EPA/600/A-92/221 Biomass Burning and the Production of Methane Joel S. Levine and Wesley R. Cofer III Atmospheric Sciences Division NASA Langley Research Center Hampton, Virginia 23665-5225 and Joseph P. Pinto Atmospheric Research and Exposure Assessment Laboratory U.S. Environmental Protection Agency Research Triangle Park, North Carolina 27711 ------- DISCLAIMER The information in this document has been funded in part by the United States Environmental Protection Agency. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ------- Our planet is a unique object in the solar system due to the presence of a biosphere with its accompanying biomass and the occurrence of fire (Levine, 1991a), The burning of living and dead biomass is a very significant global source of atmospheric gases and particulates. Crutzen and colleagues were the first to consider biomass burning as a source of gases and particulates to the atmosphere (Crutzen et al,, 1979; and Seller and Crutzen, 1980). However, in a recent paper, Crutzen and Andreae (1990) point out that "Studies on the environmental effects of biomass burning have been much neglected until rather recently but are now attracting increased attention." The "increased attention" reference in the Crutzen and Andreae paper was the Chapman Conference on Global Biomass Burning; Atmospheric, Climatic, and Biospheric Implications held in Williamsburg, Virginia in March, 1990 (Levine, 1990). The proceedings of the conference containing 63 chapters recently appeared (Levine, 1991b). Much of the information contained in this chapter is based on material in this volume. Biomass burning and its environmental implications have also become important research elements of the International Geosphere-Biosphere Program (IGBP) and the International Global Atmospheric Chemistry (IGAC) Project (Prinn, 1991). The production of atmospheric methane (CH4) by biomass burning will be assessed. The production of methane and other gaseous and particle carbon species resulting from biomass burning will be outlined. Field measurements and laboratory studies to quantify the emission ratio of methane and other carbon species will be reviewed. The historic database suggests that global biomass burning is increasing with time and is controlled by human activities. Present estimates indicate that biomass burning contributes between about 20 to about 60 Teragrams per year of carbon in the form of methane to the atmosphere. This represents only 5 to 15% of the global annual emissions of methane. Measurements do indicate that biomass burning is the overwhelming source of CH4 in tropical Africa. However, if the rate of global biomass burning increases at the rate that it has been over the last few decades, then the production of methane from biomass burning may become much more important on a global scale in the future. ------- Gaseous Emissions Due to Biomass Burning Biomass burning includes the combustion of living and dead material in forests, savannas, and agricultural wastes, and the burning of fuel wood. Under the ideal conditions of complete combustion, the burning of biomass material produces carbon dioxide (CO2) and water vapor (H20), according to the reaction CH20 + 02 — C02 + H20 (1) where CH2O represents the average composition of biomass material. Since complete combustion is not achieved under any conditions of biomass burning, other carbon species, including carbon monoxide (CO), methane (CH4), nonmethane hydrocarbons (NMHCs), and particulate carbon, result by the incomplete combustion of biomass material. In addition, nitrogen and sulfur species are produced from the combustion of nitrogen and sulfur in the biomass material. While C02 is the overwhelming carbon species produced by biomass burning, its emissions into the atmosphere resulting from the burning of savannas and agricultural wastes are largely balanced by its reincorporation back into biomass via photosynthetic activity within weeks to years after burning. However, C02 emissions resulting from the burning