM observations

Aerosol vertical distribution plays a crucial role in cloud development and thus precipitation since both aerosol indirect and semi-direct effects significantly depend on the relative position of aerosol layer in reference to cloud, but its precise influence on cloud remains unclear. In this study, we integrated multi-year Raman Lidar measurements of aerosol vertical profiles from the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) facility with available Value-Added Products of cloud features to characterize aerosol vertical distributions and their impacts on warm clouds over the continental and marine ARM atmospheric observatories, i.e., Southern Great Plains (SGP) and Eastern North Atlantic (ENA). A unimodal seasonal distribution of aerosol optical depths (AODs) with a peak in summer is found at upper boundary layer over SGP, while a bimodal distribution is observed at ENA for the AODs at lower levels with a major winter-spring maximum. The diurnal mean of upper-level AOD at SGP shows a maximum in the early evening. According to the relative positions of aerosol layers to clouds we further identify three primary types of aerosol vertical distribution, including Random, Decreasing, and Bottom. It is found that the impacts of aerosols on cloud may or may not vary with aerosol vertical distribution depending on environmental conditions, as reflected by the wide variations of the relations between AOD and cloud properties. For example, as AOD increases, the liquid water paths (LWPs) tend to be reduced at SGP but enhanced at ENA. The relations of cloud droplet effective radius with AOD largely depend on aerosol vertical distributions, particularly showing positive values in the Random type under low-LWP condition (<50gm -2 ). In conclusion, the distinct features of aerosol-cloud interactions in relation to aerosol vertical distribution are likely attributed to the continental-marine contrast in thermodynamic environments and aerosol conditions between SGP and ENA.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Particle transport-driven flow dynamics and heat transfer modulation in solar photovoltaic modules: Implications on soiling

Wind-swept debris and excessive heating reduce solar photovoltaic efficiency and accelerate panel degradation. For many solar plants in open environments, particle deposition is well-understood to exacerbate efficiency losses by blocking useable light and insulating panel surfaces. However, little is known about particle behavior in multi-panel systems, where complex wakes dominate and alter trajectories. This study examines debris-laden flow within a scaled array of two model solar panels, observing convective cooling and focusing on turbulent inter-panel flow dynamics. Convection is compared between the first and second panels (P 1 and P 2 ) and for a single inflow velocity at four particle concentrations (Φ v ), including a neutrally buoyant particle (i.e. tracer) case and three water droplet cases. Tracers and Φ v > 0 concentrations show increased convective heat transfer for P 2 compared to P 1 , while inertial particle presence and increased concentration reduces this improvement from +170% to +90%. Particle image velocimetry surrounding P 2 reveals dampened inter-panel wake features for particle-laden flow compared to the tracer case, where diminished mean flow and mean kinetic energy breakdown are observed for the particles due to their inertia. Together, the reduction in comparative convection and dampened wake effects accompanying inertial particle concentration motivates further studies on coupled array physics in debris-filled flow.

14 SOLAR ENERGY↗
DOE OSTI2021

Maternal undernutrition modulates hepatic MicroRNAs expression in the early life of offspring

Emerging studies revealed that a poor intrauterine environment elicited by maternal nutrient restriction (MNR) is associated with an increased risk of metabolic diseases in adulthood. Previous research has shown that microRNAs (miRNAs) exert pivotal roles in modulating molecular pathways involved in disease pathogenesis and progression. In this respect, we herein examined miRNA profiles in samples of liver from offspring whose mothers were fed either with a 50% food-restricted diet or standard laboratory chow during pregnancy. Our findings enumerated that miR-181a, involved in lipid metabolism, was found to be downregulated in the liver of MNR offspring at 1 day of age when compared to that of control offspring. We also noted that overexpression of miR-181a reduced the lipid droplets after treatment with oleic acid for 48 h, which suppressed the expressions levels of SIRT1, FOXO1, KLF6 and PPARγ in BRL-3A cells, while the opposite results were observed with decreased expression of miR-181a. Furthermore, the luciferase reporter assay confirmed the direct interactions between miR-181a with KLF6 and SIRT1. In adults, the MNR offspring elucidated increased TG content, decreased expression of miR-181a, and increased expressions levels of SIRT1, FOXO1, KLF6, and PPARγ in liver tissues. Collectively, these findings provided novel evidence that MNR could regulate miRNAs expression, which might be related to lipid metabolism in MNR offspring.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Lipopolysaccharide and lipoteichoic acid influence milk production ability via different early responses in bovine mammary epithelial cells

