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

(v) Dilution System
The permeation system in combination with an O3 – generator is manufactured within
one 19 unit. The temperature of the permeation oven can be set alternatively to 40 or
50 o C by using a switch on the front plate of the unit. The flowrate of diluent gas through
the permeation system is controlled by MFC 4 ( range 0-5 l/min.) Synthetic air or
purified and dried air from a compressor should be used as diluent gas for the
permeation system. The exit of the permeation system is directly connected to the
mixing chamber.
(vi) O3 – Generator
As mentioned above, the O3 generator is part of the 19” unit of the permeation system.
The generator in general consists of an UV- lamp ( length: 15” ) mounted into a glasschamber.
The voltage of the lamp and thus the intensity of radiation is controlled by a
high precision potentiometer on the front plate. The flowrate through the O3 – generator
is controlled by MFC 5 (range: 0-5 l/min). Synthetic or purified and dried air from a
compressor can be used.
The air must provide a constant fraction of O2 which is not lower than 20%. The exit of
the O3 generator is connected to an injector T. The injector is used to add NO gas to
facilitate the gas phase titration. The NO-gas is controlled by MFC 7 ( range: 0-50
ml/min). A teflon tube of 1 m length ( 6/4 mm OD/ID) is used as a reaction chamber
where the GPT takes place. The exit of this GPT- reaction chamber again is connected
to the main mixing chamber.
(iv) Generation of calibration gases using highly concentrated primary
gas standards in pressurized gas cylinders ( e.g. SO2 ,NO,CO).
MFC 6 to 8 (ranges: 0-500,0-50 and 0-5 ml/min) can be used to hook up pressurized
gas cylinders of various components as primary source to generate test or calibration
gases. Typical mixing ratios used range from 100 to 1000 ppm. To achieve practical
concentrations (also in the emission range), a suitable MFC (6-8) can be chosen
depending on the concentration of the primary gas standard and the total gas flow.
(v) Gas Phase Titration (GPT)
As a prerequisite for GPT, a constant flow of a well defined NO- concentration is
needed. Turning on the UV-lamp and choosing an appropriate setting for lamp intensity
and air flow, will give a sufficient source of O3. After mixing these two gas streams by
means of the injector system, NO will be oxidized by O3 quantitatively within the reaction
chamber (teflon tube). Assuming a yield of 100% (quantitative reaction), the amount of
NO2 formed is identical to the original amount of O3.
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