Continental river runoff enhances atmospheric aerosol formation over the Arctic Ocean

The formation of cloud condensation nuclei is a critical but uncertain factor in Arctic climate dynamics. A major nuclei contributor is new particle formation, yet the geographical variations in activity and the factors driving it remain poorly understood. Here, we present a nine-year (2010–2018) analysis of atmospheric particle number size distributions from Tiksi, Russia, integrated with air mass trajectory modelling and ocean remote sensing. We show that aerosol formation rates are significantly enhanced—particle formation rates increase by 300% and growth rates by 60%—when air masses travel over regions of the Arctic Ocean with high concentrations of terrigenous dissolved organic matter from river runoff. Using multiple analytical approaches, we identify terrigenous dissolved organic matter rich waters as key source regions for aerosol formation, likely driven by the oxidation of biotic and abiotic volatile organic compounds emitted from the air–ocean interface. We note that most atmospheric measurements are conducted far from Arctic River deltas, despite 11% of the ice-free Arctic Ocean being influenced by high terrigenous dissolved organic matter concentrations. Our findings indicate that riverine input and subsequent aerosol formation is a major source of Arctic aerosol which has been largely overlooked.