Showing papers on "Atmospheric methane published in 1990"

Ice-core record of atmospheric methane over the past 160,000 years

Abstract: Methane measurements along the Vostok ice core reveal substantial changes over the past 160,000 years which are associated with climate fluctuations. These results point to changes in sources of methane and also show that methane has probably contributed, like carbon dioxide, to glacial-interglacial temperature changes.

Consumption of atmospheric methane by tundra soils

Abstract: The results of field and laboratory experiments on methane consumption by tundra soils are reported. For methane concentrations ranging from below to well above ambient, moist soils are found to consume methane rapidly; in nonwaterlogged soils, equilibration with atmospheric methane is fast relative to microbial oxidation. It is concluded that lowering of the water table in tundra as a resulting from a warmer, drier climate will decrease methane fluxes and could cause these areas to provide negative feedback for atmospheric methane.

Role of methane clathrates in past and future climates

Abstract: Methane clathrates are stable at depths greater than about 200 m in permafrost regions and in ocean sediments at water depths greater than about 250 m, provided bottom waters are sufficiently cold. The thickness of the clathrate stability zone depends on surface temperature and geothermal gradient. Average stability zone thickness is about 400 m in cold regions where average surface temperatures are below freezing, 500 m in ocean sediments, and up to 1,500 m in regions of very cold surface temperature (<-15 °C) or in the deep ocean. The concentration of methane relative to water within the zone of stability determines whether or not clathrate will actually occur. The geologic setting of clathrate occurrences, the isotopic composition of the methane, and the methane to ethane plus propane ratio in both the clathrates and the associated pore fluids indicate that methane in clathrates is produced chiefly by anaerobic bacteria. Methane occurrences and the organic carbon content of sediments are the bases used to estimate the amount of carbon currently stored as clathrates. The estimate of about 11,000 Gt of carbon for ocean sediments, and about 400 Gt for sediments under permafrost regions is in rough accord with an independent estimate by Kvenvolden of 10,000 Gt. The shallowness of the clathrate zone of stability makes clathrates vulnerable to surface disturbances. Warming by ocean flooding of exposed continental shelf, and changes in pressure at depth, caused, for example, by sea-level drop, destabilize clathrates under the ocean, while ice-cap growth stabilizes clathrates under the ice cap. The time scale for thermal destabilization is set by the thermal properties of sediments and is on the order of thousands of years. The time required to fix methane in clathrates as a result of surface cooling is much longer, requiring several tens of thousands of years. The sensitivity of clathrates to surface change, the time scales involved, and the large quantities of carbon stored as clathrate indicate that clathrates may have played a significant role in modifying the composition of the atmosphere during the ice ages. The release of methane and its subsequent oxidation to carbon dioxide may be responsible for the observed swings in atmospheric methane and carbon dioxide concentrations during glacial times. Because methane and carbon dioxide are strong infrared absorbers, the release and trapping of methane by clathrates contribute strong feedback mechanisms to the radiative forcing of climate that results from earth's orbital variations.

Consumption of atmospheric methane in soils of central Panama: Effects of agricultural development

Abstract: Laboratory and in situ measurements of soil methane consumption in a moist forest area of central Panama indicate that the conversion of forests to agricultural lands diminishes the soil sink for atmospheric methane. Rates of microbial methane consumption in agricultural soils were one fourth those of undisturbed forest soils. This reduction in soil methane consumption may partially account for past and future increases in atmospheric methane concentrations.

The use of radiocarbon measurements in atmospheric studies.

