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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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48 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Infrared measurements of HF and HCl total column abundances above Kitt Peak, 1977-1990 - Seasonal cycles, long-term increases, and comparisons with model calculations

The paper deals with hydrogen-chloride and hydrogen-fluoride total column measurements, their estimated long-term rates of increase, seasonal cycles, and variability, deduced from the analysis of a set of high-resolution infrared solar spectra recorded at Kitt Peak. The Kitt Peak observations and methods of analysis are described, the results are presented and compared with previously reported measurements and trends. The data is analyzed by using a multilayer nonlinear least-squares spectral fitting procedure and a consistent set of spectroscopic line parameters. Model-calculated hydrogen-chloride and hydrogen-fluoride total columns obtained with a two-dimensional model are discussed, and the model results are compared with the measured hydrogen-chloride and hydrogen-fluoride total columns, seasonal cycles, and trends. It is pointed out that the observed trends of both molecules are in satisfactory agreement with the model results calculated from emission histories and photooxidation rates for the source molecules.

Rinsland, C. P.↗
NASA NTRS1991

An upper limit for the rate coefficient of the reaction of NH2 radicals with O2 using FTIR product analysis

Fourier transform infrared spectrometry has been used to study the products of the photooxidation of ammonia in the presence of oxygen at 296 K. The data have been used to derive an upper limit of 6 x 10 exp -21/cu cm molecule s for the reaction of NH2 radicals with O2 to produce NO(x) at 296 K. This upper limit, which is three orders of magnitude lower than previous estimates based on the kinetics of NH2 loss, rules out the importance of this reaction in the atmosphere and suggests that NH2 will be oxidized by O3 or NO2. The effect on the NO(x) and N2O budgets depends critically on the products of the NH2 + O3 reaction. Simulations of the experimental product yields also allow an evaluation of possible product channels for the reaction of NH2 with HO2.

Tyndall, G. S.↗
NASA NTRS1992

The photochemistry of manganese and the origin of banded iron formations

The origin of the deposition of superior-type Precambrian banded iron formations (BIFs) is investigated in experiments where the effect of UV radiation on dissolved manganese was studied to determine if the commonly accepted photochemical model for BIF formation is consistent with the distribution of Mn in BIFs. Solutions containing 0.56 M NaCl and about 180 microM MnCl2, with or without 3 to 200 microM FeCl2 were irradiated with filtered and unfiltered UV light for up to 8 hrs; the solutions were deaerated and buffered to a pH of 7, and the experiments were conducted under oxygen-free atmosphere. Data on the rate of manganese photooxidation confirmed that a photochemical model for the origin of oxide facies BIFs is consistent with field observations.

Anbar, A. D.↗
NASA NTRS1994

Reactive nitrogen oxides and ozone above a taiga woodland

Measurements of reactive nitrogen oxides (NO(x) and NO(y)) and ozone (O3) were made in the planetary boundary layer (PBL) above a taiga woodland in northern Quebec, Canada, during June-August, 1990, as part of NASA Artic Boundary Layer Expedition (ABLE) 3B. Levels of nitrogen oxides and O3 were strongly modulated by the synoptic scale meteorology that brought air from various source regions to the site. Industrial pollution from the Great Lakes region of the U.S. and Canada appears to be a major source for periodic elevation of NO(x), and NO(y) and O3. We find that NO/NO2 ratios at this site at midday were approximately 50% those expected from a simple photochemical steady state between NO(x) and O3, in contrast to our earlier results from the ABLE 3A tundra site. The difference between the taiga and tundra sites is likely due to much larger emissions of biogenic hydrocarbons (particularly isoprene) from the taiga vegetation. Hydrocarbon photooxidation leads to relatively rapid production of peroxy radicals, which convert NO to NO2, at the taiga site. Ratios of NO(x) to NO(y) were typically 2-3 times higher in the PBL during ABLE 3B than during ABLE 3A. This is probably the result of high PAN levels and suppressed formation of HNO3 from NO2 due to high levels of biogenic hydrocarbons at the ABLE 3B site.

Bakwin, Peter S.↗
NASA NTRS1995

Energy conversion at liquid/liquid interfaces: artificial photosynthetic systems

This chapter focuses on multielectron reactions in organized assemblies of molecules at the liquid/liquid interface. We describe the thermodynamic and kinetic parameters of such reactions, including the structure of the reaction centers, charge movement along the electron transfer pathways, and the role of electric double layers in artificial photosynthesis. Some examples of artificial photosynthesis at the oil/water interface are considered, including water photooxidation to the molecular oxygen, oxygen photoreduction, photosynthesis of amphiphilic compounds and proton evolution by photochemical processes.