of forests and other carbon combustion products from all biomass sources including CH,}, CO, NMHCs, and particulate carbon, are largely "net" fluxes into the atmosphere since these products are not reincorporated into the biosphere. Biomass material contains 40-45% carbon by weight, with the remainder hydrogen (6.7%) and oxygen (53.3%) (Bowen, 1979). Nitrogen accounts for between 0.3 to 3.8%, and sulfur for between 0.1 to 0.9% depending on the nature of the biomass material (Bowen, 1979). The nature and amount of the combustion products depend on the characteristics of both the fire and the biomass material burned. Hot, dry, fires with a good supply of oxygen produce mostly carbon dioxide with little CO, CH4, and NMHCs. The flaming phase of the fire approximates complete combustion, while the smoldering phase approximates incomplete combustion, resulting in greater production of CO, CH4, and .NMHCs. The percentage production of CO2, CO, 2 ------- CH4, NMHCs, and carbon ash during the flaming and smoldering phases of burning based on laboratory studies is summarized in T&ble 1 (Lobert et al., 1991). Typically for forest fires, the flaming phase lasts on the order of an hour or less, while with the smoldering phase may last up to a day or more, depending on the type of fuel, the fuel moisture content, wind velocity, topography, etc. For savanna grassland and agricultural waste fires, the flaming phase lasts a few minutes and the smoldering phase lasts up to an hour. Emission Ratios The total mass of the carbon species (CO2 + CO + CH4 + NMHCs + particulate carbon) M(C) is related to the mass of the burned biomass (M) by M(C) = f x M, where f = mass fraction of carbon in the biomass material, i.e., 40-45%. To quantify the production of gases other than. C02, we must determine the emission ratio (ER) for each species. The emission ratio for each species is defined as ER=^ <2> where AX is the concentration of the species X produced by biomass burning, and AX = X* - X and X* is the measured concentration of X in the biomass burn smoke plume and X is the background (out of plume) atmospheric concentration of the species, and ACO2 is the concentration of CO2 produced by biomass burning, ACO2 = CO 2 — CO2, where CO2 is the measured concentration in the biomass burn plume, and CO2 is the background (out of plume) atmospheric concentration of CO2. In general, aE species emission factors are normalized with respect to C02, as the concen- tration of CO2 produced by biomass burning may be directly related to the amount of biomass material burned by simple stoichiometric considerations as discussed earlier. Furthermore, the measurement of CO2 in the background atmosphere and in the smoke plume is a relatively simple and routine measurement. For the reasons outlined above, it is most convenient to quantify the combustion products of biomass burning in terms .of the species emission ratio (ER), i.e., the exoess species production ------- (i.e., above background) normalized with respect to the excess CO2 production (i.e., above background). Measurements of the emission ratio for CH4 and CO normalized with respect to CO2 for diverse ecosystems (i.e., wetlands, chaparral, and boreal) for different phases of burning, i.e., flaming and smoldering phases and combined flaming and smoldering phases, called "mixed" are summarized in Table 2. Measurements of the emission ratio for CH4 normalized with respect to CO2 for various burning sources in tropical Africa are summarized in Table 3. Some researchers present their biomass burn emission measurement in the ratio of grams of carbon in the gaseous and particle combustion products to the mass of the carbon in the biomass fuel in kilograms. Average emission factors for CO2, CO, and CH4 in these units for diverse ecosystems are summarized in Table 4 and emission factors for CO2, CO, CH4, NMHCs and carbon ash in terms of percentage of fuel carbon based on laboratory experiments are summarized in Tkble 5. Inspection of Tables 2-5 indicates that there is