Gaseous pollutants

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  • Environmental toxicology is the study of the impacts of pollutants upon the structure and function of ecological systems. For the purposes of this text, the emphasis will be upon ecological structures, from the molecular to the individual organism to the community and the ecosystem. The broad scope of environmental toxicology requires a multidisciplinary approach of a variety of specialists.

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  • Analysis and abatement of air pollution involve a variety of technical disciplines. Formation of the most prevalent pollutants occurs during the combustion process, a tightly coupled system involving fluid flow, mass and energy transport, and chemical kinetics. Its complexity is exemplified by the fact that, in many respects, the simplest hydrocarbon combustion, the methane-oxygen flame, has been quantitatively modeled only within the last several years.

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  • Since the Second World War, and especially since the publication of Rachel Carson’s Silent Spring in 1962, there has been growing concern about contamination of the environment by “man-made” chemicals. These chemicals may be present in industrial and municipal effluents, in consumer or commercial products, in mine tailings, in petroleum products, and in gaseous emissions. Some chemicals such as pesticides may be specifically designed to kill biota present in natural or agricultural ecosystems. They may be organic, inorganic, metallic, or radioactive in nature.

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  • 16 Membrane Separation 16.1 OVERVIEW Membrane separation has developed into an important technology for separating VOCs and other gaseous air pollutants from gas streams during the past 15 years. The first commercial application was installed in 1990, and more than 50 systems have been installed in the chemical process industry worldwide.1 The technology utilizes a polymeric membrane that is more permeable to condensable organic vapors, such as C3+ hydrocarbons and aromatics, than it is to noncondensable gases such as methane, ethane, nitrogen, and hydrogen.

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  • YẾU TỐ CƠ BẢN khí và chất gây ô nhiễm KHÍ Các khí độc được sản xuất trong quá trình đốt nhiên liệu và các quá trình hóa học khác có thể được loại bỏ bằng cách xử lý phá hoại, phân tán pha loãng hoặc sản phẩm phụ như thu hồi. Các con đường loại bỏ lựa chọn tại thời điểm hiện tại thúc đẩy chủ yếu bởi kinh tế, nhưng áp lực công cộng và nâng cao nhận thức của các vấn đề môi trường cũng ảnh hưởng đến sự lựa chọn.

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  • The use of industrially manufactured nitrogen (N) fertilizers increased rapidly in developed countries between 1960 and 1980. This facilitated a large increase in the production of feed and food grains (maize, wheat, and rice) per unit of cultivated land, but in some regions it also contributed to enrichment of surface and groundwater with various forms of nitrogen. Fertilizer, however, is not the only source of nitrogen that can cause contamination of surface waters.

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  • Airborne suspended particulate matter can be of primary origin, i.e. emitted directly into the atmosphere or of secondary origin, i.e. formed in the atmosphere from gaseous species by either homogeneous or heterogeneous chemical reactions. Due to these different emission sources, particles have different chemical composition and size distributions. Depending on their size, particles have a different potential to be transported over either long or short distances [1]. Primary particles can be produced from either natural or anthropogenic sources.

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  • DURING THE NINETEENTH CENTURY, when coal gas was used for street illumination, it was observed that trees in the vicinity of streetlamps defoliated more extensively than other trees. Eventually it became apparent that coal gas and air pollutants affect plant growth and development, and ethylene was identified as the active component of coal gas. In 1901, Dimitry Neljubov, a graduate student at the Botanical Institute of St.

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  • The solid product is a wet sludge of calcium sulfate which can be disposed of easily. So FGD does not eliminate pollution. What it does accomplish is to convert a big problem (emission of large volumes of air contaminated by harmful levels of gaseous SOx) into a small problem (collection and disposal of scrubber sludge). Dealing with the problem of air pollution is not cheap. An FGD system installed in a newly constructed power plant represents about one-third of the total cost of building the entire plant.

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  • In new unoccupied houses, the concentrations of formaldehyde and other VOCs of concern with respect to human health and comfort can be elevated relative to toxicity guidelines and odor thresholds (Hodgson et al., 2000). These gaseous pollutants derive from materials that are widely used to construct and to finish the interiors of houses (Hodgson et al., 2002).

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  • When technology was introduced to control air pollution by reducing emissions of particles, it was found that the gaseous emissions continued and caused problems of their own. Currently efforts to control both particulate and gaseous emissions have been partially successful in much of the developed world, but there is recent evidence that air pollution is a health risk even under these relatively favorable conditions.

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  • Although the main consideration of policy must be the reduction in pollution at source, there has been an increasing recognition that the biosphere is an important sink for many pollutants, with plant canopies being considered more effective than other land uses. Thus, the biosphere provides benefits additional to those associated directly with their aesthetic and wildlife characteristics. Plants facilitate the uptake, transport and assimilation or decomposition of many gaseous and particulate pollutants.

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  • Field data are being integrated into well-developed and tested models to better understand and characterize aerosol pollution in Mexico City. The spatial, temporal, size, and chemical characteristics of specific emissions sources are needed to allow their contributions to PM concentrations to be distinguished from each other and to provide accurate inputs to air quality models.

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  • Indoor exposures to toxic and irritating volatile organic compounds (VOCs) are of general concern. Residences are particularly important exposure environments for these compounds because people in the U.S.A. spend an average of 69 % of their time indoors at home (Klepeis et al., 2001). In addition, residential ventilation rates, which serve as the primary mechanism for removal of gaseous pollutants generated indoors, are relatively low. The median air change rate measured in the 1980s for a large number of houses in the United States was 0.

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  • Transportation involves the combustion of fossil fuels to produce energy translated into motion. Pollution is created from incomplete carbon reactions, unburned hydrocarbons or other elements present in the fuel or air during combustion. These processes produce pollutants of various species, including carbon monoxide, soot, various gaseous and liquid vapour hydro carbons, oxides of sulphur and nitrogen, sulphate and nitrate particulates, ash and lead.

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  • Unlike ozone, which has a specific chemical composition, airborne particles vary in size and composition depending on time and location. Although the components of particles may have common sources, the types and amounts of particles collected at any one time and location may be unique. To add to the problem, gaseous pollutants including ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide often are present in the atmosphere at the same time as are particles.

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  • These efforts have attenuated the emissions engendered by growth, but 24-hour PM10 (particulate matter with aerodynamic diameter less than 10 m) concentrations exceeding several hundred µg/m3 are still measured at many monitoring sites. 1,2 A persistent haze blankets the city, especially during winter, and there is great concern among residents and visitors about the effects of suspended particles on health. Aerosols that contribute to this visibility degradation are usually a combination of primary and secondary particles.

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  • Diesel engines, also known as CI engines, possess a wide field of applications as energy converters because of their higher efficiency. However, diesel engines are a major source of NOX and particulate matter (PM) emissions. Because of its importance, five chapters in this book have been devoted to the formulation and control of these pollutants. The world is currently experiencing an oil crisis. Gaseous fuels like natural gas, pure hydrogen gas, biomass-based and coke-based syngas can be considered as alternative fuels for diesel engines.

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