Detection of extremely small particles in the nanometer and ionic size range

A high-sensitivity aerosol detector using pre-onset positive corona pulses has been constructed. It is expected to be used for the detection of very fine particles in a size range down to the nanometer and ionic. Preliminary tests of the detector to find the correlation between the pulses and the particles (or ions) have revealed that three different kinds of pulses exist. Large pulses, which have the highest peak value of the three, appear only in the moist air; they do not respond to ions or particles. Small pulses, with a much smaller height, are observed in both dry air and moist air. No definite relation is observed between their number and the number of particles coming into the detector. Micropulses with the smallest height have been found to appear in response to negative ions or negatively charged particles. Using an ion filter which separates ions according to their electrical mobilities, the lowest mobility of the negative ions in the the sample air has been measured to be 0.6-0.8 cm²/Vs from the micropulses. The lower limit of the mobility of the particles detectable with the present detector is 2×10^-3-4×10^-3 cm²/V s