Abstract: (super 14) C measured in trace gases in clean air helps to determine the sources of such gases, their long-range transport in the atmosphere, and their exchange with other carbon cycle reservoirs. In order to separate sources, transport and exchange, it is necessary to interpret measurements using models of these processes. We present atmospheric 14CO (sub 2) measurements made in New Zealand since 1954 and at various Pacific Ocean sites for shorter periods. We analyze these for latitudinal and seasonal variation, the latter being consistent with a seasonally varying exchange rate between the stratosphere and troposphere. The observed seasonal cycle does not agree with that predicted by a zonally averaged global circulation model. We discuss recent accelerator mass spectrometry measurements of atmospheric 14CH (sub 4) and the problems involved in determining the fossil fuel methane source. Current data imply a fossil carbon contribution of ca 25%, and the major sources of uncertainty in this number are the uncertainty in the nuclear power source of 14CH (sub 4) , and in the measured value for delta (super 14) C in atmospheric methane.

Atmospheric methane: recent global trends.

Abstract: The authors report globally averaged concentrations of atmospheric methane for every month of the past 8 years based on measurements taken at six locations ranging in latitude from within the Arctic Circle to the South Pole. This record shows that methane concentration increased at an average rate of 16.6 {plus minus} 0.4 ppbv/yr or {approximately} 1.02 {plus minus} 0.02%/yr over 8 years. This trend has not been constant according to their record but has varied between 12 {plus minus} 2 and 23 {plus minus} 2 ppbv/yr over 2-year periods after seasonal variations are removed. The causes of these interannual variations are not known. They also show that the total mass of methane in the earth's atmosphere undergoes seasonal variations, with highest levels during late fall and early winters of the northern hemisphere and lowest levels in the summers. After the main features of the record are taken into account, residual random fluctuations remain, which have a variability of only 3 ppbv or 0.2% of the mean concentrations. The variation of the trends at different times during the past decade accounts for the differences of trends reported in various studies. Uncertainties in the estimates are reported as 90% confidence limits.

Dynamics and controls of methane oxidation in a Danish wetland sediment

Abstract: The patterns and controls of methane oxidation in a Danish wetland sediment have been determined using a combination of slurry and intact core techniques. Results from slurries indicated that methane oxidation was effectively inhibited by low concentrations of nitrapyrin (9 μM) and acetylene (0.5 μM) but that oxidation was relatively insensitive to pH between 6 and 8; in addition, high concentrations of ammonia (1 mM) decreased oxidation, especially at alkaline pH. Kinetic analyses of methane oxidation in slurries indicated that Vmax was high relative to values reported for other sediments, that Vmax changed seasonally, that Km was consistently low (2–4 μM) and that threshold values were low (3–5 nM) but insufficient to allow consumption of atmospheric methane. Analyses based on intact cores indicated that the extent of methane oxidation was highly dependent on oxygen availability, particularly as affected by benthic photosynthesis or the presence of algal mats. Methane emission and oxidation showed a light saturation response above 400 μEinsteins m−2 s−1. Both core and slurry analyses indicated that even short periods of anoxia resulted in losses of the capacity for methane oxidation after re-exposure to air. On the other hand, the presence of anoxia-insensitive organisms provided for a significant residual post-anoxia activity. Results from addition of nitrapyrin to the surface of intact cores indicated that shifts in methane emissions coincident with short-term changes in the availability of oxygen were the result of changes in methane oxidation, not methanogenesis.

Methane consumption in two temperate forest soils

Abstract: Forest soils are thought to be an important sink for atmospheric methane. To evaluate methane consumption,14C-labeled methane was added to the headspace of intact soil cores collected from a mixed mesophytic forest and from a red spruce forest located in the central Appalachian Mountains. Both soils consumed the added methane at initially high rates that decreased as the methane mixing ratio of the air decreased. The mixed mesophytic forest soil consumed an average of 2 mg CH4 m−2 d−1 versus 1 mg CH, m−2 d−1 for the spruce forest soil. The addition of acetylene to the headspace completely suppressed methane consumption by the soils, suggesting that an aerobic methane-consuming microorganism mediated the process. At both forest sites, methane mixing ratios in soil air spaces were greater than that in the air overlying the soil surface, indicating that these soils had the ability to produce methane. Models of methane emission from forest soils to the atmosphere must represent methane flux as the balance between production and consumption of methane, which are controlled by very different factors

