Natural combustion

Coal is a natural combustible rock composed of an organic heterogeneous substance contaminated with variable amounts of inorganic compounds. Most coal reserves are concentrated in North America, Europe, and China. 

Owing to the high diffusivity, low viscosity, and unique chemical nature, combustibility of hydrogen is somewhat different than the other fuels. Various combustibility properties are described in the following ... 

Polycyclic aromatic hydrocarbons (PAHs, sometimes also called polynuclear aromatics, PNA) are a hazardous class of widespread pollutants. The parent structures of the common PAHs are shown in Fig. 4 and the alkylated homologs are generally minor in combustion emissions. PAHs are produced by all natural combustion processes (e.g., wild fires) and from anthropogenic activity such as fossil fuels combustion, biomass burning, chemical manufacturing, petroleum refining, metallurgical processes, coal utilization, tar production, etc. [6,9,15,18, 20,24,131-139]. 

Sources. B[major component of polynuclear aromatic hydrocarbons, also known as polycyclic aromatic hydrocarbons, and is usually bound to small particulate matter present in urban air, industrial and natural combustion emissions, and cigarette smoke. 

The Pettaquamscutt data are from a sufficiently deep core to allow us to assess the PAH burden prior to 1900. The PAH concentrations are at a low and constant level ( <200 ppb) for the 50 yr previous to the turn of the century. This level may be indicative of PAH from natural combustion processes such as forest fires. Contributions from natural processes appear to be insignificant in areas or periods of high anthropogenic activity. 

Similarly, polychlorinated dioxins and furans form in both compost and sewage sludge (1), but the major congeners in both systems are heptachloro- and octa-chlorodibenzo-p-dioxins and their origin is not understood (2052-2056). Several studies have attempted to elucidate the importance of natural combustion events as a source of polychlorinated dioxins and furans (1), but recent reports indicate that forest fires may not be a significant source of these compounds (227, 2057) despite earlier suggestions to the contrary (1, 2058, 2059). Nevertheless, numerous studies (wood stoves, control bums, etc.) clearly demonstrate that the combustion of wood... 

The key sources of CDD releases to air are from anthropogenic combustion processes and the production and use of chemicals contaminated with CDDs. Some evidence suggests that natural combustion processes (e.g., forest fires or volcanic activity) may also be sources of CDDs, but to a much smaller extent. Toxics Release Inventory (TRI) data are not available for CDDs since CDD releases are not required to be reported (EPA 1995g). 

Polycyclic aromatic hydrocarbons are generated from anthropogenic or natural combustion processes, in addition to rapid transformation processes of biogenic precursors that occur in situ. 

The PAHs are substances mainly formed from incomplete combustion processes (e.g. pyrolysis) of petroleum and coal in connection with energy production, industrial activities, transport, etc. but also from graphite electrodes in industrial processes, from wood preservatives made up from coal tar and from products such as car tyres. The occurrence of PAHs is widespread, although often more or less concentrated to hot spots associated with anthropogenic activities. Of course, PAHs being products from combustion processes, are also formed in natural combustion processes such as forest fires, volcanic activities, etc. and they are... 

Domestic and natural combustion of coal, wood and other organic materials supply a steady source of PAHs. The environmental ubiquity of several aromatic representatives together with their procarcenogenic and mutagenic properties also created a great deal of interest in the formation of PAHs in fuel-rich flames as well as in the emission, occurrence and analysis of PAHs combined with aspects of metabolism, deoxyribonucleic acid (DNA)-adduct formation, biomarkers, exposure and risk assessment [23]. 

From these data, it appears that in areas where PAH concentrations are high, such as the northeastern United States, one can associate the PAH mixtures found with both anthropogenic activity and combustion. There is a possibility that natural combustion, such as forest fires, could contribute to the more remote areas (Maine soil, for example). The contribution of PAH to the offshore sediments (Samples 3, 4, 9) by forest fires should be minimal compared with the anthropogenic contribution because of the proximity of these sites to urban areas and their distance from large forested areas. 

The low pressure environment required for natural combustion of these rocks makes them an extreme case where each specific metamorphic reaction will have taken place at as low a temperature as possible because the volatilization reactions have positive P-T slopes. Furthermore, exchange is likely with air or groundwater, which are involved as oxidants. Values of 5 C in Mottled Zone calcites cannot be explained by volatilization. Low values of 5 C, and the unusual slope in Figure 4, reflect high temperature exchange of carbonates with bituminous matter (Kolodny and Gross 1974 Matthews and Kolodny 1978). 

From this discussion, it follows that characterisation of the physical and chemical environment of the reactive sites of a particle on a molecular level will be required to better understand its fate in the atmosphere. Exposure experiments should be continued, not only using simplified model systems, but also using natural combustion related aerosols of various particle size and matrix composition. Filter exposures of particulate matter should yield more detailed information on sampling artifacts. Exposure of aerosol particles to gaseous compounds should be tried in a static or... 

At the temperature of natural combustion, at about 1000 °C, the oxidation reactions are predominant. 

The lack of knowledge about the behavior of fluoro chemicals in water treatment also includes incomplete understanding of their behavior in the enviromnent, because some processes discussed as water or waste treatment techniques are related to chemical and physical processes in nature (combustion, UV-photolysis, formation of reactive species (e.g., ozone, hydroxyl radicals, and sulfate radical anions)) as well as biological processes. The knowledge about the fate of fluorinated chemicals in the environment can also contribute to improve treatment technologies. 

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