prof. arvind kumar_air_pollution

04/13/2023 1AIR POLLUTION

04/13/2023 3

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

AIR POLLUTION

04/13/2023 AIR POLLUTION 4

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

AIR POLLUTION

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

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

CLASSICAL AIR POLLUTANTS

Nitrogen dioxideOzone and other photochemical oxidantsParticulate matterSulfur dioxide

A major form of air pollution is emissions given off by vehicles.

What’s in smog

particulates (especially lead)

nitrous oxides potassium Carbon monoxide Other toxic chemicals

Sources of Indoor pollution

Efficient insulation Bacteria Molds and mildews Viruses animal dander and cat saliva plants house dust Mites Cockroaches pollen

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)

AIR POLLUTION

http://www.umac.org/ocp/4/info.html

H+ SO4= NO3

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

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

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.

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.

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.

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

Main pollutants used in the CAFE assessment

Particulate Matter (PM ) Pollution

- Traffic emissions including diesel engines

- Small combustion sources burnng coal and wood

- Reductions of SO2, N0x, NH3 and VOC

Ground level ozone

- VOC control to reduce ozone in cities

- N0x reduction from traffic

- Control of N0x emissions from ships

- Methane reduction

Ozone Formed

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

04/13/2023 38

Industrial Pollution Control System

Solution of the Pollution is Dilution

Particulate Matter

Pollutant

Particulate Matter (PM10)

Particulate Matter (PM2.5)

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

SRCUBBERS

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

GRAVITY SETTLING CHAMBERS

The removal of larger-sized particles, e.g., 40–60µm in diameter

Velocities (in the range of 1–10 ft/s)

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

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

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

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

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.

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.

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.

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

AIR POLLUTION

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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.

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.

Atmospheric stability …

Dry adiabatic lapse rate (stable, neutral atmosphere)

m 100C1 - dZ

P + dP

PNatural balance between hydrostatic head, g dA dZ, and pressure forces

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

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.

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.

Super-adiabatic lapse rate:

Temperature

Height

Temperature

Height

020 21 22

Inversion

Isothermal

020 21 22

Neutral

020 21 22

Subadiabatic

020 21 22

Dry Adiabatic Lapse Rate

Superadiabatic

(A) (B)

Fumigation

Temperature Trapping

Lofting

Temperature

Fanning

Coning

Looping

Temperature

Height

Temperature

Height

020 21 22

Inversion

Isothermal

020 21 22

Neutral

020 21 22

Subadiabatic

020 21 22

Superadiabatic

(A) (B)

Fumigation

Lofting

Temperature

Fanning

Coning

Looping

A “buoyant” atmosphere

Sub-adiabatic lapse rate:

Temperature

Height

Temperature

Height

020 21 22

Inversion

Isothermal

020 21 22

Neutral

020 21 22

Subadiabatic

020 21 22

Superadiabatic

(A) (B)

Fumigation

Lofting

Temperature

Fanning

Coning

Looping

Temperature

Height

Temperature

Height

020 21 22

Inversion

Isothermal

020 21 22

Neutral

020 21 22

Subadiabatic

020 21 22

Superadiabatic

(A) (B)

Fumigation

Lofting

Temperature

Fanning

Coning

Looping

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

0.1 1 10 100

Downwind distance, km

0.1 1 10 1001

1000 A

Downwind distance, km

A= Extremely unstable; B-moderately unstable; C-Slightly unstable;

D-Neutral; E-Slightly stable; F- Moderately stable

Pasquill Stability classes A - F

A= Extremely unstable; B-moderately unstable; C-Slightly unstable;

D-Neutral; E-Slightly stable; F- Moderately stable

04/13/2023 AIR POLLUTION

zyz0 x, σ

σσu π

Plume centre line Concentration

Effective stack height is zero

yz0 x, σ σu π

zyzyx, σ

σ σu π

Gaussian concentration distribution

Location Maximum concentration

The maximum ground level concentration along the x axis can be calculated

max σ

Hu πe

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.

r kind a

ttentio

r kind a

ttentio

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