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, PM_2.5 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 PM_2.5 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.