Non-NASA Center↗
NASA NTRS1985

A model for the origin of photosynthesis--III. The ultraviolet photochemistry of uroporphyrinogen

The photochemical ramifications of the high ultraviolet flux on the primordial earth prior to the formation of the ozone layer have been considered in a study of the ultraviolet photochemistry of uroporphyrinogen (urohexahydroporphyrin), a colorless compound which absorbs strongly at wavelengths less than 220 nanometers. Urohexahydroporphyrin was investigated since it is the first macrocycle formed on the biosynthetic pathway of chlorophyll and can be used to test the hypothesis that the biosynthetic pathway to chlorophyll recapitulates the evolutionary history of photosynthesis. When urohexahydroporphyrin is illuminated in aqueous anaerobic solution, hydrogen gas is produced. More hydrogen gas is produced in the presence of a colloidal platinum catalyst. The products of the photooxidation of urohexahydroporphyrin are urotetrahydroporphyrin (uroporphomethene) and uroporphyrin. This research shows how the oxidation of uroporphyrinogen to uroporphyrin, the first biogenetic porphyrin, could have occurred anaerobically and abiotically on the primordial earth.

Evolution, Chemical↗
NASA NTRS1993

Time-resolved tryptophan fluorescence in photosynthetic reaction centers from Rhodobacter sphaeroides

Tryptophan fluorescence of reaction centers isolated from Rhodobacter sphaeroides, both stationary and time-resolved, was studied. Fluorescence kinetics were found to fit best a sum of four discrete exponential components. Half of the initial amplitude was due to a component with a lifetime of congruent to 60 ps, belonging to Trp residues, capable of efficient transfer of excitation energy to bacteriochlorophyll molecules of the reaction center. The three other components seem to be emitted by Trp ground-state conformers, unable to participate in such a transfer. Under the influence of intense actinic light, photooxidizing the reaction centers, the yield of stationary fluorescence diminished by congruent to 1.5 times, while the number of the kinetic components and their life times remained practically unchanged. Possible implications of the observed effects for the primary photosynthesis events are considered.

NASA Program Exobiology↗
NASA NTRS2007

Algorithm Development and Validation for Satellite-Derived Distributions of DOC and CDOM in the US Middle Atlantic Bight

In coastal ocean waters, distributions of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) vary seasonally and interannually due to multiple source inputs and removal processes. We conducted several oceanographic cruises within the continental margin of the U.S. Middle Atlantic Bight (MAB) to collect field measurements in order to develop algorithms to retrieve CDOM and DOC from NASA's MODIS-Aqua and SeaWiFS satellite sensors. In order to develop empirical algorithms for CDOM and DOC, we correlated the CDOM absorption coefficient (a(sub cdom)) with in situ radiometry (remote sensing reflectance, Rrs, band ratios) and then correlated DOC to Rrs band ratios through the CDOM to DOC relationships. Our validation analyses demonstrate successful retrieval of DOC and CDOM from coastal ocean waters using the MODIS-Aqua and SeaWiFS satellite sensors with mean absolute percent differences from field measurements of < 9 %for DOC, 20% for a(sub cdom)(355)1,6 % for a(sub cdom)(443), and 12% for the CDOM spectral slope. To our knowledge, the algorithms presented here represent the first validated algorithms for satellite retrieval of a(sub cdom) DOC, and CDOM spectral slope in the coastal ocean. The satellite-derived DOC and a(sub cdom) products demonstrate the seasonal net ecosystem production of DOC and photooxidation of CDOM from spring to fall. With accurate satellite retrievals of CDOM and DOC, we will be able to apply satellite observations to investigate interannual and decadal-scale variability in surface CDOM and DOC within continental margins and monitor impacts of climate change and anthropogenic activities on coastal ecosystems.

Mannino, Antonio↗
NASA NTRS2013

Possible Detection of Perchlorates by the Sample Analysis at Mars (SAM) Instrument: Comparison with Previous Missions

The first chemical analysis of soluble salts in the soil was carried out by the Phoenix Lander in the Martian Arctic [1]. Surprisingly, chlorine was present as magnesium or calcium perchlorate at 0.4 to 0.6 percent. Additional support for the identification of perchlorate came from the evolved gas analysis which detected the release of molecular oxygen at 350-550C [1]. When Mars-like soils from the Atacama Desert were spiked with magnesium perchlorate (1 percent) and heated using the Viking GC-MS protocol, nearly all the organics were combusted but a small amount was chlorinated, forming chloromethane and dichloromethane [2]. These chlorohydrocarbons were detected by the Viking GC-MS experiments when the Martian soil was analyzed but they were considered to be terrestrial contaminants [3]. Reinterpretation of the Viking results suggests <0.1 percent perchlorate and ppm levels of organic carbon at landing site 1 and 2 [2]. The suggestion of perchlorate in the Viking sites [2] has been challenged on the grounds that the detected compounds (CH3Cl and CH2Cl2) were carried from Earth [4]. Recently the Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory (MSL) ran four samples from an aeolian bedform named Rocknest. The samples analyzed were portioned from the fifth scoop at this location. The samples were heated to 835C at 35C/min with a He flow. The SAM QMS detected a major oxygen release (300-500C) [5], coupled with the release of chlorinated hydrocarbons (chloromethane, dichloromethane, trichloromethane, and chloromethylpropene) detected both by SAM QMS and GC-MS derived from known Earth organic contaminants in the instrument [6]. Calcium perchlorate appears to be the best candidate for evolved O2 in the Rocknest samples at this time but other Cl species (e.g., chlorates) are possible and must be evaluated. The potential detection of perchlorates in Rocknest material adds weight to the argument that both Viking Landers measured signatures of perchlorates. Even if the source of the organic carbon detected is still unknown, the chlorine source was likely Martian. Two mechanisms have been hypothesized for the formation of soil perchlorate: (1) Atmospheric oxidation of chlorine; and (2) UV photooxidation of chlorides catalyzed by mineral catalysts [7]. The presence of soil perchlorates in the Martian surface has important implications for the detection of organics [2], carbonates [8] and nitrates [9] by SAM.

