AIR POLLUTION:

AIR POLLUTION:

• “ Air Pollution means the presence in the outdoor atmosphere of one or more contaminants, such as dust, fumes, gas mist odour smoke or vapour , in quantities , of characteristics , and of duration such as to be injurious to human, plant or animal life or to the property, to interfere unreasonably with the comfortable enjoyment of life and property”.

(Engineer‟s Joint Council, USA)

• “Air Pollution is the presence in ambient atmosphere of substances generally resulting from the activity of man, in sufficient concentration, present for a sufficient time and under circumstances which interfere significantly with the comfort, health or welfare of persons or with the full use or enjoyment of property”.

(Indian Standard Institution, IS-4167)

• “ Air Pollution is the excessive concentration of foreign matter in the air which adversely affects the well being of the individual or causes damage to the property”.

(American Medical Association)

Price of Industrialization Disease of Wealth

Global Consequences of Air Pollution:

 Radiation from the Sun;

- Black body, 600K, Max^m. energy in visible region near 0.47 micron, Energy flux at earth 1400 W/m²

 Reflection and Absorption by Earth‟s surface;

- portion of energy reflected depends on optical Albedo

- absorbed energy re-radiated from earth‟s surface as Infra-red or thermal radiation - max. wavelength in the vicinity of 10 microns

- absorption by earth according to normal surface area (circle) , radiation as spherical surface

 Albedo:

“Reflective power indicating the fraction of incident light or electromagnetic

radiation that is reflected by a surface. Black or totally absorbent bodies (such as Oceans)

have low values, while white or totally reflective bodies (such as freshly fallen snow) have

high values. Albedo is expressed in percentage”.

The Role of Atmosphere:

 Clean atmosphere ;

- almost transparent to solar radiation

- contains H₂O, CO₂, O₃ strong absorbers and radiators of IR

- atmosphere becomes essentially opaque to re-emitted radiation except a „window‟

8-10 μm

 Dust containing atmosphere;

- only 65% of incoming radiation reaches to earth

- 10 % of total IR radiated back is directly transmitted to space

- remaining IR is absorbed and re-radiated by successive layers of atmosphere

- downward radiation keeps the surface temperature relatively high (Greenhouse Effect) - radiation reaching back to space is the sum of

(i) emitted by very cold outermost layers of the atmosphere (ii) component directly reaching through the „window‟

 Layering of earth‟s atmosphere;

- troposphere extends from sea level to approx.12 km, Temp. falls down to approx. -60 C - water vapour 10 times more important than CO₂ for radiative heating and cooling

- in stratosphere, O₃is responsible for heating, CO₂for cooling, H₂O playing minor role above 20 km

Layers of Atmosphere:

Earth’s Radiation budget:

Global Climate Change:

• The above discussion sets the stage for understanding how changes in global climate can occur due to change in earth‟s environment. There are four general causes

(i) A change of the earth‟s surface albedo (ii) A change in the albedo of the atmosphere (iii) A change in the chemical composition

(iv) Release of heat which are large in relation to solar heating

• Changes in Surface Albedo:

- natural albedo of earth‟s surface varies from extremely low to very high values

Oceans– Irrigated croplands – Deserts – Freshly fallen snow

- Agricultural and Urbanization have little effect on overall surface albedo

• Changes in Atmospheric Albedo:

- distribution of water and ice clouds - Cirrus, Cumuls and Nimbus clouds - dust, smoke and aerosols (Particulate)

- Cirrus (Avg. albedo 10-25%) , thick cumulus (albedo 70-80%)

- injection of particulate by human activity has less impact than natural injection

• Changes in Atmospheric Composition:

- changes in H₂O, CO₂, O₃ concentration (major concern)

- changes in CO, SO₂, NO_x, CH₄, and other gases (lesser concern for global climate but produce intense local problems)

- 10 % increase in CO₂leads to a warming of 0.2 to 0.3 C (Manabe et al.) - change in O₃ conc. leads to change in heating pattern in stratosphere

• Other Chemical Emissions:

- lead to intense local air pollution problems

- major pollutants added to atmosphere CO, SO_x, NO_x

Different Clouds:

Cirrus Cumulus

Nimbus

Air Pollution Cycle:

• Interaction and Exchanges between Land, water and Air

• Arbitrary lines between Land, Water and Air Pollutions are non-existent

• Each type affects the other

• Technological civilization treating nature as its enemy

• Earth is used as a dumping ground

Air and Land:

