Sulfur dioxide environmental concern

The deleterious effect of sulfur dioxide and sulfites in domestic water is increased corrosivity owing to the lowered pH. However, oxidation of sulfite to sulfate in aqueous solutions uses dissolved oxygen, and lliis may retard corrosion. While llte oxichition of sulfite and sulfiirous acid to sulfate and sulfuric acid in the atmosphere is an environmental concern, this reaction is too... 

Concerns about the environmental effects of emissions resulting from the combustion of fossil fuels, particularly coal, continue to increase as the utilization of these fuels grows. The large amounts of sulfur dioxide and nitrogen oxides emitted into the atmosphere and the attempts to tie these fossil-fuel-derived pollutants directly to the undeniably difficult problem of acid rain have caused heated debates, numerous research studies, government actions, and serious efforts to reduce pollution. The issues are extremely complex, and our understanding of the origin, properties, behavior, and effects of these pollutants is incomplete. Often, theories are contradictory. 

Since the mid-1970 s, increasing interest has emerged in the environmental consequences of the large scale deposition of atmospheric contaminants. The deposition of acid-forming constituents, sulfate and nitrate, is of particular concern for potentially adverse ecological effects. These species derive from the oxidation of sulfur dioxide (SO ) and nitrogen oxides (NO and NO ). Over most if... 

Concern for the environment has resulted in moves to significantly reduce the noxious components in emissions when fuel oils are burned. Attempts are being made to minimize sulfur dioxide emissions and, as a consequence, a strategy to minimize the sulfur content of fuel oils has been implemented. Although typical diesel fuel oils have, in the past, contained 1 % or more of sulfur (expressed as elemental sulfur) by weight, environmental legislation in the United States has required that sulfur content of diesel fuel be less than 0.05% (11). These levels will be reduced to 15 ppm or less to protect new exhaust catalyst after-treatment devices. In Europe, various jurisdictions have moved to lower sulfur content. In Sweden, for example, taxation of higher sulfur, lower cetane fuels is elevated to reflect to their respective environmental cost (93). 

Humanity s major sources of energy are derived from fossil fuels, principally oil, gas, coal, and wood. The major combustion by-products of fossil fuel burning include sulfur dioxide (SO2), carbon dioxide (CO2), and nitric oxide (NO2), and partially oxidized hydrocarbons. The process of burning fossil fuels in thermal power plants, factories, homes, and motor vehicles emits enormous amounts of the aforementioned pollutants. The most important environmental concerns resulting from fossil fuel use are global climate change, acid rain, surface ozone, and partic-ulate-Zaerosol-bound toxins. 

A second concern was that under some conditions sulfur dioxide in exhaust could be emitted as sulfuric acid as a result of catalytic oxidation over the noble metal catalyst. To answer this concern General Motors conducted a 350-car test designed to simulate sulfate emissions on a busy expressway. The U.S. Environmental Protection Agency, other vehicle manufacturers, and several independent environmental monitoring organizations participated in the experiment. This experiment showed conclusively that ambient levels of sulfuric acid under this worse-case simulated exposure situation were far below threshold levels known to produce adverse health effects. 

There is currently great concern about the environmental effects of airborne sulfur dioxide. Although SO2 is released into the atmosphere from natural sources such as volcanoes, the majority (ca. 200 million tonnes per year) is man-made either from industrial processes or domestic use such as coal and oil burning. The long-term consequences of large-scale release of SO2 into the atmosphere are undoubtedly severe, and have been the subject of much public debate. The most objectionable aspect of the problem is that often the acid rain , which results from SO2, occurs hundreds of miles from the source. 

The introduction of advanced batteries based on lithium or on metal hydride technologies has not yet reached the point where they have created an environmental concern, but when their usage becomes more widespread they will introduce additional problems. In particular, lithium batteries containing thionyl chloride (TLV = 1 ppm) or sulfur dioxide (TLV = 2 ppm) and acetonitrile (TWA = 40 ppm) may create disposal problems not only because of their toxicity, but also... 

In the United States, the Occupational Safety and Health Administration (OSHA) is responsible for ensuring the safety of the environment within an industrial plant. Environmental problems caused by a facility that reaches beyond the fences of the facility become the concern of the EPA. Environmental problems can become lethal to human life if left uncontrolled. This is what happened in Donora, Pennsylvania in 1948 that resulted in the deaths of 20 people. Donora was situated in a low spot of the surrounding terrain. A meteorological temperature inversion blanketed the area for five days. Near Donora, a steel mill, sulfuric acid plant, and zinc smelter poured sulfur dioxide into the atmosphere. The weather inversion kept the sulfur dioxide close to the ground and people sickened and died. 

The inorganic constituents of coal are often expressed in the form of ash yield and sulfur content. It is, however, often necessary to express an inorganic constituent relative to environmental emissions, such as the amount of sulfur dioxide produced during combustion (Chapters 14 and 15). Furthermore, many of the elements that may be of environmental concern occur in the fly ash after coal combustion (Chapter 14) and, in the case of power plants using flue gas desulphurization (FGD) systens, in the FGD (or scrubber) by-products (Chapter 15). 

Environmental concerns and strict pollution legislation prompted action in the construction of up to date coal-fired boilers and adaptation of existing plants. At the present time, flue gas desulfurization is the only conventional method employed on a commercial scale for reducing sulfur emissions after coal combustion. Over 90% reduction of sulfur dioxide in flue gases can be achieved by this process. Combustion control techniques of the flames will effectively reduce oxides of nitrogen emissions into the atmosphere. 

There have been many attempts to classify the rate of corrosion of zinc in relation to scientific measurements of sulfur dioxide and chlorides, and time of wetness at specific locations, and this effort has led to ISO 9223 (Table 2.12). However the committee concerned recognizes that available data do not always fit the classification adequately and that further work is needed. As just noted, an important series of tests (ISOCORRAG) is still in progress by a group working within ISO TC 156/WG4. The published results are of particular value because four metals have been tested and, in many cases, some environmental data are available on sulfur dioxide, chloride, and time of wetness. The published data for zinc and the calculated steel/zinc corrosion ratio is summarized in Table 2.7B. 

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