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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Simultaneous in situ measurements and diurnal variations of NO, NO2, O3, jNO2, CH4, H2O, and CO2 in the 40- to 26-km region using an open path tunable diode laser spectrometer

Simultaneous in situ measurements of temperature, pressure, and the NO, NO2, O3, jNO2, CH4, H2O, and CO2 concentrations were conducted in the 40- to 26-km region of the stratosphere using the JPL Balloon-borne Laser In Situ Sensor, a tunable diode laser absorption spectrometer. The NO, NO2, CH4, H2O, and CO2 concentration measurements generally show good agreement with previous observations, with a tendency for somewhat lower NO2 amounts. Measured O3 concentrations at 38 km agree well with comparable measurements from in situ UV photometers, but at 28 km they are lower by about 10 percent and agree more closely with the solar backscattered UV data. A decline was found in NO2 during the night over a 5-km altitude range, which implies either lower NO2 postsunset profiles, or an NO2 decay rate that is significantly higher than current model predictions that use N2O5 chemistry.

Webster, Christopher R.↗
NASA NTRS1987

Light hydrocarbons from plasma discharge in H2-He-CH4 - First results and Uranian auroral chemistry

The production of light hydrocarbons by precipitating magnetospheric electrons in the Uranian stratosphere is simulated in laboratory experiments. The products of continuous-flow glow discharges of H2-He-CH4 mixtures containing 0.0012 or 0.022 mol pct CH4 at pressures 0.63-57 mbar are trapped at 77 K, measured manometrically, and identified by gas chromatography and mass spectroscopy; the results are presented in tables and characterized in detail. The globally averaged rate for the production of higher hydrocarbons by this mechanism on Uranus is estimated as 3 x 10 to the 6th C/sq cm sec and shown to be similar to that for photochemical production, while the local rate for the auroral zones is significantly higher than the corresponding photochemical rate. A decrease in yield with increasing molecular complexity is also noted.

Thompson, W. Reid↗
NASA NTRS1989

Ionization yields, total absorption, and dissociative photoionization cross sections of CH4 from 110-950 A

Absolute absorption and photoionization cross sections of methane have been measured with an accuracy of about 2 or 3 percent over most of the wavelength range from 950 to 110 A. Also, dissociative photoionization cross sections were measured for the production of CH4(+), CH3(+), CH2(+), CH(+), and C(+) from their respective thresholds to 159 A, and for H(+) and H2(+) measurements were made down to 240 A. Fragmentation was observed at all excited ionic states of CH4.

Samson, James A. R.↗
NASA NTRS1990

Hydrogen constituents of the mesosphere inferred from positive ions - H2O, CH4, H2CO, H2O2, and HCN

The concentrations in the mesosphere of H2O, CH4, H2CO, H2O2, and HCN were inferred from data on positive ion compositions, obtained from one mid-latitude and four high-latitude rocket flights. The inferred concentrations were found to agree only partially with the ground-based microwave measurements and/or model prediction by Garcia and Solomon (1985). The CH4 concentration was found to vary between 70 and 4 ppb in daytime and 900 and 100 ppbv at night, respectively. Unexpectedly high H2CO concentrations were obtained, with H2CO/H2O ratios between 0.0006 and 0.1, and a mean HCN volume mixing ratio of 6 x 10 to the -10th was inferred.

Kopp, E.↗
NASA NTRS1990

CH4 nonlocal thermodynamic equilibrium in the atmospheres of the giant planets

The present consideration of methane's vibrational relaxation in the Giant Planets' upper stratospheres employs a model for the thermalization of solar energy absorbed under non-LTE conditions, at the 1.7, 2.3. and 3.3 micron-centered CH4 band groups. On this basis, a range of model atmospheres was produced, reflecting current uncertainties concerning CH4 collisional excitation rates. At 0.1 mbar, all of the non-LTE models are within 2 K of the LTE reference models; the extreme non-LTE models steadily depart from reference LTE ones, however, and reach about + or - 20 K at 0,1 mbar.

Appleby, John F.↗
NASA NTRS1990

Fluorescence from excitation of CH4, CH3OH and CH3SH by extreme vacuum ultraviolet radiation

The photoabsorption and fluorescence cross sections of CH4, CH3OH, and CH3SH were measured in the wavelength regions of 52-106, 48-106, and 48-106 nm, respectively. The fluorescence spectra were dispersed to identify the emitting species. Emissions from the excited species of H(asterisk) and CH(asterisk) are commonly observed for all three molecules. Emission from the excited CH2(asterisk) is observed from CH4, OH(asterisk) from CH3OH and CS(asterisk) from CH3SH. The photoexcitation processes that may produce the observed emission bands are discussed.

