A Study on the Characteristic Variations of Fine Particle in Busan and Ulsan through Particle Extinction Efficiency Analysis

In this study, the extinction efficiency, one of the fine particle optical characteristics was calculated using the PM2.5 mass concentrations and the visibility data measured in Busan and Ulsan city during the period 2015 similar to 2019. We identified higher seasonal extinction efficiency in summer and autumn compared to spring and winter due to variations in relative humidity, particle characteristics, and wind direction. In addition, the annual extinction efficiency rate with the values of 0.72 and 0.87 (m(2)/g)/year in Busan and Ulsan, respectively, indicated an increasing trend in both regions from 2015 to 2019. However, no considerable trend was observed in relative humidity during the study period. We conclude that the annually increasing trend might be associated with the particle characteristics, such as an increase in the number of particles per unit mass due to the smaller particle size compared to the past, or an increase in the particles with the light scattering characteristics. Considering the wind direction, the extinction efficiency was also high when the eastward wind was dominant compared to other winds. Despite the reduction in PM2.5 mass concentration, citizens can not feel this effect, since they perceive the PM2.5 mass concentration reduction by an increase in visibility. Our study suggests that it can be more effective to implement the pollution reduction policies based on the particle characteristics such as particle size, particle components, and the source of particle origination, not only the fine particle weight.