It is the term used for pollution caused by SO2 and NO2 when they combine with atmospheric moisture. When coal, oil and natural gas burn, sulphur dioxide and nitrogen dioxide are produced. These react with water in air and form sulphuric acid and nitric acid and return to the ground in the form of rain, fog or snow. Any precipitate or depositions having a pH lower than 5.6 as a result of contact with airborne particles having an adverse effect on flora & fauna on which it falls is called acid rain.
Causes of Acid Rain
Acid rain is caused by smoke and gases that are given off by factories and cars that run on fossil fuels. When these fuels are burned to produce energy, the sulfur that is present in the fuel combines with oxygen and becomes sulfur dioxide; some of the nitrogen in the air becomes nitrogen oxide. These pollutants go into the atmosphere, and become acid.
Sulfur dioxide and nitrogen oxide are produced especially when coal is burnt for fuel. Burning coal produces electricity, and the more electricity that people use, the more coal is burnt. Of course, nowadays people probably couldn't live without electricity, so coal will continue to be burnt; but electricity and energy are constantly being overused. Think of it this way: every time you turn on a light switch or the television set without really needing to, you're indirectly contributing to the acid rain problem. Automobiles produce nitrogen oxides (which cause acid rain), so every time you don't carpool when you can, you are helping to cause acid rain.
Acid rain is a big problem, but it is not unstoppable. If the amount of sulfur dioxides and nitrogen oxides in the air is reduced, then acid rain will be reduced. There are many helpful things that "normal" people (people who aren't part of a power company or the government) can do. First of all, conserve energy and pollute less! Use less electricity; and carpool, use public transportation, or walk when you can. This will help more than one might think. When less energy is used, less coal is burnt, and as a result, there is less acid rain. Experts say that if energy was used more carefully, we could cut the amount of fuel burned in half!
Also, if coal was cleaned before it was burnt; the dangerous pollutants that cause acid rain would be cleaned away. If coal is crushed and washed in water, the sulfur washes out. However, this is a very costly method, and many power companies and governments do not want to spend their money cleaning coal. It is also costly to bum low-sulfur coal (low-sulfur coal gives off less sulfur in the air as opposed to high-sulfur coal).
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