HIGH VOLUME SAMPLER ENVIROTECH APM 430.pptx

Lab work

1. HIGH VOLUME SAMPLER ENVIROTECH APM 430

2. DRAWING

3. PRINCIPLE OF OPERATION High Volume Sampler is a basic instrument used primarily for measuring concentration of suspended particulate matter in atmospheric air. By definition, suspended particulates are too small in size to have an appreciable falling velocity and are likely to remain in the atmosphere for significant periods of time. These particulates usually range from 1 micron to approximately 100 microns in size.

4. It may be caused by a variety of processes such as incomplete combustion of solid, liquid, or gaseous fuels, wastes from metallurgical, chemical and refining operations, iceneration , etc. Moreover, natural sources also contribute suspended materials like spores, salt water spray and pollens.

5. High Volume Sampling is an internationally accepted standard technique for monitoring the concentration of suspended particulates. In these systems a large volume (1500 cubic meters) of atmospheric air is passed through a suitable filter medium over a period of upto 24 hours. They will thus yield measurable dust samples in areas with dust levels as low as one microgram per cubic meter of air. However, where dust concentrations are high, shorter sampling times may suffice.

6. Measurement of Particulate Concentrations The mass concentration of suspended particulates in ambient air, expressed in micrograms per cubic meter, is calculated by measuring the mass of collected particulates and the volume of air sampled. In APM 430, the flow rate of air passing through the filter is monitored by measuring the pressure drop across an Orifice Plate placed between the filter holder and the blower.

7. The scale of the manometer used to measure the pressure drop is calibrated in air flow units of cubic meters per minute. A Time Totalizer records the time in minutes/hours for which the system has sampled air. Hence the volume of air sampled is known. The mass of particulates collected is measured gravimetrically, using a balance capable of reliable measurement to the nearest milligram.

8. One must remember, however, that particulate matter which is oily, such as wood smoke or photochemical smog, may block the filter and cause a rapid decrease in air flow at a non-uniform rate. Even fog or high humidity can severely reduce the air flow through the filter since even though glass fiber filters are insensitive to changes in relative humidity, the collected particulates may be hygroscopic.

9. Hence, it is recommended that filter mediums must be carefully conditioned, both before and after sampling, prior to the measurement of their weight.

10. Measurement of Particulate Concentrations The mass concentration of suspended particulates in ambient air, expressed in micrograms per cubic meter, is calculated by measuring the mass of collected particulates and the volume of air sampled. T he flow rate of air passing through the filter is monitored by measuring the pressure drop across an Orifice Plate placed between the filter holder and the blower.

11. The scale of the manometer used to measure the pressure drop is calibrated in air flow units of cubic meters per minute. A Time Totalizer records the time in minutes/hours for which the system has sampled air. Hence the volume of air sampled is known. The mass of particulates collected is measured gravimetrically, using a balance capable of reliable measurement to the nearest milligram.

12. One must remember, however, that particualte matter which is oily, such as wood smoke or photochemical smog, may block the filter and cause a rapid decrease in air flow at a nonuniform rate. Even fog or high humidity can severely reduce the air flow through the filter since even though glass fibre filters are insensitive to changes in relative humidity, the collected particulates may be hygroscopic. Hence, it is recommended that filter mediums must be carefully conditioned, both before and after sampling, prior to the measurement of their weight.

13. Measurement of Gaseous Pollutants The APM 430 Sampler is designed to monitor only the concentration of suspended particulates in atmospheric air, and the APM 411 gaseous sampling attachment must be used if gaseous pollutants are also to be monitored. An attempt has been made to make the two units as independent of each other as possible. Hence, users who are not interested in gaseous pollutants need not acquire the APM 411 attachment.

14. However, each APM 430 system is provided with all the fixtures needed for using the gaseous sampling attachment, so that the APM 411 system can be fitted at any stage. APM 411 gaseous sampler uses wet chemical methods for the absorption and detection of gaseous pollutants. Hence, atmospheric air must be passed through absorbers containing suitable reagents which would absorb relevant gases like Sulphur dioxide, Nitrogen oxides, Hydrogen sulphides , etc.

