air pollution and meteorology
Download
Skip this Video
Download Presentation
AIR POLLUTION AND METEOROLOGY

Loading in 2 Seconds...

play fullscreen
1 / 54

AIR POLLUTION AND METEOROLOGY - PowerPoint PPT Presentation


  • 266 Views
  • Uploaded on

AIR POLLUTION AND METEOROLOGY. Dr.K . Subramaniam , Senior Lecturer (Environmental Health and Safety ). METEOROLOGY OF AIR POLLUTION. Transport and dispersion Removal mechanisms. Important Aspects of Air Pollution Meteorology. Atmospheric Turbulence

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' AIR POLLUTION AND METEOROLOGY' - maribel-herandez


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
air pollution and meteorology

AIR POLLUTION AND METEOROLOGY

Dr.K. Subramaniam,

Senior Lecturer (Environmental Health and Safety )

meteorology of air pollution
METEOROLOGY OF AIR POLLUTION
  • Transport and dispersion
  • Removal mechanisms
important aspects of air pollution meteorology
Important Aspects of Air Pollution Meteorology
  • Atmospheric Turbulence
  • Scales of Atmospheric/Turbulent Motion
  • Plume Behavior
  • Planetary Boundary Layer (PBL)
  • Effects on Dispersion
  • Applications
meteorological parameters that influence air pollution
Meteorological Parameters that Influence Air Pollution
  • Turbulence
  • Wind Speed and Direction
  • Temperature
  • Stability
  • Mixing Height
atmospheric turbulence
Atmospheric Turbulence
  • Responsible for dispersion/transport of pollutants
  • Refers to the apparently chaotic nature of fluid motions (in this case, atmospheric motions)
  • Irregular, almost random fluctuations of such parameters as:
    • velocity
    • temperature
    • scalar concentrations (pollutants)
atmospheric turbulence sources
Atmospheric Turbulence Sources
  • Mechanical Forcing
  • Buoyant or Thermal Forcing
atmospheric turbulence sources1
Atmospheric Turbulence (Sources)
  • Mechanical Forcing:
    • Air flowing over irregular surface
    • Change in horizontal wind speed with height
  • Factors Influencing Mechanical Forcing:
    • Speed of local winds
    • Roughness of terrain over which wind is blowing
adiabatic lapse rate
Adiabatic Lapse Rate
  • It is the temperatureprofile of what would happen to a parcel of air that is raised or lowered vertically, and allowed to cool or heat from expansion or contraction with no exchange of energy or heat.
atmospheric turbulence sources2
Atmospheric Turbulence (Sources)
  • Buoyant Forcing (Thermal):
    • Air rises or sinks based on temperature; heated air becomes less dense & rises on its own; cooled air becomes more dense & sinks
  • Factors Affecting Buoyant Forcing
    • “Stability” of the atmosphere
    • Vertical temperature profile of the atmosphere
    • Lapse Rate; specifically the Dry Adiabatic Lapse Rate which is:

1oC/100m = 10oC/km = 5.4oF/1000 ft

atmospheric turbulence buoyant forcing1

Unstable Conditions - Turbulence is produced

Cooler Air

Warmer Air

Cooler Air

Displaced warmer air

will now rise on its own

(Thermals; Thunderstorm updrafts)

Ground

Atmospheric Turbulence (Buoyant Forcing)
atmospheric turbulence buoyant forcing2

Stable Conditions - Turbulence is suppressed

Warmer Air

Warmer Air

Cooler Air

Displaced cooler air

will sink back to starting point

Ground

Atmospheric Turbulence (Buoyant Forcing)
planetary boundary layer pbl
Planetary Boundary Layer (PBL)
  • Top of the atmospheric boundary layer can be defined as the lowest level in the atmosphere at which the ground surface no longer influences the meteorological parameters through turbulence transfer of mass
  • During day this corresponds to Mixing height (up to 3 km in height)

Processes include:

