Air sampling

Air Sampling Techniques like Grab Sampling, Sampling system/Train, Ambient Air Quality Standards, NAAQS, Air Quality Index

1. Air Quality Sampling and Monitoring Prepared by A.VENKATESH

2. Air Quality Sampling and Monitoring... 2

3. A ir Q uality : Sampling and measurement of air pollutants is called air quality monitoring. The information so obtained is helpful in monitoring in implementing control measures for reducing pollutant concentrations. 3

4. Measurements of air quality generally fall into 2 classes: Stack Sampling - Generally deals with pollutants emitted from a source. Ambient Air Quality Measurement – Pollutant levels in the ambient atmosphere is measured. 4

5. Air Sampling Techniques 5 When obtaining a sample for air pollution analysis S ufficient sample for analysis : This is due to the fact that the concentration of pollutants in the ambient air likely to be extremely small. There are both gaseous and particulate air pollutants whose concentration occur at levels 1mg p er cubic meter of air. Pollutants collected from air sampling techniques may be reactive.

6. Site Selection 6 General Requirements for Site Selection purpose of monitoring number and type of instruments required duration of measurements should be easily accessible

7. Collection of Gaseous Air Pollutants: 7 Grab Sampling Absorption in liquids Adsorption in solids Freeze out Sampling

8. GRAB SAMPLING: In grab sampling the sample is collected by filling an evacuated flask or an inflatable bag. Plastic bags are being widely used for grab sampling. Losses in garb sampling can be minimized by performing the analysis immediately after collection.

9. Absorption in Liquids: Absorption separates the desired pollutants from air either through direct solubility in the absorbing medium or by chemical reaction. Fritted gals absorber where the gas stream is broken up into extremely small bubbles, thus promoting an intimate contact between the gas and the liquid. One of the most widely used is impinger , the gas stream is impinged at high velocity onto the a flat surface thus providing a good contact between gas and the liquid.

10. Adsorption on Solids: The sample air is passed through a packed column containing a finely divided solid adsorbent on whose free the pollutants are retained and concentrated. Most widely used adsorbers are activated carbon, silica gel and activated charcoal.

11. Freeze-out Sampling: 11 A series of cold traps which are maintained at progressively low temperature are used to draw the air where the pollutants are condensed . COOLANT TEMPERATURE (CENTIGRADES) ICE WATER ICE SALT -21 DRY ICE AND ACETONE -79 LIQUID OXYGEN -183 LIQUID NITROGEN -196

12. COLLECTION OF PARTICULATE POLLUTANTS Particulate pollutants are grouped generally into those that settle out due to force of gravity and those that remain suspended as aerosols. 1 st category consisting of large particle of size grater then 10 micrometer can be collected using sedimentation technique. 2 nd category containing particles of smaller size more sophisticated technique like filtration, electrostatic precipitator etc are used. Most instruments function is to collect pollutants, the analysis of weight is done seprately.

13. SEDIMEN T A TION (DUSTFALL JAR) Simplest device used for sampling particles larger than 10 micrometer. A collector consists of a plastic jar of about 20- 35cm height and 10-15cm diameter at the base with a slight inward tapering of the walls from top to bottom. The sample is deposited over a period of one month and the material is dried and weighed. Usually, only water insoluble dustfall reported in mg/cm2.

14. Sedimentation Dust particles larger than 10 micrometer are rarely carried for distance grater than 1km, station must be closely spaced for meaningful data. Advantages: The method is simple and inexpensive and requires no electrical power or moving parts. Disadvantages: Method lacks precision and is selective and usually nonrepeatable. Hence this method show pollution trend in a specific region over a period of time

15. HIGH VOLUME FILTRATION Method is popular for measurement of the mass concentration of suspended particulates smaller than 10micrometer. In this method, a known volume of air is sucked by a high speed blower through a fine filter and the increase in weight due to trapped particles is measured.