Ma, Guang↗
NASA NTRS1991

CH4 and N2O photochemical lifetimes in the upper stratosphere - In situ estimates using SAMS data

Upper stratospheric photochemical lifetimes are estimated in situ for CH4 and N2O for the first time, based on an analysis technique using 3 years of satellite measurements from the Stratospheric And Mesospheric Sounder (SAMS) instrument. The technique involves investigation of the time dependence of tracers injected into high northern latitudes in late winter and their subsequent photochemical decay during the dynamically quiescent summer stratosphere. Dynamical corrections are made for mean meridional circulation contributions. The lifetimes for N2O at 2 and 7 hPa (about 43 and about 35 km altitude) are found to be 1.7 and 8.3 months, respectively. For CH4, 0.6 (about 52 km altitude) and 2 hPa lifetimes are 3.3 and 3.4 months, respectively. These observed values are in good agreement with model calculations by Solomon et al. (1986).

Stanford, J. L.↗
NASA NTRS1991

Theoretical study of the C-H bond dissociation energies of CH4, C2H2, C2H4, and H2C2O

The successive C-H bond dissociation energies of CH4, C2H2, C2H4, and H2C2O (ketene) are determined using large-basis sets and a high level of correlation treatment. For CH4, C2H2, and C2H4 the computed values are in excellent agreement with experiment. Using these results, the values 107.9 + or - 2.0 and 96.7 + or - 2.0 kcal/mol are recommended for the C-H bond dissociation energies of H2C2O and HC2O, respectively.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1991

Multiple Stokes wavelength generation in H2, D2, and CH4 for lidar aerosol measurements

Experimental results are reported of multiple Stokes generation of a frequency-doubled Nd:YAG laser in H2, D2, and CH4 in a focusing geometry. The energies at four Stokes orders were measured as functions of pump energy and gas pressure. The characteristics of the Stokes radiation generated in these gases are compared for optical production of multiple wavelengths. The competition between Raman components is analyzed in terms of cascade Raman scattering and four-wave mixing. The results indicate the possibility of using these generation processes for atmospheric aerosol measurements by means of multiwavelength lidar systems. Also, this study distinguishes between the gases, as regards the tendency to produce several wavelengths (H2,D2) versus the preference to produce mainly first Stokes radiation (CH4).

Chu, Zhiping↗
NASA NTRS1993

Intense backward Raman lasers in CH4 and H2

The conversion efficiency of the first Stokes radiation generated by backward stimulated Raman scattering is measured in CH4 and H2 that are pumped by a third harmonic of a Nd:YAG laser in the 12-55-mJ energy range and in the 0.86-6.00-MPa pressure range. Our experimental results show that CH4 is a better Raman medium than H2 at moderate pressures (a few megapascals) to efficiently generate backward Raman lines.

Sentrayan, Karuppasamy↗
NASA NTRS1993

Total electron scattering and electronic state excitations cross sections for O2, CO, and CH4

Available electron collision cross section data concerning total and elastic scattering, vibrational excitation, and ionization for O2, CO, and CH4 have been critically reviewed, and a set of cross sections for modeling of planetary atmospheric behavior is recommended. Utilizing these recommended cross sections, we derived total electronic state excitation cross sections and upper limits for dissociation cross sections, which in the case of CH4 should very closely equal the actual dissociation cross section.

Kanik, I.↗
NASA NTRS1993

CLAES CH4, N2O and CCL2F2 (F12) global data

Zonal mean comparisons of CH4 (for altitude regions above the 1.35 ppmv contour), of N2O (above the 210 ppbv contour), and of F12 (above the 360 pptv contour) with UARS prelaunch climatology and with recent models shows reasonable agreement, and some interesting differences in the details of equatorial uplift and descent near the winter poles, including apparent north-south differences. Prominent features such as the double peaked uplift structure in the April-May SAMS data are clearly evident in all three CLAES tracers. Contours of SAMS CH4 and N2O occur mostly at higher pressures than in the CLAES data, presumably due in part to increased tropospheric content of these gases, and/or perhaps some dynamic difference associated with the 15 years time difference between the data sets. The CLAES F12 are the first long time base global data sets. These show more tropical uplift than climatology or models. This might suggest a somewhat shorter lifetime of F12 in the stratosphere than is currently accepted.

Kumer, J. B.↗
NASA NTRS1993

A two-dimensional model with coupled dynamics, radiative transfer, and photochemistry. 2: Assessment of the response of stratospheric ozone to increased levels of CO2, N2O, CH4, and CFC

