How can we fix it?

Acid rain can be reduced by decreasing emissions. By reducing emissions, SO2 and NOx levels will decrease. Emission controls such as the Clean Air Act have dramatically decreased air pollution, resulting in the decrease in acid rain occurrences. Liming is a temporary solution to acidic bodies of water. Limestone is known to raise pH levels and eliminate some acidification symptoms. This process is expensive and temporary but can help restore aquatic life.

Source: Acid rain and its ecological consequences

Why does it matter?

Acid rain is an important topic to learn about because it has been detrimental to soil, aquatic ecosystems, forest trees, crop plants, and human health.

Soil: The acidification of soil increases the exchange between hydrogen ion and nutrients such as potassium (K), magnesium (Mg) and calcium (Ca). This leads to nutrient deficiency in soils and causes soil fertility to decline.

Aquatic Ecosystems: Acidic water bodies have shown increased mortality rates, reproductive failure, and skeletal deformities in aquatic life. Many amphibians including frogs, toads, and salamander are sensitive to low pH. Snail and phytoplankton populations begin to decline when pH falls below 5.5. Snails are unable to live in pH levels of 5.2.

Forest Trees: Acid deposition can harm forest trees through foliage or roots. The damage of acid deposition includes reduced canopy cover, crown die back, and whole tree death. Low pH levels cause leaves and needles to discolor and decline. The leaf is most sensitive to damage as epicuticular wax erosion occurs. An injured epidermis leaves the tree viable to disease, greatly declining tree populations.

Crop Plants: Acid rain has physiological effects on crop plants. Acid rain causes photosynthetic rate to decline as well as reduce root lengths and leaf numbers.

Human Health: Acid rain has direct and indirect effects on human health. Direct effects include eye and skin irritation. Indirect effects evolve from contact with materials that have been polluted with acid deposition such as food and water. This consumption accumulates in the body and can form dry cough, asthma, headache, eye, nose, and throat irritations.


Man Made Structures: Acid rain causes deterioration to man made structures. It mostly destroys the paint on cars because of long term exposure. Historical statues also suffer from acid deposition, the Acropolis in Athens has shown great destruction.

Source: Acid rain and its ecological consequences
The Oxford Companion to Global Change
A-Z of the Environment

Acidity

The acidity is determined by the number of hydrogen ions in a substance. pH is the common measure used to determine the acidity of water. Lower pH values describe higher levels of acidity. Rain is considered acidic if it has an H+ ion greater than 2.5 and a pH less than 5.6. Naturally, all rain is acidic because the reaction between water and atmospheric carbon dioxide, forms carbonic acid. This carbonic acid partially dissociates and produces hydrogen ions which lowers pH levels. Natural acid deposition has a pH no lower than 5.0 while human forced acid deposition has a pH as low as 2.6 (7.0 is neutral).

Source: Acid rain and its ecological consequences.
The Oxford Companion to Global Change

What causes Acid Rain?

Acid rain is caused by sulfur dioxide (SO2) and nitrogen oxide (NOx).  Sulfur dioxide and nitrogen oxides enter the atmosphere through natural sources, however the man-made sources is what causes the problem. Natural sources of sulfur dioxide include oceans and volcanic eruptions. Natural sources of nitrogen oxide include lightening, volcanic eruptions, and microbial activity. Man-made pollutants of sulfur dioxide stem from the burning of coal/petroleum and the smelting of iron/other metallic ores. Man made pollutants of nitrogen oxide stem from power stations, vehicle exhausts, and industrial emission.


“When the pollutants are vented into the atmosphere by tall smoke stakes, molecules of SO2 and NOx are caught up in prevailing winds, where they interact in the presence of sunlight with vapors to form sulfuric acid and nitric acid mists. These acids remain in vapor state under the prevalent high temperatures conditions. When the temperature falls, condensation takes the form of aerosol droplets, which owing to the presence of unburnt carbon particles will be black, acidic and carbonaceous in nature” (Singh et al 2006).

Nitrogen oxides are released in the atmosphere during combustion when when atmospheric nitrogen and oxygen combine. Nitrogen oxide is also formed when the oxygen from fuels combine with atmospheric oxygen. Sulfur oxides are formed when an object containing sulfur is burned and sulfur combines with atmospheric oxygen.  Most sulfur oxide comes from the combustion of coal, oil, as well as smelting. Half of  nitrogen oxides generated is from cars.

Source: Acid rain and its ecological consequences
The Oxford Companion to Global Change
The Hutchinson Unabridged Encyclepedia
International Journal of Environmental Studies

What is Acid Rain?

Acid rain refers to the different ways acid falls from the atmosphere, including rain, fog, hail, and snow. The more accurate term is acid deposition. There are two forms of acid deposition, dry and wet. Dry deposition occurs close to the emission points while wet deposition may occur thousands of kilometers away from pollution sources.

Source: Acid rain and its ecological consequences