Emissions acid rain, Canada

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). 

Acid rain monitoring data in North America have been gathered by Environment Canada and stored in the National Atmospheric Chemistry (NatChem) Database, details of which can be found at www.airquality.tor.ec.gc.ca/natchem. Analysis of the deposition chemistry data has confirmed that wet sulfate deposition did indeed decline in concert with the decline in SO2 emissions in both eastern Canada and the... 

The Eastern Canadian Acid Rain Program was highly successful at reducing SO2 emissions and sulfate wet deposition in eastern Canada (see Figure 10). Sulfur emissions actually declined more than the desired 50% by 1994, and have continued to decline modestly in the present. These SO2 emissions in the United States have also reduced dramatically, particularly since the implementation of the Canada-United States Air Quality Accord in 1991. This has been especially important to the aquatic and terrestrial ecosystems in eastern Canada, since US emissions are responsible for a large proportion of the acid deposition received in eastern Canada due to transboundary transport. 

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 ... 

Acid rain was at one time an important point of contention between the United States and Canada. Much of this acid was the result of the emission of sulfur oxides by coal-fired electricity generating plants in southern Indiana and Ohio. These sulfur oxides, when dissolved in rainwater, formed sulfuric acid and hence acid rain. How many metric tonnes of Indiana coal, which averages 3.5% sulfur by weight, would yield the H2S04 required to produce a 0.9 in. rainfall of pH 3.90 precipitation over a 104 mile2 area ... 

Acid rain was implicated in the sterilization of lakes in North Eastern United States and in Eastern Canada. Studies showed much of the air pollution responsible for acid rain originated in the United States. The Canadian government requested the United States reduce its emissions of sulfur dioxide and nitrogen oxides. In response, the Reagan administration promised to spend 2.5 billion on a program of research and demonstration (read this to mean study). The aim was to reduce pollution from coal fired power stations. 

The major foundations for our present understanding of acid rain and its effects were laid by Eville Gorham. On the basis of his research in England and Canada, Gorham showed as early as 1955 that much of the acidity of precipitation near industrial regions can be attributed to combustion emissions, that progressive acidification of surface waters can be traced to precipitation, and that the free acidity in soils receiving acid precipitation results primarily from sulfuric acid. 

SO2 and NO, emissions, which are often dispersed by prevailing winds from the United States to Canada, create a contentious transboundary pollution problem between the two countries. In Chapter 9, Acid Rain Politics... 

Working groups under the MOI picked up where the BRCG had left off, and eventually produced reports (United States-Canada 1983). The MOI, however, ultimately proved not to be the kick-start to the negotiation process that Ottawa, at least, had intended it to be. In early 1982 Canada proposed formally that SO2 emissions be reduced by 50% in both countries. This target was designed to achieve a level of deposition of no more than 20 kg of wet sulphate per hectare per year in areas sensitive to acidification. The United States rejected the proposal, firmly. The Reagan administration made clear its conviction that action was premature and, for the rest of the decade, consistently took the position that more research had to be done on the problem of acid rain before control actions could be considered. 

The western provinces refused to take part. Their argument was that their own emissions had little impact on either the eastern part of the country or on the highly alkaline soils of western Canada, and that acid rain was therefore an eastern problem. 

---