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NASA NTRS2012

Cosmic Complexity

What explains the extraordinary complexity of the observed universe, on all scales from quarks to the accelerating universe? My favorite explanation (which I certainty did not invent) ls that the fundamental laws of physics produce natural instability, energy flows, and chaos. Some call the result the Life Force, some note that the Earth is a living system itself (Gaia, a "tough bitch" according to Margulis), and some conclude that the observed complexity requires a supernatural explanation (of which we have many). But my dad was a statistician (of dairy cows) and he told me about cells and genes and evolution and chance when I was very small. So a scientist must look for me explanation of how nature's laws and statistics brought us into conscious existence. And how is that seemll"!gly Improbable events are actually happening a!1 the time? Well, the physicists have countless examples of natural instability, in which energy is released to power change from simplicity to complexity. One of the most common to see is that cooling water vapor below the freezing point produces snowflakes, no two alike, and all complex and beautiful. We see it often so we are not amazed. But physlc!sts have observed so many kinds of these changes from one structure to another (we call them phase transitions) that the Nobel Prize in 1992 could be awarded for understanding the mathematics of their common features. Now for a few examples of how the laws of nature produce the instabilities that lead to our own existence. First, the Big Bang (what an insufficient name!) apparently came from an instability, in which the "false vacuum" eventually decayed into the ordinary vacuum we have today, plus the most fundamental particles we know, the quarks and leptons. So the universe as a whole started with an instability. Then, a great expansion and cooling happened, and the loose quarks, finding themselves unstable too, bound themselves together into today's less elementary particles like protons and neutrons, liberating a little energy and creating complexity. Then, the expanding universe cooled some more, and neutrons and protons, no longer kept apart by immense temperatures, found themselves unstable and formed helium nuclei. Then, a little more cooling, and atomic nuclei and electrons were no longer kept apart, and the universe became transparent. Then a little more cooling, and the next instability began: gravitation pulled matter together across cosmic distances to form stars and galaxies. This instability is described as a "negative heat capadty" in which extracting energy from a gravitating system makes it hotter -- clearly the 2nd law of thermodynamics does not apply here! (This is the physicist's part of the answer to e e cummings' question: what is the wonder that's keeping the stars apart?) Then, the next instability is that hydrogen and helium nuclei can fuse together to release energy and make stars burn for billions of years. And then at the end of the fuel source, stars become unstable and explode and liberate the chemical elements back into space. And because of that, on planets like Earth, sustained energy flows support the development of additional instabilities and all kinds of complex patterns. Gravitational instability pulls the densest materials into the core of the Earth, leaving a thin skin of water and air, and makes the interior churn incessantly as heat flows outwards. And the heat from the sun, received mostly near the equator and flowing towards the poles, supports the complex atmospheric and oceanic circulations. And because or that, the physical Earth is full of natural chemical laboratories, concentrating elements here, mixing them there, raising and lowering temperatures, ceaselessly experimenting with uncountable events where new instabilities can arise. At least one of them was the new experiment called life. Now that we know that there are at least as many planets as there are stars, it is hard to imagine that nature's ceasess experimentation would not be able to produce life elsewhere -- but we don't know for sure. And life went on to cause new Instabilities, constantly evolving, with living things in an extraordinary range of environments, changing the global environment, with boom-and-bust cycles. with predators for every kInd of prey, with criminals for every possible crime, with governments to prevent them, and instabilities of the governments themselves. One of the instabilities Is that humans demand new weapons and new products of all sort, leading to serious investments in science and technology. So the natural/human world of competition and combat is structured to lead to advanced weaponry and cell phones. So here we are In 2012, with people writing essays and wondering whether their descendents will be artificial life forms travelling back into space. And, pondering what are the origins of those forces of nature that give rise to everything. Verllnde has argued that gravitation, the one force that has so far resisted our efforts at a Quantum description, is not even a fundamental force, but is itself it a statistical force, like osmosis. What an amazing turn of events! But after all I've just said, I should not be surprised a bit.

