Engineering topics

Mcelroy, M. B.

Publications and source records attributed to Mcelroy, M. B..

At least 55 records · Page 3

NASA NTRS1977

Nitrous oxide in fresh water systems: An estimate for the yield of atmospheric N2O associated with disposal of human waste

The N2O content of waters in the Potomac and Merrimack Rivers was measured on a number of occasions over the period April to July 1977. The concentrations of dissolved N2O exceeded those which would apply in equilibrium with air by factors ranging from about 46 in the Potomac to 1.2 in the Merrimack. Highest concentrations of dissolved N2O were associated with sewage discharges from the vicinity of Washington, D. C., and analysis indicates a relatively high yield, 1.3 to 11%, for prompt conversion of waste nitrogen to N2O. Measurements of dissolved N2O in fresh water ponds near Boston demonstrated that aquatic systems provide both strong sources and sinks for atmospheric N2O.

Kaplan, W. A.↗

NASA NTRS1977

Sources and sinks for atmospheric H2 - A current analysis with projections for the influence of anthropogenic activity

Oxidation of CH4 provides the major source for atmospheric H2, which is removed mainly by reaction with OH. Biological activity at earth's surface appears to represent at most a minor sink for H2. Anthropogenic activity is a significant source for both H2 and CO in the present atmosphere and may be expected to exert a growing influence in the future. Models are presented which suggest a rise in the mixing ratio of H2 from its present value of 5.6 ten-millionths to about 1.8 millionths by the year 2100. The mixing ratio of CO should grow from 9.7 hundred-millionths to 2.3 ten-millionths over the same time period, and there should be a rise in CH4 by about a factor of 1.5 associated with anthropogenically induced reductions in tropospheric OH.

Penner, J. E.↗

NASA NTRS1977

The sodium and hydrogen gas clouds of Io

Models are developed to describe the spatial distribution of gases emitted by Io and are applied to recent observations which indicate extensive gas clouds of hydrogen and sodium in orbit around Jupiter. Hydrogen and sodium atoms are emitted from Io with velocities in the range from 2 to 3 km/sec, with fluxes of about 10 billion and 100 million per sq cm/sec for hydrogen and sodium, respectively. Hydrogen atoms may be formed by photodecomposition of gases such as NH3 or H2S released from the satellite surface and may escape thermally from an exosphere whose temperature is about 500 K. Sodium may be ejected from the surface by energetic particles or by ultraviolet radiation, and it appears that a nonthermal mechanism drawing energy from Jupiter's magnetic field is required in order to account for its release to space.

Smyth, W. H.↗

NASA NTRS1977

Distribution functions for energetic oxygen atoms in the earth's lower atmosphere

Direct photolysis of O3 and quenching of O(1D) by N2 provide abundant sources of fast oxygen atoms for earth's lower atmosphere. The concentration of atoms with energy above 0.7 eV may exceed the concentration of O(1D) for all altitudes below 18 km, and these atoms may play an important role in lower-atmospheric chemistry. Distribution functions for O(3P) are given for the energy interval 0.1-1.3 eV and a range of altitudes from 0 to 62 km.

Logan, J. A.↗

NASA NTRS1977

Photochemistry of nitrogen in the Martian atmosphere

Models are developed for the photochemistry of a CO2-H2O-N2 atmosphere on Mars. Estimates are given for the concentrations of N, NO, NO2, NO3, N2O5, HNO2, HNO3, and N2O as a function of altitude. Nitric oxide is the most abundant form of odd nitrogen, present with a mixing ratio relative to CO2 of the order of 1 hundred-millionth. Deposition rates for nitrite and nitrate minerals could be as large as 300,000 N equivalent atoms per sq cm/sec under present conditions and may have been higher in the past.

Yung, Y. L.↗

NASA NTRS1977

Ultraviolet absorption: Experiment MA-059

A technique devised to permit the measurement of atmospheric species concentrations is described. This technique involves the application of atomic absorption spectroscopy and the quantitative observation of resonance fluorescence in which atomic or molecular species scatter resonance radiation from a light source into a detector. A beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation was sent from Apollo to Soyuz. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Results of postflight analysis of the resonance fluorescence data are discussed.

Donahue, T. M.↗

NASA NTRS1976

Composition and structure of the Martian upper atmosphere - Analysis of results from Viking

Densities for carbon dioxide measured by the upper-atmospheric mass spectrometers on Viking 1 and Viking 2 are analyzed to yield height profiles for the temperature of the Martian atmosphere between 120 and 200 kilometers. Densities for nitrogen and argon are used to derive vertical profiles for the eddy diffusion coefficient over the same height range. The upper atmosphere of Mars is surprisingly cold, with average temperatures for both Viking 1 and Viking 2 of less than 200 K, and there is significant vertical structure. Model calculations are presented and shown to be in good agreement with measured concentrations of carbon monoxide, oxygen, and nitric oxide.

Mcelroy, M. B.↗

NASA NTRS1976

Structure of the neutral upper atmosphere of Mars - Results from Viking 1 and Viking 2

Neutral mass spectrometers carried on the aeroshells of Viking 1 and Viking 2 indicate that carbon dioxide is the major constituent of the Martian atmosphere over the height range 120 to 200 kilometers. The atmosphere contains detectable concentrations of nitrogen, argon, carbon monoxide, molecular oxygen, atomic oxygen, and nitric oxide. The upper atmosphere exhibits a complex and variable thermal structure and is well mixed to heights in excess of 120 kilometers.