considerable variability in both the emission ratio and emission factor for carbon species as a function of ecosystem burning and the phase of burning (i.e., flaming or smoldering). A recent compilation of C02-normalized emission ratios for carbon species is listed in Table 6. This table gives the range for both field measurements and laboratory studies and provides a "best guess." Emission of Methane Once the mass of the burned biomass (M) and the species emission ratios (ER) are known, the gaseous and particulate species produced by biomass burn combustion may be calculated. The mass of the burned biomass (M) is related to the area (A) burned in a particular ecosystem by the following relationship (Seiler and Crutzen, 1980): M = AxBxox/3 (3) where B is the average biomass material per unit area in the particular ecosystem (g/m^), a is the fraction of the average above-ground biomass relative to the total average biomass B, and /? is the burning efficiency of the above-ground biomass. Parameters B, a, and 0 vary with the 4 ------- particular ecosystem under study and are determined by assessing the total biomass before and after burning. The total area burned during a fire may be assessed using satellite data. Recent reviews have considered the extent and geographical distribution of biomass burning from a variety of space platforms: astronaut photography (Wood and Nelson, 1991), the NOAA polar orbiting Advanced Very High Resolution Radiometer (AVHRR) (Brustet et al., 1991a; Cahoon et al., 1991; and Robinson, 1991a; and 1991b), the Geostationary Operational Environmental Satellite (GOES) Visible Infrared Spin Scan Radiometer Atmospheric Sounder (VAS) (Menzel et al., 1991); and the Landsat Thematic Mapper (TM) (Brustet et al., 1991b). Hence, the contribution of biomass burning to the total global budget of methane or any other species depends on a variety of ecosystem and fire parameters, including the particular ecosystem that is burning (which determines the parameters B, a, and 0), the mass consumed during burning, the nature of combustion (complete vs. incomplete), the phase of combustion (flaming vs. smoldering), and knowledge of how the species emission factors (EF) vary with changing fire conditions in various ecosystems. The contribution of biomass burning to the global budgets of any particular species depends on precise knowledge of all these parameters. While all these parameters are known imprecisely, the largest uncertainty is probably associated with the total mass (M) consumed during biomass burning on an annual basis (and there are large year-to-year variations in this parameter!). The total mass of burned biomass material on an annual basis according to source of burning is summarized in Table 7 (Seller and Crutzen, 1980; Haoet al., 1990; Crutzen and Andreae, 1990; and Andreae, 1991). The estimate for carbon released of 3940 Tg/yr includes all carbon species produced by biomass combustion (CO 2 + CO CH4 -f- NMHCs + particulate carbon). About 90% of the released carbon is in the form of C02 (about 3550 Tg/yr). Knowledge of the C02-normalized emission ratio for CH4 coupled with information on the total production of CO2 due to biomass burning allows us to estimate the total global production of CH4 due to biomass burning on an annual basis. Field measurements and laboratory studies 5 ------- indicate that the emission ratio for CH4 is in the range of 6.2 to 16 grams of carbon in the form of CH4 (C(CH4)) per kilogram of carbon in the form of CO2 (C(C02)) (see Table 6), which corresponds to a CH4 to CO2 emission ratio in the range of 0.62 to 1,6%. Using a "best guess" of 1.1% and assuming that biomass burning produces about 3550 Tg/yr of C(C02), then the global annual production of CH4 due to biomass burning is in the range of 21.7 to 56 Tg/yr of C(CH4), with a "best guess" of 38.9 Tg/yr of C(CH4). The production of CH4 by different burning sources on a global scale is summarized in the fourth column of Table 7. A detailed study using a chemical transport model with a