Analysis of PM 2.5 Mass Extinction Efficiency Characteristics in Busan, South Korea Using Long-Term Scanning LiDAR Observations

This study investigates the variation characteristics of the mass extinction efficiency (MEE) of particulate matter (PM; PM10, PM2.5-10, and PM2.5) in the Busan port (Busan, South Korea) area using longterm Scanning Light Detection and Ranging (LiDAR) and in situ measurement data.The results show that the mean MEE of PM2.5 (7.72 ± 3.86 m² g -¹) is significantly higher than that of PM10 (5.19 ± 1.99 m² g -¹) and PM2.5-10 (1.95 ± 1.26 m² g -¹), confirming the dominant optical role of fine particles.MEE exhibits a decreasing trend with increasing PM2.5 mass concentration due to particle growth and aggregation under high-loading conditions, while it increases with a higher PM2.5/PM10 ratio, indicating the importance of particle composition.The combined analysis of MEE and relative humidity (RH) reveals a nonlinear interaction: MEE increases under moderate RH (60-70%) due to hygroscopic growth but decreases at high concentration or low RH (< 40%) as particle agglomeration dominates.These results demonstrate that MEE is controlled by the coupled effects of concentration, composition, and humidity rather than by a single variable.The findings provide a physical basis for developing region-specific correction factors for converting LiDAR extinction coefficients to PM mass concentrations in coastal and port environments.