• Exchange of Pollutants like SO

, NO

, PM, CO, HC and Photo-chemical oxidants

• Natural scrubbing action of rain causes water pollution

• Oceans produce CO

• Water becomes septic when dissolved oxygen falls to zero,

release of H

S and odorous compounds occurs

Air and Land:

• Land acts as a sink for many air pollutants through microbial or chemical means

• PM transferred back to soil by gravity and precipitation

• Waste products on land can contribute to air pollution

• Fine materials on land can be entrained, causing particulate

problems downwind

Land and Water:

• Leaching is the process of extracting water soluble material from a solid (e.g. soluble organic matter from land-fills

• Oxidation of sulphur bearing mineral in the mines by air and

water to form acids (mine drainage)

Atmospheric Interactions, Dispersion, Meteorology :

• Atmospheric interactions include all chemical and physical phenomena occurring to a mixture of air borne pollutants

• Upon emission these pollutants undergo a mass redistribution and photochemical changes, varying over many temporal and spatial scales

• These interactions can be found within the theoretical framework of the

atmospheric motions responsible for these changes of pollutant state and

distribution

Planetary Boundary Layer :

• Frictional effects of underlying terrain

• All significant atmospheric interactions on pollutants occur within this layer

• Small scale turbulence

• Boundary conditions vary Upper layer– wind speed

Lower layer-- geographic distribution

Mechanical and Convective Turbulence:

• Convective Turbulence : -- convective heating, expansion and subsequent rising of air (during the day) -- cooling of earth‟s surface and subsequent cooling of air (negative turbulence during the night)

• Mechanical Turbulence: -- irregular terrain generates three dimensional swirls called „eddies‟

 Dispersion of pollutants depend on total turbulent energy

 Intensity of turbulence varies „diurnally‟

 Mechanical turbulence depends on wind speed and under-lying terrain

 Convective turbulence depends on vertical temperature structure

Stability Considerations, Inversions :

• Lapse Rate :-

“When a small volume of air displaced upward in the atmosphere, it will encounter a lower pressure and undergo an expansion to a lower temperature.

Usually the expansion is rapid enough that it can be assumed that no heat transfer takes place between that parcel of air and the surrounding atmosphere”.

Adiabatic Lapse rate

= (- dT / dZ)

=1 C/ 100m =5.4 F/ 1000 ft

• For International Standard Atmosphere, the standard or the normal temperature gradient is given by

( dT / dZ )

= - 0.0066 C/ m = 0.66 C/100 m

Contd.

Stability Conditions :

• Comparison of ELR and ALR

• ELR > ALR --- Super-adiabatic --- Unstable

• ELR < ALR --- Sub-adiabatic --- Strongly stable

• ELR = ALR --- Adiabatic --- Neutral

Inversions:

• Subsidence inversion

• Radiation inversion

• Advective inversion

Contd.

Advective inversion Combined Radiation and

Subsidence inversions

Pollutant Entry, Sources and Emission Factors:

• Source Types and Composition:

Fixed sources Moving sources

Power Plants, Incinerators, Chemical Refineries, Specialized Industrial Processing Plants and during the winter season, Domestic Space Heating units.

vehicular traffic and airplanes

SO2 from coal, particulate matter.

Nitric oxides, various hydrocarbons ,Oxides of particular process products.

Carbon monoxide, hydrocarbons,

nitric oxides and particulates

Atmospheric Entry:

 Pollutant entry into the ambient atmosphere can occur at a point , along a line or over an entire area.

 Instantaneous sources emit „Puff’

 Continuous sources discharge ‘Plume’

Continuous Point Source : Strong Power Plants Continuous Line Source : Main Urban Traffic Artery Continuous Area Source : An entire Urban Complex Continuous Volume Source : An entire Urban Complex

Virtual Point Source : A series of power plants whose

emissions are entrained within the plant volume, can be extrapolated behind the emission complex to a virtual point.

Instantaneous Point Source : Explosions, Volcanic Eruptions Instantaneous Line Source : A Plane emitting Pesticides

Once the pollutants enter the atmosphere, their life histories depend entirely on the local atmospheric processes occurring within the emission area.

Diurnal Effects:

• Vertical temperature and wind fields in the planetary boundary layer

• During the day, strong solar heating induces a large of convective turbulence

• At night, the radiational cooling causes low-based temperature inversions

Plume Behaviour:

FANNING:Due to radiational cooling, the inversion reaches up to the plume height. The plume fans out in the horizontal.