l°x 1° spatial grid yielded an annual average CH4 production due to biomass burning of 63.4 Tg (Taylor and Zimmerman, 1991), which is somewhat larger than the maximum CH4 production value calculated here of 56 Tg(C)/yr. Assuming that the total annual global production of CH4 from all sources is about 380 Tg/C (Cicerone and Oremland, 1988), then 21.7 to 56 Tg(C) of CH4 corresponds to between 6% and 15% of the global emissions of CH4, while the calculations of Tkylor and Zimmerman (1991) suggest that biomass burning produces about 17% of the global emissions of CH4. Considering all of the uncertainties in these calculations, there is very good agreement between these two estimates. While biomass burning may not be the overwhelming source of CH4 on a global scale, there are measurements that indicate it may be the dominant source in tropical Africa. Delmas et al. (1991) have studied the CH4 budget of tropical Africa. They considered the emission of CH4 from biogenic processes in the soil and from biomass burning. They found that the dry African savanna soil is always a net sink for CH4. They measured an average soil uptake rate for atmospheric CH4 of 2 x 1010 CH4 molecules cm"^ s-1. They calculated the production of CH4 (and CO2) due to biomass burning and found that biomass burning supplies about 9.22 Tg(C)/yr of CH4 (and 3750 Tg(C)/yr of CO2) (see Table 8). Hence, in tropical Africa, biomass burning, not biogenic emissions from the soil control the CH4 budget. In addition to the direct production of CH4 by the combustion of biomass material, there is recent evidepce to suggest that burning stimulates biogenic emissions of CH4 from wetlands ------- (Levine et al., 1990). Flux chamber measurements indicate higher fluxes of CH4 from wetlands following burning (Levine et al., 1990). It has been suggested that combustion products, carbon dioxide, carbon monoxide, acetate, and formate entering the wetlands following burning are used by methanogenic bacteria in the metabolic production of CH4 (Levine et al., 1990). While it does not appear that biomass burning is a significant global source of CH4 at the present time, the situation may change in the future (see section on Historic Changes in Biomass Burning). At the present time, biomass burning is indeed a significant global source of several important radiatively and chemically active species. Biomass burning may supply 40% of the world's Annual gross production of CO2 or 26% of the world's annual net production of CO2 (due to the burning of the world's forests) (Seiler and Crntzen, 1980; Crutzen and Andreae, 1990; Hao et al., 1990; Levine, 1990; Andreae, 1991; and Houghton, 1991). Biomass burning supplies 32% of the world's annual production of CO; 24% of the NMHCs, excluding isoprene and terpenes; 21% of the oxides of nitrogen (nitric oxide and nitrogen dioxide); 25% of the molecular hydrogen (H2); 22% of the methyl chloride (CH3CI); 38% of the precursors that lead to the photochemical production of tropospheric ozone; 39% of the particulate organic carbon (including elemental carbon); and more than 86% of the elemental carbon (Andreae, 1991; Levine, 1990). Historic Changes in Biomass Burning It is generally accepted that the emissions from biomass burning have increased in recent decades, largely as a result of increasing rates of deforestation in the tropics (Houghton, 1991). Houghton (1991) estimates that gaseous and particulate emissions to the atmosphere due to deforestation have increased by a factor of 3 to 6 over the last 135 years. He also believes that the burning of grasslands, savannas, and agricultural lands has increased over the last century because rarely burned ecosystems, such as forests, have been converted to frequently burned ecosystems, such as grasslands, savannas, and agricultural lands. In Latin America, the area of grasslands, pastures, and agricultural lands increased by about 50% between 1850 and 1985 (Houghton, 1991). The same trend is true for South and Southeast Asia (Houghton, 1991). In summary, Houghton (1991) estimates that total biomass burning may have increased by about 7 ------- 50% since 1850. Most of the increase results from the ever-increasing rates of forest burning, with other contributions of burning (grasslands, savannas, and agricultural lands) having increased by 15% to 40% (Houghton, 1991). The increase in biomass burning is not limited to the tropics. In analyzing 50 years of fire data from the boreal forests of Canada, the U.S.S.R., the Scandinavian countries, and Alaska, Stocks (1991) has reported a dramatic increase in area burned in the 1980s. The largest fire in the recent past destroyed more than 12 million acres of boreal forest in the Peoples Republic of China and Russia in a period of less than a month in May, 1987 (Cahoon et al., 1991). The historic data indicate that biomass burning has increased with time and that the production of greenhouse gases from biomass burning has increased with time. Furthermore, the bulk of biomass burning is human-initiated. As greenhouse gases build up in the atmosphere and global warming begins, our planet will become warmer and drier, as predicted by most general circulation models. The warmer and drier conditions are conducive to an enhanced frequency of fires. The enhanced frequency of fires may be an important positive feedback in a warming Earth. However, it has been suggested that the bulk of biomass burning worldwide may be significantly reduced (Andrasko et al., 1991). Policy options for mitigating biomass burning have been developed by Andrasko et al. (1991). For mitigating burning in the tropical forests, where much of the burning is aimed at land clearing and conversion to agricultural lands, policy options include the marketing of timber as a resource and improved productivity of existing agricultural lands to reduce the need for conversions of forests to agricultural lands. Improved productivity will result from the application of new agricultural technology, i.e., fertilizers, etc. For mitigating burning in tropical savanna grasslands, animal grazing could be replaced by stall feeding since savanna burning results from the need to replace nutrient-poor tall grass with nutrient-rich short grass. For mitigating burning on agricultural lands and croplands, incorporate crop wastes into the soil, instead of burning, as is the present practice throughout the world. The crop wastes could also be used as fuel for household heating and cooking rather thai} cutting down and destroying forests for fuel- as is presently done. 8 ------- Uncertainties and Future Research The construction of a global emissions inventory for methane from biomass burning must account for the high degree of variability of these emissions in both space and time. Biomass burning exhibits strong seasonal and geographic variations. As shown earlier, methane emissions from biomass burning are highly dependent on the type of ecosystem being burned, which determines the total amount of biomass consumed and the extent of flaming and smoldering phases during combustion. The calculations by Taylor and Zimmerman (1991) go a long way towards deriving a global inventory in that they have simulated the variability of biomass burning. They basically scaled the burning rate inversely with precipitation as global data sets are currently not available. Satellite techniques, when they are developed, offer a promising way to obtain global coverage. Taylor and Zimmerman (1991) also used a constant emission ratio in their calculations since measurements of the emission ratio for methane are lacking for many different ecosystems. While some data exist for mid-latitude ecosystems, measurements are needed to better define the contributions from burning tropical forests and savannas. In addition, airborne measurements are limited to the outer edges of biomass burn plumes so little is known about variability across the plume. The use of long path remote measurements across plumes is also planned for the future. At the present time, while biomass burning may be