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

10.3.1 Flow Conditions - Insure that the air and gas flow systems are calibrated under
the conditions of use against an authoritative standard. Different output
calibration gas concentrations are obtained simply by changing the ratios of flow
rates between the NO and dilution air channels. It is preferable to maintain a
constant dilution air-flow and to vary the NO flow. The total flow required at the
sampling manifold should equal the analyzer demand plus at least 50% excess.
The following equations can be used to pre-calculate the specific gas dilution airflow
rates required for the desired calibration points, usually 20, 40, 60 and 80%
of the instrument range.
Where :
STD x FS
S = ------------------ (1)
FS + FD
S = desired output concentrations of NO in ppm
STD = NO standard cylinder concentration in ppm
FS = NO standard cylinder flow rate
FD = dilution air flow rate in cm 3 /min.
Solving equation (1) for the NO standard flow rate (FS) that will produce the
desired concentration for a given dilution flow rate (FD) gives :
S x FD
FS = --------------- (2)
STD - S
Example : For a corrected dilution flow FD = 5.00 L/min. a NO cylinder
concentration STD = 100 ppm v/v, and a desired output concentration S = 0.90
ppm, we substitute into equation (2) and obtain for the NO standard flow rate.
(0.90) x (5,000)
FS = ---------------------- = 45.4 cm 3 /min
(100) - (0.90)
10.3.2 Zero Calibration - Activate the zero air source and allow the analyzer to sample
the zero air until a stable zero response is obtained. Adjust the analyzer NOx,
NO and NO2 zero controls as described in the instrument manual. It is good
practice to recheck the zero at the end of the multipoint calibration, especially if
large span adjustments were made.
10.3.3 Preparation for the NO and NOx Calibration - Set the zero air and NO
standard flow rates as determined in 10.3.1 for generating a NO concentration at
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