acid rain

• causes of acid rain?

  acid rain is the combination of the pollution problems caused by a range of acidic gases and other pollutants that contribute to the problem

  (precipitation with a pH less than 5.6)
• Pollutants involved in Acid rain

  Primary Pollutants-

  • sulphur dioxide (SO2) -> from burning fossil fuels, dissolves in water forming sulphuric acid
  • oxides of nitrogen (NOx) -> from internal combustion engine, not product of combustion but nitrogen from air reacting with oxygen under high temp + pressure, dissolves in water to form nitric acid + nitrous acid
• Pollutants involved in Acid rain

  Secondary Pollutants-

  • sulphur dioxide (SO2) -> reacts with atmospheric oxygen, usually ozone, to form sulphur trioxide (SO3), reacts with water to form sulphuric acid
• Impacts of acidic rain

  Abiotic-

  damage to limestone (erosion)

  corrosion to metal-> damaging water pipes and train lines
• Impacts of acidic rain

  Biotic-

  DIRECT

  denatures proteins and enzymes- changes pH outside of the range of tolerance of living organisms

  damage to exposed tissues-

  leaf waxy layers and cells, root hair cells, prevents germination of seeds and fish eggs

  respiratory problems- sulphur dioxide can create breathing difficulties
• Impacts of Acidic rain

  Biotic-

  INDIRECT

  the solubility of many metal ion is affected by pH, becoming more soluble at low pH

  metal leaching- decreasing soil pH can also cause metal ions to be leached from the soil (Ca2+, Mg2+, Al3+, Pb+)

  these toxic ions can inhibit the action of enzymes in root hair cells and can immobalise detritivores and decomposers

  leached metals can accumulate- in rivers which become toxic to aquatic life
• how can we control acid rain?

  -natural gas desulphuristation

  -natural gas

  -crude oil desulphurisation

  -coal desulphurisation

  -flue-gas desulphurisation

  -dry flue-gas desulphurisation

  -wet flue-gas desulphurisation

  -low temperature combustion

  -catalytic converters

  -urea sprays
• natural gas desulphurisation


  removal of sulphur from the fuel before it is burned
• natural gas


  hydrogen sulphide is removed from natural gas by dissolving it in an alkaline solution or reacting with iron particles

  -prevents corrosion of refinery pipeline equipment

  -prevents production of sulphur dioxide when burnt
• crude oil desulphurisation


  sulphur compounds are removed from crude oil during distillation using molybdenum catalysts in the process of hydrodesulphurisation
• coal desulphurisation


  iron pyrites (FeS2) is removed by crushing the coal then washing and streaming it fast enough to wash out the coal and leaving the denser pyrites behind
• flue-gas desulphurisation


  several process can be used to remove sulphur dioxide from the power station emissions released after fuel combustion
• dry flue-gas desulphurisation


  flue gases (mixture of gases produced by burning of fuel in power stations and industrial plants) are passed through a bed of crushed calcium carbonate producing solid calcium sulphur

  if the effluent gases are cleaned to remove smoke particles, then the calcium sulphur can be used to make plaster board
• wet flue-gas desulphurisation


  scrubbing by bubbling flue-gases through liquid sodium sulphite producing sodium hydrogen sulphite

  the sodium hydrogen sulphite produced is heated and broken down into sodium sulphite, water and concentrated pure sulphur dioxide which can be reused
• low temperature combustion


  produces less NOx fluidised bed combustion when an increased surface area for combustion which maintains rapid combustion without the need for high tempuratures
• catalytic converters


  exhaust pipe chamber with catalytic metals such as platinum which chemically reduces NOx to nitrogen and oxygen
• urea sprays


  removing NOx by reacting it with urea