Mather, John C.↗
DOE OSTI2022

Activation of Transition Metal (Fe, Co and Ni)-Oxide Nanoclusters by Nitrogen Defects in Carbon Nanotube for Selective CO 2 Reduction Reaction

The electrochemical carbon dioxide reduction reaction (CO2RR), which can produce value-added chemical feedstocks, is a proton-coupled-electron process with sluggish kinetics. Thus, highly efficient, cheap catalysts are urgently required. Transition metal oxides such as CoO x , FeO x , and NiO x are low-cost, low toxicity, and abundant materials for a wide range of electrochemical reactions, but are almost inert for CO 2 RR. Here, we report for the first time that nitrogen doped carbon nanotubes (N-CNT) have a surprising activation effect on the activity and selectivity of transition metal-oxide (MO x where M = Fe, Ni, and Co) nanoclusters for CO 2 RR. MO x supported on N-CNT, MOx/N-CNT, achieves a CO yield of 2.6–2.8 mmol cm -2 min -1 at an overpotential of -0.55V, which is two orders of magnitude higher than MO x supported on acid treated CNTs (MOx/O-CNT) and four times higher than pristine N-CNT. The faraday efficiency for electrochemical CO 2 -to-CO conversion is as high as 90.3% at overpotential of 0.44V. Both in-situ XAS measurements and DFT calculations disclose that MO x nanoclusters can be hydrated in CO 2 saturated KHCO 3 , and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions, which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

36 MATERIALS SCIENCE↗
NASA NTRS2021

The Efficacy of Seasonal Terrestrial Water Storage Forecasts for Predicting Vegetation Activity Over Africa

Terrestrial water storage (TWS) provides important information on terrestrial hydroclimate and may have value for seasonal forecasting because of its strong persistence. We use the NASA Hydrological Forecast and Analysis System (NHyFAS) to investigate TWS forecast skill over Africa and assess its value for predicting vegetation activity from satellite estimates of leaf area index (LAI). Forecast skill is high over East and Southern Africa, extending up to 3–6 months in some cases, with more modest skill over West Africa. Highest skill generally occurs during the dry season or beginning of the wet season when TWS anomalies from the previous wet season are most likely to carry forward in time. In East Africa, this occurs prior to and during the transition into the spring “Long Rains” from January–March, while in Southern Africa this period of highest skill starts at the beginning of the dry season in April and extends through to the start of the wet season in October. TWS is highly and positively correlated with LAI, and a logistic regression model shows high cross-validation skill in predicting above or below normal LAI using TWS. Combining the LAI regression model with the NHyFAS forecasts, 1-month lead LAI predictions have high accuracy over East and Southern Africa, with reduced but significant skill at 3-month leads over smaller sub-regions. This highlights the potential value of TWS as an additional source of information for seasonal forecasts over Africa, with direct applications to some of the most vulnerable agricultural regions on the continent.

Terrestrial water shortage↗
NASA NTRS2003

Mechanical Testing of PMCs under Simulated Rapid Heat-Up Propulsion Environments: In-Plane Compressive Behavior - II