Methane fluxes in wetland and forest soils, beaver ponds, and low‐order streams of a temperate forest ecosystem

Abstract: This study was conducted to determine whether temperate wetlands and forests play important roles in the global balances of atmospheric methane. Flux measurements for methane in several different wetland, forest, and open-water (e.g., beaver pond and low-order stream) sites were determined using collection chambers placed over the soil- or water-air interface. All of the sites were located in the Appalachian Mountain region of West Virginia and western Maryland. Between June 1987 and April 1989 the wetland sites acted as small sources of atmospheric methane, with emission rates for methane usually lower than 200 mg CH4/sq m per day; consumption of atmospheric methane in the wetland soils was observed frequently.

Production of methane and ethylene in organic horizons of spruce forest soils.

Abstract: Concomitant production of CH4 and C2H4 was measured during anaerobic laboratory incubations of organic soils collected from Appalachian red spruce forests. Ethylene production generally exceeded methanogenesis, with greater production occurring in L and F compared with H and Al soil horizons. Slerilants significantly reduced production of both gases in all soils. However, treatment with 2-bromo ethane sulfonic acid (BES) or chloramphenicol decreased C2H4 but not CH4 production. Methane production was not further stimulated by the addition of non-limiting concentrations of H2. Arrhenius slopes for CH4 compared with C2H4 production at temperatures from 5 to 45 C were not significantly different among any of the soils tested. Anaerobiosis due to water saturation may produce sufficient C2H4 to adversely affect plant root growth, however, coniferous forest soils appear to be minor potential sources of atmospheric methane. The methane produced in these soils could have resulted from microorganisms other than methanogenic archaebacteria.

The photochemistry of methane in the atmosphere of Triton

Abstract: The model of Summers and Strobel (1989) for photochemical reactions in the Uranus atmosphere was modified and used for quantitative calculations of methane in the atmosphere of Triton. The principal adjustable parameters in the new model are the surface CH4 concentrations and the vigor of vertical mixing in Triton's lower atmosphere. It is shown the rate of methane photolysis that was calculated is sufficient to generate a smog of condensed C2H2, C2H4, C2H6, and C4H2 particles in the lowest 30 km of Triton's atmosphere, with an optical depth consistent with the Voyager imaging results.

An evaluation of the relationship between the production and use of energy and atmospheric methane emissions

Abstract: The purpose of this document is to examine the role energy plays in the emission of CH{sub 4} to the atmosphere. We begin with an overview of the CH{sub 4} cycle, briefly discussing the current understanding of sources and sinks for CH{sub 4}. We then proceed to a detailed discussion of the energy-related sources of CH{sub 4} to the atmosphere. These include coal mining, natural gas production and distribution, combustion of traditional biomass, and landfill methane (the rightmost four categories of figure 1.1). This examination will then be used to develop estimates of the total global energy-related emissions of CH{sub 4}. 55 refs., 26 figs., 7 tabs.

Methane and carbon monoxide emissions from asphalt pavement: Measurements and estimates of their importance to global budgets

Abstract: We measured emissions of methane from asphalt surfaces used in pavement for roadways Maximum emissions were 22 mg/m2/hr for 1- to 4-week-old pavement during maximum sunlight intensity Emissions were much smaller at low sunlight intensity and dropped off to negligible amounts at night Smaller emissions were observed for asphalt pavement of 25 to 3 years approximate age under similar conditions Companion measurements of carbon monoxide emissions resulted in maximum emissions of about 26 mg/m2/hr for 1-week-old pavement These findings indicate that emissions of CH4 and CO are a function of both sunlight and temperature Based on our results, methane emissions from asphalt pavement cannot be a significant source of atmospheric methane as compared to other identified methane sources Therefore, although asphalt methane emissions are a form of fossil fuel methane, they cannot explain the relatively high fraction of 14C-depleted methane in the atmosphere

Comment on “Detection of multiply deuterated methane in the atmosphere”

