Engineering topics

Gunawardena, R.

Publications and source records attributed to Gunawardena, R..

3 records

NASA NTRS1994

Long term trend of selected halogenated hydrocarbons

The so-called 'Library of Background Air' at the Oregon Graduate Institute was used to determine the trend in volume mixing ratios of selected halogenated hydrocarbons in the time period 1977-1989. This library consists of background air samples most of them taken at Cape Meares (Oregon). For storage stainless steel containers are used. Tests have shown the gases under consideration to be stable in these containers. Analyses using a GC/MS-system were performed for the CFCs 11, 12, 12B1 (HALON 1211, CBrClF2), 22, 113, 114 and CH3Cl, CH3Br, CH3CCl3, CCl4. The advantage of this unique investigation: different aged air samples are analyzed at the same time with the same instrument. No calibrations or intercalibrations are needed. All data are presented in normalized mixing ratios versus time. We discuss the results, derive rate constants and present a formula to describe the nonlinear increases.

Borchers, R.↗

NASA NTRS1993

Atmospheric methyl bromide - Trends and global mass balance

A decadal time series of global CH3Br concentrations in the earth's atmosphere is presented. It is shown that average concentrations are about 10 pptv and during the last 4 yr may be increasing at 0.3 +/- 0.1 pptv/yr. It is estimated that the atmospheric lifetime of CH3Br that is due to reaction with OH is about 2 yr, which results in a calculated global emission rate of about 100 Gg/yr. Ocean supersaturations of 140-180 percent are observed, and atmospheric concentrations over the open oceans are higher than at comparably located coastal sites. The ocean source is estimated to be about 35 Gg/yr. The remaining emissions must come from other natural sources and anthropogenic activities.

Khalil, M. A. K.↗

NASA NTRS1982

Atmospheric methyl iodide /CH3I/

It is found that atmospheric concentrations of CH3I are not greater than about 3 pptv over most of the earth's surface and drop to less than half this value above the boundary layer, suggesting that the compound is not likely to play such important roles, on a global scale, as the destruction of tropospheric O3 and free radicals and the increasing of the NO2/NO ratio and hydroxyl radical densities. It is hypothesized that a large portion of the global CH3I comes from oceanic regions of high biomass productivity, where the compound may play a key role in local atmospheric chemistry. Attention is given to CH3I measurement uncertainties with regard to global distribution, sources, and sinks.

Rasmussen, R. A.↗