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Air Pollution– Inorganic Gaseous Pollutants. Major inorganic gaseous pollutants. Carbon monoxide (CO) Sulfur dioxide (SO2) Nitrogen Oxide (NO, NO2) NOx=NO+NO2 Ozone (O3). HK 1-hour Air Quality Objectives for various air pollutants. a : 3-hr standard, b : annual arithmetic mean. O-O. O2.

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Air Pollution– Inorganic Gaseous Pollutants

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major inorganic gaseous pollutants
Major inorganic gaseous pollutants
  • Carbon monoxide (CO)
  • Sulfur dioxide (SO2)
  • Nitrogen Oxide (NO, NO2) NOx=NO+NO2
  • Ozone (O3)
hk 1 hour air quality objectives for various air pollutants
HK 1-hour Air Quality Objectives for various air pollutants

a: 3-hr standard, b: annual arithmetic mean

carbon monoxide health effect








Carbon monoxide: Health effect

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

320 times stronger than hemoglobin-O2 binding

carbon monoxide sources and sinks
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
carbon monoxide atmospheric chemistry
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.

carbon monoxide control strategies on the automobile source
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
sulfur dioxide health effect
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.
sulfur dioxide sources and sinks
Sulfur dioxide: Sources and sinks


  • Combustion of S-containing fuel in electric power plants, vehicles.
  • S (organic S + FeS2 pyrite) + O2 --> SO2
  • Oxidation of H2S: 2H2S + 3 O2 --> 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


  • Converted into sulphuric acid in either gas or liquid phase
formation of sulfuric acid and sulfate from so2
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 pH>5)
    • H2O2 (dominant pathway when pH<5)
    • organic peroxides
    • O2 catalyzed by iron and manganese
  • Sulfate formation:

2 NH3 + H2SO4  (NH4)2SO4

sulfur dioxide control strategies
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 --> CaO + CO2,

CaO + SO2 --> 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.

sulfur dioxide control strategies continued
Sulfur dioxide: Control strategies (Continued)

3. Dilution

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

nitrogen oxides health effects
Nitrogen oxides: Health Effects


  • Cellular inflammation at very high concentrations.
  • May be incorporated into hemoglobin in the blood to interfere with the transport of oxygen around the body.


  • irritate the lungs
  • lower resistance to respiratory infection such as influenza.
nitrogen oxides sources and sinks
Nitrogen oxides: Sources and sinks


  • Fuel combustion in power plants and automobiles.

N2 + O2 --> NO

2 NO + O2 --> 2 NO2

  • Natural sources: electrical storms; bacterial decomposition of nitrogen-containing organic matter
nitrogen oxides atmospheric chemistry
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

nitrogen oxides atmospheric chemistry1
Nitrogen oxides: Atmospheric chemistry

Formation of nitric acid

Gas-phase reaction

NO2 + OH  HNO3daytime (dominate pathway)

Heterogeneous reaction

NO2 + O3  NO3 + O2

NO3 + NO2 Û N2O5

N2O5 + H2O (aq) 2 HNO3 (aq)

Minor pathway

Only operative during nighttime

nitrogen oxides atmospheric chemistry2
Nitrogen oxides: Atmospheric chemistry

Formation of nitrate

HNO3 + NH3  NH4NO3

HNO3 + NaCl(s)  NaNO3 + HCl

nitrogen oxides control strategies
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.

two stage combustion to reduce both nox and vocs
Two-stage combustion to reduce both NOx and VOCs
  • First stage: combustion condition—rich in fuel
  • Second stage: combustion condition—rich in air
three way catalytic converter for automobile exhaust remove co no and hc
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

nox control in power plants
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