Environmental Problems Related to Electric Power Plant Emissions

Electric power plant emissions are factors in three major environmental issues: acid rain, urban air quality, and global climate change. These issues are discussed below.

Acid rain refers to rain, fog, mist, or snow that is more acidic than normal. The acidity of precipitation is stated in terms of its pH level, which describes the concentration of hydrogen ions along a scale (from 0 to 14) that defines the continuum from acid to base. The pH scale is logarithmic; pH levels of 4.0 and 3.0, for example, are 10 and 100 times more acidic, respectively, than a pH level of 5.0. Although a pH level of 7.0 is neutral, unpolluted rainfall is normally slightly acidic (pH=5.6). Acid rain is defined as any precipitation with a pH of 5.5 or less.

Chemical analysis of data collected by means of cloud sampling and experimentation reveals the presence of sulphuric acid and nitric acid in precipitation in the United States .Sulphur dioxide and nitrogen oxides in the air, partly the result of emissions from electric power plants, gradually react with water vapor and become acids. Precipitation becomes acidic by mixing with these acids. The acidity of the precipitation depends upon the amount of acid in the atmosphere and the amount of water in which it is dissolved. Undissolved acids may also fall to Earth by themselves or in combination with dust particles.

The most severely acidic conditions are found in the eastern United States. EPA believes that acid rain has been the primary cause of the acidification of hundreds of streams in the mid-Atlantic highlands and the New Jersey Pine Barrens and of many lakes in the Adirondack Mountains of New York.The National Acid Precipitation Assessment Program (NAPAP) identified acid rain as one of several possible causes of increased nitrate leaching and acidification of surface waters in several northeastern watersheds. Episodes of acidification are believed to harm populations of fish and invertebrates in small streams and lakes.

Field studies have implicated acid rain in observed damage to high-elevation red spruce forests in the northeastern United States. Nutrient leaching and changes in soil chemistry due to acid deposition have also been detected in forests south of the Great Lakes. In general, NAPAP concluded that acid deposition, among other stressors, threatens the long-term structure, function, and productivity of many sensitive ecosystems.

Some research suggests that emissions of sulphates and other pollutants from the combustion of fossil fuels may be linked to abnormally high mortality rates in humans.Clinical studies have shown lung irritation and impaired lung cleansing in human subjects exposed to acidic aerosols.

Urban ozone - Electric power plants contribute heavily to NOx emissions, which are precursor chemicals that (along with VOCs) react in the atmosphere in the presence of sunlight to form ozone. Strong concentrations of ozone often occur in and downwind of large urban areas.

During cardiovascular exercise, human exposure to ozone at concentrations both above and below the 120-part-per-billion maximum allowed under the NAAQS has been shown to result in transient respiratory problems.Ozone can also seriously irritate the eyes and mucous membranes. The effects of elevated ozone levels are not known for all types of vegetation, but such levels are harmful to many types of trees and crops. High ozone concentrations seem to be more detrimental than low-level extended exposure.

The assessment of the impact of NOx controls on ozone concentrations is complex and must be studied carefully in developing ozone abatement strategies, according to a 1992 report from a National Research Council committee. The committee found that ambient measurements of VOC/NOx ratios--which, as they vary, have different effects on ozone formation--were larger than expected from an assessment of emission inventories. The committee also determined that the effectiveness of efforts to control VOC and NOx emissions depends on ambient VOC/NOx ratios. Generally, at ratios of 10 or less, VOC control is more effective and NOx control may be counterproductive. At ratios greater than 20, NOx control is generally more effective. Hence, if VOC emission inventories have been understated, past ozone control strategies may have been misdirected. Tighter controls on NOx may be more effective in controlling ozone under certain circumstances.

The committee also found that combinations of biogenic VOCs and anthropogenic NOx can significantly affect ozone formation in some urban and rural regions of the United States and concluded, again, that the appropriate strategy may be to monitor and control NOx emissions.

EFFECTS OF ACID RAIN, SNOW AND FOG

Acid deposition, from human-caused emissions of oxides of sulphur and nitrogen, is probably the greatest threat to small boreal lakes in Canada and Eurasia.[2] Acidifying sulphur oxide emissions have been reduced by over 50% in Canada. Legislation has been passed to compel similar reductions in the United States by early in the twenty-first century. However, these measures are estimated to have reduced the potential effect of acid precipitation on Canadian lakes by only about half.