16. HIGH VOLUME SAMPLER Filter is made of fibrous material, provide a dense porous medium through which an air stream must change direction in a random fashion, allowing the entrained particles to impact on the filter material A glass fiber filter used in air sampler has an efficiency of 99% for particles of size 0.3 micrometer and it is moderately effective for trapping particles of size as 0.05 micrometer. Sampling time is 24 hour and during this time over 2000 m3 of air is sucked through filter. The particulate level is generally expressed in terms of microgram/ cubic meter .

17. Sample calculation Air flow through clean filter =1.7 m^3/min Air flow through filter at the end of the test=1.4 m^3/min Average air flow=1.55m^3/min = 2232m^3 in 24 hour Weight of the clean filter= 5.000 gm Weight of the filter after exposure= 5.348 gm Weight of the particulate dust= 0.348gm =0.348x10^6 microgram Suspended particulate concentration= (0.348x10^6)/2232= 156 microgram/m^3

18. TAPE SAMPLER Tape sampler is also known as ‘ beta gauge ’. It has appearance that looks like a reel to reel tape recorder. In this method known volume of air is passed through a paper tape which is advanced in discrete time intervals from a supply reel to take- up reel. During sampling tape is held stationary. Sampling time could be from 10 min to 2 hours, depending upon the amount of particulates. The air is passed through the nozzle and the particulates are collected on the paper tape forming a spot.

19. A more realistic analysis of spot is based upon beta-ray attenuation from which the mass concentration of particulates can be estimated. Here a beam of beta ray of I o intensity is passed through tape and intensity is measured. Tape s ampler

20. T ape sampler

21. The measurement is reported as ‘ CO H /1000 ft’ where CO H is known as coefficient of optical haze. Some guidelines are required for interpreting CO H values in terms of the degree of pollution. This table provides a typical rating system for values of CO H per 1000 linear feet versus the degree of air pollution. Spots so obtained are evaluated by analyzing the amount of light transmitted. COH DEGREE OF POLLUTION - 0.9 Light 1 – 1.9 Medium 2 – 2.9 Heavy 3 – 3.9 Very heavy 4 – 4.9 Extremely heavy Tape sampler

22. Electrostatic Precipitators Prof S S Jahagirdar, NKOCET 22 Electrostatic precipitators (ESP) are particulate collection devices that use electrostatic force to remove the particles less than 5 micron in diameter. It is difficult to use gravity settlers and cyclones effectively for the said range of particles. Particles as small as one-tenth of a mic r ome t e r c a n b e 10 % e f fi c iency r e m o v e d w i th almo s t u s in g elect r o s t a t i c precipitators.

23. Plate Type Prof S S Jahagirdar, NKOCET 23

24. Prof S S Jahagirdar, NKOCET 24

25. 13 step by step process of removing particles Ionization - Charging of particles Migration - Transporting the charged particles to the collecting surfaces Collection - Precipitation of the charged particles onto the c o llect in g su r P r f o f a S S J c a h a g e i r d a s r , N K OCET

26. Charge Dissipation - Neutralizing the charged particles on the collecting surfaces Particle Dislodging - Removing the particles from the collecting surface to the hopper Particle Removal - Conveying the particles from the hopper to a disposal point Prof S S Jahagirdar, NKOCET 26

27. Prof S S Jahagirdar, NKOCET 27

28. Emission norms for passenger cars ( Petrol) Norms CO( g/km) HC+ NOx)(g/km) 1991Norms 14.3-27.1 2.0(Only HC) 1996 Norms 8.68-12.40 3.00-4.36 1998Norms 4.34-6.20 1.50-2.18 stage 2000 norms 2.72 0.97 Bharat stage-II 2.2 0.5 Bharat Stage-III 2.3 0.35(combined) Bharat Stage-IV 1.0 0.18(combined)

