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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

It takes a village: using a crowdsourced approach to investigate organic matter composition in global rivers through the lens of ecological theory

Though community-based scientific approaches are becoming more common, many scientific efforts are conducted by small groups of researchers that together develop a concept, analyze data, and interpret results that ultimately translate into a publication. Here, we present a community effort that breaks these traditional boundaries of the publication process by engaging the scientific community from initial hypothesis generation to final publication. We leverage community-generated data from the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) consortium to study organic matter composition through the lens of ecological theory. This community endeavor will use a suite of paired physical and chemical datasets collected from 97 river corridors across the globe. With our first step aimed at ideation, we engaged a community of scientists from 20 countries and 60 institutions, spanning disciplines and career stages by holding a virtual workshop (April 2021). In the workshop, participants generated content for questions, hypotheses, and proposed analyses based on the WHONDRS dataset. These ideation efforts resulted in several narratives investigating different questions led by different teams, which will be the basis for research articles in a Frontiers in Water collection. Currently, the community is collectively analyzing, interpreting, and synthesizing these data that will result in seven crowdsourced articles using a single, existing WHONDRS dataset. The use of a shared dataset across articles not only lowers barriers for broad participation by not requiring generation of new data, but also provides unique opportunities for emergent learning by connecting outcomes across studies. Here we will explain methods used to enable this community endeavor aimed to promote a greater diversity of thinking on river corridor biogeochemistry through community science.

Borton, Mikayla A.↗
DOE OSTI2025

Fluorogenic Biosensing with Tunable Polydiacetylene Vesicles

Polydiacetylenes (PDAs) are conjugated polymers that are well known for their colorimetric transition from blue to red with the application of energetic stimulus. Sensing platforms based on polymerized diacetylene surfactant vesicles and other structures have been widely demonstrated for various colorimetric biosensing applications. Although less studied and utilized, the transition also results in a change from a non-fluorescent to a highly fluorescent state, making polydiacetylenes useful for both colorimetric and fluorogenic sensing applications. Here, we focus on the characterization and optimization of polydiacetylene vesicles to tune their sensitivity for fluorogenic sensing applications. Particularly, we look at how the structure of the diacetylene (DA) hydrocarbon tail and headgroup affect the self-assembled vesicle size and stability, polymerization kinetics, and the fluorogenic, blue to red phase transition. Longer DA acyl tails generally resulted in smaller and more stable vesicles. The polymerization kinetics and the blue to red transition were a function of both the DA acyl tail length and structure of the headgroup. Decreasing the acyl tail length generally led to vesicles that were more sensitive to energetic stimuli. Headgroup modifications had different effects depending on the structure of the headgroup. Ethanolamine headgroups resulted in vesicles with potentially increased stimuli responsivity. The lower energy stimulus to induce the chromatic transition was attributed to an increase in headgroup hydrogen bonding and polymer backbone strain. Boronic-acid headgroup functionalization led to vesicles that were generally unstable, only weakly polymerized, and unable to fully transform to the red phase due to strong polar, aromatic headgroup interactions. This work presents the design of PDA vesicles in the context of biosensing platforms and includes a discussion of the past, present, and future of PDA biosensing.

Chemistry↗
DOE OSTI2025

Photo-Induced Hydrogen Production from Formic Acid Using a Palladium Catalyst

Liquid organic hydrogen carriers (LOHCs) are recognized as promising sustainable hydrogen (H 2 ) carriers due to their high volumetric capacity and ability to store H 2 at ambient conditions, eliminating the need for energy-intensive liquefaction or compression processes associated with H 2 or ammonia gas. One of the main current drawbacks, however, is LOHCs’ high energy demand for H 2 release. This work presents the photo-induced liberation of H 2 from formic acid (FA) as a liquid H 2 carrier, using visible light and well-established 5 wt% palladium nanoparticles supported over carbon (Pd/C). We show that low-power light-emitting diodes (LEDs) produced higher gas flow than their thermal baseline (35 °C), with 27.2 mL/min and 7.72 mL/min, respectively. Further, the rate of gas evolved with light intensity, catalyst loading, and the concentration of FA. Light-induced dehydrogenation shows similar deactivation as the known thermal mechanisms, such as the decreased Pd 2+ /Pd 0 ratio and Pd nanoparticle agglomeration. Hence, these observations suggest a photothermal mechanism, whereby the LED provides heat efficiently absorbed by the Pd/C catalyst and enhanced by Pd’s ability to absorb light, thereby driving the FA dehydrogenation reaction at ambient conditions.

