Sources of major ions and heavy metals in rainwater associated with typhoon events in southwestern Taiwan

Dissolved chemical compositions in rainwater have provided valuable information on pollutant sources in the atmosphere and short-term environmental changes. However, baseline chemical data associated with typhoon is rather limited. In this study, a suite of time-series rain specimens including four typhoon events are collected from Tainan city, southern Taiwan and analyzed for major ions, heavy metals and Pb isotopes to elucidate mechanisms causing dissolved components variation in rainwater and to understand how heavy metals are transported by air-mass along typhoon pathways.Being different from previous views, dissolved major ions and heavy metals in typhoon rains show high concentration and large variability compared with normal period. In particular, dissolved Ni, Cu and Pb change more than several hundred times during typhoon events. This agrees with a scenario that typhoons disturb surface environments and enhance particles scavenged from anthropogenic sites along air-mass pathways. The ²⁰⁶Pb/²⁰⁷Pb ratios are significantly low in high Pb contents specimens, which are mostly associated with high precipitation and confirm local anthropogenic sources due to intense water-particle interaction. In particular, the Cu and Pb fluxes increase >10,000 and >10,000,000 times respectively during typhoon events and thus impact importantly the chemical budgets of these metals in coastal ocean. Combining backward trajectories and PCA results demonstrates consistently that air-mass routes dictate critically the dissolved chemical characteristics in rains; furthermore, it highlights the importance of migration pathways to heavy metals distribution in typhoon rainwater.