15. The absorbing reagents must be analyzed in a laboratory to work out the quantity of gas absorbed. The APM 411 system has been provided with a set of four midget impingers for gaseous sampling. A gas manifold with separate flow control valves allows independent flow rates to be set in individual impingers . A flow-meter has been incorporated which allows a precise measurement of sampling rate when the system is being set up. The impingers have been kept in an ice-tray to improve the absorption efficiency of the system and prevent loss of absorbers by evaporation.

16. OPERATING INSTRUCTIONS Selection of Sampling Site. The High Volume Sampler is usually operated at ground level. In normal usage it is never operated more than 15 meters above ground level. In order to obtain a representative sample, the Sampler should not be positioned near a wall or other obstructions that would prevent free air flow.

17. In excessively turbulent conditions or in the presence of strong surface winds or otherwise inclement weather, the sampling rate is likely to decrease rapidly and perhaps in a non-linear fashion due to filter choking. If the sampler is operating in the vicinity of a source, day-to-day variations in the measurement are expected due to varying meteorological conditions and changing atmospheric phenomena, like wind speed and direction, disperal , diffusion, etc.

18. Selection of Filter Medium For most cases where interest is limited to a gravimetric determination of the total suspended particulate concentration, glass microfibre filters having a low resistance to airflow, a low affinity for moisture and a 98% collection efficiency for particles of 0.5 micron or larger size are suitable.

19. However, where further analysis of the particulates is to be attempted to detect specific elements/radicals, care should be taken to choose special filter mediums having a low background concentration of the substances of interest. For instance, special grades of glass microfibre filters are available which have a controlled and low concentration of metals like Iron, Zinc, Cadmium, Lead, Arsenic, Nickel, etc.

20. Preparing the Filter Prior to use, expose each filter to a light source and inspect for pinholes, particles and other imperfections. Filters with visible defects should not be used. A small brush is often used to remove stray particles adhering to the surface of new filters. Always handle filter papers from their edges and do not crease or fold the filter medium prior to use.

21. Both blank and samples should be conditioned at 20 to 25 degrees Centigrade, and relative humidity below 50% for at least 16 hours prior to weighing. It is usual to put an identification number and date of sampling on the filters. Weigh the filters to the nearest milligram and record the weight and filter identification number.

22. Installation of the Filter Always install or remove the filter only when the Sampler is OFF. Open the gable roof of the shelter, loosen the wing nuts and remove the face plate from the filter holder. Place a numbered, pre-weighed filter in position with its rough side up. Replace the face plate without disturbing the filter and fasten securely. Under tightening will allow air leakage, over tightening will damage the rubber face plate gasket. A very light application of talcum powder may be used on the rubber gasket to prevent the filter from sticking. Close the roof of the shelter

23. Operation of the Orifice Meter The Orifice meter is really a differential manometer used to measure the pressure drop across an Orifice Plate. It uses distilled water as the indicating fluid which must be topped up from time to time. The brass screw mounted on the meter plate is a filling plug which must be opened to fill in the manometer fluid. Use the syringe provided with the instrument to fill distilled water upto the “zero” mark on the meter scale.

24. When adequate fluid has been filled into the system, close the filling plug. Do not over tighten the plug since it would damage its seal ring. A drain plug has been provided on left side of cover in order to drain out excessive water.

25. DRAWING

26. TIMER OPERATION SETTING UP THE TIMER FOR MANUAL OPERATION Pullout all the pins on the timing dial outwards. Use the main ON-OFF switch on the instrument panel / manometer plate to manually switch the blower ON or OFF. (Note : with the pins in outward positions, the timer remains connected to the mains but is unable to control operation of the Sampler.)

27. SETTING UP THE TIMER FOR AUTOMATIC OPERATION Pull outwards all the pins located on the timing wheel. Rotate the wheel clockwise until it is synchronized with the real time of the day. e.g. Rotate the timing wheel clock-wise until the number aligned to the pointer (marked as a triangle- ) on the center wheel corresponds to the real time of the day. For example, if the actual time is 10 A.M., the pointer should be aligned to number 10.

