acid rain
...O2 and NOx react with water vapor to form weak solutions of nitric and sulfuric acid. The areas of greatest acidity (lowest pH values) are located in the Northeastern United State. This pattern of high acidity is caused by the large number of cities, the dense population, and the concentration of power and industrial plants in the Northeast. In some regions of New York State, rain with a pH of 2.6 has been measured. The average pH of rainfall in central Ontario is currently about 4.2. Around Washington, D.C., however, the average rain pH is between 4.2 and 4.4. In addition, the prevailing wind direction brings storms and pollution to the Northeast from the Midwest, and dust from the soil and rocks in the Northeastern United States is less likely to neutralize acidity in the rain. More than 90% of the SO2 and NOx present in the atmosphere over eastern North America is a result of human activities. The major sources of sulfur emissions are coal (and to a lesser extent, oil) burning electric power plants, and industries such as ore smelting. Together, these two industries account for more than 70% of the sulfur emissions in North America. About 40% of NOx emissions come from the transportation sector, (cars, trucks, planes etc.). The rest are emitted from fossil fuel fired power plants and other combustion processes. Once emitted into the atmosphere, acid gases can travel for thousands of kilometers before being deposited back onto the ground. In fact, about half of the acid rain that falls on Canada originated from United States sources. A similar situation exists in Scandinavia where Sweden, Norway and Finland are exposed to acid rain from Great Britain and other northern European countries. Acid rain has a wide variety of environmental and health impacts. The magnitude of these impacts is very dependant upon the type of bedrock and soil in a specific region. Regions where the bedrock and/or soil contains carbonates such as limestone and dolomite are less susceptible to damage by acid rain than areas with igneous bedrock. This is because the carbonate material acts to neutralize the acidity of the precipitation. Carbonates act as a "buffer"; they tend to keep both surface and groundwater at a constant pH. Areas such as the "Canadian Shield" in Ontario and Quebec are very susceptible to damage by acid rain because the igneous bedrock has no natural buffering capacity and the soils are very shallow. The amount of damage to aquatic and terrestrial ecosystems is therefore dependant upon both the amount of acid deposition, and the type of soil and bedrock. Soils, surface waters such as lakes and rivers, and forests can all be damaged by acid rain. In Canada, thousands of lakes are found in regions such as the Canadian Shield which are highly sensitive to changes in the pH of precipitation. The actual interactions between aquatic organisms (such as fish, crustaceans, insects and amphibians) and changes in water chemistry are extremely complex. Acidification can hinder the ability of aquatic organisms to reproduce. This is especially true for fish and amphibians that spawn in streams or shallow bays in the early spring. Large influxes of runoff from melting (acid) snow can drastically depress the pH in these areas for short periods in the spring. This "acid shock" can kill the eggs of many species. Many species of frogs and salamanders, for example, can't reproduce when the acidity of their breeding habitat goes below a pH of five. In addition to reproductive failures, acidification can reduce the amount of calcium available to vertebrates such as fish, as well as increasing the concentration of toxic heavy metals in surface waters. Both of the above can result in deformed bone structures, and poor growth in fish. The decline of any one member of a food chain impacts on many other species. Birds such as loons and osprey, which eat fish, can't survive without their main source of food. Similarly many mammals depend upon aquatic organisms such as crustaceans for their food. Acidification can eventually result in a "dead" lake. Such lakes exhibit very clear water, because there are no aquatic organisms such as plankton to color the water. The affects of acid rain on terrestrial (land based) plants and animals are also both complex and potentially devastating. Soils can be damaged by removing needed nutrients and dissolving toxic heavy metals from the soil. Metals such as aluminum can get into the roots of plants and prevent the uptake of other important nutrients. Forests in areas with sensitive soils can be severely affected by acidification. Acid rain can damage the foliage of trees (leaves etc.), and retard their growth. In Quebec, for example, sugar maple forests have been heavily damaged by acid rain. Similarly, there are forests in Poland and Czechoslovakia where 40% of the trees are dead or dying, as a result of acid rain. It has been estimated that acid rain causes $197 million in damage to commercial forests in Canada each year. Acid rain can also result in human health concerns and damage to buildings. Acid rain can aggravate respiratory ailments such as bronchitis and asthma. Humans may also be affected by drinking water which contains higher levels of toxic metals which have been dissolved from soils and pipes by the increased acidity of drinking water supplies. Construction materials such as limestone, marble and sandstone can also be damaged by acid rain, resulting in eroded buildings and monuments. The value of this damage was estimated to by $830 million in Canada, as of 1985. The silver lining in the acid rain cloud is our knowledge of how to reduce emissions of acid gases; and once acidic deposition is decreased, it seems that eco...