Carbon fiber thermoset polymer matrix composites (PMC) with high temperature polyimide based in-situ polymerized monomer reactant (PMR) resin has been used for some time in applications which can see temperatures up to 550 F. Currently, graphite fiber PMR based composites are used in several aircraft engine components including the outer bypass duct for the GE F-404, exit flaps for the P&W F-100-229, and the core cowl for the GE/Snecma CF6-80A3. Newer formulations, including PMR-II-50 are being investigated as potential weight reduction replacements of various metallic components in next generation high performance propulsion rocket engines that can see temperatures which exceed 550 F. Extensive FEM thermal modeling indicates that these components are exposed to rapid heat-up rates (up to -200 F/sec) and to a maximum temperature of around 600 F. Even though the predicted maximum part temperatures were within the capability of PW-II-50, the rapid heat-up causes significant through-thickness thermal gradients in the composite part and even more unstable states when combined with moisture. Designing composite parts for such extreme service environments will require accurate measurement of intrinsic and transient mechanical properties and the hygrothermal performance of these materials under more realistic use conditions. The mechanical properties of polymers degrade when exposed to elevated temperatures even in the absence of gaseous oxygen. Accurate mechanical characterization of the material is necessary in order to reduce system weight while providing sufficient factors of safety. Historically, the testing of PMCs at elevated temperatures has been plagued by the antagonism between two factors. First, moisture has been shown to profoundly affect the mechanical response of these materials at temperatures above their glass transition temperature while concurrently lowering the material's Tg. Moisture phenomena is due to one or a combination of three effects, i.e., plastization of polymeric material by water, the internal pressure generated by the volatilization of water at elevated temperatures, and hydrolytic chemical decomposition. However, moisture is lost from the material at increasing rates as temperature increases. Second, because PMCs are good thermal insulators, when they are externally heated at even mild rates large thermal gradients can develop within the material. At temperatures where a material property changes rapidly with temperature the presence of a large thermal gradient is unacceptable for intrinsic property characterization purposes. Therefore, long hold times are required to establish isothermal conditions. However, in the service environments high-heating-rates, high temperatures, high-loading rates are simultaneous present along with residual moisture. In order to capture the effects of moisture on the material, holding at- temperature until isothermal conditions are reached is unacceptable particularly in materials with small physical dimensions. Thus, the effects due to moisture on the composite's mechanical characteristics, ie., their so-called analog response, may be instructive. One approach employed in this program was rapid heat-up (approx. 200 F/sec.) and loading of both dry and wet in-plane compressive specimens to examine the effects of moisture on this resin dominated mechanical property of the material.

Stokes, Eric H.↗
DOE OSTI2024

Design principles for energy transfer in the photosystem II supercomplex from kinetic transition networks

Photosystem II (PSII) has the unique ability to perform water-splitting. With light-harvesting complexes, it forms the PSII supercomplex (PSII-SC) which is a functional unit that can perform efficient energy conversion, as well as photoprotection, allowing photosynthetic organisms to adapt to the naturally fluctuating sunlight intensity. Achieving these functions requires a collaborative energy transfer network between all subunits of the PSII-SC. In this work, we perform kinetic analyses and characterise the energy landscape of the PSII-SC with a structure-based energy transfer model. With first passage time analyses and kinetic Monte Carlo simulations, we are able to map out the overall energy transfer network. We also investigate how energy transfer pathways are affected when individual protein complexes are removed from the network, revealing the functional roles of the subunits of the PSII-SC. In addition, we provide a quantitative description of the flat energy landscape of the PSII-SC. We show that it is a unique landscape that produces multiple kinetically relevant pathways, corresponding to a high pathway entropy. These design principles are crucial for balancing efficient energy conversion and photoprotection.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Bridging the length scales in ionic separations via data-driving machine learning

We pursued a data science driven machine learning (ML) approach that blended molecular scale attributes informed from molecular dynamics (MD) simulation and materials properties to the selectivity and energy efficiency in targeted ionic separations using electric fields. The model mixtures investigated for ionic separations are pH sensitive and include organic acids, silica and boron, transition metals, such as copper and chromium. There were two major research thrusts of this project. Firstly, we investigated surrogate models and deep learning that relate material chemistries and structures to selective transport of ionic species under applied electric fields. Secondly we investigated how the bipolar junction interfacial design and water dissociation catalyst in bipolar membranes affect reverse bias polarization behavior and pH modulation in deionization platforms as a function of the platform operating parameters (e.g., cell voltage, residence time, and salt feed concentration). As a result of this work, we also were able to start a new direction, namely ML models for molecular design of surfactants.

