In this reseach project the ability of a microfabricated acoustic-wave microsensor to detect volatile organic compounds in indoor air was studied. The microsensors were made in the Berkeley Microfabrication facility following designs developed at the Berkeley Sensor & Actuator Center. The devices were exposed in a four-liter chamber to vapor-phase concentrations of six representative VOCs one at a time: tetrachloroethylene, 1,1,1-trichloroethane, toluene, benzene, ethanol, and formaldehyde. The device sesnitivity to each VOC was computed from the measured oscillator frequency and temperature data. From this information, the minimum detectable concentration level was computed for each case. The minimum detectable concentration was found to be as low as 180 ppb for tetrachloroethylene with a device coated with poly(vinylpropionate).
A sensor coated with ethyl cellulose was set up in LBL's 20-cubic-meter test chamber to evaluate its response in a room-sized environment. The sensor's response obtained in this chamber was similiar to that obtained in the four-liter test chamber which indicated that the FPQ sensor is a promising candidate for measuring concentrations of volatile organic compounds in room-sized environments.
Theoretical exploration of the use of the FPW sensor to measure other indoor air pollutants such as fine mode particles was conducted. Minimum detectable levels were claculated for various particle sizes. Particle transport and deposition mechanisms such as diffusion, electrostatic field, thermophoresis, and impaction were considered. For each case the equations were derived to estimate the change in the oscillator frequency as a function of airborne particle mass concentration. From the estimates of the oscilaltor frequency change in a typical indoor environment it was concluded that the FPW sensor could be used to measure airborne particle mass concentration.