Below-cloud scavenging of fine and coarse particulate matters in Seoul and its change with rainfall types

초록

Below-cloud scavenging is an important removal process of particulate matter (PM) and its effects change with characteristics of rainfall as well as PM. This study examines below-cloud scavenging of fine and coarse PMs in Seoul, South Korea and its change with rainfall types using PM and Parsivel2 disdrometer observation data during ∼7 years. PM concentrations 1 h before and after rainfall events are compared for PM10, PM2.5, and PM2.5−10. The scavenging effects on the PM concentrations increase with increasing rainfall amount, and PM2.5−10 is more effectively scavenged than PM2.5. Both the increases in rainfall duration and rainfall intensity lead to the increase in scavenging effect but the rainfall duration plays a more important role in increasing scavenging effect than the rainfall intensity. To examine the change in scavenging effect with microphysical characteristics of rainfall, stratiform-type (type S) and convective-type (type C) rainfall events are grouped and compared. For similar rainfall amounts, the type S rainfall events exhibit longer duration, weaker intensity, and higher scavenging efficiency than the type C rainfall events. The higher scavenging efficiency of the type S rainfall events is associated with their smaller raindrop sizes, which lead to larger total volume swept by raindrops and higher collision efficiency between PMs and raindrops. Empirical relations between rainfall rate and scavenging coefficient are obtained for PM10, PM2.5, and PM2.5−10 concentrations in Seoul. The relations tend to yield smaller scavenging coefficients compared with the relations obtained from Beijing, China and Sado island, Japan. © 2026

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