Highlights: • LPS and LTA affect on the milk production of lactating BMECs in different manners. • LPS/TLR4 and LTA/TLR2 signaling induce different innate immune responses in BMECs. • Inhibition of p38 and NF-κB may help recover decrease in milk production in mastitis. Lipopolysaccharide (LPS) and lipoteichoic acid (LTA) are cell wall components of Escherichia coli and Staphylococcus aureus, which cause clinical and subclinical mastitis, respectively. However, the reason of the difference in symptoms by pathogen type remains unclear. In this study, the influence of LPS and LTA on early response and milk production in lactating bovine mammary epithelial cells (BMECs) was comparatively investigated. The results showed that LPS decreased the secretion of β-casein, lactose, and triglycerides, whereas LTA decreased the secretion of lactose and triglycerides but increased lactoferrin production without any influence on β-casein secretion. In addition, the influence of milk lipid droplet size in BMECs and gene expression related to milk fat synthesis was different between LPS and LTA. LPS increased the gene expression of interleukin (IL)-1β, tumor necrosis factor-α, and IL-8 through the activation of the nuclear factor-κB (NF-κB), p38, and c-Jun N-terminal kinase pathways, whereas LTA increased IL-1β and CC chemokine ligand 5 expression through the activation of the NF-κB pathway. Moreover, these cytokines and chemokines differently affected the milk production ability of BMECs. These results suggested that the pathogen-specific symptoms may be related to the differences in the early response of BMECs to bacterial toxins.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

miR-23b Ameliorates nonalcoholic steatohepatitis by targeting Acyl-CoA thioesterases 4

Non-alcoholic fatty liver disease (NAFLD) and its more advanced stages, Non-alcoholic steatohepatitis and Cirrhosis, are the most common liver diseases in the worldwide, especially in developing countries. NAFLD is distinguished by the accumulation of triglycerides within hepatocytes. An increasing body of evidence suggests that hepatic MicroRNAs play an important role in NAFLD by controlling lipid metabolism, inflammation, and fibrosis. However, the precise causative functions of miRNA in NAFLD remain unknown. Here, we discovered that mice lacking MicroRNA-23b developed NAFLD-like phenotypes such as increased serum triglyceride and lipid droplet accumulation. In db/db mice fed a high fat diet, MicroRNA-23b overexpression reduced liver weight and alleviated liver inflammation, apoptosis, and fibrosis. MicroRNA-23b regulates the acyl-CoA metabolic process via Acyl-CoA thioesterase 4 (Acot4), which interacts with Acetyl CoA Carboxylase (ACC), according to the RNA-seq analysis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Effects of Molecular Size on Resolution in Charge Detection Mass Spectrometry

Instrumental resolution of Fourier transform-charge detection mass spectrometry instruments with electrostatic ion trap detection of individual ions depends on the precision with which ion energy is determined. Energy can be selected using ion optic filters or from harmonic amplitude ratios (HARs) that provide Fellgett’s advantage and eliminate the necessity of ion transmission loss to improve resolution. Unlike the ion energy-filtering method, the resolution of the HAR method increases with charge (improved S/N) and thus with mass. An analysis of the HAR method with current instrumentation indicates that higher resolution can be obtained with the HAR method than the best resolution demonstrated for instruments with energy-selective optics for ions in the low MDa range and above. However, this gain is typically unrealized because the resolution obtainable with molecular systems in this mass range is limited by sample heterogeneity. Here, this phenomenon is illustrated with both tobacco mosaic virus (0.6–2.7 MDa) and AAV9 (3.7–4.7 MDa) samples where mass spectral resolution is limited by the sample, including salt adducts, and not by instrument resolution. Nevertheless, the ratio of full to empty AAV9 capsids and the included genome mass can be accurately obtained in a few minutes from 1× PBS buffer solution and an elution buffer containing 300+ mM nonvolatile content despite extensive adduction and lower resolution. Empty and full capsids adduct similarly indicating that salts encrust the complexes during late stages of droplet evaporation and that mass shifts can be calibrated in order to obtain accurate analyte masses even from highly salty solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Mass Spectrometry-Based High-Throughput Quantification of Bioproducts in Liquid Culture

