Acid rain, or "acid deposition" as it is technically called, occurs when SO2 and NOx react in the atmosphere with water, oxygen, and oxidants to form various acidic compounds that later fall to earth in the form of precipitation or dry deposition of acidic particles.
Acid deposition contributes to damage of trees at high elevations and in extreme cases may cause lakes and streams to become so acidic that they cannot support aquatic life.
While fish species vary in their sensitivities to acidification, those with low tolerance tend to die out, at times to the point of extinction.
Acid deposition primarily affects bodies of water that rest atop soil with a limited ability to neutralize acidic compounds.
The US National Surface Water Survey (NSWS) investigated the effects of acidic deposition in over 1,000 lakes larger than 10 acres and in thousands of miles of streams. It found that acid deposition was the primary cause of acidity in 75 percent of the acidic lakes and about 50 percent of the acidic streams.
Acid deposition contributes to the degradation of high-elevation spruce forests that populate the ridges of the Appalachian Mountains from Maine to Georgia. This area includes national parks such as the Shenandoah and Great Smoky Mountain National Parks.
While much research has been devoted to studies in North America and Western Europe, relatively little has been done in Asia where most of the growth in acid-depositing emissions is expected over the next few decades.
Other effects:
- reduces the availability of nutrients in soil
- enhances the solubility of metals
- accelerates the decay of building materials and paints, including irreplaceable statues and sculptures
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