Development of a personal dust monitor with a piezoelectric quartz crystal sensor

A monitoring system using the collection technique of electrostatic precipitation on to a piezoelectric sensing element is examined. The transduction mechanism is the change in the resonant frequency of the sensing element from its unloaded nominal value of 9 MHz caused by the collected dust. The monitor had the three main design areas (point-to-plane distance, precipitator voltage and electrode-to-dust-inlet distance) optimized at a flow rate of approximately 1 I min^-1. This led to collection efficiencies greater than 97% with crystal mass sensitivity constants in the range 30-130 Hz µg^-1 for the aerosol Arizona Road Dust. The total sampling time is limited by overloading of the sensing element by dust. A method of extending the sampling time by using compressed air to clean the sensing element is described.