To meet the ever-increasing need for high-throughput screening in metabolic engineering, information-rich, fast screening methods are needed. Mass spectrometry (MS) provides an efficient and general approach for metabolite screening and offers the capability of characterizing a broad range of analytes in a label-free manner, but often requires a range of sample clean-up and extraction steps. Liquid extraction surface analysis (LESA) coupled MS is an image-guided MS surface analysis approach that directly samples and introduces metabolites from a surface to MS. Here, we combined the advantages of LESA–MS and an acoustic liquid handler with stable isotope-labeled internal standards. This approach provides absolute quantitation of target chemicals from liquid culture-dried droplets and enables high-throughput quantitative screening for microbial metabolites. In this paper, LESA–MS was successfully applied to quantify several different metabolites (itaconic acid, triacetic acid lactone, and palmitic acid) from different yeast strains in different mediums, demonstrating its versatility, accuracy, and efficiency across a range of microbial engineering applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Strain-Mediated Sn Incorporation and Segregation in Compositionally Graded Ge 1– x Sn x Epilayers Grown by MBE at Different Temperatures

We investigated the process of Sn incorporation and surface segregation for compositionally graded Ge 1–x Sn x epilayers grown on high-quality Ge (001) substrates. Here, the growth resulted in pseudomorphic GeSn layers with a ~6% maximal Sn fraction at a constant substrate temperature. The maximal fraction of Sn was increased to 9.0% when the growth temperature was continuously lowered while increasing the Sn flux. The analysis of surface droplets and SIMS profiles of elemental composition give evidence of Sn rejection during the growth, potentially associated with a critical energy of elastic strain. The intentional reduction of the coherent strain by decreasing the Sn flux near the sample surface has been shown to trap a higher fraction of Sn in the Ge 1–x Sn x layer and lower surface segregation. Our results demonstrate that strain relief by misfit dislocations in the compositionally graded layer is inhibited, which leads to Sn segregation. Specifically, the compressive strain in the graded Ge 1–x Sn x epilayer is effectively “zero” near the interface with the Ge substrate and increases up to about –1.5 × 10 –2 near the surface. Thus, although the nucleation of a dislocation may reduce the compressive strain for the top region of the epilayer, it is not beneficial for the bottom region.

42 ENGINEERING↗
DOE OSTI2024

Emergent Properties from Three-Dimensional Assemblies of (Nano)particles in Confined Spaces

The assembly of (nano)particles into compact hierarchical structures yields emergent properties not found in the individual constituents. The formation of these structures relies on a profound knowledge of the nanoscale interactions between (nano)particles, which are often designed by researchers aided by computational studies. These interactions have an effect when the (nano)particles are brought into close proximity, yet relying only on diffusion to reach these closer distances may be inefficient. Recently, physical confinement has emerged as an efficient methodology to increase the volume fraction of (nano)particles, rapidly accelerating the time scale of assembly. Specifically, the high surface area of droplets of one immiscible fluid into another facilitates the controlled removal of the dispersed phase, resulting in spherical, often ordered, (nano)particle assemblies. In this review, we discuss the design strategies, computational approaches, and assembly methods for (nano)particles in confined spaces and the emergent properties therein, such as trigger-directed assembly, lasing behavior, and structural photonic color. Finally, we provide a brief outlook on the current challenges, both experimental and computational, and farther afield application possibilities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Functional Nano-to-Microstructures by Jet Printing and Direct Ink Writing

Jet-based printing techniques and direct ink writing have emerged as complementary, convergent technologies serving as key platforms in additive manufacturing for functional nano- to microscale architectures. This review highlights how these approaches enable fine feature resolution and three-dimensional structures in advanced electronics and biointerfacing applications. The interplay of fluid mechanics, viscoelastic ink rheology, droplet–substrate interactions, and drying dynamics is examined as a critical determinant of printing fidelity. Application-focused case studies, from flexible thin-film transistors to bioprinted artificial tissues, demonstrate how precise structural control via printing translates to enhanced device performance and new functionality in electronic and biological systems. Finally, we discuss the challenges and future opportunities driving the evolution of these printing platforms toward autonomous, adaptive, and intelligent manufacturing systems.

