E C O P H Y S I C S Gas Phase Titration
CLD 780 TR / July 2000 156
A3.5 Procedure
a) Assemble a dynamic calibration system such as the one shown in Fig.
A3.
b) Insure that all flowmeters are calibrated under the conditions of use a-
gainst a reliable standard such as a soap bubble meter or wet test me-
ter. All volumetric flow rates should be corrected to 25 °C and 1013
mbar (760 mm Hg). A discussion on the calibration of flowmeters is gi-
ven in Reference 1.
c) Precautions must be taken to remove O
2
and other contaminants from
the NO pressure regulator and delivery system prior to the start of ca-
libration to avoid any conversion of the standard NO to NO
2
. Failure
to do so can cause significant errors in calibration. This problem may
be minimized by
1. carefully evacuating the regulator, when possible after the regula-
tor has been connected to the cylinder and before opening the cyl-
inder valve;
2. thoroughly flushing the regulator and delivery system with NO after
opening the cylinder valve;
3. not removing the regulator from the cylinder between calibrations
unless absolutely necessary. Further discussion of these procedures
is given in Reference 1.
d) Select the operating range of the NO-NO
2
-NO
x
analyzer to be calibra-
ted. (The EPA designated range is 0.5 ppm full scale; CLD 780 TR ran-
ge setting: 500 ppb)
No EPA designated methods exist for measurements in very clean air.
Calibrate that measuring range which covers the highest expected
NO
x
values, which may well be the 5 or 10 ppb „Range“. A GPT at
these concentrations can only be performed with instruments specially
optimized for this purpose.
e) Connect the chart recorder to the analyzer. All adjustments to the ana-
lyzer should be performed based on the appropriate strip chart rea-
dings. References to analyzer responses in the procedures given be-
low refer to recorder responses.
f) Determine the GPT flow conditions required to meet the dynamic pa-
rameter specification as indicated in Section A3.4.
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