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L 35 final


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AIR POLLUTION CONTROL course material by Prof S S JAHAGIRDAR,NKOCET,SOLAPUR for BE (CIVIL ) students of Solapur university. Content will be also useful for SHIVAJI and PUNE university students

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L 35 final

  1. 1. L-35 Ambient air quality monitoring and High volume sampler Unit-V
  2. 2. Instruments needed for sampling Sr. No Parameter Instrument used Measuring unit 1 Temperature Thermometer 0C 2 Wind speed Anemometer m/sec 3 Relative humidity Arm. pressure No unit (Expressed in percentage) Millibars or mm of Hg 4 Page 2 Hygrometer Barometer 15-10-2013
  3. 3. The Aim of Sampling: •The principal requirement of a sampling system is to obtain a sample that is representative of the atmosphere at a particular place and time and that can be evaluated as a mass or volume concentration. •The sampling system should not alter the chemical or physical characteristics of the sample in an undesirable manner.
  4. 4. The major components of most sampling systems are: 1) An inlet manifold 2) An Air mover (Blower) 3) A collection medium 4 ) Flow measurement device
  5. 5. (1)The inlet manifold transports the material from the ambient atmosphere to the collection medium or analytical device in an unaltered condition, all inlet of ambient air must be rainproof. (2)The air mover (Blower) provides the force to create a vacuum or lower pressure at the end of the sampling system (pumps).
  6. 6. (3) The collecting medium, may be solid or liquid sorbent for dissolving gases a filter surface for collecting particles. (4)The flow device measures the volume of air associated with the sampling system.
  7. 7. PARTICULATE SAMPLING METHODS Page 7 15-10-2013
  8. 8. • Gravitational method • For collecting dust particles of 1µ (micron) or larger 40 µ (micron ) in the atmosphere, clean glass jars are kept in the area where dust fall is to be determined and after a few hours or days, the dust is collected from each jar and then weighed. • The average weight of dust in each jar is estimated and the dust fall is expressed as weight of dust per unit area per unit time. Page 8 15-10-2013
  9. 9. • Containers, generally conical plastic jars, 10-15 cm in diameter, open at the top are used. • The jars are kept in strategic locations throughout a community or in the vicinity of particulate sources under study. • Grit and dust fall into the jars which sometimes have water to hold the dust. After a one month exposure, the jars are collected and brought into the laboratory where their contents are analysed. Page 9 15-10-2013
  10. 10. • In most cases only the total particulate matter is determined, and the results are expressed in terms of tons per square kilometer per month or g/sq. m / month. • Monthly isopleth maps can be constructed showing the variation of dust fall throughout the area. Page 10 15-10-2013
  11. 11. Page 11 15-10-2013
  12. 12. Dust fall jar Page 12 15-10-2013
  13. 13. Dust depositor Page 13 15-10-2013
  14. 14. Filtration • A fibrous filter which is woven with randomly oriented fibers acts as a target for the collection of fine particles. When airborne particles enter a filter and flow around the fibers, they are subjected to aerodynamic forces which result in their collection on the fibers. • The principal mechanisms operating are gravitation, inertia, interception and diffusion. Page 14 15-10-2013
  15. 15. • Many types of filters are available for removal of particulate matter from gas streams. • The chief variations are in the filter media material and in the shape of the membrane. • One common type is the thimble filter shown diagrammatically. • The filter paper thimble is filled with wellfluffed cotton which operates at a sampling rate of 2 cf/min. Page 15 15-10-2013
  16. 16. • By determining the change in weight of the dried filter after exposure, dust concentration in the gas stream is determined. • The paper thimble cannot be used with high temperature gases; an alundum thimble is useful in this case. Page 16 15-10-2013
  17. 17. Page 17 15-10-2013
  18. 18. Cyclones • Cyclones are a special type of impactors where the impaction (on the side walls of the cyclone) is combined with the gravitational settling of the large particles. • The effect is that the large particles will get trapped before they reach the collecting filter and thus giving a cut off size dependent of the size, geometry and air flow velocity through the cyclone. • Cyclones (often) have the advantage of being both small and cheap but still accurate enough for most modern requirements. Page 18 15-10-2013
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  21. 21. Cascade Impactors • Cascade impactors are consists of a number of impactor stages connected in series with smaller and smaller cutoff diameter. • The cut-off diameter in each stage depends on the air velocity and geometry of the stage (i.e. the distance from the nozzle to the impaction plate). Page 21 15-10-2013
