Download 5.8 Acid Deposition

5.8 Acid Deposition (Rain)
The pH Scale…What is acidic?
Acid Deposition (Process)
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
Primary pollutants by source
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
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)
 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
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
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
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)
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