Luo, Junchen [Sichuan Univ. of Arts and Science (C↗
DOE OSTI2022

Perspectives on Microfluidics for the Study of Asphaltenes in Upstream Hydrocarbon Production: A Minireview

The utilization of microfluidics has generated deep insights into asphaltene precipitation mechanisms and oil–water emulsion stabilization. Agglomeration and precipitation of asphaltenes can cause flow assurance problems during the extraction and transportation of crude oil. Change in temperature, pressure, reservoir conditions, and solvents can change the local environment, leading to asphaltene precipitation. Understanding asphaltene properties and precipitation pathways becomes critical in devising mitigation methods, demulsifiers, and suitable conditions during hydrocarbon processing. Microfluidics has helped in high throughput measurement studies, understanding critical processing conditions, fast demulsifier screening, and the effect of solvent concentration on deposition, generating useful information for utilization at the point of resource extraction facilitating improved resource management. It has become possible to capture the porous, complex nature of reservoir formations and the interaction of chemicals during precipitation through integrated analytics and visualization studies available only through microfluidics. The use of droplet microfluidics, with optical microscopy and high-speed imaging to study the oil–water interface, has resulted in greater understanding of the role of asphaltenes in interfacial properties and emulsion stabilization. Here, this minireview highlights the crucial aspects of microfluidics that have been used to understand physicochemical behavior and dynamics of asphaltene deposition. Some of the unique devices have been presented focusing on the key elements of microfluidics design, fabrication, and analysis, as the insight obtained from microfluidics strongly depends on the device design and the controllability of the experimental parameters. Successful implementation of microfluidics for efficient and controlled experiments, short analysis time scales and rapid screening, and generation of high-quality, reliable data that convey asphaltene deposition issues and interface behavior in emulsions shows the importance of microsystems for advancing knowledge in hydrocarbon production and processing.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Dissolving Nonionic Surfactants in CO 2 to Improve Oil Recovery in Unconventional Reservoirs via Wettability Alteration

CO 2 injection is a promising method for enhanced oil recovery (EOR) in unconventional shale reservoirs. Here, in this work, we postulate that CO 2 EOR may be improved by the dissolution of surfactants into CO 2 . Although CO 2 is a relatively good solvent for oil, we show that CO 2 and Eagle Ford oil are immiscible at compositions above 70 wt % CO 2 , even at pressures as high as 62 MPa. The presence of a CO 2 –oil interface at reservoir conditions indicates that the addition of a surfactant has the potential to improve oil recovery–via wettability alteration from oil-wet to CO 2 -wet, CO 2 –oil interfacial tension (IFT) reduction, or both. Three nonionic surfactants (branched tridecyl ethoxylate Indorama SURFONIC TDA-9, branched nonylphenol ethoxylate Indorama SURFONIC N-100, and linear dodecyl ethoxylate Indorama SURFONIC L12-6) were evaluated for CO 2 -solubility, shale wettability alteration, effect on CO 2 –oil IFT, ability to generate CO 2 –oil foams, and ability to increase oil extraction from Eagle Ford, Mancos, and Bakken shale cores. Each surfactant dissolved in CO 2 up to 1 wt % at pressures and temperatures commensurate with CO 2 EOR. CO 2 -dissolved surfactants did not significantly affect CO 2 –oil IFT or generate CO2–oil foams, but they did induce a dramatic change in the contact angle of an oil droplet on an oil-aged shale chip in CO 2 from strongly oil-wet (11°) toward intermediate CO 2 –oil wettability (82°) (at 80 °C, 27.6 MPa). The branched tridecyl ethoxylated surfactant, SURFONIC TDA-9, afforded the highest oil recovery in core soaking experiments–75%, compared to 71% by pure CO 2 . Analysis of oil extracts by gas chromatography revealed that heavier oil components were produced when the surfactant was added to CO 2 . These results indicate that CO 2 -dissolved surfactants may increase oil recovery from shale by wettability alteration from oil-wet toward CO 2 -wet.

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2020

SARS-CoV-2 RNA in Wastewater Settled Solids Is Associated with COVID-19 Cases in a Large Urban Sewershed

Wastewater-based epidemiology may be useful for informing public health response to viral diseases like COVID-19 caused by SARS-CoV-2. Here, we quantified SARS-CoV-2 RNA in wastewater influent and primary settled solids in two wastewater treatment plants to inform the preanalytical and analytical approaches and to assess whether influent or solids harbored more viral targets. The primary settled solids samples resulted in higher SARS-CoV-2 detection frequencies than the corresponding influent samples. Likewise, SARS-CoV-2 RNA was more readily detected in solids using one-step digital droplet (dd)RT-PCR than with two-step RT-QPCR and two-step ddRT-PCR, likely owing to reduced inhibition with the one-step ddRT-PCR assay. We subsequently analyzed a longitudinal time series of 89 settled solids samples from a single plant for SARS-CoV-2 RNA as well as coronavirus recovery (bovine coronavirus) and fecal strength (pepper mild mottle virus) controls. SARS-CoV-2 RNA targets N1 and N2 concentrations correlated positively and significantly with COVID-19 clinically confirmed case counts in the sewershed. Together, the results demonstrate that measuring SARS-CoV-2 RNA concentrations in settled solids may be a more sensitive approach than measuring SARS-CoV-2 in influent.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Polymeric Microcapsules as Robust Mimics of Emulsion Liquid Membranes for Selective Ion Separations

