Burning biomass

Biomass burning is known to be a significant source of many air pollutants, as estimated from a large number of measurements (reviewed by Andreae and Merlot 2001, Simoneit 2002, and Koppman et al. 2005). Biomass burning eaused by fires 

Production of gases from wood heating (called dry distillation) was known since ancient times to produce charcoal and tar. Methanol was first produced as a by-product in the manufacture of charcoal through the destructive distillation of wood, with yields of 12-24 L p er ton of wood. With the begimung of the nineteenth century, wood distillation became a manufacturing process. 

Although some care must be taken when determining acetonitrile concentrations from the ion intensity at mJz 42, acetonitrile is still the dominant VOC contributing to that mass channel. From the PTR-MS airborne measurements of acetone, methanol, PAN and acetonitrile over the Mediterranean Sea during the Mediterranean Intensive Oxidants Study 

Erom both airborne and ground-based field campaigns during the 2004 Amazon dry season as part of the Tropical Forest and Fire Emissions Experiment (TROFFEE), Yokelson et al. quantified the volatile emissions from a pristine tropical forest and several plantations [168]. In addition to this the emissions, fuel consumption and fire ecology of tropical deforestation fires were also quantified. About 80% of the mass of non-methane organic compounds emitted by the tropical deforestation fires were found to be associated with reactive, oxygenated VOCs. Recommended values for the emission factors for most of the major compounds released by deforestation fires globally were provided. 

As part of the Megacity Initiative Local and Global Research Observations (MILAGRO) project, a comprehensive airborne study by Yokelson et al. reported the first detailed field measurements of biomass emissions in the Northern Hemisphere tropics [169]. Volatile emissions were measured from 20 deforestation and crop residue fires on the Yucatan peninsula. This included two trace gases which are often considered to be useful as indicators of biomass burning. One we have discussed before, namely acetonitrile, and the other is hydrogen cyanide. A variety of instrumentation was co-deployed for this investigation (FTIR spectroscopy, GD-FID, a GC-Trace Analytical Reduction Gas Detector, fluorescence and chemiluminescence instruments and various other spectrometers). PTR-MS was used to monitor methanol, acetonitrile, acetaldehyde, acetone, methyl ethyl ketone, methyl propanal, hydroxyacetone plus methyl acetate, benzene and 13 other volatile species. 

Although the use of PTR-MS in the environmental science area has been primarily used in field campaigns, it has also been successfully used in laboratory and enclosed environments for VOC emission investigations of importance to atmospheric chemistry. Laboratory studies, which are divorced from the complex and uncontrolled chemical environment of the atmosphere, can considerably improve our understanding of the reaction processes occurring within the drift tube of the PTR-MS. In particular, the investigation of individual 

The first of these studies not only reported the potential use of E/N dependences, but also presented details on the use of collision-induced processes in a quadrupole ion trap to differentiate monoterpenes. Although it was possible to identify specific monoterpenes based on collision-induced dissociation, the identification of several monoterpenes in a complex mixture would still be difficult. Misztal et al. also investigated the effect of varying E/N over a limited range of approximately 100-140 Td in a bid to extend the selectivity of PTR-MS this was specifically attempted in order to discriminate individual monoterpenes. By using a detailed analysis of fragmentation pathways the researchers have proposed that PTR-MS could be used to determine individual monoterpenes in a complex chemical mixture. 

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Certainly, photochemical air pollution is not merely a local problem. Indeed, spread of anthropogenic smog plumes away from urban centers results in regional scale oxidant problems, such as found in the NE United States and many southern States. Ozone production has also been connected with biomass burning in the tropics (79,80,81). Transport of large-scale tropospheric ozone plumes over large distances has been documented from satellite measurements of total atmospheric ozone (82,83,84), originally taken to study stratospheric ozone depletion. 

Concerns over atmospheric methane as a greenhouse gas and the large contribution of biomethanogenesis as a source of this gas make it important to determine the relative significance of various components of this activity. A recent paper (8) summarized estimates (28-30) of source fluxes of atmospheric methane based on several carbon isotopic studies and presented new data on natural sources and biomass burning. These data (Table III) show that of a total flux of 594 million tons (Tg) per year, 83% is produced via biomethanogenesis from a combination of natural (42%) and anthropogenic (41%) sources. 

Introduction The Global Extent of Deforestation and Biomass Burning... 

Deforestation, Biomass Burning and the Biogeochemical Balance of Forests... 

Figure 1. Generalized nutrient balance of ecosystems in the intervals between disturbance events. Natural disturbances such as wildfires, hurricanes, and floods as well as anthropogenic disturbances such as deforestation and biomass burning can dramatically influence nutrient inputs, internal cycles, and ecosystem outputs (losses).

Soil physical properties most likely to be altered by biomass burning are soil structure, soil wettability, and clay mineralogy (Table HI) (43). The destruction of organic matter results in losses of soil structure, increases in bulk density, diminished aggregate stability and decreases in macropore space (44). 

Nutrient Losses Associated With Biomass Burning. Nutrient losses associated with slash fires occur through volatilization and convective losses of ash. Elements with low temperatures of volatilization (e.g. N, K, S, and some organic forms of P) will be lost in the highest quantities (Table III) (57). Conversely, Ca and Mg have volatilization temperatures higher than that recorded during most vegetation fires. Almost all fire-induced losses of these elements are due to particulate transfer by convective processes. 

Much of the surface soil erosion and hence nutrient loss occurs when deforestation and biomass burning removes and/or consumes the organic materials that protect the soil surface. Significant losses may occur by dry ravel or overland water erosion associated with precipitation events. Under a shifting cultivation system in a tropical deciduous forest ecosystem in Mexico, Maass et al. 61) reported first year losses of N, P, K, and Ca were 187, 27, 31, and 378 kg ha" respectively. In contrast, losses in adjacent undisturbed forests were less than 0.1 kg ha for all nutrients except Ca (losses were 0.1-0.5 kg ha for Ca). 

Figure 7. Another temperate coniferous forest site of the Pacific Northwest, USA following clearcutting and slash burning. Severe levels of deforestation result in large quantities of nutrient losses through wood export, biomass burning and accelerated erosion and leaching losses. (Photograph is by courtesy of Dian L. Cummings. ...

Global atmospheric CO2 has increased by approximately 25% since the industrial revolution (circa 1850). The primary source is the combustion of fossil fuels (72). However, recent estimates indicate that biomass burning may comprise 40% of... 

Tropical forests and savannas are the primary source of C emissions that originate from biomass burning (73, 75). However, temperate forests are also sources of atmospheric carbon. Harmon et al. (77) reported that conversion of primary temperate forests to younger, second-growth forests lead to increases in atmospheric CO2 levels, due to losses in long-term carbon storage within these forests. They ascertained that timber exploitation of 5 million hectares of primaiy forests in the Pacific Northwest of North America during the past century has resulted in the addition of 1,500 Tg of C to the atmosphere. 

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