Personal Ozone Monitor Manual Rev. E-2
1
1.
PERSONAL OZONE MONITOR INTRODUCTION
The 2B Technologies Personal Ozone Monitor
TM
(POM
TM
) is designed to enable
accurate measurements of ozone in air over a wide dynamic range extending from a
limit of detection of 3 parts-per-billion by volume (ppb) to an upper limit of 10 parts-
per-million (ppm) based on the well-established technique of absorption of ultraviolet
light at 254 nm.
Note that throughout this manual and in the instrument output, “ppb”
(identical to “ppbv”) refers to parts-per-billion by volume (not weight). The Personal
Ozone Monitor is small (4.0
″ × 3.0″ × 1.5″; 10.2 × 7.6 × 3.9 cm), lightweight (0.75 lb;
0.34 kg) and has a low power consumption (3.0 watt) relative to conventional
instruments and is therefore well suited for applications such as:
•
Long-term monitoring at remote locations where power is highly limited
•
Monitoring and control of ozone in industrial settings
•
Monitoring of exposure to individuals in the workplace
•
Personal exposure monitoring for studies of health effects of air
pollutants
For aircraft flights where high temporal and spatial resolution is desired, the Model
205 Ozone Monitor is recommended.
1.1.
Theory of Operation
Absorption of UV light has long been used for measurements of atmospheric ozone
with high precision and accuracy. The ozone molecule has an absorption maximum
at 254 nm, coincident with the principal emission wavelength of a low-pressure
mercury lamp. Fortunately, few molecules found at significant concentrations in the
atmosphere absorb at this wavelength. However, interferences, such as organic
compounds containing aromatic rings, can occur in highly polluted air. For additional
information about UV-absorbing interferences and how to estimate their contributions
see
Tech Note #040
.
Figure 1.1 is a schematic diagram of the Personal Ozone Monitor. Ozone is
measured based on the attenuation of light passing through a 15-cm absorption cell
fitted with quartz windows. The 15-
cm cell length is accomplished by using a “U”
shaped cell with mirrors in the corners to transmit light from the lamp at one end to the
detector at the other. A low-pressure mercury lamp is located on one side of the
absorption cell, and a photodiode is located on the opposite side of the absorption
cell. The photodiode has a built-in interference filter centered on 254 nm, the principal
wavelength of light emitted by the mercury lamp. An air pump draws sample air into
the instrument at a flow rate of approximately 0.75 L/min. A solenoid valve switches
so as to alternately send this air directly into the absorption cell or through an ozone
scrubber and then into the absorption cell.
