## 2 Materials and Methods
### Classification of Meteorological Phenomena for Aerosol Physical Properties  
A method for classifying meteorological phenomena occurring in Busan considering various sources using the aerosol observation data from the LPC during the periods of intensive observation in the spring seasons of 2009-2011 was proposed in the study. As the meteorological data obtained by the KMA were provided daily, the classification algorithm was set to daily intervals in the present study. Based on the mass concentration distribution results, wherein the aerosol mass concentration for each phenomenon was derived as described in Sections 3.1 and 3.2, and considering the aerosol detection range of APS and LPC equipment, the channels between 0.5 \(\upmu\)m and 1 \(\upmu\)m were classified as Mode 1, and those between 3 \(\upmu\)m and 5 \(\upmu\)m were classified as Mode 2. The results derived by the classification algorithm were verified considering cases where Asian dust (AD), haze (HZ), mist (MI), and precipitation (PR) phenomena occurred individually based on daily weather status observed at the synoptic weather station of KMA in Busan. The details of the classification algorithm are as follows:  
1. The PR cases were first classified by determining the presence or absence of precipitation during the day. 2. If precipitation did not occur, the results wherein the Mode 2 concentrations of the AD and HZ were higher than those of the CD were used, and the cases were classified based on the median mass concentration (0.162 \(\upmu\)g\(\cdot\)m\({}^{-3}\)) in Mode 2 during CD. 3. If the concentration was higher than the standard value, the capacity for long-distance transport was determined by comparing it with the aerosol size distribution data of Busan (LPC) and Anmyeondo (APS) and performing backward trajectory analysis using the HYSPLIT model at PKNU, whereby the LPC observation location was considered the starting point. When comparing the aerosol data between the two sites, the mass concentrations of both Modes 1 and 2 were compared. If it was not a long-distance transport phenomenon, we proceeded to Step 5. When the air masses undergo long-range transport through the Yellow Sea, the concentration of aerosol number may be influenced by sea salt particles. According to a previous study [34] on aerosol and sea salt particles in Busan, the same area analyzed in this study, the concentration of sea salt particles relative to the PM\({}_{10}\) concentration was 3.86 \(\upmu\)g/m\({}^{3}\) when transported from the Shandong Peninsula, China, and 4.04 \(\upmu\)g/m\({}^{3}\) otherwise. In the case of aerosols transported over long distances to Busan, the authors judged that there was no large difference, and the influence near Busan was greater. Therefore,the difference according to the chemical properties of the particles did not exert a significant effect, and this study focused on the physical properties of the aerosols. * If long-distance transport was confirmed, based on the AD cases with significantly higher mass concentration than HZ cases in Mode 2, the phenomenon was classified as a reference value (0.487 \(\upmu\)g\(\cdot\)m\({}^{-3}\)) based on the Q1 value of the mass concentration in Mode 2 of AD cases. If the concentration exceeded or was below this reference value, the phenomenon was classified as AD, or long-range transported haze (LH), respectively. * If the mass concentration was lower than the standard value in Step 2, the cases were classified by setting the RH to 75% as the reference value. As MI and HZ events are visibility disturbances (from 1 to \(\leq\) 10 km), these were classified based on the RH [35]. If RH was \(>\)75%, the phenomenon was considered an MI event. * If RH was \(<\)75% in Step 5, the cases were classified based on the median mass concentration (0.055 \(\upmu\)g\(\cdot\)m\({}^{-3}\)) in Mode 1 during CD cases. If the concentration was lower than the standard value, the phenomenon was classified as CD.