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Air Pollutionfor CEL 212-Environmental Engineering
(Second Semester 2010-2011)
Dr. Arun Kumar Civil Engineering (IIT Delhi)
Courtesy: Dr. Irene Xagoraraki (U.S.A.)
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Atmosphere
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Air Pollution
• Indoor
• Regional
• Global
• Stratospheric
– Sources
– Effects
– Treatment
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Air Pollutants
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Air Pollution Standards
• Criteria pollutants
– Primary standards (for protecting human health)
– Secondary standards (for preventing environmental and property damage)
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1) Carbon Monoxide
• Most abundant air pollutant
• Produced by incomplete combustion
– insufficient O2
– low temperature
– short residence time
– poor mixing
• Major source is motor vehicle exhaust
http://www.epa.gov/oar/aqtrnd97/brochure/co.html
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CO and Health Effects
1 ppm = 1 parts per million = 1 mg/L1 ppm = 1 parts per million = 1 mg/L
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1. For a given exposure duration, severity of disease increases with CO conc.
2. For a given CO conc., severity of disease increases with exposure duration after certain critical exposure duration.
3. Look at effect of critical exposure duration on severity of diseases for a given CO conc.
CO and Health Effects
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2) Ozone: Health Effects
• Increased incidents of respiratory distress.
• Repeated exposures to ozone:
– Increased susceptibility to respiratory infection
– Lung inflammation
– Aggravation of pre-existing respiratory diseases, such as asthma.
– Decreases in lung function and increased respiratory symptoms, such as chest pain and cough.
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Ozone: Environmental Effects
Ozone also affects vegetation and
ecosystems
– reductions in agricultural and commercial forest yields
– reduced growth and survivability of tree seedlings
– increased plant susceptibility to disease, pests, and other environmental stresses (e.g., harsh weather).
http://www.ncl.ac.uk/airweb/ozone/greece.jpg
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3) Oxides of Nitrogen (NOx)
• Primarily NO and NO2
• NO3, N2O, N2O3, N2O4, N2O5 are also known to occur
• Thermal NOx (created by oxidation of atmospheric N2
when T > 1000 K)
• Fuel NOx from oxidation of N in fuel (high temperature combustion processes in power plants and automobiles)
http://www.epa.gov/oar/aqtrnd97/brochure/no2.html
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NOx-Health Effects
• NO => few health effects, but is oxidized to NO2
• NO2 => irritates lungs and promotes respiratory
infections
• NO2 => reacts with hydroxyl radicals to produce
nitric acid – acid rain
• NO2 => reacts with hydrocarbons in presence of
sunlight to produce smog
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4) Photochemical Smog
hydrocarbons + NOx + sunlight →
photochemical smog (oxidants)
primary oxidants produced:
– ozone (O3)
– formaldehyde
– peroxyacetylnitrate (PAN)
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Photochemical Smog-depends on time of the day also
London
(on a clear day)
London
(smog in summer
and winter time)
See the effect of time
of day on
concentrations of different components
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5) Sulfur Oxides (SOx)
• SO2, SO3, SO42- formed during combustion of fuel
containing sulfur (coal, oil), metal smelting, other industrial processes.
• H2S released is converted to SO2
http://www.epa.gov/oar/aqtrnd97/brochure/so2.html
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Sulfur Dioxide: Health Effects
• High concentrations of SO2 can result in temporary breathing impairment.
• Longer-term exposures to high concentrations of SO2, in conjunction with high levels of PM, include respiratory illness, alterations in the lungs defenses, and aggravation of existing cardiovascular disease
• Short-term exposures of asthmatic individuals to elevated SO2 levels may result in reduced lung function.
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Sulfur Dioxide: Environmental Effects
1) Acid Rain2) Decreased Visibility: SO2, NOx,
and VOC interact with other compounds in
the air to form fine particles.
http://www.epa.gov/oar/vis/rockymtn.html
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6) Particulate Matter
• Solid or liquid particles with sizes from 0.005 – 100 µm (i.e., aerosols)
• Dust originates from grinding or crushing
• Fumes are solid particles formed when vapors condense
• Smoke describes particles released in combustion processes
• Smog used to describe air pollution particles
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Particulate Matter
PM-10 (1987)
< 10 µm diameter; fuel combustion (45%); industrial processing (33%); transportation (22%)
Original standards did not account for size – larger particles that were not problematic dominated
PM-2.5 (1997)
< 2.5 µm diameter; Similar sources, but tend to be more toxicologically active particles; EPA estimates new standard will save 15,000 lives/yr
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Particulate Matter: Health Effects
• Large particles trapped in nose
• Particles >10 µm removed in tracheobronchial system
• Particles <0.5 µm reach lungs but are exhaled with air
• Particles 2 – 4 µm most effectively deposited in lungs
Environmental Effects• Decreased visibility
• Damage to paints and building materials
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Indoor Air Pollution
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Sources of Indoor Air Pollutants
• Combustion processes furnaces, stoves, water heaters CO, NOx, HC, PM, SO2
• Tobacco smoke CO, benzene, aldehydes, PM,
4000+ organic compounds
• New building materials VOCs, PM)
• Old building materials Pb, asbestos
• Drains HsS
• Household Products cleaning solvents etc.• Equipment heating and cooling systems• Moisture fungal spores• Furnishings allergens• Soil and rock radon• Other outdoor sources pesticides etc.