Navarro-Gonzalex, Rafael↗
NASA NTRS2019

Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System

Some atmospheric gases have been proposed as counter indicators to the presence of life on an exoplanet if remotely detectable at sufficient abundance (i.e., antibiosignatures), informing the search for biosignatures and potentially fingerprinting uninhabited habitats. However, the quantitative extent to which putative antibiosignatures could exist in the atmospheres of inhabited planets is not well understood. The most commonly referenced potential antibiosignature is CO, because it represents a source of free energy and reduced carbon that is readily exploited by life on Earth and is thus often assumed to accumulate only in the absence of life. Yet, biospheres actively produce CO through biomass burning, photooxidation processes, and release of gases that are photochemically converted into CO in the atmosphere. We demonstrate with a 1D ecosphere-atmosphere model that reducing biospheres can maintain CO levels of approximately 100 ppmv (parts per million by volume) even at low H2 fluxes due to the impact of hybrid photosynthetic ecosystems. Additionally, we show that photochemistry around M dwarf stars is particularly favorable for the buildup of CO, with plausible concentrations for inhabited, oxygen-rich planets extending from hundreds of ppm to several percent. Since CH4 buildup is also favored on these worlds, and because O2 and O3 are likely not detectable with the James Webb Space Telescope, the presence of high CO (greater than 100 ppmv) may discriminate between oxygen-rich and reducing biospheres with near-future transmission observations. These results suggest that spectroscopic detection of CO can be compatible with the presence of life and that a comprehensive contextual assessment is required to validate the significance of potential antibiosignatures.

Earth↗
NASA NTRS2022

Anoxic photochemical weathering of pyrite on Archean continents

Sulfur is an essential element of life that is assimilated by Earth’s biosphere through the chemical breakdown of pyrite. On the early Earth, pyrite weathering by atmospheric oxygen was severely limited, and low marine sulfate concentrations persisted for much of the Archean eon. Here, we show an anoxic photochemical mechanism of pyrite weathering that could have provided substantial amounts of sulfate to the oceans as continents formed in the late Archean. Pyrite grains suspended in anoxic ferrous iron solutions produced millimolar sulfate concentrations when irradiated with ultraviolet light. The Fe2+(aq) was photooxidized, which, in turn, led to the chemical oxidation of pyritic sulfur. Additional experiments conducted with 2.68 Ga shale demonstrated that photochemically derived ferric iron oxidizes and dissolves sedimentary pyrite during chemical weathering. The results suggest that before the rise of atmospheric oxygen, oxidative pyrite weathering on Archean continents was controlled by the exposure of land to sunlight.

Jihua Hao↗
NASA NTRS2023

Sources of Formaldehyde in U.S. Oil and Gas Production Regions

We analyzed observational and model data to study the sources of formaldehyde over oil and gas production regions and to investigate how these observations may be used to constrain oil and gas VOC emissions. The analysis of aircraft and satellite data consistently found that formaldehyde over oil and gas production regions during spring and summer is mostly formed by the photooxidation of precursor VOCs. Formaldehyde columns over the Permian basin, one of the largest oil and gas producing regions in the United States, are correlated with production locations. Formaldehyde simulations by the atmospheric chemistry and transport model WRF-Chem, which included oil and gas NOx and VOC emissions from the fuel-based oil and gas inventory, were in very good agreement with TROPOMI satellite measurements. Sensitivity studies illustrated that VOCs released from oil and gas activities are important precursors to formaldehyde, but other sources of VOCs contribute as well, and that the formation of secondary formaldehyde is highly sensitive to NOx. We also investigated the ability of the chemical mechanism used in WRF-Chem to represent formaldehyde formation from oil and gas hydrocarbons by comparing against the Master Chemical Mechanism. Further, our work provides estimates of primary formaldehyde emissions from oil and gas production activities, with per basin averages ranging from 0.07 kg h -1 to 2.2 kg h -1 in 2018. A separate estimate for natural gas flaring found that flaring emissions could contribute 5% to 12% to the total primary formaldehyde emissions for the Permian basin in 2018.

SAF↗