Model 306 Ozone Calibration Source Manual Rev. G-1
3
1.2
Summary of Schematic Diagram
An air pump pushes air through a particle filter, then through a mass flow meter. The
microprocessor controls the flow rate at a value of 4.0 L/min volumetric by means of
pulse-width modulation of the power to the pump. Before entering the photolysis
chamber, the air passes through an ozone/NO
x
scrubber to remove any ambient
ozone and NO
x
. The air passes through another particle filter, and then passes
through the photolysis chamber containing a low-pressure mercury lamp where
absorption of atomic lines near 185 nm produces oxygen atoms from molecular
oxygen, and the oxygen atoms react with molecular oxygen to form ozone (reactions
1, 2, and 3 above). The lamp intensity is monitored by a photodiode and controlled by
the microprocessor. The photodiode voltage is calibrated against the output ozone
concentration. Pressure within the gas stream is measured but not controlled.
Instead, the lamp intensity is varied to compensate for changes in pressure using a
proprietary algorithm. Air containing ozone exits the photolysis cell through an
overflow tee, where excess air not sampled by the ozone monitor being calibrated is
exhausted through an internal ozone scrubber. If it is desired to have the full 4.0
L/min of air/ozone exit the instrument, the internal ozone scrubber may be capped.
The other end of the overflow tee goes to a valve which selects either the ambient
sample air or the calibration air to exit through the output of the 306.
Further information about 2B Tech’s Model 306 Ozone Calibration Source may be
found in the journal article published in
Atmospheric Measurement Techniques:
Portable ozone calibration source independent of changes in temperature, pressure
and humidity for research and regulatory applications, J.W. Birks, C.J. Williford,
P.C. Andersen, A.A. Turnipseed, S. Strunk, and C.A. Ennis,
Atmospheric
Measurement Techniques
,
11
, 4797-4807, 2018.
The paper is accessible through the link here:
https://twobtech.com/2018_AMT_O3_Calibration_Source.pdf
