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

is to assess its ability to perform tests competently. It thus helps to demonstrate its own
quality system procedures. These also complement the technique of onsite laboratory
assessment by technical assessors usually used by laboratory accrediting bodies. The
accrediting bodies generally evaluate the quality system of the laboratory as per
national and international criteria. Thus the proficiency testing gives a chance to the
laboratory to evaluate its own quality system. In case the performance of the laboratory
in the proficiency testing is not found satisfactory, the laboratory should find out its
causes of inadequacy. Once the causes are analysed, it would be possible for the
laboratory to identify the number of areas wherein improvement is needed. The
laboratory should then be able to initiate appropriate action to improve its quality system
for that testing in particular and as a whole for the organization.
5.1.1 Ring Test Facility at CPCB
The Ring Test Facility as described by Dr. J. Kettenbach and Dr. S. Jacobi, HLfU 1997
is detailed below. The ring test-facility is laid out for a maximum number of 20
participants. The maximum sample flowrate is 250 l/min. To assure accurate mixing of
gases as well as constant flowrates, the system is controlled by means of 8 mass flow
controllers (MFC) of different ranges. Different sources (permeation tubes, highly
concentrated gas standards from pressurized cylinders) can be used as primary
reference gas standards.
To provide well known O3 concentrations, an O3 - generator along with a reaction
chamber for “Gas Phase Titration” (GPT) is included. To check the influence of water
vapour to the measurements, it is possible to add different amounts of moisture to the
gas flow. All gas flows are controlled by means of high precision MFC’s and are fed into
a reaction or mixing chamber made out of glass. The outlet of this reaction chamber is
distributed to all individual gas sampling exit ports via a glass tube of 27mm (ID). All
parts which are in contact with the gas are made from glass or teflon ( ¼”, 1/8”) tubes.
(iv) Carrier Gas
In general, different carrier gases for different trace gases (gas standards) are to be
used. To achieve correct and clean NO-concentrations, N2 is used as carrier gas. For
all other gases, synthetic air should be used as carrier gas. MFC 1 and 2 are used to
control the carrier gas supply. The range of each of those MFC’s is 100 l/min. Therefore
a maximum carrier gas flowrate of 200 l/min can be achieved. The controlled carrier gas
supply is directly connected to the mixing chamber. MFC 3 ( range:0-50 l/min) is used to
control the amount of water vapour added to the total gas mixture, if necessary. The
separate flow of carrier gas via MFC 3 is passed through an impinger system filled with
water. It is assumed that the gas stream is saturated by water vapour (relative humidity
about 100%) after having passed the water reservoir through a fritted glass filter. To
assure complete water vapour saturation, the level of water in the glass vessel must be
at least 5 cm above the inlet of the gas into the water.
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