Showing papers on "Atmospheric methane published in 1973"

Methane concentrations in various marine environments

Abstract: Methane concentrations have been measured in the surface waters and at depth for several different marine environments. Measurements have also been made in rain water collected in Washington, D.C., over the Pacific Ocean, and in Hawaii. In tropical open ocean areas, surface water concentrations average 4.5 × 10−5 ml/l and decrease to values approaching 0.6 × 10−5 ml/l at a depth of 5000 meters. In natural anoxic conditions (i.e., Cariaco Trench, Black Sea, Lake Nitinat) concentrations can increase as much as four orders of magnitude. In the case of Lake Nitinat, 1.6 ml/l is found at a depth of 200 meters. Nearshore and bay concentrations can be 2–3 orders of magnitude higher than open ocean surface values. Open ocean surface waters are slightly supersaturated with methane, whereas estuary systems are highly supersaturated. Open ocean surface values remain fairly constant, whereas bay and river systems vary considerably, depending on the time of year, addition of pollutants, and tidal mixing. Rain water analyses yielded an average concentration of 5.0 × 10−5 ml/l for the Hawaiian and Pacific samples, and an average concentration of 8.8 × 10−5 ml/l was found for the Washington, D.C., area. Atmospheric methane concentrations over the open ocean remain fairly constant at 1.4 ppm. Atmospheric values in Washington, D.C., at NRL averaged 1.7 ppm.

Sources, sinks, and concentrations of light hydrocarbons in the Gulf of Mexico

Abstract: A survey of the concentrations of light hydrocarbons in the Gulf of Mexico has been made aboard the R.V. Alaminos of Texas A&M University. The hydrocarbon analyzer consists of a modified Beckman process gas chromatograph with a flame ionization detector. For surface profiling, gases are ‘stripped’ from seawater taken 3 meters below the sea surface by vacuum extraction with a 12-stage booster pump. These gases are injected periodically into the gas stream of the chromatograph for analysis. The system also has the capability of analyzing discrete seawater samples either by the method of McAullife or by the method of Swinnerton and his co-workers. Coastal waters of the Gulf of Mexico are not in equilibrium with the atmosphere insofar as low molecular weight hydrocarbons are concerned, even though methane in most of the open Gulf of Mexico is in fairly close equilibrium with the atmosphere. The coastal waters of the gulf act both as a source and as a sink for atmospheric methane. The important man-derived sources of methane in the gulf are ports with their associated shipping and industrial activity, offshore petroleum drilling and production operations, and open ocean shipping activity. High light hydrocarbon concentrations have been found in the vicinity of a tanker discharging ‘clean ballast water.’ The important natural sources include seepage from oil and gas reservoirs and anaerobic production of methane. The main sink for atmospheric methane in the Gulf of Mexico is in the Yucatan area, where there is major upwelling of deep water with low hydrocarbon concentrations.

Gas-Phase Nitrogen and Methane Chemistry in the Atmosphere

Abstract: The chemistry (and meteorology) of the stratosphere has become a very important and controversial topic, since it was proposed that large scale SST operation could cause a reduction in atmospheric O3 due to the catalytic action of nitrogen oxides emitted from the exhaust (Crutzen, 1971; Johnston, 1971.) There are strong indications that oxides of nitrogen play the dominant role in controlling the natural atmospheric O3 content (Crutzen, 1970), but too little is known about the details of the chemistry of nitrogen oxides in the stratosphere, a subject which is treated by Nicolet (1971). Important new ideas have emerged in recent years about the main chemical processes in the stratosphere. The main purpose of this paper is to outline some of these ideas and to indicate the main problems. Some possible consequences for the gas phase chemistry of the troposphere have been indicated on the basis of recent models by Levy (1971, 1972) and McConnell et al. (1971).

Methane in the atmosphere.

Abstract: Methane is present in the troposphere with a volume concentration of about 1.5 ppm. Estimates of Koyama indicate a predominantly biological origin with a total production rate of about 2.7 x 10/sup 14/ g CH/sub 4//yr. From that the author estimated the atmospheric lifetime of methane to be around 20 years. Measurements of the C-14 in methane by Libby and later by Bainbridge, et al. gave a C-14 content of 75% of recent wood and, therefore, confirm the predominant biological origin, the addition of inactive CH; from industrial sources being only about 25%. Much less is known about sinks of CH/sub 4/. Cadle reported fairly high destruction rates by atomic O, a reaction which should be important at high altitude. Bainbridge reports a decrease in the measured methane concentration above the tropopause. He, however, considers this decrease too small to account for the destruction rate of 20 years estimated by Koyama. Measurements on air samples collected on aircraft flights at various altitudes show a high variability of the CH/sub 4/ content both with time and altitude.