Ambient Air quality Monitoring Guidlines. - Maharashtra Pollution ...

7.0 APPARATUS
7.1 Sampling equipment: The sampling equipment to be used for air sampling will
consists of a standard impinger of 35-ml capacity, a trap, a flow meter or critical
orifice device and a suction pump. The arrangement of the sampling train is
shown in the (Figure 1). The commonly used apparatus is an integrated gas
sampling assembly attached with High Volume Sampler or Handy Sampler.
7.2 Sampling Train: A typical sampling train consists of impinger, trap, flowmeter,
valve and pump. Instead of this assembly critical orifice device can also be
substituted. (Figure- 1).
7.2.1 Impingers: All glass impingers, commonly called midget impingers are of 35 ml
capacity 22cm in length and 2.6 cm wide, impinging end of the tube 1mm bore
size or preferably with fritted disc having porosity of 50 microns or less. Details of
two types of midget impingers are given in (Figure 2 & 3). Units which use frits of
approximately 50 microns or less pore size gradually become clogged with use.
They may be cleaned by purging the appropriate cleaning solution back and forth
through the frit and then rinsing with distilled water in the same fashion. Various
substances may be removed from the frits by cleaning with the appropriate
solvent namely; hot hydrochloric acid for dirt, hot concentrated sulphuric acid
containing sodium nitrite for organic matter.
7.2.2 Flowmeter: A rotameter calibrated accurately for the flow ranges 0 to3
litre/minute.
7.2.3 Critical Orifice Device: Critical orifice (Figure 4) to give a flow of about 1
litre/minute. Normally hypodermic needles are used as critical orifice devices.
7.2.4 Trap: This can be a glass wool tray or a membrane filter as shown in Figure 1.
7.2.5 Volume Meters: Volume meters may be of the wet type (wet test meters) or the
dry type (diaphragm). The wet type gives the most precise result .The volume
meters have the advantage that variation in rate of sampling will not introduce
large error.
7.2.6 Soap Bubble Meter: Soap bubble meter is used to calibrate rotameter.
8.0 REAGENTS
All the reagents should be of A.R/G.R. grade.
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