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Khalil, M. A. K.

Publications and source records attributed to Khalil, M. A. K..

27 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Atmospheric methane /CH4/ - Trends and seasonal cycles

On the basis of 22 months of almost continuous automated, GC/FID measurements of atmospheric CH4 and Cape Meares (45 deg N), it is shown that the concentration of CH4 is increasing at about 2% per yr (+ or - 0.5%/yr). The data also revealed stable seasonal cycles with peak concentrations in October and minimum concentrations in July. The magnitude of the seasonal variations during these months is about + or - 20 ppby from the average (+ or - 1.2%). If the current trend continues, the increased CH4 concentration may result in a 0.2 K to 0.4 K average increase in earth's surface temperature over the next 40 years or so (based on calculations of Wang et al. (1976)). The coupling of CH4 to tropospheric and stratospheric chemical processes is discussed.

Rasmussen, R. A.↗
NASA NTRS1981

Trends of atmospheric methane in the Southern Hemisphere

Atmospheric observations spanning the past three years show that methane increased at 1.2 (plus or minus 0.3)% per year at Cape Grim in Tasmania (41 deg S). This rate of increase can be compared to the 1.9 (plus or minus 0.4)% per year observed at Cape Meares in Oregon (45 deg N) over the past two years. Over the corresponding period the concentration at Cape Grim increased by 1.4 (plus or minus 0.4)% per year. The Southern Hemisphere data also suggest seasonal variations with minimum concentrations in March and maximum in September. These results are based on 26 large-volume stable air samples collected cryogenically in stainless steel flasks and 75 smaller-volume air samples collected in glass flasks, all analyzed by a gas chromatograph using a flame ionization detector.

Fraser, P. J.↗
NASA NTRS1981

Global atmospheric distribution and trend of methylchloroform /CH3CCl3/

Results of global measurements of the concentration of atmospheric methylchloroform, a man-made gas with potentially harmful environmental consequences, performed over a two-year period are presented. Samples were collected weekly at Pt. Barrow and Poker Flats, Alaska, Cape Meares, Oregon, Cape Kumakahi, Hawaii, Samoa, and Cape Grim, Tasmania, and yearly at the South Pole, and methylchloroform concentrations were determined by electron capture-gas chromatographic techniques. A latitudinal profile of CH3CCl3 concentrations derived from the data exhibits a bump at high northern latitudes, where most of the sources are located. Average concentrations calculated for the Northern and Southern Hemispheres showed a rise in global concentrations at a rate of 6.7 + or - 2.0%/year for the period from January 1979 to January 1981, with concentrations rising more slowly in 1980 than in 1979. These yearly increases are also smaller than earlier rates of increase, explainable by a reduction in the rate of emission increase, and are consistent with an atmospheric lifetime of between 6 and 10 years.

Rasmussen, R. A.↗
NASA NTRS1981

Atmospheric trace gases - Possibility of sources in the Southern Hemisphere

When measurements of globally distributed trace gases establish their existence in the Southern Hemisphere, it is not always clear whether their presence is due to transport from the Northern Hemisphere or partly from significant sources in the Southern Hemisphere. In this paper a simple criterion is developed whereby one can determine if significant Southern Hemisphere sources exist for a given trace gas. Despite the limitations of the model, there are strong indications that C2 hydrocarbons (C2H2, C2H4, C2H6), CO and CH4 have significant Southern Hemisphere sources.

Khalil, M. A. K.↗
NASA NTRS1981

Interlaboratory comparison of fluorocarbons-11, -12, methylchloroform and nitrous oxide measurements

Measurements conducted by 19 participating laboratories were considered in the reported interlaboratory comparison study. The results show that there is considerable disagreement among laboratories regarding the absolute concentrations of all four trace gases (CCl3F, CCl2F2, H3CCl3, N2O). The magnitude of this disagreement is discussed. Laboratories in Group II showed considerable disagreement among themselves. Their results were scattered within large intervals of concentration. Laboratories in Group I (using common standards) were in excellent (+ or - 5%) agreement among themselves. A systematic disagreement was noted between Groups I and II laboratories. Generally, the mean values of concentrations determined from the measurements of Group II laboratories were lower than the mean values reported by Group I laboratories.

Rasmussen, R. A.↗
NASA NTRS1981

Differences in the concentrations of atmospheric trace gases in and above the tropical boundary layer

Weekly air samples were collected at Cape Kumakahi (0 km) and at nearby Mauna Loa Observatory (3.4 km) which is above the boundary layer. EC/GC and GC/FID techniques were used to measure CH3I, CHCl3, CO and CH4 which are largely natural in origin, and C2Cl4, CCl4, CH3CCl3, (F-11), CCl2F2, (F-12), CHClF, (F-22) and C2F3Cl3 (F-113), which are due to anthropogenic (CCl3F) etc. activities. It was found that all these gases are significantly (alpha is equal to or less than 0.05) more abundant in the boundary layer than above it.

Rasmussen, R. A.↗
NASA NTRS1980

Concentration distribution of methyl chloride in the atmosphere

Electron capture gas chromatography techniques were used to obtain measurements of methyl chloride concentrations in the atmosphere, at latitudes ranging from about 65 N to 90 S. Most of the measurements were made over the Pacific Ocean. Average global concentrations within the boundary layer were found to be 815 plus or minus 25 pptv in 1977 and 755 plus or minus 37 pptv in 1978. Lower concentrations were observed above the boundary layer with average values of 629 plus or minus 23 pptv and 618 plus or minus 23 pptv in 1977 and 1978, respectively. Within 20 deg of the equator, the boundary layer concentrations were significantly higher than those above the boundary layer. The sources, the sinks, the budgets, and the latitudinal distributions of methyl chloride are discussed in the paper.

Rasmussen, R. A.↗
NASA NTRS1980

CHClF2 /F-22/ in the earth's atmosphere

Recent global measurements of CHClF2 (F-22) are reported. Originally, GC/MS techniques were used to obtain these data. Since then, significant advances using an O2-doped electron capture detector have been made in the analytical techniques, so that F-22 can be measured by EC/GC methods at ambient concentrations. The atmospheric burden of F-22 calculated from these measurements (average mixing ratio, mid-1979, approximately 45 pptv) is considerably greater than that expected from the estimates of direct industrial emissions (average mixing ratio, mid-1979, approximately 30 pptv). This difference is probably due to underestimates of F-22 emissions.

Rasmussen, R. A.↗