Environmental chemistry air pollution

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Environmental chemistry
air pollution

• Option E in Paper 3
• study of the effect of human activity on the
  chemical processes in the environment
• concerns political and natural borders
• global issue
• applied chemistry

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Main topics core

• air pollution
• acid deposition
• greenhouse effect
• ozone depletion

• dissolved oxygen in water
• water treatment
• soil
• waste

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Main topics AHL

• ozone depletion
• smog
• acid deposition
• water and soil

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Where is the air?
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How does the temperature change in the atmosphere?
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Primary air pollutants

• waste products from human activity
• added directly to the air
• pollutant chemical in the wrong concentration
  
• in the wrong place
• primary air pollutants
• CO NOx
  particulates
• SOx volatile organic compounds (VOCs)

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Air pollutants

• For each air pollutant you need to know
• sources natural and man-made
• (effects on health)
• methods of reducing its emissions
• any relevant balanced symbol equations

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Carbon monoxide sources

• Natural
• atmospheric oxidation of methane
• CH4 1/2O2 ? CO 2H2
• natural forest fires
• Man-made
• incomplete combustion of carbon-containing fuels
  mainly in cities localized problem as well as
  fluctuations during the day
• forest fires

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Carbon monoxide health effect

• CO combines with Fe in haemoglobin in blood
  bonds 320 times stronger than oxygen oxygen
  cannot bond onto heamoglobin
• Less oxygen supplied to body cells
• Effects
• headaches,
• shortness of breath,
• in case of high concentration (e.g. rush hour)
  unconsciousness, death

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Carbon monoxide reduction (1)

• Lean burn engines Decrease fuel /air ratio,
  for instance from 114.7 (stoichiometric ratio)
  to 118.
• (or increase air /fuel ratio)

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Carbon monoxide reduction (2)

• Catalytic converter in car exhaust system
• oxidation of CO and unburnt hydrocarbons
• reduction of nitrogen oxide
• equations

2CO (g) O2 (g) ?? 2CO2 (g)   2NO
(g) 2CO (g) ?? 2CO2 (g) N2 (g)
  2C8H18 (g) 25O2 (g) ?? 16CO2 (g) 18H2O
(g)
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Catalytic converter
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Sulphur oxides sources

• Natural
• volcanoes
• sea spray
• biological decay of organic matter which contains
  sulphur
• reduction of sulphates
• Man-made
• coal-burning power stations (equation starting
  from S in coal)
• roasting of metal sulphides e.g. ZnS and Cu2S
  (equation)

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Sulphur oxides health effects

• acidic oxides
• lung irritants, affect in particular those
  suffering from respiratory problems e.g. asthma
• formation of sulphuric acid aerosols (droplets of
  sulphuric acid) (equation) (often catalysed by
  metal particulates) effects of aerosols
• irritant to the eyes
• irritate vessels in lungs causing impaired
  breathing

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Sulphur oxides methods of reduction

• use of low-sulphur content fuels
• removal of SO2 from fumes before they are
  released
• limestone based fluidised bed (equations showing
  decomposition of calcium CaCO3 reaction of CaO
  with SO2)
• alkaline scrubbing (wet scrubber) (also called
  flue gas desulphurization) (equations showing
  reaction of CaO and Mg(OH)2)

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Sulphur oxides reduction (1)
Wet scrubber
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Sulphur oxides reduction
Limestone based fluidized bed
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Nitrogen oxides sources

• Natural
• Electrical storms release enough energy to cause
  oxidation of atmospheric nitrogen (equations
  showing oxidation of nitrogen and further
  oxidation of NO)
• Decomposition of organic matter containing
  nitrogen
• Man-made
• Combustion of fossil fuels produces enough heat
  to cause oxidation (equation showing oxidation
  of nitrogen)

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Nitrogen oxides health effects

• choking irritating gas, affects eyes and people
  with respiratory problems
• forms nitric acid aerosols/acid rain (equation
  showing dissolution of nitric acid in water)
• nitric acid also increases the rate of oxidation
  of SO2 (see later)
• plays an important role in the formation of
  secondary pollutants e.g. ozone and smog

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Nitrogen oxides reduction

• catalytic converter
• lean burn engines high air/fuel ratio or low
  fuel/air
• Recirculation/reburn of exhaust gases nitrogen
  oxide emissions are reduced by reintroducing
  exhaust gases into the fuel mixture, lowering
  peak combustion temperatures as it is the high
  temperature in the combustion engine which causes
  nitrogen oxide production.

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Particulates sources

• particulates airborne/suspended liquid and
  solid particles
• Natural
• volcanic eruptions
• large forest fires
• Man-made
• burning fossil fuels e.g. diesel
• forest fires
• industrial emissions chemical processes
• incinerators

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Particulates health effects

• particulates penetrate lungs and may block air
  passages
• some are poisonous e.g. Pb and asbestos
• adsorb chemicals and can act as catalysts in
  reactions producing secondary pollutants
• by adsorbing also increase concentration and rate
  of reaction
• reduce visibility

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Particulates reduction

• Electrostatic precipitator particulates are
  charged negatively and then attracted onto
  positively collection plates

.
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Particulates reduction
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Volatile organic compounds sources

• Natural sources
• methane bacterial anaerobic decomposition of
  organic matter (e.g. in rice paddies)
• from plants e.g. terpenes
• leakage from natural fossil reserves
• Man-made
• evaporation of fuels
• partial combustion of fuels
• leakage from storage reservoirs

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VOCs health effects

• photochemical smog
• can lead to carcinogenic compounds
• fatigue, weakness
• respiratory problems
• VOCs reduction
• catalytic converter