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Trace gases in the atmosphere of Mars - An indicator of microbial life

The detection of certain trace gases in the atmosphere of Mars would indicate the presence of microbial life on the surface. Candidate biogenic gases include CH4, NH3, N2O, and several reduced sulfur species. Chemical thermodynamic equilibrium and photochemical calculations preclude the presence of these gases in any measurable concentrations in the atmosphere of Mars in the absence of biogenic production. A search for these gases utilizing either high-resolution (spectral and spatial) spectroscopy from a Mars orbiter, such as the Mars Observer orbiter, and/or in situ measurements from a Mars lander or rover is proposed.

Levine, Joel S.

Trends in source gases

Source gases are defined as those gases that, by their breakdown, introduce into the stratosphere halogen, hydrogen, and nitrogen compounds that are important in stratospheric ozone destruction. Given here is an update of the existing concentration time series for chlorocarbons, nitrous oxide, and methane. Also reviewed is information on halogen containing species and the use of these data for establishing trends. Also reviewed is evidence on trends in trace gases that influence tropospheric chemistry and thus the tropospheric lifetimes of source gases, such as carbon dioxide, carbon monoxide, or nitrogen oxides. Much of the information is given in tabular form.

Ehhalt, D. H.

Characterisation of Q-gases and other noble gas components in the Murchison meteorite

Noble gases in several HF/HCl resistant residues of the CM2 chondrite Murchison were measured by closed-system stepped etching, in order to study the planetary gases in their major carrier 'Q'-an ill-defined minor phase, perhaps merely a set of adsorption sites. Neon, Ar, Kr, Xe, and probably also He in 'Q' of Murchison have the same isotopic and nearly the same elemental abundances as their counterparts in Allende (CV3). The isotopic composition of Ne-Q is consistent with mass-dependent fractionation of either solar wind Ne or Ne from solar energetic particles. Unlike Allende, Murchison during HNO3 attack release, besides Q-gases, large amounts of two other Ne-components, Ne-E and Ne-A3, a third subcomponent of Ne-A. This work confirms that Q-gases of well-defined composition were an important noble gas component in the early solar system an are now found in various classes of meteorites, such as carbonaceous chondrites, ureilites, and ordinary chondrites. Ne-Q may have played a role in the formation of noble gas reservoirs in terrestrial planets.

Wieler, Rainer

The Gaseous Explosive Reaction : The Effect of Inert Gases

Attention is called in this report to previous investigations of gaseous explosive reactions carried out under constant volume conditions, where the effect of inert gases on the thermodynamic equilibrium was determined. The advantage of constant pressure methods over those of constant volume as applied to studies of the gaseous explosive reaction is pointed out and the possibility of realizing for this purpose a constant pressure bomb mentioned. The application of constant pressure methods to the study of gaseous explosive reactions, made possible by the use of a constant pressure bomb, led to the discovery of an important kinetic relation connecting the rate of propagation of the zone of explosive reaction within the active gases, with the initial concentrations of those gases: s = K(sub 1)(A)(sup n1)(B)(sup n2)(C)(sup n3)------. By a method analogous to that followed in determining the effect of inert gases on the equilibrium constant K, the present paper records an attempt to determine their kinetic effect upon the expression given above.

Stevens, F W

The fractionation of noble gases in diamonds of CV3 Efremovka chondrite

It was shown that in diamonds of Efremovka CV3 the noble gases with normal isotopic compositions are fractionated in different degree while the correlation of isotopic anomalous components is nearly constant. Some data for noble gases in DE-4 sample of Efremovka chondrite are considered. In contrast to DE-2 sample the DE-4 was treated except conc. HClO4, 220 C in addition with mixture of conc. H2SO4+H3PO4 (1:1), 220 C, twice. Noble gases analysis were performed in Germany at Max Plank Institute fur Chemie. Noble gases were released by oxidation of samples at stepped heating from 420 C to 810 C and by pyrolysis at 580, 590, and 680 C.

Fisenko, A. V.

