Engineering Papers⌕ Search

Engineering topics

Schiff, H. I.

Publications and source records attributed to Schiff, H. I..

14 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

An intercomparison of airborne nitrogen dioxide instruments

Results on NO2 instruments are reported from the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) program in summer 1986. The instruments tested were (1) a two-photon LIF system using a laser for NO2-NO photolysis, (2) a chemiluminescence (CL) detector using FeSO4 for NO2-NO conversion, (3) a CL detector using an arc lamp for NO2-NO photolysis, and (4) a tunable-laser-diode multipath-absorption system. The procedures for the CITE 2 ground-based and flight tests are described in detail, and the results are presented in extensive graphs. Instrument (2) was eliminated because the FeSO4 converted atmospheric PAN to NO, resulting in spuriously high NO2 values. The remaining instruments gave readings in 30-40-percent agreement at NO2 mixing ratios of 100-200 parts per trillion by volume (pptv). At ratios below 50 pptv, the correlation among the measurements was very poor, with a tendency for system (4) to give higher values than (1) or (3).

Gregory, G. L.↗
NASA NTRS1990

A tunable diode laser system for aircraft measurements of trace gases

The advantages of tunable-diode-laser absorption spectrometry (TDLAS) for measuring trace atmospheric gases are universality, positive identification, good sensitivity, and rapid response time. A TDLAS system is described which is capable of making measurements aboard an aircraft. The instrument was employed during the Chemical Instrumentation Test and Evaluation (CITE) 2 program to measure NO2 on 11 flights and HNO3 on five flights. Detection limits were determined to be 25 parts per trillion by volume (pptv) for NO2 and 75 pptv for HNO3 with response times of 3 min. This was sufficient to permit measurements of NO2 in the free troposphere and HNO3 in the continental boundary layer a significant fraction of the time.

Schiff, H. I.↗
NASA NTRS1990

Measurements of tropospheric nitric acid over the western United States and northeastern Pacific Ocean

HNO3 measurements obtained in the free troposphere (FT) and boundary layer (BL) over the western U.S. and the NE Pacific during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation 2 (CITE 2) program in summer 1986 are reported. The CITE 2 HNO3 instruments and flight protocols are described, and the results are presented in tables and graphs. Over the ocean, the average HNO3 mixing ratios were found to be 108 parts per trillion by volume (pptv) in the FT and 62 pptv in the BL, suggesting removal of HNO3 from the BL by dry deposition. The corresponding values over land were 61 pptv for the FT and 767 pptv for the BL, and the horizontal distribution of BL HNO3 indicated an anthropogenic origin.

Lebel, P. J.↗
NASA NTRS1990

Measurements of tropospheric nitric acid over the Western United States and Northeastern Pacific Ocean

Over 240 measurements of nitric acid (HNO3) were made in the free troposphere as well as in the boundary layer. Marine HNO3 measurement results were strikingly similar to results from GAMETAG and other past atmospheric field experiments. The marine boundary layer HNO3 average, 62 parts-per-trillion by volume (pptv), was 1/3 lower than the marine free tropospheric average, 108 pptv, suggesting that the boundary layer is a sink for tropospheric nitric acid, probably by dry deposition. Nitric acid measurements on a nighttime continental flight gave a free tropospheric average of 218 pptv, substantially greater than the daytime continental free tropospheric 5-flight average of 61 pptv. However, the nighttime results may be influenced by highly convective conditions that existed from thunderstorms in the vicinity during that night flight. The continental boundary layer HNO3 average of 767 pptv is an order of magnitude greater than the free tropospheric average, indicating that the boundary layer is a source of free tropospheric HNO3. The distribution of continental boundary layer HNO3 data, from averages of 123 over rural Nevada and Utah to 1057 pptv in the polluted San Joaquin Valley of California suggest a close tie between boundary layer HNO3 and anthropogenic activity.

Lebel, P. J.↗
NASA NTRS1986

Tunable-diode laser absorption spectrometry

Tunable-diode laser absorption spectrometry (TDLAS) affords a number of advantages for atmospheric measurements. It is a universal method, applicable, in principle, to all gases of atmospheric interest. Because of its extremely high spectral resolution it provides unequivocal identification of the target species, with no interferences from other gases. It provides real-time, in situ measurements with time resolutions better than 1 minute. The sensitivity of the current TDLAS system is marginally capable of measuring HO2. This species exists in the troposphere at concentrations which are up to 2 orders of magnitude higher than those of HO and, in addition, is much less susceptible to removal by the surfaces of the instrument and its sampling system. HO2 is an important HO sub x species in its own right but can also give direct information on the HO concentration by virtue of the rapid partitioning between these two species. The addition of the high-frequency modulation technique to the TDLAS system would ensure its ability to measure HO2 under most atmospheric conditions. The ability of the TDLAS to measure hydrogen peroxide (H2O2) in the ambient atmosphere was also demonstrated. H2O2 measurements give a clear indication of HO sub x mixing ratios and are also important as a photolytic source of HO and as an important oxidant for other atmospheric consitituents such as SO2.

Schiff, H. I.↗
NASA NTRS1985

Hydrogen species

Measurements of the members of the HO(x) family (OH, HO2, and H2O2) and their major source gases, H2O, and CH4 are discussed. Emphasis is placed on measurements which were made since the 1982 World Meteorologic Organization (WMO) report. Measurement techniques, available data, an assessment of data reliability, and a comparison of the data with theoretical distributions of stratospheric HO(x) species predicted from one and two dimensional photochemical models are discussed.

