Acid Deposition: Causes & Effects (SL IB Environmental Systems & Societies (ESS))

Acid Deposition

• Acid deposition is a significant environmental issue caused by human activities
• It occurs when sulfur dioxide and nitrogen oxides are released into the atmosphere primarily from the combustion of fossil fuels
• These gases can undergo chemical reactions and transform into secondary pollutants, resulting in both dry and wet acid deposition

Causes of acid deposition

Primary Pollutants from the Combustion of Fossil Fuels

• Fossil fuel combustion in power plants, industrial processes, and motor vehicles releases sulfur dioxide (SO₂) and nitrogen oxides (NO_x) into the atmosphere
  • Power plants that burn coal, oil, or natural gas are major contributors to SO₂ emissions, while NO_x emissions primarily come from vehicle exhausts
  • Sulfur dioxide is released when fossil fuels containing sulfur compounds are burned and contributes to the formation of acid rain directly
  • Oxides of nitrogen are produced through high-temperature combustion processes, such as those occurring in vehicle engines and industrial furnaces

Formation of Secondary Pollutants

• SO₂ and NO_x gases can undergo chemical reactions with other compounds already present in the atmosphere, such as oxygen, water vapor, and various pollutants
  • These reactions lead to the formation of secondary pollutants, including sulfuric acid and nitric acid

Dry Deposition of Secondary Pollutants

• Sulfuric acid and nitric acid can combine with ash and other particles present in the air, forming dry particles
  • Dry deposition occurs when these particles settle on surfaces, including vegetation, buildings, and soil, causing damage over time

Wet Deposition of Secondary Pollutants

• Sulfuric acid and nitric acid can dissolve in rainwater or snowflakes, forming acidic precipitation
  • Wet deposition occurs when this acidic precipitation falls to the ground, affecting surface water and soils

• These processes of conversion from primary pollutants to secondary pollutants contribute to the phenomenon of acid deposition
• Understanding the causes of acid deposition is crucial in developing effective strategies to reduce emissions, mitigate its environmental impacts, and promote sustainable practices

• Acid deposition has significant environmental effects that can impact various ecosystems and regions
• The effects of acid deposition are diverse and can have direct and indirect consequences on aquatic organisms, forests, and nutrient cycling

Direct Effects

• Acid deposition can react with metals and rocks (such as limestone) damaging buildings and statues
  • Limestone and marble both contain calcium carbonate (CaCO₃)
  • The calcium carbonate reacts with sulfuric acid or nitric acid causing stonework to corrode and weaken

The impact of acid deposition can be seen on buildings, statues and metallic structures, particularly in polluted cities

• Acidic deposition, particularly in bodies of water, directly affects aquatic organisms such as fish, amphibians, and invertebrates
  • Acidic deposition lowers the pH of the water, making it difficult for some species to survive and reproduce

• As well as acid deposition directly falling on leaves, causing leaf damage and eventually killing plants, acid particulates can also block stomata (plant pores), preventing gaseous exchange
• Coniferous forests, such as those composed of pine or spruce trees, are sensitive to acid deposition due to their shallow root systems and thin bark
  • Acid rain also damages their foliage and inhibits nutrient absorption

The impacts of acid deposition on plant life

Indirect Toxic Effects on Fish

• Acid deposition can increase the solubility of metals like aluminium in water bodies
  • High levels of aluminium ions become toxic to fish, affecting their respiratory systems, impairing growth, and even causing mortality

The impact of acid deposition on waterways

Indirect Nutrient Effects

• Acidic deposition accelerates the leaching of essential nutrients from soil, such as calcium, magnesium, and potassium
  • Leaching of nutrients reduces their availability for plants, leading to nutrient deficiencies and impacting plant growth and overall ecosystem productivity

Geographic and Transboundary Impacts

• The impacts of acid deposition are not confined to the immediate vicinity of emission sources
  • Areas downwind of major industrial regions are more likely to experience the adverse effects of acid deposition
  • It is also possible for the impacts of acid deposition to extend across national boundaries, affecting regions in different countries than the source of emissions

• These effects of acid deposition highlight the environmental risks associated with high levels of sulfur dioxide and nitrogen oxides emissions
• Efforts to reduce acid deposition involve emission control measures, such as the use of cleaner technologies and regulations on industrial and transportation emissions
• International cooperation and agreements are also necessary to address transboundary impacts