an overwhelming regional or continental- scale source of CH4 (i.e., tropical Africa), it is not a major global source of CH4 (although it is a significant global source of CO2, CO, NMHCs, H2, tropospheric O3, and particulate carbon). However, this situation may change if biomass burning continues to increase at the rate it has been increasing over the last century. It is appropriate to conclude this chapter with an observation of fire historian, Stephen Pyne (1991): "We are uniquely fire creatures on a uniquely fire planet, and through fire the destiny * of humans has bound itself to the destiny of the planet." 9 ------- Table 1. Percentage of Production of C02, CO, CH4) and NMHCs During Flaming and Smoldering Phases of Burning Based on Laboratory Experiments (Lobert et al., 1991). Percentage in burning stage (%) Flaming Smoldering C02 63 17 CO 16 84 CH4 27 73 NMHCs 33 67 ------- Table 2. Emission Ratios for CO, CH4, and NMHCs for Diverse Ecosystems (In units of AX/ACO2, in percent) (Cofer et ah, 1991). Wetlands Flaming Mixed Smoldering Chaparral Flaming Mixed Smoldering Boreal Flaming Mixed Smoldering CO 4.7 ± 0.8 5.0 ± 1.1 5.4 ± 1.0 5.7 ± 1.6 5.8 ± 2.4 8.2 ± 1.4 6.7 ± 1.2 11.5 ± 2.1 12.1 ± 1.9 CH4 0.27 ±0.11 0.28 ± 0.13 0.34 ±0.12 0.55 ± 0.23 0.47 ± 0.24 0.87 ± 0.23 0.64 ± 0.20 1.12 ± 0.31 1.21 ± 0.32 NMHCs 0.39 ± 0.17 0.45 ± 0.16 0.40 ± 0.15 0.52 ± 0.21 0.46 ±0.15 1.17 ± 0.33 0.66 ± 0.26 1.14 ± 0.27 1.08 ± 0.18 ------- Table 3. Emission Ratio for CH4 for Different Fires In Tropical Africa (In units of ACH4/ACO2 in percent (Delmas et al., 1991) Type of Combustion Emission Ratio = ACH4/ACO2 Natural savanna bushfire Forest fire Emissions from traditional charcoal oven Firewood Charcoal Mean 0.28 ± 0.04 1.23 ± 0.60 12.06 ± 2.86 1.79 ± 0.81 0.14 Range 0.23- 0.34 0.56- 2.22 6.7 - 14.2 1.04 - 3.2 ------- Table 4. Average Emission Factors for CO2, CO, and CH4 for Diverse Ecosystems (In units of grams of combustion product carbon to kilograms of fuel carbon) (Eadke et al., 1991). Chaparral-1 Chaparral-2 Pine, Douglas fir and brush Douglas fir, true fir and hemlock Aspen, paper birch, and debris from jack pine Black sage, sumac, and chamise Jack pine, white and black spruce "Chained" and herbicidal paper birch and poplar "Chained" and herbicidal birch, polar and mixed hardwoods Debris from hemlock, deciduous and Douglas fir Overall average C02 CO 1644 ± 44 74 ± 16 1650 ±31 75 ± 14 1626 ± 39 106 ± 20 1637 ± 103 89 ± 50 1664 ± 62 82 ± 36 1748 ± 11 34 ± 6 1508 ± 161 175 ± 91 1646 ± 50 90 ± 21 1700 ± 82 55 ± 41 1600 ± 70 83 ± 37 1650 ± 29 83 ± 16 CH4 2.4 ± 0.15 3.6 ± 0.25 3.0 ± 0.8 2.6 ± 1.6 1.9 ± 0.5 0.9 ± 0.2 5.6 ± 1.7 4.2 ± 1.3 3.8 ± 2.8 3.5 ± 1.9 3.2 ± 0.5 ------- Table 5. Emission Factors for CO2, CO, CH4, and NMHC and Ash Based on Laboratory Experiments (In % of Fuel Carbon) (Lobert et al., 1991). Mean Range co2 82.58 49.17 - 98.95 CO 5.73 2.83 - 11.19 ch4 0.424 0.14- 0.94 NMHC (as C) 1.18 0.14- 3.19 Ash (as C) 5.00 0.66 - 22.28 Total sum C 94.91 ------- Table 6. C02-Normalized Emission Ratios for Carbon Species: Summary of Field Measurements and Laboratory Studies (In units of grams of species per kilograms of C in CO2) (Andreae, 1991). Field measurements Laboratory studies "Best guess" CO 6.5 - 140 59 - 105 100 CH4 6.2-16 11-16 11 NMHCs 6.6-11.0 3.4-6.8 7 Particulate organic carbon (including elemental carbon) 7.9 - 54 20 Element carbon (black soot) 2.2 -16 5.4 ------- Table 7. Global Estimates of Annual Amount of Biomass Burning and the Resulting Release of Carbon to the Atmosphere (Seiler and Crutzen, 1980; Crutzen and Andreae, 1990; Hao et al., 1990; and Andreae, 1991). Source of Biomass burned Carbon released CH4 released burning (Tg/yr)1 (Tg(C)/yr)2 (Te(C)/yr)3 Savanna 3690 1660 16.4 Agricultural waste 2020 910 9.0 Fuel wood 1430 640 6.3 lYopical forests 1260 570 5.6 Temperature and boreal forests 280 130 1.3 Charcoal 21 30 0.3 World total 8700 3940 38.9 1 1 Tg (teragram) = 106 metric tons — 1012 grams. 2 Based on a carbon content of 45% in the biomass material. In the case of charcoal, the rate of burning has been multiplied by 1.4. 