and automobiles.
             Scientists determine whether rain or lake water is acidic by measuring its pH (the measure of acidity or alkalinity of a solution on a scale of 0 to 14). A value of 7 is considered neutral, whereas values less than 7 are acidic and values over 7 are alkaline or basic. A change of one unit on the pH scale represents a factor of ten in acidity; for example, a solution with a pH of five is ten times as acid as one with a pH of six (Somerville, 1996, p.174). Normal or clean rainfall, without pollutants, is slightly acidic due to carbon dioxide, a natural gas in the air that dissolves in water to form weak carbonic acid. But rain, snow, or other moisture is not called "acid rain" until it has a pH value below 5.6 (Gay, 1992, p.44). Rainfall in eastern North America is often acidic with a pH of 4 to 5.
             Acid rain is more common in the Eastern U.S. and Canada than in the Western U.S. because emissions rise high into the atmosphere and are carried by prevailing winds from the west, falling out with precipitation in the east. Some areas in the U.S. where acid rain is most common
             ...