Significance of an urban river as a local source of ice nucleating particles

The concentration of ice nucleation particles (INP) in river waters surpasses the levels found in oceans and in the sea by orders of magnitude. Therefore, despite covering a small surface area, lakes and rivers could be a significant local source of INPs along river systems and also beyond when the INPs contained in river waters flow into the sea. Most aerosolisation mechanisms that occur in the sea (e.g., wave breaking and bubble bursting) also occur in flowing systems such as rivers or lakes. However, how efficiently INPs are aerosolized from rivers remains an open question, limiting the estimation of the impact of rivers as a source of INPs.

In this work, we present INP measurements from the urban section of the Vantaa river in Helsinki, Finland. We characterise the INP concentrations both in the water and in the adjacent air at an artificial weir next to the mouth of the river. Additionally, we study the aerosolisation mechanisms and examine how INP concentrations in the water change at the river mouth, where the river water mixes into the Baltic Sea.

This work was supported by the Research Council of Finland Flagship ACCC (grant 337552) and MEDICEN project (grants no. 336557 and 345125)