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At least 73 records · Page 4
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NASA NTRS2019

Anthropogenic Nitrogen Inputs and Impacts on Oceanic N2O Fluxes in the Northern Indian Ocean: the Need for an Integrated Observation and Modelling Approach

Anthropogenically-derived nitrogen input to the northern Indian Ocean has increased significantly in recent decades, based on both observational and model derived estimates This external nutrient source is supplied by atmospheric deposition and riverine fluxes, and has the potential to affect the vulnerable biogeochemical systems of the Arabian Sea and Bay of Bengal, influencing productivity and oceanic production of the greenhouse-gas nitrous-oxide (N2O). We summarize current estimates of this external nitrogen source to the northern Indian Ocean from observations and models, highlight implications for regional marine N2O emissions using model-based analyses, and make recommendations for measurement and model needs to improve current estimates and future predictions of this impact. Current observationally-derived estimates of deposition and riverine nitrogen inputs are limited by sparse measurements and uncertainties on accurate characterization of nitrogen species composition. Ocean model assessments of the impact of external nitrogen sources on regional marine N2O production in the northern Indian Ocean estimate potentially significant changes but also have large associated uncertainties. We recommend an integrated program of basin-wide measurements combined with high-resolution modeling and more detailed characterization of nitrogen-cycle process to address these uncertainties and improve current estimates and predictions.

Parvadha Suntharalingam↗
NASA NTRS1971

Photodissociation of the CH3Cl/+/ and N2O/+/ cations.

Use of the ion cyclotron resonance (icr) technique to observe the photodissociation of the cations CH3Cl(+) and N2O(+) in the gas phase. Ions were trapped in the icr cell for periods of the order of seconds, which permitted the photodissociation process to be observed with wavelength-selected light. A cyclotron resonance ejection technique was employed to show that CH3Cl(+) ions were being dissociated rather than the CH3ClH(+) ions which were also present. The photodissociation cross section for N2O(+) was found to be without strong wavelength dependence between 4000 and 6500 A. The cross section for CH3Cl(+) showed a large peak at 3150 A. Possible assignments of this peak are considered, and it is suggested that a photodissociation occurs through an ion excitation involving a change in occupation of the bonding or antibonding orbitals of the C-Cl bond.

Dunbar, R. C.↗
NASA NTRS1974

Vacuum UV photolysis of N2O

Emission from N2 B (3 Pi g) and O(1 S) produced during vacuum UV irradiation of N2O was studied as a function of the wavelength of the incident radiation. Two different processes were responsible for producing N2(B 3 Pi g) close to its production threshold. One process formed B 3 Pi g molecules directly and one indirectly via an unidentified precursor having a lifetime about 27 microsec. The quantum yield of O(1 S) atoms produced by photodissociation of N2O was determined as a function of incident photon energy. This yield is near 100% at 129 nm.

Mcewan, M. J.↗
NASA NTRS1978

Interhemispheric gradients of CF2Cl2, CFCl3, CCl4, and N2O

Direct real-time gas-chromatographic measurements of CF2Cl2, CFCl3, CCl4, and N2O were made at latitudes from 74 deg N to 62 deg S aboard a NASA Convair 990 as part of the 1976 NASA CV-990 Latitude Survey Mission between Alaska and New Zealand. A difference was found in the average mixing ratios of CF2Cl2 and CFCl3 between the Northern and Southern Hemispheres, but no differences were noted for CCl4 and N2O. The results support some of the previous studies of interhemispheric tropospheric gradients and suggest the lack of any significant tropospheric sinks.

Tyson, B. J.↗
NASA NTRS1978

Decomposition of N2O over particulate matter

Nitrous oxide is shown to undergo both a thermal and a photochemical decomposition at 296 K when it is adsorbed on various dry sands. The photochemical process occurs with light of wavelengths greater than 280 nm, where gaseous N2O does not absorb. At low pressures (less than 0.1 torr) the half-life for the thermal decomposition of nitrous oxide to nitrogen when placed in contact with about 5 gm of heat-treated Tunisian sand in a one-liter vessel was 350 + or - 35 days. Under certain photolytic conditions this half-life was reduced. The efficiency of the photolytic process for a particular sand depends on the pressure and on the wavelength of light. For Tunisian sand at 1.1 torr and with the full mercury arc, the destruction efficiency is about 0.00002 molecule/incident photon. These results indicate that particulate matter in the troposphere may be responsible for the decomposition of nitrous oxide and hence act as an atmospheric sink for N2O. However, moisture causes a drastic reduction in the number of molecules dissociated per incident photon.

