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Chapter 5. Air Pollution Meteorology

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Chapter 5. Air Pollution Meteorology Selami DEM R Asst. Prof. – PowerPoint PPT presentation

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Title: Chapter 5. Air Pollution Meteorology


1
Chapter 5. Air Pollution Meteorology
  • Selami DEMIR
  • Asst. Prof.

2
Outline
  • Introduction
  • Solar Radiation
  • Atmospheric Pressure
  • Lapse rate Potential Temperature
  • Atmospheric Stability
  • Coriolis Force Gravitational Force
  • Pressure Gradient Force
  • Overall Atmospheric Motion
  • Equations of Motion
  • Wind Speed Profile

3
Introduction (1/2)
  • Air pollutant cycle
  • Emission
  • Transport, diffusion, and transformation
  • Deposition
  • Re-insertion
  • In large urban areas, there are several
    concentrated pollutant sources
  • All sources contribute to pollution at any
    specific site
  • Determined by mainly meteorological conditions
  • Dispersion patterns must be established
  • Need for mathematical models and meteorological
    input data for models

4
Introduction (2/2)
  • Three dominant dispersion mechanisms
  • General mean air motion that transport pollutants
    downwind
  • Turbulent velocity fluctuations that disperse
    pollutants in all directions
  • Diffusion due to concentration gradients
  • This chapter is devoted to meteorological
    fundamentals for air pollution modelling

5
Solar Radiation (1/6)
  • Solar constant ? 8.16 J/cm2.min
  • 0.4-0.8 µ ? visible range, maximum intensity

Ref http//www.globalwarmingart.com/images/4/4c/S
olar_Spectrum.png
6
Solar Radiation (2/6)
  • Distribution of solar energy on earth

Ref OpenLearn Web Site,
http//openlearn.open.ac.uk/file.php/1697/t206b1c0
1f26.jpg
7
Solar Radiation (3/6)
  • At right angle on June, 21 ? Tropic of cancer
  • At right angle on December, 21 ? Tropic of
    capricorn
  • At right angle on March, 21 and september, 21 ?
    Equator

http//upload.wikimedia.org/wikipedia/commons/8/84
/Earth-lighting-equinox_EN.png
8
Solar Radiation (4/6)
  • Example What is the Suns angle over Istanbul on
    June, 21? Note that Istanbul is located on 40 N
    latitude.
  • Solution Sunlight reaches Tropic of Cancer (23
    27') at right angle on June, 21.
  • Where
  • ? Suns angle at the given latitude
  • L2 Latitude of given region
  • L1 Latitude of region where sunlight reaches
    surface at right angle

9
Solar Radiation (5/6)
  • Example What is the Suns angle over a city
    located on 39 N latitude when the sunlight
    reaches surface at right angle on 21 S latitude?
  • Solution

10
Solar Radiation (6/6)
  • Homework (due 18.04.2008)
  • Make a brief research on Stefan-Boltzman Law and
    write a one page report for your research.
  • Comment on what would happen if earths
    inclination were 24 instead of 2327'.
  • What determines the seasons? Why some regions of
    earth get warmer than other regions.
  • Calculate the sunlight angle over Istanbul
  • on March, 21
  • on June, 21
  • on September, 21
  • on December, 21

11
Atmospheric Pressure (1/4)
  • Force on earth surface due to the weight of the
    atmosphere
  • Defined as force exerted per unit surface area
  • Units of measurement ? Pascal (Pa), atmospheric
    pressure unit (apu, atm), newtons per
    meter-squared (N/m2), water column (m H2O), etc.
  • 1 atm 101325 Pa
  • 1 atm 10.33 m H2O
  • 1 atm 760 mm Hg
  • 1 Pa 1 N/m2
  • Atmospheric pressure at sea level is 1 atm

12
Atmospheric Pressure (2/4)
  • Consider a stationary air parcel as shown
  • Force balance (assuming no horizontal pressure
    gradient)

13
Atmospheric Pressure (3/4)
  • Integrating from h z0 to h z produces

14
Atmospheric Pressure (4/4)
  • Homework (due 18.04.2008)
  • Make a research about pressure measurement
    devices and prepare a one-page report for your
    research. Give brief explanations for each type.
  • Calculate the atmospheric pressure on top of
    Everest if it is 1013 mb at sea level.