36 MATERIALS SCIENCE↗
NASA NTRS1999

Climatic Implications of the Observed Temperature Dependence of the Liquid Water Path of Low Clouds in the Southern Great Plains

Satellite observations of low-level clouds have challenged the assumption that adiabatic liquid water content combined with constant physical thickness will lead to a negative cloud optics feedback in a decadal climate change. We explore the reasons for the satellite results using four years of surface remote sensing data from the Atmospheric Radiation Measurement Program Cloud and Radiation Testbed site in the Southern Great Plains of the United States. We find that low cloud liquid water path is approximately invariant with temperature in winter but decreases strongly with temperature in summer, consistent with the satellite inferences at this latitude. This behavior occurs because liquid water content shows no detectable temperature dependence while cloud physical thickness decreases with warming. Thinning of clouds with warming is observed on seasonal, synoptic, and diurnal time scales; it is most obvious in the warm sectors of baroclinic waves. Although cloud top is observed to slightly descend with warming, the primary cause of thinning is the ascent of cloud base due to the reduction in surface relative humidity and the concomitant increase in the lifting condensation level of surface air. Low cloud liquid water path is not observed to be a continuous function of temperature. Rather, the behavior we observe is best explained as a transition in the frequency of occurrence of different boundary layer types: At cold temperatures, a mixture of stratified and convective boundary layers is observed, leading to a broad distribution of liquid water path values, while at warm temperatures, only convective boundary layers with small liquid water paths, some of them decoupled, are observed. Our results, combined with the earlier satellite inferences, imply that the commonly quoted 1.50 C lower limit for the equilibrium global climate sensitivity to a doubling of CO2, which is based on models with near-adiabatic liquid water behavior and constant physical thickness, should be revised upward.

DelGenio, Anthony D.↗
NASA NTRS1999

Climatic Implications of the Observed Temperature Dependence of the Liquid Water Path of Low Clouds in the Southern Great Plains

Satellite observations of low-level clouds have challenged the assumption that adiabatic liquid water content combined with constant physical thickness will lead to a negative cloud optics feedback in a decadal climate change. We explore the reasons for the satellite results using four years of surface remote sensing data from the Atmospheric Radiation Measurement Program Cloud and Radiation Testbed site in the Southern Great Plains of the United States. We find that low cloud liquid water path is approximately invariant with temperature in winter but decreases strongly with temperature in summer, consistent with the satellite inferences at this latitude. This behavior occurs because liquid water content shows no detectable temperature dependence while cloud physical thickness decreases with warming. Thinning of clouds with warming is observed on seasonal, synoptic, and diurnal time scales; it is most obvious in the warm sectors of baroclinic waves. Although cloud top is observed to slightly descend with warming, the primary cause of thinning, is the ascent of cloud base due to the reduction in surface relative humidity and the concomitant increase in the lifting condensation level of surface air. Low cloud liquid water path is not observed to be a continuous function of temperature. Rather, the behavior we observe is best explained as a transition in the frequency of occurrence of different boundary layer types. At cold temperatures, a mixture of stratified and convective boundary layers is observed, leading to a broad distribution of liquid water path values, while at warm temperatures, only convective boundary layers with small liquid water paths, some of them decoupled, are observed. Our results, combined with the earlier satellite inferences, imply that the commonly quoted 1.5C lower limit for the equilibrium global climate sensitivity to a doubling of CO2 which is based on models with near-adiabatic liquid water behavior and constant physical thickness, should be revised upward.

DelGenio, Anthony↗
NASA NTRS2008

The NASA Energy and Water Cycle Extreme (NEWSE) Integration Project

Skillful predictions of water and energy cycle extremes (flood and drought) are elusive. To better understand the mechanisms responsible for water and energy extremes, and to make decisive progress in predicting these extremes, the collaborative NASA Energy and Water cycle Extremes (NEWSE) Integration Project, is studying these extremes in the U.S. Southern Great Plains (SGP) during 2006-2007, including their relationships with continental and global scale processes, and assessment of their predictability on multiple space and time scales. It is our hypothesis that an integrative analysis of observed extremes which reflects the current understanding of the role of SST and soil moisture variability influences on atmospheric heating and forcing of planetary waves, incorporating recently available global and regional hydro- meteorological datasets (i.e., precipitation, water vapor, clouds, etc.) in conjunction with advances in data assimilation, can lead to new insights into the factors that lead to persistent drought and flooding. We will show initial results of this project, whose goals are to provide an improved definition, attribution and prediction on sub-seasonal to interannual time scales, improved understanding of the mechanisms of decadal drought and its predictability, including the impacts of SST variability and deep soil moisture variability, and improved monitoring/attributions, with transition to applications; a bridging of the gap between hydrological forecasts and stakeholders (utilization of probabilistic forecasts, education, forecast interpretation for different sectors, assessment of uncertainties for different sectors, etc.).

