Meteorology%20

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Meteorology Air PollutionDr. Wesam Al Madhoun
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• Dispersion Advection (Transport)
  Dilution (Diffusion)
• Ficks law of diffusion J - D
  D C/Dx
• Where, J Mass Flux D Diffusivity
  coefficient, D C/Dx Concentration gradient
• Diffusion of pollutants occur due to turbulence,
  which further depends upon many factors
• Ambient temperature
• Temperature of emissions
• Roughness factors
• Wind velocity
• Wind direction

Transport
Source
Receptor
Re-entrainment
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Air Pollutant Cycle
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Dispersion

• General mean air motion
• Turbulent velocity fluctuations
• Diffusion due to concentration gradients from
  plumes
• Aerodynamic characteristics of pollution
• Particles
• Size
• Shape
• Weight

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Turbulence

• Not always completely understood
• Two types
• Atmospheric heating
• Causes natural convection currents
• Thermal eddies
• Mechanical turbulence
• Results from shear wind effects
• Result from air movement over the earths
  surface, influenced by location of buildings and
  relative roughness of terrain.

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Lapse Rate

• Important characteristic of atmosphere is
• ability to resist vertical motion stability
• Affects ability to disperse pollutants
• When small volume of air is displaced upward
• Encounters lower pressure
• Expands to lower temperature
• Assume no heat transfers to surrounding
  atmosphere
• Called adiabatic expansion

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Adiabatic Expansion

• To determine the change in temp. w/ elevation due
  to adiabatic expansion
• Atmosphere considered a stationary column of air
  in a gravitational field
• Gas is a dry ideal gas
• Ignoring friction and inertial effects
• ( dT/dz)adiabatic perfect gas - (g M/ Cp)
• T temperature
• z vertical distance
• g acceleration due to gravity
• M molecular weight of air
• Cp heat capacity of the gas at constant
  pressure

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Adiabatic Expansion

• ( dT/dz)adiabatic perfect gas -0.0098C/m
• or
• ( dT/dz)adiabatic perfect gas -5.4F/ft
• Change in Temp. with change in height

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Lapse rate

• Lapse rate is the negative of temperature
  gradient
• Dry adiabatic lapse rate
• Metric
• G - 1C/100m or
• SI
• G - 5.4F/1000ft

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Conti.

• Important is ability to resist vertical motion
  stability
• Comparison of G to actual environment lapse rate
  indicates stability of atmosphere
• Degree of stability is a measure of the ability
  of the atmosphere to disperse pollutants

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Atmospheric Stability

• Affects dispersion of pollutants
• Temperature/elevation relationship principal
  determinant of atmospheric stability
• Stable
• Little vertical mixing
• Pollutants emitted near surface tend to stay
  there
• Environmental lapse rate is same as the dry
  adiabatic lapse rate

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Stability Classes

• Developed for use in dispersion models
• Stability classified into 6 classes (A F)
• A strongly unstable
• B moderately unstable
• C slightly unstable
• D neutral
• E slightly stable
• F moderately stable

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• Vertical Temperature Profiles
• Environmental lapse rate (ELR)
• Dry adiabatic lapse rate (DALR)
• If,
• ELR gt DALR sub adiabatic condition, atmosphere
  is stable.
• ELR gtgt DALR Inversion conditions. Very stable
  atmosphere.
• ELR DALR atmosphere is neutral.
• ELRlt DALR super adiabatic condition,
  atmosphere is unstable.
• Shapes of plumes depends upon atmospheric
  stability conditions.

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Mixing Height of atmosphere The height of the
base of the inversion layer from ground surface.
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General Characteristics of Stack Plumes

• Dispersion of pollutants
• Wind carries pollution downstream from source
• Atmospheric turbulence -- causes pollutants to
• fluctuate from mainstream in vertical and
  crosswind directions
• Mechanical atmospheric heating both present at
  same time but in varying ratios
• Affect plume dispersion differently

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Plume Types

• Plume types are important because they help us
  understand under what conditions there will be
  higher concentrations of contaminants at ground
  level.

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Looping Plume

• High degree of convective turbulence
• Superadiabatic lapse rate -- strong instabilities
• Associated with clear daytime conditions
  accompanied by strong solar heating light winds
• High probability of high concentrations
  sporadically at ground level close to stack.
• Occurs in unstable atmospheric conditions.

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Coning Plume

• Stable with small-scale turbulence
• Associated with overcast moderate to strong winds
• Roughly 10 cone
• Pollutants travel fairly long distances before
  reaching ground level in significant amounts
• Occurs in neutral atmospheric conditions

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Fanning Plume

• Occurs under large negative lapse rate
• Strong inversion at a considerable distance above
  the stack
• Extremely stable atmosphere
• Little turbulence
• If plume density is similar to air, travels
  downwind at approximately same elevation

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Lofting Plume

• Favorable in the sense that fewer impacts at
  ground level.
• Pollutants go up into environment.
• They are created when atmospheric conditions are
  unstable above the plume and stable below.

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Fumigation

• Most dangerous plume contaminants are all coming
  down to ground level.
• They are created when atmospheric conditions are
  stable above the plume and unstable below.
• This happens most often after the daylight sun
  has warmed the atmosphere, which turns a night
  time fanning plume into fumigation for about a
  half an hour.