Showing papers on "Atmospheric methane published in 1982"

Methane flux in the Great Dismal Swamp

Abstract: The paper reports measurements made over a 17-month period of the methane flux in the Great Dismal Swamp of Virginia in light of the potential implications of variations in atmospheric methane concentrations. Gas flux measurements were made by a technique combining a gas filter correlation IR absorption analyzer with improved sampling chambers that enclose a soil area under conditions ranging from totally flooded soils to dry soils resulting from drought conditions. Methane emissions are found to range from 0.0013 g CH4/sq m per day to 0.019 g CH4/sq m per day, depending on temperature and season, when the soil is in a waterlogged state. During drought conditions, the peat soils in the swamp were a sink for atmospheric methane, with fluxes from less than 0.001 to 0.005 g CH4/sq m per day and decreasing with decreasing temperature. Results illustrate the potential complexity of the processes which regulate the net flux of methane between wetland soils and the atmosphere.

Termites: a potentially large source of atmospheric methane, carbon dioxide, and molecular hydrogen.

Abstract: Termites may emit large quantities of methane, carbon dioxide, and molecular hydrogen into the atmosphere. Global annual emissions calculated from laboratory measurements could reach 1.5 x 10(14) grams of methane and 5 x 10(16) grams of carbon dioxide. As much as 2 x 10(14) grams of molecular hydrogen may also be produced. Field measurements of methane emissions from two termite nests in Guatemala corroborated the laboratory results. The largest emissions should occur in tropical areas disturbed by human activities.

Methane: The record in polar ice cores

Abstract: Methane mixing ratios in trapped air in the Dye 3 Greenland ice core decrease from 1.25 ppmv below the firn-ice transition (∼90 years B.P.) to a baseline value of 0.70 ppmv at a depth of ∼250 m (∼500 years B.P.). Below this level to a depth of 1950 m (∼27,000 years B. P.) the mixing ratio appears to be constant at the base-line level, and in agreement with data of Robbins et al. (1973) on 700-2470 year-old Antarctic ice. The uniformity of these CH4 mixing ratios in both hemispheric ice caps and over some 26 millennia indicates that, whether or not the absolute values correctly reflect the true atmospheric mixing ratios vs. time, the atmospheric CH4 mixing ratios were nevertheless essentially constant over this range of time. Above 250 m depth the trapped-air CH4 mixing ratios increase linearly up to ∼100 m depth, and then increase sharply just below the firn-ice transition. The mixing ratio vs. age trajectory is strongly offset from the estimated atmospheric record of the past 15 years, but when corrected for the ∼90 year difference in age of air and ice at firn closure, the ice-core data track quite precisely into the recent atmospheric record. Thus we believe that these data correctly reflect past CH4 atmospheric mixing ratios. The increase in atmospheric methane concentration begins at ∼1580 A.D. and amounts to ∼0.40 ppmv by 1918, and ∼0.90 ppmv by 1980; the equilibrium greenhouse warming associated with this increased CH4 concentration is about 0.23°C over the past 400 years, and at the current rate of increase the warming due to CH4 is about 38% of the CO2 warming effect.

Global increase in atmospheric methane concentrations between 1978 and 1980

Abstract: The concentration of methane has been measured in tropospheric air samples collected in remote locations between 55°N and 53°S during six collection periods between November 1977 and November 1980. The observed concentrations of CH4 have increased in each of six latitude locations by an average of 0.052±0.005 ppmv between January 1978 and January 1980. This (1.4±0.2)×1014 gram increase in the total atmospheric burden of CH4 corresponds to 35±12% of the yearly flux of (4.0±1.3)×1014 grams needed to maintain the CH4 concentration in steady-state at its recent level of about 1.6 ppmv. The 1978-1980 excess of about 0.7×1014 grams per year of sources over sinks for CH4 could arise from either an increase in biogenic releases or from a decrease in the average OH radical concentration in the lower troposphere, or from both.

The carbon isotopic composition of atmospheric methane

Abstract: Recent measurements of the carbon isotopic abundance of atmospheric methane give a value of δ(13C/12C) = −47.0 ± 0.3‰, which is significantly different from earlier values measured by others between 1950 and 1970. The isotopic composition of various sources and the possibility of a temporal trend are discussed. The average methane concentration measured was 1.66 ppm, which is in accord with the increase in concentration since 1965–1970 observed in other studies.

Inventory of global methane sources and their production rates

Abstract: On the basis of 17 ecosystems, it is estimated that 9.1×1014 g CH4/year are emitted into the atmosphere from the biosphere. Enteric fermentation in animals and humans, decomposition of organic wastes, and biomass burning contribute an additional 2.0×1014 g CH4/yr. Various fossil sources emit another 1×1014 g CH4/yr. When all sources are considered, they emit 12.1×1014 g CH4 each year. As with earlier inventories, this study indicates that the fossil methane contribution is less than 10% of the total annual global production rate. Chemical kinetic relationships are established between the bacteriamediated anaerobic decomposition of humic matter, the mean residence time (MRT) of humus, and methane fluxes. These equations and the 14C specific activity are used to obtain an average MRT of 1365 years for the earth's 1.8×1018 grams of humic carbon. Use of the global methane production rate and the concentration of atmospheric methane results in an average 3.3 year residence time and an average global hydroxyl radical concentration of 2.7×106 per cm3.

