AIR POLLUTION AND CONTROL METHODS UNIT 2 - METEOROLY AND PLUME DISPERSION.pptx

Gives Brief Idea about Lapse Rate, PLume Diserpsion

1. METEOROLOGY By V. Nikhila Bhavani Assistant Professor VJIT, HYD

2. Air Pollution meteorology deals with the meteorological processes near to the earth’s surface which consist of the impacts of  meteorology on air pollutants  and the effects of pollutants on meteorology. If the air is still and pollutants are unable to disperse, the local concentration of pollutants will rise. Strong, turbulent winds, on the other hand, remove pollutants fast, resulting in reduced pollutant concentrations.

3. Thus, the destiny of air pollutants is influenced by air movements. As a result, any study of air pollution should also include a look at the weather patterns in the area that is meteorology.  

4. The earth's atmosphere is about 100 miles deep. That thickness and volume sometimes are suggested to be enough to dilute all of the chemicals and particles thrown into it. However, 95% of this air mass is within 12 miles of the earth's surface. This 12-mile depth contains the air we breathe as well as the pollutants we emit. This layer, called the troposphere, is where we have our weather and air pollution problems.

5. Weather patterns determine how air contaminants are dispersed and move through the troposphere, and thus determine the concentration of a particular pollutant that is breathed or the amount deposited on vegetation. An air pollution problem involves three parts: 1. The pollution source 2. The movement or dispersion of the pollutant 3. The recipient

6. PLUME RISE

7. Plume Dispersion Plume behaviour refers to the dispersal pattern of gaseous pollutants in atmosphere depending upon wind conditions, atmospheric stability and vertical temperature profile. It shows seasonal as well as diurnal variations. Accordingly, there are various types of plume discussed below and represented diagrammatically in figure 1.

8. Looping plume: It takes place when the atmosphere is very unstable, wind speed is greater than 10 ms-1 , has super-adiabatic lapse rate and is accompanied with solar heating. It follows a wave like pattern and provides high degree of mixing at lower levels, sometimes reaching the ground.

9. Fumigation: It occurs when plume reaches the ground level along the length of the plume and is caused by a super-adiabatic lapse rate beneath an inversion. The super-adiabatic lapse rate at the ground level occurs due to the solar heating and is quite undesirable since the pollutants remain at ground level. This condition is favoured by clear skies and light winds.

10. Coning plume: It results when the vertical air temperature gradient occurs between dry adiabatic and isothermal, the air being slightly unstable with some horizontal and vertical mixing occurring. Coning is most likely to occur during cloudy or windy periods.

11. Fanning plume: They spread out horizontally but do not mix vertically. Fanning plumes take place when inversion condition exists in atmosphere, that is, the air temperature increases with altitude. The plume rarely reaches the grounds level unless the inversion is broken by surface heating or a topographical barrier such as a hill. At night, with light winds and clear skies, fanning plumes are quite common.

12. Lofting plume: It diffuses upward but not downwards and occurs when there is a super-adiabatic layer above a surface inversion. A lofting plume will generally not reach the ground surface, so there is less pollution at ground level.

13. F. Trapping: This condition is accompanied by weak lapse below inversion aloft.

14. PROPERTIES OF THE ATMOSPHERE

15. PPMV – Parts per million by volume

16. Pressure in the atmosphere

17. Layers of atmosphere

18. ACID RAIN

19. METEOROLOGICAL FACTORS

20. PRIMARY SECONDARY Wind Direction and Speed Precipitation Temperature Humidity Atmospheric Stability Solar Radiation Mixing Height Visibility

21. PRIMARY

22. TEMPERATURE

23. Dry Adiabatic lapse Rate (9.8°c/Km) Wet Adiabatic Lapse Rate( 6°c/Km)

24. SECONDARY

25. HUMIDITY

26. RAINFALL

27. HEAT Heat is the critical atmospheric variable This comes from the sun as short wave radiation (0.5micrometre) in the form of visible light. After striking the earth it loses energy and reradiates to the space as long-wavelength radiation (10-18 micro metre ) in the form of non-visible heat radiation. Some of these solar rays never reach the earth as they are reflected back to space by air and clouds

28. Earth also reflects solar rays eg : ice, snow, desert sands have a high rate of reflection while forests and cultivated fields have low rate. Appearance of sky is in blue color this is because some of the sun rays are scattered by particulates. At horizon this scattering will be more due to this sunrise and sunset are in red color. While some of the rays are absorbed by co2, ozone, water vapour , clouds, dust but most of the sun rays are absorbed by the earth.

