Enduring Understanding:

• Human activities have physical, chemical, and biological consequences for the atmosphere.

Learning Objective:

• Describe acid deposition.

• Describe the effects of acid deposition on the environment.

Essential Knowledge:

• Acid rain and deposition is due to nitrogen oxides and sulfur oxides from anthropogenic and natural sources in the atmosphere.

• Nitric oxides that cause acid deposition come from motor vehicles and coal-burning power plants. Sulfur dioxides that cause acid deposition come from coal-burning power plants.

• Acid deposition mainly affects communities that are downwind from coal-burning power plants.

• Acid rain and deposition can lead to the acidification of soils and bodies of water and corrosion of human-made structures.

• Regional differences in soils and bedrock affect the impact that acid deposition has on the region—such as limestone bedrock’s ability to neutralize the effect of acid rain on lakes and ponds.

• Normal rain should be at about a 5.6 pH, which is a little more acidic than distilled water

• Acid rain tends to be around 4.3

  • This may seem like a small difference, but for the ecosystems that hang is a delicate balance, it can be a great disturbance

Process

• Vehicles burning fossil fuels emit nitrogen oxides (NOx)

  • Nitrogen oxide reacts with water once in the air, creating nitrous acid and nitric acid

• Coal-burning power plants release nitrogen oxides 9NOx) and sulfur dioxide (SO2)

  • Sulfur dioxide reacts with water in the air, resulting in sulfurous acid and later sulfuric acid

• Natural sources emit some acid-forming compounds

  • Volcanoes, geysers, and hot springs can contribute sulfur dioxides, nitrogen oxides, and carbon dioxide to the atmosphere

  • Most of the pollutants that cause acid rain are from the burning of fossil fuels, as these natural sources are small and infrequent

• SOx and NOx can be carried long distances

  • Pollutants released high into the atmosphere are given more time to react with water, increasing the likelihood that acid rain will form

  • Acid deposition can greatly impact communities and environments downwind of coal-burning power plants

  • Pollutants high in the atmosphere can end up damaging areas far from the source

• Nitric acid and sulfuric acid can be in the form of dry deposits or precipitation

Effects

• Forest soils, and aquatic systems, even human structures, are impacted by acid deposition

• Acid rain promotes aluminum ions to leach from soils

  • This is toxic to plants and aquatic life

• Tree roots are unable to take up calcium when aluminum ions are present

  • Calcium is critical for normal cell processes, without it trees and plants suffer

• Damaged needles and leaves, as well as nutrient deficiencies caused by changing soil chemistry, means plants don’t photosynthesis as effectively

• Aquatic life has a certain range of tolerance for acidic conditions

  • More acidic lakes and streams can result in death, skeletal deformities, and damages the eggs of fish and other aquatic life

  • Even if a species has a high tolerance and can survive the acidity changes, its prey might not be able to, starving out the organism

• Acid rain also damages human-made structures

  • Metal and stone can be eroded by acid deposition

  • Many statues are made of marble, a rock that contains calcite, which is dissolved by acid deposition

  • This is especially problematic for old structures that are delicate and need to be preserved but have been around and been exposed to acid rain the longest

Regional Responses

• The bedrock and soils determine how vulnerable an area is to acid rain

• Soils rich in magnesium, calcium carbonate, and limestone can buffer, or neutralize, the acid

• Lakes surrounded by granite that have thin, nutrient-poor soils, are vulnerable

  • Forests and lakes of New England, and high elevations, have those conditions