Abstract: It has recently been reported [Mroz et al., 1989] that the abundance of mass-20 isotopes of methane (CH4), which correspond to either of the highly deuterated forms 12CD4 or 13CHD3, is some 500 times that expected based on the statistical combination of H, D, 12C, and 13C and observed CH4 amounts. These authors then suggested that it is possible that the enhanced concentration of these species is due to their longer lifetimes than that of CH4 itself because of their slower rate of loss by reaction with the hydroxyl radical (OH). We have tested this hypothesis with a two-dimensional atmospheric chemical-dynamical model and found that no large enhancements of 13CHD3 and 12CD4 can result in this way; in the troposphere enhancement factors of between 4 and 5 and between 7 and 8, respectively, were found, with enhancements becoming only slightly larger (14 and 25, respectively) in the stratosphere. The factor of 500 enhancement reported by Mroz et al. must have other origins.

Atmospheric methane data for the period 1983-1985 from the NOAA/GMCC global cooperative flask sampling network. Technical memo

Abstract: The report presents details of relevant aspects of the NOAA/GMCC program to measure atmospheric methane concentrations through its global, cooperative, flask sampling network. These aspects include the history of the development of the program; details of the sampling network; the flasks and the flask sampling methods; the analytical instrumentation and methods; and the calibration gases and methods. The data from individual flask samples are tabulated, as are the monthly average methane concentrations. Through adequate documentation it is more likely that the full value of these methane measurements will be realized in long-term studies of the greenhouse effect and climate change.

Climate Monitoring and Diagnostics Laboratory No. 18. Summary report, 1989

Abstract: Contents: CMDL station information; observatory reports; aerosols and radiation monitoring group; carbon cycle group; ozone group; acquisition and data management; air quality group; nitrous oxide and halocarbons group; a joint U.S./U.S.S.R. experiment for the study of desert dust and its impact on local meteorological conditions and climate; annual ozone cycle and decade trend at South Pole; wintertime black carbon aerosol measurements over the southwestern United States, December 1989; cooperative programs; precipitation chemistry; continuous aerosol monitoring with the epiphaniometer at mlo; antarctic ultraviolet spectroradiometer monitoring program; chemical resolution of fine aerosol mass at mlo: the role of organic matter; artificial windshielding of precipitation gauges in the arctic; UVB monitoring data from Rockville, Maryland; Robertson-Berger UVB meter; the CSIRO latitudinal gradient study: methane data from air samples collected at Cape Grim, Tasmania; secular variation in the carbon-13 content of atmospheric carbon dioxide; snow bunting nesting study at Barrow, Alaska; optical depth retrieval with the sunphotometer; tropospheric nitrogen oxide during spring at Barrow; chemical analyses of atmospheric particulates and gases at mlo; a temperature inversion climatology for barrow: 1976-1985; the global precipitation chemistry project; radioactivity in the surface air at brw, mlo, smo, and spo; total nitrate variations at Mauna Loa; seasonal andmore » latitudinal trends in the (13)c/(12)c ratio of methane; aerosol constituents at American Samoa, November 1989; update on the o-ring bias; trends of the carbon isotopi composition of atmospheric methane in the southern hemisphere; bromine and surface ozone atmospheric chemistry at Barrow, Alaska, during spring 1989; USGS Barrow Observatory; radon from distant continents detected at the Mauna Loa Observatory.« less

Climate and water

Abstract: There is considerable consensus among the international scientific community that we are facing global warming due to increasing levels of atmospheric carbon dioxide, methane, CFCs and other greenhouse gases. The perceived wisdom is that the average global temperature has increased 0.5°–0.7°C since the turn of the century or, according to some, since the 1860s. Current estimates from models indicate that temperatures may increase 1°–3°C during the next 40–60 years. However, since there are considerable gaps in our knowledge and data availability, reliability of such models leaves much to be desired.