The rapid decline in DOC caused by acidification caused much greater increases in UV-B penetration than climate warming alone. In the most acidified lake, 302S, the depth of 1% UV-B penetration increased from about 0.3 meters to over 2.8 meters --nearly a tenfold increase. As a result, the proportion of the lake's volume exposed to greater than 1% of UV-B increased over eightfold, from 6% to nearly 50%.Overall, the study's authors estimate about 140,000 of the nearly 700,000 lakes (i.e., about 20 percent) in eastern Canada may have DOC concentrations low enough for UV-B penetration to be of concern. The highest concern, they say, must be for clear, shallow lakes, streams and ponds, where even modest declines in DOC may eliminate the small regions that are deep enough to provide refuges from damaging UV- B radiation. 

However, most species disappear in natural aquatic ecosystems at higher pH values (less acidic conditions) than predicted by laboratory tests, thus suggesting that, in ecosystems, additional stresses enhance the effects of acidification. It is possible that one such stress is the increased exposure to UV-B caused by DOC decreases in acidified lakes. These results indicate that in aquatic systems, climate warming and/or acidification can increase the exposure of organisms to UV-B much more than changes in UV-B caused by depletion of the stratospheric ozone layer. The authors say that, in clear oligotrophic lakes [(.e., clear, healthy lakes that lack excessive nutrients for plants, and have plenty of dissolved oxygen), the decreases in DOC caused by climate warming, drought and acidification should be of much more concern than depletion of stratospheric ozone, so far as UV-B exposure is concerned.

Effect of Acid Rain on Lakes and Rivers

It is in aquatic habitats that the effects of acid rain are most obvious. Acid rain runs off the land and ends up in streams, lakes and marshes - the rain also falls directly on these areas.As the acidity of a lake increases, the water becomes clearer and the numbers of fish and other water animals decline. Some species of plant and animal are better able to survive in acidic water than others. Freshwater shrimps, snails, mussels are the most quickly affected by acidification followed by fish such as minnows, salmon and roach. 

Lakes, rivers and marshes each have their own fragile ecosystem with many different species of plants and animals all depending on each other to survive. If a species of fish disappears, the animals which feed on it will gradually disappear too. If the extinct fish used to feed on a particular species of large insect, that insect population will start to grow, which in turn will affect the smaller insects or plankton on which the larger insect feeds.

Life of Aquatic Organisms:
 
Some types of plants and animals are able to tolerate acidic waters. Others, however, are acid-sensitive and will be lost as the pH declines. Generally, the young of most species are more sensitive to environmental conditions than adults. At pH 5, most fish eggs cannot hatch. At lower pH levels, some adult fish die. Some acid lakes have no fish.

The roe and fry (eggs and young) of the fish are the worst affected as the acidity of the water can prevent eggs from hatching properly, can cause deformity in young fish which also struggle to take in oxygen.The acidity of the water does not just affect species directly, it also causes toxic substances such as aluminum to be released into the water from the soil, harming fish and other aquatic animals.
 
Makes Drinking water unsafe:

Water that is slightly acidic should not be dangerous, as there are many foods that have low pH
value; for example, lemon juice has a pH of 2.4. However, a low pH can indicate that there may
be other contaminants in the water, because if pollutants have been added to a water source,
the pH typically will change.

Water treatment facilities monitor the pH level of the water while they are treating it for
municipal use. Acidic or basic water is harder to disinfect than water with a pH that is closer to
7.0. As well, if acidic water was sent through pipes and into homes, there would be a greater
danger of pipe corrosion, which could allow metals to dissolve into the drinking water as it flow
through the pipes. According to the World Health Organization, a pH less than 8.0 is necessary
for effective chlorination. If the pH is too high, water treatment facilities can decrease the acidity
in a number of ways. One common method that is used to increase the pH is to send the water
through a calcium carbonate filter, which neutralizes the acid and increases the pH of the water. Another common method is to inject a sodium carbonate solution into the water.