Rebbert, R. E.↗
NASA NTRS1979

N2O and CO production by electric discharge - Atmospheric implications

Enhanced levels of N2O and CO were measured in tropospheric air samples exposed to a 17,500-J laboratory discharge. These enhanced levels correspond to an N2O production rate of about 4 trillion molecules/J and a CO production rate of about 10 to the 14th molecules/J. The CO measurements suggest that the primary region of chemical production in the discharge is the shocked air surrounding the lightning channel, as opposed to the slower-cooling inner core. Additional experiments in a simulated Venus atmosphere (CO2 - 95%, N2 - 5%, at one atmosphere) indicate an enhancement of CO from less than 0.1 ppm prior to the laboratory discharge to more than 2000 ppm after the discharge. Comparison with theoretical calculations appears to confirm the ability of a shock-wave/thermochemical model to predict the rate of production of trace species by an electrical discharge.

Levine, J. S.↗
NASA NTRS1981

Production of NO and N2O by soil nitrifying bacteria

The composition of the atmosphere is influenced both directly and indirectly by biological activity. Evidence is presented here to suggest that nitrification in soil is a potentially significant source of both NO and N2O. Between 0.3 and 10% of the ammonium oxidized by cultures of the soil bacterium Nitrosomonas europaea is converted to these gases. The global source for NO associated with nitrification could be as large as 15,000,000 tonnes N/yr, with a source for N2O of 5,000,000-10,000,000 tonnes N/yr. Nitric oxide has a key role in tropospheric chemistry, participating in a complex set of reactions regulating OH and O3. Nitrous oxide is a dominant source of stratospheric NO and has a significant influence on climate.

Lipschultz, F.↗
NASA NTRS1981

Band parameters of N2O and CO2 determined by whole band analysis

Whole band analysis, a method of obtaining band parameters from spectra by nonlinear least squares fitting of calculated to observed spectra, has been applied to bands of N2O and CO2. The retrieved N2 broadened widths of the 02(0)00 - 00(0) and 12(0)0 - 00(0)0 bands of N2O suggest that the air broadened widths on the AFGL listing are about 10% high. The intensities and (C-12)(O-16)2 broadened widths of the 20002-00001 and 21102-01101 bands of (C-12)(O-16)(O-18) and the 20002-00001 band of (C-12)(O-16)(O-17) have also been determined.

Hawkins, R. L.↗
NASA NTRS1984

The source of stratospheric NO and N2O

The photodissociation of O3 was investigated as a possible sources of N2O production in the stratosphere. Photolysis was conducted at 1576 A to generate the excited O2 states that react with N2 to form N2O. At this wavelength, there is a quantum yield of two for prompt production of oygen atoms, which is a consequence of the existence of two photodissociative channels giving comparable yields. One of these channels gives O(D1) and O2(b1sigma(+)subg), with a quantum yield of 0.6, whereas the other results in fragmentation of the O3, with production of three ground state oxygen atoms. The O2(b) is generated with vibrational excitation, and there are comparable populations in levels O to 3. These observations are the first to show O2(b) production from any photodissociative process, and were made under conditions in which the kinetics of vibrationally excited O2(b) can be studied. It appears that O3 photodissociation at 1576 A is not a good system for generating the higher electronic states of O2; it is likely that better results will be obtained at 1930 A.

Slanger, T. G.↗
NASA NTRS1985

Sensitivity of N2O, CFCl3, and CF2Cl2 two-dimensional distributions to O2 absorption cross sections

A good test of the transport and ultraviolet radiation treatment for any model can be based on the consideration of the three gases N2O, CFCl3 (F-11), and CF2Cl2 (F-12). Attention is given to a two-dimensional model which makes it possible to study changes in seasonal and latitudinal distributions which result from O2 cross-section changes. A latitude-dependent ozone decrease has already been predicted by two-dimensional models for chlorofluoromethane (CFM) release. For this reason, it is of interest to determine if a strong latitude-dependent change is detectable in the CFM profiles. One-dimensional models have pointed toward a trend of decreased trace gas concentrations in correlation with decreased O2 cross sections. The O2 cross sections between 180 and 230 nm are changed within a range of experimentlly allowed values. It is found that lower O2 absorption cross sections lead to larger photodissociation rates for the trace gases F-11, F-12, and N2O.

Jackman, C. H.↗
NASA NTRS1985

Biologically produced volatile compounds: N2O emissions from soils

Tropospheric nitrous concentration has increased by 0.2 0.4% per year over the period 1975 to 1982, amounting to net addition to the atmosphere of 2.8 - 5.6 Tg N2O-N per year. This perturbation, if continued into the future, will affect stratospheric chemical cycles, and the thermal balance of the Earth. In turn it will have direct and indirect global effects on the biosphere. Though the budget and cycles of N2O on Earth are not yet fully resolved, accumulating information and recent modelling efforts permit a more complete evaluation and better definition of gaps in our knowledge.

Banin, A.↗
NASA NTRS1985

Lasing in N2O and CO2 isotope mixtures pumped by blackbody radiation

The use of N2O and CO2 isotopes as active species for a blackbody radiation pumped laser has been experimentally demonstrated and theoretically analyzed. The results obtained for mixtures containing N2O, (C-13) (O-16)2, and (C-12) (O-18)2 are presented. For the first time, continuous lasing action with blackbody radiation pumping has been obtained for this species. Two active species mixtures were tested, obtaining up to a 100 percent increase in output power due to v-v transfer. A simple model was developed and gain calculations are presented.

