Treasure Bowl: PM2.5 Aggregation in the Eye of a Tropical Cyclone

Abstract A local tropical cyclone (TC) in South China Sea was observed making its first complete landfall on an island. Following the arrival of the TC eye, PM2.5 concentration rose from 4 µg/m³ to 44 µg/m³. Mass reconstruction results reveal that sea salt emerged as the primary source. The similar molar ratios of elements before and after landfall confirm that the source of PM2.5 is associated with the local terrigenous sediment. The ratio of Na+/Cl− in the TC eyewall is approximately 5:1 indicating the existence of chlorine depletion. Meanwhile, the concentration of Cl− and molar ratios like Si/Fe inside the TC eyewall show a rapid increase, and reach a peak in the TC eye, indicating that marine particulate matter invades and presents a treasure‐bowl‐like stepwise aggregation. Our findings provide statistical and theoretical foundations for understanding extreme air pollution events, offering direct evidence of sea‐land transport throughout the entire TC.