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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Measurements of NO and total reactive odd-nitrogen, NOy, in the Antarctic stratosphere

Measurements of NO and total reactive N, NOy, were made as part of the Airborne Antarctic Ozone Experiment conducted in Punta Arenas, Chile during Aug. and Sept. 1987. The total reactive N reservoir includes the species NO, NO2, NO3, N2 O5, HNO3, and ClONO2. The instrument was located on board the NASA ER2 aircraft which conducted 12 flights over the Antarctic continent reaching altitudes of 18 km at 72 deg S latitude. The NOy technique utilized the conversion of component NOy species to NO on a gold catalyst and the subsequent detection of NO by the chemiluminescence reaction of NO with ozone. Since the inlet sample line is heated and the catalyst operates at 300 C, NOy incorporated in aerosols evaporates and is converted to NO. NO was measured on two separate flights by removing the catalyst from the sample inlet line.

Fahey, D. W.↗
NASA NTRS1988

Photochemical trajectory modelling studies of the 1987 Antarctic spring vortex

Simulations of Antarctic ozone photochemistry performed using a photochemical model integrated along air parcel trajectories are described. This type of model has a major advantage at high latitudes of being able to simulate correctly the complex interaction between photolysis and temperature fields, which, because of the polar night cannot be represented accurately in a zonally averaged framework. Isentropic air parcel trajectories were computed using Meteorological Office global model analyses and forecast fields from positions along the ER-2 flight paths during the Airborne Antarctic Ozone Experiment in Austral Spring 1987. A photochemical model is integrated along these trajectories using the aircraft observations to initialize constituent concentrations. The model includes additional reactions of the ClO dimer and also bromine reactions, which are thought to play a significant role in Antarctica. The model also includes heterogeneous reactions which are invoked when the air parcel passes through a polar stratospheric cloud (PSC). The existence of a PSC is determined throughout the course of the model integration from the parcel temperature and the saturated vapour pressure of water over an assumed H2O/HNO3 mixture. The air parcel temperature is used to determine the saturated vapor pressure of HNO3 over the same mixture. Mixing ratios which exceed saturation result in condensation of the excess in the model and hence lead to a reduction of the amount of gas phase NO2 available for chemical reaction.

Austin, J.↗
NASA NTRS1988

Photochemical modeling of the Antarctic stratosphere: Observational constraints from the airborne Antarctic ozone experiment and implications for ozone behavior

The rapid decrease in O3 column densities observed during Antarctic spring has been attributed to several chemical mechanisms involving nitrogen, bromine, or chlorine species, to dynamical mechanisms, or to a combination of the above. Chlorine-related theories, in particular, predict greatly elevated concentrations of ClO and OClO and suppressed abundances of NO2 below 22 km. The heterogeneous reactions and phase transitions proposed by these theories could also impact the concentrations of HCl, ClNO3 and HNO3 in this region. Observations of the above species have been carried out from the ground by the National Ozone Expedition (NOZE-I, 1986, and NOZE-II, 1987), and from aircrafts by the Airborne Antarctic Ozone Experiment (AAOE) during the austral spring of 1987. Observations of aerosol concentrations, size distribution and backscattering ratio from AAOE, and of aerosol extinction coefficients from the SAM-II satellite can also be used to deduce the altitude and temporal behavior of surfaces which catalyze heterogeneous mechanisms. All these observations provide important constraints on the photochemical processes suggested for the spring Antarctic stratosphere. Results are presented for the concentrations and time development of key trace gases in the Antarctic stratosphere, utilizing the AER photochemical model. This model includes complete gas-phase photochemistry, as well as heterogeneous reactions. Heterogeneous chemistry is parameterized in terms of surface concentrations of aerosols, collision frequencies between gas molecules and aerosol surfaces, concentrations of HCl/H2O in the frozen particles, and probability of reaction per collision (gamma). Values of gamma are taken from the latest laboratory measurements. The heterogeneous chemistry and phase transitions are assumed to occur between 12 and 22 km. The behavior of trace species at higher altitudes is calculated by the AER 2-D model without heterogeneous chemistry. Calculations are performed for solar illumination conditions typical of 60, 70, and 80 S, from July 15 to October 31.

