Acid rain is a general expression that refers to the concoction of wet and dry deposited substances from the atmosphere that have a greater than usual quantity of nitric and sulfuric acid. This is caused by both natural and man made sources. Natural sources include rotting vegetable matter, methane and volcanic eruptions; man made sources include burning of fossil fuels. The major culprits contributing to acid rain are sulfur dioxide (SO2) and nitrogen oxides (NOX).
The SO2, NOX and carbon dioxide mix with atmospheric moisture and form acid precipitation. The acids can return to the ground via any form of wet weather rain, fog, snow or mist. In contrast to wet deposit of the acids are the dry deposits. In this situation the acids mix with dust or smoke and stick to whatever surface they come in contact with. This may be a tree, a car or a building.
Acid rain impacts water bodies, plants, and trees, buildings, statues, animals, fish, and people. The buffering effects of the soil surrounding a water body will determine the acidification of the water body. Normal pH for lakes and streams runs between 6 and 8. With the addition of acid rain, the pH is reduced causing poor buffering soils to leach aluminum into the water bodies. Aluminum is lethal to many water residing species. For those fish that do not directly die, they become highly stressed and less able to survive and reproduce.
Another problem for water bodies is the condition referred to as "episodic acidification." This situation occurs when the pH levels decrease due to spring snow melts or heavy precipitation periods. This periodic acid deposition often times leads to fish kills.
As the pH declines down to a level of five, many fish eggs cannot hatch and those fry that already have, will die off. Some animals are more tolerant of the lower pH but their food sources may not have the same ability. For example, if the mayfly perishes in a lower pH environment, the frogs that usually eat them too will be impacted by a diminished food supply.
Another impact to water bodies comes from the excess amount of nitrogen deposited from acid rain. The nitrogen produces a condition called eutrophication (oxygen depletion) which triggers algal blooms, loss of sea grass beds and coral reefs. This in turn affects the health of fish and shellfish. A decreased coastal ecosystem will impact the quality of life in the oceans and water ways and ultimately influence mans food supply, recreation and economy.
Trees and forests are not immune from acid rain's effects. Often trees will grow more slowly, have reduced ability to ward off insects and diseases, and drop their leaves or needles without cause. As with the waterways, the soils' buffering ability will influence the impact on the trees, however trees have an additional exposure issue. Higher elevation forests tend to have more fog and clouds than lower elevations. The concentration of the acid in these mists is higher than raindrops and the excess exposure damages the trees' foliage.
Food crops do not usually receive the same damage as water bodies and forests do from acid rain. Farmers often add alkaline products to the soil along with additional nutrients that have leached over time. This tends to buffer the effects of acid rain. Decorative plants and trees that do not have their soil amended may suffer some ill effects from acid rain.
Material items such as cars and statues are not immune from the effects of acid rain. Paint coatings on horizontal surfaces suffer the worst etching from the acidic wet and dry deposits. Statues, especially bronze tend to corrode in the presence of acidic materials. Limestone and marble structures will deteriorate in the presence of the wet and dry acid deposits.
So what can be done? By turning to cleaner forms of energy such as wind, solar, geothermal energy, hydropower, and nuclear power the production of SO2 and NOX emissions can be reduced. As individuals, we can each make a small effort by conserving energy and reducing the amount of fossil fuels we use.