Dr. Arun Kumarweb.iitd.ernet.in/~arunku/files/CEL795_Y13/Air Pollution1.pdf · Dr. Arun Kumar Civil...

transcript

Air Pollutionfor CEL 212-Environmental Engineering

(Second Semester 2010-2011)

Dr. Arun Kumar Civil Engineering (IIT Delhi)

arunku@civil.iitd.ac.in

Courtesy: Dr. Irene Xagoraraki (U.S.A.)

April 14, 2011 arunku@civil.iitd.ac.in 2

Atmosphere

Air Pollution

• Indoor

• Regional

• Global

• Stratospheric

– Sources

– Effects

– Treatment

Air Pollutants

Air Pollution Standards

• Criteria pollutants

– Primary standards (for protecting human health)

– Secondary standards (for preventing environmental and property damage)

Pollution

Standards

“Criteria” air pollutants

(USEPA)

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

CO and Health Effects

1 ppm = 1 parts per million = 1 mg/L1 ppm = 1 parts per million = 1 mg/L

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

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.

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

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

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

4) Photochemical Smog

hydrocarbons + NOx + sunlight →

photochemical smog (oxidants)

primary oxidants produced:

– ozone (O3)

– formaldehyde

– peroxyacetylnitrate (PAN)

Photochemical Smog Formation-A Continuous

Process

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

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

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.

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

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

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

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

Indoor Air Pollution

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.

Air Quality and Meteorology

Dry Adiabatic Lapse Rate

Temperature, T (oC)

Altitude, z (

Adiabatic lapse rate

= (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:

z2= (10-20)oC/(2000-1000)m

= -1 oC/100m

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

Example 1

Z(m) T(ºC)

10 5.11

202 1.09

C/m °−=−

∆0209.0

11.509.1

m C/100 °−= 09.2

Since lapse rate is more negative than Г, (-1.00 ºC/100 m)=> atmosphere is unstable

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

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

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

Why are these plumes so different?

neutral

under inversion layer

Above inversion

Prediction for Pollutant Concentration

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

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)

1exp,0,,

zyzy s

πχ C (x,y)

Effective Stack Height

Where:

H = Effective stack height (m)

h = height of physical stack (m)

∆H = plume rise (m)

HhH ∆+=

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)

−×+=∆

ass 21068.25.1

Atmospheric Stability Categories

Horizontal Dispersion

Vertical Dispersion

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

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.

1. Determine stability class

Assume wind speed is 4 km at ground surface. Description suggests strong solar radiation.

Stability class B

Example 2

2. Determine σy and σz

σy = 290, σz = 220

Example 2

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

Example 2

4. Determine concentration

a. x = 2000, y = 0

)6.5)(220)(290(

80)0,2000(

33 µg/m g/m 3.641043.6)0,2000( 5=×=

Example 2

b. x = 2000, y = 0.1 km = 100 m

)6.5)(220)(290(

80)100,2000(

33 µg/m g/m 6.601006.6)0,2000( 5 =×= −C

Example 2

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

Dr. Arun Kumarweb.iitd.ernet.in/~arunku/files/CEL795_Y13/Air Pollution1.pdf · Dr. Arun Kumar Civil...

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