acid rain

• Measured on a pH scale - logarithmic 
• Rain water is naturally slightly acidic. 

  • CO2 in the air dissolves in the falling water to make carbonic acid 
• Two causes of acid rain:

  • NOxs - high temperature combustion, 
  • Car engines, power stations 
  • Sulphur dioxide - coal, diesel 
• NOx reaction with water vapour:

  • NOx + H2O --> nitrous acid 
  • NOx + H2O --> nitric acid 
• Sulphur dioxide reaction with water:

  • SO2 + H2O --> sulphurous acid 
• Causes of acid rain:

  • Sulphur trioxide reacts with water --> sulphuric acid 
  • Tropospheric ozone reacts with sulphur dioxide to make sulphur trioxide 
  • Sulphuric acid is very bad 
  • Synergism 
• Sources of NOx and SO2:

  • Sulphur dioxide - 50% from coal power stations 30% from oil/diesel transport 
  • Oxides of nitrogen - high temperature combustion 
  • 45% from diesel transport 
  • 20% from electricity production
  • Fertilisers being denitrified 
• Acid rain is mobile - moves with the wind and travel long distances. 

  • Western nation pollution pollution is blown east
  • Affected Scandinavian countries 
• Properties of acid rain:

  • Reactive - reacts with water vapour 
  • Soluble - water soluble but not liposoluble 
  • Synergistic - sulphur dioxide reacts with ozone to make sulphuric acid 
  • Mobility - gases are highly mobile 
  • Gas and liquid state of matter 
• Impacts:

  • Acid denatures proteins and membranes 
  • Waxy cuticle is dissolved 
  • Stomata damage 
  • Root hairs damaged 
  • Germination of seeds prohibited 
  • Synergism - ozone breaks down cuticle exposing tissue to acids.
  • Dissolves limestone buildings 
  • Organisms with exoskeletons 
  • Organisms that lay eggs - shells 
• Impacts to soil:

  • Soil deflocculation - separation of peds 
  • Nutrient leaching - poor nutrient content 
  • Mobilisation of toxic chemicals 
• Impacts to soil organisms:

  • Beyond range of tolerance 
  • Low pH denatures proteins in cells 
  • Kills mycorrhizal fungi and bacteria 
  • Detritivores die - less breakdown of organic matter 
  • Bacteria die 
• Indirect impacts on plants:

  • Reduced nutrient uptake 
  • No mycorrhizae or micro-organisms 
  • Hydrogen ions inhibit uptake 
  • Uptake of toxic minerals 
• Impacts in aquatic organisms:

  • Changes range of tolerance - impacts biodiversity 
  • Denatures enzymes 
  • Exposes tissues 
  • Damage to gills and eggs 
  • Dissolves exoskeletons 
• Indirect impacts on aquatic organisms:

  • Crustaceans and molluscs 
  • Calcium unavailable for shell maintenance 
  • Aluminium poisoning 
• Critical load - maximum amount of pollutant that an ecosystem can accept before significant impacts happen 

  • Higher in limestone catchments - higher pH so more acid required to reduce pH 
• Snow:

  • Accumulation of acid snow in cold regions 
  • Melt water has low pH
  • Flows into soils and rivers