08 HYDROGEN↗
DOE OSTI2026

Transformative Impacts of Laser-Induced Breakdown Spectroscopy on Environmental and Biological Research at Oak Ridge National Laboratory

This manuscript will present an advancement of transformative research that has been conducted at Oak Ridge National Laboratory (ORNL) over a 25-year period (2000–2025) on a variety of environmental and biological matrices. These investigations derived a fundamental understanding of how elemental detection and analysis of these matrices led to the knowledge and discovery of natural processes in plants and the environment. Each project led to the initiation of a new research area which unearthed awesome and novel breakthroughs. Highlights are listed below: 1. The preliminary research at ORNL centered on the detection of aerosols utilizing Laser-induced Breakdown Spectroscopy (LIBS) technology. The Clean Air Act Amendment (CAAA) of 1990 highlighted the importance of identifying hazardous air pollutants (HAPs) due to their impact on environmental and human health, thereby underscoring the need to detect various toxic elements. Research in aerosol chemistry aimed to identify these harmful elements released by factories during periods of increased emissions in their manufacturing processes. LIBS emerged as the most effective method for real-time, in situ measurements of metal species in both gaseous and aerosol phases. 2. An understanding of the presence of total carbon in soils gives perspective on how to develop carbon sequestration strategies. The recognition that carbon sinks can evolve back to carbon sources to emit back to the atmosphere was an important consideration. Also, the concentration of carbon in soil indicates the health of land areas for growing crops successfully. 3. The direct detection of most of the elements in a wood sample in a single emission spectrum, without sample preparation, encouraged the research to use the LIBS technique for preservative treated wood coupled with use of multivariate statistical methodology. Additionally, it encouraged the researchers to try to differentiate natural woods from different parts of the country, and it was successfully demonstrated that LIBS coupled with MVA analysis could differentiate wood of different species from each other and of similar species grown in different environments based on their elemental spectra. This was a breakthrough since it revealed a systematic approach to connect elemental scarcity and abundance to either drought or typical rainfall conditions for the hardwood trees grown in specific areas. 4. Furthermore, the research progressed to reveal physiological and developmental processes contributing to biomass production such that the variation in leaf elemental composition increases our understanding of terrestrial nutrient cycles, as well as tracking the transfer of toxic elements from soils to living organisms. 5. Recently another breakthrough viz., ionomics initiated the correlation of elements to specific genes, uncovering the function that the element performed in the plant. More recently, this has been extended from plants to fungi as well as fungi growing in symbiotic relations with plants.

09 BIOMASS FUELS↗
DOE OSTI2022

Influence of Superlattice Structure on V-Defect Distribution, External Quantum Efficiency and Electroluminescence for Red InGaN Based µLEDs on Silicon

Achieving high quantum efficiency in long-wavelength LEDs has posed a significant challenge to the solid-state lighting and display industries. In this article, we use V-defect engineering as a technique to achieve higher efficiencies in red InGaN LEDs on (111) Si through lateral injection. We investigate the effects of superlattice structure on the V-defect distribution, the electroluminescence properties, and the external quantum efficiency. Increasing the relative thickness of In in the InGaN/GaN superlattice and the total superlattice thickness correlate with a reduction of active region defects and increased external quantum efficiencies. The highest measured on-chip EQE was 0.15% and based on Monte-Carlo ray tracing simulations for light extraction we project this would correspond to a flip-chip EQE of ~2.5%.

