Aerosol size distributions observed at the Seoul National University campus in Korea during the Asian dust and non-Asian dust periods

Aerosol size distributions of observed mass concentration and number concentration at the Seoul National University (SNU) campus site in Korea during the non-Asian dust and the Asian dust (Hwangsa) periods have been examined using the 8-stage cascade impactor and the 8-channel airborne particle counting system, respectively. The particle size distribution of the observed mass concentration during the Asian dust period at the SNU site is compared with that observed at the Asian dust source site of Duolun in Inner Mongolia, China. The results indicate that the size distribution of both the mass concentration and the number concentration shows a bi-modal distribution that can be regressed optimally with two log-normal distribution functions. It is found that the optimally regressed probability density function of the mass concentration distribution during the non-Asian dust period at the SNU site shows two log-normal distributions with the particle mean diameters of 0.66 and 8.51 μm and the standard deviations of 1.78 and 2.14 μm, respectively. The probability density of the small size mode is slightly smaller than that of the large size mode. During the Asian dust period at the SNU site the estimated probability density function of the mass concentration also composes of two log-normal distributions with the particle mean diameters of 0.89 and 9.12 μm and the standard deviations of 2.40 and 2.14 μm, respectively. However, the high probability density is greatly shifted to the large size mode. The probability density of the small size mode is only 6% of that of the large size mode. A quite similar size distribution pattern is found in the Asian dust source region of Duolun, suggesting the high probability density at the large particle-size mode during the Asian dust period being mainly attributed to long-range transport of particles from the Asian dust source region. It is also found that the estimated probability density function of the number concentration distribution observed at the SNU site during the non-Asian dust period has a bi-modal distribution with the particle mean diameters of 0.36 and 1.12 μm and the mean standard deviations of 1.48 and 1.91 μm, respectively. Much higher probability density is found in the small size mode in contrast to that of the mass concentration distribution where the probability density of both modes is almost the same.