Nier, A. O.↗

NASA NTRS1976

Oxygen isotopes in the Martian atmosphere - Implications for the evolution of volatiles

Nonthermal escape of oxygen by recombination of exospheric O2(+) combined with diffusive separation of gases at lower altitude provides a mechanism through which the Martian atmosphere may be enriched in O-18 relative to O-16. Measurement of the abundance of O-18 relative to O-16 together with a determination of the turbopause may be used to develop important constraints on the history of Martian volatiles. Models for the interpretation of these data are developed and discussed in light of present information.

Mcelroy, M. B.↗

NASA NTRS1976

Isotopic composition of the Martian atmosphere

Results from the neutral mass spectrometer carried on the aeroshell of Viking 1 show evidence for NO in the upper atmosphere of Mars and indicate that the isotopic composition of carbon and oxygen is similar to that of earth. Mars is enriched in N-15 relative to earth by about 75 per cent, a consequence of escape that implies an initial abundance of nitrogen equivalent to a partial pressure of at least 2 millibars. The initial abundance of oxygen present either as CO2 or H2O must be equivalent to an exchangeable atmospheric pressure of at least 2 bars in order to inhibit escape-related enrichment of O-18.

Nier, A. O.↗

NASA NTRS1976

Isotopic composition of nitrogen - Implications for the past history of Mars' atmosphere

Models are presented for the past history of nitrogen on Mars, based on Viking measurements showing that the atmosphere is enriched in N-15. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N2 and by dissociative recombination of N2(+). The initial partial pressure of N2 should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO2 and HNO3.

Mcelroy, M. B.↗

NASA NTRS1976

Oxidation of the Martian surface - Constraints due to chemical processes in the atmosphere

Dissociation of water in the Martian atmosphere may supply oxygen to the surface and may result in the formation of minerals such as goethite, as proposed by Huguenin. The supply rate is limited by chemical processes in the atmosphere which regulate the abundance of O2. The net surface sink for atmospheric oxygen can be as large as 33 million atoms per sq cm per sec which compares to the escape rate of 60 million atoms per sq cm per sec.

Mcelroy, M. B.↗

NASA NTRS1976

Composition and structure of the Martian atmosphere - Preliminary results from Viking 1

Results from the aeroshell-mounted neutral mass spectrometer on Viking 1 indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO. The mixing ratios by volume relative to CO2 for N2, Ar, and O2 are about 0.06, 0.015, and 0.003, respectively, at an altitude near 135 kilometers. Molecular oxygen is a major component of the ionosphere according to results from the retarding potential analyzer. The atmosphere between 140 and 200 kilometers has an average temperature of about 180 plus or minus 20 deg K. Atmospheric pressure at the landing site for Viking 1 was 7.3 millibars at an air temperature of 241 deg K. The descent data are consistent with the view that CO2 should be the major constituent of the lower Martian atmosphere.

Nier, A. O.↗

NASA NTRS1976

Sources and sinks for atmospheric N2O

Observations of the temporal and spatial distribution of N2O in solution are not yet sufficient to permit quantitative assessment of the role of the ocean in the budget of atmospheric N2O. Consideration of the global nitrogen cycle suggests that the land should be the primary source of N2O. The gas is removed in the atmosphere by photolysis and by reaction with O(1D), and there may be additional sinks in the ocean.

Mcelroy, M. B.↗

NASA NTRS1976

Ultraviolet absorption experiment MA-059

The ultraviolet absorption experiment performed during the Apollo Soyuz mission involved sending a beam of atomic oxygen and atomic nitrogen resonance radiation, strong unabsorbable oxygen and nitrogen radiation, and visual radiation, all filling the same 3 deg-wide field of view from the Apollo to the Soyuz. The radiation struck a retroreflector array on the Soyuz and was returned to a spectrometer onboard the Apollo. The density of atomic oxygen and atomic nitrogen between the two spacecraft was measured by observing the amount of resonance radiation absorbed when the line joining Apollo and Soyuz was perpendicular to their velocity with respect to the ambient atmosphere. Information concerning oxygen densities was also obtained by observation of resonantly fluorescent light. The absorption experiments for atomic oxygen and atomic nitrogen were successfully performed at a range of 500 meters, and abundant resonance fluorescence data were obtained.

Donahue, T. M.↗

NASA NTRS1975

Atmospheric halocarbons - A discussion with emphasis on chloroform

Bleaching of paper pulp represents a major industrial use of chlorine and could provide an environmentally significant source of atmospheric halocarbons. The related global production of chloroform is estimated at 300,000 ton per year and there could be additional production associated with atmospheric decomposition of perchloroethylene. Estimates are given for the production of methyl chloride, methyl bromide and methyl iodide, 5.2 million, 77 thousand, and 740 thousand ton per year respectively. The relative yields of CH3Cl, CH3Br and CH3I are consistent with the hypothesis of a marine biological source for these compounds. Concentrations of other halocarbons observed in the atmosphere appear to indicate industrial sources.

Yung, Y. L.↗

NASA NTRS1975

The chemistry of atmospheric bromine

Bromine may act as a catalyst for recombination of ozone and could be more efficient than either nitric oxide or chlorine. The lower atmosphere contains small concentrations of gaseous bromine produced in part by marine activity and volatilization of particulate material released during the combustion of leaded gasoline, with an additional contribution due to the use of methyl bromide as an agricultural fumigant. Observations by Lazrus et al., (1975) indicate small concentrations of bromine, about 10 to the -11th power (v/v), in the contemporary stratosphere and appear to imply a reduction of approximately 0.3% in the global budget of O3. Estimates are given for future reductions in O3 which might occur if the use of CH3Br as an agricultural fumigant were to continue to grow at present rates.

Wofsy, S. C.↗

NASA NTRS1975

The earth's trapped radiation belts

The near-earth charged particle environment is discussed in terms of spacecraft design criteria. Models are presented of the trapped radiation belts and based on in-situ data obtained from spacecraft.

Noll, R. B.↗