1. 6.4 Acid Deposition (Rain)

2. The pH Scale…What is acidic?

3. Acidity Rain is naturally slightly acidic pH 5.6
Caused by carbon dioxide in the air dissolving into the water forming carbonic acid

4.
However, when sulfur and nitrogen oxides dissolve in the rain they form sulfuric and nitric acid and can have a very low pH (1-3)
pH scale is logarithmic, pH1 is x10 more acidic that pH 2, and x100 stronger than pH 3

5. Acid Deposition (Process)

6. Chemistry of acidified precipitations
Acid deposition can be either wet or dry:
Wet deposition - acidic rain, snow, or other precipitation
Dry deposition - acidic gas or dry particles, not mixed with water
Pollutants can be classified as either primary or secondary:
Primary pollutants - those directly emitted by a factory or automobile
SO2 - sulfur dioxide
NO and NO2, usually identified as NOx

7. Primary pollutants by source

8. Chemistry Cont.
Secondary pollutants - primary pollutants react with other substances in the atmosphere and create different pollutants
H2SO3 - sulfurous acid
H2SO4 - sulfuric acid
HNO3 - nitric acid

9. Effects of acid deposition on environment
Direct effects (Know 1):
Inhibits embryonic development of fish
Chlorophyll loss & yellowing of tree leaves and buds → diminished growth
Thinning of cuticle (the waxy coating on needles)
Symbiotic root microbes killed (i.e. Rhizobium spp. and other beneficial fungi)

10. Effects of acid deposition on environment
Toxic effects (Know 1):
Aluminum (Al) leaches out of soil into streams
Al disrupts salt, water, and oxygen regulating mechanisms in fish
Al can also adhere to fish gills, causing suffocation
Lichens sensitive to SO2 gases and used as indicator species

11. Effects of acid deposition on environment
Nutrient effects (Know 1):
Soil particles can’t retain Ca, Mg, K, and other nutrients in acidic environment, so those nutrients are leached out of soil and not available to trees
Dissolved Al ions damage root hairs (the smallest roots, which are the most effective at absorbing nutrients), so the trees are unable to absorb as many nutrients
N-fixing bacteria don’t function as well, so less N is added to soil matrix

12. Effects of acid deposition on environment
Damage to human infrastructure:
acid rain dissolves limestone structures, especially buildings and statues

13. Acid deposition is regional
Acid precipitation falls back to Earth rather than entering stratospheric jet stream
Most areas are downwind of pollution sources
Canadian forests damaged by coal-fired power plants in USA
Scandinavian and German forests damaged by British coal plants

14. Potential problem areas
because of sensitive soils
Potential problem areas because
of air pollution: emissions leading
to acid deposition
Current problem areas
(including lakes and rivers)

15. Reducing the effects of acid deposition
find out about the following techniques:
Liming lakes to neutralise acidity.
Precombustion (before burning) techniques.
End of pipe measures (after burning).
Of course we could always reduce our use of fossil fuels to help solve this problem.
Nuclear power? Electric cars?

16. Pollution management strategies for acid deposition
See Table 15.7 on p.298 of the IB ESS 2010 Course Companion
Replace
Switch to renewable energy sources (reduce fossil fuel use)
Increase energy efficiency (better light bulbs and appliances)
More public transportation (fewer automobiles on the road)
Use low-sulfur fuels
Regulate
Install ‘scrubbers’ on smokestacks of coal-fired power plants to remove SO2
Catalytic converters installed on automobiles (required by law in the US, Canada, and Europe)

17. Management cont. Freshwater ecosystems much more vulnerable Restore
Add limestone to acidified lakes and streams
Using limestone or calcium carbonate (CaCO3) can neutralize (buffer) the impact of acids.
Freshwater ecosystems much more vulnerable
Expensive and hard to determine how much to add

19. Remember, this is not a Global problem but a regional one most serious in
Mountain top forests
Areas with high auto traffic
Areas downwind from industrial centers

20. CASE STUDY Research the effect of acid deposition and intergovernmental agreements or legislation and their effectiveness
In groups you are going to create a poster to show the impact and pollution management strategies in one of the cases below.
Canada affected by acid deposition from the USA.
Sweden and Norway affected by acid deposition from Poland, Germany and UK.
China