36 MATERIALS SCIENCE↗
DOE OSTI2021

An Environmental and Societal Analysis of the US Electrical Energy Industry Based on the Water–Energy Nexus

To meet rising energy demands, power plant operations will expand, influencing the interactions between the water–energy nexus and society. However, a major challenge is integration of social dimensions within electricity generation. To address this, we generate a baseline dataset using US public data (2014–2019) from the Energy Information Administration and US Bureau of Labor Statistics. We identify the rate of energy consumed, CO 2 , SO 2 and NO x emissions generated, and water used per MWh net electricity as well as employee wellbeing per unit MW capacity during electricity generation. Rates of energy consumption (MMBtu/MWh) decreased 4.9%, but water consumption and withdrawal (m 3 /MWh) both increased 0.93% and 0.31%, respectively. Emissions of CO 2 , SO 2 and NO x decreased 22.64%, 75% and 25% MT/MWh, respectively. Thermoelectric cooling withdrawal and consumption is led by natural gas (50.07%, 38.31%), coal (29.61%, 25.07%), and nuclear energies (13.55%, 18.99%). Electric power generation contributes 0.06 injuries–illnesses/TWh and 0.001 fatalities/TWh, of which fossil fuels contributed 70% and 15%, respectively. Fossil fuels led in average annual employment (0.02 employees/MW) with low cost salaries (USD 0.09/MW) likely due to high collective capacity, which is declining. Estimated rates in this study and framework will aid power industry transition and operational decision makers.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

The Landscape of RNA-Protein Interactions in Plants: Approaches and Current Status

RNAs transmit information from DNA to encode proteins that perform all cellular processes and regulate gene expression in multiple ways. From the time of synthesis to degradation, RNA molecules are associated with proteins called RNA-binding proteins (RBPs). The RBPs play diverse roles in many aspects of gene expression including pre-mRNA processing and post-transcriptional and translational regulation. In the last decade, the application of modern techniques to identify RNA–protein interactions with individual proteins, RNAs, and the whole transcriptome has led to the discovery of a hidden landscape of these interactions in plants. Global approaches such as RNA interactome capture (RIC) to identify proteins that bind protein-coding transcripts have led to the identification of close to 2000 putative RBPs in plants. Interestingly, many of these were found to be metabolic enzymes with no known canonical RNA-binding domains. Here, we review the methods used to analyze RNA–protein interactions in plants thus far and highlight the understanding of plant RNA–protein interactions these techniques have provided us. We also review some recent protein-centric, RNA-centric, and global approaches developed with non-plant systems and discuss their potential application to plants. We also provide an overview of results from classical studies of RNA–protein interaction in plants and discuss the significance of the increasingly evident ubiquity of RNA–protein interactions for the study of gene regulation and RNA biology in plants.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Microstructure and Mechanical Properties of Intercritically Treated Grade 91 Steel

Premature creep failures at the intercritical heat affected zone (ICHAZ) of creep-resistant steel weldments have been frequently reported. However, the creep degradation mechanism of different microstructure constituents in ICHAZ is complicated and needs further clarification. In this work, Grade 91 steel was intercritically heat-treated at a temperature (860 °C) between the critical temperatures AC1 and AC3, and a correlation between microstructure and mechanical properties of the heat-treated specimen was built. The effects of austenitization and tempering resulting from the intercritical treatment (IT) differentiated the local strain energies between the two microstructure constituents: newly transformed martensite (NTM) and over-tempered martensite (OTM). The formation of NTM grains led to a hardness increase from 247 HV0.5 in the base metal to 332 HV0.5 in the IT specimen. The ultimate tensile strength (UTS) increased from 739 MPa in the base metal to 1054 MPa in the IT specimen. Extensive growth of the OTM grains and rapid recovery of NTM grains took place simultaneously in the IT specimen during a typical tempering at 760 °C. These microstructure degradations led to a lowered hardness of 178 HV0.5, a reduced UTS of 596 MPa, and a poor creep resistance with a minimum creep strain rate of 0.49 %/h at 650 °C in an IT + tempering (ITT) specimen.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Photoinitiator Selection and Concentration in Photopolymer Formulations towards Large-Format Additive Manufacturing

