Showing papers on "Atmospheric methane published in 1985"

Methane emissions to the atmosphere through aquatic plants

Abstract: The movement of methane (CH4) from anaerobic sediments through the leaves, stems, and flowers of aquatic plants and into the atmosphere was found to provide a significant pathway for the emission of CH4 from the aquatic substrates of flooded wetlands. Methane concentrations well above the surrounding ambient air levels were found in the mesophyll of 16 varies of aquatic plants and are attributed to transpiration, diffusion, and pressure-induced flow of gaseous CH4 from the roots when they are embedded in CH4-saturated anaerobic sediments. Methane emissions from the emergent parts of aquatic plants were measured using floating chamber techniques and by enclosing the plants in polyethylene bags of known volume. Concentration changes were monitored in the trapped air using syringes and gas chromatographic techniques. Vertical profiles of dissolved CH4 in sediment pore water surrounding the aquatic plants' rhizomes were obtained using an interstitial sampling technique. Methane emissions from the aquatic plants studied varied from 14.8 mg CH4/d to levels too low to be detectable. Rooted and unrooted freshwater aquatic plants were studied as well as saltwater and brackish water plants. Included in the experiment is detailed set of measurements on CH4 emissions from the common cattail (Typha latifolia). This paper illustrates that aquatic plants play an important gas exchange role in the C cycle between wetlands and the atmosphere.

Increase of Atmospheric Methane Recorded in Antarctic Ice Core

Abstract: Air entrapped in bubbles of cold ice has essentially the same composition as that of the atmosphere at the time of bubble formation. Measurements of the methane concentration in air extracted by two different methods from ice samples from Siple Station in western Antarcitica allow the reconstruction of the history of the increase of the atmospheric methane during the past 200 years.

Methane flux from coastal salt marshes

Abstract: It is thought that biological methanogenesis in natural and agricultural wetlands and enteric fermentation in animals are the dominant sources of global tropospheric methane. It is pointed out that the anaerobic soils and sediments, where methanogenesis occurs, predominate in coastal marine wetlands. Coastal marine wetlands are generally believed to be approximately equal in area to freshwater wetlands. For this reason, coastal marine wetlands may be a globally significant source of atmospheric methane. The present investigation is concerned with the results of a study of direct measurements of methane fluxes to the atmosphere from salt marsh soils and of indirect determinations of fluxes from tidal creek waters. In addition, measurements of methane distributions in coastal marine wetland sediments and water are presented. The results of the investigation suggest that marine wetlands provide only a minor contribution to atmospheric methane on a global scale.

A model study of the greenhouse effects due to increasing atmospheric CH4, N2O, CF2Cl2, and CFCl3

Abstract: Study of the greenhouse effects of increasing atmospheric trace gases has so far relied mainly on the use of one-dimensional models, especially the radiative-convective models (cf. World Meteorological Organization, 1982; National Research Council, 1983). Here we use the two-dimensional (altitude-latitude) radiative-dynamical model of Wang et al. (1984) to investigate the effects on vertical and meridional temperatures of increases of atmospheric methane, nitrous oxide, and chlorofluorocarbons. The model, consisting of a high-latitude zone and a low-latitude zone, couples the meridional and vertical temperature structure through energy balance between radiative flux and vertical and meridional heat transports. First, we show that the thermal radiation flux perturbations, i.e., the driving force for the subsequent climate change, caused by increases of these trace gases and carbon dioxide, are different in nature. Next, a comparison of model-calculated present climate and climate change between the one-dimensional and two-dimensional models is performed. The results indicate that the two-dimensional model simulates much more realistic temperature and humidity distributions. For a doubling of the atmospheric CO2 concentration of 330 parts per million by volume, the two-dimensional model computes a global surface warming of 3.7 K with larger high-latitude amplification, which is in good agreement with results obtained from general circulation models. For the study of the surface warming due to increases of trace gases, it is found that the one-dimensional model using a 6.5 K km−1 critical lapse rate for convective adjustment appears to calculate a much larger surface warming than the two-dimensional model. On the other hand, the one-dimensional model using the moist adiabatic critical lapse rate, although it can not simulate adequately the present tropospheric temperature structure, calculates surface warming effects in close agreement with those of two-dimensional model results. We have used the two-dimensional model to estimate on the time scale of decades the potential greenhouse effects due to increases of these gases. Although the calculations depend largely on the adopted scenarios for future increases, the results nevertheless reveal that the trace gases could potentially augment the surface warming due to carbon dioxide increase by more than 60%.

On the Rise: Methane in the Global Atmosphere

Abstract: (1985). On the Rise: Methane in the Global Atmosphere. Environment: Science and Policy for Sustainable Development: Vol. 27, No. 10, pp. 6-33.

