Introduction to Aerobiology : Origin, Sources, Fate and Transport of Air Pollutants Prof. Mukesh...

Introduction to Aerobiology : Origin, Sources, Fate and Transport of Air Pollutants

Prof. Mukesh KhareDepartment of Civil Engineering

Indian Institute of Technology DelhiE-mail ID: [email protected]

International Perspectives on Quantitative Microbial Risk Assessment

IIT Delhi Summer School 2014

What is Aerobiology? Bio-aerosols/characteristics Sources of bio-aerosols Bio-aerosols: stability Bio-aerosols: fate and transport Fate and transport modelling techniques ADMS modelling techniques Application in Aerobiology Building assessment References

Overview


The study of the sources, dispersion, and effects of airborne biological materials, such as pollen, spores, and microorganisms.

The movement of bioaerosols is generally passive and is greatly influenced by the surrounding environment.The viability of bioaerosols is dependent on the environmental conditions.

What is Aerobiology?


Mixture of solid or liquid particles in air containing whole or part of biological materials

Biological materials include human pathogens, toxic or allergic pieces of microorganisms, dust mite parts or feces, animal dander, fur, dried saliva and animal waste products

Biological agents carried in the air as large molecules, volatile compounds, single particles, or clusters of particles that are living or were released from a living organisms

Particle sizes: typically 0.5µm to 100µm. Generally assumed having properties of gases.

Capable of eliciting diseases that may be infectious, allergic, or toxigenic with the conditions being acute or chronic

Bio-aerosol: Characteristics


Bio-aerosol: Sources

Natural sources Pollen (Part of the life cycle of plants) Spores (Part of the life cycle of fungi) Microorganisms/plant Substances from of animals

Anthropogenic sources Indoor Air: Damp and mouldy buildings Laboratory activities Recycling facilities (e.g. composting) Intensive mass animal farming Human


Physical Sunlight Open air factors (e.g. ozone) Air movement (e.g. wind shear)

Biological Oxygen Radiation (e.g. UV, Ƴ-rays, X-rays) Suspended media (salts, proteins, sugars)

Environmental Temperature Relative Humidity Composition (moisture, salts, protein, etc.)

Bioaerosol: Stability

Source: ACGIH, 1999 IIT Delhi Summer School 2014

Bio-aerosol: Fate and Transport


The movement, motion, dissemination and equilibrium in the environment fall in category of fluid mechanics.

Bioaerosol: Mobility


Molecular scaleThe motion is called Molecular Diffusion

Ex- Diffusion within sediments

Global scaleThe motion is called Dispersion

Ex- Transport of gases and aerosols by large air masses

Scale of Motion


What is Flux ?Mass of diffusing particles/gases crossing unit area in unit time in direction of motion.

Motion of the pollutants is accomplished by flux of that pollutant.

Pollutant flux = f (Mass flux, Dispersion flux, Diffusion flux, Source, Sinks)

The Flux


Advection x

yz

Turbulent Diffusion

Turbulent Eddies

x

zy

Dispersion

a

b

c

Advection, Diffusion & Dispersion


Atmospheric Turbulent Flows

Dissipation Dispersion RandomFluctuations

Mixing and KEDissipates depending upon the density stratification in the atmosphere

Diffusion and Advection

Case A: If Density of lower layer of air > Density of upper layers

Case B: If Density of lower layer of air < Density of upper layers

Case B: Applicable to atmosphere in day time

Case A: Applicable to atmosphere during night timeReduced

Enhanced


The Dispersion

Source ReceptorTransport

Re-entrainment

Source : Point, Line, AreaReceptors : HumansTransport : Fate of air pollutantsRe-entrainment : Re-suspensions of air pollutants

Dispersion = Advection (Transport) + Dilution (Diffusion)


The Diffusion: Types

Nomalous

Molecular/Brownian

Diffusion

Anomalous

Atmospheric


The Diffusion Equation: Basic

c = + ; ui = + ’

= 0 ; = 0

Conservation of mass principle In Cartesian coordinate, C = C(x, t) It neglects small terms due to molecular diffusivity


The Gaussian Diffusion Equation

Analytical solutions to the diffusion equation

Simplest case: One dimensional (In the z - direction)Vertical diffusion (Kz) = constant

Mean wind speed () = x/t

(z, t) e^[- (1/2) * (z/ )2]


Fate and Transport Modelling Techniques


System approach to air quality model

A relationship between emissions and air quality that incorporates the transport, dispersion and transformation of compounds emitted into the air.

What is Air Quality Model?


Three step process:i. Pre-processor : emission data- micro-organism

characteristics, emission rates, meteorological data, grids, emitter coordinates etc.

ii. Processor : Gaussian based dispersion model, settling velocity etc.

iii.Post-processor: Micro-organism concentration map, frequency map etc.

Bio-aerosol Modelling


Bio-aerosol Modelling

PROCESS FLOW CHART IIT Delhi Summer School 2014

Emission: Release of air pollutants into the atmosphere which are put into the air or emitted by various sources.

Emission Inventory (EI): A list of the amount of pollutants from all sources entering the air in a given time period. The boundaries of areas are fixed.

The Emission


Why emission inventory (EI) is needed?

