## 3 Results and Discussion  
### Aerosol Concentration Distributions  
To analyze the distinct aerosol fluctuation characteristics for each dust phenomenon, including the most severe Asian dust on 20 March 2010, data observed from 2009 to 2011 during the spring seasons were analyzed. In addition, because few in situ sites were present where the aerosol number concentration was observed based on the particle size, the data observed by LPC was used in this study. Here, the smaller the particle size of aerosols, the larger is the contribution to total number concentration, and the lower is the proportion of the total surface or volume concentration. Figure 3 shows the total period of measured aerosols for each particle size and number concentration. The number concentration distribution showed a typically decreasing tendency in concentration as the particle size increased, whereas the mass concentration distribution tended to increase based on the 1-3 \(\upmu\)m channel, which was notably distinct from the number concentration results. For the 5 th and 95 th percentiles of 3-5 \(\upmu\)m and 5-10 \(\upmu\)m, the concentration distribution was wider than those in the other channels, with the values peaking in the 3-5 \(\upmu\)m channel (0.123 \(\upmu\)g\(\cdot\)m\({}^{-3}\)). Based on the LPC observation data across the study period, hourly data for a total of 173 days were included in the analysis. If data loss affected >6 h\(\cdot\)d\({}^{-1}\), that day was excluded from the analysis. Figure 4 shows the frequency of occurrence on days where AD, HZ, MI, PR, multiple events (ME), and clear days (CD) were observed by the KMA. Among all the cases, the numbers of single-case occurrence days were 19, 13, 7, and 3 for PR, MI, HZ, and AD cases, respectively, and the physical properties of the aerosols were investigated for these cases. In this study, the analysis was conducted focusing on each individual meteorological phenomenon. Median values \(\pm\) MAD were used in the present study to effectively analyze the wide distribution of concentrations based on aerosol particle size. In the distribution of aerosol mass concentration by meteorological phenomena (Figure 5), the highest mass concentrations in coarse particle mode (>1 \(\upmu\)m) were observed for AD, which were 0.124 \(\pm\) 0.046, 0.722 \(\pm\) 0.322, and 1.028 \(\pm\) 0.944 \(\upmu\)g\(\cdot\)m\({}^{-3}\) for particle size 1-3, 3-5, 5-10 \(\upmu\)m, respectively. For the fine particle mode (<1 \(\upmu\)m), the highest mass concentrations in the first channel observed were for MI (2.213 \(\pm\) 0.950 \(\upmu\)g\(\cdot\)m\({}^{-3}\)), and the phenomenon of HZ showed the highest mass concentrations in the second channel (0.192 \(\pm\) 0.106 \(\upmu\)g\(\cdot\)m\({}^{-3}\)). The lowest concentrations in the total channel were recorded for CD. The mass concentrations in the coarse particle mode (5 th channel) were observed to be in the order of AD > MI > HZ > CD > PR, whereas the concentrations in the fine particle modes (1 st channel) followed the order of MI > HZ > AD > CD > PR (Table 2). Figure 3: (**a**) Number and (**b**) mass concentration size distributions observed at each channel over the entire period. The bottom and top of each box represent the lower and upper quartiles, respectively, whereas the line within each box represents the median. Figure 4: Frequency distribution of the Asian dust (AD), haze (HZ), mist (MI), precipitation (PR), multiple events (ME), and clear days (CD) cases for the spring, 2009–2011 in Busan. Values in parenthesis indicate frequency number and percentage (%), respectively. Figure 5: Aerosol mass concentration size distribution for cases of the following: (**a**) Asian dust (AD), (**b**) haze (HZ), (**c**) mist (MI), (**d**) precipitation (PR), and (**e**) clear days (CD) over the entire analysis period. The MAD and IQR were calculated to measure the overall deviation. Overall, the patterns of MAD and IQR for each phenomenon were similar.