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
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
Carbon monoxide,Health effect
CO enters the blood stream and binds
preferentially to hemoglobin,thereby replacing
oxygen,
Fe
O2
CO
Fe
Fe
C-O
O-O
320 times stronger than
hemoglobin-O2 binding
Carbon monoxide,sources and sinks
? 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
Such as automobiles
CO formation from methane oxidation
C H
4
+ O H
C H
3
+ H
2
O
+ O
2
C O
H
H
H
C H
3
O O
N ON O
2
+
O
2
C
H H
O
+ H O
2
h v
H
O
+
H O
2
O
2
H O
2
C O
CO emission sources in Hong Kong
F u e l
c o m b u s t i o n
( I n d u s t r i a l,
c o m m e r c i a l &
d o m e s t i c )
p o w e r
g e n e r a t i o n
a i r c r a f t
m a r i n e v e s s e l
m o t o r v e h i c l e
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
? 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
? 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
Sources
? 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
Sink
? Converted into sulphuric acid in either gas or liquid
phase
SO2 emission sources in Hong Kong
p o w e r g e n e r a t i o n
m o t o r v e h i c l e
F u e l c o m b u s t i o n
( I n d u s t r i a l,
c o m m e r c i a l &
d o m e s t i c )
m a r i n e v e s s e l
a i r c r a f t
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
1,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.
2,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)
3,Dilution
Installation of tall stacks reduces SO2 levels
in the immediate neighborhood by
dispersing them more widely
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,
Nitrogen oxides,Sources and sinks
Sources
? 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
NOx emission sources in Hong Kong F u e l c o m b u s t i o n
( I n d u s t r i a l,
c o m m e r c i a l &
d o m e s t i c )
4%
a i r c r a f t
9%
m a r i n e v e s s e l
32%
m o t o r v e h i c l e
8%
p o w e r g e n e r a t i o n
47%
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)
NO2 + hv ? NO + O (1)
O + O2 + M ? O3 + M (2)
HO2,+ NO? NO2 + OH (4)
RO2,+ NO ? NO2 + RO,(5)
No net O3
formation
O3 is
formed
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 ? N2O5
N2O5 + H2O (aq)? 2 HNO3 (aq)
Minor pathway
Only operative during nighttime
Nitrogen oxides,Atmospheric chemistry
Formation of nitrate
HNO3 + NH3 ?NH4NO3
HNO3 + NaCl(s) ?NaNO3 + HCl
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
? 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)
HC + H2O = H2 + CO
2NO + 2H2 = N2 + 2 H2O
2CO + O2 = 2CO2
HC + 2O2 = CO2 + 2H2O
Catalyst,Rhodium Catalyst,Platium/palladium
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
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
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
Carbon monoxide,Health effect
CO enters the blood stream and binds
preferentially to hemoglobin,thereby replacing
oxygen,
Fe
O2
CO
Fe
Fe
C-O
O-O
320 times stronger than
hemoglobin-O2 binding
Carbon monoxide,sources and sinks
? 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
Such as automobiles
CO formation from methane oxidation
C H
4
+ O H
C H
3
+ H
2
O
+ O
2
C O
H
H
H
C H
3
O O
N ON O
2
+
O
2
C
H H
O
+ H O
2
h v
H
O
+
H O
2
O
2
H O
2
C O
CO emission sources in Hong Kong
F u e l
c o m b u s t i o n
( I n d u s t r i a l,
c o m m e r c i a l &
d o m e s t i c )
p o w e r
g e n e r a t i o n
a i r c r a f t
m a r i n e v e s s e l
m o t o r v e h i c l e
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
? 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
? 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
Sources
? 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
Sink
? Converted into sulphuric acid in either gas or liquid
phase
SO2 emission sources in Hong Kong
p o w e r g e n e r a t i o n
m o t o r v e h i c l e
F u e l c o m b u s t i o n
( I n d u s t r i a l,
c o m m e r c i a l &
d o m e s t i c )
m a r i n e v e s s e l
a i r c r a f t
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
1,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.
2,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)
3,Dilution
Installation of tall stacks reduces SO2 levels
in the immediate neighborhood by
dispersing them more widely
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,
Nitrogen oxides,Sources and sinks
Sources
? 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
NOx emission sources in Hong Kong F u e l c o m b u s t i o n
( I n d u s t r i a l,
c o m m e r c i a l &
d o m e s t i c )
4%
a i r c r a f t
9%
m a r i n e v e s s e l
32%
m o t o r v e h i c l e
8%
p o w e r g e n e r a t i o n
47%
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)
NO2 + hv ? NO + O (1)
O + O2 + M ? O3 + M (2)
HO2,+ NO? NO2 + OH (4)
RO2,+ NO ? NO2 + RO,(5)
No net O3
formation
O3 is
formed
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 ? N2O5
N2O5 + H2O (aq)? 2 HNO3 (aq)
Minor pathway
Only operative during nighttime
Nitrogen oxides,Atmospheric chemistry
Formation of nitrate
HNO3 + NH3 ?NH4NO3
HNO3 + NaCl(s) ?NaNO3 + HCl
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
? 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)
HC + H2O = H2 + CO
2NO + 2H2 = N2 + 2 H2O
2CO + O2 = 2CO2
HC + 2O2 = CO2 + 2H2O
Catalyst,Rhodium Catalyst,Platium/palladium
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
