Acid Precipitation Notes

Understanding Acid Precipitation

  • Definition of Acid Precipitation
  • Any form of precipitation (rain, snow, dew) with a pH less than 5.6.
  • Created when sulfur dioxide (SO2) and nitrogen oxides (NOx) combine with atmospheric moisture.
  • Contains acids like sulfuric acid (H2SO4) and nitric acid (HNO3).

  • Key Pollutants

  • Sulfur Dioxide (SO2):

    • Clear, colorless gas with a strong odor.
    • Produced mainly from industrial activities: burning coal, metal refining (smelting).
    • Contributes to acid rain through atmospheric reactions:
    • SO2 + O2 → SO3
    • SO3 + H2O → H2SO4

  • Nitrogen Oxides (NOx):

    • Represents nitrogen monoxide (NO) + nitrogen dioxide (NO2).
    • Major source from vehicle emissions and fossil fuel burning.
    • Contributes to acid precipitation:
    • 2 NO + O2 → 2 NO2
    • 3 NO2 + H2O → 2 HNO3 + NO
  • Formation Processes:
  • Wet Deposition: Acidic substances fall as rain or snow.
  • Dry Deposition: Acid-forming chemicals directly settle on surfaces as gas or particles (e.g., dust).
  • Environmental Impact of Acid Precipitation
  • Affects aquatic ecosystems:
    • Changes pH levels impacts fish survival; aquatic life can only tolerate small pH changes.
    • Loss of fish affects food chain; predators must adapt or relocate for food.
  • Impacts Soil:
    • Acid leaches essential nutrients (Ca, Mg) and leaches toxic metals (Al).
    • Soil's buffering capacity can mitigate acidity but may degrade over time.
  • Damage to Structures:
    • Corrodes buildings, monuments, and bridges.
  • Economic Impact of Acid Precipitation
  • Decreases fish populations affecting tourism and fishing industries.
  • Causes additional costs in maintenance and restoration of infrastructure.
  • Mitigation Measures:
  • Transition to low-sulfur fossil fuels.
  • Install technologies (scrubbers) to reduce emissions from power plants and factories.
  • Enforce stricter vehicle emissions laws.
  • Current Status and Outlook:
  • Emissions of acid-forming pollutants have decreased but many ecosystems are still recovering.
  • Continued efforts and policy changes are necessary to fully restore health to affected regions.
  • Chemistry Involved:
  • Buffering reaction in soil:
    • CaCO3 + H2SO4 → CaSO4 + H2O + CO2 (reduction of acidity).
  • Acid precipitation reduces biodiversity and disrupts ecosystems which can take decades to recover.
  • Examples of Acid Precipitation:
  • Historical issues faced due to emissions from the U.S. affecting the Canadian landscape.
  • Current legislative changes have led to improvements, but challenges remain in persisting pollution sources.