prof. arvind kumar_air_pollution
DESCRIPTION
Air pollutionTRANSCRIPT
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Gas Concentration, % by volume
Nitrogen 78.1
Oxygen 21.0
Argon 0.9
Carbon dioxide* 3.3 x 10-2
Hydrogen 5 x 10-5
Ozone 1 x 10-6
Methane* 2 x 10-4
The Atmosphere
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Air Pollution: Sources, Effects & Remediation
Fresh air is good if you do not take too much of it; most of the achievements and pleasures of life are in bad air.
Oliver Wendell Holmes
Definition: contamination of the air by noxious gases and minute particles of solid and liquid matter (particulates) in concentrations that endanger health-Air pollution only occurs outdoors
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Criteria Air Pollutants: Air Quality Index (AQI)
Do we have a way to determine local air quality? AQI/PSI (formerly Pollutants Std Index)
Assigns numerical rating to air quality of six criteria pollutants (TSP, SO2, CO, O3, NO2, and TSP*SO2)
API Value Air Quality Descriptor
0-50 Good
51-100 Moderate
101-199 Unhealthful
200-299 Very unhealthful
300 Hazardous
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Sources of Air PollutionNatural Sources (Biogenic sources)
Volcanoes Coniferous forests Forest fires Pollens Spores Dust storms Hot springs
Anthropogenic
Fuel combustion - Largest contributor
Chemical plants Motor vehicles Power and heat
generators Waste disposal sites Operation of internal-
combustion engines
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Sources of Outside Air Pollution
Combustion of gasoline and other hydrocarbon fuels in cars, trucks, and airplanes
Burning of fossil fuels (oil, coal, and dinosaur bones)
Insecticides Herbicides Everyday radioactive
fallouts Dust from fertilizers Mining operations Livestock feedlots04/13/2023 11AIR POLLUTION
Physical Forms of an Air Pollutant
Gaseous form o Sulfur dioxide o Ozone o Hydro-carbon vapors
Particulate form o Smoke o Dust o Fly ash o Mists
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CLASSICAL AIR POLLUTANTS
Nitrogen dioxideOzone and other photochemical oxidantsParticulate matterSulfur dioxide
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A major form of air pollution is emissions given off by vehicles.
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What’s in smog
particulates (especially lead)
nitrous oxides potassium Carbon monoxide Other toxic chemicals
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Sources of Indoor pollution
Efficient insulation Bacteria Molds and mildews Viruses animal dander and cat saliva plants house dust Mites Cockroaches pollen
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Effects on the environment
Acid rain Ozone depletion Global warming In human population-
respiratory problems, allergies, strengthens lugs, and a risk for cancer
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Comparative Photos Showing Yuschenko Immediately Prior To And Immediately Following Dioxin Poisoning http://en.wikipedia.org/wiki/Viktor_Yushchenko (Note: this is an extreme case of dioxin poisoning)
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http://www.umac.org/ocp/4/info.html
H+ SO4= NO3
-
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Acid rain contains high levels of sulfuric or nitric
acids contaminate drinking water and
vegetation damage aquatic life erode buildings Alters the chemical equilibrium of some
soils
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Strategies Air Quality Management Plan
Development of new technology- electric cars, cleaner fuels, low nitrogen oxide boilers and water healers, zero polluting paints
Use of natural gas Carpooling Follow the laws enacted
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Urban Emissions
• There are small emissions of NOx from industrial processes
• The main emissions are from combustion.
• There is negligible nitrogen in gasoline or diesel fuels so the nitrogen oxides arise from the N2 and O2 in the air.
• Sulphur dioxides arise from the sulphur present in most fuels.
• Particulate matter describes matter below 10μm aerodynamic diameter.
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Role of Engines and Fuel
Different engines and fuel combinations give out different emissions in different quantities.
Some engines have catalysts which effectively remove part of the harmful gases.
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Catalytic Converters and Particle Traps
Catalytic converters can be fitted to cars to reduce NOx emissions.
CO + HC + NOx H2O + N2 + CO2
Platinum Honeycomb
Particle traps can be used to reduce PM10 and NOx, but the effectiveness is severely reduced if the fuel the vehicle burns has a high sulphur content.
The major target in the battle for cleaner cities is diesel.
