The Effect of the Particle Refractive Index on the Accuracy of Aerosol Measurement With Optical Particle Counters

The optical particle counter (OPC) is widely used in the measurements of aerosols, owing to its advantages such as simple operation, real time output of results, and maintenance of the measured particles in the original suspended state. The calculated results of response curves for several commercial counters given in Cook et al. (1975) and Tan et al. (1984) indicate that these curves are quite sensitive to the refractive index, especially to its imaginary part. However, the effect of the particle refractive index on the characteristics of the aerosol size distribution has not been analysed. Especially, the difference between the real and measured size distributions of particles, determined with a calibration curve, has not been analysed quantatively. As a result, the effect of the particle refractive index on the determination of the particle size distribution has not received adequate attention. It can be seen in a number of measurement reports (Pinnick et al., 1976; Fitch and Cress, 1981; Wang et al., 1984, etc.) on OPC that the particle size is still determined with the calibration curve of the instrument. Therefore, this is an indispensable subject, not only for examining the reliability of the particle size distribution determined by the calibration curve, but also for proper use of OPC. In this paper, the aerosol measurement data are used for analysing this effect.