Methane emission rates

Schutz H, Holzapfel-Pschom A, Conrad R, Rennenberg H, Seiler W. A 3-year continuous record on the influence of daytime, season, and fertilizer treatment on methane emission rates from in Italian rice paddy. J. Geophys. Res. 1989 94 16405-16416. 

Organic carbon is lost from Amazon flood-plain lakes by permanent burial, emission as CO2 and CH4 to the atmosphere or export to the river. Sufficient data are now available to estimate most of these losses. Methane is produced predominantly in anoxic environments associated with flooded habitats. Methane emission rates have been estimated in a variety of habitats and sites along the central Amazon floodplain (Devol et al. 1988, 1990, 1994, Crill et al. 1988, Bartlett et al. 1988, 1990, Wassmann et al. 1992, Wassmann and Thein 1994, Engle and Melack 2000). The average emission rates encountered in aquatic macrophyte beds, flooded forest and open water, including... 

Fig. 4-5. Methane emission rates measured as a function of temperature open circles, from incubated paddy soils (Koyama, 1963) filled circles, from wetlands (Baker-Blocker et al., 1977). The solid curve F = 0.46-0.00056T+0.0026T2 g/m2 day is the best fit to the observational data according to Baker-Blocker et al. (1977).

Table 4-8 summarizes methane emission rates as estimated by different authors. Most source estimates sum to a total of about 500 Tg/yr. An exception is the value derived by Sheppard et al. (1982) from a classification of natural ecosystems similar to that described in Section 11.2.4 for the turnover of biogenic carbon. Even this estimate, however, agrees with the others within a factor of 2-3. We think that is too high, mainly because it cannot be compensated by the known methane sinks, which are discussed next. 

Methane Emission Rates through Plants and Open Water in Outdoor Wetland Microcosms (n = 4)... 

Another environmental parameter that is important to methane emissions is soil temperatnre. Soil temperature affects the metabolic activity of microorganisms that prodnce substrates for inhibitors of methanogenesis as well as the methanogens themselves. Temperatnre is directly related to methanogenesis under field conditions (Schutz et al., 1990 Westermann, 1993). Methane emission rates generally parallel soil temperature levels. 

In general there is a homogenous consumption rate of methane in soils as opposed to a highly variable methane emission rate within specific geographical regions. Both methane prodnction and consumption are microbially mediated. Methane oxidation rates in soil are controlled in part by nonbiological factors, primarily redox status, and soil porosity. Generally, the rate of methane diffusion into the soil controls the rate of consumption (Keller et al., 1990). 

Dise (1993) and Dise et al. (1993) discussed the large variability in methane emission rates observed from Minnesota peat. Their work explains the disparate ranges reported earlier by... 

The simulation assumes that the gas emission position locates at the top of the roof-fall carving in the return airway. The relative methane emission rate is 1.78 mVt and the absolute rate is 0.0033 mVs. According to the Coal Mine Safety Regulations, the gas concentration of airflow in return airway... 

At some landfills, operators have installed flares to combust the gas without recovering any energy. Typically, these cases arise because electricity seU-back rates are too low to justify generation equipment, and laws require a reduction in methane emissions. 

Night-time emission rates in rural and urban areas are listed in Table I together with initial concentrations and land deposition velocities. The initial concentrations were chosen to reflect unpolluted air arriving at the West Coast of England. Methane is assumed to be present in the atmospheric boundary layer at a constant concentration of 1.6 ppm. Water vapour is also assumed to be invariant in rural and urban air at a concentration of 104 ppm. This corresponds to ca. 60% relative humidity at 288 K. The initial concentration and emission over land of DMS have been taken to be zero as have all other species in the chemical scheme which are not listed in Table I. Emissions over land of NO, SO hydrocarbons, CO and H are subject to diurnal variation and this has been treated as before (13.141. Rural emission rates are assumed to prevail throughout the traversal of Scandinavia. All species are assumed to be hilly mixed within an atmospheric boundary layer of constant depth, taken to be... 

One advantage of partial oxidation is that significant reductions in NOx and C02 emission rates can be achieved compared to steam methane reforming. In one case a reduction of 20% was achieved when partial oxidation replaced steam methane reforming. This is because the point source emissions related to the furnace flue gas exhaust are not a part of this process. Emissions from partial oxidation processes are relatively small by comparison and primarily come from fired heaters that may be used to preheat the process feed177. 

The upper states of both emission bands can be populated by either direct excitation from the ground state of the corresponding molecule or by dissociative excitation from methane or higher hydrocarbons. Figure 4.9 shows a compilation of emission rate coefficients for the A2A — X 277 CH band (v = 0,1,2, 3 — v" = 0,1, 2, 3) and the C2 Swan band (v = 0 — v" = 0) [41]. There is experimental evidence that for CD the same rate coefficients than for CH can be applied [42]. The emission rate coefficient for direct excitation is several orders of magnitude higher than the emission rate coefficient for dissociative excitation. The dominant excitation mechanism depends on the... 

Table 1 shows the mean emission rates (X) and standard errors (s/ V n) for CH4, CO2, and CO from three Reticulitermes and two Gnathermitermes Colonies [19] n is the number of days during which samples which were analyzed during the 55-day showed little variability ( 10%). The variability between days was sometimes much higher. These emission rates are about in the middle of methane production rates reported by... 

More direct measurements of methane oxidation rates, particularly in wetlands and ocean waters, are needed. The use of stable isotope estimates of methane oxidation, which give an indication of total oxidation, should continue, but direct rate measurements using both " C-CH4 and H-CH4 should be a priority. Pulse-labeling experiments conducted through a growing season are needed to resolve the effect of plant phenology on methane emission. The methane oxidation threshold suggested by a number of open ocean rate measurements should be studied in open ocean samples from areas near and well removed from shelf vent sources. 

Because of its abundance in anoxic aquatic environments and its importance as a greenhouse gas, methane transformation by anaerobic oxidation has been the subject of numerous studies. The rates of anaerobic methane oxidation and the environments where it has been found were reviewed by Spormann and Widdel (2000). In marine systems, sulfate reduction has been shown to be an important part of the methane oxidation process. Landhlls, however, not hydrocarbon contaminations per se, are the main source of anthropogenic methane emissions in the US and, therefore, methane degradation processes are not discussed further in this chapter (see Chapter 9.16 for a discussion of methane generation from landfills). 

Warneck (1988) has estimated the annual global emission rates of non-methane organic compounds, expressed in units of 1012 g yr-1 ... 

Stem D. I. and Kaufman R. K., 1996. Relative rates of methane emission sources. Chemosphere, 33 159-176. 

Gas analysis for the determination of emission rate correction factor or excess air Determination of carbon dioxide, methane, nitrogen, and oxygen from stationary sources Determination of moisture content in stack gases Determination of particulate matter emissions from stationary sources... 

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