The impact of increased levels of carbon dioxide (CO2), chlorofluorocarbons (CFCs), and other trace gases on stratospheric ozone is investigated with an interactive, two-dimensional model of gas phase chemistry, dynamics, and radiation. The scenarios considered are (1) a doubling of the CO2 concentration, (2) increases of CFCs, (3) CFC increases combined with increases of nitrous oxide (N2O) and methane CH4, and (4) the simultaneous increase of CO2, CFCs, N2O, and CH4. The radiative feedback and the effect of temperature and circulation changes are studied for each scenario. For the double CO2 calculations the tropospheric warming was specified. The CO2 doubling leads to a 3.1% increase in the global ozone content. Doubling of the CO2 concentrations would lead to a maximum cooling of about 12 C at 45 km if the ozone concentration were held fixed. The cooling of the stratosphere leads to an ozone increase with an associated increase in solar heating, reducing the maximum temperature drop by about 3 C. The CFC increase from continuous emissions at 1985 rate causes a 4.5% loss of ozone. For the combined perturbations a net loss of 1.3% is calculated. The structure of the perturbations shows a north-south asymmetry. Ozone losses (when expressed in terms of percent changes) are generally larger in the high latitudes of the southern hemisphere as a result of the eddy mixing being smaller than in the northern hemisphere. Increase of chlorine leads to ozone losses above 30 km altitude where the radiative feedback results in a cooler temperature and an ozone recovery of about one quarter of the losses predicted with a noninteractive model. In all the cases, changes in circulation are small. In the chlorine case, circulation changes reduce the calculated column depletion by about one tenth compared to offline calculations.

Schneider, Hans R.↗
NASA NTRS1994

Temperature dependence of Lorentz air-broadening and pressure-shift coefficients of (12)CH4 lines in the 2.3-micron spectral region

High-resolution (0.01/cm) absorption spectra of lean mixtures of CH4 in dry air were recorded with the McMath-Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory on Kitt Peak at various temperatures between 24 and -61 C. The spectra have been analyzed to determine the values at room temperature of pressure-broadened widths and pressure-induced shifts of more than 740 transitions. The temperature dependence of air-broadened widths and pressure-induced shifts was deduced for approx. 370 transitions in the nu(sub 1) + nu(sub 4), nu(sub 3) + nu(sub 4), and nu(sub 2) + nu(sub 3) bands of (12)CH4 located between 4118 and 4615/cm. These results were obtained by analyzing a total of 29 spectra simultaneously using a multi-spectral non-linear least-squares fitting technique. This new technique allowed the determination of correlated spectral line parameters (e.g. intensity and broadening coefficient) better than the procedure of averaging values obtained by fitting the spectra individually. This method also provided a direct determination of the uncertainties in the retrieved parameters due to random errors. For each band analysed in this study the dependence of the various spectral line parameters upon the tetrahedral symmetry species and the rotational quantum numbers of the transitions is also presented.

Devi, V. Malathy↗
NASA NTRS2000

BOREAS TGB-1 CH4 Concentration and Flux Data from NSA Tower Sites

The BOREAS TGB-1 team made numerous measurements of trace gas concentrations and fluxes at various NSA sites. This data set contains half-hourly averages of ambient methane (CH4) measurements and calculated fluxes for the NSA-Fen in 1996 and the NSA-BP and NSA-OJP tower sites in 1994. The purpose of this study was to determine the CH4 flux from the study area by measuring ambient CH 4 concentrations. This flux can then be compared to the chamber flux measurements taken at the same sites. The data are provided in tabular ASCII files.

Hall, Forrest G.↗
NASA NTRS2000

BOREAS TGB-1 Soil CH4 and CO2 Profile Data from NSA Tower Sites

The BOREAS TGB-1 team made numerous measurements of trace gas concentrations and fluxes at various NSA sites. This data set contains methane (CH4) and carbon dioxide (CO2) concentrations in soil profiles from the NSA-OJP, NSA-OBS, NSA-YJP, and NSA-BP sites during the period of 23-May to 20-Sep-1994. The soil gas sampling profiles of CH 4 and CO 2 were completed to quantify controls on CO2 and CH4 fluxes in the boreal forest. The data are provided in tabular ASCII files.

Crill, Patrick↗
NASA NTRS2000

BOREAS TF-4 CO2 and CH4 Chamber Flux Data from the SSA

The BOREAS TF-4 team measured fluxes of CO2 and CH4 across the soil-air interface in four ages of jack pine forest at the BOREAS SSA during August 1993 to March 1995. Gross and net flux of CO2 and flux of CH4 between soil and air are presented for 24 chamber sites in mature jack pine forest, 20-year-old, 4-year-old, and clear cut areas. The data are stored in tabular ASCII files.

Anderson, Dean↗
NASA NTRS2002

In Situ Measurements of N2O and CH4 During SOLVE on the ER-2 Using a New Tunable Diode Laser Instrument

This report is the final report for Cooperative Agreement NCC2-1105: 'In Situ Measurements of N2O and CH4 during SOLVE on the ER-2 using a new tunable diode laser instrument.' The tasks outlined in the proposal are listed below with a brief comment. The publications and the conference presentations are listed. Finally the important publications are attached. The Cooperative Agreement made possible a research effort to produce high precision and high accuracy in situ measurements of methane and nitrous oxide on the ER-2 during the SOLVE field campaign and to analyze these measurements. These measurements of CH4 and N2O were of utmost importance to studies of the ozone losses in the Arctic winter and spring. The concentrations measured over a large spatial and temporal range allowed the separation of the dynamical and chemical ozone loss. The most important results of the SOLVE program were contained in two scientific papers. This Cooperative Agreement allowed the participation of the Argus instrument in the program and the analysis of the data.

Jost, Hansjurg↗