For many years, there was considerable debate and disagreement over what caused acid rain.  Recent scientific work, however, has helped to clarify this

The primary causes of acid rain are sulfur dioxide and nitrogen oxides.  These chemicals are released by certain industrial processes, and as a result, the more industrialized nations of Europe as well as the US suffer severely from acid rain.

Most sulfur dioxide comes from power plants that use coal as their fuel.  These plants emit 100 million tons of sulfur dioxide, 70% of that in the world.

Automobiles produce about half of the world's nitrogen oxide.  As the number of automobiles in use increases, so does the amount of acid rain.  Power plants that burn fossil fuels also contribute significantly to nitrogen oxide emission.

Though human causes are primarily responsible for acid rain, natural causes exist as well.  Fires, volcanic eruptions, bacterial decomposition, and lightening also greatly increase the amount of nitrogen oxide on the planet.  However, even the gigantic explosion of Mt. St. Helens released only about what one coal power plant emits in a year.

Once the tiny pollutant molecules have entered the atmosphere, they can travel for thousands of miles.  Eventually, the particles will combine with other compounds to produce new, often harmful, chemicals.

Acid rain comes down to the earth in the form of rain, snow, hail, fog, frost, or dew.  Once it reaches the ground, the acidity in the substance can harm and even destroy both natural ecosystems and man-made products, such as car finishes.