"Normal" rainfall is slightly acidic because of the presence of dissolved carbonic acid. Carbonic acid is the same as that found in soda pop.
- Acid Rain
- The pH of "normal" rain has traditionally been given a value of 5.6. However scientists now believe that the pH of rain may vary from 5.6 to a low of 4.5 with the average value of 5.0. Acid rain or acid snow is a direct result of the method that the atmosphere cleans itself. The tiny droplets of water that make up clouds, continuously capture suspended solid particles and gases in the atmosphere. The gases of sulfur oxides and nitrogen oxides are converted into sulfuric and nitric acids.
- Acid Rain Transport
- The reactions of sulfur oxides to form sulfuric acid are quite slow. Sulfur dioxide may remain airborne for 3-4 days.As a consequence acid rain derived from sulfur oxides may travel for hundreds of miles or even a thousand miles. Nitrogen oxides may persist for only about one half day and therefore may travel only tens or hundreds of miles.
- Acid Snow
- The impact of acid precipitation on aquatic ecosystems may be intensified by melting snow. When snow melts rapidly in the spring, the stream or lake may be "shocked" with an excessive amount of acid. In the spring, at the time of acid snow melting, the various aquatic organisms are reproducing and are the most sensitive increases in acid.
- Electricity Generation
- Electricity is produced at a an electric power plant. Some fuel source, such as coal, oil, natural gas, or nuclear energy produces heat, which is used to boil water to create steam. The steam under high pressure is then used to spin a turbine that interacts with a system of magnets to produce electricity. The electricity is transmitted as moving electrons through a series of wires to homes and business.
- Sources of Nitrogen Oxides
- A natural source of nitrogen oxides occurs from a lightning stroke. The very high temperature in the vicinity of a lightning bolt causes the gases oxygen and nitrogen in the air to react to form nitric oxide.
- Sources of Sulfur Oxides
- It has been estimated that on a global basis, natural sources, such as volcanoes, contribute about as the same amount of sulfur oxides to the atmosphere as human industrial activities. This amounts to 75-100 million tons from each source per year. However, in industrial countries such as in Europe and North America, human activities contribute 95 % of the sulfur oxides and natural sources only 5 %. In the Western States, natural sources of sulfur oxides may be more important.
Thumbnail: Acid rain and weathering. Image used with permission (Public Domain; Slick).