Fluorescent primary bioaerosol particle measurements in mixed phase cloud residuals at Mount Helmos, Greece

The partitioning between liquid- and ice-phase cloud water content can have a substantial impact on the cloud’s radiative effect and on precipitation. This partitioning is expected to change on average with global warming due to warmer temperatures, more atmospheric moisture, and different cloud nucleating particle distributions, which then feed back into the changing climate. Changes in mixed phase clouds (MPCs)  are difficult to predict due to the complexity of microphysical processes that determine cloud phase partitioning and the uncertainty of future aerosol emissions, both natural and anthropogenic. The characteristics of MPCs are particularly sensitive to the availability of ice-nucleating particles (INPs), which are generally few in number relative to overall aerosol concentrations. Primary bioaerosol emissions are understood to be important to INP availability, making these aerosols and the processes affecting them critical to understanding how clouds and precipitation might change with global warming and with different anthropogenic emissions.

The CleanCloud project under which this research is conducted targets these aerosols and MPCs in order to improve our understanding and climate predictions of a post-aerosol drawdown and warmer world with different natural aerosol sources. We present preliminary observations from the CleanCloud Helmos Orographic SIte Experiment (CHOPIN) campaign targeting primary bioaerosols at the Helmos Hellenic Atmospheric Aerosol Climate Change Station (HAC²) on Mount Helmos in the Peloponnese peninsula, southern Greece, carried out between October 2024 and April 2025. At an altitude of 2314 m, atmospheric conditions at HAC² are at times within the planetary boundary layer and otherwise more representative of the free troposphere. During wintertime at this altitude, MPCs can be frequently observed at HAC². We employed a ground-based counterflow virtual impactor (GCVI; Brechtel Industries) in order to sample clouds and observe cloud residuals using a multiparameter bioaerosol spectrometer (MBS; CAIR, University of Herefordshire), scanning electrical mobility spectrometer (SEMS; Brechtel Industries), and a portable ice nucleation experiment (PINE; EPFL). Samples were also taken for offline analysis with transmission electron microscopy (TEM; MRI-JMA).

We present a preliminary overview of fluorescent primary bioaerosol particle (fPBAP) measurements at HAC² in both cloud residuals and whole air as part of the CHOPIN campaign. We relate these to observed INP concentrations measured by the PINE, and to cloud properties measured by a fog monitor (FM120; DMT, Inc.) and a ground-based fog and aerosol sensor (GFAS; DMT, Inc.).