E C O P H Y S I C S Gas Phase Titration
CLD 780 TR / July 2000 150
A3.1 Principle
This calibration technique is based upon the rapid gas phase reaction be-
tween NO and O
3
, to produce stoichiometric quantities of NO
2
, in accor-
dance with the following equation:
NO + O
3
→
NO
2
+ O
2
The quantitative nature of this reaction is such that when the NO concen-
tration is known, the concentration of NO
2
can be determined. Ozone is
added to excess NO in a dynamic calibration system, and the NO chan-
nel of the chemiluminescence NO/NO
x
/NO
2
analyzer is used as an indi-
cator of changes in NO concentration. Upon the addition of O
3
, the de-
crease of NO concentration observed on the calibrated NO channel is
equivalent to the concentration of NO
2
produced. The amount of NO
2
generated may be varied by adding variable amounts of O
3
from a stable
uncalibrated O
3
generator.
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