Acid rain

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. https://www.youtube.com/watch?v
=Nf8cuvl62Vc • 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

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

17. Management cont.
 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