Infrared Measurements of Atmospheric Gases Above Mauna Loa, Hawaii, in February 1987

Infrared solar absorption spectra recorded at 0.02/ cm resolution from the National Oceanic and Atmospheric Administration (NOAA) Geophysical Monitoring for Climate Change (GMCC) program station at Mauna Loa, Hawaii (latitude 19.5 deg N, longitude 155.6 deg W, elevation 3.40 km), in February 1997 have been analyzed to determine simultaneous total vertical column amounts for 13 atmospheric gases. Average tropospheric concentrations of CO2, N2O, CH4, and CHCIF2 and the daytime diurnal variations or the total columns of NO and NO2 have also been inferred. The retrieved total columns (in molecules /sq cm) of the nondiurnally varying gases are 1.6 +/- 0.2 x 10(exp 15) for HCl, 5.9 +/- 1.2 x 10(exp 15) for HNO3, 2.0 +/- 0.2 x 10(exp 21) for H2O16, 4.4 +/- 0.7 x 10(exp 18) for H2O18, 2.7 +/- 0.1 x 10(exp 17) for HDO, 2.3 +/- 0.2 x 10(exp 19) for CH4, 5.0 +/- 0.5 x 10(exp 21) for CO2, 6.7 +/- 0.8 x 10(exp 18) for O3, 4.3 +/- 0.4 x 10(exp 18) for N2O, 1.0 +/- 0.2 x 10(exp 16) for C2H6, and 9.7 +/- 2.5 x 10(exp 14) for CHClF2. We compare the total column measurements of HCl and HNO3 with previously reported ground-based, aircraft, and satellite measurements. The results for HCl are or particular interest because of the expected temporal increase in the concentration of this gas in the stratosphere. However, systematic differences among stratospheric HCl total column measurements from 1978 to 1980 and the absence of observations of free tropospheric HCl above Mauna Loa make it impossible to obtain a reliable estimate of the trend in the total burden of HCl. The measured HNO3 total column is consistent with aircraft measurements from approx. 12 km altitude. The O3 total column deduced from the IR spectra agrees with correlative Mauna Loa Umkehr measurements within the estimated error limits. The column-averaged D/H ratio of water vapor is (68 +/- 9) x- 10(exp -6), which is 0.44 +/- 0.06 times the reference value of 155.76 x 10(exp -6) for standard mean ocean water (SMOW). This large depletion in the D content of water vapor is similar to published measurements of the upper troposphere and lower stratosphere. Average tropospheric concentrations deduced for CO2, N2O, and CH4 are in good agreement with correlative NOAA GMCC surface data, indicating consistency between the measurement techniques for determining tropospheric volume mixing ratios. Results of the present study indicate that Mauna Loa is a favorable site for infrared monitoring of atmospheric gases. The site is particularly favorable for monitoring the tropospheric volume mixing ratios of long-lived gases, since the high altitude of the tropopause reduces corrections required to account for the decrease in volume mixing ratio in the stratosphere.

Rinsland, C. P.

Fullerenes and the Nature of Planetary Gases

Over the past several decades, two issues have dominated the discussion of planetary noble gas patterns: 1) the general resemblance of the noble gas abundances in carbonaceous chondrites to those measured in the Earth s atmosphere and; 2) atmospheric inventories of argon and neon that fall off significantly with increasing distance from the Sun. The recognition of the latter has led to the conclusion that the planetary component is not found on planets. In particular, the inability to explain the missing xenon reservoir, once thought to be sequestered in crustal rocks has been extremely troublesome. Some models have focused on various fractionations of solar wind rather than condensation as the process for the evolution of noble gases in the terrestrial planets. However, these models cannot explain the observed gradient of the gases, nor do they account for the similar Ne/Ar ratios and the dissimilar planetary Ar/Kr ratios. More recent studies have focused on hydrodynamic escape to explain the fractionation of gases, like neon, in the atmosphere and the mantle. Escape theory also seems to explain, in part, the isotopically heavy argon on Mars, however, it does not explain the discrepancies observed for the abundances of argon and neon on Venus and the Earth. This has led to the assumption that some combination of solar wind implantation, absorption and escape are needed to explain the nature of planetary noble gases.