  22. 22. • Cascade impactors often have up to some ten stages ranging from a cut-off diameter on the first stage of 10 – 30 m to a diameter of 0.1 m or lower on the backup filter in the end. • This gives the opportunity to analyse (e.g. chemical or gravimetrical) a number of small size intervals. Page 22 15-10-2013
  23. 23. • Some drawbacks are the risk of bounce off from one stage to the next (i.e. particles of wrong size at some of the stages) as well as the problem of obtaining sharp cut-off diameters in the last stages (cut-off diameter less than 0.1 – 0.2 m). • Coating the impaction plates with oil or some other sticky substance, which catches the particles more effectively, can reduce the risk of bounce of. • This will then prevent or severely complicate direct mass concentration calculations of the different stages. Page 23 15-10-2013
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  26. 26. Electrostatic precipitators • An electrostatic precipitator consists of an ionizing electrode charged with a high negative potential and a collector to be maintained at positive potential produced by a special transformer and rectifier. • A known volume of air is allowed to pass through the precipitator where the incoming particles become negatively charged by the electrode and adhere to the positively charged collecting tube. Page 26 15-10-2013
  27. 27. • The collected particles are weighed and their number can also be counted accurately by using a microscope. • This method of collection of particulate matter is very efficient as high flow rates with small pressure drops can be used. Page 27 15-10-2013
  28. 28. Thermal precipitator • In thermal precipitators the particles in the sampled stream move past a very hot wire and are repulsed to the nearby cold plate where they are collected. • However, it can operate only at very low sampling rates-approximately 50 mililitres per minute and is useful only for R&D work. Figure shows a thermal precipitator of the type supplied by Casella Company Ltd., London, England. Page 28 15-10-2013
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  30. 30. L-36 High Volume Sampler Page 30 15-10-2013
  31. 31. Page 31 15-10-2013
  32. 32. INTRODUCTION • High Volume Samplers are the basic instruments used to monitor Ambient Air Quality. • They are in widespread use all over the world to measure air pollution in industrial areas, urban areas, on the shop floor, near monuments and other sensitive areas. Page 32 15-10-2013
  33. 33. • The High Volume Sampler is a vital tool for studies relating to impact of industrialisation to the air analysis, and for work related diseases of the respiratory system to air pollution. • These are very much essential for various Environmental Impact Assessment studies Page 33 15-10-2013
  34. 34. Components of HVS • Heavy Duty Blower, • Orifice flow meter- measures flow, • Time Totaliser-records time, • Programmable Timer- measures time, • Instrument Cabinet- acts as protection, • Filter Holder assembly- holds the filter in position, • Voltage Stabiliser- guards against voltage fluctuation, • Detachable Gable roof- allows passage of air and protects filter. Page 34 15-10-2013
  35. 35. PRINCIPLE OF OPERATION • In these samplers, air-borne suspended particulates (SPM) are measured by passing air at a high flow-rate of 1.1 to 1.7 cubic meters per minute through a high efficiency filter paper which retains the particles. • The instrument measures the volume of air sampled, while the amount of particulates collected is determined by measuring the change in weight of the filter paper as a consequence of the sampling. Page 35 15-10-2013
  36. 36. • The passage for air reaching the filter is designed to prevent heavier settleable dust particles from reaching the filter (by provision of cyclone) thus measuring the concentration of Suspended Particulate Matter (SPM) in atmospheric air. Page 36 15-10-2013
  37. 37. • In high volume sampler provisions have been made for simultaneous sampling of gaseous pollutants. • Here the air is passed through suitable reagents that would absorb specific gases where gaseous pollutants like SO2, NOx, Cl2, H2S, CS2, NH3, etc. are analysed subsequently by simple wet chemistry method to determine the concentration of specific pollutant. Page 37 15-10-2013
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  42. 42. Applications of HVS • Routine Monitoring by air monitoring networks • Open Spaces like forests and national park air monitoring. • Monitoring around ecologically sensitive monuments • Page 42 15-10-2013
  43. 43. • Data reporting for monthly and • • • • yearly averages by local area air quality networks. Site Monitoring by industries. Evaluative Studies Lab Applications Research Studies Page 43 15-10-2013
  44. 44. Calculation of SPM concentration Page 44 15-10-2013
  45. 45. Theory Questions Q1. State principles used for sampling of particulate matter. Explain any one in detail. (Nov 2008, May 2009, 8 marks) Q2. Explain working of high volume sampler with sketch. (May 2011, 8 marks). Q3. Explain various principles used in particulate matter sampling. (May 2011, 8 marks) Q4. Explain procedure for determining concentration of SPM in ambient air. Page 45 15-10-2013