Greenhouse Gas Emissions from High Demand, Natural Gas-Intensive Energy Scenarios

Abstract: Since coal and oil emit 70% and 30% more CO2 per unit of energy than natural gas (methane), fuel switching to natural gas is an obvious pathway to lower CO2 emissions and reduced theorized greenhouse warming. However, methane is, itself, a strong greenhouse gas so the CO2 advantages of natural gas may be offset by leaks in the natural gas recovery and supply system. Simple models of atmospheric CO2 and methane are used to test this hypothesis for several natural gas-intensive energy scenarios, including the work of Ausubel et al. (1988). It is found that the methane leaks are significant and may increase the total "greenhouse effect" from natural gas-intensive energy scenarios by 10%. Furthermore, because methane is short-lived in the atmosphere, leaking methane from natural gas-intensive, high energy growth scenarios effectively recharges the concentration of atmospheric methane continuously. For such scenarios, the problem of methane leaks is even more serious. A second objective is to explore some high demand scenarios that describe the role of methane leaks in the greenhouse tradeoff between gas and coal as energy sources. It is found that the uncertainty in the methane leaks from the natural gas system are large enough to consume the CO2 advantages from using natural gas instead of coal for 20% of the market share.

Long-term trend and seasonal cycle of atmospheric methane

Abstract: Ⅰ. INTRODUCTIONMethane is one of the most abundant trace gases in the earth’s atmosphere with the current concentration of 1.7 ppm. It appears to be primarily of biogenic origins, and has long been regarded as one natural component unchanging in concentration. However, the observations corroborated by our recent work have indicated that the concentration of at-

Methane fluxes in the Southern North Sea: The role of European rivers

Abstract: Methane is an important greenhouse gas and plays a major role in tropospheric chemistry. Therefore its global budget has received considerable attention. On aspect of the global methane cycle which remains poorly understood is the role played by the oceans and rivers as sources of methane to the atmosphere. We recently conducted a study of methane in the Southern Bight of the North Sea, both before and during the spring bloom, in which we examined the distribution of methane as well as sinks for methane such as oxidation by bacteria and loss to the atmosphere. In most of the Southern North Sea during March and April 1989, waters were at or near saturation with the atmosphere, and both biological oxidation and gas exchange rates were low. However in a narrow zone along the Dutch coast, sampled during the March cruise, extremely high methane concentrations (up to 360 nM) were observed. In general elevated methane levels correlated will with low salinities. Linear extrapolations of the CH[sub 4]/Salinity surves to S = O were made to estimate the concentration in the riverine endmember(s). Results suggested the presence of two methane sources (of about 50 nM and about 5000 nM). Using a modelmore » developed by the Delft Hydraulics Laboratory, we estimate river concentrations of about 70-15- nM if the Rhine is the major source and of 6000 nM if the Scheldt outflow were most important. These river concentrations are within the range of observe values for a variety of other rivers suggesting river outflow may represent an important local methane source.« less

Energy potential of modern landfills

Abstract: Methane produced by refuse decomposition in a sanitary landfill can be recovered for commercial use. Landfill methane is currently under-utilized, with commercial recovery at only a small percentage of US landfills. New federal regulations mandating control of landfill gas migration and atmospheric emissions are providing impetus to methane recovery schemes as a means of recovering costs for increased environmental control. The benefits of landfill methane recovery include utilization of an inexpensive renewable energy resource, removal of explosive gas mixtures from the subsurface, and mitigation of observed historic increases in atmospheric methane. Increased commercial interest in landfill methane recovery is dependent on the final form of Clean Air Act amendments pertaining to gaseous emissions from landfills; market shifts in natural gas prices; financial incentives for development of renewable energy resources; and support for applied research and development to develop techniques for increased control of the gas generation process in situ. This paper will discuss the controls on methane generation in landfills. In addition, it will address how landfill regulations affect landfill design and site management practices which, in turn, influence decomposition rates. Finally, future trends in landfilling, and their relationship to gas production, will be examined. 19 refs., 2 figs., 3more » tabs.« less