      • Roughness of terrain
      • Obstructed flow
      • Heat and energy transfer
the effect of boundary layer stability on plume behavior
The effect of boundary layer stability on plume behavior

In a well-mixed turbulent boundary layer on a hot day (forced by buoyancy), the turbulent eddies may be large and intense enough to advert the whole plume down to the ground. This can result in extremely high plume concentrations in the vicinity of the source.

the effect of boundary layer stability on plume behavior1
The effect of boundary layer stability on plume behavior

This is the kind of form assumed for a Gaussian plume, when the boundary layer is well-mixed and turbulent eddies are smaller than the plume scale. The plume forms a cone downstream.

the effect of boundary layer stability on plume behavior2
The effect of boundary layer stability on plume behavior

In a stable boundary layer, the plume spreads out horizontally at its level of neutral buoyancy. Vertical motion is weak, so there is little upward spread, but the plume forms a `fan\' when viewed from above. The plume is not well-mixed in the vertical, which implies relatively slow dilution, but there are not likely to be high plume concentrations at the ground. Unfortunately, this kind of plume may be the precursor to a `fumigation\' event if the inversion is subsequently mixed to ground level.

the effect of boundary layer stability on plume behavior3
The effect of boundary layer stability on plume behavior

At early evening, if a surface inversion is developing, vertical motion may be inhibited below the plume while remaining active above: the plume is diluted but does not reach the ground. This is a favorable situation.

the effect of boundary layer stability on plume behavior4
The effect of boundary layer stability on plume behavior

There is a strong inversion restricting mixing above, and the plume is mixed throughout the boundary layer. This can occur quite rapidly. For example, after sunrise when the nocturnal inversion is being eroded from below by buoyant eddies, plume-level air of high concentration may be brought down to the surface over a wide area.

effects of pbl height on stack pollutant dispersion
Effects of PBL Heighton Stack Pollutant Dispersion

PBL below stack top: little or no concentration of pollutants at the surface

Horizontal Winds

PBL Top

PBL

effects of pbl height on stack pollutant dispersion1
Effects of PBL Height on Stack Pollutant Dispersion

PBL Top

Buoyant

Turbulence

PBL

PBL well above stack top: decreased concentrations of pollutants at the surface

effects of pbl height on stack pollutant dispersion2
Effects of PBL Height on Stack Pollutant Dispersion

PBL just above stack top: increased concentrations of pollutants at the surface

PBL Top

Buoyant

Turbulence

PBL

temperature profile in atmosphere
Temperature Profile in Atmosphere

1. INVERSIONS

2. ATMOSPHERIC STABILITY

effects of stability on stack pollutant dispersion
Effects of Stability on Stack Pollutant Dispersion

Unstable Conditions: leads to greater dispersion of pollutants

PBL Top

PBL

effects of stability on stack pollutant dispersion1
Effects of Stability on Stack Pollutant Dispersion

Stable conditions: lead to less dispersion of pollutants

PBL Top

PBL

effects of stability ground source pollutant dispersion
Effects of Stability(Ground Source Pollutant Dispersion)

Buoyant

Turbulence

XXX

Unstable Conditions: Lead to lower concentration of

pollutants at surface

effects of stability ground source pollutant dispersion1
Effects of Stability(Ground Source Pollutant Dispersion)

Stable Conditions: Leads to greater concentration of

pollutants at surface

XXX

wind speed and direction
WIND SPEED AND DIRECTION
  • Mesoscale circulation
  • Large scale circulation
mesoscale circulations affecting dispersion
Mesoscale Circulations Affecting Dispersion

Land-Sea Breeze: Daytime (Sea Breeze)

Upper Level Return Flow

Air Warmed over Land Expands

(Becomes Less Dense)

Air Cooled over Water Contracts

(Becomes More Dense)

Sea Breeze (arises due to density differences)

