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TAPI Model 265A Chemiluminescence Ozone Analyzer
Manual Addendum, Rev. B, DCN 5254
15
PRINTED DOCUMENTS ARE UNCONTROLLED
3 THE M265A OZONE ANALYZER
3.1 Principle of Operation
The Teledyne API Model 265A analyzer is designed to measure the concentration of ozone
using the chemiluminescence reaction below. The signal comes from the light emitted by the
gas phase reaction of nitric oxide (NO) and ozone (O
3
) as follows:
2
*
23
ONOONO
hvNONO
2
*
2
The reaction of ozone with NO results in electronically excited NO
2
*
molecules as shown in
the first equation. The excited NO
2
*
molecules release their excess energy by emitting a
photon hν and dropping to a lower energy level as shown in the second equation. It has been
shown that the number of emitted photons is directly proportional to the O
3
concentration in
the reaction cell.
Periodically, an AutoZero valve switches the sample stream to vacuum, allowing the reaction
cell to be evacuated and the analyzer to read zero background. The AutoZero readings are
subtracted from the concentration readings, which improves zero baseline stability.