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NASA NTRS2000

The Application of TOMS Ozone, Aerosol and UV-B Data to Madagascar Air Quality Determination

Total Ozone Mapping Spectrometer (TOMS) data products for the area of Madagascar are presented. In addition to total ozone, aerosols and UV-B tropospheric ozone results are shown from 1979 to the present. Tropospheric ozone over Africa and Madagascar is enhanced by 10 to 15 DU in October. This maximum coincides with the time of maximum biomass area burning in Africa and Madagascar. Ozone observations were made from 1979 to 1999 using the TOMS tropospheric ozone convective cloud differential method. As a result of easterly trade winds, ozone originating on Madagascar is transported to the west over the Mozambique Channel. In El Nino years higher level westerly winds descend to transport low level ozone easterly. This results in African continental ozone being transported east of Madagascar. Long range transport of African ozone is observed during El Nino periods. The potential of TOMS and other space data for use in public education and research on Madagascar air quality is demonstrated.

Aikin, A.C.↗
NASA NTRS2001

Changes in the Earth's UV Reflectivity (1979 to 1992)

Measurements of the Earth,s 380 nm UV reflectivity combine the effects of surface reflectivity, aerosols, haze, cloud optical thickness, and the fraction of the scene covered by clouds. Since the 380 nm surface reflectivity is low (2 to 8%) over most surfaces, water and land, the observed reflectivity changes are mostly caused by changes in the amount of snow/ice, cloudiness and aerosols. Time-series analysis of TOMS reflectivity over the period from 1979 to 1992 shows that there were no significant changes in annually-averaged zonal-average reflectivity at latitudes within 60 degrees S to 60 degrees N, even though there were changes at higher latitudes (e.g., 3% per decade, in reflectivity units, between 60 degrees N and 70 degrees N). When the effects of the 11-year solar cycle and ENSO (El Nino Southern Oscillation) are removed from the data, statistically significant reflectivity changes are observed poleward of both 40 degrees S and 40 degrees N. The solar-cycle results suggest a possible Sun-weather relationship.

Hermana, J. R.↗
NASA NTRS2001

UV Timing and Spectroscopy of the Crab Nebula Pulsar

We have used the Hubble Space Telescope and Space Telescope Imaging Spectrograph to obtain Near Ultraviolet (NUV) (1600-3200 Angstroms) and Far Ultraviolet (FUV) (1140-1720 Angstroms) spectra and pulse profiles of the Crab Nebula's pulsar. The pulse period agrees well with the radio predictions. The NUV and FUV pulse profiles are little changed from the visible wavelength profile. Spectra obtained with the Nordic Optical Telescope were combined with the UV spectra for full coverage from 1140-9250Angstoms. Dereddening the spectrum with a standard extinction curve achieves a flat spectrum for E(B-V)=0.52, R=3.1. Lyman alpha absorption indicates a column density of 3.0=/-0.5 x 10(exp 21) cm -2, consistent with the E(B-V) of 0.52. The dereddened spectrum can be fitted by a power law with spectral index alpha=0.11+/-0.04. A broad, blueshifted absorption is seen in CIV (1550Angstroms), reaching a velocity of about 2500 kilometer per second.

Gull, Theodore R.↗
NASA NTRS2001

Effects of Contamination, UV Radiation, and Atomic Oxygen on ISS Thermal Control Materials

Thermal control surfaces on the International Space Station (ISS) have been tailored for optimum optical properties. The space environment, particularly contamination, ultraviolet (UV) radiation, and atomic oxygen (AO) may have a detrimental effect on these optical properties. These effects must be quantified for modeling and planning. Also of interest was the effect of porosity on the reaction to simulated space environment. Five materials were chosen for this study based on their use on ISS. The thermal control materials were Z-93 white coating, silverized Teflon, chromic acid anodized aluminum, sulfuric acid anodized aluminum, and 7075-T6 aluminum. Some of the samples were exposed to RTV 560 silicone; others were exposed to Tefzel offgassing products. Two samples of Z-93 were not exposed to contamination as clean "controls". VUV radiation was used to photo-fix the contaminant to the material surface, then the samples were exposed to AO. All samples were exposed to 1000 equivalent sun-hours (ESH) of vacuum ultraviolet radiation (VUV) at the AZ Technology facility and a minimum of 1.5 x 10(exp 20) atoms/sq cm of AO at Marshall Space Flight Center. Half of the samples were exposed to an additional 2000 ESH of VUV at Huntington Beach prior to sent to AZ Technology. Darkening of the Z-93 white coating was noted after VUV exposure. AO exposure did bleach the Z-93 but not back to its original brightness. Solar absorptance curves show the degradation due to contamination and VUV and the recovery with AO exposure. More bleaching was noted on the Tefzel-contaminated samples than with the RTV-contaminated samples.

