Acid rain begins when sulfur dioxide and nitrogen oxide emitted by coal-burning power plants mixes with water vapor in the atmosphere. Eventually, the mixed molecules clump together and form droplets, which fall as acid rain. Acid rain is usually much more acidic than regular rainfall. It can damage natural environments, such as lakes and forests, and it can also cause damage to man-made materials and structures, including asphalt shingles. There are multiple known effects of acid rain on asphalt shingles.
Corrosion
According to the American Chemical Society, asphalt shingles that are exposed to acid rain over long periods can corrode and leak. Leaking, in turn, causes more damage to the shingles and the roof by further degrading the composition of the asphalt. Aged or oxidized asphalt shingles are even more likely to attract damage from corrosion because they contain a higher percentage of polarized molecules, which attract water molecules deep into the asphalt itself.
Structural Damage
Leaking asphalt roof shingles can produce structural damage to the beams of a house. This is particularly true in older or historic houses, according to Old House Web. Asphalt shingles produced from the 1940s through the 1970s in the United States consisted of up to 1/3 cotton or wool fibers. These fibers do not protect either the asphalt shingles or the roofing materials underneath them from acid rain. Older homes can develop warped or rotting roofs, beams, and ceilings as acid rain seeps in through the older asphalt shingles.
Pollution
Asphalt itself contains about 6 percent sulfur, according to the American Chemical Society. When asphalt shingles corrode under the effects of acid rain, their basic composition, which includes petroleum manufacturing byproducts along with other chemicals such as sulfur, breaks down. The various chemicals in the asphalt may be washed down the gutters of the building and into storm sewers. In particular, the sulfur used in asphalt shingle production may make its way into the atmosphere as sulfur dioxide, where it will combine with nitrogen oxide and water vapor to fall again as acid rain, causing further damage.
