Acid Precipitation

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

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

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)

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

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

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

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

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

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!

Video: Interactions Science & Society Acid Rain