Rodriguez, Jose M.↗
NASA NTRS1988

Crystallization of supercooled solutions

Crystallization of uniformly supercooled solutions (Na2SO4, NaCl, H2SO4, HNO3, HCl) was studied. It is shown how crystal growth velocity and habit depend on solution and concentration. The segregation coefficient for the solute in ice is measured by analysis of ice and solution, separated immediately after initial freezing, at different supercoolings. Subsequent solidification gives ion rejection at a varying rate depending on the geometry of the freezing, and may result in separation of hydrates, particularly when the initial concentration is high, as in haze (inactivated) droplets and low temperatures found in the Antarctic stratosphere. Electrical effects associated with rapid freezing are also investigated. Results suggest that more extensive measurements need to be made in solutions at different supercoolings, and that substantial electrical effects may be present for higher concentrations under these conditions. Damage to vegetation could occur under specific conditions as concentrated solutions (possibly H2SO4) are rejected in the freezing of rime or dew.

Harrison, K.↗
NASA NTRS1988

Biospheric traumas caused by large impacts and predicted relics in the sedimentary record

When a large asteroid or comet impacts the Earth the supersonic plume ejected on impact causes severe shock heating and chemical reprocessing of the proximal atmosphere. The resultant NO is converted rapidly to NO2, foliage damage due to exposure to NO2 and HNO3, toxicosis resulting from massive mobilization of soil trace metals, and faunal asphyxiation due to exposure to NO2. One class of relic evidence for the above effects arises because extinction of species caused by these chemically induced traumas would be selective. A second class of relic evidence arises because the acid rain will cause massive weathering of continental rocks and soils characterized by large ratios of the relatively insoluble metals, to the more soluble metals. This weathering would be best recorded in fossils in unperturbed deltaic, neritic, or limnetic sediments and for metals with very long oceanic residence times in deep ocean sediments as well. This evidence is discussed.

Prinn, R. G.↗
NASA NTRS1988

Stratospheric NO2 over Antarctica as measured by the Solar Mesosphere Explorer during austral spring, 1986

This paper presents the results of polar NO2 measurements carried out by the SME satellite during the fall and spring of 1985 and 1986 and compares the results with observations at the north pole and the results of model calculations. During the austral spring, a polar low was observed in stratospheric NO2 densities measured between 24 and 40 km, consistent with the predictions of standard photochemical theory. The geographic extent of the area of low NO2 densities was found to decrease as the hours of sunlight increased, in marked contrast to the behavior of the Antarctic ozone hole during the same period. A comparison of measurements with model calculations for NO2 imply that much of the odd nitrogen is converted to HNO3 during the polar night. Data also suggest no evidence that changes in high-altitude odd nitrogen are influencing the ozone below, or that the 'ozone hole' penetrates above 24 km to affect odd nitrogen there.

Thomas, Ronald J.↗
NASA NTRS1988

Stratospheric composition measurements of earth and Titan using high-resolution tunable diode laser spectroscopy

Field and laboratory measurements of species of atmospheric interest made as part of the JPL diode laser spectroscopy program are presented. Stratospheric measurements of NO2, NO, CO2, and H2O made in November 1985 using the BLISS instrument are reported, together with recent laboratory measurements of spectral line parameters of HNO3 and HO2NO2. In addition, a novel diode laser instrument concept for the in situ sensing of Titan's atmosphere is described for the Saturn Orbiter/Titan Probe (SOTP) Cassini Mission.

Webster, Christopher R.↗
NASA NTRS1989

Impact of heterogeneous reactions on stratospheric chemistry of the Arctic

The possible depletion of ozone due to heterogeneous reactions occurring in Arctic polar stratospheric clouds (PSCs) is fundamentally different from the Antarctic situation. PSCs in the Arctic are relatively short-lived and occur over limited regions of the Arctic stratosphere. The Arctic situation is examined using a model which calculates photochemical processes as a function of longitude in air circulating with fixed velocity around the pole at fixed pressure level and latitude. The model allows sunlight to vary diurnally and PSCs to occur in specified subregions of the domain. Measurements of chemical species including HCl, ClO, NO2 and HNO3 downwind from a PSC should show obvious changes compared to measurements in air unaffected by clouds. These species concentrations are found to be sensitive to sticking coefficients, cloud characteristics including particle number density and surface area, and to the PSC exposure time.

