What is acid rain? Most people think that rain is pure, clean water. But even clean rain contains some acid, though not enough to cause harm.
Acid rain, however, has way more acid that clean rain. In fact, some drops are almost as acidic as vinegar. Acid rain doesn't even have to be rain. It can be any precipitation, such as snow, sleet, or fog, that has unusually high amounts of acid.
Rain PollutionAcid rain is caused by air pollution. The coal, oil, and natural gas we burn to run power plants, factories, homes, and vehicles, release gases into the air. Two in particular, sulfur dioxide and nitrogen oxide, are specially dangerous, at least when they combine with water vapor to become sulfuric acid or nitric acid.
Acid rain damages the environment, washing away nutrients in soil. It can kill fish and other marine life. Acid rain even harms buildings as it dissolves minerals in stone.
The Good NewsThe good news is that efforts to combat acid rain are working. In 1990, the Clean Air Act required power plants to reduce the amount of sulfur dioxide they released into the atmosphere. Today, pollution levels are lower. Lakes that were once too acidic for fish are now teeming with life. Forests are coming back as well. But the work is far from over and more efforts will be needed to help reduce acid rain even further.
The pH Scale
Scientists measure acidity on a pH scale that goes from zero all the way up to 14. The stronger the acid, the lower its pH. Battery acid, for instance, is 0 on the scale. Tomato juice is 5. A solution that measures 7, such as distilled water, is right in the middle. It isn't acid at all. Neither is it alkaline, the opposite of acid. Liquid drain cleaner, an alkaline, tops the scale at 14.
A scientist collects pollutants to determine the effects of acid rain.
Unpolluted rain has a pH rating of 5.6, just a bit more than the amount found in a banana. To be considered acid rain. The water must measure 5 or less on the scale.