Photopolymers are an attractive option for large-format additive manufacturing (LFAM), because they can be formulated from structural thermosets and cure rapidly in ambient conditions under low-energy ultraviolet light-emitting diode (UV LED) lamps. Photopolymer cure is strongly influenced by the depth penetration of UV light, which can be limited in the 2–4 mm layer thicknesses typical of LFAM. Photoinitiator (PI) systems that exhibit photobleaching have proven useful in thick-section cure applications, because they generate a photoinitiation wavefront, but this effect is time-dependent. This study investigates the light transmission and through-thickness cure behavior in (meth)acrylate photopolymer formulations with the photobleaching initiator bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (BAPO). Utilizing an optical model developed by Kenning et al., lower concentrations (0.1 wt% to 0.5 wt%) of BAPO were predicted to yield rapid onset of photoinitiation. In situ cure measurements under continuous UV LED irradiation of 380 mW/cm2 showed that a 0.1 wt% concentration of BAPO achieved peak polymerization rate within 2.5 s at a 3-mm depth. With only 1 s of irradiation at 1.7 W/cm2 intensity, the 0.1 wt% BAPO formulation also achieved the highest level of cure of the formulas tested. For an irradiation dose of 5.5 J/cm2 at a duration of 3.7 s, cured polymer specimens achieved a flexural strength of 108 MPa and a flexural modulus of 3.1 GPa. This study demonstrates the utility of optical modeling as a potential screening tool for new photopolymer formulations, primarily in identifying an upper limit to PI concentration for the desired cure depth. The results also show that photobleaching provides only a limited benefit for LFAM applications with short (1.0 s to 3.7 s) UV irradiation times and indicate that excess PI concentration can inhibit light transmission even under extended irradiation times up to 60 s.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Optical analysis of III-nitride micro-light-emitting diodes with different sidewall treatments at low current density operation

Here, in this work, the optical efficiency of III-nitride blue micro-LEDs (μLEDs) ranged from 5 × 5 to 60 × 60 μm 2 with different sidewall treatments at low current density range was investigated. The results showed dielectric sidewall passivation using atomic layer deposition (ALD) has superior optical enhancement compared to conventional RF sputtering, where most of the enhancement occurred at low current density range. Additionally, the use of ALD sidewall passivation and chemical treatment offered significant efficiency improvement for different sizes of μLEDs at operating less than 1 A cm −2 and the devices without sidewall treatments did not emit light. The effect of sidewall treatments to the effective Shockley–Read–Hall (SRH) nonradiative recombination coefficient, or the effective A coefficient from the ABC model, was estimated. The effective SRH nonradiative recombination coefficient was suppressed by two orders of magnitude for devices with sidewall treatments compared to devices without sidewall passivation.

Wong, Matthew S.↗
DOE OSTI2016

Detailed opacity comparison for an improved stellar modeling of the envelopes of massive stars

Seismic observations have led to doubts or ambiguities concerning the opacity calculations used in stellar physics. Here, we concentrate on the iron-group opacity peak, due to iron, nickel, and chromium, located around T = 200,000 K for densities from 10{sup −8} to 10{sup −4} g cm{sup −3}, which creates some convective layers in stellar radiative envelopes for masses between 3 and 18 M{sub ⊙}. These conditions were extensively studied in the 1980s. More recently, inconsistencies between OP and OPAL opacity calculations have complicated the interpretation of seismic observations as the iron-group opacity peak excites acoustic and gravity modes in SPB, β Cephei, and sdB stars. We investigate the reliability of the theoretical opacity calculations using the modern opacity codes ATOMIC and SCO-RCG. We show their temperature and density dependence for conditions that are achievable in the laboratory and equivalent to astrophysical conditions. We also compare new theoretical opacity spectra with OP spectra and quantify how different approximations impact the Rosseland mean calculations.This detailed study estimates new ATOMIC and SCO-RCG Rosseland mean values for astrophysical conditions which we compare to OP values. Some puzzling questions are still under investigation for iron, but we find a strong increase in the Rosseland mean nickel opacity of a factor between 2 and 6 compared to OP. This appears to be due to the use of extrapolated atomic data for the Ni opacity within the OP calculations. A study on chromium is also shown.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

A 3π Search for Planet Nine at 3.4 μm with WISE and NEOWISE

The recent “Planet Nine” hypothesis has led to many observational and archival searches for this giant planet proposed to orbit the Sun at hundreds of astronomical units. While trans-Neptunian object searches are typically conducted in the optical, models suggest Planet Nine could be self-luminous and potentially bright enough at ∼3–5 μm to be detected by the Wide-field Infrared Survey Explorer (WISE). We have previously demonstrated a Planet Nine search methodology based on time-resolved WISE coadds, allowing us to detect moving objects much fainter than would be possible using single-frame extractions. In the present work, we extend our 3.4 μm (W1) search to cover more than three-quarters of the sky and incorporate four years of WISE observations spanning a seven-year time period. This represents the deepest and widest-area WISE search for Planet Nine to date. We characterize the spatial variation of our survey’s sensitivity and rule out the presence of Planet Nine in the parameter space searched at W1 < 16.7 in high Galactic latitude regions (90% completeness).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

