BayCEER Workshop 2024

Bi-directional vertical transport of atmospheric cluster ions in the Fichtelgebirge mountains

P 6.2 in Posters

Atmospheric ions can play a role in new particle formation, e.g. by increasing the growth rates of molecular clusters and nanoparticles. Turbulent flux measurements can help to gain insight into the strength of different source and sink processes of atmospheric cluster ions. We present first eddy covariance flux measurements of the vertical transport of atmospheric cluster ions during new particle formation events above a forest canopy.

Eddy covariance flux measurements were carried out at the Waldstein ecosystem research site of BayCEER in the Fichtelgebirge mountains, Germany, in August and September 2022. On top of a scaffolding tower at 32 m above ground level, total concentrations of negative and positive cluster ions were measured with a Cluster Ion Counter (CIC, Airel OÜ, Tõravere, Estonia). The three-dimensional wind vector was measured with a sonic anemometer (Model 81000, R. M. Young, Traverse City, MI, USA) co-located with the cluster ion sampling inlet for eddy covariance calculations of turbulent vertical ion fluxes.

Concentrations of positive cluster ions were considerably higher than of negative cluster ions but the diurnal patterns of positive and negative ion concentrations were similar. Interestingly, the turbulent fluxes of positive and negative ions were directed in opposite directions. Negative ion fluxes were mostly from the surface to the atmosphere. At the same time, positive ion fluxes were mostly from the atmosphere to the surface. Thus, the canopy below the measuring height acts as an effective source for negative cluster ions, and as an effective sink for positive cluster ions. This is consistent with the presence of a net positive charge in the atmosphere above the measuring height and a net negative charge of soil and vegetation surfaces as generally expected.

We are grateful to the Atmospheric Chemistry and Micrometeorology groups at University of Bayreuth for support of our measurements at the Waldstein field site.

Keywords: atmospheric ions, turbulent fluxes, atmospheric aerosol, new particle formation