House, P. R.↗
NASA NTRSDate not supplied

Multispectral Imagery Research and Applications

The NASA Short-term Prediction Research and Transition (SPoRT) Center developed techniques to improve the quality and interpretation of multispectral imagery derived from NASA/NOAA geostationary satellites using statistical and machine learning approaches. A physically-based machine learning approach, DustTracker-AI, was developed to overcome the problem of night-time dust detection and to augment dust analysis with satellite products such as the Dust RGB. Additionally, an updated limb-correction and intercalibration methodology for short-wave, near-infrared, thermal infrared, and water vapor bands was developed for the purpose of developing a suite of high-quality RGB imagery that can be used at high viewing angles and across the constellation of geostationary sensors. This presentation will briefly highlight the techniques developed to detect dust in difficult night-time scenes and improve the quality and interpretation of multispectral imagery.

Emily Berndt↗
NASA NTRS1992

Lidar Observation of Aerosol and Temperature Stratification over Urban Area During the Formation of a Stable Atmospheric PBL

In recent years, the processes in the atmospheric planetary boundary layer (PBL) over urban areas were intensely investigated, due to ecological problems related to the air, soil, and water pollution. New pollution sources in new residential districts, when in contradiction to the microclimate and topography requirements of that region, create a number of considerable hazards and problems. The present study is a continuation of our preceding investigations and aims at revealing the aerosol structure and stratification during the transition after sunset as measured by two lidars. Such observation of the nocturnal, stable PBL formation over an urban area in Bulgaria has not been reported before. The lidars' high time and spatial resolutions allow the changes of the internal structure of the PBL's part located above the surface layer to be observed.

Kolev, I.↗
DOE OSTI2020

Strategies for thorium fuel cycle transition in the SD-TMSR

Liquid-fueled Molten Salt Reactor (MSR) systems represent advances in safety, economics, and sustainability. The MSR has been designed to operate with a Th/ 233 U fuel cycle with 233 U used as startup fissile material. Since 233 U does not exist in nature, we must examine other available fissile materials to start up these reactor concepts. This work investigates the fuel cycle and neutronics performance of the Single-fluid Double-zone Thorium-based Molten Salt Reactor (SD-TMSR) with different fissile material loadings at startup: High Assay Low Enriched Uranium (HALEU) (19.79%), Pu mixed with HALEU (19.79%), reactor-grade Pu (a mixture of Pu isotopes chemically extracted from Pressurized Water Reactor (PWR) spent nuclear fuel (SNF) with 33 GW d/tHM burnup), transuranic elements (TRU) from Light Water Reactor (LWR) SNF, and 233 U. The MSR burnup routine provided by SERPENT-2 is used to simulate the online reprocessing and refueling in the SD-TMSR. The effective multiplication factor, fuel salt composition evolution, and net production of 233 U are studied in the present work. Additionally, the neutron spectrum shift during the reactor operation is calculated. The results show that the continuous flow of reactorgrade Pu helps transition to the thorium fuel cycle within a relatively short time (≈ 4.5 years) compared to 26 years for 233 U startup fuel. Finally, using TRU as the initial fuel materials offers the possibility of operating the SD-TMSR for an extended period of time (≈ 40 years) without any external feed of 233 U.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Spatially resolved X-ray imaging and molecular characterisation of sulfur and iron in organic- and sulfur-rich hydrocarbon source mudstones