How the First Stars Regulated Star Formation. II. Enrichment by Nearby Supernovae

Metals from Population III (Pop III) supernovae led to the formation of less massive Pop II stars in the early universe, altering the course of evolution of primeval galaxies and cosmological reionization. There are a variety of scenarios in which heavy elements from the first supernovae were taken up into second-generation stars, but cosmological simulations only model them on the largest scales. We present small-scale, high-resolution simulations of the chemical enrichment of a primordial halo by a nearby supernova after partial evaporation by the progenitor star. We find that ejecta from the explosion crash into and mix violently with ablative flows driven off the halo by the star, creating dense, enriched clumps capable of collapsing into Pop II stars. Metals may mix less efficiently with the partially exposed core of the halo, so it might form either Pop III or Pop II stars. Both Pop II and III stars may thus form after the collision if the ejecta do not strip all the gas from the halo. The partial evaporation of the halo prior to the explosion is crucial to its later enrichment by the supernova.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

The Aemulus Project. I. Numerical Simulations for Precision Cosmology

The rapidly growing statistical precision of galaxy surveys has led to a need for ever more precise predictions of the observables used to constrain cosmological and galaxy formation models. The primary avenue through which such predictions will be obtained is suites of numerical simulations. These simulations must span the relevant model parameter spaces, be large enough to obtain the precision demanded by upcoming data, and be thoroughly validated in order to ensure accuracy. In this paper, we present one such suite of simulations, forming the basis for the AEMULUS Project, a collaboration devoted to precision emulation of galaxy survey observables. We have run a set of 75 (1.05 h(-1) Gpc)(3) simulations with mass resolution and force softening of 3.51 x 10(10) (Omega(m)/0.3) h(-1) M-circle dot and 20 h(-1) kpc, respectively, in 47 different wCDM cosmologies spanning the range of parameter space allowed by the combination of recent cosmic microwave background, baryon acoustic oscillation, and Type Ia supernova results. We present convergence tests of several observables including spherical overdensity halo mass functions, galaxy projected correlation functions, galaxy clustering in redshift space, and matter and halo correlation functions and power spectra. We show that these statistics are converged to 1% (2%) or to the sample variance of the statistic, whichever is larger, for halos with more than 500 (200) particles, respectively, and scales of r > 200 h(-1) kpc. in real space or k similar to 3 h Mpc(-1). in harmonic space for z <= 1. We find that the dominant source of uncertainty comes from varying the particle loading of the simulations. This leads to large systematic errors for statistics using halos with fewer than 200 particles and scales smaller than k similar to 4 h Mpc(-1). We provide the halo catalogs and snapshots detailed in this work to the community at. https://AemulusProject.github.io.

large-scale structure of universe↗
DOE OSTI2019

Antimicrobial activity of bacteriophage derived triple fusion protein against Staphylococcus aureus

The increasing spread of antibiotic-resistant microorganisms has led to the necessity of developing alternative antimicrobial treatments. The use of peptidoglycan hydrolases is a promising approach to combat bacterial infections. In our study, we constructed a 2 kb-triple-acting fusion gene (TF) encoding the N-terminal amidase-5 domain of streptococcal LambdaSA2 prophage endolysin (Dglutamine-L-lysin endopeptidase), a mid-protein amidase-2 domain derived from the staphylococcal phage 2638A endolysin (N-acetylmuramoyl-L-alanine amidase) and the mature version (246 residues) of the Staphylococcus simulans Lysostaphin bacteriocin (glycyl-glycine endopeptidase) at the C-terminus. The TF gene was expressed in Nicotiana benthamiana plants using the nonreplicating Cowpea mosaic virus (CPMV)-based vector pEAQ-HT and the replicating Alternanthera mosaic virus (AltMV)-based pGD5TGB1L8823-MCS-CP3 vector, and in Escherichia coli using pET expression vectors pET26b+ and pET28a+. The resulting poor expression of this fusion protein in plants prompted the construction of a TF gene codon-optimized for expression in tobacco plants, resulting in an improved codon adaptation index (CAI) from 0.79 (TF gene) to 0.93 (TFnt gene). Incorporation of the TFnt gene into the pEAQ-HT vector, followed by transient expression in N. benthamiana, led to accumulation of TFnt to an approximate level of 0.12 mg/g of fresh leaf weight. Antimicrobial activity of purified plant- and bacterial-produced TFnt proteins was assessed against two strains of Gram-positive Staphylococcus aureus 305 and Newman. The results showed that plant-produced TFnt protein was preferentially active against S. aureus 305, showing 14% of growth inhibition, while the bacterial-produced TFnt revealed significant antimicrobial activity against both strains, showing 68 (IC50 25 µg/ml) and 60% (IC50 71 µg/ml) growth inhibition against S. aureus 305 and Newman, respectively. Although the combination of codon optimization and transient expression using the non-replicating pEAQ-HT expression vector facilitated production of the TFnt protein in plants, the most functionally active antimicrobial protein was obtained using the prokaryotic expression system.

