A new, portable, real-time ozone monitor

New methods are needed to assess microenvironmental and personal exposures to ozone. A real-time ozone sensor using a piezoelectric quartz crystal has been developed and evaluated. The crystal is coated with polybutadiene whi ch reacts irreversibly with ozone, resulting in a mass increase on the surf ace of the crystal which, in turn, alters its natural oscillation frequency . The rate of change in frequency is proportional to the concentration of o zone and is recorded by a datalogger with a time resolution of 10 min. Expe riments were conducted to investigate sensor response, useful lifetime, and potential interferences. Monitor components such as a pump, power supply, and datalogger were arranged to fit within a compact enclosure. Five protot ype ozone monitors were assembled and evaluated in the laboratory and in a field study of two offices and two residences in Southern California. Field measurements made with two quartz crystal-based ozone monitors exhibited p recision ranging from 6 to 27% (13% on average) and bias ranging from -37 t o 2% (-13% on average) when compared to a reference method (UV photometric detection) for real-time ozone measurement. The monitor has a sensitivity o f 3 ppb ozone (limit of detection for S/N = 3) and a useful lifetime of sim ilar to 20 that an average ozone concentration of 50 ppb (1000 ppb-h). This prototype monitor is smaller, lighter, and more affordable than existing U V ozone analyzers and with further development may be suitable for real-tim e personal ozone monitoring.