Section 15 vid 4

Acid Rain and Acid Deposition

• Definition: Acid rain or acid deposition refers to a mixture of acidic substances in the atmosphere that can fall as various forms of precipitation—rain, snow, fog, and even as dry deposition (acidic dust).

Sources of Acid Pollution

• Industrial Emissions: In developed areas, tall smokestacks are utilized to release pollutants above inversion layers, aiming to prevent local air pollution.

• Pollutants: Main pollutants include sulfur dioxide (SO2) and nitrogen oxides (NOx), which can travel hundreds of miles and react in the atmosphere to form secondary pollutants like sulfuric and nitric acids.

• pH Levels: Normal rainwater has a pH of about 5.6, while acid rain can drop to levels of 4.2 to 4.7, and some areas experience fog with pH as low as 2.3 (1,000 times more acidic than normal).

Chemistry of Acid Rain

• pH Scale: The pH scale ranges from 0 (very acidic) to 14 (very basic), with 7 being neutral. A change of one unit represents a tenfold change in hydrogen ion concentration.

• Buffers: Some soils can neutralize acid deposition through limestone or calcium carbonate which buffers hydrogen ions. However, regions lacking such soils can face severe impacts.

Effects on Health and Economy

• Human Health: Sulfur dioxide and nitrogen oxides irritate lungs and can worsen respiratory conditions. Toxic metals can leach from soil into crops and drinking water.

• Economic Impact: Damages to car finishes, corrosive effects on metals and buildings, and decreased productivity in agriculture, forests, and fisheries due to lower quality and quantity.

Environmental Impact

• Aquatic Systems: pH levels below 6, especially below 5, damage aquatic life. Many freshwater organisms cannot survive in waters below a pH of 4.5.

• Aluminum Toxicity: During acid rain events, aluminum ions can mobilize and harm aquatic organisms by damaging gills and leading to asphyxiation.

• Long-term Effects: Chronic acidification leads to decreased fish populations in lakes, particularly in regions like Canada, Norway, and certain areas in the US.

Soil and Vegetation Effects

• Soil Composition: Acid deposition leaches essential nutrients like magnesium and calcium from soil, reduces productivity, and inhibits plant nutrient uptake.

• Toxic Compounds: Plants can absorb toxic metals like mercury and cadmium from acidified environments, which impact both plant and animal life.

• Plant Health: Acid rain damages plant leaves, weakens trees, and makes them vulnerable to diseases and environmental stresses.

Geographic and Industrial Factors

• Influenced Areas: Areas downwind of urban sites, heavy traffic, and carbon burning power plants experience severe acid deposition due to their environmental profiles.

• Sensitive Regions: Areas with thin soils and high elevation forests are particularly vulnerable, with mountain-dwelling evergreen species suffering from acidic conditions.

Solutions to the Problem

• Pollution Control: Reducing the burning of coal and improving energy efficiency are vital steps toward minimizing acid deposition.

• Renewable Energy: Transitioning away from nonrenewable resources and increasing reliance on cleaner, renewable energy sources is critical for long-term solutions.

• Current Measures: Efforts to neutralize acidified lakes with calcium carbonate are ongoing, though they have limited effectiveness and can harm aquatic ecosystems.

Conclusion and Review

• Understand and explain the causes of acid deposition, its environmental impacts, and potential solutions.

• Key Action for Reduction: Reducing fossil fuel use is the most effective long-term solution to decrease acid rain and deposition issues.