Sirota, J. M.↗
NASA NTRS1986

A global three-dimensional model of the circulation and chemistry of CFCl3, CF2Cl2, CH3CCl3, CCl4, and N2O

The use of a three-dimensional spectral model to study the tropospheric and stratospheric circulation, chemistry, and photochemistry of the CFCl3, CF2Cl2, CH3CCl3, CCl4, and N2O atmospheric species is examined. The components of the model are described. Lifetime, regional, and global trends and budgets for the species are evaluated. Calculated horizontal, vertical, and temporal distributions of the atmospheric species are compared with observations; good correlation is detected. The differences observed between calculated and observed surface distributions of CH3CCl3 and the vertical distribution of CCl4 are analyzed. The calculated global atmospheric lifetimes of CFCl3, CF2Cl2, CCl4, and N2O are 73, 210, 48, and 182 years, respectively.

Golombek, A.↗
NASA NTRS1986

Emissions of N2O, CH4 and CO2 from tropical forest soils

Emissions of nitrous oxide, methane, and carbon dioxide were measured at diverse locations in tropical forests of Brazil, Ecuador, and Puerto Rico using a static open chamber technique. Mean fluxes to the atmosphere were 1.7 x 10 to the 10th, -0.7 x 10 to the 10th, and 1.5 x 10 to the 14th molecules/sq cm per s for N2O, CH4, and CO2, respectively. The data indicate that tropical forests contribute a significant fraction of the global source for atmospheric N2O, about 40 percent of the current source, and possibly 75 percent of the preindustrial source. Methane is consumed by soils on average, but the sink is an insignificant part (less than 5 percent) of the atmospheric cycle for the gas. Emissions of CO2 from forest soils are higher at equatorial sites than at middle or high latitudes, as expected from ecological considerations. Soils emit CO2 at rates more than twice as large as the rate of carbon infall in litter; hence much of the emitted CO2 must arise from root metabolism.

Keller, Michael↗
NASA NTRS1988

Correlation of N2O and ozone in the Southern Polar vortex during the airborne Antarctic ozone experiment

In situ N20 mixing ratios, measured by an airborne laser spectrometer (ATLAS), have been used along with in situ ozone measurements to determine the correlation of N2O and ozone in the Antarctic stratosphere during the late austral winter. During the 1987 Airborne Antarctic Ozone Experiment (AAOE), N2O data were collected by a laser absorption spectrometer on board the ER-2 on five ferry flights between Ames Research Center (37 deg N) and Punta Arenas, Chile (53 deg S), and on twelve flights over Antarctica (53 S to 72 S). Of all the trace gas species measured by instruments on board the ER-2, only one showed a relationship to the N2O/O3 correlations in the vortex. With few exceptions, positive N20/O3 correlations coincided with total water mixing ratios of greater than 2.9 ppmv, and total water mixing ratios of less than 2.9 ppmv corresponded to negative correlations. The lower water mixing ratios, or dehydrated regions, are colocated with the negative correlations within the vortex, while the wetter regions always occur near the vortex edge.

Strahan, S. E.↗
NASA NTRS1989

Jet-resolved vibronic structure in the higher excited states of N2O - Ultraviolet three-photon absorption spectroscopy from 80,000 to 90,000/cm

Ionization-detected UV multiphoton absorption spectroscopy of the excited states of N2O is presented, showing Rydberg structure within 20,000/cm of the first ionization threshold. Despite evidence for strong Rydberg-continuum coupling in the form of broadened bands and Fano line-shapes, the Rydberg structure persists, with atomic-like quantum defects and vibration structure well-matched with that of the ion. In the most clearly resolved spectrum, corresponding to the 3p(delta)1Pi state, Renner-Teller and Herzberg-Teller coupling of electronic and vibrational angular momentum are revealed. It is suggested that these mixings are properties of the N2O(+)Pi ion core.

Patsilinakou, E.↗
NASA NTRS1990

Reconstruction of O3 and N2O fields from ER-2, DC-8, and balloon observations

Measurements of N2O and O3 during the Airborne Arctic Stratospheric Expedition have been composited using the potential vorticity and potential temperature of each measurement as coordinates. For ozone, data sources included the ER-2 and balloon ozonesonde in situ measurements, DC-8 DIAL lidar, and Stratospheric Aerosol and Gas Experiment satellite profiles. For N2O, only ER-2 data were used. These chemical composites have been reconstructed onto average meteorological fields for the mission in a latitude-altitude cross section, yielding a picture of the chemical composition of the polar vortex during this period. Tracers inside the vortex show an apparent descent of about 2 km relative to those outside, resulting in an apparent chemical edge on isentropic and isobaric surfaces.

Schoeberl, Mark R.↗
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.↗