For planning and zoning the area study.EI can point out major sources.EI is helpful in deciding control strategies.EI is used in mathematical models to determine the

degree of overall control necessary to meet ambient air quality standards.

EI can be used to indicate type of sampling network and location of monitoring station.

Contd….


SBER Measurement

Portable Wind Tunnel

Schematic diagram of wind tunnel (Case study)*

Reference: Taha, M.P.M., Pollard, S.J.T, Sarkar, U., Longhurst, P. (2005). Estimating fugitive bio-aerosol releases from static compost windrows: feasibility of portable wind tunnel approach. Waste Management, 25 (4), 445-450.

Note: Only baseline fugitive emission are measured. No other influencing factor are considered.

SBER/A

whereSBER= specific bio-aerosol emission rate (cfu/m2/s);Q = flow rate through the wind tunnel (m3/s);BC = bio-aerosol concentration in air (cfu/m3); andA= area covered by the wind tunnel (m2)

SBER = f { Source material, outside condition/process, individual bio-aerosol properties, geographical, topographical and meteorological condition}


The Meteorology

Atmospheric Characteristics

Meteorology is the interdisciplinary scientific study of the atmosphere that focuses on weather processes and short term forecasting (in contrast with climatology).

Characteristic of atmosphere is its ability to resist vertical motion: Stability

Affects atmospheric ability to disperse pollutants When parcel of air is displaced upward

Encounters lower pressure Expands to lower temperature Assume no heat transfers to surrounding atmosphere

(adiabatic)IIT Delhi Summer School 2014

Different variables affecting air pollutants transport of diffusion in the atmosphere are:

a) Wind speed and directionb) Vertical temperature gradient (lapse rate)c) Stability of the atmosphered) Roughness element of the earth surfacee) Humidity or water vapor in the atmospheref) Solar radiation

Contd….


Wind speed profile with height

Contd….

u p

u1 = reference wind velocity at 10m; z1 = reference height of 10m; p =depends upon stability and surface configuration


Wind direction profile with heightZ

Y

X

Z

Y

X

Circular plume [a=b] Elongated plume [a>b]

Wind direction changes with height It produces crosswind horizontal shear – this increases the

horizontal dispersion

Contd….


Rate of change of temperature of the parcel of air (smoke) with height.

Types of Lapse Rate ( dT/dz)Dry Adiabatic Lapse rate (Гd) : - 1°C/100m or (DALR) - 5.4°F/1000ftSaturated Adiabatic Lapse Rate (Гsat) : -0.60C/100m

(SALR)Environmental Lapse Rate: Actual change in

temperature of the (ELR) surrounding environment

Lapse rate (Г)


• Comparison of Γd to ELR classifies stability of atmosphere.

• Degree of stability is a measure of the ability of the atmosphere to disperse pollutants

Significance of Lapse Rate


ADMS modeling technique


Cambridge Environmental Research Consultants3, King’ s Parade, Cambridge CB2 1SJ, UK

Telephone : +44 -1223357773Email: [email protected]

Website : http://www.cerc.co.uk

Emission rate

Management Practices


• Atmospheric Dispersion Modeling System• Can be use for Point, Line, Area, Volume,

Grid sources• Can model for continuous as well as discrete

point source• Flat or complex terrain• Multiple buoyant industrial emissions• Urban or rural areas• Valid to 60km, useful to 100 km

Model Features


Integrated meteorological pre-processor, choice of met input parameters like cloud cover, surface sensible heat flux, radiation.

Can input albedo and Bowen ratio. Integrated processing for buildings, complex

terrain. Utility to convert US met data to ADMS format,

including AERMOD data. Wet and dry deposition. Time varying source parameters.

Contd…


Salient Point• Bioaerosol are modelled as particles • Passive particles• Dry deposition • Agglomeration of particles • Gaussian distribution

SOURCE: G.H. DREW, A. TAMER, M.P.M. TAHA, R. SMITH, P.J. LONGHURST, R. KINNERSLEY and S.J.T POLLARD (2006), “Dispersion of Bioaerosols from Composting Facilities”, Proc. Waste Conf. Integrated Waste Management and Pollution Control. Stratford-upon-Avon, UK, 19-21 September 2006.

Application in Aerobiology


Building Assessment

Building Assessment (Sick Building Syndrome)


References ACGIH. Bio-aerosols: Assessment and Control. American Conference of Governmental

Industrial Hygienists, Cincinnati, OH. 1999. Aerotech Laboratories, Inc. IAQ Microbial Reference Guide, IAQ Tech Tips,

www.aerotechlabs.com. 2000. ASTM. Biological Contaminants in Indoor Environments. Morey/ Feely/ Otten ed. STP

1071, Philadelphia, Pennsylvania. 1990. G.H. DREW, A. TAMER, M.P.M. TAHA, R. SMITH, P.J. LONGHURST, R. KINNERSLEY and S.J.T

POLLARD (2006), “Dispersion of Bioaerosols from Composting Facilities”, Proc. Waste Conf. Integrated Waste Management and Pollution Control. Stratford-upon-Avon, UK, 19-21 September 2006.


Introduction to Aerobiology : Origin, Sources, Fate and Transport of Air Pollutants Prof. Mukesh...

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