1. Acid Precipitation

2. BIG Idea of the Unit
Chemical reactions have a negative impact on the environment but they can also be used to address environmental concerns

3. What is Acid Precipitation?
Term used to describe any precipitation (rain, snow, fog) that has become acidic
Forms when pollutants (most commonly sulfur oxides and nitrogen oxides) combine with water in the atmosphere
Acid precipitation has pH less than 5.6 (normal pH of rain)
Acid deposition – when acidic substances reach earth & combine with water in soil, lakes, or on leaves

4. Sources of Acid Forming Pollutants
Sulfur Oxides SOx
Produced by industry – burning coal & mining industry
Sulfur reacts with oxygen in air to form sulfur dioxide, which reacts with more oxygen to form sulfur trioxide
Sulfur trioxide combines with water in atmosphere to form sulfuric acid (H2SO4)

5. Sources of Acid Forming Pollutants
Nitrogen oxides (NOx)
Produced by vehicles that burn fossil fuels (gasoline)
Temperatures in engines react atmosphere nitrogen and oxygen to form nitrogen monoxide
NO reacts with more oxygen to form nitrogen dioxide (makes up smog)
NO2 reacts with water in atmosphere to form nitric acid HNO3

7. Environmental Impact of Acid Precipitation
Aquatic Ecosystems
Aquatic life can only tolerate minor changes in pH
As pH decreases, young & fragile organisms die
This loss affects organisms higher on food chain
Predators must find other food or move elsewhere to survive
Aluminum ions from acidified soil can enter streams and lakes – damage gills of fish

8. Environmental Impact of Acid Precipitation
Soils
Acidic ground water can dissolve and wash away metals ions
Soils have buffering capacity – substances in soil act as bases to neutralize acid
Soils in areas where rock is mostly limestone, have high buffering capacity

9. Environmental Impact of Acid Precipitation
Forest
Some ions (calcium, potassium, magnesium) are essential nutrients for plant growth
Ions are dissolved in soil by acid precipitation
Acid precipitation rarely kills trees but it weakens them
Tree are more vulnerable to disease, wind, extreme weather

11. The Economic Impact of Acid Precipitation
Acid precipitation can harm environment and harm economy
Damage to steel structures, limestone buildings, stone monuments
Loss of trees = loss of wood, affects lumber industry
Reduction in fish stocks, affects fishing industry

12. Cleaning Up Acid Precipitation
Improvements since 1980’s
Switch to low sulfur emission fossil fuels
Installation of scrubbers to remove emissions from mining operations and fossil fuel burning power plants
Stricter laws governing vehicle emissions
It will take a long time for ecosystems to recover – longer than it took to pollute them!

13. Video: Interactions Science & Society Acid Rain