Absolute calibration of a photoelectric condensation nucleus counter at low values of nucleus concentration

Summary A new absolute condensation nucleus counter was constructed to investigate the accuracy of the calibration widely used with the Pollak-Nolan photoelectric condensation nucleus counter. An attempt was made to standardize the conditions affecting calibration and, using the new counter, to recalibrate the photoelectric counter at values of extinction less than 16%.Over this extinction range, the present work indicates nucleus concentrations which are higher by about 30% than those given by the calibration ofPollak andMetnieks 8]³). In view of the great natural variability of Aitken nucleus concentrations, this discrepancy, if real, is of little meteorological importance.