Visentine, Jim↗
NASA NTRS2000

Star Formation in the Galaxy and the Fluctuating UV Radiation Field

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this Field on the star-forming interstellar medium. Following previous researchers such as Habing (1968), we calculate the average interstellar radiation field at the Solar Circle of the Galaxy. However, our new calculations follow more closely the time dependence of the field at any point. We show that there is a significant difference between the mean field and the median field, and that there are substantial fluctuations of the field (on timescales of order 100 million years) at a given point. Far Ultraviolet Radiation (FUV, photon energies of 6 eV - 13.6 eV) has been recognized as the main source of heating of the neutral interstellar gas. Given the pressure of the interstellar medium (ISM) the FUV field determines whether the thermal balance of the neutral gas results in cold (T approximately 50 - 100 K) clouds (CNM), warm (T about 10,000 K) (WNM), for a combination of the two (the two phase ISM) We present results for the time history of the FUV field for points in the local ISM of the Milky Way Galaxy. The presence of this fluctuating heating rate converts CNM to WNM and vice versa. We show how to calculate the average fractions of the gas in the CNM and WNM when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties (i.e. mean density and composition) and on the FUV-sources (i.e. the star formation rate, or the IMF, or the size distribution of associations) is a basic step in building any detailed model of the large scale behavior of the ISM and the mutual relation between the ISM and the SFR.

Hollenbach, David↗
NASA NTRS2001

Deep UV Native Fluorescence Imaging of Antarctic Cryptoendolithic Communities

An interdisciplinary team at the Jet Propulsion Laboratory Center for Life Detection has embarked on a project to provide in situ chemical and morphological characterization of Antarctic cryptoendolithic microbial communities. We present here in situ deep ultraviolet (UV) native fluorescence and environmental scanning electron microscopy images transiting 8.5 mm into a sandstone sample from the Antarctic Dry Valleys. The deep ultraviolet imaging system employs 224.3, 248.6, and 325 nm lasers to elicit differential fluorescence and resonance Raman responses from biomolecules and minerals. The 224.3 and 248.6 nm lasers elicit a fluorescence response from the aromatic amino and nucleic acids. Excitation at 325 nm may elicit activity from a variety of biomolecules, but is more likely to elicit mineral fluorescence. The resultant fluorescence images provide in situ chemical and morphological maps of microorganisms and the associated organic matrix. Visible broadband reflectance images provide orientation against the mineral background. Environmental scanning electron micrographs provided detailed morphological information. The technique has made possible the construction of detailed fluorescent maps extending from the surface of an Antarctic sandstone sample to a depth of 8.5 mm. The images detect no evidence of microbial life in the superficial 0.2 mm crustal layer. The black lichen component between 0.3 and 0.5 mm deep absorbs all wavelengths of both laser and broadband illumination. Filamentous deep ultraviolet native fluorescent activity dominates in the white layer between 0.6 mm and 5.0 mm from the surface. These filamentous forms are fungi that continue into the red (iron-rich) region of the sample extending from 5.0 to 8.5 mm. Using differential image subtraction techniques it is possible to identify fungal nuclei. The ultraviolet response is markedly attenuated in this region, apparently from the absorption of ultraviolet light by iron-rich particles coating the filaments. Below 8.5 mm the filamentous morphology of the upper layers gives way to punctate 1-2 micron particles evidencing fluorescent activity following excitation at both deep ultraviolet wavelengths.

Storrie-Lombardi, M. C.↗
NASA NTRS2001

Solar UV Radiation and the Origin of Life on Earth

We have embarked on a program aimed at understanding the atmosphere of the early Earth, because of its importance as a greenhouse, radiation shield, and energy source for life. Here, we give a progress report on the first phase of this program: to establish the UV radiation from the early Sun. We are presently obtaining ultraviolet spectra (STIS, FUSE, EUVE) of carefully selected nearby, young solar-type stars, which act as surrogates for the early Sun. We are currently making detailed non-LTE analyses of the spectra and constructing models of their photospheres + chromospheres. once validated, these models will allow us to extrapolate our theoretical spectra to unobserved spectral regions, and to proceed to the next step: to develop photochemical models of the pre-biotic and Archean atmosphere of the Earth.

Heap, S. R.↗
NASA NTRS2001

The Formation of Racemic Amino Acids by UV Photolysis of Interstellar Ice Analogs

Small biologically relevant organic molecules including the amino acids glycine, alanine, and marine were formed in the laboratory by the UV (Ultraviolet) photolysis of realistic interstellar ice analogs, composed primarily of H2O, and including CH3OH, NH3, and HCN, under interstellar conditions. N-formyl glycine, cycloserine (4-amino-3-isoxazolidinone), and glycerol were detected before hydrolysis, and glycine, racemic alanine, racemic marine, glycerol, ethanolamine, and glyceric acid were found after hydrolysis. This suggests that some meteoritic amino acids (and other molecules) may be the direct result of interstellar ice photochemistry, expanding the current paradigm that they formed by reactions in liquid water on meteorite parent bodies.