Selective ion separations are increasingly needed to combat water scarcity, recover resources from wastewater, and enable the efficient recycling of electronics waste. Emulsion liquid membranes (ELMs) have received interest due to rapid kinetics, high selectivities, and low solvent requirements but are too unstable for industrial usage. Here, we demonstrate that polymeric microcapsules can serve as robust, solvent-free mimics of ELMs. As a proof of concept, we incorporated the copper-selective ligand Lix 84-I in the walls of microcapsules formed from a commercial polystyrene-b-polybutadiene-b-polystyrene triblock polymer. The microcapsules were formed from a double-emulsion template, resulting in particles typically 20–120 μm in diameter that encapsulated even smaller droplets of a dilute (≤0.5 M) H 2 SO 4 solution. Batch experiments demonstrated facilitated-transport behavior, with equilibrium reached in as little as 10 min for microcapsules with 1% ligand, and with ~15-fold selectivity for Cu 2+ over Ni 2+ . Furthermore, the microcapsules could be packed readily in columns for flow-through operation, thus enabling near-complete Cu 2+ removal in ~2 min under certain conditions, recovery of Cu 2+ by flowing through fresh dilute H 2 SO 4 , and reuse for at least 10 cycles. The approach in this work can serve as a template for using selective ligands to enable robust and simple flow-through processes for a variety of selective ion separations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

The Significant Role of New Particle Composition and Morphology on the HNO 3 -Driven Growth of Particles down to Sub-10 nm

New particle formation and growth greatly influence air quality and the global climate. Recent CERN Cosmics Leaving OUtdoor Droplets (CLOUD) chamber experiments proposed that in cold urban atmospheres with highly supersaturated HNO 3 and NH 3 , newly formed sub-10 nm nanoparticles can grow rapidly (up to 1000 nm h –1 ). Here, we present direct observational evidence that in winter Beijing with persistent highly supersaturated HNO 3 and NH 3 , nitrate contributed less than ~14% of the 8–40 nm nanoparticle composition, and overall growth rates were only ~0.8–5 nm h –1 . To explain the observed growth rates and particulate nitrate fraction, the effective mass accommodation coefficient of HNO 3 (α HNO 3 ) on the nanoparticles in urban Beijing needs to be 2–4 orders of magnitude lower than those in the CLOUD chamber. We propose that the inefficient uptake of HNO 3 on nanoparticles is mainly due to the much higher particulate organic fraction and lower relative humidity in urban Beijing. To quantitatively reproduce the observed growth, we show that an inhomogeneous “inorganic core–organic shell” nanoparticle morphology might exist for nanoparticles in Beijing. Finally, this study emphasized that growth for nanoparticles down to sub-10 nm was largely influenced by their composition, which was previously ignored and should be considered in future studies on nanoparticle growth.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Volatilized Ammonia Supports Subterranean Ecosystems with Unusual Nitrogen Isotopic Signatures

The Frasassi cave system hosts a robust subterranean ecosystem based on microbial lithoautotrophy. Curiously, acidic biofilms forming above degassing sulfidic cave streams, and the invertebrates that feed on them, are extremely depleted in nitrogen-15 (δ 15 N values less than −20‰). In this study, we tested the hypothesis that these low δ 15 N values result from the volatilization, trapping, and uptake of ammonia degassed from circumneutral streams. We found that dissolved ammonium in the streams had δ 15 N values near +3‰, whereas NH 3(g) in the cave atmosphere above streams exhibited δ 15 N values as low as −27‰, consistent with fractionation by NH 3 volatilization. Extremely acidic condensation droplets on cave walls efficiently trapped airborne NH 3 , accumulating up to 4 mM NH 4 + with δ 15 N values as low as −29‰, thereby confirming volatilized and trapped ammonia as the primary N source to cave wall biofilms and the extensive subsurface ecosystem they support. Airborne ammonia trapping represents a novel mechanism for biological N acquisition and provides abundant N for growth in an extreme subsurface environment that otherwise receives very limited nutrient input.

Nitrogen↗