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Unit 2 meteorology
The document discusses the various meteorological factors influencing air pollution, including primary and secondary parameters such as wind direction, temperature, and atmospheric stability. It covers measurement techniques for these parameters and details the lapse rates and types of inversions that affect air pollution dispersion. Additionally, it explains different plume behavior under varying atmospheric conditions, including looping, coning, fanning, lofting, fumigation, and trapping.
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Unit 2 meteorology
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- 4. Meteorological Factors InfluencingAir Pollution Primary Parameters Secondary Parameters
- 5. Primary Parameters Wind Directionand Speed Temperature Atmospheric Stability Mixing Height Primary Parameters
- 6. Methods for Measurementof Meteorological Variables • Wind Direction Recorder • Wind Speed Recorder • Temperature Measurement • Solar Radiation Measurement
- 7. Wind Direction Recorder •Flat Plate vane • Splayed vane • Aerofoil vane • Running average anemograph
- 8. Wind Direction Aloft •Pilot Balloons (Pibals) • Tetroons • Kite Balloons • Radio and Radar • Smoke trails
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- 12. Mixing Height The mixingheight is the height of vertical mixing of air and suspended particles above the ground. This height is determined by the observation of the atmospheric temperature profile.
- 13. Atmospheric Turbulence • Atmosphericturbulence, small-scale, irregular air motions characterized by winds that vary in speed and direction. Turbulence is important because it mixes and churns the atmosphere and causes water vapour, smoke, and other substances, as well as energy, to become distributed both vertically and horizontally.
- 14. Secondary Parameters Precipitation Humidity SolarStability Visibility Secondary Parameters
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- 18. Solar Radiation Measurement PyrheliometerSolarimeter Actinometer
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- 22. Lapse Rate • Thelapse rate is the rate at which an atmospheric variable, normally temperature in Earth's atmosphere, changes with altitude. Lapse rate arises from the word lapse, in the sense of a gradual change.
- 23. Lapse Rate • Adiabaticlapse rate: Change of temperature with a change in altitude of an air parcel without gaining or losing any heat to the environment surrounding the parcel. • Dry adiabatic lapse rate: Assumes a dry parcel of air. Air cools 1°C/100 m rise in altitude (5.4°F/1000 ft). • Wet adiabatic lapse rate: As parcel rises, H2O condenses and gives off heat, and warms air around it. Parcel cools more slowly as it rises in altitude, ≈6°C/1000 m (≈3°F/1000 ft). • Ambient or prevailing lapse rate: The actual atmospheric temperature change with altitude; not only does water content modify lapse rates, but wind, sunlight on the Earth’s surface, and geographical features change actual lapse rates.
- 24. • Superadiabatic: Ambientlapse rate > adiabatic indicates unstable atmosphere. Vertical motion and mixing processes are enhanced. Dispersion of pollution plume is enhanced. • Subadiabatic: Ambient lapse rate < adiabatic. It indicates stable atmosphere, vertical motion, and mixing are suppressed. Dispersion is suppressed, and contamination is trapped.
- 25. Inversion Temperature actually increaseswith altitude near the ground before it begins to decrease with altitude. This results in warm, low-density air riding on top of cool high density air; a very stable air column that traps pollution near the ground Types of Inversion • Radiation Inversion • Subsidence Inversion • Double Inversion (Sometimes both occur simulatneously)
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- 28. Radiation Inversion • Radiationinversions generally happen in places where it cools off a lot at night. During the night, the ground cools off, radiating the heat to the sky. Hence, an inversion.
- 29. Subsidence Inversion • Asubsidence inversion is sinking air that produces an inversion. When air sinks then it warms adiabatically at the dry adiabatic lapse rate. A situation in which this can occur is within a warm core high pressure system. It can also occur on the lee side of a mountain range.
- 30. Atmospheric Stability • Stability– Ability to resist vertical motion • Affects dispersion of pollutants • 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
- 31. Plume • Plume refersto the path and extent in the atmosphere of the gaseous effluents released from a source, usually a stack.
- 34. Looping • High degreeof 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.
- 35. Coning • Stable withsmall-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
- 36. Faning • Occurs underlarge 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
- 37. Lofting • Favorable inthe 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.
- 38. Fumigation • Most dangerousplume: 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.
- 39. Trapping • When theinversion layer exists above the stack and as well as below the stack, the plume neither goes up nor goes down, rather it gets trapped between these two inversion layers. • This Plume is not ideal for dispersion of pollutants as it cannot go above a certain height.
- 40. Wind profile powerlaw • The wind profile power law is a relationship between the wind speeds at one height, and those at another. • The wind profile power law relationship is : • Limits The wind profile of the atmospheric boundary layer (surface to around 2000 metres) is generally logarithmic in nature and is best approximated using the log wind profile equation that accounts for surface roughness and atmospheric stability.