A measuring method using a reference CNC (Condensation Nucleus Counter) combined with the conventional DMA/CNC system has been developed to obtain the correct size distribution of atmospheric ultrafine aerosols. It is difficult to measure correct size distributions of atmospheric aerosols because of the fluctuation of size distribution and concentration in a sizing period. The method proposed here is capable of correcting the fluctuation of the particle concentration in each particle size range of DMA by the simultaneous measurement of total number concentration of aerosol with the use of the additional set of reference CNC. Some simulation studies assuming the variation patterns of size distribution have been performed. It was found that this technique was useful to measure size distributions which fluctuate with time like atmospheric aerosols.
Studies on Kosa flying to Japan were performed by using the concentration of SPM monitor (DKK Inc., Model GRH-76) at 6 air pollution monitoring stations in Nara prefecture during the period from 1980 to 1993. Kosa event was able to be estimated to a certain extent when the maximum concentration of SPM in a day measured by SPM monitor of β-ray absorption method was high concentration. At Kosa event, in the comparison of SPM concentration by light scattering method with β-ray absorption method, β-ray absorption method was able to detect Kosa event, but light scattering method was not. Criteria of Kosa event by SPM concentration measured by SPM monitor of β-ray absorption method were as follows : SPM concentration in a wide area were appeared over 100 μg/m3 simultaneously or were similar pattern (correlation coefficients were significant). The case over 100 μg/m3 of SPM concentration measured by SPM monitor of β-ray absorption method throughout the whole area of Nara prefecture were 72 days during the period from 1987 to 1993. The number of Kosa event was the most (28 days) in 1988, and then became to be less year by year. It was found that the most Kosa event was in January, and the secondary was in April during the observation period in Nara.