Becker, Luann

Differential Radiometers Using Fabry-Perot Interferometric Technique for Remote Sensing Determination of Various Atmospheric Trace Gases

New type of remote sensing instrument based upon the Fabry-Perot inte rferometric technique has been developed at NASA's Goddard Space Flight Center. Fabry-Perot interferometry (FPI) is a well known, powerful spectroscopic technique and one of its many applications is to be use d to measure greenhouse gases and also some harmful species in the at mosphere. With this technique, absorption of particular species is me asured and related to its concentration. A solid Fabry-Perot etalon is used as a frequency filter to restrict the measurement to particular absorption bands of the gas of interest. With adjusting the thicknes s of the etalon that separation (in frequency) of the transmitted fri nges can be made equal to the almost constant separation of the gas a bsorption lines. By adjusting the temperature of the etalon, which changes the index of refi-action of its material, the transmission fring es can be brought into nearly exact correspondence with absorption li nes of the particular species. With this alignment between absorption lines and fringes, changes in the amount of a species in the atmosph ere strongly affect the amount of light transmitted by the etalon and can be related to gas concentration. The instrument that we have dev eloped detects the absorption of various atmospheric trace gases in d irect or reflected sunlight. Our instrument employing Fabry-Perot interferometer makes use of two features to achieve high sensitivity. The first is high spectral resolution enabling one to match the width of an atmospheric absorption feature by the instrumental band pass. The second is high optical throughput enabled by using multiple spectral lines simultaneously. For any species that one wishes to measure, thi s first feature is available while the use of multiple spectral features can be employed only for species with suitable spectra and freedom from interfering species in the same wavelength region. We have deve loped an instrument for use as ground based, airborne and satellite s ensor for gases such as carbon dioxide (1570 nm), oxygen (762 nm and 768 nm lines sensitive to changes in oxygen pressure and oxygen temper ature) and water vapor (940 nm). Our current goal is to develop an ul tra precise, inexpensive, ground based device suitable for wide deplo yment as a validation instrument for the Orbiting Carbon Observatory (OCO) satellite. We show sensitivity measurements for CO2, 02, and H2 O, compare our measurements to those obtained using other types of sensors and discuss some of the peculiarities that must be addressed in order to provide the very high quality column detection required for solving problems about global distribution of greenhouse gases and cl imatological models. In another area of research we are interested in developing a small-size channel for CO2 capable of doing simultaneous measurements with the AERONET (Aerosol Robotic Network) at NASA, God dard to study the hypothesis that atmospheric aerosols affect the reg ional terrestrial carbon cycle. We present recent data from our groun d based measurements of O2, CO2, H2O and (13)CO2 and discuss extensio n of the technique to new species and applications.

Georgieva, E. M.

Reactor for producing large particles of materials from gases

A method and apparatus is disclosed for producing large particles of material from gas, or gases, containing the material (e.g., silicon from silane) in a free-space reactor comprised of a tube (20) and controlled furnace (25). A hot gas is introduced in the center of the reactant gas through a nozzle (23) to heat a quantity of the reactant gas, or gases, to produce a controlled concentration of seed particles (24) which are entrained in the flow of reactant gas, or gases. The temperature profile (FIG. 4) of the furnace is controlled for such a slow, controlled rate of reaction that virtually all of the material released condenses on seed particles and new particles are not nucleated in the furnace. A separate reactor comprised of a tube (33) and furnace (30) may be used to form a seed aerosol which, after passing through a cooling section (34) is introduced in the main reactor tube (34) which includes a mixer (36) to mix the seed aerosol in a controlled concentration with the reactant gas or gases.

Flagan, Richard C.

Diode-Laser-Based Spectrometer for Sensing Gases

A diode-laser-based spectrometer has been developed for measuring concentrations of gases and is intended particularly for use in analyzing and monitoring combustion processes under microgravitational conditions in a drop tower or a spacecraft. This instrument is also well suited for use on Earth in combustion experiments and for such related purposes as fire-safety monitoring and monitoring toxic and flammable gases in industrial settings. Of the gas-sensing spectrometers available prior to the development of this instrument, those that were sensitive enough for measuring the combustion gases of interest were too large, required critical optical alignments, used far too much electrical power, and were insufficiently rugged for use under the severe conditions of spacecraft launch and space flight. In contrast, the present instrument is compact, consumes relatively little power, and is rugged enough to withstand launch vibrations and space flight. In addition, this instrument is characterized by long-term stability, accuracy, and reliability. The diode laser in this spectrometer is operated in a wavelength-modulation mode. Different gases to be measured can be selected by changing modular laser units. The operation of the laser is controlled by customized, low-power electronic circuitry built around a digital signal-processor board. This customized circuitry also performs acquisition and analysis of data, controls communications, and manages errors.

