Canada acid rain sources

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

Atmospheric emissions of sulphur dioxide are either measured or estimated at their source and are thus calculated on a provincial or state basis for both Canada and the United States (Figure 2). While much research and debate continues, computer-based simulation models can use this emission information to provide reasonable estimates of how sulphur dioxide and sulphate (the final oxidized form of sulphur dioxide) are transported, transformed, and deposited via atmospheric air masses to selected regions. Such "source-receptor" models are of varying complexity but all are evaluated on their ability to reproduce the measured pattern of sulphate deposition over a network of acid rain monitoring stations across United States and Canada. In a joint effort of the U.S. Environmental Protection Agency and the Canadian Atmospheric Environment Service, eleven linear-chemistry atmospheric models of sulphur deposition were evaluated using data from 1980. It was found that on an annual basis, all but three models were able to simulate the observed deposition patterns within the uncertainty limits of the observations (22). 

Sulfuric acid is a stronger acid than sulfurous [pAa(l) < 0, p7fa(2) = 1.99 at 25 °C and infinite dilution] rain as acidic as pH 2.1 has been recorded at Hubbard Brook, New Hampshire, and the pH of water droplets in clouds can be as low as 1.5 (for comparison, the pH of rainwater saturated with atmospheric CO2 is about 5.6 at 15 °C). Acid rain destroys building materials (especially marble), kills fish and vegetation, accelerates metallic corrosion (Sections 16.5 and 16.7), and can be directly harmful to humans (e.g., it causes the alligator skin condition reported in Cubatao, Brazil). Sulfate rain is not completely without redeeming features, as many soils (e.g., in southern Alberta, Canada) are sulfur-deficient. On balance, however, its acidity is unacceptable, and sulfur oxide emissions must be controlled at the source. Several control measures are possible ... 

The presence of SO2 in the atmosphere and the sulfuric acid that it produces result in the phenomenon of acid rain. (Nitrogen oxides, which form nitric acid, are also major contributors to acid rain.) Uncontaminated rainwater is naturally acidic and generally has a pH value of about 5.6. The primary source of this natural acidity is CO2, which reacts with water to form carbonic acid, H2CO3. Add rain, however, is more addic than normal rainwater and typically has a pH value of about 4. This addity has affected many lakes in northern Europe, northern United States, and Canada, reducing fish populations and affecting other parts of the ecological network within flie lakes and surrounding forests. 

Transport processes that move atmospheric acids and their precursor acid gases from their sources to downwind areas are very important in determining areas affected by acid rain. The northeastern United States and southeastern Canada are affected by acid originating from stack gas emissions carried by prevailing southwesterly winds from Missouri, Illinois, Kentucky, and other regions to the southwest. Southern Norway, Sweden, and Finland receive acid precipitation originating farther south in Europe. 

The news media disseminated the myth that the sources of acid rain are mysterious. National Public Radio interviewed Dr. Mohnen and announced that "At least one scientist says that the Ohio Valley is being blamed prematurely as the source of acid rain in Canada and New England." " In the ensuing interview. Dr. Mohnen again referred to the Adirondack study We ask, where has the air been over the past two days that brought (to the Adirondacks) this pollution in the rain We find that it does not matter where the air has been. Simply, there is always enough material in the air to be converted into acidity that comes down... 

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