Air Pollution

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• Air Pollution Inorganic Gaseous Pollutants

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Major inorganic gaseous pollutants

• Carbon monoxide (CO)
• Sulfur dioxide (SO2)
• Nitrogen Oxide (NO, NO2) NOxNONO2
• Ozone (O3)

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HK 1-hour Air Quality Objectives for various air
pollutants
Air Pollutants AQ Objectives (mg/m3) AQ Objectives (ppm) US AQ Standards (ppm)
Carbon monoxide 30000 26.2 35
Sulfur dioxide 26.2 0.306 0.50a
Nitrogen dioxide 35 0.159 0.05 b
Ozone 800 0.122 0.12
a 3-hr standard, b annual arithmetic mean
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Carbon monoxide Health effect

• CO enters the blood stream and binds
  preferentially to hemoglobin, thereby replacing
  oxygen.

320 times stronger than hemoglobin-O2 binding
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Carbon monoxide sources and sinks
Such as automobiles

• Sources
• Incomplete combustion (internal engine)
• Biomass burning
• Methane oxidation
• Oxidation of non-methane hydrocarbon
• Decay of plant matter
• Sink
• Reaction with OH radical
• .OH CO ? CO2 H.
• H. O2 M ? HO2. M
• Removal by soil microorganism

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CO formation from methane oxidation
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CO emission sources in Hong Kong
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Carbon monoxide Atmospheric chemistry

• CO OH O2 ? CO2 HO2.
• HO2. NO ? NO2 OH
• NO2 hv ? NO O
• O O2 M ? O3 M
• Net CO 2 O2 hv ? CO2 O3

The net reaction can be viewed as a catalytic
oxidation of CO to CO2. Net formation of O3
occurs.
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Carbon monoxide control strategies on the
automobile source

• Employ a leaner air/fuel mixture (higher air/fuel
  ratio)
• Employ catalytic exhaust reactors
• Excess air is pumped into the exhaust pipe.
• Air-exhaust mixture pass through a catalytic
  converter to oxidize CO to CO2.
• Addition of oxygenates to gasoline
• Examples of oxygenates methanol, ethanol, MTBE

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Sulfur dioxide Health effect

• Produce irritation and increasing resistance in
  the respiratory tract.
• Mucus secretion
• In sensitive individuals, the lung function
  changes may be accompanied by perceptible
  symptoms such as wheezing, shortness of breath,
  and coughing.
• may also lead to increased mortality, especially
  if elevated levels of suspended particles are
  also present.

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Sulfur dioxide Sources and sinks

• Sources
• Combustion of S-containing fuel in electric power
  plants, vehicles.
• S (organic S FeS2 pyrite) O2 --gt SO2
• Oxidation of H2S 2H2S 3 O2 --gt 2 SO2 2 H2O
• H2S is produced as an end product of the
  anaerobic decomposition of S-containing compounds
  by micro organisms.
• Oxidation of DMS
• Sink
• Converted into sulphuric acid in either gas or
  liquid phase

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SO2 emission sources in Hong Kong
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Formation of sulfuric acid and sulfate from SO2

• In gas-phase
• SO2 .OH M ? HOSO2. M
• HOSO2. O2 ? HO2. SO3
• SO3 H2O M ? H2SO4 M
• In aqueous phase, dissolved SO2 is oxidized to
  sulfate by
• O3 (dominant pathway when pHgt5)
• H2O2 (dominant pathway when pHlt5)
• organic peroxides
• O2 catalyzed by iron and manganese
• Sulfate formation
• 2 NH3 H2SO4 ? (NH4)2SO4

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Sulfur dioxide Control strategies

• Removal of S before DURING burning.
• Fludized bed combustion Coal is burned with
  limestone (CaCO3) (finely pulverized) or dolomite
  (Ca-Mg carbonate) or both.
• CaCO3 --gt CaO CO2,
• CaO SO2 --gt CaSO3.
• CaSO3 is removed from the stack by an
  electrostatic precipitator.
• removal of S from smokestacks before entering the
  atmosphere.
• Flue-gas desulfurization SO2 is washed from the
  chimney (flue) gases by absorption in an alkaline
  solution.

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Sulfur dioxide Control strategies (Continued)

• 3. Dilution
• Installation of tall stacks reduces SO2 levels
  in the immediate neighborhood by dispersing them
  more widely

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Nitrogen oxides Health Effects

• NO
• Cellular inflammation at very high
  concentrations.
• May be incorporated into hemoglobin in the blood
  to interfere with the transport of oxygen around
  the body.
• NO2
• irritate the lungs
• lower resistance to respiratory infection such as
  influenza.

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Nitrogen oxides Sources and sinks

• Sources
• Fuel combustion in power plants and automobiles.
• N2 O2 --gt NO
• 2 NO O2 --gt 2 NO2
• Natural sources electrical storms bacterial
  decomposition of nitrogen-containing organic
  matter

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NOx emission sources in Hong Kong
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Nitrogen oxides Atmospheric chemistry

• Interconversion of NO and NO2

NO2 hv ? NO O (1) O O2 M ? O3
M (2) NO O3 ? NO2 O2 (3)
No net O3 formation
NO2 hv ? NO O (1) O O2 M ? O3
M (2) HO2. NO? NO2 OH (4) RO2. NO ? NO2
RO. (5)
O3 is formed
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Nitrogen oxides Atmospheric chemistry

• Formation of nitric acid

Gas-phase reaction NO2 OH ? HNO3 daytime
(dominate pathway)
Heterogeneous reaction NO2 O3 ? NO3 O2 NO3
NO2 Û N2O5 N2O5 H2O (aq)? 2 HNO3 (aq)
Minor pathway Only operative during nighttime
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Nitrogen oxides Atmospheric chemistry

• Formation of nitrate

HNO3 NH3 ? NH4NO3 HNO3 NaCl(s) ? NaNO3 HCl
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Nitrogen oxides Control strategies

• 1. Lower the combustion temperature of the
  furnace in electric power plants
• 2. Install catalytic converters catalytic
  converters in automobiles can remove 76 of NOx
  from tailpipes.

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Two-stage combustion to reduce both NOx and VOCs

• First stage combustion conditionrich in fuel
• Second stage combustion conditionrich in air

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Three-way catalytic converter for automobile
exhaust (Remove CO, NO and HC)
HC H2O H2 CO 2NO 2H2 N2 2 H2O
2CO O2 2CO2 HC 2O2 CO2 2H2O
Catalyst Rhodium
Catalyst Rhodium
Catalyst Platium/palladium
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NOx control in power plants

• Ammonium reduction of NO
• 4NH3 6NO 5 N2 6 H2O
• Urea reduction of NO
• 2CO(NH2)2 6NO 5 N2 2 CO2 4 H2O