Douglass, Anne R.↗
NASA NTRS1989

The use of assimilated stratospheric data in constituent transport calculations

A stratospheric assimilation system has been developed, which generates wind data that is consistent with the geopotential height (and temperature) field and the primitive equations in the general circulation model. This paper reports the first known calculations to use data from an assimilation to calculate constituent transport in the stratosphere. Nitric acid (NHO3) during the Limb IR Monitor of the Stratosphere (Gille et al., 1984) period is studied. The high-latitude time variance of the HNO3 is accurately captured. These studies suggest that data from an assimilation process offers tremendous potential for studying stratospheric dynamics, constituent transport, and chemistry.

Rood, Richard B.↗
NASA NTRS1989

Ozone minimum occurs in Antarctica in the springtime

Observations on the formation of the Antarctic ozone hole in the upper atmosphere are summarized, and the mechanism responsible for the ozone depletion in the spring is examined. It is shown that the sequence of events begins with the absorption of H2O, N2O5, HCl, and ClONO2 on the cloud ice particles in the winter and chemical reactions among absorbed chemicals which release (HNO3)s, Cl2, HOCl, and ClNO2. With the return of sunlight in the spring, the clouds evaporate, and the Cl2, HOCl, and ClONO2 molecules are destroyed by sunlight to form Cl atoms. These attack ozone, producing a reduction of ozone that accounts for the bulk of the ozone decrease observed by the ground-based ozone monitors. Data on the ozone concentration for the period between 1957 through 1987 indicate that the southern ozone hole has been intensifying since 1975 as the amount of man-made chlorine increases.

Aikin, Arthur C.↗
NASA NTRS1989

Comparison of model results transporting the odd nitrogen family with results transporting separate odd nitrogen species

A fast two-dimensional residual circulation stratospheric family transport model, designed to minimize computer requirements, is developed. The model was used to calculate the ambient and perturbed atmospheres in which odd nitrogen species are transported as a family, and the results were compared with calculations in which HNO3, N2O5, ClONO2, and HO2NO2 are transported separately. It was found that ozone distributions computed by the two models for a present-day atmosphere are nearly identical. Good agreement was also found between calculated species concentrations and the ozone response, indicating the general applicability of the odd-nitrogen family approximations.

Douglass, Anne R.↗
NASA NTRS1988

Quantification of several atmospheric gases from high resolution infrared solar spectra obtained at the South Pole in 1980 and 1986

High-resolution solar absorption spectra recorded at the Amundsen-Scott South Pole Station were analyzed to obtain total column amounts of O3, N2O, HNO3, CO2, CH4, and CF2Cl2, and to investigate the differences in the values obtained in December 1980 with those obtained in December 1986. In addition, vertical column amounts for HCl, NO, NO2, and C2H6 were derived for December 1986. One interesting feature of these results is that the total column amounts of HCl measured for several days at the South Pole (/6.4 + or - 0.8/ x 10 to the 15th molecules/sq cm) were high compared with the HCl column amounts reported for lower latitudes.

Goldman, Aaron↗
NASA NTRS1990

New spectral features of stratospheric trace gases

A new Michelson-type interferometer system operating in the infrared at very high resolution (0.002 to 0.003 wavenumber FWHM) was used to record numerous balloon-borne solar absorption spectra of the stratosphere, ground-based solar absorption spectra, and laboratory spectra of molecules of atmospheric interest. Results obtained are reported for several important stratospheric trace gases, HNO3, ClONO2, HO2NO2, NO2, and COF2, in the 8 to 12 micron spectral region. Many features of these gases were identified in the stratospheric spectra. Comparison of the spectra with line-by-line simulations shows previous spectral parameters are often inadequate. New analysis of high resolution laboratory and atmospheric spectra and improved theoretical calculations will be required for all bands. Preliminary versions of several sets of improved line parameters are presented.