Non-methane Organics in the Remote Troposphere

Abstract: The atmosphere is now understood to contain many gaseous species at concentrations varying by many orders of magnitude. At one end of the concentration scale, gases such as oxygen are vital to sustaining animal respiration, whilst at the other end, trace species such as nitrogen oxides control fundamental geochemical phenomena such as the earth’s ozone shield and the level of hydroxyl radicals present in the troposphere. The most numerous trace gases present are organic molecules which have a variety of sources including combustion processes, biogenic decay on land and in the ocean, solvent usage, natural gas leakage, etc. The measurement of these many compounds at concentration levels down to parts in 1012 and below has presented atmospheric scientists with severe analytical problems. These are now being solved by using a variety of modern techniques based upon spectroscopy and gas chromatography. Data on the distribution of many compounds is still exceedingly scarce. This is urgently needed to quantify major sources and to test current theories of atmospheric oxidation leading to the creation of soluble molecules capable of being removed by rain. Some of the limited amount of concentration data available is discussed by compound type: namely, halocarbons, hydrocarbons, oxygenated compounds, and sulfur compounds. The main object of this discussion is an attempt to find some consistent indicators for the degree of chemical reaction which can be attributed to attack by hydroxyl radicals in the troposphere. It appears that the level of oxidation indicated by the latitudinal distribution of molecules such as perchloroethylene and acetylene, and possibly benzene, toluene, and some other compounds, is considerably less than that predicted from a study of the carbon monoxide cycle. However, much more data on the distribution of these molecules throughout the troposphere are needed before final conclusions can be drawn. A low oxidation rate for many molecules tends to lower the amounts that can be removed each year by natural processes occurring in the atmosphere. This makes pollution more of a problem, of course, and at the same time it affects the current assessments of the efficiency of the biosphere for producing trace gases in the atmosphere, including those involved in the creation of condensation nuclei by direct gas to particle conversion processes. Finally, there are indications from a comparison of the concentration distribution of acetylene and sulfur dioxide, both of which are largely pollution derived, that oxidation of soluble species in atmospheric droplets may be a very efficient process, possibly by reaction with hydrogen peroxide.

Methane: Interhemispheric concentration gradient and atmospheric residence time.

Abstract: The ground level concentrations of methane in the atmosphere have been measured to be in the range from 1.45 to 1.62 parts per million by volume (ppmv) of dry air in remote locations between 62°N and 54°S latitudes during the time period from November 1977 to July 1979. The average (±rms) concentration for the northern hemisphere was 1.57 ± 0.02 ppmv in January 1978 and 1.59 ± 0.02 in July 1979. The average concentration in the southern hemisphere was lower—1.47 ± 0.02 in January 1978 and 1.51 ± 0.01 in July 1979. The ratio of concentrations between the two hemispheres was 1.068 ± 0.016 in January 1978 and 1.055 ± 0.013 in July 1979, for an average of 1.06 ± 0.01. The higher concentrations in the northern hemisphere require either that the sources of methane lie preferentially in the northern hemisphere or that the removal processes operate more rapidly in the southern hemisphere or both. The primary removal process for CH4 is reaction with tropospheric OH radicals and its estimated atmospheric lifetime is 10.5 ± 1.8 yr. The observed interhemispheric gradient is consistent with this lifetime and preferential release of methane in the northern hemisphere. Measurements taken in the Amazon basin region indicate the presence of a substantial source of methane in that area.

The Potential effects of increased methane on atmospheric ozone

Abstract: Using a one dimensional atmospheric model, we investigate the possible influence of an increase in atmospheric methane on ozone. The couplings between methane and the catalytic destruction of ozone by NOx, HOx, and ClX are discussed. Our model calculations suggest that doubling the ground-level flux of methane, with fixed atmospheric temperatures and currently recommended chemical reaction rates, would increase the total ozone column by 3.5%. Calculations showing the very significant moderating effects of a methane increase on ozone perturbations due to N2O and chlorofluorocarbons are discussed.

Sources of atmospheric methane from coastal marine wetlands

Abstract: Biological methanogenesis in wetlands is believed to be one of the major sources of global tropospheric methane. The present paper reports measurements of methane distribution in the soils, sediments, water and vegetation of coastal marine wetlands. Measurements, carried out in the salt marshes Bay Tree Creek in Virginia and Panacea in northwest Florida, reveal methane concentrations in soils and sediments to vary with depth below the surface and with soil temperature. The fluxes of methane from marsh soils to the atmosphere at the soil-air interface are estimated to range from -0.00067 g CH4/sq m per day (methane sink) to 0.024 g CH4/sq m per day, with an average value of 0.0066 g CH4/sq m per day. Data also demonstrate the important role of tidal waters percolating through marsh soils in removing methane from the soils and releasing it to the atmosphere. The information obtained, together with previous studies, provides a framework for the design of a program based on in situ and remote sensing measurements to study the global methane cycle.

Secular trends of atmospheric methane (CH/sub 4/)

Abstract: Due partly to human activities the present yearly emissions of CH/sub 4/ exceed the atmospheric sinks, thus leading to a 1.2 to 1.9% per year atmospheric increases in the concentration of CH/sub 4/. New evidence based on studies of polar ice cores suggests that several hundred years ago the concentrations of CH/sub 4/ were perhaps only half of current values. These diverse findings are tied together in a single unified logistic model of atmospheric concentrations past, present and future. Using realistic growth rates of the sources of CH/sub 4/ caused by human activities, the model explains the concentrations and current growth rates. It also predicts that a doubling of CH/sub 4/ relative to present levels is possible given the long (9-year) atmospheric lifetime. Such increases of CH/sub 4/ concentrations may have already perturbed our global environment and may continue to do so in the future. The environmental effects include increased surface temperature of the earth, additional O/sub 3/ and CO in the clean non-urban atmosphere, depletions of trophospheric OH radicals, but perhaps also protection of the stratospheric ozone layer from destruction by man-made fluorocarbons.