28. Similarly, if the actual time is 3 P.M. the pointer should be aligned to number 15. At this position the timer is ON as in the manual position. Decide the OFF time and push all the pins on dial from selected OFF time to the start time inwards. This will switch off the blower at desired time. The sampler may now be left unattended and will automatically operate for the desired time. (Caution : The timing wheel provides and endless loop, and so the timer will repeat the operation after 24 hours, unless the sampler is externally switched off.)

29. Each pins of the tuning dial corresponds to approximately 15 minutes. It enables to select many ON time and OFF time intervals as per requirement . Caution : In case the timer function not to be use then pullout all the pins on the timing dial outwards.

30. Using the Time Totalizer The Time Totalizer uses a clock motor to drive a geared numerical display. As shown in Drg . No 43015-00, the system has been wired so that it operates only when the heavy duty blower receives power. Hence its display indicates the true time, in minutes/hours for which the Sampler has sampled atmospheric air. The Time Totalizer performs two important functions : (a) it keeps check on the actual sampling time when the instrument is operated, and (b) it facilitates timely preventive maintenance .

31. Time Totalizer readings must be noted before and after each air-sampling, so that the exact duration of the sampling can be worked out. The same readings can be used to determine when the Orifice-meter system is due for cleaning. As such, we strongly recommend that Time-Totalizer readings be recorded in the form of a Log and used to establish a preventive maintenance schedule as per maintenance instructions given in section 5 of the manual.

32. In the event of power failure, both the Timer and Time Totalizer (as also the Sampler) stops . Hence , when power is restored, the Sampler will continue to operate for the balance time period set on the Timer. It will, however, loose synchronicity with the real time of the day . The Time Totalizer will still indicate the actual number of hours and fraction of hours (i.e ., .... x x.xx hrs ) for which the Sampler has operated.

33. Sampler Start-up Sequence Before commencing any air sampling operations using the APM 430 High Volume Air Sampler , check the following : (1) The system is suitably located as per section 4.1 (2) A fresh, pre-weighed filter is installed in the filter holder. (3) The fluid in the orifice meter is at ‘Zero’ level. (4) In case both particulate and gaseous pollutants are to be sampled, check that impingers with suitable reagents are in place and are connected as per Section 4.12. If only suspended particulates are to be sampled, the entire APM 411 gaseous sampling attachment can be removed.

34. Connect the mains chord of the sampler to a live 220 V.A.C. outlet. Switch on the machine. Allow the Blower to run for a minute so that it attains full speed and then record the sampling rate indicated by the orifice meter. In case gases are also to be sampled, set the desired flow rates (for gaseous sampling) using the needle valves of the gas manifold. Record the sampling rates for gases.

35. Sampler Shut-off Sequence (1) Record the flow-rate indicated by the orifice meter. (2) Record the flow-rate indicated by the rotameter (for gaseous sampling). (3) In case the system was operating under the control of the Timer and the blower has already been shut off, restart the blower using the ON-OFF switch and allow the flow rate to stabilize for a minute before recording the flow rates mentioned above.

36. (4) Switch off the sampler using the MCB switch. (5) Record the final sampling time indicated by the Time Totalizer. (6) Open the filter-holder and carefully remove the Filter Paper. Fold the paper along its length so that the soiled sides are in contact and are facing inwards. Store the filter paper in a clean envelope. (7) Remove the Sampler from the Sampling Site to a safe storage area.

37. Calculations (For Suspended Particulate Sampling) Weight of suspended particulates (W) W = W2 - W1 (grams) W2 = Weight of the filter paper after sampling (grams) W1 = Weight of fresh filter paper (grams) Note: Both W2 and W1 are to be measured after filter conditioning as mentioned under heading , preparing the filter Volume of Air Sampled (V) V = Q x T (Cubic Meters) Q = Average sampling rate (Cubic meters per minute)

38. T = Sampling Time (Minutes) Q = (Q1 + Q2) / 2 Q1 = Initial sampling rate indicated by the Orifice Meter at the start of sampling Q2 = Final Sampling rate indicated by the Orifice Meter just before the end of sampling. Concentration of Suspended Particulate Matter= W/V( grms /cubic meter)