codon optimization↗
DOE OSTI2012

Battery Electric Vehicle Driving and Charging Behavior Observed Early in The EV Project

As concern about society's dependence on petroleum-based transportation fuels increases, many see plug-in electric vehicles (PEV) as enablers to diversifying transportation energy sources. These vehicles, which include plug-in hybrid electric vehicles (PHEV), range-extended electric vehicles (EREV), and battery electric vehicles (BEV), draw some or all of their power from electricity stored in batteries, which are charged by the electric grid. In order for PEVs to be accepted by the mass market, electric charging infrastructure must also be deployed. Charging infrastructure must be safe, convenient, and financially sustainable. Additionally, electric utilities must be able to manage PEV charging demand on the electric grid. In the Fall of 2009, a large scale PEV infrastructure demonstration was launched to deploy an unprecedented number of PEVs and charging infrastructure. This demonstration, called The EV Project, is led by Electric Transportation Engineering Corporation (eTec) and funded by the U.S. Department of Energy. eTec is partnering with Nissan North America to deploy up to 4,700 Nissan Leaf BEVs and 11,210 charging units in five market areas in Arizona, California, Oregon, Tennessee, and Washington. With the assistance of the Idaho National Laboratory, eTec will collect and analyze data to characterize vehicle consumer driving and charging behavior, evaluate the effectiveness of charging infrastructure, and understand the impact of PEV charging on the electric grid. Trials of various revenue systems for commercial and public charging infrastructure will also be conducted. The ultimate goal of The EV Project is to capture lessons learned to enable the mass deployment of PEVs. This paper is the first in a series of papers documenting the progress and findings of The EV Project. This paper describes key research objectives of The EV Project and establishes the project background, including lessons learned from previous infrastructure deployment and PEV demonstrations. One such previous study was a PHEV demonstration conducted by the U.S. Department of Energy's Advanced Vehicle Testing Activity (AVTA), led by the Idaho National Laboratory (INL). AVTA's PHEV demonstration involved over 250 vehicles in the United States, Canada, and Finland. This paper summarizes driving and charging behavior observed in that demonstration, including the distribution of distance driven between charging events, charging frequency, and resulting proportion of operation charge depleting mode. Charging demand relative to time of day and day of the week will also be shown. Conclusions from the PHEV demonstration will be given which highlight the need for expanded analysis in The EV Project. For example, the AVTA PHEV demonstration showed that in the absence of controlled charging by the vehicle owner or electric utility, the majority of vehicles were charged in the evening hours, coincident with typical utility peak demand. Given this baseline, The EV Project will demonstrate the effects of consumer charge control and grid-side charge management on electricity demand. This paper will outline further analyses which will be performed by eTec and INL to documenting driving and charging behavior of vehicles operated in a infrastructure-rich environment.

