20 exam questions - air quality (1)
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ES 200
Air Quality
20 Questions for the Exams
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Guidelines
• Use this material as pointers to prepare for the Exam for the Air Quality Module
• Use books on Air Pollution to understand the details
• If you have questions/need clarifications, please contact me by email [email protected]
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Q 1 : What are the classes of air pollutants ? How are they managed ?
• Criteria Pollutants for Ambient Air Quality• Primary : PM10, NOx, SOx, CO, Lead • Secondary : Ozone
• Emission Factors for Sources• For Industrial / Vehicular emissions• Based on per unit product ( eg CO mg/km travelled)• Compliance and Best Available Control Technology (BACT)• Trading Permits
• MoEF > CPCB > SPCBMoEF : Ministry of Environment and Forests; CPCB : Central Pollution Control Board; State Pollution Control Boards.
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•Dispersion – Gaussian Plume– Meteorological conditions
• Temperature Profiles• Wind Conditions
– Source Strength
– Stack height
Q2 : How is the effect of a source estimated in the ambient ?
WIND
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Q3 : What is a Wind Rose ?
http://www.epa.gov/ttn/naaqs/ozone/areas/wind.htm#dlfi
1 knot = 1.82 km/hr
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Windrose
1. Direction2. Speed and 3. Frequency
• A wind rose is divided into 16 wind directions
• Each wind direction is divided into wind speeds
• As the percent of time the wind blows from a particular directions gets larger, the portion of the bar representing the wind speed gets larger both in length and width]
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Q4 : What are Lapse Rates ?
• Atmosphere cools with height– What rate ?
• Dry (Adiabatic) 10°C/km• Wet (Adiabatic) 6°C/km
– (Release of heat with condensation)
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Q5 : What is Atmospheric Stability?
http://www.tpub.com/content/aerographer/14312/css/14312_47.htm
Wet Lapse Rate
Dry Lapse Rate
Average
Unstable
Stable
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ADIABATIC (1°C/100 m)
1000 m (say)
20 °C
20 °C Air Parcel
1100 m
ACTUAL
Q6 : If the parcel of air (as shown) were lifted, would it continue to rise ?
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CO
LLE
CT
ION
/ R
EM
OV
AL
EF
FIC
IEN
CY
PARTICLE DIAMETER (m)
Q7 : What are the removal mechanisms for larger/smaller particles in the atmosphere ?
Iner
tia/G
ravi
tyD
Iffusion
0.01 1.0 100
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(Source: Kittelson et al. 1999)
Q8 : What are the three plots in this graph ? What are the likely sources of the three modes?
Factional deposition of particles with sp gr = 1
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Source: Flagan and Seinfeld, 1988
Particle formation in coal combustion
Q9 : What are the possible pathways for the formation of particles in different modes ?
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Q10 : How would you size aerosol particles smaller than 1 m?
• Optical Microscopes (limited to 0.1 m by )
• Cascade Impactors (0.056 to 18 m)
• Optical Particle Counters (0.09 m)
• Electrical Mobility + Condensation Particle Counters (0.003 m or 3 nm)
• Electron Microscopy
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Source : TSI Inc.
Differential Mobility Analyser (For size
separation using electrical mobility)
Q11 : How is the Electrical Mobility Principle used ?
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Source : TSI Inc.
Condensation Particle Counter (For growing the size separated particles and detecting them using light scattering)
Q12 : How does the Condensation Particle Counter work ?
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NOZZLE
Impaction Stage
Filter (to capture the smallest particles that could not impact on upper stages)
To Vacuum Pump
Q13 : How does a Cascade Impactor work ?
Nozzle diameter gets progressively smaller and smaller, and smaller particles gain inertia to then impact out at lower stages.
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• Particles smaller than 10 m are inhalable. (Particles greater than 10 m get stopped in the nasal passage).
• Total Mass concentration of particles in air that are smaller than
10 m is PM10
• Anthropogenic sources (combustion/industry) emit particles predominantly in the ~ 2.5 m size range. PM2.5 is the mass of particles smaller than 2.5 m, and is a measure of anthropogenic sources (greater health concern as these may be more toxic)
Q14 (a) : What is PM10 ? What is PM2.5 ?
Q14(b) : What could be the difference in the size distribution of atmospheric particles at a road crossing in peak traffic hour and a rural site in Thar desert ?
• The relative mass fraction of PM2.5 for the traffic crossing site is more (Vehicular emissions vs. Sand particles in Thar).
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Q15(a) : What are the control measures for particulate pollutants ?
Q15(b) : What are the control measures for gaseous pollutants ?
PRINCIPLE
•Settling Chambers Gravity
•Cyclones Inertia
•Scrubbers Physical contact with liquids
•Electrostatic Precipitators Electrical Mobility
•Filters Interception/Diffusion
PRINCIPLE
•Absorption (Scrubbers) Affinity in liquid
•Adsorption Affinity at solid surface
•Incineration
•Membrane separation
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■ Low Vertical Mixing
■ Ozone (Energy Absorption)
Ionosphere
■ 80% of total mass
Q16: What is the structure of Earth’s atmosphere ?
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Q17 : What is the difference in the incoming and outgoing radiation on earth ?
How do the presence of different gases/vapours influence the radiation balance ?
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Absorption: Individual GasesCH4
N2O
O3, O2
CO2
H2O
solar terrestrial
Peixoto and Oort: Physics of Climate
Q :
17
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Q 18 : What are the possible implications of global warming ?
• Descibed in the film “An Inconvenient Truth”
• Some , based on Global Circulation Models – Increase in temperatures by 4.2 °C– Precipitation to increase by 10 % (by 2050)– Sea levels to rise by 0.3-1.4 m
– Agricultural cycles would be affected
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Q 19 : What is the Relative Global Warming Potential (GWP) for different greenhouse gases ?
Gas* Lifetime GWP(20 Years)
GWP(100 Years)
CO2 1 1
CH4 12.2 56 21
CFC-11 50 5000 4000
N2O 120 290 320
•This list of gases is a small subset of all the greenhouse gases and serve only as examples
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Q 20 : What is Albedo ? If the albedo changed to 0.30, how would it affect the Earth’s temperature ?
• Albedo is the ratio of the reflected radiation to the incident radiation.
• SIMPLE RADIATION BALANCE • Solar Energy Striking Earth = S(1-) .R2
– S = solar constant (1370 W/m2)– = 0.31(Current estimate of Albedo)
• Energy radiated back to Space by earth
= 4 R2 Te4 (W/m )
• EquatingTe = [ S(1-)/(4 ]1/4 = 255 K (-18°C)