Sulfurisation of organic matter (OM) is a prominent preservation mechanism, however iron sulfide precipitation, particularly pyrite (FeS2), can counteract this mechanism. There is a dearth of high-resolution, spatially-resolved spectroscopic (redox) information on sulfur and iron inventories within organic-rich rocks that would improve our understanding of prevailing environmental conditions during deposition. Here, state-of-the-art synchrotron-based X-ray absorption and fluorescence analyses of key organic- and sulfur-rich mudstones demonstrate the potential of these techniques to non-destructively map and produce detailed spectroscopic information. Detailed high-resolution analyses (μm- to mm-scale) reveal the presence of widespread sulfurised OM in the Blackstone Band of the Kimmeridge Clay Formation, in line with a persistence of euxinia over a long temporal span and low reactive iron input, facilitating the preservation of OM through sulfurisation. In contrast, the presence of sulfurised OM was transitional in the Monterey Formation, consistent with fluctuating water column redox conditions, and is less significant in the Whitby Mudstone Formation, likely due to the high reactive iron concentrations outcompeting sulfurised OM formation. Analyses of sulfur species using model compounds further indicate that the Whitby Formation is strongly enriched in inorganic reduced sulfur minerals, while both the Kimmeridge Clay and Monterey Formations are dominated by organic sulfur species. These synchrotron-based observations improve our understanding of environmental conditions during the time of deposition of these mudstones and thus show great promise in the study of organic-rich sediments, especially in allowing their depositional settings to be more accurately reconstructed.

Kimmeridge Clay Formation↗
DOE OSTI2023

Hydrobiogeochemical Controls on the Delivery of Dissolved Organic Matter to Boreal Headwater Streams

Understanding controls on the delivery of dissolved organic matter (DOM) from terrestrial to aquatic systems is key for constraining carbon balances and fluxes in boreal headwater catchments. The largest export of DOM generally occurs during intense periods of water delivery to the landscape (e.g., rain events); however, the timing and magnitude of DOM is complicated by geomorphological, hydrometeorological, and biogeochemical variability. To better assess mechanisms controlling the delivery of DOM to boreal streams, DOM was investigated in two morphologically distinct catchments of an experimental forest watershed in western Newfoundland, one dominated by low relief wetlands and the other by steep hillslopes. The DOM was compared during two fall storms of similar magnitude but contrasting moisture conditions during the autumn transition. Variable concentrations and optical character highlighted antecedent conditions are important for the delivery of DOM to boreal streams. Concentration-discharge relationships with stream hydrograph separation analysis suggest preferential flowpaths through shallow mineral horizons as a key pathway for delivery of DOM in the hillslope dominated catchment compared to rapid input from near-stream wetlands in the low relief catchment. Loss of DOM via preferential pathways suggests an additional mechanism for surface soil carbon loss not directly informed by lateral flow and soil hydrology, which has important implications for our conceptualization and modeling of carbon fluxes in boreal systems. These results suggest watershed scale responses of DOM in boreal headwater catchments are complex, and better linkages between catchment scale hydrology and landscape hydrobiogeochemistry are required to constrain terrestrial to aquatic carbon fluxes in boreal landscapes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Disentangling Oxygen and Water Vapor Effects on Optoelectronic Properties of Monolayer Tungsten Disulfide

By understanding how the environmental composition impacts the optoelectronic properties of transition metal dichalcogenide monolayers, we demonstrate that simple photoluminescence (PL) measurements of tungsten disulfide (WS 2 ) monolayers can differentiate relative humidity environments. In this paper, we examine the PL and photoconductivity of chemical vapor deposition grown WS 2 monolayers under three carefully controlled environments: inert gas (N 2 ), dry air (O 2 in N 2 ), and humid nitrogen (H 2 O vapor in N 2 ). The WS 2 PL is measured as a function of 532 nm laser power and exposure time and can be decomposed into the exciton, trion, and lower energy state(s) contributions. Under continuous illumination in either O 2 or H 2 O vapor environment, we find dramatic (and reversible) increases in PL intensity relative to the PL in an inert environment. The PL bathochromically shifts in an O 2 environment and is dominated by increased trion emission and diminished exciton emission. In contrast, the WS 2 PL increase in a H 2 O environment results from an overall increase in emission from all spectral components where the exciton contribution dominates. The drastic increases in PL are anticorrelated with corresponding decreases in photoconductivity, as measured by time-resolved microwave conductivity. The results suggest that both O 2 and H 2 O react photochemically with the WS 2 monolayer surface, modifying the optoelectronic properties, but do so via distinct pathways. Thus, we use these optoelectronic differences to differentiate the amount of humidity in the air, which we show with 0%, 40%, and 80% relative humidity environments. This deeper understanding of how ambient conditions impact WS 2 monolayers enables novel humidity sensors as well as a better understanding of the correlation between TMDC surface chemistry, light emission, and photoconductivity. Moreover, these WS 2 measurements highlight the importance of considering the impact of the local environment on reported results.

