Development of a Monitoring Device of Wall Deposition and Evaluation of Deposition Behavior for Gaseous and Cluster Contaminants in Air

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(1) A piezo sensor was constructed by combining a quartz crystal oscillator and a high-frequency generator to develop a high-sensitivity mass monitor for indicating the amount of deposited contaminants. Performance evaluation of the monitor was made by using test contaminant gas. The time resolution of the measurements of deposited amount was improved drastically by increasing the standard frequency of the crystal oscillator.(2) The time resolution of the present monitor was found to be several tens of seconds, which verified the availability of the monitor as a real-time monitoring device. The change of deposition rate with environmental factors was clarified. The dependence of deposition rate on the material of walls was also clarified by coating the crystal oscillator with different materials.(3) Performance evaluation using a clean room under operation was made. The present monitor could measure the deposited amount with sufficiently high time-resolution even when deposition and desorption take place successively. A real-time estimation of the sources of contaminant gas was also found possible by performing simultaneous measurements using multiple sensors. A monitoring of air downstream of a chemical filter was made to prove that the monitor could detect the breakthrough of the filter promptly.(4) The size distribution of clusters generated from airborne ions was clarified by constructing a measurement system. The deposition rate of water clusters onto a wall was obtained as well as the deposition behavior of clustered gases onto fine particles.(5) Models to describe the transport and deposition of contaminant gas considering both adsorption and desorption were presented for the case in which more than one species of contaminant gas coexisted. By comparing the calculated results with the experimental data on deposition, the models were verified well and the factors influencing on the deposition of contaminant gas could be organized.