15
Lapse Rate Potential Temperature (1/5)
  • Adiabatic ? no heat exchange with surroundings
  • Consider an air parcel moving upward so rapidly
    that it experiences no heat exchange with
    surrounding atmosphere
  • Enthalpy change
  • where
  • H1 initial enthalpy of air parcel
  • H2 final enthalpy of air parcel
  • U1 initial internal energy
  • U2 final internal energy
  • V1 initial volume
  • V2 final volume

16
Lapse Rate Potential Temperature (2/5)
  • By enthalpys definition
  • In infinitesimal expression
  • Internal energy substitution
  • By internal energy definition
  • Enthalpy change is a function of only temperature
    when pressure is constant
  • Substituting differential pressure as follows
  • Since the process is adiabatic, no heat exchange
    occurs

17
Lapse Rate Potential Temperature (3/5)
  • This approximation assumed there is no phase
    change in the air parcel
  • called Dry Adiabatic Lapse Rate (DALR)
  • If any phase change takes place during the
    motion, the temperature change will be far more
    different from DALR
  • Called Saturated (Wet) Adiabatic Lapse Rate
    (SALR, WALR)
  • Variable, must be calculated for each case
  • Also significant in some cases this course does
    not focus on it
  • For standardization purposes, Standard Lapse Rate
    (SLR), also known as Normal Lapse Rate (NLR), has
    been defined
  • On average, in middle latitude, temperature
    changes from 1C to -56.7C
  • SLR -0.66C/100 m

18
Lapse Rate Potential Temperature (4/5)
  • Lapse rate measurements are taken by a device
    called Radiosonde
  • Results of measurements are plotted to obtain
    Environmental Lapse Rate (ELR)
  • ELR is real atmospheric lapse rate
  • Another significant concept is Potential
    Temperature
  • Defined as possible ground level temperature of
    an air parcel at a given altitude

where ? Tp potential temperature of air
parcel T Temperature of air parcel H Height
of air parcel from ground DALR Dry adiabatic
lapse rate
19
Lapse Rate Potential Temperature (5/5)
  • Homework (due 18.04.2008)
  • Calculate potential temperature for given data
  • Calculate the atmospheric temperature at 800 m
    from the ground if the atmosphere shows adiabatic
    characteristic and the ground level temperature
    is 12C.

Height, m Temperature, C
350 8
750 2
1200 14
20
Atmospheric Stability (1/8)
  • If ELR lt DALR Then
  • Superadiabatic meaning unstable
  • ElseIf ELR DALR Then
  • Neutral
  • ElseIf DALR lt ELR lt 0 Then
  • Subadiabatic meaning stable (weakly stable)
  • ElseIf DALR lt 0 lt ELR Then
  • Inversion meaning strongly stable
  • EndIf

21
Atmospheric Stability (2/8)
  • Superadiabatic

22
Atmospheric Stability (3/8)
  • Neutral

23
Atmospheric Stability (4/8)
  • Subadiabatic

24
Atmospheric Stability (5/8)
  • Inversion

25
Atmospheric Stability (6/8)
  • If d?/dz lt 0 Then
  • Superadiabatic
  • ElseIf d?/dz 0 Then
  • Neutral
  • ElseIf d?/dz gt 0 Then
  • Subadiabatic
  • EndIf

26
Atmospheric Stability (7/8)
  • Example Calculate vertical temperature gradient
    and comment on atmospheric stability condition if
    the atmospheric temperature at 835 m is 12 C
    when the ground temperature is 25 C.
  • Solution
  • The atmosphere is said to be unstable since ELR lt
    DALR

27
Atmospheric Stability (8/8)
  • Homework (due 25.04.2008)
  • Following measurements are taken over Istanbul at
    different times. Determine atmospheric stability
    condition for each case.
  • Briefly explain stable air, unstable air, neutral
    air and inversion.
  • Make a brief research about the role of
    atmospheric stability in dispersion of pollutants
    in the atmosphere and prepare a-one-page report
    for your research.
  • What is conditional stability? Explain.