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

Experimental Determination of the Relationship Between Organic Aerosol Viscosity and Ice Nucleation at Upper Free Tropospheric Conditions

Abstract This work presents measurements of the ice nucleating ability of secondary organic material recorded between −40 and −70°C and relative humidity with respect to ice (RH ice ) between 150% and 220%. For a subset of systems, temperature and humidity dependence of particle viscosity as well as dry glass transition temperature were characterized using the dual tandem differential mobility analyzer method. Eleven unique monoterpene, sesquiterpene and aromatic precursors were used to generate secondary organic material (SOM) using either an oxidation flow reactor (OFR) or an environmental chamber (EC). For the SOM for which viscosity was measured, the particle glass transition temperatures varied between 6 and 23°C ( n = 8). Measurements were performed to verify that increased relative humidity did not plasticize the particles below −10°C at residence times similar to those in the ice nucleation instrument. No heterogeneous ice nucleation was observed at the ∼0.5% onset threshold for any of the materials generated. The ice nucleation occurs by the freezing of SOM solution droplets consistent with homogeneous freezing indicating that they form an aqueous solution, or the SOM particles required water saturation to freeze, indicating that they were hydrophobic. Experiments exploring the influence of functional groups and mass loading did not reveal any obvious influence of particle chemistry or generation conditions on the results. Close structural matches between known organic ice nucleating particles as precursor or formed products did not yield materials that promoted freezing. These experiments suggest that heterogeneous ice formation of glassy secondary organic materials is likely uncommon under upper free tropospheric conditions.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2015

Evidence from Hydrogen Isotopes in Meteorites for a Subsurface Hydrogen Reservoir on Mars

The surface geology and geomorphology of Mars indicates that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained. We have conducted in situ hydrogen isotope (D/H) analyses of quenched and impact glasses in three Martian meteorites (Yamato 980459, EETA79001, LAR 06319) by Cameca ims-6f at Digital Terrain Models (DTM) following the methods of [1]. The hydrogen isotope analyses provide evidence for the existence of a distinct but ubiquitous water/ice reservoir (D/H = 2-3 times Earth's ocean water: Standard Mean Ocean Water (SMOW)) that lasted from at least the time when the meteorites crystallized (173-472 Ma) to the time they were ejected by impacts (0.7-3.3 Ma), but possibly much longer [2]. The origin of this reservoir appears to predate the current Martian atmospheric water (D/H equals approximately 5-6 times SMOW) and is unlikely to be a simple mixture of atmospheric and primordial water retained in the Martian mantle (D/H is approximately equal to SMOW [1]). Given the fact that this intermediate-D/H reservoir (2-3 times SMOW) is observed in a diverse range of Martian materials with different ages (e.g., SNC (Shergottites, Nakhlites, Chassignites) meteorites, including shergottites such as ALH 84001; and Curiosity surface data [3]), we conclude that this intermediate-D/H reservoir is likely a global surficial feature that has remained relatively intact over geologic time. We propose that this reservoir represents either hydrated crust and/or ground ice interbedded within sediments. Our results corroborate the hypothesis that a buried cryosphere accounts for a large part of the initial water budget of Mars.

Usui, Tomohiro↗