Silver, Joel A.

Hydrogen Peroxide Enhances Removal of NOx from Flue Gases

Pilot scale experiments have demonstrated a method of reducing the amounts of oxides of nitrogen (NOx) emitted by industrial boilers and powerplant combustors that involves (1) injection of H2O2 into flue gases and (2) treatment of the flue gases by caustic wet scrubbing like that commonly used to remove SO2 from combustion flue gases. Heretofore, the method most commonly used for removing NOx from flue gases has been selective catalytic reduction (SCR), in which the costs of both installation and operation are very high. After further development, the present method may prove to be an economically attractive alternative to SCR.

Collins, Michelle M.

Miniaturized Laser Heterodyne Radiometer (LHR) for Measurements of Greenhouse Gases in the Atmospheric Column

This passive laser heterodyne radiometer (LHR) instrument simultaneously measures multiple trace gases in the atmospheric column including carbon dioxide (CO2) and methane (CH4), and resolves their concentrations at different altitudes. This instrument has been designed to operate in tandem with the passive aerosol sensor currently used in AERONET (an established network of more than 450 ground aerosol monitoring instruments worldwide). Because aerosols induce a radiative effect that influences terrestrial carbon exchange, simultaneous detection of aerosols with these key carbon cycle gases offers a uniquely comprehensive measurement approach. Laser heterodyne radiometry is a technique for detecting weak signals that was adapted from radio receiver technology. In a radio receiver, a weak input signal from a radio antenna is mixed with a stronger local oscillator signal. The mixed signal (beat note, or intermediate frequency) has a frequency equal to the difference between the input signal and the local oscillator. The intermediate frequency is amplified and sent to a detector that extracts the audio from the signal. In the LHR instrument described here, sunlight that has undergone absorption by the trace gas is mixed with laser light at a frequency matched to a trace gas absorption feature in the infrared (IR). Mixing results in a beat signal in the RF (radio frequency) region that can be related to the atmospheric concentration. For a one-second integration, the estimated column sensitivities are 0.1 ppmv for CO2, and <1 ppbv for CH4. In addition to producing a standalone ground measurement product, this instrument could be used to calibrate/validate four Earth observing missions: ASCENDS (Active Sensing of CO2 Emissions over Nights, Days, and Seasons), OCO-2 (Orbiting Carbon Observatory), OCO-3, and GOSAT (Greenhouse gases Observational SATellite). The only network that currently measures CO2 and CH4 in the atmospheric column is TCCON (Total Carbon Column Observing Network), and only two of its 16 operational sites are in the United States. TCCON data is used for validation of GOSAT data, and will be used for OCO-2 validation. While these Fourier-transform spectrometers (FTS) can measure the largest range of trace gases, the network is severely limited due to the high cost and extreme size of these instruments (these occupy small buildings and require personnel for operation). The LHR/AERONET instrument offers a significantly smaller (carry-on luggage size) autonomous instrument that can be incorporated into AERONET s much larger (450 instruments) global network.

Steel, Emily

Characterization of Wildfire Emissions in California: Analysis of Airborne Measurements of Trace Gases from 2013 to 2016

Biomass burning, which includes wildfires, prescribed, and agricultural fires, is an important source of trace gases and particles, and can influence air quality on a local, regional, and global scale. Biomass burning emissions are an important source of several key trace gases including carbon dioxide (CO2) and methane (CH4). With the threat of wildfire events increasing due to changes in land use, increasing population, and climate change, the importance of characterizing wildfire emissions is vital. In this work we characterize trace gas emissions from 9 wildfire events in California between 2013 – 2016, in some cases with multiple measurements performed during different burn periods of a specific wildfire. During this period airborne measurements of CO2, CH4, water vapor (H2O), ozone (O3), and formaldehyde (HCHO) were made by the Alpha Jet Atmospheric eXperiment (AJAX). Located in the Bay Area of California, AJAX is a joint effort between NASA Ames Research Center and H211, LLC. AJAX makes in-situ airborne measurements of trace gases 2-4 times per month, resulting in 229 flights to date since 2011. Results presented include emission ratios (ER) of trace gases measured by AJAX during fire flights, and comparisons of ERs are made for each fire, which differ in time, location, burning intensity, and fuel type. We also use our airborne measurements to compare with photochemical grid model results to assess model approximations of plume transport and chemical evolution from select wildfires.