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STRATEGIE
The Clean Air approach: Based on scientific knowledge Using
best available, quality-controlled real-world data With close involvement of stakeholders:
1. Project future emissions and air quality resulting from full implementation
2. Explore scope and costs for further measures3. Analyze cost-effective policy scenarios4. Estimate benefits of policy scenarios
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Main pollutants used in the CAFE assessment
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Particulate Matter (PM ) Pollution
- Traffic emissions including diesel engines
- Small combustion sources burnng coal and wood
- Reductions of SO2, N0x, NH3 and VOC
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Ground level ozone
- VOC control to reduce ozone in cities
- N0x reduction from traffic
- Control of N0x emissions from ships
- Methane reduction
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Ozone Formed
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Climate Problems/Global Change/Air Pollution 21st
Century Greenhouse gases: global warming (CO2, CFCs, NOx, CH4, H20)
Air pollution: NOx, SO2, haze, aerosols, O3, heavy metals (Hg, Pb, Cd), organic compounds
Ozone depletion: O3
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Industrial Pollution Control System
Solution of the Pollution is Dilution
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Particulate Matter
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Pollutant
Particulate Matter (PM10)
Particulate Matter (PM2.5)
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Two possible fates Factors affecting fate
Aerodynamic properties
Physiological behavior
Methods of DepositionImpaction*Interception*Diffusion*Electrostatic AttractionGravitational Settling
INCINERATOR
organic compounds from process industries are destroyed at high temperature (590 and 650oC & 1800 to 2200oF for most hazardous waste)
Oxidizing organic compounds containing sulfur or halogens produce unwanted pollutants such as sulfur dioxide, hydrochloric acid, hydrofluoric acid, or phosgene
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SRCUBBERS
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Control Techniques
Gravity settling chamber
Mechanical collectors
Particulate wet
scrubbers
Electrostatic
precipitators
Fabric filters
Fabric Filter High collection Efficiency over a
broad range of particles sizes Application: Cement kiln, Foundries,
Steel furnaces and Grain handling plants
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GRAVITY SETTLING CHAMBERS
The removal of larger-sized particles, e.g., 40–60µm in diameter
Velocities (in the range of 1–10 ft/s)
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CYCLONES
Large diameter cyclones have good collection efficiencies for particle 40-50µm dia
<23 cm diameter cyclones have good collection efficiencies for particle 15-20µm dia
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Device Min. Particle size µm
Efficiency %(mass basis)
Advantage Disadvantages
Gravitational settler
>50 <50 •Low pressure loss,•Simplicity of design•maintenance
•Much space required•Low collection efficiency
Centrifugal collector
5-25 50-90 •Simplicity of design and maintenance •Little floor space required•Dry continuous disposal of collected dusts•Low to moderate pressure loss•Handles high dust loadings•Temperature independent
•Much head room required•Low collection efficiency for small particles•Sensitive to variables dust loading and flow rates
ELECTROSTATIC PRECIPITATORS
Extremely efficient for wide range of particle sizes; even submicron size
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Wind Rose
how wind speed and direction are typically distributed at a particular location
The directions of the rose with the longest spoke show the wind direction with the greatest frequency
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Applications Urban Planning Siting of industrial locations including chimney & other air polluting source Industrial zoning & industrial estate planning Air pollution modeling. Disaster Management Street layout Ventilation of urban, industrial and housing Environmental Impact Assessment study. Oceanography Wind Energy Agriculture Engineering Ambient Air Monitoring Noise Impact Modeling
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Parameters Affecting Dispersion
wind speedAs the wind speed increases, the plume becomes longer and
narrower; the substance is carried downwind faster but is diluted faster by a larger quantity of air.
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ground conditions Ground conditions affect the mechanical mixing at the surface and
the wind profile with height. Trees and buildings increase mixing, whereas lakes and open
areas decrease it.
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height of the release above ground level
The release height significantly affects ground-level concentrations. As the release height increases, ground-level concentrations are reduced because the plume must disperse a greater distance vertically.
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momentum and buoyancy of the initial material released
The buoyancy and momentum of the material released change the effective height of the release.
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Smokestack plume demonstrating initial buoyant rise of hot gases
Gases cool as they Neutralmix and dilute with COOl air . Neutral Buoyancy
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Calculation of effective stack height
Using following dataa) Physical stack is 203 m tall with 1.07m diameterb) Wind velocity is 3.56 m/sc) Air temperature is 13 oCd) Barometric pressure is 1000 millibarse) Stack gas velocity is 9.14 m/sf) Stack gas temperature is 149oC.
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Atmospheric stabilityAtmospheric stability relates to vertical mixing of the air. During the day, the air temperature decreases rapidly with height, encouraging vertical motions. At night the temperature decrease is less, resulting in less vertical motion.
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Atmospheric stability …
Dry adiabatic lapse rate (stable, neutral atmosphere)
m 100C1 - dZ
dT
dA
P + dP
dZ
PNatural balance between hydrostatic head, g dA dZ, and pressure forces
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Dry adiabatic lapse rate (dry adiabat, DALR or unsaturated lapse rate): lapse rate of unsaturated air (i.e., air with a relative humidity of less than 100%)
Wet adiabatic lapse rate (wet adiabat, saturated lapse rate, SALR, moist adiabatic lapse rate or MALR) : the air parcel is saturated and, because of the release of the heat of vaporization, the rate of cooling will decrease to what is known as the wet adiabatic lapse rate.