29. As some of these are reflected to the sky by the earth surface thus heat transfer happens thus the radiation energy is balanced.

30. LAPSE RATE

31. WIND ROSE DIAGRAM

32. Wind Rose: A wind rose is defined as, “Any one of a class of diagrams designed to show the distribution of wind direction experienced at a given location, over a considerable period”. In other words, the wind rose shows the prevailing direction of wind, The most common form consists of a circle from which eight or sixteen lines emerge, one for each direction. The length of each line is proportional to the frequency of wind from that direction and the frequency of calm conditions is entered in the centre.

33. There are many variations in the construction of wind roses. Some indicate the range of wind speeds from each direction, and some relate wind direction with other meteorological conditions. Wind roses may be constructed from the data obtained over a given time period such as a particular month or season or a year. In constructing or interpreting wind roses, it is necessary to keep in mind the meteorological convention that wind direction refers to the direction from which the wind is blowing.

34. A line or bar extending to the north on the wind rose indicates the frequency of winds blowing from the north. The wind rose diagram is prepared using an appropriate scale to represent percentage frequencies of wind directions and appropriate index shades, lines etc., to represent various wind speeds. Observations corresponding to wind speed below 1 km/h are recorded as calm (Fig. 3.6).

35. Special wind roses are sometimes constructed like: 1. Precipitation wind rose 2. Smoke wind rose 3. Sulphur dioxide wind rose 4. Hydrocarbons wind rose Instead of wind speed the parameters of precipitation, smoke, sulphurdioxide , hydro carbons etc. are attached to the wind direction. These areknown as ‘Pollution Roses’,

36. TYPES

37. USES OF THE WIND ROSE

38. PRESSURE SYSTEMS

39. The earth atmosphere has a pressure system that is particularly high or low compared to the air surrounding it. Air expands when heated and gets compressed when cooled. This results in atmospheric variations. Due to the difference in atmospheric pressure, air now starts moving from high pressure to low pressure. The movement of the wind is horizontal, and thereby a constant temperature is maintained on the planet.

40. Pressure systems of the earth are widely divided into two parts: High-pressure system and The low-pressure system. The weather of an area is determined locally by the pressure system. Low-pressure systems bring about clouds and rain while high-pressure systems are responsible for clear skies. 

41. HIGH PRESSURE SYSTEM The high-pressure system is relative to the air around it. As the air starts becoming warm or cold, it can be said that a high-pressure system has been created. The high-pressure system is composed of air that is heavy and cool. In the high-pressure system, the air is not rising and forming clouds. Therefore the weather remains comfortable, and skies stay clear. In the Northern Hemisphere, the high-pressure system revolves in a clockwise direction, while in the Southern Hemisphere it is in the anti-clockwise direction. 

42. LOW PRESSURE SYSTEM A low-pressure system, commonly known as depression, is created in an area of warm air. As we all know, warm air rises, and cold air falls. The low-pressure system rotation is in the clockwise direction in the Southern Hemisphere and in the opposite direction in the anti-clockwise direction in the northern hemisphere. A low-pressure system brings about heavy rainfall. Depression can often mature into a cyclonic storm in case the low pressure persists. Over the Atlantic Ocean, during the autumn season, the low-pressure system increases, bringing with it windy weather, rain, storms and heavy thundershowers. 