25 ENERGY STORAGE↗
DOE OSTI2016

Understanding the optical properties of ambient sub- and supermicron particulate matter: results from the CARES 2010 field study in northern California

Abstract. Measurements of the optical properties (absorption, scattering and extinction) of PM1, PM2.5 and PM10 made at two sites around Sacramento, CA, during the June 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES) are reported. These observations are used to establish relationships between various intensive optical properties and to derive information about the dependence of the optical properties on photochemical aging and sources. Supermicron particles contributed substantially to the total light scattering at both sites, about 50 % on average. A strong, linear relationship is observed between the scattering Ångström exponent for PM10 and the fraction of the scattering that is contributed by submicron particles (fsca, PM1) at both sites and with similar slopes and intercepts (for a given pair of wavelengths), suggesting that the derived relationship may be generally applicable for understanding variations in particle size distributions from remote sensing measurements. At the more urban T0 site, the fsca, PM1 increased with photochemical age, whereas at the downwind, more rural T1 site the fsca, PM1 decreased slightly with photochemical age. This difference in behavior reflects differences in transport, local production and local emission of supermicron particles between the sites. Light absorption is dominated by submicron particles, but there is some absorption by supermicron particles ( ∼ 15 % of the total). The supermicron absorption derives from a combination of black carbon that has penetrated into the supermicron mode and from dust, and there is a clear increase in the mass absorption coefficient of just the supermicron particles with increasing average particle size. The mass scattering coefficient (MSC) for the supermicron particles was directly observed to vary inversely with the average particle size, demonstrating that MSC cannot always be treated as a constant in estimating mass concentrations from scattering measurements, or vice versa. The total particle backscatter fraction exhibited some dependence upon the relative abundance of sub- versus supermicron particles; however this was modulated by variations in the median size of particles within a given size range; variations in the submicron size distribution had a particularly large influence on the observed backscatter efficiency and an approximate method to account for this variability is introduced. The relationship between the absorption and scattering Ångström exponents is examined and used to update a previously suggested particle classification scheme. Differences in composition led to differences in the sensitivity of PM2.5 to heating in a thermodenuder to the average particle size, with more extensive evaporation (observed as a larger decrease in the PM2.5 extinction coefficient) corresponding to smaller particles; i.e., submicron particles were generally more susceptible to heating than the supermicron particles. The influence of heating on the particle hygroscopicity varied with the effective particle size, with larger changes observed when the PM2.5 distribution was dominated by smaller particles.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Impacts of droughts and extreme-temperature events on gross primary production and ecosystem respiration: a systematic assessment across ecosystems and climate zones

Extreme climatic events, such as droughts and heat stress, induce anomalies in ecosystem–atmosphere CO 2 fluxes, such as gross primary production (GPP) and ecosystem respiration (R eco ), and, hence, can change the net ecosystem carbon balance. However, despite our increasing understanding of the underlying mechanisms, the magnitudes of the impacts of different types of extremes on GPP and R eco within and between ecosystems remain poorly predicted. Here we aim to identify the major factors controlling the amplitude of extreme-event impacts on GPP, R eco , and the resulting net ecosystem production (NEP). We focus on the impacts of heat and drought and their combination. We identified hydrometeorological extreme events in consistently downscaled water availability and temperature measurements over a 30-year time period. We then used FLUXNET eddy covariance flux measurements to estimate the CO 2 flux anomalies during these extreme events across dominant vegetation types and climate zones. Overall, our results indicate that short-term heat extremes increased respiration more strongly than they downregulated GPP, resulting in a moderate reduction in the ecosystem's carbon sink potential. In the absence of heat stress, droughts tended to have smaller and similarly dampening effects on both GPP and R eco and, hence, often resulted in neutral NEP responses. The combination of drought and heat typically led to a strong decrease in GPP, whereas heat and drought impacts on respiration partially offset each other. Taken together, compound heat and drought events led to the strongest C sink reduction compared to any single-factor extreme. A key insight of this paper, however, is that duration matters most: for heat stress during droughts, the magnitude of impacts systematically increased with duration, whereas under heat stress without drought, the response of R eco over time turned from an initial increase to a downregulation after about 2 weeks. This confirms earlier theories that not only the magnitude but also the duration of an extreme event determines its impact. Our study corroborates the results of several local site-level case studies but as a novelty generalizes these findings on the global scale. Specifically, we find that the different response functions of the two antipodal land–atmosphere fluxes GPP and R eco can also result in increasing NEP during certain extreme conditions. Apparently counterintuitive findings of this kind bear great potential for scrutinizing the mechanisms implemented in state-of-the-art terrestrial biosphere models and provide a benchmark for future model development and testing.

54 ENVIRONMENTAL SCIENCES↗

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