Produced by Stephen Hutcheson and the Online Distributed Proofreading Team at http://www.pgdp.net Acid Rain and Our Nation’s Capital _A Guide to Effects on Buildings and Monuments_ _by_ Elaine McGee For sale by the U.S. Government Printing Office Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328 ISBN 0-16-048068-X [Illustration: Marble surfaces exposed to rain develop a rough “sugary” texture because the calcite grains are loosened as the edges dissolve in the rain water. Column capital volute, Jefferson Memorial, Washington, D.C.] [Illustration: A summer rain storm in Washington, D. C. (Memorial Continental Hall)] When polluted air mixes with rain, snow, and fog, acid precipitation forms. This acidity has caused people to worry about the environment; some reports show that acid rain has affected lakes, trees, and fish populations in the Northeastern United States and Canada. Another concern is its effect on historic buildings and monuments. The booklet focuses on acid rain and its impact on our Nation’s capital. Rain in Washington, D. C., has an average acidity of 4.2, about as acid as a carbonated drink and more than ten times as acid as clean, unpolluted rain. This booklet will define acid rain, explain what effects it has on marble and limestone buildings, and show, on a walking tour, some of the places in our Nation’s capital where you can see the impact of acid precipitation. [Illustration: The pH scale: pH = 7 is neutral, neither acid or alkaline; smaller pH values are acid, larger pH values are alkaline. A liquid with a pH of 3 is ten times as acid as one with a pH of 4.] 1 Battery Acid 2.8 Vinegar 4 Adult fish die <5.5 ACID RAIN 5.2-6.5 Normal range of precipitation 6-8 Normal range of stream pH <7 Acid 7 Neutral >7 Alkaline 8.6 Baking soda and sea water 13 Lye What is acid rain? The term “acid rain” is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. The more accurate term is “acid precipitation.” Distilled water, which contains no carbon dioxide, has a neutral pH of 7. Liquids with a pH less than 7 are acid, and those with a pH greater than 7 are alkaline (or basic). “Clean” or unpolluted rain has a slightly acidic pH of 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid. Around Washington, D.C., however, the average rain pH is between 4.2 and 4.4.