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Air Quality and Meteorology
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Dry Adiabatic Lapse Rate
Temperature, T (oC)
Altitude, z (
km
)
Adiabatic lapse rate
1
2
= (T2-T1)/(z2-z1)
When any parcel of air moves up or down, it’s
temperature will change according to the adiabatic
lapse rate
For this parcel of air the
change in temperature with
altitude was:
T1T2
z1
z2= (10-20)oC/(2000-1000)m
= -1 oC/100m
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Stability
• Dry adiabatic lapse rate: temperature decreases with increased altitude
• Atmospheric (actual) lapse rate
< Г (temperature falls faster) unstable (super-adiabatic)
> Г (temperature falls slower) stable (sub-adiabatic)
= Г (same rate) neutral
ft 1000F mC/100 /4500.1 °=°−=−=Γ .- dz
dT
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Example 1
Z(m) T(ºC)
10 5.11
202 1.09
C/m °−=−
−=
−
−=
∆
∆0209.0
10202
11.509.1
12
12
zz
TT
z
T
m C/100 °−= 09.2
Since lapse rate is more negative than Г, (-1.00 ºC/100 m)=> atmosphere is unstable
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Unstable Conditions Rapid vertical mixing
takes place.
-1.25 oC/100 m < -1 oC/100m Unstable air encourages the
dispersion and dilution of pollutants.actual temperature falls faster than Г
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Stable Conditions Air at a certain altitude remains
at the same elevation.
-0.5 oC/100 m > -1 oC/100m
Stable air discourages
the dispersion and
dilution of pollutants.actual temperature falls slower than Г
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Neutral Conditions Air at a certain altitude remains
at the same elevation.
Neutrally stable air
discourages the dispersion and dilution of pollutants.
-1 oC/100 m = -1 oC/100m
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Why are these plumes so different?
neutral
under inversion layer
Above inversion
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Prediction for Pollutant Concentration
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Point-Source Gaussian Plume Model
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Point-Source Gaussian Plume Model
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Point-Source Gaussian Plume Model
• Model Structure and Assumptions
– pollutants released from a “virtual point source”
– advective transport by wind
– dispersive transport (spreading) follows normal (Gaussian) distribution away from trajectory
– constant emission rate
– wind speed constant with time and elevation
– pollutant is conservative (no reaction)
– terrain is flat and unobstructed
– uniform atmospheric stability
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Point-Source Gaussian Plume Model
Where: C = downwind concentration at ground level (g/m3)
E = Q = emission rate of pollutant (g/s)
sy,sz = plume standard deviations (dispersion coefficients) (m)
u = wind speed (m/s)
x, y, z, H = distances (m)
( )
−
−
=
22
2
1exp
2
1exp,0,,
zyzy s
H
s
y
uss
EHyx
πχ C (x,y)
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Effective Stack Height
Where:
H = Effective stack height (m)
h = height of physical stack (m)
∆H = plume rise (m)
HhH ∆+=
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Effective Stack Height (Holland’s formula)
where vs = stack velocity (m/s)
d = stack diameter (m)
u = wind speed (m)
P = pressure (kPa)
Ts = stack temperature (ºK)
Ta = air temperature (ºK)
( )
−×+=∆
−d
T
TTP
u
vH
a
ass 21068.25.1
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Atmospheric Stability Categories
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Horizontal Dispersion
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Vertical Dispersion
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Wind Speed Correction
• Unless the wind speed at the virtual stack height is known, it must be estimated from the ground wind speed
Where: ux = wind speed at elevation zx
p = empirical constant
p
z
zuu
=
1
212
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Example 2
• A stack in an urban area is emitting 80 g/s of NO. It has an effective stack height of 100 m. The wind speed is 4 m/s at 10 m. It is a clear summer day with the sun nearly overhead.
• Estimate the ground level concentration at: a) 2 km downwind on the centerline and b) 2 km downwind, 0.1 km off the centerline.
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1. Determine stability class
Assume wind speed is 4 km at ground surface. Description suggests strong solar radiation.
Stability class B
Example 2
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3. Estimate the wind speed at the effective stack height
Note: effective stack height given – no need to calculate using Holland’s formula
m/s 65.510
1004
15.0
1
212 =
=
=
p
z
zuu
Example 2
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4. Determine concentration
a. x = 2000, y = 0
−
−=
22
220
100
2
1exp
290
0
2
1exp
)6.5)(220)(290(
80)0,2000(
πC
33 µg/m g/m 3.641043.6)0,2000( 5=×=
−C
Example 2
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b. x = 2000, y = 0.1 km = 100 m
−
−=
22
220
100
2
1exp
290
100
2
1exp
)6.5)(220)(290(
80)100,2000(
πC
33 µg/m g/m 6.601006.6)0,2000( 5 =×= −C
Example 2
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Air Pollution Control
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Air Pollution Control
• Stationary sources
– Pre-combustion controls (improved fuel quality)
– Combustion controls (improved combustion process)
– Post-combustion controls (capture emissions after they are formed but before they are released to the air)
• Motor vehicles
– Cleaner gasoline
– Exhaust system controls
– Improved engines
– Alternative fuels