43. Features of Atmospheric Pressure   Atmospheric pressure indicates weather conditions of an area.  Low pressure causes cloudiness, thunderstorms, storms and cyclonic winds. High pressure contributes to calm weather conditions.  An instrument known as the barometer measures atmospheric pressure. Therefore the barometer is also known as barometric pressure.  One atmosphere is 1013 millibars or 760 millimetres . 

44. The atmospheric pressure is an important environmental factor. It affects all the three states of matter that are solid, liquid and gas. This atmospheric parameter has been used quite a number of years to predict weather conditions all over the world. The composition of water and its chemistry is also affected by atmospheric or barometric pressure. The earth’s atmosphere has five layers. From highest to lowest they are: Exosphere Thermosphere  Mesosphere Stratosphere  Troposphere 

45. METHODS FOR MEASUREMENT OF METEOROLOGICAL VARIABLES

46. WIND DIRECTION RECORDER

47. Flat plate vane: In this type the sensing element which governs the azimuth angle of a vertical shaft specifying the wind direction, is a vertical plate which is mounted at one end of a horizontal rod. There is a counterweight at the other end of the horizontal rod. The rod is fastened to the vertical shaft. Wind pressure acting on the flat plate keeps the counterweight heading into the wind. 2. Splayed vane: In this instrument, two flat plates which are joined at a small angle at one end of a horizontal rod act as the wind direction sensor.

48. Aerofoil vane: In this instrument the vane has an aerofoil cross-section, with the span often being three or four times the chord. Running average anemograph: It is often advantageous to be able to directly obtain a recording of the running average of the wind speed or direction or both. In averaging the wind direction, a difficulty arises from the discontinuity 360°—0° as the wind direction fluctuates around north. An anemograph which automatically produces the running averages of both wind speed and direction has been developed.

49. Pilot balloons : In this method a small balloon inflated with hydrogen or helium is left aloft and the direction of the wind aloft is determined by tracking the balloon by means of one or more theodolites on the ground. The average wind direction is obtained using triangulation techniques at successive height intervals. The pilot balloon technique of determining wind aloft is of limited value because the balloon may be lost with low cloud, fog or smoke.

50. (b) Tetroons : A tetroon is a constant volume Mylar balloon in the shape of a tetrahedron which is kept in a zero lift condition and carried by the wind in an almost horizontal direction. Zero lift balloons are produced by filling pilot balloons with a mixture of two gases, one more dense and the other less dense than air. As the mixture of gases leaks from the bal-loon, the loss of the heavier gas causes a decrease in its weight. Thus an approximate mixture of gases will keep the balloon in a zero lift or balanced condition for lengthy periods of time.

51. Such a balloon, when accurately tracked, acts as a sensor for wind direction. The advantage of this type of balloon lies in the fact that it can indicate wind trajectories near cities, over shorelines and in valleys where complicated patterns of airflow are commonly observed. If substantial distances are to be tracked, a radar installation with a transponder suspended from the tetroon will be required which is an expensive method

52. (c) Kite balloons: A kite balloon is an elongated captive balloon with fins at one end. It acts as an ordinary captive spherical balloon in light wind sand as a kite in stronger winds, thus maintaining altitude under both conditions. The azimuth angle of the horizontal projection of the tethering cable is measured at the ground to determine the wind direction at the height of the balloon. The inflating gas lost by slow leakage is replaced by refilling it at intervals.

53. (d) Radio and radar: In the radio method, a small radio transmitter is carried aloft by a freely rising balloon and is tracked. With the radar system, pulses of electrical energy emitted by the radar are reflected back to it by a target carried by the free balloon. The distance to the target as well as azimuth and elevation angles are measured by the system. This gives more accurate results than the radio direction finder. However, operation and maintenance costs of radio and radar theodolites are prohibitively high.

54. (e) Smoke trails: Information un wind directions aloft may be obtained by finding at intervals the position in space of smoke trails released above the ground by a rising rocket or an aeroplane . However, observations in fog, smoke, or at night, are not possible. Also, this method requires more operating personnel than the pilot balloon method.

55. WIND SPEED RECORDER

56. TEMPERATURE MEASUREMENTS