## 4 Conclusions  
In this study, the aerosol characteristics and meteorological classification algorithms for high-concentration aerosol phenomena were investigated according to aerosol physical properties. Each phenomenon was investigated by analyzing the aerosol mass concentrations based on particle diameter during AD, HZ, MI, and CD events. During AD events, the overall mass concentration of aerosols in terms of particle size distribution increased by 4.4 times compared to the mass concentration during CD cases, whereas that in the coarse mode (\(\geq\)1 \(\upmu\)m) increased by six times. During HZ events, the concentration of accumulation-mode aerosols \(<\) 1 \(\upmu\)m increased by 2.5 times. The concentration of the MI particles in Mode 2 decreased by 0.7 times due to the washout effect of rainfall on the overall particle size distribution. Furthermore, to statistically examine the distribution of mass concentration according to aerosol particle size, an optimal probability density function was derived for each weather condition using mass concentration data based on particle diameter. The function was categorized into accumulation and coarse modes, and the total aerosol mass concentration, geometric mean diameter of particles, and geometric SD were calculated for each phenomenon. In the coarse mode, the total mass concentration during AD events was the highest (16.3 \(\upmu\)g\(\cdot\)cm\({}^{-3}\)), whereas in the accumulation mode, HZ events exhibited the largest value (22.86 \(\upmu\)g\(\cdot\)cm\({}^{-3}\)). The average diameters were 4.41 and 0.41 \(\upmu\)m in the coarse and accumulation modes, respectively. Finally, a classification algorithm was proposed for the meteorological phenomena occurring in Busan based on the determined physical properties of aerosols, meteorological variables, and the physical properties for each phenomenon. First, the presence of precipi  
Figure 11: (**a**) Backward trajectory of air masses at 0300 UTC 13 April 2010 in Busan. Time series of aerosol mass concentrations in (**b**) Mode 1 and (**c**) Mode 2 at Busan (black line) are presented with those of Annyeondo (red line) for 9–12 January 2009. The dashed lines are the median aerosol mass concentrations for the CD cases in Modes 1 and 2, respectively. tation was assessed, and when present, it was classified as PR. When precipitation did not occur, using the daily median value of Mode 2, we determined whether the daily values exceeded the standard values for CD cases. If the value in Mode 2 did not exceed this threshold, RH had the greatest effect on the fluctuation of aerosol concentrations. Thus, the phenomena were classified using 75% RH as a reference value, whereas if RH? 75%, it was classified as an MI event. Alternatively, if RH! 75%, the phenomena were classified as HZ and CD cases based on the standard value of aerosol mass concentration in Mode 1 during CD cases or classified as LH and UH events when considering long-distance transport. If both Modes 1 and 2 exceeded the standard values, the differences between aerosol concentrations in Anmyeondo and Busan, in conjunction with the results of backward trajectory analysis, were used to determine whether long-distance transport had occurred. Finally, distinctions between AD and LH, UH, and CD were accomplished by considering the ratio of aerosol mass concentrations in Modes 1 and 2. Among the nine daily verification cases, all the cases coincided with the observation results of KMA. In this study, meteorological phenomena at high aerosol concentrations were split into more objective and scientific classes, including UH, LH, AD, MI, PR, and CD event categories. The results presented herein can help identify regional characteristics based on the physical properties of aerosols, as well as infer external factors, such as long-distance transport.