29. Emission Norms for 2/3 Wheelers ( Petrol) Norms CO ( g/km) HC+ NOx (g/km) 1991 norms 12-30 8-12 (only HC) 1996 norms 4.5 3.6 stage 2000 norms 2.0 2.0 Bharat stage-II 1.6 1.5 Bharat Stage-III 1.0 1.0 Emission Norms for 2/3 Wheelers ( Petrol)

30. Emission norms for Heavy diesel vehicles: Norms CO HC NOx PM 1991 Norms 14 3.5 18 - 1996 Norms 11.2 2.4 14.4 - stage 2000 Norms 4.5 1.1 8.0 0.36 Bharat stage-II 4.0 1.1 7.0 0.15 Bharat Stage-III 2.1 1.6 5.0 0.10 Bharat Stage-IV 1.5 0.96 3.5 0.02

31. Stack Sampling Stack sampling or source sampling may be defined as a method of collecting representative samples of Pollutant laden air/gases at the place of origin of pollutants to determine the total amount of pollutants emitted into the atmosphere from a given source in a given time. The purpose of stack sampling is to determine emission levels from plant processes to ensure they are in compliance with any emission limits set by regulatory authorities to prevent environmental air pollution.

32. Sampling System: Stack sampling is carried out by diverting a part of the gas stream through a sampling “train” of which a general arrangement is shown below: 1 Nozzle 2 Sampling probe 3 Particulate collector 4 Gas collector 5 Gas flow meter 6 Flow control valve 7 To vacuum pump

33. Nozzle : It is at the end of the probe is sharp edged, pointing inward from the outside edge and the traversing probe is made of stainless steel with glass or Teflon lining. For Sampling hot gases whose temperature are above 400 degree C, these probes are provided with a circulating coolant system to prevent combustion of particulate materials inside the probe and to prevent the temperature from exceeding the maximum allowable temperature of filtration materials. Devices: Collection of particulates : Filtration, wet or dry electrostatic and thermal precipitation. Collection of gases : Absorption, adsorption, freeze out Flow measurement: Use rotameter or orifice meter or dry gas meter if the information on the total volume of the gas sampled is required.

34. Different conditions: Sample collection Velocity (V) > Stack gas velocity (W) 2. Sample collection Velocity (V) < Stack gas velocity (W) 3. Sample collection Velocity (V) = Stack gas velocity (W)

35. TYPES OF SAMPLING:

36. Iso – similar or the same Kinetic – Moving energy, motion DEFINITION Sampling at such a rate that the velocity of the gas entering the sampling Nozzle is the same as that of the gas in the duct/stack at the same sampling point

37. Diagrammatic Representation of Sampling Points in a Duct/Stack :

38. Method Prescribed in the standard are: SO2 1. Improved West and Gaeke 2. Ultraviolet Fluorosence NOx 1. Jacob & Hochheiser (Na- Arsenite ) 2. Chemiluminescence's PM10 & PM 2.5 1.Gravimetric

39. West- Gaeke Colorimetric Procedure: 1. SO 2 is absorbed in Sodium Tetra- Chloromercurate ( Cl 4 HgNa 2 )to form a stable and non-volatile Dichlorosulphitomercurate complex. 2. The formed compound is then reacted with Formaldehyde and Pararosaniline yielding a magnet colored Pararosaniline Sulphonic Acid. 3. concentration over a range of 0.002 to 5 ppm .

40. Ambient Air quality Standards 43

41. NAAQM network is operated through NEERI and CPCB Ambient Air Quality Status is described as Low (L), Moderate (M), High (H) and Critical (C) 2 types of NAAQS: primary and secondary

42. NAAQS

43. NAAQS

44. Revised NAAQS 2009 PM 2.5 and ozone have been included Standards for NOx has been made more stringent Standards for short duration exposure to deadly gases like ozone and CO have been set Tighter standards for „sensitive areas‟ have been notified. (forest &natural vegetation)

45. Air Quality Index Is a number used by government agencies to characterize the quality of the air at a given location.

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