Parworth, Caroline L.

Extreme Wet and Dry Conditions Affected Differently by Greenhouse Gases and Aerosols

Global warming due to greenhouse gases and atmospheric aerosols alter precipitation rates, but the influence on extreme precipitation by aerosols relative to greenhouse gases is still not well known. Here we use the simulations from the Precipitation Driver and Response Model Intercomparison Project that enable us to compare changes in mean and extreme precipitation due to greenhouse gases with those due to black carbon and sulfate aerosols, using indicators for dry extremes as well as for moderate and very extreme precipitation. Generally, we find that the more extreme a precipitation event is, the more pronounced is its response relative to global mean surface temperature change, both for aerosol and greenhouse gas changes. Black carbon (BC) stands out with distinct behavior and large differences between individual models. Dry days become more frequent with BC-induced warming compared to greenhouse gases, but so does the intensity and frequency of extreme precipitation. An increase in sulfate aerosols cools the surface and thereby the atmosphere, and thus induces a reduction in precipitation with a stronger effect on extreme than on mean precipitation. A better understanding and representation of these processes in models will provide knowledge for developing strategies for both climate change and air pollution mitigation.

Sillmann, Jana

Simultaneous Retrievals of Biomass Burning Aerosols and Trace Gases From the Ultraviolet to Near-Infrared Over Northern Thailand During the 2019 Pre-Monsoon Season

With the advent of spaceborne spectroradiometers in a geostationary constellation, measuring high spectral resolution ultraviolet–visible (UV-VIS) and selected near-/shortwave-infrared (NIR/SWIR) radiances can enable the probing of the life cycle of key atmospheric trace gases and aerosols at higher temporal resolutions over the globe. The UV-VIS measurements are important for retrieving several key trace gases (e.g., O 3 , SO 2 , NO 2 , and HCHO) and particularly for deriving aerosol characteristics (e.g., aerosol absorption and vertical profile). This study examines the merit of simultaneous retrievals of trace gases and aerosols using a ground-based spectroradiometer covering the UV-NIR to monitor their physicochemical processes and to obtain reliable aerosol information for various applications. During the 2019 pre-monsoon season over northern Thailand, we deployed a ground-based SMART–s (Spectral Measurements for Atmospheric Radiative Transfer–spectroradiometer) instrument, which is an extended-range Pandora with reliable radiometric calibration in the 330–820 nm range, to retrieve remotely sensed chemical and aerosol properties for the first time near biomass burning sources. The high spectral resolution (∼ 1.0 nm full width half maximum with ∼ 3.7 × oversampling) of sun and sky measurements from SMART–s provides several key trace gases (e.g., O 3 , NO 2 , and H 2 O) and aerosol properties covering the UV where significant light absorption occurs by the carbonaceous particles. During the measurement period, highly correlated total column amounts of NO 2 and aerosol optical thickness (т aer ) retrieved from SMART–s (correlation coefficient, R=0.74) indicated their common emissions from biomass burning events. The SMART–s retrievals of the spectral single scattering albedo (ω 0 ) of smoke aerosols showed an abrupt decrease in the UV, which is an important parameter dictating photochemical processes in the atmosphere. The values of ω 0 and column precipitable water vapor (H 2 O) gradually increase with the mixing of biomass burning smoke particles and higher water vapor concentrations when approaching the monsoon season. The retrieved ω 0 and weighted mean radius of fine-mode aerosols from SMART–s showed positive correlations with the H 2 O (R=0.81 for ω 0 at 330 nm and 0.56 for the volume-weighted mean radius), whereas the real part of the refractive index of fine-mode aerosol (n f ) showed negative correlations (R = -0.61 at 330 nm), which suggest that aerosol aging processes including hygroscopic growth (e.g., humidification and cloud processing) can be a major factor affecting the temporal trends of aerosol optical properties. Retrieved n f and ω 0 were closer to those of the water droplet (i.e., n f of about 1.33 and ω 0 of about 1.0) under lower amounts of NO 2 during the measurement period; considering that the NO 2 amounts in the smoke may indicate the aging of the plume after emission due to its short lifetime, the tendency is also consistent with active hygroscopic processes of the aerosols over this area. Retrieved UV aerosol properties from SMART–s generally support the assumed smoke aerosol models (i.e., the spectral shape of aerosol absorption) used in NASA's current satellite algorithms, and their spectral ω 0 retrievals from ground and satellites showed good agreements (R = 0.73–0.79). However, temporal and spectral variabilities in the aerosol absorption properties in the UV emphasize the importance of a realistic optical model of aerosols for further improvements in satellite retrievals.