FUMIGATION:Due to solar heating, and the gradual warming of atmosphere from the ground upwards “ burns off “ the inversion. As the strong convective mixing reaches the fanned plume, it mixes the large pollutant concentrations towards ground level.

LOOPING: In the afternoon, strong solar radiation producing an excessive amount of convective turbulence causes the plume to loop in the vertical in response to the strong eddy motion.

CONING:On cloudy days and nights with strong winds, mechanical

turbulence prevails and “normal”

dispersion occurs, forming a cone.

LOFTING:Over rural areas, just after sunset. A superadiabatic layer exists over the newly forming ground-based inversion

TRAPPING:The trapped plume occurs when the plume effluent is caught between two inversion layers.

Plume Buoyancy:

• Plume Buoyancy depends on - Ambient temperature - Stack gas temperature - Efflux velocity

- Wind speed

Heat Island Effect:

• City area absorbs more solar energy than an equal area in the countryside/suburbs

• Retains it for a longer period at night

• City also releases large quantities of particulates into the air

• Warm air rises up then cools and comes down

• Self-contained circulatory system is established, Known as „Heat Island Effect‟

Modeling Atmospheric Interactions:

• Capacity of the atmosphere to absorb, disperse, modify and deposit pollutant materials

• Comparison of calculated concentrations with the acceptable risk levels

• Criteria in urban, regional and general land-use planning and development.

Urban Modeling Techniques:

There are three complexity levels of Urban Modeling

 The Box Model:- The box model is the simplest model. An urban area is divided into a Checkerboard grid , and it is assumed that all atmospheric interactions occur simultaneously for each box , so that the box is treated as a well mixed vessel.

 Puff and Plume Model:- This model employs Gaussian Statistical assumption for instantaneous and continuously emitting sources respectively , then integrated over the entire urban area.

 The Highest Level Model:- It involves the solution of the mass continuity equations of the turbulent planetary boundary layer.

Recently developed models include modules for calculations

involving photochemical kinetics, topographical interactions and

deposition processes.

Air pollution Severity:- (PINDEX)

Sample calculation for PINDEX

Given Information

Particulate Matter (PM) = 143.0 g/m³

Sulphur Oxides (SO_x) = 123.0 g/m³

Nitrogen Oxides (NO_x) = 136.0 g/m³

Carbon monoxide (CO) = 7250.0 g/m³

Hydrocarbons (HC) = 2157.0 g/m³

Oxidant (OOO) = 43.2 g/m³

Solar Radiation (SR) = 400.0 cal/cm²-day

Convert Reactants to mol/m³

NO_x = 136.0/46.0 = 3.0 mol/m³

HC = 2157.0/16.0=134.5 mol/m³

OOO = 43.2/48.0 =0.9 mol/m³

Determine limiting reactant for Oxidant Synthesis (NO_xor HC) NO_xis limiting

Create Oxidant

OOO = 0.0006 x SR x (Limiting Reactant)

= 0.0006 x 400.0 x 3.0 = 0.72 mol/m³

Determine total oxidant and excess HC and NO_x

OOO = 0.9 + 0.72 = 1.6 mol/m³

HC = 134.5 – 0.72 = 133.8 mol/m³

NO_x = 3.0 – 0.72 = 2.3 mol/m³

Convert reactants back to weight basis

OOO = 1.6 x 48.0 = 77.3 g/m³ HC = 133.5 x 16.0 = 2140.0 g/m³ NO_x = 2.3 x 46.0 = 105.0 g/m³

Contd.

Apply Tolerance factor

PM =143.0 / 375.0 = 0.381 SO_x = 123.0 / 1430.0 = 0.086 NO_x = 105.0 / 514.0 = 0.204 CO = 7250.0 / 40000.0 = 0.181 HC = 2140.0 / 19300.0 = 0.111 OOO = 77.3 / 214.0 = 0.361 Determine Synergism term (SYN)

SYN = SO_x or PM ( Whichever is smaller) SYN = SO_x= 0.086

Sum the terms to determine PINDEX

Pindex = PM + SO_x+ NO_x+ CO + HC + OOO + SYN

= 0.381 + 0.086 + 0.204 + 0.181 + 0.111 + 0.361 + 0.086

= 1.41