Height, m Temperature, C Temperature, C Temperature, C Temperature, C
Height, m Case 1 Case 2 Case 3 Case 4
0 14 22 17 4
1000 8 8 7 6
28
Coriolis Force
  • The Coriolis effect is an apparent deflection of
    moving objects from a straight path when they are
    viewed from a rotating frame of reference.
    Coriolis effect is caused by the Coriolis force,
    which appears in the equation of motion of an
    object in a rotating frame of reference.
    (Wikipedia Web Site, http//en.wikipedia.org/wiki/
    Coriolis_Force)

29
Gravitational Force (1/3)
  • The force exerted by the earth on an object in
    earths attraction range
  • Caused by attraction forces between two masses
  • m1 being the mass of earth (M) and m2 is that of
    an object near earth surface

FA attraction force ? 6.66810-11
Nm2/kg2 m1,m2 objects masses r distance bw
masses
30
Gravitational Force (2/3)
  • Example Determine the acceleration of an object
    near the Eraths surface due to gravitational
    attraction force
  • Solution

31
Gravitational Force (3/3)
  • Homework (due 25.04.2008)
  • Determine the acceleration of an object near the
    Martian surface due to gravitational attraction
    force
  • Determine the acceleration of an object near the
    Moons surface due to gravitational attraction
    force

32
Pressure Gradient Force
  • Consider an air parcel accelerating in a
    horizontal direction
  • In three dimensional representation,

33
Overall Atmospheric Motion (1/7)
  • Consider an air parsel accelerating around the
    Earth
  • Overall acceleration

34
Overall Atmospheric Motion (2/7)
  • Neglecting vertical terms and re-arranging, we get

u velocity of atmospheric motion in east-west
direction v velocity of atmospheric motion in
north-south direction O rotational speed of
earth 7.2910-5 r/s F latitude on which the
motion occurs
35
Overall Atmospheric Motion (3/7)
  • Example Briefly explain the mechanisms that
    forced radioactive pollutants towards Turkeys
    coasts after Chernobyl. Tell about the
    meteorological conditions then. Show the pressure
    centers and wind patterns on the day of accident
    and two day after the accident on a brief map.
    Consider the aspects of geostrophic winds.


36
Overall Atmospheric Motion (4/7)
  • Solution

37
Overall Atmospheric Motion (5/7)
  • Example Isobars are shown in the figure below,
    for 40 latitude in the Northern Hemisphere, at
    an altitude of 5600 meters. Determine the
    geostrophic wind speed in km/hour
  • Temperature at 5600 m -28C
  • Coriolis force 2 ? V sin ß
  • ? 7.3 x 10-5 radians/s ß Latitude degrees
    V geostrophic wind speed
  • 1 mb 100 N/m3

38
Overall Atmospheric Motion (6/7)
  • ExampleSuppose a nuclear accident occurs at a
    place of 3,000 km west of Istanbul. Radioactive
    pollutants are pumped above the planetary
    boundary layer (PBL) with the power of explosion.
    On the day of nuclear accident, the radiosonde
    data taken at different places of Europe shows
    that atmospheric pressure is decreasing towards
    north at a rate of 0.0015 N/m3 and this pattern
    is valid for the whole Europe. Will the
    radioactivity affect Istanbul? If yes, when? Note
    that Istanbul is located on 40 northern latitude
    and worlds angular speed of rotation is 7.3
    10-5 radians/sec. You may assume the density of
    air at the level where geostrophic wind equations
    apply as 0.70 kg/m3.

39
Overall Atmospheric Motion (7/7)
  • Solution

40
Equations of Motion (1/3)
  • Eularian Approach
  • The observer stays stationary and observes the
    change in the value of a function f
    (concentration, atmospheric parameters, etc.)
  • The coordinate system (reference frame) is
    stationary
  • The objective is moving
  • Lagregian Approach
  • The observer moves with the moving objective and
    observes the change in the value of a function f
  • The coordinate system is moving with the
    objective at the same speed and direction

41
Equations of Motion (2/3)
  • Lagregian Approach (contd)

42
Equations of Motion (3/3)
  • Examples will be given later

43
Wind Speed Profile (1/2)
  • Due to friction near surface, wind speed
    increases with height exponentially
  • Wind speed is measured by a device called
    anemometer
  • 10 m should be chosen for anemometer height

Stability Class P
A 0.15
B 0.15
C 0.20
D 0.25
E 0.40
F 0.60
44
Wind Speed Profile (2/2)
  • Homework (due 25.08.2008)
  • Calculate wind speeds for Class B stability at
    20, 30, 50, 100, 200, and 500 m if it is 1.2
    m/sec. Plot the results.
  • Comment on how the wind speed would change with
    altitude if the stability class were Class E.
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