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1. Precipitation absorbs carbon dioxide from the atmosphere and falls to earth as an extremely weak solution of carbonic acid. This is a natural occurrence that poses no threat to the environment. However, when sulfur and nitrogen oxides from industrial pollution chemically combine with the precipitation it becomes dangerously acidic and is termed "acid precipitation" or as it is more commonly called, "acid rain".

2. To understand acid rain, we first must understand what an acid is. Acidity or alkalinity is measured on a pH scale which ranges from 1 to 14. A substance with a pH of 7 is considered neutral. Low pH values ??indicate acidity while high values ??indicate alkaline conditions, the lower the number, the stronger the acid.

3. Unpolluted rain is slightly acidic with a pH of 5.0 to 5.2. In areas of central and northern Europe, the eastern United States, and Russia the annual average pH of precipitation is now between 4 and 4.5 which is 5 to 8 times more acidic than unpolluted rain.

4. The acid-forming compounds come from natural as well as manmade sources. A volcanic eruption can cause acidic conditions covering half the globe. Decay processes involving both plant and animal materials, which occur in marshes, swamps, and oceans, can also produce chemicals that can increase acidic deposits. Many researches, however, believe that a major source of increased acid in rainfall is such industrial activity as the burning of fossil fuels like coal, gasoline, fuel oil, and natural gas.

5. The effects of acid rain are difficult to pinpoint. We know that when a stream or lake becomes too acidic, fish and their food sources are effected. Acid stress can cause fish to die. Small amounts of acid can also affect the ability of fish to reproduce.

6. Acid rain is also believed to reduce crop yields and deteriorate buildings and roads. There are also indications that acid precipitation also may be causing a reduction in forest production.

7. Since air moves without restriction from region to region, from nation to nation, and from continent to continent, any solution to the problem will require international cooperation.

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When does the precipitation become dangerously acidic?



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