Schiff, H. I.↗
NASA NTRS1978

Temperature dependence of the rate constants for reactions of O/1D/ atoms with a number of halocarbons

Results are reported for an experimental study of the reactions of O(1D) with CCl4, CFCl3, CF2Cl2, CHFCl2, CHF2Cl, and CF2ClCFCl2 over the temperature range from 173 to 343 K, based on the time-resolved emission of O(1D) at 630 nm. The experiments involved photolysis of O3 by Nd-YAG laser pulses and measurements of 630-nm emission intensity in mixtures with He and the various halocarbons. Pseudo-first-order rate constants are derived from plots of the logarithms of the 630-nm emission intensities as a function of time for particular He/O3/halocarbon mixtures, and second-order rate constants are then obtained from plots of these pseudo-first-order rate constants as a function of halocarbon concentration at constant He and O3 concentrations. No temperature dependence of the second-order rate constants is observed over the range studied, within the precision of the measurements. It is found that the rate constants decrease as H is substituted for Cl in a halocarbon molecule and as F is substituted for H or Cl.

Davidson, J. A.↗
NASA NTRS1978

Rate constants for the deactivation of O/1D/ by Xe, Kr, and Ar over the range 110-330 K

The rate constants for the deactivation of O(1D) by Xe, Kr, and Ar were measured over the range 110-330 K. Only Xe had a significant temperature dependence. Its Arrhenius expression is (8.5 + or - 1.7) times 10 to the -11th power exp(-103 + or - 52)/RT cu cm/molecule-sec. The rate constants for Kr and Ar are (6.4 + or - 1.3) times 10 to the -12th power and (5.0 + or - 1.5) times 10 to the -13th power cu cm/molecule-sec, respectively. The observed trend in deactivation efficiency, Xe (greatest), Kr, Ar (least), and the observed temperature effects support the results and the spin-orbit interaction mechanism for deactivation given by Husain and co-workers.

Davidson, J. A.↗
NASA NTRS1978

Temperature dependence of the deactivation of O/1D/ by CO from 113-333 K

Absolute rate constants for the deactivation of O(1D) by CO have been measured at temperatures between 113 and 333 K. A very small temperature dependence is observed and is described by the Arrhenius expression (4.7 + or - 0.9) times 10 to the -11th power exp(126 + or 33)/RT cu cm/molecule-sec, where E is in cal/mol.

Davidson, J. A.↗
NASA NTRS1976

O2/1-Sigma sub g/+// relaxation in collisions - Temperature dependence of the interaction with HBr

Rate constants for the quenching of O2(1-Sigma sub g(+)) in the temperature range 170-400 K were obtained by observing the change in the rate of decay of this oxygen emission as a function of HBr concentration. At each temperature the decay was observed at eight different HBr concentrations ranging from 0 to 6 x 10 to the -6th moles/l. It is found that long range multipolar interactions make a major contribution to the quenching of the oxygen molecule by H2, with the quenching shown to be most effective at low temperatures. Short range repulsive interactions may also contribute to the quenching process, especially at high temperatures. The suggestion that the quenching process is dominated by the ability of the quencher to take up the energy of the oxygen molecule transition in vibrational and rotational motion is confirmed.

Braithwaite, M.↗
NASA NTRS1976

Absolute rate constant determinations for the deactivation of O/1D/ by time resolved decay of O/1D/ yields O/3P/ emission

Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time-resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) at 298 K are reported for N2, O2, CO2, O3, H2, D2, CH4, HCl, NH3, H2O, N2O, and Ne. The results obtained are compared with previous relative and absolute measurements reported in the literature.

Davidson, J. A.↗
NASA NTRS1975

Nitric oxide, water vapor, and ozone in the atmosphere as measured in SITU from an aircraft

As part of the instrument evaluation plan for the NASA Global Atmospheric Sampling Program, prototype instruments were tested aboard the NASA Convair 990 during four flights in January and February of 1974. All the data were taken in maritime air between Hawaii and San Francisco and between Hawaii and 155 deg W, 35 deg N. A chemiluminescent instrument was used to measure nitric oxide. Water vapor, which was measured by using an aluminum oxide hygrometer, ranged from 5.2 micro g/g to saturation. Ozone was measured by an instrument using the ultraviolet absorption technique and ranged up to 235 ppbv. Typical temporal plots of the concentrations of the three constituents are presented. All the constituents showed considerable spatial and day-to-day variation in concentration at each altitude flown. Measurements of the three constituents were made simultaneously at various altitudes between 7.6 and 12.5 km.

Briehl, D.↗
NASA NTRS1974

In situ measurements of nitric oxide, water vapour and ozone from an aircraft

This paper describes flight tests of prototype instruments for the NASA global atmospheric sampling program (GASP). Three gas sampling instruments were included in the installation: (1) a chemiluminescent nitric oxide monitor; (2) an ultraviolet absorption ozone monitor; and (3) an aluminum oxide water vapor hygrometer. Results indicate the range and kind of variability in NO, H2O, and O3 that can be expected in routine tropospheric air sampling. They have also demonstrated the need for increasing instrument sensitivities, particularly in NO measurement.

Briehl, D. C.↗