Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic-weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic-weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope-abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope-abundance variations potentially are large enough to result in future expansion of their atomic-weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope variations in materials of natural ter- restrial origin are too small to have a significant effect on their standard atomic-weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio.
A set of photoelectric detectors for airborne measurements of the photolysis frequency of NO2, i.e., JNO2, was developed and integrated aboard the research aircraft Hercules C‐130 operated by the U.K. Meteorological Office. The instrument consists of two separate sensors, each of which provides an isotropic response over a solid angle of 2π steradian (sr). The sensors are mounted on top and below the aircraft, respectively, to obtain a field of view of 4π sr, and permit the discrimination of the upwelling and downwelling components of the actinic flux. From experimental tests and model calculations it is demonstrated that small differences between the spectral sensitivity of the sensors and the spectral response of JNO2 can lead to significant errors in the determination of JNO2, especially under cloudy conditions. We present correction factors for clear sky conditions and suggest the use of a new filter combination in the sensors which requires only small corrections and provides acceptable accuracy, even under cloudy conditions. A climatology of JNO2 values is presented from a series of flights made in 1993 at latitudes of 36°–59°N. For clear sky conditions and solar zenith angles of 33°–35°, JNO2 was 8.3 × 10−3 s−1 at sea level and increased with altitude to values of 13 × 10−3 s−1 at 7.5 km altitude. Above clouds, JNO2 reached maximum values of 24 × 10−3 s−1, and peak values of 29 × 10−3 s−1 were observed for very short periods in the uppermost layers of clouds. Enhancement of the actinic flux due to light scattered from clouds was also observed at altitudes below 0.5 km. Comparison of the clear sky data with predictions from different radiative transfer models reveals the best agreement for models of higher angular resolution. The Delta Eddington method underpredicts the measurements significantly, whereas the JNO2 values predicted by the discrete ordinate method and multidirectional model are only about 5% smaller than our measurements, a difference that is within the experimental uncertainties.
The absolute isotopic ratios of the hydrogen content of two reference water standards called ''SMOW"e and "SLAP* were measured to define an absolute isotopic scale. This isotopic scale can be used to normalize measurements of the natural isotopic variations in waters. The principle of the method used to define the zero of the scale is given. The absolute D/H ratios of SMOW and SLAP were measured by mass spectrometric comparison with calibration mixtures prepared in the laboratory. The following values are obtained: (g)sMow = 155.76f0.05 x lo-' @) = 89.02 0.05 x lo-' SLAP/SMOV= 428.50+0.10Samples of about 20 cc of the reference standards SMOW and SLAP are available from the International Atomic Energy Agency, on request.
The absolute isotopic ratios of the hydrogen content of two reference water standards called “SMOW”2 and “SLAP3 were measured to define an absolute isotopic scale. This isotopic scale can be used to normalize measurements of the natural isotopic variations in waters. The principle of the method used to define the zero of the scale is given. The absolute D/H ratios of SMOW and SLAP were measured by mass spectrometric comparison with calibration mixtures prepared in the laboratory. The following values are obtained: Samples of about 20 cc of the reference standards SMOW and SLAP are available from the International Atomic Energy Agency, on request.
OH has been detected in the lower troposphere by optical absorption of the Q1 2 (A²Σ+, v = O, X²Π, v = O) line at 307.995 nm along a 7.8 km path above Jülich (51° North, 6° East). The detection limit depended on the quality of the photographic exposure and reached 2 · 106 cm−3 in the most favourable cases. OH generally remained below 4 · 106 cm−3, the average detection limit. But on several occasions during the observation period from mid August to November 1975 concentrations up to 7 · 106 cm−3 were observed.
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