Goldman, A.↗
NASA NTRS1989

Solar activity, the QBO, and tropospheric responses

The suggestion that galactic cosmic rays (GCR) as modulated by the solar wind are the carriers of the component of solar variability that affects weather and climate has been discussed in the literature for 30 years, and there is now a considerable body of evidence that supports it. Variations of GCR occur with the 11 year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasibiennial oscillation of equatorial stratospheric winds (the QBO). Variations in GCR occur on the time scale of centuries with a well defined peak in the coldest decade of the little ice age. New evidence is presented on the meteorological responses to GCR variations on the time scale of a few days. These responses include changes in the vertical temperature profile in the troposphere and lower stratosphere in the two days following solar flare related high speed plasma streams and associated GCR decreases, and in decreases in Vorticity Area Index (VAI) following Forbush decreases of GCR. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. Both short and long term tropospheric responses are understandable as changes in the intensity of cyclonic storms initiated by mechanisms involving cloud microphysical and cloud electrification processes, due to changes in local ion production from changes in GCR fluxes and other high energy particles in the MeV to low GeV range. The nature of these mechanisms remains undetermined. Possible stratospheric wind (particularly QBO) effects on the transport of HNO3 and other constituents incorporated in cluster ions and possible condensation and freezing nuclei are considered as relevant to the long term variations.

Tinsley, Brian A.↗
NASA NTRS1989

Cryogenic Limb Array Etalon Spectrometer (CLAES) - Experiment overview

The Cryogenic Limb Array Etalon Spectrometer (CLAES) is one of a complement of instruments on the NASA Upper Atmosphere Research Satellite which is expected to study atmospheric photochemistry, energy input, and dynamics following a 1991 launch. CLAES measures stratospheric altitude profiles of temperature, pressure, O3, H2O, CH4, N2O, NO, NO2, N2O5, HNO3, ClONO2, HCl, CFC-11, and CFC-12. These data are obtained typically between 10 and 60 km, with 2.5-km vertical resolution and 500-km horizontal grid size. Coverage is obtained between latitudes 80 deg north and south, thereby providing substantial coverage of the Antarctic spring polar ozone-hole region. CLAES derives the listed geophysical parameters from measurement of earth-limb spectral emissions between 3.5 and 13 microns. Brief discussions of the measurement concept, instrument design, and performance are presented, followed by a more detailed discussion of scientific capabilities and measurement modes.

Roche, Aidan E.↗
NASA NTRS1989

New spectral features of stratospheric trace gases identified from high-resolution infrared balloon-borne and laboratory spectra

A new Michelson-type interferometer system operating in the infrared at very high resolution has been used to record numerous balloon-borne solar absorption spectra of the stratosphere, ground-based solar absorption spectra, and laboratory spectra of molecules of atmospheric interest. In the present work results obtained for several important stratospheric trace gases, HNO3, CIONO2, HO2NO2, NO2, and COF2, in the 8- to 12-micron spectral region are reported. Many new features of these gases have been identified in the stratospheric spectra. Comparison of the new spectra with line-by-line simulations shows that previous spectral line parameters are often inadequate and that new analysis of high-resolution laboratory and atmospheric spectra and improved theoretical calculations will be required for many bands. Preliminary versions of several sets of improved line parameters under development are discussed.

Goldman, A.↗
NASA NTRS1989

Measurements of nitric oxide and total reactive nitrogen in the Antarctic stratosphere - Observations and chemical implications

Results are presented on measurements of NO and the sum of reactive nitrogen species, NO(y), which include NO, NO2, NO3, N2O5, HNO3, and ClONO2 (in addition to ClO, O3, H2O, and N2O measurements), obtained aboard the NASA ER-2 aircraft flying over the Antarctica between the latitudes of 53 and 72 deg S during the Airborne Antarctic Ozone Experiment. The boundary of the chemically perturbed region (CPR), as indicated by a sharp increase in the level of ClO, occurred near 66 deg S; outside or equatorward of the CPR, the NO(y) mixing ratios ranged between 6 and 12 ppbv, with values decreasing poleward and reaching total NO(y) levels of 4 ppbv or less within 5-deg poleward of the boundary. Data presented in this paper clearly associate the Antarctic ozone decrease with perturbed conditions of ClO, NO(y), and H2O, which are in turn associated with processes defined as nonstandard heterogeneous chemistry, denitrification, and dehydration, respectively.

Fahey, D. W.↗
NASA NTRS1989

Computer processing of tunable diode laser spectra

A computer-controlled tunable diode laser spectrometer and spectral analysis software are described. The three-channel system records simultaneously the transmission of a subject gas, a temperature-stabilized etalon, and a calibration gas. The software routines are applied to diode laser spectra of HNO3 and NO2 to illustrate the procedures adopted for conversion of raw spectral data to useful transmission and harmonic spectra. Extraction of line positions, absorption intensities, collisional broadening coefficients, and gas concentrations from recorded spectra is also described.

May, Randy D.↗