3 Assuming that 90% of the carbon released is in the form of CO2 and that the "best guess" emission ratio of CJi« to COj is 1.1% (see Table 5). ------- Table 8. Total Emissions of CO2 and CH4 from the Burning of Biomass in Tropical Africa C02 CH4 Biomass Emission Emission CO2 CH4 Source Burned* Factor^ Factor^ Emissions'* Emissions'* Savanna 2.52 1370 1.65 3.45 4.14 bushfires Forest fires 0.13 957 6.94 0.12 0.90 Firewood 0.12 957 5.42 0.11 0.65 burning Charcoal 0.11 641 21.0 0.07 2.31 production Total 2.88 3.75 9.22 1 Biomass burned in units of Gigagram = 103 Tg = 109 metric tons — 1015 grams 2 Emission factors units of g/kg 3 CO2 emissions in units of Gigagram/yr * CH* emissions in units of Teragram/yr 17 ------- References Andrasko, K. J.; Ahuja, D. R.; Winnett, S. M.; and Tirpak, D. A., 1991. Policy Options for Managing Biomass Burning to Mitigate Global Climate Change. Global Biomass Burning: Atmospheric. Climatic, and Biospheric Implications (J. S. Levine, editor), The MIT Press, Cambridge, Massachusetts, 445-456. Andreae, M. O., 1991. 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Stocks, B. J., 1991. The Extent and Impact of Forest Fires in North Circumpolar Countries. Global Biomass Burning: Atmospheric. Climatic, and Biospheric Implications (J. S. Levine, ed- itor), The MIT Press, Cambridge, Massachusetts, 197-202. Wood, C. A.; and Nelson R., 1991. Astronaut Observations of Global Biomass Burning. Global Biomass Burning: Atmospheric. Climatic, and Biospheric Implications (J. S. Levine, ed- itor), The MIT Press, Cambridge, Massachusetts, 29-40. T&ylor, J. A.; and Zimmerman, P. R., 1991. Modeling TV ace Gas Emissions from Biomass Burning. Global Biomass Burning: Atmospheric. Climatic, and Biospheric Implications (J. S. Levine, ed- itor), The MIT Press, Cambridge, Massachusetts, 345-350. 21 ------- TECHNICAL REPORT DATA 1 REPORT NO EPA/600/A-92/221 2. 3' PB9 3- 1 1982J4 4. TITLE AND SUBTITLE Biomass Burning and the Production of Methane 5.REPORT DATE 6.PERFORMING ORGANIZATION CODE 7. AUTHOR(S) Joel S. Levine and Wesley R. Cofer III Joseph P Pinto 8.PERFORMING ORGANIZATION REPORT NO. 9 PERFORMING ORGANIZATION NAME AND ADDR£SS NASA Langley Research Center, Hampton, Va. Atmospheric Research and Exposure Assessment Laboratory, U.S Environmental Protection Agency Research Triangle Park, N.C. 27711 10.PROGRAM ELEMENT NO. 11. CONTRACT/GRANT NO. 12. SPONSORING AGENCY NAME AND ADDRESS Same as 9. 13.TYPE OF REPORT AND PERIOD COVERED 14. SPONSORING AGENCY CODE 15 SUPPLEMENTARY NOTES 16. ABSTRACT Biomass burning and its environmental implications have also become important research elements of the International Geosphere-Biosphere Program and the International Global Atmospheric Chemistry Project. The production of atmospheric methane (CH4) by biomass burning will be assessed. The production of methane and other gaseous and particle carbon species resulting from biomass burning will be outlined. Field measurements and laboratory studies to quantify the emission ratio of methane and other carbon species will be reviewed. The historic database suggests that global biomass burning is increasing with time and is controlled by human activities. Present estimates indicate that biomass burning contributes between about 20 to about 60 Teragrams per year of carbon in the form of methane to the atmosphere. This represents only 5 to 15% of the global annual emissions of methane. Measurements do indicate that biomass burning is the overwhelming source of CH4 in tropical Africa. However, if the rate of global biomass burning increases at the rate that it has been over the last few decades, then the production of methane from biomass burning may become much more important on a global scale in the future. 17. KEY WORDS AND DOCUMENT ANALYSIS a. DESCRIPTORS b.IDENTIFIERS/ OPEN ENDED TERMS c.COSATI 13 . DISTRIBUTION STATEMENT 19. SECURITY CLASS (This ReDort.1 21.NO. OF PAGES 24 20. 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