Acid deposition (dry deposition) occurs when NOX (vehicles, burning coal) and sulfur dioxides (burning coal, volcanoes) are released to the atmosphere. These may react with naturally occurring ammonia gas and fall back to the ground as nitric salts and sulfates. This may be in the form of a gas, particulate, or aerosol.
Acid precipitation (acid rain/snow, wet deposition) is when NOX and SO2 undergo chemical reactions with water to form nitric acid (HNO3) and sulfuric acid (H2SO4). The acids dissolve in rain and snow before falling to the ground.
Often the effects of acid precipitation and deposition are not felt by the areas that created them. Winds often carry the gases downwind creating a problem for other communities. Acid rain affects both the living and the non-living.
Plants that experience acid deposition (dry or wet) suffer leaf damage and possible stunted growth. Damaged leaves reduce photosynthesis and may be more susceptible to disease.
Soils absorb the contaminated rains and have their pH lowered. This may lead to dissolving needed nutrients or releasing toxic metals like aluminum.
The acidification of bodies of water has also occurred. Acid rain lowers the pH of lakes, ponds, and rivers. This, in turn, harms aquatic life (inability to release eggs and negative affecting gills).
You may have seen the effects of acid rain on old statues and gravestones. Some of the loss of features is due to acid dissolving the rock away.
There are regional soil differences that can mitigate the effects of acid rain. Soils that have calcium or limestone are able to neutralize some of the acids. Also if the bedrock is comprised of limestone or marble (both having a more basic pH) the acid may be neutralized.
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