Bernstein, Max P.↗
NASA NTRS2002

Solar UV Radiation and the Origin of Life On Earth

We have embarked on a program aimed at understanding the atmosphere of the early Earth, because of its importance as a greenhouse, radiation shield and energy source for life. Here, we give a progress report on the first phase of this program to establish the UV radiation from the early Sun. We have obtained ultraviolet spectra (STIS, FUSE, EUVE) of carefully selected nearby, young solar-type stars, which act as surrogates for the early Sun We are making detailed non-LTE analyses of the spectra and constructing models of their photospheres + chromospheres. Once validated, these models will allow us to extrapolate our theoretical spectra to other metallicities and to unobserved spectral regions.

Heap, S. R.↗
NASA NTRS2003

DEM Measurements of Moving UV Features in Prominences

Multi-thermal features with speeds of 5-70 km/s perpendicular to the line of sight are common in the prominences which showed traceable motions. These speeds are noticeably higher than the typical speeds of 5-20 km/s observed in H-alpha data from "quiet" prominences and are more typical of "activated" prominences in which H-alpha blob speeds of up to 40 km/s have been reported. In order to make a more quantitative determination of the thermal properties of the moving features seen in the UV, we use the SOHO Cororial Diagnostic Spectrometer to take a time series of exposures from a single pointing position, providing a measurement of spectral line properties as a function of time and position along the slit. The resulting observations in lines of O III, O IV, O V, Ne IV, Ne V, Ne VI, and Ne VII allow us to calculate the differential emission measure of moving features and provide a test of models of flows in prominences.

Oegerle, William↗
NASA NTRS2002

New Atomic Data for Doubly Ionized Iron Group Atoms by High Resolution UV Fourier Transform Spectroscopy

Currently available laboratory spectroscopic data of doubly ionized iron-group element were obtained about 50 years ago using spectrographs of modest dispersion, photographic plates, and eye estimates of intensities. The accuracy of the older wavelength data is about 10 mAngstroms at best, whereas wavelengths are now needed to an accuracy of 1 part in 10(exp 6) to 10(exp 7) (0.2 to 2 mAngstroms at 2000 Angstroms). The Fourier transform (FT) spectroscopy group at Imperial College, London, and collaborators at the Harvard College Observatory have used a unique VUV FT spectrometer in a program focussed on improving knowledge of spectra of many neutral and singly and doubly ionized, astrophysically important, iron group elements. Spectra of Fe II and Fe III have been recorded at UV and VUV wavelengths with signal-to-noise ratios of several hundred for the stronger lines. Wavelengths and energy levels for Fe III are an order of magnitude more accurate than previous work; analysis is close to completion. f-values for Fe II have been published.

Smith, Peter L.↗
NASA NTRS2003

Survey for Life-related Species During a Planetary Surface Exploration; System Type I - UV Stimulated Fluorescent Sensor

The widely accepted minimum requirements for life on Earth include the presence of water and accessible sources of carbon. We assume that the same criteria must hold for putative life on past or present Mars. The evidence for CO2 and H2O at or near the Martian surface, carbon in Martian meteorites, aqueous alteration, and probable hydrothermal activity suggest that conditions conducive to the origin and evolution of life on Mars may have existed for long periods of time and may still obtain at present. Surface exploration on Mars that enables the direct detection of water in minerals and of organic carbon (including not just organic and biogenic materials but their degradation products such as kerogen-like hydrocarbons and graphitized carbon) that might be products or residues of biologic activity, is crucial. The search for evidence of life, past or present, will nevertheless be difficult. The lack of direct evidence for organic carbon and the low amounts of water found in the soils at the Viking sites demonstrated the difficulties. Recent results of GRS experiment of Odyssey mission indicated the existence of abundant water ice beneath the Mars surface. Mineralogical evidence for the presence of carbonate, sulfates, or clay minerals, products of weathering and aqueous deposition, have not been identified unambiguously on Mars. Rocks such as shales and, more particularly, limestones, which we associate with moist and benign environments on Earth, are evidently not abundant. Presumably, then, neither were the photosynthetic organisms that might have produced them. In addition, the harsh present environment on Mars (e.g., dryness, low temperatures, large temperature cycles, high level of UV light on the surface, frequent dust storms, etc.) can both destroy carbon- and water-bearing materials and hide them. Therefore, directly detecting life-related materials on Mars was likened to seeking and examining proverbial needles in haystacks. We argue that survey type instruments, that can frequently and quickly check a relatively large amount of material at many locations during a mission, are essential.

