Pollution sources stack height

The effects of local air contaminants on forests have stabilized in the vicinity of existing point-sources of air pollutants. In numerous cases improvements have been achieved. In the case of sulfur dioxide, increasing stack heights and use of scrubbers have reduced ground level concentrations of sulfur dioxide. New industries and electrical plants in the U.S. can employ the best available air quality technology. 

Area sources include the multitude of minor sources with individually small emissions that are impractical to consider as separate point or line sources. Area sources are typically treated as a grid network of square areas, with pollutant emissions distributed uniformly within each grid square. Area source information required are types and amounts of pollutant emissions, the physical size of the area over which emissions are prorated and representative stack height(s) for the area. 

Much more detailed studies were carried out by Doolgindachbaporn (1995) and Ross et al (1998) for the Moe Moh valley, the relatively small area in Northern Thailand were the Mae Moh Power Plant is located. The resolutions were selected to be in the range of 5 to 10km cells. Differing in some details, these models indicate the area of the most polluted zone to be about 100 km. Similar pollution areas from individual sources with stack heights of 75-125 m, were shown for many other regions and reviewed in workshop reports on HM deposition (Pacina et al, 1993 de Leeuw, 1994, EMEP/MSC-E, 1996). 

National Emissions Data System NEDS EPA Public c Emissions data on the pollutants for which there are Primary Ambient Air Standards are collected from about 75000 point sources and 3200 area sources. Data are also included on SIC Code, and such modeling parameters as stack height and diameter, emissions rate, and temperature... 

The environmental effects of pollutants and wastes have traditionally been confronted with actions at the immediate vicinity level. A typical example involves the emissions resulting from fossil fuel burning in industrial and power plants, where taller stacks were built in the past to disperse pollutants in the air (mainly sulfur oxides) in a more efficient way. However, it is now recognized that these oxides can have important effects even in regions far away from the emission source due to environmental transport phenomena. Consequently, increasing the height of the stacks did not solve the problem. 

A second point concerning the subject of how much local sources Interfere with precipitation concerns the effect of the emission height. This came up earlier tdien we were talking about Sudbury. I had to do a few sums first to make sure of my ground, but In the case of a tall stack Injecting Into the free atmosphere above the mixed layer, pollutants might remain there for a considerable period. At this latitude radioactive fallout studies Indicate residence times of as much as ten days. But a cloud gets much of Its air from the mixed layer. 

Transport involves the mean wind speed and direction. Dispersion is produced primarily by atmospheric turbulence and is discussed in more detail below. Transformations of the pollutants are due to chemical reactions, deposition, and interactions with liquid water. These constitute separate problems treated elsewhere. Most air pollution arises from continuous emitting sources, such as stacks or highways. They may be groimd or elevated sources. An important parameter in the determination of concentration is the effective source height, which is the sum of physical source height and plume rise. 

Taller and taller smokestacks were built in order to disperse emissions as far as possible from the source. ("The solution to pollution," one motto put it, "is dilution.") The height of the tallest smokestack in the United States doubled since the 1950s and the average height of smokestacks tripled. Ironically, the Clean Air Act of 1970 encouraged the construction of ever-taller smokestacks tall stacks enabled more pollution to be emitted without exceeding ground-level limits. Tall stacks thus became a substitute for pollution control. As a result, pollution was carried far beyond cities and industrial centers to the once-pristine countryside, and even further, beyond national boundaries. The whole of eastern North America and western Europe became the acid equivalent of the proverbial smoke-filled room. Acid rain was transformed from a local, urban problem into an international threat. 

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