6.4: Acid deposition

major causes of acid rain

sulfur dioxide and nitrogen oxides produced when fossil fuels are burned

dry deposition

occurs close to the source of emission and causes damage to structures and buildings

sulfur dioxide and nitrogen oxide are emitted from industrial areas and fall as dry deposition

wet deposition

occurs when acids are dissolved in precipitation and are further from the source of emission

sulfur dioxide and nitrogen oxide will be oxidised to sulfuric acid and nitric acid when they remain in the air → dissolves in cloud droplets

why is wet deposition an example of ‘trans-frontier’ pollution?

it occurs further from the source of emission and crosses international boundaries

examples of dry deposition

dry particles; aerosols; gases

examples of wet deposition

rain; snow; mist; hail

effects of acid deposition on soil

direct effects:

• change in pH → some organisms can’t adapt → earthworms cannot tolerate a pH below 4.5

• hinders nitrogen-fixing bacteria ability to add nitrate ions to soil

indirect effects:

• reduces population of soil microorganisms

• leaching of plant nutrients

• reduced ability to hold nutrients

effects of acid deposition in water

direct effects:

• excess aluminium → makes aquatic environments toxic

• damages organisms

indirect effects:

• eutrophication

• increased solubility of metals (aluminium ions)

effects of acid deposition on living organisms

direct effects:

• weakens tree growth

• yellowing of leaves, loss of chlorophyll; shedding of leaves and needles; loss of nutrients from leaves (leaching)

indirect effects:

• trees uptake aluminium ions from soil

• damage to humans’ respiratory system

• reduced ability to carry out photosynthesis

pollution management strategies

altering human activity:

• replace fossil fuels with renewable energies

• reduce use of fossil fuels

• international agreements; set targets and limitations

regulation:

• catalytic converters to convert nitrous oxides to nitrogen gas

• legislating standards of emission

Clean-up and restoration:

• spread ground limestone in acidified lakes to balance acidity

main areas experiencing transboundary pollution

Scandinavia → industrial pollution from UK, Germany, Poland travel to Scandinavia; eutrophication; loss of trout and salmon populations in Norway; 400+ lakes were lifeless in Sweden

US and Canada → The Great Lakes; industrial pollution from the US travels north as wet deposition