Wang, Alian↗
NASA NTRS2004

Variable Intrinsic UV Absorption in the Seyfert 1.5 Galaxy NGC 3516

We have examined the physical conditions in the intrinsic UV absorbing gas in the Seyfert 1.5 galaxy NGC 3516, using echelle spectra obtained with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope on 2000 October 1. We confirm the presence of the 4 kinematic components detected in earlier Goddard High Resolution Spectrograph (GHRS) spectra, as well as 4 new absorption features with radial velocities ranging from -692 to -1372 kilometers per second. The C IV column densities of components 3 and 4 appear to have increased significantly compared to the GHRS epoch. Based on photoionization modeling and our analysis of contemporaneous Chandra X-ray Observatory spectra, we argue that these changes are in response to the drop in ionizing flux.

Kraemer, S. B.↗
NASA NTRS2004

Improving Total Column Ozone Retrievals by Using Cloud Pressures Derived from Raman Scattering in the UV

The higher spectral resolution, coverage, and sampling of the Aura satellite ozone monitoring instrument (OMI), as compared with the total ozone mapping spectrometer (TOMS) should allow for improved ozone retrievals, including estimates of tropospheric ozone. By default, the TOMS-like OMI total column ozone algorithm uses climatological cloud-top pressures based on infrared (IR) measurements to estimate the column ozone below the clouds. Alternatively, cloud pressure can be retrieved using atmospheric rotational Raman scattering with OMI. The retrieved cloud pressures should be more consistent with assumptions made in the total ozone algorithm. Here, we use data from the global ozone monitoring experiment (GOME) to estimate total ozone using both the IR-climatological and retrieved cloud pressures. The exceed approximately 15 DU. Use of the UV cloud pressure retrievals leads to a smoother distribution of ozone along a satellite track by reducing small spatial irregularities presumably caused by errors in the climatological cloud pressures.

Vasilkov, A.↗
NASA NTRS2004

Supplementing the Digitized Sky Survey for UV-Mission Planning

The Space Telescope Science Institute worked on a project to augment the Digitized Sky Survey archive by completing the scanning and processing of the POSS-I blue survey. This will provide an additional valuable resource to support UV-mission planning. All of the data will be made available through the NASA optical/UV archive (MAST) at STScI. The activities completed during this project are included.

McLean, Brian↗
NASA NTRS1998

Single photon infrared emission spectroscopy: a study of IR emission from UV laser excited PAHs between 3 and 15 micrometers

Single-photon infrared emission spectroscopy (SPIRES) has been used to measure emission spectra from polycyclic aromatic hydrocarbons (PAHs). A supersonic free-jet expansion has been used to provide emission spectra of rotationally cold and vibrationally excited naphthalene and benzene. Under these conditions, the observed width of the 3.3-micrometers (C-H stretch) band resembles the bandwidths observed in experiments in which emission is observed from naphthalene with higher rotational energy. To obtain complete coverage of IR wavelengths relevant to the unidentified infrared bands (UIRs), UV laser-induced desorption was used to generate gas-phase highly excited PAHs. Lorentzian band shapes were convoluted with the monochromator-slit function in order to determine the widths of PAH emission bands under astrophysically relevant conditions. Bandwidths were also extracted from bands consisting of multiple normal modes blended together. These parameters are grouped according to the functional groups mostly involved in the vibration, and mean bandwidths are obtained. These bandwidths are larger than the widths of the corresponding UIR bands. However, when the comparison is limited to the largest PAHs studied, the bandwidths are slightly smaller than the corresponding UIR bands. These parameters can be used to model emission spectra from PAH cations and cations of larger PAHs, which are better candidate carriers of the UIRs.

Non-NASA Center↗
NASA NTRS1999

The influence of UV radiation on protistan evolution

Ultraviolet radiation has provided an evolutionary challenge to life on Earth. Recent increases in surficial ultraviolet B fluxes have focused attention on the role of UV radiation in protistan ecology, cancer, and DNA damage. Exploiting this new wealth of data, I examine the possibility that ultraviolet radiation may have played a significant role in the evolution of the first eukaryotes, that is, protists. Protists probably arose well before the formation of a significant ozone shield, and thus were probably subjected to substantial ultraviolet A, ultraviolet B, and ultraviolet C fluxes early in their evolution. Evolution consists of the generation of heritable variations and the subsequent selection of these variants. Ultraviolet radiation has played a role both as a mutagen and as a selective agent. In its role as a mutagen, it may have been crucial in the origin of sex and as a driver of molecular evolution. As a selective agent, its influence has been broad. Discussed in this paper are the influence of ultraviolet radiation on biogeography, photosynthesis, and desiccation resistance.

NASA Center ARC↗
NASA NTRS1999

UV irradiation of polycyclic aromatic hydrocarbons in ices: production of alcohols, quinones, and ethers

Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis.

NASA Center ARC↗