biomass burning

Noble Gases in Samples Returned From Asteroids Ryugu and Bennu

Introduction: The asteroid sample return missions, JAXA’s Hayabusa2 [1] and NASA’s OSIRIS-REx [2], fromC-rich asteroids Ryugu and Bennu offer unique opportunities to sample pristine early solar system material, unaffected by terrestrial weathering and contamination, and with a known geological context. The comparison with most primi-tive members of carbonaceous –and inner solar system ordinary and enstatite– chondrite classes allows us to (i) assess the variation (or the lack of thereof) of the distribution of the most volatile elements throughout the entire early solar system, (ii) determine the effects of parent body thermal and aqueous alteration, and (iii) learn about the dynamic evolution and history of the various parent bodies, as sampled by both return missions and meteorite delivery. Here we will present noble gas data obtained from newly received particles from Ryugu and Bennu. Samples & Analysis: We received nine particles allocated by JAXA, with masses of 0.5-1.7 mg mass: four col-lected during Hayabusa2’s first touchdown (chamber A) and five from a small artificial crater (chamber C). We received three particles from Bennu of 0.07, 0.89 and 0.94 mg mass (OREX-800032-102/3/4). All particles were processed, allocated, weighed, and transferred into our UHV sample chamber within pure N2, to prevent any contact with air. We examined all He-Xe isotopes with our custom-built mass spectrometer “Albatros” ([3,4]). Gases were extracted individually from each particle by melting induced by a 1064 μm Nd:YAG IR laser in 2–4 heating steps. Large amounts of water and other reactive volatiles were released, consistent with the presence of abundant volatiles from both Ryugu and Bennu. Residues of Ryugu particles remaining after lasering, subsequently exposed to air, were additionally extracted in a crucible to verify complete gas extraction. Only the particle that still showed a “crystalline” structure after lasering contained detectable Ryugu noble gases, whereas all other particles turned immediately into glassy spheres by laser heating and lacked any gas. Results & Discussion: Ryugu and Bennu matter contains noble gases similar to the most pristine, unheated aqueously altered meteorites, e.g., CM or CI chondrites [5,6]. Remarkably, all four chamber A samples that originated from Ryugu’s surface show solar wind (SW) Ne (trapped (20Ne/22Ne)tr ~12–13), whereas all five chamber C samples do not ((20Ne/22Ne)tr ~9.0–10.7 consistent with the presence of non-solar trapped Ne components such as Q and HL). This demonstrates that JAXA’s sampling strategy succeeded: Chamber C samples analyzed in this work originated from areas shielded from SW, slightly below the surface, that was sampled after the impactor excavated material. The three Bennu particles populate the same range as the Ryugu particles in Ne isotope space with one particle containing SW suggesting that it was part of the uppermost surface layer of Bennu during sampling, while Ne in the smallest sample can be explained best by mixing Ne from presolar diamonds and SiC or graphite, and that in the third one by mixing of, e.g., Q and HL. Using cosmic ray production rates given by [7] yields preliminary exposure ages for Ryugu particles in the same range as determined in [7]. There is, as expected, also no systematic difference between samples from chambers A and C because both sample sets were likely collected within the uppermost layer of Ryugu, which were not shielded from cosmic rays. The concentration of cosmogenic (cos) Ne in the Bennu particle, where Necos was resolvable, is in the same range as found for Ryugu, suggesting roughly similar exposure time to cosmic rays for 5–8 Ma for all particles examined here. The Xe isotopic compositions of all particles are consistent with those of phase Q, with small additions of Xe-HL from presolar diamonds and excess 129Xe* from short-lived 129I decay. The comparably high 129Xe*/129XeQ ratio is similar in all samples, suggesting similar initial I concentrations and closure to Xe loss –or the incorporation of a well-mixed Xe reservoir. The Bennu material was in brief contact with air in the capsule, after atmospheric entry and before storage in pure N2 in a clean room. Both, the –most diagnostic– Xe isotopes and the Ar/Xe vs. Kr/Xe systematics prove that the noble gases are not affected by terrestrial contamination, in contrast to many CI, CY, and CM chondrites found on Earth [5,6], illustrating the importance of sample return. He-Xe concentrations in all particles unaffected bySW are comparable to but at the upper end of ranges reported [5-7]. In accordance with the strong aqueous alteration experienced on the parent bodies of Ryugu and Bennu [1,2], all samples lack the Ar-rich and water-susceptible noble gas components found in less aqueously altered CMs or CRs [e.g., 5,8] and all COs.

