Model 306 Ozone Calibration Source Manual Rev. G-1
2
absorbed by O
2
to produce oxygen atoms. The oxygen atoms attach to O
2
to form
ozone, O
3
. The well-known mechanism, which is responsible for the presence of
Earth’s protective ozone layer, is as follows:
O
2
+ h
→
O + O
(1)
2 [O + O
2
+ M
→
O
3
+ M]
(2)
____________________
Net: 3 O
2
+ h
→
2 O
3
(3)
where h
symbolizes a photon of light and M is any molecule (e.g., N
2
, O
2
, Ar).
Absorption of one photon of light by O
2
results in the formation of two ozone
molecules. The concentration of ozone produced in a flowing stream of air depends
on the intensity of the photolysis lamp, the concentration of oxygen (determined by
pressure and temperature), and the residence time in the photolysis cell (determined
by volumetric flow rate and cell volume). By holding these parameters constant, it is
possible to produce a flow of air containing a constant concentration of ozone, and the
concentration of ozone produced can be varied most conveniently by varying the lamp
intensity. Figure 1-1 is a schematic diagram of the Ozone Calibration Source
™.
Figure 1-1.
Schematic diagram of the Model 306 Ozone Calibration Source
™.
Photolysis Chamber
UV Lamp
Ozone/Zero Calibration Air
from Model 306
Mass Flow Meter
Air Pump
Ozone & NO
x
Scrubber
Air In
Photodiode
2
B
Technologies Model 306
Ozone Calibration Source™
Ambient
Sample Air
To User’s Ozone Monitor or
System: Ozone/Zero Calibration
Air or Ambient Sample Air
3-Way Valve
Overflow/
O
3
Scrubber
