Evaluation of acoustical particle counter for the sizing of fog droplets

An acoustical particle counter (or acoustical particle sizing device) was evaluated for counting and sizing of fog droplets. Fog droplets were generated under controlled conditions in the laboratory. Fog droplet sizes were measured by an optical and an electron microscope and compared to results from the acoustical particle counter. Most of the droplets were found to be in the size range of 5–30 µm. The mean diameters estimated from the acoustical particle counter were in agreement with the microscope values of mean droplet diameter. A Rich 100 condensation nuclei monitor was also operated simultaneously during the fog droplet counting to monitor the condensation nuclei counts in the laboratory. The results indicate that condensation nuclei count is inversely correlated with the fog droplet threshold diameter. Aerosols of uniform size (35 µm) were generated by the vibrating orifice monodisperse aerosol generator and counted at three different flow rates by the acoustical particle counter. The counts/liter/minute were similar, indicating the reliability of the acoustical particle counter.