Henner Busemann

Quantum Emitters Induced by High Pressure and UV Laser Irradiation in Multilayer GaSe

In this work, we report on defect generation in multilayer GaSe through hydrostatic pressure quenching and UV laser irradiation. The Raman line width from the UV 266 nm irradiated sample is much wider than that in pressure-quenched GaSe, corresponding to a wider defect energy distribution range in the former sample than the latter. After quenching from 11.2 GPa, three photoluminescence (PL) peaks from defect states are observed at 657, 681, and 695 nm at a low temperature of 93 K. Defect-related peaks at 649, 694, 750, and 774 nm also appear in low-temperature PL spectra after UV laser irradiation, with a nonmonotonous intensity dependence on irradiation duration. There are common features in defects produced by these two methods: the PL peaks with the lowest energy are sharp, and their PL intensities increase linearly with the excitation laser power and saturate above a certain excitation laser power. These two features are similar to those in defects for single-photon emission (SPE) in other 2D materials at even lower temperatures. Fluorescence lifetime imaging shows distinguished short (2.3 ns) and long (75.6 nm) lifetimes of the 695 nm PL line in pressure-quenched GaSe. The density functional theory predicts defect energy levels related to Se vacancy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH

Impact Delivery of Reduced Greenhouse Gases on Early MARS

While there is abundant evidence for flowing liquid water on the ancient Martian surface, a widely accepted greenhouse mechanism for explaining this in the presence of a faint young sun has yet to emerge. Gases such as NH3, CO2 alone, SO2, clouds, and CH4, have sustainability issues or limited greenhouse power. Recently, Ramirez et al. proposed that CO2-H2 atmospheres, through collision induced absorptions (CIA), could solve the problem if large amounts are present (1.3-4 bars of CO2, 50-20% H2). However, they had to estimate the strength of the H2- CO2 interaction from the measured strength of the H2- N2 interaction. Recent ab initio calculations show that the strength of CO2-H2 CIA is greater than Ramirez et al. assumed. Wordsworth et al. also calculated the absorption coefficients for CO2-CH4 CIA and show that on early Mars a 0.5 bar CO2 atmosphere with percent levels of H2 or CH4 can raise mean annual temperatures by tens of degrees Kelvin. Freezing temperatures can be reached in atmospheres containing 1-2 bars of CO2 and 2-10% H2 and CH4. The new work demonstrates that less CO2 and reduced gases are needed than Ramirez et al. originally proposed, which improves prospects for their hypothesis. If thick weakly reducing atmospheres are the solution to the faint young sun paradox, then plausible mechanisms must be found to generate and sustain the required concentrations of H2 and CH4. Possible sources of reducing gases include volcanic outgassing, serpentinization, and impact delivery; sinks include photolysis, oxidation, and hydrogen escape. The viability of the reduced greenhouse hypothesis depends, therefore, on the strength of these sources and sinks.

Martian surface