Determining the influence of fluorescent primary biological aerosol particles on low-level Arctic clouds

Mixed-phase clouds are integral to the Arctic climate system as they regulate the energy transport to and from the surface. Their ice content, which influences the cloud's optical and physical properties, is regulated by the presence of ice nucleating particles (INP).  Despite this, knowledge of the sources and concentrations of INP in the Arctic is notably lacking.  Here, we investigate the abundance and variability of fluorescent primary biological aerosol particles (fPBAP) within cloud residuals at a key site at 79° North over an entire year. fPBAP have been found to be active INP at warmer temperatures. Samples were continuously collected using a multiparameter bioaerosol spectrometer coupled to a ground-based counterflow virtual impactor inlet at the Zeppelin Observatory in Ny-Ålesund, Svalbard. We found that fPBAP concentrations within cloud residuals closely aligned with the expected concentration of high-temperature INP. Transmission electron microscopy confirmed the presence of fPBAP, likely bacteria, in the cloud residual samples. Seasonal analysis demonstrated a higher presence of fPBAP within cloud residuals over the summer, with water vapor isotope measurements revealing a connection between summer cloud formation and regionally sourced air masses. Low-level MPC were predominantly observed at the beginning and end of summer, possibly due to the presence of high-temperature INP. Our study - currently under interactive discussion* - provides observational evidence supporting the role of fPBAP in determining the phase of low-level Arctic clouds, with implications for the composition of respective cloud condensation nuclei sources in the future under rapid Arctic climate and environmental change.*Pereira Freitas, G., Kopec, B., Adachi, K., Krejci, R., Heslin-Rees, D., Yttri, K. E., Hubbard, A., Welker, J. M., and Zieger, P. 2023: Contribution of fluorescent primary biological aerosol particles to low-level Arctic cloud residuals, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2023-2600.