Methane in the global atmosphere

Abstract: Long familiar as marsh gas or natural gas, methane has come to be recognized as an important constituent of the stratosphere since it acts as a sink for chlorine atoms and absorbs infrared radiation, contributing to the greenhouse effect. Man is now increasing the amount of atmospheric methane. This increase in methane could cause an increase in the earth's surface temperature of between 0.3/sup 0/ and 0.5/sup 0/. This paper provides a comprehensive overview of the methane problem. 20 references, 6 figures, 3 tables.

Sources of atmospheric methane from wetlands

Abstract: Through the use of a computerized Geographic Information Service (GIS), field data on methane emissions and water inundation levels have been combined with remotely sensed vegetation cover data This permits a more precise extrapolation of point flux measurements to regional scale flux estimates Since the GIS allows changes in environmental variables to be included in the model, the sensitivity of emissions on large scales to changes in these parameters may be studied Here, methane flux measurements from the Everglades marsh complex are reported, giving the flux by vegetation class

Validated infrared transmittance band model for methane in the atmosphere: corrigenda.

Abstract: Joseph H. Pierluissi, Ralph D. Hippenstiel, and Christos E. Maragoudakis University of Texas at El Paso, Electrical Engineering Department, El Paso, Texas 79968. Received 22 January 1985. 0003-6935/85/121729-02$02.00/0. © 1985 Optical Society of America. In a recent paper on development and validation of a mo­ lecular transmittance band model for atmospheric methane (CH4), one of the three significant IR bands (from 4105 to 4730 cm) was unintentionally ignored, and an error in the vertical concentration profile was accidentally introduced. The purpose of this Letter is to make the necessary corrections and provide illustrative transmittance spectra for this band. These corrections are deemed important because methane forms part of the group of five gases originally modeled in LOWTRAN as a single model for the so-called uniformly-mixed gases. In the earlier cited reference use was made of a double ex­ ponential transmission function together with nonlinear op­ timization techniques to develop a band model for the methane bands from 1085 to 1755 cm and from 2370 to 3215 cm. The data consisted of line-by-line calculations com­ puted using FASCOD1C and of laboratory measurements made by Gryvnak et al. The model parameters were determined at 5 cm -1 for the 20-cm spectral resolution for LOWTRAN. Since there were no laboratory measurements for the band being presented here, its modeling was done using the same transmission function and numerical methods used with the other bands but with degraded line-by-line data only. Briefly stated, the band model is given by

A trend study of atmospheric methane: 1965-81 GC and polar icecore measurements

Abstract: A TREND STUDY OF ATMOSPHERIC METHANE: 1965-81 GC AND POLAR ICECORE MEASUREMENTS Suresh Santanam Oregon Graduate Center Beaverton, Oregon Thesis Advisor: Professor M.A.K. Khalil An investigation of methane increase during tbe period 1965-81 is presented. A critical review of the literature has been carried out t o isolate background methane measurements. A seasonal and global correction procedure has been applied t o these selected GC measurements of diflerent researchers. The corrected d a t a have been analyzed t o quantify the trend of methane. T h e results show an annual methane rise of about 1%. A survey of continuous, systematic measurements of methane made in the 80s indicate a similar result. Polar ice core measurements of methane, both from arctic and antarctic, have been examined to determine the period during which the recent rapid rise has begun. T h e analyses demonstrate t b a t methane increase s tar ted about 150 years ago. A doubling of atmospheric methane level during this period has now occured. A review of IR spectroscopic d a t a and Russian methane measurements has also been carried out. T h e Russian observations have large variabilities associated with them; the higher mean of these d a t a indicate possible non background levels of methane. Analysis of CH, sources and possible efiects of increasing methane imply that a 20% depletion of hydroxyl radicals may already have occured, while a large portion of the CH4 increase may have occured because of increasing emissions from sources controlled by human activities.

Long term monitoring of methane in the atmosphere by multiplex gas chromatography

Abstract: Methane is of interest in the study of the Earth's atmosphere because of its implication in the future global warming of the surface. This warming is produced by the absorption of infrared energy by trace gases. It has been estimated that in the next 40 to 50 years, methane could contribute 20 to 25 pct. as much atmospheric warming as that expected from carbon dioxide increases. Studies to examine sources, sinks, and cycles of methane will require analytical methods capable of continuous unattended measurement with temporal resolution of an hour or less for weeks at a time. Gas chromatography (GC) is one of the most practical methods available to conduct the analysis of air, but limitations in this technique still exist which can be alleviated with multiplex GC (MGC). MGC is a technique where many samples are pseudo-randomly introduced to the chromatograph without regard to the length of time required for an analysis. The resulting data must then be reduced using computational methods such as cross correlation. In the technique reported, a tube packed with silver oxide was used at the inlet of the GC column to create concentration pulses of methane in a sample stream of air. By using only one carrier, i.e., ambient air, an effective and accurate method to monitor the variations in concentration of methane in the atmosphere over long periods of time was developed. Methane in ambient air was monitored for an eight day period and an interesting temporal variability was found. This work has shown the utility of a relatively simple MGC for the analysis of a real environmental sample.