Environmental lapse rate (ELR, prevailing lapse rate or ambient lapse rate) : The actual real-world profile of temperature versus altitude that exists at any given time and in any given geographical location is called the environmental lapse rate
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the atmospheric stability can be characterized by these four categories A very stable atmosphere is one that has very little, if any, vertical
motion of the air. A stable atmosphere is one that discourages vertical motion but does
have some motion of the air. An unstable atmosphere is one that encourages continual vertical motion
of the air, upwards or downwards. A neutral atmosphere is one that neither discourages nor encourages
vertical motion of the air and is often referred to as conditionally stable.
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Lapse Rate Effect
ELR > 0 1
the atmospheric temperature increases with altitude. There is essentially no vertical turbulence and the atmosphere is said to be very stable or extremely stable.
ELR> – 5.5 K/km2
some small amount of vertical turbulence and the atmosphere is said to be stable. It is also referred to as being sub-adiabatic.
MALR> ELR> DALR3
the atmosphere is said to be neutral. *U.S. Standard Atmosphere of – 6.5 K/km in most cases
ELR < DALR 4
there turbulence in the atmosphere and it is said to be unstable. It is also referred to as being super-adiabatic.
ELR= 0 the atmosphere would be in an isothermal condition (no change of temperature with altitude) and would be also be said to be very stable.
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Super-adiabatic lapse rate:
Temperature
Height
Height
Height
Temperature
Height
Height
Height
100
020 21 22
100
020 21 22
Inversion
Isothermal
100
020 21 22
Neutral
100
020 21 22
Subadiabatic
100
020 21 22
Dry Adiabatic Lapse Rate
Superadiabatic
(A) (B)
Fumigation
Temperature Trapping
Lofting
Temperature
Temperature
Temperature
Fanning
Coning
Looping
Temperature
Height
Height
Height
Temperature
Height
Height
Height
100
020 21 22
100
020 21 22
Inversion
Isothermal
100
020 21 22
Neutral
100
020 21 22
Subadiabatic
100
020 21 22
Dry Adiabatic Lapse Rate
Superadiabatic
(A) (B)
Fumigation
Temperature Trapping
Lofting
Temperature
Temperature
Temperature
Fanning
Coning
Looping
A “buoyant” atmosphere
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Sub-adiabatic lapse rate:
Temperature
Height
Height
Height
Temperature
Height
Height
Height
100
020 21 22
100
020 21 22
Inversion
Isothermal
100
020 21 22
Neutral
100
020 21 22
Subadiabatic
100
020 21 22
Dry Adiabatic Lapse Rate
Superadiabatic
(A) (B)
Fumigation
Temperature Trapping
Lofting
Temperature
Temperature
Temperature
Fanning
Coning
Looping
Temperature
Height
Height
Height
Temperature
Height
Height
Height
100
020 21 22
100
020 21 22
Inversion
Isothermal
100
020 21 22
Neutral
100
020 21 22
Subadiabatic
100
020 21 22
Dry Adiabatic Lapse Rate
Superadiabatic
(A) (B)
Fumigation
Temperature Trapping
Lofting
Temperature
Temperature
Temperature
Fanning
Coning
Looping
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atmosphere’s dispersive capability = maximum mixing depth*the average wind speed. This product is known as the ventilation coefficient (m2/s) . Values of ventilation coefficient less than about 6000 m2/s are considered indicative of high air pollution potential
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0.1 1 10 100
10
100
1000
10000
ABC
DE
F
Downwind distance, km
y, m
0.1 1 10 1001
10
100
1000 A
B
C
D
E
F
Downwind distance, km
z, m
A= Extremely unstable; B-moderately unstable; C-Slightly unstable;
D-Neutral; E-Slightly stable; F- Moderately stable
Pasquill Stability classes A - F
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A= Extremely unstable; B-moderately unstable; C-Slightly unstable;
D-Neutral; E-Slightly stable; F- Moderately stable
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2
zyz0 x, σ
H
2
1exp
σσu π
QC
Plume centre line Concentration
Effective stack height is zero
yz0 x, σ σu π
QC
2
y
2
zyzyx, σ
y
2
1exp
σ
H
2
1exp
σ σu π
QC
Gaussian concentration distribution
2
Hz
Location Maximum concentration
131
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The maximum ground level concentration along the x axis can be calculated
y
z2r
max σ
σ
Hu πe
2QC
Determining Max. ground level concentration:
A power plant burns 5.45 tonnes of coal/hr and discharges the combustion products through a stack that has an effective height of 75 m. The coal has sulfur content of 4.2 %, and the wind velocity at the top of the stack is 6 m/s. The atm conditions are moderately to slightly stable.
Determine Max. ground level concentration of
SO2 and the distance from the stack at which the maximum occurs
Determine the ground-level concentrations at a distance of 3 km downwind at the centre line of the plume and at a crosswind distance of 0.4 km on either side of the centerline.
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