1. Acid Deposition
Acid Deposition Movie of Awesomeness

2. Acidity and pH
Acid Deposition is a general term for acid coming down from the air.
Dry: Acid comes down as ash or dry particles
Wet: Rain or snow
Review
Acids are chemicals that can give H+ ions away
Measured on pH scale (7 is neutral)
Normal rain has a pH of about 5.6 naturally
Can sometimes be lower than 2!

3. Pollutants that lead to acid deposition
Review
Primary Pollutants: Emitted directly from source
Secondary Pollutants: Are made in the atmosphere
Main Primary Pollutants leading to acid deposition
Sulphur Dioxide (SO2)
Nitrogen Oxides (NOx)
Both react with water to form strong acids
Carbon Dioxide (CO2)
Also acidic, but forms a weak acid

4. Sources of pollution that lead to acid deposition
Natural
SO2 from volcanoes
NOx from lightning strikes
Human Caused
Combustion of fossil fuels
Cars, industry, power plants
Sulphur is common in coal and oil

5. The Formation of Acid Rain

6. The Effects of Acid Deposition
Direct Effects
Weakening tree growth, decreasing pH in surface water affecting organisms
Indirect Effects
Toxic effects, increased solubility, nutrient effects
Coniferous Forest Example
Leaves and buds show yellowing
Growth is reduced
Symbiotic root microbes are killed
Nutrients are leached out of soil
Releases toxic aluminum which damages root hairs
(Weakened trees die)

7. Toxic Effects of Acid Deposition
Aluminum Ions
Aluminum is common in soil, but is usually not soluble
Lower pH increases solubility
Ex: Affects the ability of fish to regulate salt and oxygen
Lichens
Very sensitive to pollution
(indicator species often used to estimate pollution)
Nutrient Removal
Causes nutrients to leach out of soil
Inhibits nitrogen fixing bacteria as well
Buildings
Limestone buildings literally dissolve
Human Health
Dry deposition forms small particles of sulphates
and nitrates

8. Regional Effect of Acid Deposition
***Climate change and ozone depletion are global… Acid deposition is regional because the pollutants return to the surface before spreading over long distances***
Dry
Usually occurs quite close to the source
Mostly Sulphur dioxide, Sulphur trioxide, and the nitrogen oxides
Wet
Slightly longer distances from source
Mainly Sulphurous acid, sulphuric acid, nitric acid
Therefore…
Areas downwind of major industrial centers are strongly affected
Ex:
Scandinavian forests affected by Western Europe
Canada affected by USA
Southeast Asia affected by China

9. Regions of Acid Deposition

10. Managing Acid Deposition
“Replace, Regulate, and Restore”

11. Reducing the Effects of Acid Deposition
Liming Lakes
By 1990 over 400 lakes were virtually lifeless
Did not really work, just a temporary fix
Reducing Emissions
Reduce SO2 and NOx by reducing the combustion of fossil fuels (next unit)
Precombustion Techniques
Remove Sulphur before combustion
The removed Sulphur can be used in
several applications
End of Pipe Measures
Remove SO2 and NOx after combustion
Ex: Wet Scrubber, Catalytic Converter,