Research Projects

Project at a Glance

Project Status: complete

Report Published May 1999:

Title: Continuous, real-time, miniature ozone monitor.

Principal Investigator / Author(s): Harley, Robert

Contractor: UC Berkeley

Contract Number: 94-342


Research Program Area: Health & Exposure

Topic Areas: Indoor Air Quality, Monitoring


Abstract:

In this study, a portable real-time ozone monitor has been developed. The ozone sensor consists of a piezoelectric quartz crystal coated with polybutadiene. The polybutadiene coating reacts irreversibly with ozone resulting in a mass increase on the surface of the crystal, which, in turn, alters the natural oscillation frequency of the crystal. The rate of change in frequency is proportional to the concentration of ozone and is recorded by a datalogger with a time resolution of 10 minutes.

Major effort was devoted to designing and optimizing the configuration of the ozone sensor. The design variables included: (i) direction of sample air flow over the crystal, (ii) sample air flow rate, (iii) type of polybutadiene coating, and (iv) amount of coating. Experiments were conducted to investigate the sensor's response, useful lifetime, and potential interferences related to these variables. Monitor components such as a pump, power supply, and datalogger were specified and arranged to fit within a compact enclosure. Five ozone monitors have been assembled and evaluated in the laboratory and in a field study of two offices and two residences in Southern California. Measurements of indoor ozone concentrations were also made in a photocopy room in Berkeley, CA.
The ozone monitor has been shown to measure ozone levels with a response time comparable to ultraviolet (UV) photometric analyzers. Field measurements made with two quartz crystal-based ozone monitors and an UV analyzer exhibited precision and accuracy within 10 and 20 percent, respectively. When the monitor's detection limit for ozone was set to 30 ppb it exhibited a useful lifetime of ~20 hours at an average ozone concentration of 50 ppb (1000 ppb-hr). This new monitor is smaller, lighter, and more affordable than existing UV ozone analyzers.


 

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