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Chapter 5 . Air Pollution Meteorology

Chapter 5 . Air Pollution Meteorology. Selami DEMİR Asst. Prof. Outline. Introduction Solar Radiation Atmospheric Pressure Lapse rate & Potential Temperature Atmospheric Stability Coriolis Force & Gravitational Force Pressure Gradient Force Overall Atmospheric Motion

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Chapter 5 . Air Pollution Meteorology

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  1. Chapter 5. Air Pollution Meteorology Selami DEMİR 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 S. Demir

  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 S. Demir

  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 S. Demir

  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/Solar_Spectrum.png S. Demir

  6. Solar Radiation (2/6) • Distribution of solar energy on earth Ref: OpenLearn Web Site, http://openlearn.open.ac.uk/file.php/1697/t206b1c01f26.jpg S. Demir

  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 S. Demir

  8. Solar Radiation (4/6) • Example: What is the Sun’s 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 θ = Sun’s angle at the given latitude L2 = Latitude of given region L1 = Latitude of region where sunlight reaches surface at right angle S. Demir

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

  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 earth’s inclination were 24° instead of 23°27′. • 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 S. Demir

  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 S. Demir

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

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

  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. S. Demir

  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 S. Demir

  16. Lapse Rate & Potential Temperature (2/5) • By enthalpy’s 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 S. Demir

  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 1°C to -56.7°C • SLR = -0.66°C/100 m S. Demir

  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 θ = Tp = potential temperature of air parcel T = Temperature of air parcel H = Height of air parcel from ground DALR = Dry adiabatic lapse rate S. Demir

  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 12°C. S. Demir

  20. Atmospheric Stability(1/8) • If ELR < DALR Then • Superadiabatic meaning unstable • ElseIf ELR = DALR Then • Neutral • ElseIf DALR < ELR < 0 Then • Subadiabatic meaning stable (weakly stable) • ElseIf DALR < 0 < ELR Then • Inversion meaning strongly stable • EndIf S. Demir

  21. Atmospheric Stability (2/8) • Superadiabatic S. Demir

  22. Atmospheric Stability (3/8) • Neutral S. Demir

  23. Atmospheric Stability (4/8) • Subadiabatic S. Demir

  24. Atmospheric Stability (5/8) • Inversion S. Demir

  25. Atmospheric Stability (6/8) • If dθ/dz < 0 Then • Superadiabatic • ElseIf dθ/dz = 0 Then • Neutral • ElseIf dθ/dz > 0 Then • Subadiabatic • EndIf S. Demir

  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 < DALR S. Demir

  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. S. Demir

  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) S. Demir

  29. Gravitational Force (1/3) • The force exerted by the earth on an object in earth’s 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 γ = 6.668*10-11 Nm2/kg2 m1,m2 = objects’ masses r = distance bw masses S. Demir

  30. Gravitational Force (2/3) • Example: Determine the acceleration of an object near the Erath’s surface due to gravitational attraction force • Solution: S. Demir

  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 Moon’s surface due to gravitational attraction force S. Demir

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

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

  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 Ω = rotational speed of earth = 7.29*10-5 r/s Φ = latitude on which the motion occurs S. Demir

  35. Overall Atmospheric Motion (3/7) • Example:Briefly explain the mechanisms that forced radioactive pollutants towards Turkey’s 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. S. Demir

  36. Overall Atmospheric Motion (4/7) • Solution S. Demir

  37. N 500 mb 180 km 504 mb 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 : -28°C • Coriolis force: 2 Ω V sin β • Ω= 7.3 x 10-5 radians/s; β= Latitude degrees ; V= geostrophic wind speed • 1 mb = 100 N/m3 S. Demir

  38. Overall Atmospheric Motion (6/7) • Example:Suppose 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 world’s 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. S. Demir

  39. Overall Atmospheric Motion (7/7) • Solution S. Demir

  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 S. Demir

  41. Equations of Motion (2/3) • Lagregian Approach (cont’d) S. Demir

  42. Equations of Motion (3/3) • Examples will be given later… S. Demir

  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 S. Demir

  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. S. Demir

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