Cooler Water

Warmer Land

Reverses at Night as Water Remains Warmer than Land to Make Land Breeze

mesoscale circulations affecting dispersion1
Mesoscale Circulations Affecting Dispersion

1. Mountain/Valley Winds

Day:

Night:

Warm

Mtn

Cool

Mtn

2. Urban/Heat Island (Night)

PBL Top

CITY

large scale circulation
Large Scale Circulation
  • Transboundary air pollution
  • Acid deposition
  • Ozone transport
applications of air pollution meteorology
Applications of Air Pollution Meteorology
  • Atmospheric Dispersion Modeling
  • Study of Accidental Release of Hazardous Substances Including Radioactive Nuclides
  • Applications of air quality meteorology can be used for dispersion modeling, i.e., predicting the path of the pollutant concentration and for calculations of ground sources, such as hazardous waste spills.
  • Let’s first look at dispersion modeling.
air pollution meteorology
Air Pollution Meteorology
  • Meteorology very important factor in developing strategies for air pollution control
  • State of the lower troposphere (PBL) plays large role in dispersion of pollutants and plumes:
    • Mechanical Turbulence
    • Buoyant Turbulence
    • Circulation
wind speed and direction1
Wind Speed and Direction
  • The average ground level wind speed is about 4.5 m/s.
    • “Calm” wind is less than 0.5m/s
  • Wind speed almost always increases with height.
    • ground friction slows lower level winds
wind speed with height
Wind Speed With Height
  • Deacon’s power law:

u2 / u1 = (z2 / z1)p

where:

u1 is the wind speed at elevation z1

u2 is the wind speed at elevation z2

and p is an exponent that depends on stability and ground characteristics

Note: Wind speed measured by the NWS is usually obtained at z = 10 meters (z1)

impact of fixed geographic features
Impact of Fixed Geographic Features
  • TERRAIN EFFECTS
  • Sea breeze
  • Valley wind
  • Drainage wind
  • Flow patterns due to topographical features
temperature gradient
TemperatureGradient
  • Air temperature is not uniform with altitude at a given location.
  • Reasons:
    • heating by the ground
    • heating by the sun
    • cloud cover
    • evaporative cooling over the oceans
    • expansion of gases due to air movement
stability and lapse rate
Stability and Lapse Rate
  • The lapse rate determines how readily parcels of air move upward or downward.
  • In stable atmospheres = vertical movement is opposed by the temperature gradient
  • In unstable atmospheres = vertical movement is enhanced
  • In neutral atmospheres = neither
stability classes
Stability Classes

A = very unstable

B = moderately unstable

C = slightly unstable

D = neutral

E = slightly stable

F = stable

why is stability important
Why is stability important?
  • Stability affects plume rise.
  • Plume rise can be calculated using information about the stack gases and meteorology.
  • Stability can effect the dispersion and appearance of plumes being emitted from stacks.
inversions
Inversions
  • An inversion is a situation of increasing temperature with height.
  • Pre-dawn mornings have an inversion that reached up to about 1000 ft (100m).
  • Atmospheres within an inversion are extremely stable, with damped vertical mixing.
surface temperature inversions
Surface Temperature Inversions:
  • Are very common
  • Are easy to recognize
  • Affect the dispersal of very small spray droplets suspended in the air
  • Do not increase the amount of off-site movement
  • Can increase the potential for offsite affects & the distance at which affects can be observed
atmospheric stability
Atmospheric Stability
  • Indicator of atmospheric turbulence
  • Depends on static stability, thermal and mechanical turbulence
  • Unstable : Lapse rate > dry adiabatic lapse rate
  • Neutral : Lapse rate = dry adiabatic lapse rate
  • Stable : Lapse rate < dry adiabatic lapse rate
  • Turner method: solar angle, cloud cover and wind speed
importance of meteorology
IMPORTANCE OF METEOROLOGY
  • Dispersion
  • Transport
  • Wind speed and direction
  • Temperature
  • Stability
  • Mixing height
ad