| Acid rain is a popular phrase used to describe rain, | | | | definition of acid precipitation refers to a pH less than |
| snow, fog, or other precipitation that is full of acids | | | | 5.65. |
| that collect in the atmosphere due to the burning of | | | | Measured values of acid rain vary according to |
| fuels such as coal, petroleum, and gasoline. Acid rain | | | | geographical area. When pH levels are drastically |
| was first recognized in Europe in the late 1800s but | | | | upset in soil and water, entire lakes and forests are |
| did not come to widespread public attention until | | | | endangered. Evergreen trees in high elevations are |
| about 1970, when its harmful effects on the | | | | especially vulnerable. Although the acid rain itself does |
| environment were publicized. Research has shown | | | | not kill the trees, it makes them more susceptible to |
| that in many parts of the world, lakes, streams, and | | | | disease. Also, high acid levels in soil cause leaching of |
| soils have become increasingly acidic, prompting a | | | | other valuable minerals such as calcium, magnesium, |
| corresponding decline in fish populations. Acid rain | | | | and potassium. Small marine organisms cannot survive |
| occurs when polluted gases become trapped in clouds | | | | in acidic lakes and rivers, and their depletion affects |
| that drift for hundreds, even thousands, of miles and | | | | the larger fish who usually feed on them, and, |
| are finally released as acidic precipitation. Trees, lakes, | | | | ultimately, the entire marine-life food chain. Snow |
| animals, and even buildings are vulnerable to the slow, | | | | from acid rain is also damaging; snowmelt has been |
| corrosive effects of acid rain. | | | | known to cause massive, instant death for many |
| Acidification, the process of making acid, is not just | | | | kinds of fish. Some lakes in Scandinavia and New |
| caused by deposits of acidic rain but also by | | | | York's Adirondack Mountains are completely devoid |
| chemicals in snow and fog and by gases and | | | | of fish life. Acid rain also eats away at buildings and |
| particulates when precipitation is not occurring. The | | | | metal structures. From the Acropolis in Greece to |
| major human-made causes of acid deposition are (1) | | | | Renaissance buildings in Italy, ancient structures are |
| emissions of sulfur dioxide from power plants that | | | | showing signs of corrosion from acid rain. In some |
| burn coal and oil and (2) emissions of nitrogen oxides | | | | industrialized parts of Poland, trains cannot exceed 40 |
| from automobiles. These emissions are transformed | | | | miles (65 kilometers) per hour because the iron |
| into sulfuric acid and nitric acid in the atmosphere, | | | | railway tracks have been weakened from acidic air |
| where they accumulate in cloud droplets and fall to | | | | pollution. Usually, waters affected by acid rain are |
| Earth in rain and snow, wet deposition. Other sources | | | | treated by adding limestone or lime, an alkaline |
| of acid deposition are gases like sulfur dioxide and | | | | substance (base) that reduces acidity. Fishery |
| nitrogen oxides, as well as very small particulates. | | | | biologists especially are interested in liming acidic lakes |
| These gases and particulates are usually deposited | | | | to make them more habitable for sport fish. In some |
| when it is not raining or snowing which is called dry | | | | parts of Scandinavia, for instance, liming is used |
| deposition. | | | | extensively to make the biological damage of |
| While large areas of Europe and North America are | | | | acidification less severe. |
| exposed to acidifying depositions, only certain types | | | | While neutralizing ecosystems that have become |
| of ecosystems are affected by these depositions. | | | | acidic, treats the symptoms but not the sources of |
| The most vulnerable ecosystems usually have a thin | | | | acidification. Although exact sources of acid rain are |
| cover of soil, containing little calcium and sitting upon | | | | difficult to pinpoint and the actual amount of damage |
| solid rock made up of hard minerals such as granite | | | | caused by acid deposition is uncertain, it is agreed |
| or quartz. Many freshwater lakes, streams, and rivers | | | | that acid rain levels need to be reduced. Scientific |
| have become acidic, resulting in the decline or local | | | | evidence supports the notion that what goes up |
| destruction of some plant and animal populations. It is | | | | must come down, and because of public awareness |
| not yet certain that land-based ecosystems have | | | | and concerns about acid rain in many countries, |
| been affected by acidic deposition. After acid rain | | | | politicians have begun to act decisively in controlling or |
| was discovered in Europe, scientists began measuring | | | | eliminating human causes of such pollution. Emissions |
| the acidity of rain in North America. Initially, they | | | | of sulfur dioxide and nitrogen oxides are being |
| found that the problem was concentrated in the | | | | reduced, especially in Western Europe and North |
| northeastern states of New York and Pennsylvania | | | | America. For example, in 1992 the governments of |
| because the type of coal burned there was more | | | | the United States and Canada signed an air-quality |
| sulfur containing. | | | | agreement aimed at reducing acidifying depositions in |
| Acid rain is measured through pH tests that | | | | both countries. While countries in Western Europe |
| determine the concentration of hydrogen ions in a | | | | and North American have actively carried out actions |
| liter of fluid. The pH scale is used to measure acidity | | | | to reduce emissions of gases leading to acid |
| or alkalinity. It runs from 0 to 14. Water has a neutral | | | | deposition for a number of years, countries in other |
| pH of 7. The greater the concentration of hydrogen | | | | parts of the world have only recently addressed the |
| ions and the lower the pH number, the more acidic a | | | | issue. In Eastern Europe, Russia, China, India, |
| substance is and the lower the concentration of | | | | Southeast Asia, Mexico, and various developing |
| hydrogen ions and the higher the pH number, the | | | | nations, acid rain and other pollution problems are |
| more alkaline or basic a substance is. So a pH greater | | | | finally gaining notice. For example, in 1999, scientists |
| than 7 indicates an alkaline substance while a pH less | | | | identified a haze of air pollution that hovers over the |
| than 7 indicates an acidic substance. It is important to | | | | Indian Ocean near Asia during the winter. The 3.8 |
| note that a change of only one unit in pH equals a | | | | million-square-mile haze (about the size of the |
| tenfold change in the concentration of hydrogen ions. | | | | combined area of all fifty American states) is made |
| For example, a solution of pH 3 is 10 times more | | | | up of small by-products from the burning of fossil |
| acidic than a solution of pH 4. Normal rain and snow | | | | fuels. Such a cloud has the potential to cool Earth, |
| measure about pH 5.60. In environmental science, the | | | | harming both marine and terrestrial life. |