Eugene J. Mroz

Determination of deuterated methanes for use as atmospheric tracers

The deuterated methanes, /sup 13/CD/sub 4/ and /sup 12/CD/sub 4/, are useful as tracers for long-range (>500-km) atmospheric transport. They are easily synthesized and released. Sampling is accomplished by collecting about 330 l of air and chromatographically separating the methane fraction, which is then analyzed by mass spectrometry for the /sup 13/CD/sub 4///sup 12/CH/sub 4/ and /sup 12/CD/sub 4///sup 12/CH/sub 4/ ratios. Detection limits in air are about 7 x 10/sup -16/ STP mol m/sup -3/ for /sup 13/CD/sub 4/ and 2 x 10/sup -15/ STP mol m/sup -3/ for /sup 12/CD/sub 4/. 11 refs., 5 figs.

Three-dimensional simulations of atmospheric methyl chloroform : effect of an ocean sink

A global three-dimensional chemical tracer model of the distribution and seasonal cycles of the surface concentration of CH3CCl3 is compared with surface observations from the Atmospheric Lifetime Experiment (ALE) for the years 1980–1985. Two-dimensional OH distributions calculated by a photochemical model are empirically adjusted from observed trends in the global average and the interhemispheric ratio of methyl chloroform. The effects of the recently discovered ocean sink for methyl chloroform were investigated. The model simulates the 5-year record of observations made at the five ALE sampling sites to generally within ±5% of the observed mean. The calculated average global lifetime of methyl chloroform is 5.7 ± 0.3 years. The estimated global mean OH concentration is 6.5 ± 0.4 × 105 cm−3. However, the inclusion of the ocean sink does not significantly improve the simulation of the observed interhemispheric gradient of methyl chloroform. Atmospheric transport dominates the simulated CH3CCl3 seasonal cycle throughout the northern hemisphere but is less important in the southern hemisphere.

Tropospheric relative diffusion to hemispheric scales

Abstract A three-range model of the atmospheric energy spectrum, suggested by the recent GASP spectra and consisting of an enstrophy-cascade range (I), an energy-cascade range (II), and a dissipation range (III), is applied to the problem of long-range atmospheric diffusion. Clouds and plumes are observed to diffuse rapidly and coherently in range-II. This spreading extends to hundreds of kilometers, at rates satisfactorily described by existing diffusion theories, including similarity theories. The Lagrangian time-scale of the range-II diffusion is shown to be defined by tII = 1/f, where /tf is the Coriolis parameter. Diffusion at greater distances is much less regular because it is due to the quasi-two-dimensional, range-I eddies. Clouds and plumes are quickly distorted into streaks and patches by the 2D motions of range-I; but individual pieces of cloud continue to be diffused at the asymptotic (parabolic) rate of the range-II 3-D eddy turbulence. The effect of these processes is a lumpy, streaky cloud, clearly depicted by the results of a numerical modeling study. Concentrations of a unique tracer (heavy methane), released in the troposphere near Antarctica and followed by surface and aircraft observations for several weeks, support this characterization of the longrange diffusion process.

Deuteromethanes: potential fingerprints of the sources of atmospheric methane

Abstract The purpose of this paper is to suggest that development of analytical techniques to determine the deuterium substitution pattern of 12C- and 13C-methane might lead to better constraints on the apportionment of source strengths among the major methane source categories. Traditional methods of determining the isotopic composition of methane require both combustion of the molecule to CO2 for δ13C analysis and reduction of the concomitant water to H2 for δD analysis. When only δ13C-CH4 and δD-CH4—and even δ14C-CH4—are used, the problem of source attribution is fundamentally underdetermined. There are more source categories than unique tracers for each source category. If isotopic analysis could be accomplished without the combustion step, then there are ten isotopomers (a conjunction of “isotope” and “isomer”) of methane available for fingerprinting the sources of methane in the atmosphere. The tritium content of methane also warrants close examination as another constraint on the apportionment of biogenic and fossil methane.

Gas Permeation Testing Results from the Mixed Waste Focus Area Improved Hydrogen Getter Program

Abstract: The gas permeabilities of more than 20 polymers were measured using pure and mixed gas techniques. The motivation was to determine potential materials that could be used to protect hydrogen getter particles from poisons while permitting sufficient hydrogen rates to enable the getters use in TRUPACT types of containers. A rate of five barrers or larger is needed. Of the materials screened in the pure gas tests, more than 15 qualified. Nine materials qualified in the mixed gas tests, but of the nine only three had high CCI4 rejection rates and four others would greatly reduce the transport of the CCl4.

The potential changes of methane due to an assumed increased use of natural gas: A global three-dimensional model study

Abstract In this paper, we use a global methane model to study the potential changes in global methane if natural gas were substituted for coal in energy production. At present, the global methane leakage from natural gas industry is estimated to be between 6 Tg/year (0.5% leakage of natural gas production) and 48 Tg/year (4% leakage of natural gas production). The model results show that in the low leakage case increased use of natural gas will slow the current increase trend of methane from 1% per year to about 0.6% per year. However, in the high leakage case increased use of natural gas will speed the current methane increase trend from 1% per year to about 2% per year. Thus, it is important to precisely understand the magnitude of methane emission from the gas industry, and the consequent impact of the increased use of natural gas on global climate.